The living world is rich in variety. Millions of plants and animals have been identified and described but a large number still remains unknown. The very range of organisms in terms of size, colour, habitat, physiological and morphological features make us seek the defining characteristics of living organisms. In order to facilitate the study of kinds and diversity of organisms, biologists have evolved certain rules and principles for identification, nomenclature and classification of organisms. The branch of knowledge dealing with these aspects is referred to as taxonomy. The taxonomic studies of various species of plants and animals are useful in agriculture, forestry, industry and in general for knowing our bio-resources and their diversity. The basics of taxonomy like identification, naming and classification of organisms are universally evolved under international codes. Based on the resemblances and distinct differences, each organism is identified and assigned a correct scientific/biological name comprising two words as per the binomial system of nomenclature. An organism represents/occupies a place or position in the system of classification. There are many categories/ranks and are generally referred to as taxonomic categories or taxa. All the categories constitute a taxonomic hierarchy.

Taxonomists have developed a variety of taxonomic aids to facilitate identification, naming and classification of organisms. These studies are carried out from the actual specimens which are collected from the field and preserved as referrals in the form of herbaria, museums and in botanical gardens and zoological parks. It requires special techniques for collection and preservation of specimens in herbaria and museums. Live specimens, on the other hand, of plants and animals, are found in botanical gardens or in zoological parks. Taxonomists also prepare and disseminate information through manuals and monographs for further taxonomic studies. Taxonomic keys are tools that help in identification based on characteristics.

Classification : Grouping of organisms in to categories based on observable characters. (category –taxa )
Taxonomy : Characterization, identification , classification and nomenclature are the process of taxonomy.
Systematics : Different kinds of organisms and their relationships Linnaeus – Systema Naturae (evaolutionary relationships among organisms).
Taxonomical Hierarchy : Similarities decreases/ Differences increases

Species : Panthera leo, Panthera pardus, Panthera tigris.
Genus : Panthera (Lion, Leopad,Tiger )
Family : Panthera and Felis together into Felidae
Order : Felidae (cat family) , Canidae (dog family) - Carnivora
Class : Carnivora (tiger, cat, dog), Primates (monkeys )- Mammalian
Phylum : Pisces, Amphibian, Reptilian, Aves & Mammals
Kingdom : Plantae, Animalia.

Biological classification of plants and animals was first proposed by Aristotle on the basis of simple morphlogical characters. Linnaeus later classified all living organisms into two kingdoms – Plantae and Animalia. Whittaker proposed an elaborate five kindgom classification – Monera, Protista, Fungi, Plantae and Animalia. The main criteria of the five kingdom classification were cell structure, body organisation, mode of nutrition and reproduction, and phylogenetic relationships.

In the five kingdom classification, bacteria are included in Kingdom Monera. Bacteria are cosmopolitan in distribution. These organisms show the most extensive metabolic diversity. Bacteria may be autotrophic or heterotrophic in their mode of nutrition. Kingdom Protista includes all single-celled eukaryotes such as Chrysophytes, Dianoflagellates, Euglenoids, Slime-moulds and Protozoans. Protists have defined nucleus and other membrane bound organelles. They reproduce both asexually and sexually. Members of Kingdom Fungi show a great diversity in structures and habitat. Most fungi are saprophytic in their mode of nutrition. They show asexual and sexual reproduction. Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes are the four classes under this kingdom. The plantae includes all eukaryotic chlorophyll-containing organisms. Algae, bryophytes, pteridophytes, gymnosperms and angiosperms are included in this group. The life cycle of plants exhibit alternation of generations – gametophytic and sporophytic generations. The heterotrophic eukaryotic, multicellular organisms lacking a cell wall are included in the Kingdom Animalia. The mode of nutrition of these organisms is holozoic. They reproduce mostly by the sexual mode. Some acellular organisms like viruses and viroids as well as the lichens are not included in the five kingdom system of classification.

Five kingdom classification. (R.H Whittaker 1959)

Main criteria for classification:
Complexity of cell structure (prokaryotes/ eukaryote )
Body organization (unicellular/ multicellular)
Mode of nutrition (autotrophic / heterotrophic / holozoic)
Life style ( producers / consumers / decomposers)
Phylogenic relationships (revolutionary history)

Five kingdoms are

1.Kingdom Monera (eg. Bacteria ):
Habitats- omnipresent
Grouped in to 4 groups based on their shape.
1.Cocus (spherical) 2. Bacillus (rod) 3. Vibrio (comma) 4. Spirillum (spiral)

Mode of nutrition – autotrophs and heterophs.

Kingdom Monera includes:

a)Archaebacteria : Harsh habitats, Halophiles (saline) Thermoacidophiles (hot spring), Methanogens (gut of ruminants)

b)Eubacteria : True bacteria - Rigid cell wall - Motile flagellum
Autotrophic bacteria - Cyanobacteria (BGA) have chlorophyll a unicellular, colonial/ filamentous.
Marine /terrestrial habitat/ gelatinous sheath
Form blooms - can fix nitrogen in heterocysts. Eg. Nostoc, Anabaena.
Chemosynthetic bacteria – Oxidise nitrates , nitrites and ammonia release energy (ATP) help in
Recycling of nutrients ( eg. Pseudomonas, nitrobacter )
Heterotrophic bacteria – Decomposers – making curd from milk, antibiotics, nitrogen fixing (Rhizobium ) some are pathogenic ( cause diseases ) cholera, T.B, diarrhea.
Reproduction by binary fission, spore / sexual reproduction.

c)Mycoplasma : No cell wall,smallest living cell.
Anaerobic – pathogenic in animals and plants.

2.Kingdom protista :
Unicellular : Eukaryotic – aquatic
Flagella / cilia - Reproduce sexually / asexually

Chrysophyta :
Planktons diatoms and golden algae ( desmids )
Fresh water/ marine
Microscopic – photosynthetic
In diatoms , cell wall is indestructible (silica )form diatomaceous earth, its being gritty used for polishing, fitration of oil and syrups.
Chief producers in oceans.

Marine photosynthetic, yellow, green, blue or red pigments
Cell wall is cellulosic
have 2 flagella
Red dionflagellate (Gonyaulax ) forms red tides and toxins are released.

Euglenoid eg. Euglena :
Fresh water,stagnant water
no cell wall but protein rich layer is present, called pellicle. Pellicle is flexible with flagella.
they are Myxotrophic, because Photosynthetic (in light) Heterotrophs (when no light).(Myxotrophs are Mixture of both autotrophs and heterotrophs)

Slime moulds:
Saprophytic : body moves on decaying twigs and leaves
During suitable conditions from aggregation called plasmodium (mass of slime moulds)
Unfavourable conditions form spores and survive for many years.

predators/ parasites
· Amoeboid protozoans. Fresh water, sea and moist soil -pseudopodia – marine forms have silica shells . Entamoeba (parasite) cause Amoebic dysentery
· Flagellated protozoans - free living / parasites have flagella – parasites cause diseases – Sleeping sickness (Trypanoroma) is a parasite of flagellated protozoans.
· Ciliated protozoans – aquatic cilia, cavity gullet eg. Paramoecium.
· Sporozoans – Spore stage in their life cycle. Plasmodium causes malarial fever.

Kingdom Fungi:
· Multicellular – eukaryotic – heterotrophic - cosmopolitan - grow in warm and humid places.
· Fungi are filamentous with long, slender thread like Hyphae and the net work of hyphae is known as Mycelium – They can be septate or non septate (aseptate)
· Multinucleated cytoplasm (coenocytic hyphae)
· Cell wall is chitin.
· Parasitic/ symbionts (Lichens and Mycorrhizae)
· Symbionts of algae and fungi (Lichens) and Pine trees roots and fungi (Mycorrhizae) on roots to absorb water.
· Reproduction by fragmentation, fission, buddin.
· Asexual reproduction by oospores, ascospores, basidiospores.
· Sexual reproduction steps.

1. Plasmogamy
2. Karyogamy and
3. Meiosis in zygote result in haploid spores – dikaryon

Based on morphology of mycelium mode of spore formation, fruiting bodies , there 4 classes;
1. Phycomycetes :
· Aquatic decaying wood mycelium is aseptate coenocytic
· asexual reproduction by zoospores (motile ) / aplanospores ( non motile )
· Eg. Rhizopus, mucor.

2. Ascomycetes : (Sac fungi)
· Multicellular (penicillium ) / Unicellular ( yeast )
· Saprophytic – decomposers – parasitic – coprophilous
· Mycelium is branched and septate –asexual spores are called conidia
· Sexual spores are called ascospores.
· Eg. Aspergillus, Neurospora

3. Basidiomycetes : (Eg. Mushroom/ bracket fungi/ puffballs)
· Grow in soil, logs, tree stumps, in plant bodies as parasitic (as rust and smuts)
· Mycelium is branched and septate
· Reproduction by fragmentation
· Dikaryon – basidium –karyogamy
· Eg. Agaricus (mushroom)

4. Deuteromycetes :
· Imperfect fungi mycelium is septate and branched.
· Only asexual reproduction by conidial spores
· Saprophytes / parasitic / decomposers
· Help in Mineral cycling
· Eg. Trichoderma, Alternaria

4.Kingdom Plantae :
Autotrophs – size varies from herbs to tall trees. There are different groups;

· Simple, thalloid, autotrophic, aquatic organisms.
· Habitats – grow in moist soil and wood.
· Symbiotic ( Lichens) grow on other animals (sloth bear)
· Size ranges from Unicellular colonial (volvox), Filamentous ( spirogyra) and Massive bodies (kelp)
· Reproduce vegetatively, asexually and sexually
· Spores are Zoospores (male) à isogamous / anisogamous; Oospores (egg).

Economic importance:
1. Porphyra, Laminaria, Sargassum are used as food.
2. Marine brown algae (Algin) and red algae (Carrageen) are used as Hydrocolloids, which is a fibrous structure holds water and used to transport seedling.
3. Gelidium, Graularia are used to grow microbes, make ice creams and jellies.
4. Chlorella and Spirullina are rich in proteins and used as food supplements.

Alage is divided into 3 main classes;

a)Chlorophycease (Green algae):
· Colonial / filamentous / unicellular
· Possess chlorophyll a & b
· Stored with proteins / starch
· Some store oil forms
· Cell wall is rigid and made of inner cellulose and outer pectose
· Vegetative reproduction is by fragmentation / spores
· Asexual reproduction is by flagellated Zoospores
· Sexual reproduction is by isogamous / anisogamous / oogamous
Examples : - Volvox, Spirogyra, Chlamydomonas

b)Phaeophycease (Brown algae)
· Marine habitats – vary in size and form from simple branched to filamentous form, Kelp (100 m) possess chlorophyll a & c, carotenoid, Xanthophylls and Fucoxanthin.
· Food is stored as carbohydrates in the form of Laminarin / Mannitol
· They have cellulose wass with gelatinous coating of algin.
· They are attached to substratum by Holdfast (root like), Stalk (stipe) and leaf (frond)
· Vegetative reproduction by fragmentation
· Asexual reproduction is by biflagellated zoospores
· Sexual reproduction is by Isogamous / Anisogamous / Oogamous.
Examples :- Laminaria, Srgassum, Ectocarpus, Dictyota, Fucus.

c)Rhodophycease ( Red algae)
· They have red pigment called "r-phycoerythrin".
· They are marine.
· Food is stored as Floridean starch, which is similar to amylopectin and glycogen in structure.
· Vegetative reproduction is by fragmentation.
· Asexually by non-motile spores.
· Sexually by non-motile gametes.
Examples : - Porphyra, Gracilaria, Gelidium.

· They live in moist shaded areas in the hill.
· It is known as "amphibians of plant kingdom".
· They occur in damp soil, humid and shaded places.
· Plant body lacks true roots, stem, leaves, they are attached to the substratum by unicellular / multicellular Rhizoids.
· The main plant is haploid and they produce gametes (Gametophyte – dominant).
· The male sex organ is Antheridium (antherozoids)
· The female sex organ is Archegonium (single egg)
· Antherozoids are released in water come into contact with Archegonium to form Zygote.
· Zygote develops into Sporophyte (diploid) undergoes meiosis to form haploid spores germinate to produce Gametophyte.

Economic importance:
· Provide food for herbaceous mammals / birds.
· Sphagnum species (mosses) provide peat, used as a fuel.
· Due to its water holding capacity is is used as packing material for trans-shipment of living materials.
· Mosses and Lichens form Pioneer community on bare rocks.
· Form dense mats on soil, so reduce the impact of rain and soil erosion.

Classes: - There are two classes à Liverworts, Mosses.

a)Liverworts :
· Moist, shady habitats, damp soil, bark of trees and deep in the woods.
· Plant body is Thalloid, have a tiny leaf structures.
· Asexual reproduction is by fragmentation / form gemmae (gree, multicellular, asexual bodies) they detach from parent body and form as a new individual.
· Sexual reproduction à form male & female sex organs sporophyte is differentiated into a foot, setae and capsule.
· Spore germinate to form gametophyte.

Example :- Marchantia

b)Mosses :
· Gametophyte shows two stages à Protonema (spores) and Leafy stage (Secondary protonema)
· Attached to the soil by Rhizoids
· Vegetative reproduction is by fragmentation / budding
· Sexual reproduction is by antheridia and archegonia
· Zygote develops into sporophyte and form capsule and it contains spores (haploid)

Example : - Sphagnum, Funaria

III.PTERIDOPHYTES (first land plants):
They are used for medical purpose, ornamental and as soil binders and first terrestrial plants.
· They grow in cool, damp, shady places
· Possess vascular tissues (xylem and phloem)
· Main plant body is Sporophytes
· The body is differentiated into true roots, stem and leaves.
· Leaves may be small (microphylls – selaginella) or large (macrophylls – ferns) and bear sporangia and form sporophylls (leaf carrying spores).
· Sporangia produce spores by meiosis.
· Spore germinates to form gametophyte, called Prothallus.
· They need water for fertilization.
· Gametophyte bear male & female sex organs called Antheridia and Archaegonia respectively.
· Gamete fusion results in zygote formation. Zygote develops into sporophytes (dominant phase).
· If all the spores are similar kind, it is called Homospores.
· Selaginella produce two kinds of spores, Macro and micro spores, hence known as Heterosporous.
· Macro and micro spores develop into female and male gametophytes respectively.
· Female gametophyte retained on sporophyte. It leads to the development of seed habit.

Classes: - There are four classes in Pteridophtae;
a) Psilopsida – Ex. Psilotum
b) Lycopsida – Ex. Selaginella
c) Sphenopsida – Ex. Equisetum
d) Pteropsida – Ex. Pteris

IV. GYMNOSPERMS (Naked seeds)
· They are seed bearing plants.
· The ovules are not enclosed in an ovary, so no fruits.
· Tallest gymnosperm is Sequoia (red wood tree)
· Plant body is differentiated into roots, stems and leaves
· Roots are tap root – associated with other organisms like Pinus roots with Mycorrhizae and Cycas roots with Cyanobacteria like Nostoc and Anabaena (nitrogen fixing microbes)
· Stem can be branched / unbranched
· Leaves are simple / needle like – leaves show Xerophytic adaptation
· Gymnosperms are heterosporous, produce microspores and megaspores
· They form male cones & female cones
· Both cones can occur on some plant / different.
· Fertilization results in Zygote and embryo develops.
· Ovules form seeds.
· Gymnosperms show diplontic life cycle.
· They show Alternation of generation.

Examples ; - Pinus, Cycas, Cedrus

V. ANGIOSPERMS (flowering plants)


· They are flowering plants
· Seeds are covered by fruits – live in wide range of habitats.
· Size varies from tiny microscopic Wolfia to tall trees Eucalyptus.
· Provide food, fodder, fuel and medicine.
· There are two classes à Dicotyledons and Monocotyledons.
· Male sex organ is Stamen and female is Pistil.
· Ovules have embryo sac; it undergoes meiosis and form egg apparatus with one egg and 2 synergids, 3 antipodal cells and 2 polar nuclei.
· Polar nuclei fuses to form secondary polar nucleus.
· Pollen dispersal is by pollination – pollen tube grows in to stigma and style of pistil, one male gamete fuses with egg and form zygote and other male gamete fuses with secondary polar nucleus (2n) to form Primary Endosperm Nucleus (PEN - 3n).
· Due to two fusions, it is called Double fertilization.

a) Zygote à Embryo
b) PEN à Endosperm (and nourishes embryo)
c) Synergids and antipodal cells à degenerate
d) Ovules à seeds
e) Ovary à Fruits

5.Kingdom Animalia :
Heterotrophs – locomotory – holozoic / saprophytic / parasitic – cosmopolitans.
It consists of two sub kingdom Invertebrata with 9 Phylum and Phylum Vertebrata (Chordata) with 5 Classes.

1.Level of organization
· Cellular level - organ level
· Tissue level – organ system level ( open and closed circulation )
· Complete/incomplete digestive system. (hydra )

2.Body symmetry
· A symmetry – Ex. Sponges
· Symmetrical à Bilatral symmetry (Annelids and Arthropods) and Radial symmetry (Ctenophora, Coelenterate and Echinoderms)

3.Nature of Coelom (Body cavity)
· Coelomate – body cavity with ecto, endo and mesoderms - Ex. Annelids, Molluscs, Arthropods, Echinoderms, hemichordates and chordates.
· Pseudococlomate – no mesoderm, have only ectoderm and enderm layers - Ex. Aschelminthes (round worms)
· Acoclomate – no body cavity - Ex. Platyhelminthes (flat worms)

4.Body plan
· Cell aggregate plan
· Blind sac body plan

5.Embryonic germinal layers
· Diploblastic (Coelenterates) – only ectoderm and endoderm
· Triploblastic organization (Platyhelminthes to Chordates)- ectoderm, enderm and mesoderm

6.Segmentation: Metameric segmentation – true segmentation(metamerism) – Ex. - Earthworm

· It is a mesodermal origin – rod like structure – animals with notochord is chordates and without that are non-chordates.

In plants, both haploid and diploid cells can divide by mitosis. This ability leads to the formation of different plant bodies - haploid and diploid. The haploid plant body produces gametes by mitosis. This plant body represents a gametophyte. Following fertilisation the zygote also divides by mitosis to produce a diploid sporophytic plant body. Haploid spores are produced by this plant body by meiosis. These in turn, divide by mitosis to form a haploid plant body once again. Thus, during the life cycle of any sexually reproducing plant, there is an alternation of generations between gamete producing haploid gametophyte and spore producing diploid sporophyte.

However, different plant groups, as well as individuals representing them, differ in the following patterns:

1. Sporophytic generation is represented only by the one-celled zygote. There are no free-living sporophytes. Meiosis in the zygote results in the formation of haploid spores. The haploid spores divide mitotically and form the gametophyte. The dominant, photosynthetic phase in such plants is the free-living gametophyte. This kind of life cycle is termed as haplontic. Many algae such as Volvox, Spirogyra and some species of Chlamydomomas represent this pattern (Figure 3.7 a).
2. On the other extreme, is the type wherein the diploid sporophyte is the dominant, photosynthetic, independent phase of the plant. The gametophytic phase is represented by the single to few-celled haploid gametophyte. This kind of lifecycle is termed as diplontic. All seed-bearing plants i.e. gymnosperms and angiosperms, follow this pattern
3. Bryophytes and pteridophytes, interestingly, exhibit an intermediate condition (Haplo-diplontic); both phases are multicellular and often free-living. However, they differ in their dominant phases.


1.Phylum - Porifera - Ex. Sponges.
. Marine , asymmetrical, cellular level of organization
. Have water canal system
. Ostia à Spongocoel à Osculum
. Choanocytes/ collar cells line in the spongocoel
. Digestion is intracellular
. Skeleton made up of spicules/ sponging fibres
. Hermaphrodite –male and female organs present on the same body.
. Reproduce asexually by fragmentation
. Sexually by gametes
. Fragmentation is internal and development is indirect

Eg. Sycon, spongilla.

2.Phylum Coelenterata ( cnidaria) - Ex. Hydra
. Aquatic / marine
. Sessile (fixed ) / free swimming
. Radially symmetrical
. Have cnidoblasts / cnidocytes, stinging capsule on tentacles
. Used for defense, anchorage and to capture the prey
. Tissue level of organization diploblastic
. Mouth on hypostome.
. Digestion extracellular and intracellular
. Corals have skeleton made of calcium carbonate.
. Exhibit 2 basic forms called polyp and medusa.
. Polyp is sessile cylindrical (hydra )
. Medusa is umbrella shaped free living ( jelly fish )
. They show alternation of generation ( metagenesis ) where polyp forms medusa asexually and
. medusa forms polyp sexually. Ex. Obelia

Ex. - Hydra, Physalia, Sea anemone, Sea pen, Sea fan, Brain coral.

3.Phylum - Ctenophora ( sea walnuts/comb jellies )
. Marine , radially symmetrical diploblastic
. Tissue level of organization
. Body bears 8 rows ciliated comb plates help in locomotion
. Digestion by intra and extra cellular
. Bioluminescence is well developed
. Sexes are not separate (monoecious)
. Reproduce by sexual reproduction
. Fertilization is external and indirect development.

Ex. - Pleurobrachia and ctenoplana

4.Phylum – Platyhelminthes ( flat worms )
. Dorso-ventrally flattened body
. Endoparasites, bilaterally symmetrical
. Organ level of organization
. Triploblastic - acoclomate
. Hooks and suckers are present
. Flame cells for excretions
. Sexes are not separate - fertilization is internal and development is through many larval stages
. Have high regeneration capacity

Ex.- Tape worm, Planaria, Liver fluke

5.Phylum - Aschelminthes (round worms )
. Free living, aquatic, terrestrial parasitic
. Organ system level of body organization
. Bilaterally symmetrical and triploblastic
. Pseudocoelomate
. Digestive system is complete (mouth and anus)
. Sexes are separate (dioecious )
. Fertilization is internal and development is direct.

Ex. Ascaris, Wuchereria ( filarial worm ) and Ancylostoma (hookworm)

6.Phylum – Annelida ( annulus little ring )
. Aquatic/terrestrial
. Freeliving/ parasites
. Organ system level of body organization
. Bilaterally symmetrical
. Triploblastic
. Metamerically segmented – coelomate
. Metameres/body is segmented
. Marine Nereis possess parapodia
. Possess longitudinal and circular muscles help in locomotion
. Closed circulatory system
. Nephridia help in osmoregulation and excretion
. Dioecious (sexes are separate)
. Earthworm and leeches are monoecious
. Reproduction is sexual

Eg. Nereis, Pheretima ( earth worm ) and Hirudinaria ( blood sucking leech )

7.Phylum – Arthropoda – (jointed legs)
. Largest phylum 2/3 are insects
. Organ system level of body organization
. Bilaterally symmetrical
. Segmented and coelomate
. Chitinous exoskeleton.
. Body has head thorax and abdomen.
. Have jointed appendages( organs for locomotion ) respiratory organs are gills/book gills/Book lungs / tracheal system
. Open circulatory system.
. Sense organs are antennae, eye, statocysts ( balance organs )
. Fertilization is internal.
. Excretion by malpighian tubules.
. Sexes are separate (Dioecious)
. Oviparous
. Development may be direct/ indirect
. Economic importance-
- Honey bees (Apis)
- Silkworm worm (Bombyx)
- Vectors. Mosquito, Housefly
- Aquatic –crab, prawn, lobster

7.Phylum - Mollusca: (soft bodied and shelled)
. Second largest phylum
. Terrestrial and aquatic
. Organ system level of body organization
. Bilaterally symmetrical
. Triploblastic and Coelomate
. Calcareous shell and unsegmented body with head muscular foot and visceral hump
. Soft spongy layer of skin forms a mantle over the visceral hump
. Gills for respiration and excretion
. Head has sensory tentacles
. Mouth has file like rasping organ for feeding radula
. Sexes are separate (Dioecious)
. Oviparous
. Indirect development

Eg. Oyster, snail, squid, devil fish

8.Phylum - Echinodermata: (spiny skinned)
. Spiny skin has exoskeleton which is calcarious ossicles
. Marine organ level of body organization
. Radially symmetrical
. Coelomate
. Triploblastic
. Mouth of the lower side and anus on the upper side.
. Have water vascular system, help in locomotion, to capture and transport of food and for respiration
. Excretory system is absent
. Dioecious and fertilization is external, development is indirect with free swimming larva

Ex. Starfish, sea urchin, sea lily, sea cucumber

9.Phylum – Hermichordata
. Under non chordate
. Worm like marine animals
. Organ system level of organization
. Bilaterially symmetrical , triploblstic
. Coclomate – body has anterior proboscis , a collar and a long trunk
. Circulatory system is open type
. Respiration is through gills
. Excretory organ is proboscis gland
. Sexes are separate
. Fertilization is external
. Development is indirect

Ex. Balanoglossus 10.Phylum – Chordata
. Presence of notochord dorsal hollow spinal cord –nerve cord and paired pharyngeal gill slits
. Bilaterally symmetrical and triploblastic
. Coelomate organ system level of organization
. Have post and tail
. Closed circulatory system
ChordatesNon chordates
1. Notochord present 1. Notochord is absent
2. Central nervous system is dorsal 2. Central nervous system is ventral, solid and double hollow and single
3. Gills are present 3. Gills are absent
4. Heart is ventral 4. Heart is dorsal
5. Tail is present 5. Tail is absent

Chordata -Urochordata, Cephalochordate and Vertebrata (protochordates)

Urochordata – notochord present in larval tail eg. Ascidia, salpa

Cephalochordate – notochord extends from head to tail eg. Amphioxus

1.Subphylum – Vertebrata:
. Possess notochord (replaced by vertebral column)
. All vertebrates are chordates but not all chordates are vertebrates (all vertebrates have vertebral column, but all chordates do not have vertebral chord).
. Ventral muscular heart
. Excretion by kidneys
. Fins / limbs for locomotion

a)Super class – Agnatha (without jaw)

Class – Cyclostomata
. Ectoparasites on some fishes.
. Elongated body with 6-15 pairs of gill slits
. Sucking circular mouth without jaw
. Body is devoid of scales – paired fins
. Cranium and vertebral column are cartilaginous
. Circulation is closed –marie but migrate to fresh water for spawning
. After spawning they die
. Larvas, metamorphosis and return to the ocean

Ex. Lamprey, Hagfish

b)Super class - Gnathostomata (with jaw)
. Jaws are present
. Paired lateral appendages

There are six classes:

Class – Chondrichthyes:

. Cartilage fish, endoskeleton is cartilage
. Body is stream lined
. Pelvic fins in male with claspers
. 5-7 pairs of gills.
. No operculum
. Mouth in ventral with teeth.
. Jaws are powerful
. Air bladder is absent
. Heart is 2 chambered ( I auricle and one ventricle )
. Some possess electric /poison stings
. Poikilothermous (cold blooded)
. Body has placoid scales
. Unisexual
. Viviparous and fertilization is internal

Eg. Shark, sting rays.

Class – Osteichthyes - boney fish

. Endoskeleton is bone. Skin is covered by cycloid scales.
. Four pairs of gill slits with operculum, mouth is terminal, air bladder is present and help in buoyancy.
. Heart is two chambered ( I auricle and I ventricle )
. Poikilotherms ( cold blooded )
. Sexes are separate ,fertilization is external and oviparous

Ex. Angel fish, Clown fish, Rohu, Katla, Tilapia, Hippocampus.

Class – Amphibia - dual life

. Live on land and move to water for breeding
. Body has head and trunk
. Tail is in larval stage – two paires of limbs
. Digits without claws.
. Poikilotherms – eyes are with nictitating membranes
. Skin is smooth and moist with mucous glands
. Tympanum is ear drum
. Heart is three chambered ( two auricle and one ventricle )
. Respiration by gills in larva and by lungs and skin in adults.
. Digestive system
. Urinary tract and reproductive tract open in to a common cloacal chambers and the
. Opening is called cloacal aperture.
. Sexes are separate
. Oviparous
. Fertilization is external and development is indirect with tadpole larva

Ex. Toad, Frog

Class – Reptilia

. Skin is dry without glands.
. Covered by horny epidermal scales ( scutes )
. Tympanum is small no external opening
. 12 pairs of cranial nerves
. Trunk bears two pairs of pentadactyl limbs with claws.
. Heart with three and half chambered (two auricle, one which is incompletely partitioned ventricle)
. Only Crocodiles have four chambered heart
. Respiration is by lungs.
. Fertilization is internal.
. Oviparous and egg is covered by hard calcareoue shells

Ex. Snake, Tortoise, Turtle, Viper, Lizard

Class – Aves

. Streamlined body and covered with feathers
. Jaws are modified in to beaks, teeth absent , various shapes and sizes of beaks
. Digestive system has two structures – crop and gizzard ( grinding the food )
. Forelimbs form wings.
. Hind limbs modified for perching, swimming, running, etc.
. Voice box called syrinx is present
. Respiration is by lungs.
. Skin is dry with oil glands, at the base of tail.
. Bones are pneumatic bones (air cavities) helps to make the body light.
. Homeiothermous
. Heart is 4 chambered
. Oviparous and egg is with calcareous shells.
. Fertilization is internal.

Ex. Pigeon, Crow, Sparrow, Ostrich.

Class- Mammalia

Body has head, neck, trunk and tail
Have mammary glands in females
External ear (pinna) is present
Skin has sweat glands and sebaceous glands
Heart is 4 chambered
Respiration is by lungs.
Body has hair
Excretion is by kidneys (ureotelic – urea)
Sexes are separate
Viviparous (give birth young ones)

Few are ovoviviparous – egg laying mammals (Platypus)

Few are marsupials – pouched mammals with brood pouches (Kangaroo)

Viroids : In 1971 T.O. Diener discovered a new infectious agent that was smaller than viruses and caused potato spindle tuber disease. It was found to be a free RNA; it lacked the protein coat that is found in viruses, hence the name viroid. The RNA of the viroid was of low molecular weight.

Lichens : Lichens are symbiotic associations i.e. mutually useful associations, between algae and fungi. The algal component is known as phycobiont and fungal component as mycobiont, which are autotrophic and heterotrophic, respectively. Algae prepare food for fungi and fungi provide shelter and absorb mineral nutrients and water for its partner. So close is their association that if one saw a lichen in nature one would never imagine that they had two different organisms within them. Lichens are very good pollution indicators – they do not grow in polluted areas.


In majority of the dicotyledonous plants, the direct elongation of the radicle leads to the formation of primary root which grows inside the soil. It bears lateral roots of several orders that are referred to as secondary, tertiary, etc. roots. The primary roots and its branches constitute the tap root system, as seen in the mustard plant. In monocotyledonous plants, the primary root is short lived and is replaced by a large number of roots. These roots originate from the base of the stem and constitute the fibrous root system, as seen in the wheat plant. In some plants, like grass, Monstera and the banyan tree, roots arise from parts of the plant other than the radicle and are called adventitious roots .The main functions of the root system are absorption of water and minerals from the soil, providing a proper anchorage to the plant parts, storing reserve food material and synthesis of plant growth regulators.

Regions of root:
Region of maturation
Region of elongation
Region of meristematic tissues.
Root cap

Modification of roots:
· Storage- carrot, turnip
· Prop root- banyan tree (support)
· Stilt root – maize, sugarcane
· Pneumatophores- rhizophora (mangroves)

The stem:
Plumule have nodes and internodesbears with axillary /terminal buds

Modification of stems :
1. Storage - potato, ginger, tturmeric (perennation)
2. Tendrils – axillary buds –coils - support (watermelon)
3. Thorns - axillary buds – citrus (protection)
4. Flattened stem – opuntia (do photosynthesis)
5. Vegetative propagation (grass, jasmine, banana)

The leaf:

· Short apical meristem gives rise to leaves arranged in acropetal order
· Do photosynthesis
· Three main parts are leaf base, petiole and lamina (leaf blade)
· Have stipules
· Leguminous petioles have pulvinus. (midrib)

Venation : arrangement of veins and veinlets on a leaf.
Types of venation :
· Parallel- monocot leaves
· Reticulate – dicot leaves

Types of leaves:
1. Simple leaves
2. Compound leaves - Pinnately compound (eg. Neem) and Palmately compound (eg. Silk cotton)

Phyllotaxy: Pattern of arrangement of leaves on the stem /branch.
1. Alternate- china rose
2 Opposite- guava
3. Whorled- alstonia

Modification of leaves:
1. Tendrils - pea (support)
2. Spines - cacti (protection, water ioss)
3. Storage - onion/ garlic
4. Petiole leaves – acacia
5. Pitcher leaves – insectivorous plant (venus fly trap)

The inflorescence: Arrangement of flowers on the floral axis

Types of inflorescence: Depending on whether the apex gets converted in to a flower/continues to grow there are two major types;
1. Racemose. Main axis continues to grow laterally (in an acropetal succession)
2. Cymose. Main axis terminates in a flower so limited growth (basipetal order)

The flower:
· Four whorls. Sepal, petal, gynoecium, and androecium
· Thalamus/receptacle
· Trimerous/tetramerous/pentamerous/polymerous
· Bracteates/ebracteate/bract. (Protective sheet around the flower)
· Bisexual/unisexual
· Actinomorphic (mustard ) zygomorphic ( pea ) asymmetric ( canna )
Based on the position of ovary:
1. Hypogynous ovary ( mustard ) superior
2. Perigynous ovary ( rose ) half inferior
3. Epigynous ovary ( guava, cucumber ) inferior

Parts of flower:

1. Calyx. Made of sepals. Can be gamosepalous/polysepalous
2. Corolla. Made of oetals. Gamopetalous/ polypetalous
· Aestivation: Arrangement of sepals/ petals in floral bud

· Main types are valvate (petunia alba , calotropis)
twisted(china rose ), imbricate( gulmohur) vexillary (pea, bean )
3. Androecium.
· Staminode- sterile stamen
· Epipetalous. Attached to the petal
· Epiphyllous- attached to the perianth
· Polyadelphous- Free stamens
· Monoadelphous- united as one bunch ( china rose )
· Diadelphous – united two bundles ( pea )
· Polyadelphous – many bundles ( citrus )
4. Gynoecium- one/ more carpels
· Ovules attached on the wall of ovary called placenta.
· Apocarpous - Free carpels ( lotus, rose )
· Syncarpous - Carpels are fused (mustard, tomato )
· After fertilization ovules devopls into seed.
· Ovary develops into fruit
· Placentation: Arrangement of ovules within the ovary.
· Different types are marginal (pea), axile (china rose, lemon, tomato),
Parietal (mustard), freecentral (primrose) and basal (sunflower)

The fruit:
· Parthenocarpic fruit: Formation of fruits without fertilization of ovary. Ex. Seedless grapes, seedless orange.
· Two parts of a fruit are pericarp and seeds.
· Pericarp has epicarp, mesocarp and endocarp
· Both mango and coconut are known as drupe fruits (fruits formed from single ovary /carpel)
· Perianth: Fused petals and sepals.

The seed:
· Fertilized ovules.
· Made up of seed coat and an embryo
· Embryo with radical and plumule with one cotyledon or two cotyledon

Structure of a dicot seed:
· Seed coat, Testa and tegmen
· Hilum - small pore (place where it is attached to fruit)
· Micropyle. (water enters)
· Endosperm, cotyledons, embryonal axis (plumule and radicle)
· Mature seeds in dicot do not have endosperm called non-endospermic seeds. ( stored food is utilized by embryo)

Structure of monocotyledonous seed:
· Mostely endosperm except orchids
· Endosperm is bulky and store food
· Aleurone layer (produce enzymes to hydrolise proteins for embryo )
· Cotyledon is scutellum
· Protective coats- coleoptiles (piumule ), coleorhizae ( radical )

Semi-technical description of a typical flowering plant:

Various morphological features are used to describe a flowering plant. The description has to be brief, in a simple and scientific language and presented in a proper sequence. The plant is described beginning with its habit, vegetative characters – roots, stem and leaves and then floral characters inflorescence and flower parts. After describing various parts of plant, a floral diagram and a floral formula are presented. The floral formula is represented by some symbols.


Tissues - a group of similar cells performing same function.
< span >
Types of plant tissues - meristematic tissues and permanent tissues.

Meristematic tissues

·         Have power of cell division

Characteristics features

·         Cells are thin walled

·         No intercellular places

·         Abundant cytoplasm

·         Retains power of cell division

Classification based on position. Three types

1.       Apical meristem

2.       Lateral meristem

3.       Intercalary meristem

Based on the origin – three types

1.       Promeristem- embryo/ seedlings

2.       Primary meristem

3.       Secondary meristem

Permanent tissues:


I.Simple permanent tissues

1.       Parenchyma( storage)-living

2.       Collenchymas (support ) below epidermis, living

3.       Sclerenchyma – sclereids and fibres- dead

II.Compound permanent tissues

·         Xylem- xylem vessels, xylem tracheids, xylem parenchyma, xylem fibres

·         Phloem – sieve tubes, sieve cells, companion cells, phloem parenchyma

Tissue system in plants :

1.       Epidermal tissues

2.       Vascular tissues

3.       Ground /fundamental tissues

Meristematic tissues:

·         Growth in plants is largely restricted to specialized regions of active cell division called meristem.

·         Apical meristems are the meristems which occur at the tips of roots and shoots and produce primary tissues

·         Intercalary meristem are the ones which occur between mature tissues

·         Lateral meristem occurs in mature regions of roots and shoots and appear later than primary meristem

Permanent tissues/ mature:


·         The newly formed cells from primary and secondary meristems which become structurally and functionally specalised and lose the ability to divide are permanent tissues

I.Simple tissues. (made up of only one type of cells )

1.       Parenchyma -

o   major component within organs

o   Isodiametric,spherical, oval,round, polygonal,elongated in shape.

o   Thin cell walls made of cellulose.

o   Closely packed or have intercellular spaces

o   Function. Photosynthesis, storage, secretion.

2.       Collenchymas

·         occurs in layers below epidermis, either in homogeneous layer or in patches

·         Thickened at the corners due to pectin, cellulose, oval, spherical, polygonal

·         Assimilate food when chloroplasts is present

·         Intercellular spaces absent- function. Mechanical support

3.        Sclerenchyma -  

·         long narrow cells, lignified walls, with pits

·         Dead- fibers-thick walled, elongated, pointed

·         Sclereids- spherical, dead, narrow cavity-lumen

·         Found in – guava, pear, sapota

·         Function. Mechanical support

II. Complex tissues (more than one type of cells)

1.       Xylem. Conducting tissue for  water and minerals

·         Tracheids. Elongated or tube like cells, dead, main water transporting element

·         Vessels. Long cylindrical, lignin in cell walls, large central cavity, devoid of protoplasm.

·         Xylem fibres- lumens present, septate/aseptate

·         Xylem parenchyma- living thin- walled, cell walls, cellulose, store food as starch or fat, tannins

2.       Phloem - (transports food material)

·         Sieve tubes- long, tube like, perforated, forms sieve plates

·         Companion cells – pit is present , helps in maintenance of pressure gradient in the sieve tubes

·         Phloem parenchyma – elongated, tapering, dense cytoplasm, cell wall, cellulose, pits

·         Phloem fibres - unbranched, pointed, quite thick.

Tissue system :

1.       Epidermal tissue system

·         Cuticle present- contains stomata ( guard cells, subsidiary cells, stomatal apparatus )

·         Trichomes – (on stem) multicellular, secrete oils. Root hairs- single celled.

2.       Ground tissues

·         Tissues except epidermal and vascular tissues.

·         Mesophyll. ( collenchymas, sclerenchyma, parenchyma )

3.       Vascular tissue system

·         Cambium. ( lateral meristem )

·         Radial vascular bundle – in roots

·         Conjoint open vascular bundle  - in dicot stem and leaves

·         Conjoint closed vascular bundle – in monocot stem and leaves

Anatomy of dicotyledonous and monocotyledonous plants:

1.       Dicotyledonous root

Epidermis – root hair – cortex ( Parenchyma ) endodermis – suberin layer as casparian strips

Pericycle (lateral roots) pith is small – conjuctive tissues ( between xylem and phloem )

Cambium ring  ( 2-4 xylem and phloem )

Stele ( endodermis, pericycle, vascular bundle and pith )

2.       Monocotyledonous root

No cambium in the vascular bundles.  (6 vascular bundles and are scattered) called polyarch - pith is large – since no cambium, and no secondary growth

3.       Dicotyledonous stem

·         Epidermis, cuticle, trichomes, hypodermis (collenchymas)

·         Cortical layer ( parenchyma ) endodermis(starch sheath)

·         Pericycle - vacular bundles – medullary rays

·         Vascular bundles are in a ring

·         Conjoint, open, and endarch protoxylem

·         Pith is larger  (parenchyma)

4.       Monocotyledonous stem

·         Epidermis – hypodermis ( sclerenchyma ) scattered vascular bundles, sclerenchyma.

·         Bundle sheath – vascular bundles are conjoint, closed, no cambium

·         Peripheral  vascular bundle are smaller than central

·         No secondary growth- no trichomes

·         Water containing cavities are present- no distinct pith

Stem :

1.       Trichomes present / absent

2.       Vascular bundle scattered/ rings

3.       Vascular bundles closed/ open – cambium

4.       Pith present /absent

Leaves :

1.       Dorsiventral leaf /dicot leaf:

·         Epidermis are adaxial epidermis (upper) and abaxial epidermis (lower)

·         Cuticle – stomata is more on lower epidermis

·         Mesophyll – it has two types of cells , palisade parenchyma and spongy parenchyma

·         Vascular system  vascular bundle are present in vein and midrib

·         Reticulate venation –vascular bundle are surrounded by bundle sheath

2.       Isobilateral / monocot leaf:

·         Same anatomy –  but no spongy parenchyma and stomata on both side

·         Bulliform cells – parallel venation

Secondary growth:

·         Primary growth- apical meristem ( grows length wise )

·         Secondary growth –increase  in girth

·         It involves lateral meristem vascular cambium and cork cambium

·         Vascular cambium

Formation of cambial ring

·         Intrafacicular cambium

·         Interfascicular cambium

·         Activity of cambial ring

·         Formation of secondary xylem secondary phloem

·         More active on the inner side so more xylem

·         Spring early wood –more active and light coloured

·         Autumn late wood – less active and dark coloured

·         The two kinds of wood that appear as alternate concentric rings, constitute an annual ring

·         Heart wood – dead, elements, highly lignified provides mechanical support

·         Sap wood – peripheral region , secondary xylem, light in colour, conduction of water and minerals

Cork cambium:


·         Cortical and epidermis layer get broken

·          Replaced to provide new protective cell layers

·         Cork cambium/ phellogen –develop in cortex region and produce new cells towards both sides

·         Outer cells form cork / phellum

·         Inner cells form secondary cortex / phelloderm

·         Bark  - soft early bark – formed early in the season

·         Late / hard bark – formed late in the season

·         Lenticels. Lens shaped openings  helps in exchange of gases.

Secondary growth in roots:

·         Wavy ring – later becomes circular

·         Secondary growth occurs in gymnosperms too (except in monocots) as monocot do not have cambium.

Summary of the whole
Anatomically, a plant is made of different kinds of tissues. The plant tissues are broadly classified into meristematic (apical, lateral and intercalary) and permanent (simple and complex). Assimilation of food and its storage, transportation of water, minerals and photosynthates, and mechanical support are the main functions of tissues. There are three types of tissue systems – epidermal, ground and vascular. The epidermal tissue systems are made of epidermal cells, stomata and the epidermal appendages. The ground tissue system forms the main bulk of the plant. It is divided into three zones – cortex, pericycle and pith. The vascular tissue system is formed by the xylem and phloem. On the basis of presence of cambium, location of xylem and phloem, the vascular bundles are of different types. The vascular bundles form the conducting tissue and translocate water, minerals and food material.Monocotyledonous and dicotyledonous plants show marked variation in their internal structures. They differ in type, number and location of vascular bundles. The secondary growth occurs in most of the dicotyledonous roots and stems and it increases the girth (diameter) of the organs by the activity of the vascular cambium and the cork cambium. The wood is actually a secondary xylem. There are different types of wood on the basis of their composition and time of production.


Tissues – a group of similar cells which perform same function together.

Types of tissues are – Epithelial tissue, Connective tissues, Muscular tissues and Nervous tissues.

1.Epithelial tissues:


·         Covers external surface and lines internal surface

·         Three specialized junctions are tight junction, adhering junction and gap junction

·         Non cellular basement membrane

·         No blood vessels

·         Receives nutrients from underlying connective tissues

Classification :

a)Simple epithelial  (one layer)

·         Squamous epithelium

·         Cuboidal epithelium

·         Columnar epithelium

·         Pseudo stratified epithelium

b)Compound epithelium  (many strata)

·         Stratified compound epithelium (squamous, cuboidal, columnar)

·         Transitional epithelium (urinary bladder)

2.Muscular tissues :

·         Striated muscle / Striated muscle / Voluntary muscle

·         Unstriated muscle / Smooth muscle / Involuntary muscle


Cardiac muscle (heart)

3.Neural tissue
– longest cell – neuron

Structure of neuron: Dentrite – Cyton – Axon with myelinated sheath with node of ranvier – axon ending

Organ and organ system:


Earthworm is a reddish brown terrestrial invertebrate that inhabits the upper layer of the moist soil. During day time, they live in burrows made by boring and swallowing the soil. In the gardens, they can be traced by their faecal deposits known as worm castings. The common Indian earthworms are Pheretima and Lumbricus.


Earthworms have long cylindrical body. The body is divided into more than hundred short segments which are similar (metameres about 100-120 in number). The dorsal surface of the body is marked by a dark median mid dorsal line (dorsal blood vessel) along the longitudinal axis of the body. The ventral surface is distinguished by the presence of genital openings (pores). Anterior end consists of the mouth and the prostomium, a lobe which serves as a covering for the mouth and as a wedge to force open cracks in the soil into which the earthworm may crawl. The prostomium is sensory in function. The first body segment is called the peristomium (buccal segment) which contains the mouth. In a mature worm, segments 14-16 are covered by a prominent dark band of glandular tissue called clitellum. Thus the body is divisible into three prominent regions – preclitellar, clitellar and postclitellar segments. In each body segment, except the first, last and clitellum, there are rows of S-shaped setae, embedded in the epidermal pits in the middle of each segment. Setae can be extended or retracted. Their principal role is in locomotion.


Body Wall: The body wall of earthworm is covered by thin non-cellular cuticle. Epidermis lies below the cuticle. This is followed by two muscle layers; circular and longitudinal. The innermost layer is the coelomic epithelium. The epithelium is composed of a single layer of columnar epithelial cells. The epithelial cells contain gland cells as well.

Alimentary Canal: The alimentary canal is a straight tube. It runs between the first to last segment. Mouth is terminal and opens into the buccal cavity (1- 3 segments). The mouth leads into muscular pharynx.

Pharynx continues into oesophagus (5-7 segments) which is a small narrow tube. The oesophagus continues into a muscular gizzard (8-9 segments). The gizzard helps in grinding the food. The stomach extends from 9th – 14th segments.

Decaying leaves and organic matter; mixed with soil; are the foods of the earthworm. The humic acid; present in humus; is neutralized by the calciferous glands in the stomach.

The intestine continues from the 15th segment to the last segment. On the 26th segment, a pair of short and conical caecae project from the intestine. Between 26th -35th segments, internal median fold of dorsal wall is present in the intestine. This internal fold is called typhlosole. The typhlosole increases the area of absorption in the intestine.

The alimentary canal opens to the exterior by a small rounded aperture; called anus.

Blood Vascular System: Closed type blood vascular system is present in earthworm. The blood vascular system is composed of a heart, blood vessels and capillaries. Smaller blood vessels supply the gut, nerve cord and body wall. Blood glands are present on the 4th, 5th and 6th segments. The blood glands produce blood cells and haemoglobin. Blood cells are phagocytic in nature. Exchange of gases occurs through moist body surface into the blood stream.

Excretory System: Nephridia are the excretory organs in earthworm. Nephridium is composed of coiled tubules. There are three types of nephridia, viz. septal, integumentary and pharyngeal nephridia.

Septal Nephridia: These are present on both sides of intersegmental septa of segment 15 to the last. The septal nephridia open into intestine.

Integumentary Nephridia: These are attached to the lining of the body wall of segment 3 to the last. The integumentary nephridia open on the body surface.

Pharyngeal Nephridia: These are present as paired tufts in the 4th, 5th and 6th segments.

A neprhidium is a funnel-like structure. It collects excess fluid from coelomic chamber. The tube at the end of the funnel carries the wastes into the digestive tube; through a pore on the surface in the body wall.

Nervous System: The nervous system is composed of a ventral pair of nerve cord. Ganglia are arranged in each segment on this paired nerve cord. The nerve cord in the anterior region (3rd and 4th segments) bifurcates and encircles the pharynx to join the cerebral ganglia. This forms a dorsal nerve ring.

Sensory System: There is no eye in the earthworm. But light and touch sensitive receptor cells are present. Chemoreceptors are also present. The sense receptors are present on the anterior part of the body.

Reproductive System: Earthworm is hermaphrodite.

Male Reproductive System: There are two pairs of testes present in the 10th and 11th segments. The vasa deferentia run up to the 18th segment; where they join the prostatic duct. Two pairs of accessory glands are present in the 17th and 19th segments. The common prostate and spermatic duct opens to the exterior by a pair of male genital pores. The male genital pores are present on the ventro-lateral side of the 18th segment. Four pairs of spermathecae are located in 6th to 9th segments. During copulation, spermatozoa are stored in the spermathecae.

Female Reproductive System: One pair of ovaries is attached at the inter-segmental septum of the 12th and 13th segments. Ovarian funnels are present beneath the ovaries. The ovarian funnels continue into oviduct. They join together and open on the ventral side as a single median female genital pore on the 14th segment.

Fertilization & Development: During mating, a mutual exchange of sperms occurs between two worms. Mature sperm and egg cells and nutritive fluid are deposited in cocoons produced by the gland cells of clitellum. Cocoons are deposited in soil. Fertilization and development occur within the cocoons. After about 3 weeks, each cocoon produces two to twenty baby worms. The average number of baby worms from a cocoon is four. Development is direct.

Economic Importance: Earthworms are called 'Friends of Farmers'. They burrow in the soil and make it porous. It helps in respiration and penetration of developing plant roots. Earthworms are also used as bait in fishing.


Class: insect

Phylum: arthropoda


·         1/4   -3  inches

·         nocturnal omnivorous

·         body- head, thorax and abdomen

·         body is covered with chitinous exoskeleton with hardened plates. Plates are called  sclerites (tergites and sternites ) connected by arthrodial membrane.

·         Compound eyes. Antennae, bitting and chewing mouth parts.

·         Mouth part consists of a labrum ( upper lip ), a pair of mandible, a pair of maxillae and a

·         Labium ( lower lip ) and a tongue called hypopharynx.

·         Throax  consists of three parts- prothorax, mesothorax, metathorax ( each has a pair of legs )

Anatomy :


a)Digestive system. Mouth-oesophagus-crop-gizzard-hepatic caecae- midgut-hind gut- rectum-anus

b)Circulatory system. Open blood vascular system- blood (haemolymph) - Pumped in to space (haemo coel ) blood (plasma + haemocytes ) heart is elongated muscular tube in dorsal line, heart is opening called ostia (blood enters pumped anteroirly.

c)Respiratory system.  Tracheary  system. (net work of trachea) - External opening called spiracles – trachea – tracheoles – blood.

d)Excretory system. Malphigian tubules - Collect uric acid -  Uricotelic – in  addition fat bodies, nephrocytes and Urecose glands.

e)Nervous system. Ganglian - 3 pair in thorax and 6 pair in abdomen.

f)Sense organs. Antennae, compound eyes, maxillary palps, labial palps and  anal cerci - Eye is compound, made of 2000 ommatidium (mosaic vision)

g)Reproductive system.

·         Male. Testes. (4-6 ) vas deferens- seminal vesicle - ejaculatory duct.

·         Female- ovaries (2-6) oviduct- vagina – genital chamber - fertilized egg – ootheae ( 9-10 oothecae) development is paurometabolous, devevelopmrnt Is through nymphal stage. It looks like adult grows of moulting 13 times.




In India, the most common species of frog is Rana tigrina. The frogs are cold-blooded or poikilotherms. They have the ability to camouflage. The frogs also show mimicry as a tool for protection. During summers, the frogs live in summer sleep (aestivation) and during winters, they live in winter sleep (hibernation).


The skin of frog is moist and slippery due to the presence of mucus. The dorsal side of body is usually olive green with dark irregular spots. The skin on the ventral side is uniformly pale yellow.

The body of a frog is divisible into head and trunk. A pair of nostrils is present above the mouth. Eyes are bulged and covered by a nictitating membrane. These membranes protect the eyes while the frog is under water. Ears are represented by membranous tympanum on either side of the eyes.

The forelimbs and hind limbs help in swimming, walking, leaping and burrowing. The hind limbs have five digits. The hind limbs are large and more muscular than forelimbs. The forelimbs have four digits. Webbed digits help in swimming. Sexual dimorphism is present in frogs. Sound producing vocal sacs and a copulatory pad (on the first digit of the fore limb) are present in male frogs.


Digestive System: The alimentary canal is short because frogs are carnivorous. The alimentary canal is composed of buccal cavity, pharynx, oesophagus, stomach, intestine and rectum. The rectum opens out by cloaca. Liver produces bile and the pancreas produces pancreatic juice. Digestive enzymes are present in the pancreatic juice. The bilobed tongue helps in capturing prey.

Digestion: Gastric juices and HCl are secreted in the stomach; where partial digestion of food takes place. Bile and pancreatic juice are received in the duodenum. Bile emulsifies fat. Pancreatic juices digest carbohydrates and protein. Final digestion takes place in the intestine.

Absorption: Numerous finger-like folds are present in the inner wall of intestine. These are called villi and microvilli and facilitate absorption of food. The undigested food goes to the rectum from where it is expelled out through cloaca.

Respiration: Frogs respire through lungs when they are on land. The exchange of gases takes place through skin when the frog is in water. The lungs are a pair of elongated, pink-coloured, sac-like structures. Lungs are present in the upper part of the thorax. During aestivation and hibernation, exchange of gases takes place through skin.

Blood Vascular System: The vascular system is closed type and is well developed. Lymphatic system is also present in frogs. The blood vascular system of frog is composed of a heart, blood vessels and blood. The lymphatic system consists of lymph, lymph channels and lymph nodes.

Heart: The heart is situated in the upper part of the body cavity. There are three chambers in the heart of frog. There are two atria and one ventricle. The heart is covered by a membrane; called pericardium. A triangular structure; called sinus venosus; joins the right atrium. Blood from the vena cava reaches the sinus venosus. The ventricle opens into a sac-like conus arteriosus on the ventral side of the heart.

Arteries and Veins: Arteries carry blood from the heart to all parts of the body. The veins carry blood from all parts of the body to the heart. Hepatic portal system and renal portal system are present in frogs. The hepatic portal system is a system of special venous connection between liver and intestine. The renal portal system is a system of special venous connection between the kidneys and the lower parts of the body.

Blood: The blood is composed of plasma and cells. RBCs and WBCs and platelets are present in the blood of frogs. RBCs are nucleated and contain haemoglobin. Lymph lacks few proteins and RBCs and hence is different from blood.

Excretory System: The excretory system is composed of a pair of kidneys, ureters, cloaca and urinary bladder. The kidneys are compact, dark red and bean-like structures. The kidneys are situated a little posteriorly in the body cavity; on both sides of the vertebral column.

Each kidney is composed of several nephrons. Two ureters emerge from the kidneys in the male frogs. In males, the ureters act as urogenital duct and opens into the cloaca. In females, the ureters and oviduct open separately in the cloaca. The frog is a ureotelic animal.

Control & Coordination: Frog has a highly evolved neural system and endocrine glands.

Coordination By Hormones: Hormones are secreted by various endocrine glands and facilitate chemical coordination. The main endocrine glands in frog are; pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenal and gonads.

Nervous System: The nervous system is organized into central nervous system, peripheral nervous system and autonomic nervous system.

Central Nervous System: The central nervous system is composed of the brain and the nerve cord. The brain is enclosed in a bony structure; called brain box or cranium. The brain is divided into forebrain, midbrain and hindbrain.

Forebrain includes olfactory lobes, paired cerebral hemispheres and unpaired diencephalon.

A pair of optic lobes is present in the midbrain.

The hindbrain consists of cerebellum and medulla oblongata. The medulla passes out through the foramen magnum and continues into the spinal cord. The spinal cord is enclosed in the vertebral column.

Ten pairs of cranial nerves arise from the brain.

Sense Organs: Organs of touch (sensory papillae), taste buds, olfactory receptors (in nasal epithelium), eyes and internal ears are the sense organs of frog. The eyes and internal ears are well developed, but the rest of the sense organs are cellular aggregations around nerve endings.

Frogs have simple eyes. The ear also serves as the organ of balancing (equilibrium).

Reproductive System:

Male Reproductive Organs: The male reproductive system of frog is composed of a pair of yellowish ovoid testes. The testes are adhered to the upper part of kidneys by a double fold of peritoneum called merorchium. There 10 – 12 vasa efferentia arising from the testes. They enter the kidneys on their side and open into Bidder's canal. Finally, it communicates with the urinogenital duct which comes out of the kidneys. The urogenital ducts open into the cloaca. The cloaca is used to pass faecal matter, urine and sperms to the exterior.

Female Reproductive Organs: There is a pair of ovaries which are situated near kidneys. There is no functional connection between the ovaries and the kidneys. The oviducts open separately into the cloaca. A female frog can lay 2500 to 3000 ova at a time.

Fertilization: Fertilisation is external and takes place in water. Development is indirect and the larva is called tadpole.

Significance for Humans:
Frogs eat insects and thus protect the crops. Frogs serve as an important link in the food chain and hence maintain the ecosystem. Frog meat is used as delicacy in some countries.

All organisms are made of cells or aggregates of cells.  Cells vary in their shape, size and functions.  Based on the presence or absence of a membrane bound nucleus and other organelles, cells can be named as Prokaryotic or Eukaryotic.

Cell is the fundamental structural and functional unit of all living organisms.

Anton Von Leeuwenhoek first observed and described a liver cell.

Robert Brown later discovered the nucleus.

Cell theory – Schleiden and Schwann ( later Virchow) 

All living organism are made of cells and their products.

All cells arise from pre – existing cells.

Prokaryotic cell  : Bacteria, Blue-green algae, Mycoplasma, PPLP (Pleuro Pneumonia Like Organisms.

·         Glycocalyx, cell wall, plasma membrane

·         Based on staining property gram + and gram –ve bacteria.

·         Mesosome, chromatophores (extension of plasma membrane)

·         Motile, non motile,

·         Flagellum- three parts are – filament. Hook, and basal body

·         Pili, fimbriae – surface structure do not play a role in motility but helps in attachment

·         Ribosomes and inclusion bodies.

·         Ribosomes. 15-20 nm, 2 sub – units 50S and 30S-together form 70S. – help in Protein synthesis – polysomes / polyribosomes on m RNA

·         Inclusion bodies. Reserve materials: Phosphate granules, Cyanophycean , Glycogen granules, Gas vacuoles.

Eukaryotic cell :

·         Protists, Fungi, Plant cell and animal cell

·         Cell membrane – fluid mosaic model by Singer & Nicholson (1972) - bilipid layer of phospholipids

with two types of membrane proteins called peripheral protein and integral proteins with cholestral, glycolipids and glycoproteins.

Cell wall : It gives shape, mechanical support, cell-to-cell interaction – made of cellulose, hemicelluloses, pectins (in plants) and cellulose, galactans, mannans, calcium carbonate (in algae).

·         Primary cell wall – in young plant cell, capable of growing till cell matures

·         Secondary cell wall – formed on the inner side of the cell.

·         Middle lamellae – calcium pectate

·         The cell wall middle lamellae may be traversed by plasmodesmata which connect the cytoplasm of neighbouring cells.

Endoplasmic reticulum :

·         SER – no ribosomes on its surface, appears smooth (helps in lipid synthesis/ steroids)

·         RER – ribosomes are present on its surface, appears rough surface (helps in protein synthesis) 

Golgi apparatus – first observed by Camillo Golgi  - packaging unit - makes glycoprotein and glycolipids.

Lysosomes – contain enzyme, hydrolases – help intra cellular digestion.

Vacuoles :  tonoplast is vacuole membrane - contractile vacuole (for excretion) – food vacuole (engulfing).

Mitochondria – power house of the cell –  sites of aerobic respiration, produce energy capsules ATP – double membrane structure, inner compartment is known as Matrix – inner membrane forms a number of infoldings called Cristae to increase the surface area – matrix possesses single circular DNA, few RNA and ribosomes (70S).

Plastids – chloroplast, chromoplast and leucoplasts - Leucoplasts  - amyloplasts,  (starch); Elaioplasts (oil/fat); Aleuroplasts  (proteins).

Ribosomes (George Palade) - Composed of RNA and proteins - Eukaryotic ribosomes are 80 S

‘S’ stand for the sedimentation coefficient (Svedbergs unit) - Site of protein synthesis.

Cytoskeleton: Network of filaments proteinaceous structures in the cytoplasm - made up of microtubules and micro philaments. Functions:- Mechanical support, motility, maintenance of the shape of the cell.

Cilia and flagella: Core is called axoneme - has 9 pairs of  doublets of microtubules on peripheral and one pair in the centre 9+2 array emerged from centriole like structure called the Basal bodies.

Centrosome and centrioles: Centrosome contains 2 centrioles - Each centriole has a cart wheel like organization with 9 evenly spaced microtubule  - triplets connected to central  hub by radial spokes –produces spindle apparatus dueing cell division

Nucleus  ( Robert brown, 1831) :

  • ·         Chromatin named by Flemming. 

  • ·         Nucleoli – active ribosomal  RNA synthesis

  • ·         Nucleoplasm – nucleolus + chromatin

  • ·         Nuclear membrane – with perinuclear space

  • ·         Chromosome – DNA + histone proteins

  • ·         Centromere –primary constriction – disc is known as kinetochores

  • ·         No nucleus in erythrocytes (RBC) of mammals and sieve tube cells in vascular plants

  • ·         Based on the position of centromere

  • ·         Metacentric, sub-metacentric, acrocentric, telocentric

Microbodies: Minute vesicles containing various enzyme (in plant and animal cell).

Cell Division

Phases of Cell Cycle

The cell cycle is divided into two basic phases:

Interphase: The phase between subsequent cell divisions is called the interphase. The interphase lasts for more than 95% of the cell cycle.

M Phase (Mitosis phase): The actual cell division takes place in the M phase. The M phase lasts for less than 5% of the cell cycle. The M phase is composed of two major steps, viz. karyokinesis and cytokinesis. Division of nucleus happens during karyokinesis. Division of cytoplasm happens during cytokinesis.

The interphase is further divided into three phases, which are as follows:

G1 phase (Gap 1): During this phase, the cell is metabolically active and continuously grows.

S phase (Synthesis): During this phase, DNA synthesis or replication takes place. The amount of DNA becomes double during this phase, but the number of chromosomes remains the same.

G2 phase (Gap 2): During this phase, protein synthesis takes place.

Quiescent Stage (G0): Cells which do not divide further, exit G1 phase to enter an inactive stage. This stage is called quiescent stage (G0) of the cell cycle. The cells in this stage remain metabolically active but do not undergo division. But these cells can resume division as and when required.


Mitosis is divided into four stages, viz. Prophase, Metaphase, Anaphase and Telophase


Condensation of chromosomal material takes place. A chromosome is seen to be composed of two chromatids. The chromatids are attached together at the centromere.
Spindle fibres are formed.
Various cell organelles; like golgi bodies and ER cannot be seen during this staged. Nucleolus and nuclear envelope also disappear.

All the chromosomes come to lie at the equator. In each chromosome, one chromatid is connected to the spindle fibre from one pole and another chromatid is connected to the spindle fibre from another pole. The plane of alignment of chromosomes during this phase is called metaphase plate.

Centromeres split which results in separation of chromatids.
After that, chromatids move to opposite poles.

The chromosomes form clusters at opposite poles. They become inconspicuous. Nuclear envelope is formed around the chromosome clusters. Nucleolus, golgi complex and ER are also formed.


Division of cytoplasm is achieved by cytokinesis. In animal cell, a furrow appears in the plasma membrane. The furrow gradually deepens and finally joins in the centre. Thus, the cytoplasm is divided into two parts. In plant cells, cell wall formation begins in the centre. This grows outwards to meet the existing lateral walls and thus, the cytoplasm is divided into two parts.

Significance of Mitosis
Mitosis results in the formation of new cells which are required for growth and repair.
Mitosis results in the formation of two daughter cells; which have identical genetic make up, similar to the mother cell.

II Meiosis

  • It is the process which involves the reduction in the amount of genetic material.
  • It mainly occurs in germ cells.
  • At the end of meiosis II, four haploid cells are formed.
  • It is comprised of two successive nuclear and cell division with a single cycle of DNA replication.
  • The phases of meiosis are as shown below-
Meiosis I

1. Prophase I – It comprises of 5 stages:

i. Leptotene

  • Chromosomes start condensing.
ii. Zygotene

  • Pairing of chromosomes called synapsis occurs.
  • A pair of synapsed homologous chromosomes is called bivalent or tetrad.
iii. Pachytene

  • Exchange of genetic material (crossing over) between non-sister chromatids occurs.
  • Chiasmata formation
iv. Diplotene

  • Bivalents formed during pachytene separate from each other (except at chiasmata) due to dissolution of synaptonemal complex.
v. Diakinesis

  • Terminalisation of chiasmata can be observed.
  • By the end of this stage, the nucleolus disappears and the nuclear envelope breaks.
2. Metaphase I

  • Bivalents (tetrad) get aligned along metaphase plate through spindle fibres.
3. Anaphase I

  • Homologous chromosomes separate while chromatids remain attached at their centromere.
4. Telophase

  • Nucleolus and nuclear membrane reappear around chromosome clusters at each pole.
  • Inter-kinesis – It is the stage between two meiotic divisions.
Meiosis II

1. Prophase II

  • Chromosomes become compact.
  • Nuclear membrane disappears.
2. Metaphase II

  • Chromosomes align at the equator.
  • Kinetochores of sister chromatids attach to spindle fibres at each pole.
3. Anaphase II

  • Chromatids separate by splitting of centromere.
  • As a result, chromatids move towards their respective poles in the cell.
4. Telophase II

  • Nuclear envelope and nucleolus reform around the chromosome clusters.

  • After meiosis II, the process of cytokinesis results in the formation of four haploid cells.
Significance of meiosis:

  • It results in reduction of chromosome number by half in gametes, which again doubles during fertilization. Therefore, it helps to conserve the chromosome number of species from generation to generation.
  • Crossing-over, occurring in pachytene stage of meiosis I, is a source of genetic variation in sexually reproducing organisms.
  • The variation thus formed helps in evolution.


Living cells are composed of both organic and inorganic components.

How to analyse chemical composition:

For organic compounds:

·         Living tissue + trichloro acetic acid and grind it to form slurry.

·         Filter the slurry to obtain 2 fractions like  Filtrate/ acid soluble and Retentate/ acid insoluble

For inorganic compounds:

Sample of tissue should be burnt to obtain ash and different kinds of inorganic compounds were identified.

Types of biomolecules  - Micro molecules and Macro molecules

·         Micro molecules are known as monomers

·         Macromolecules are known as polymers

Primary and Secondary metabolites: These are biomolecules in living cells metabolites.

Primary metabolites are those which have identifiable functions and play specific roles in normal physiological processes. Eg. Amino acids, nitrogenous bases, proteins and nucleic acid.

Secondary metabolites are product of certain metabolic pathways from primary metabolites.

·         Pigments – anthocyanin, carotenoids

·         Drugs – vinblastin, curcumin

·         Alkaloids - morphine, codeine

·         Essential oils – lemon grass oil

·         Polymeric compounds - rubber gum, cellulose, resins

It is molecules with weight greater than 1000 dalton found in acid insoluble fraction.

Eg- polysaccharides, nucleic acid, proteins and lipids.

Polysaccharides :

·         Long chain of polymers of monosaccharides – 2 types of Mono-polysaccharides (cellulose, starch – made of only Glucose monomers).

·         Heteropolymer – chitin

·         Inulin  -is a polymer of fructose

·         Glycogen – polymer of glucose in animal tissues

·         Monosaccharides are joined by Glycosidic acid bond, right end is reducing and left end is non reducing.

·         Starch forms helical secondary structures. Starch can hold Iodine molecules in helical portion and form blue colour. But Cellulose does not contain complex helices and cannot hold iodine.

·         Complex polysaccharide: .Plant cell wall (cellulose ), Paper (plant pulp ), Cotton, Fibre (cellulose) Exoskeleton of animals, building blocks, amino-sugars and chemically modified Sugars like, Eg. – Giucosamine (N – acetyl galactosamine).

Nucleic acids:  
·         DNA – Polynucleotide chain, double stranded (deoxy ribose sugar) – nitrogenous bases are A, G, C and T

·         RNA – single stranded Polymer of ribo-nucleotides (ribose sugar) – A, G, C and U

·         Nucleotides – nitrogenous base + pentose sugar + phosphate group

·         Nucleoside – nitrogenous base + pentose sugar

·         Nitrogenous  bases

1.       Adenine (A)

2.       Guanine(G)

3.       Cytosine( C )

4.       Thymine (T)


Phospho-diester bonds – covalent bond formed between nucleotides.


·         Polymer of amino acids (peptide bonds)

1.       Primary structure – linear chain of aminoacids linked by peptide bonds – non functional.

2.       Secondary structure – alpha-helix or beta-pleated structure with peptide and hydrogen bonds.

3.       Tertiary structure – long chain of coiled structure with peptide, hydrogen, disulphide and ionic bonds – functional structurte of protein.

4.       Quaternary structure – group of more than two tertiary structured proteins (eg- haemoglobin – made of two alpha and two beta chains).

Nature of bonds linking monomers in a polymer:  

1.       Amino acids are linked by Peptide bonds

2.       Monosaccharides are linked by Glycosidic bond

3.       Nucleotides are linked by  Phosphodiester bond between 3-C of one nucleotide with

5-C of another - Each helix of DNA contains 10 base pairs with the length of 3.4 nm (34 Ao).

Concept of Metabolism:   

·         Biomolecules have turn over (because constantly changing from one form to another)

·         Chemical reactions are called metabolism.


·         Amino acids can be formed by the removal of amino group in a nucleotide base.

·         Hydrolysis of disaccharides – 2  monosacharides

·         Linked chemical reactions are called Metabolic pathways, it is a catalysed reaction by enzymes.

Metabolic pathways in living system:

·         Anabolic pathways - making / constructing big molecules from micromolecules (eg – photosynthesis)

·         Catabolic pathways – breaking down of big molecules in to smaller ones  (eg – respiration)

·         For both ATP is required (energy currency)

The living state

·         Blood glucose – should be 4.5 -5.0mM

·         Hormones – in nanograms/mL

·         System at equilibrium cannot perform work

·         As living organisms work constantly, it is non equilibrium.

·         Hence the living state is non equilibrium steady state to be able to perform work.

Enzymes Vs Catalysts:  

·         Enzyme –  helps in chemical reactions

·         Inorganic reaction :- Ba(OH)2 + H2SO4 --> BaSO4 + 2H2O – No enzyme used.

·         Organic reaction  - Enzyme used

·         Carbonic anhydrase – fastest enzyme - without enzyme 200 molecules / hr - with enzyme 600,000 molecules / sec.

·         Activation energy  is the energy needed to do work.

Nature of enzyme action:

Enzyme + Substrate --> ES complex --> Enzyme + Product


It is produced by living cells and made of protein.

It is chemical substances and help in chemical reactions.

It can work well at optimum temperature of 40o C.

It can work even at 80 – 90o C.

It reduces the activation energy.

It requires different level of energy.

Properties of Enzymes:

1.       All enzymes are proteins, but all proteins are not enzymes.

2.       Enzymes are specific with their substrates as their active sites are different for different substrates.

3.       Enzymes are of 2 types 1. Builders. 2. Breakers

4.       Enzyme does not get used up during the reaction, as it does not change its shape – hence less enzymes are required.


The enzyme changes its shape and the substrate cannot bind with the enzyme - affect tertiary structure of the protein.


Factors affecting enzyme activity:

·         Effect of temperature: temperature at which the enzyme gives its maximum rate of reaction is known as optimum temperature (40o C).

·         Effect of pH  - different enzymes work at different pH, for example, enzyme pepsin works at pH 2, and enzyme amylase at pH 7, it is called optimum pH.

·         Substrate concentration -

Enzyme inhibition – enzyme action can be inhibited by other chemical molecules called inhibitors.

Competitive inhibition: Inhibitor chemical molecule resembles the structure of substrate and bind with

                                          the active site of enzyme instead of substrate, hence there is no production of


Eg. Inhibition of Succinic dehydrogenase by Malonate (inhibitor), which resembles the

       substrate Succinate  in structure.

·         All enzymes are proteins but all proteins are not enzymes. Eg. Heamoglobin is a protein but not an enzyme.

·         Enzymes at low temperature become inactive, enzymes at high temperature denatures.

Classification and nomenclature of enzymes: Based on type of reaction they classified into 6 classes.

1.       Dehydrogenases/ oxidoreductases -

S reduced + S’ oxidized  ------ S oxidized + S’ reduced

2.       Transferases -

S-G + S’------- S+S’-G

3.       Hydrolases -

Hydrolysis of ester ether, peptide and glycoside

C –C , C- halides , P-N bonds

4.       Lyases -

Removal of group from substrates other than hydrolysis ( from double bond )


l   l

C  C  ------ X-Y+C =C

5.       Isomerases  - Inter-conversion of optical geometrical or positional isomers.

6.       Ligases – linking two compounds. C-O, C-S, C-N, P-O


·         It is a non – protein part, makes enzyme more active – protein part is called Apoenzyme.

·         There are 3 kinds of factors:

1.       Prosthetic group - tightly bound with apoenzyme. Eg. Peroxidase, Catalases.

2.       Co-enzyme – bound transient form. Eg. NAD, NADP (Nicotinamide Adenine Dinucleotide Phosphate)

3.       Metal ions -  Form coordination bonds. Eg. Fe, Zn.

Means of Transport

Three means of transport in plants:

  • Diffusion
  • Facilitated Diffusion
  • Active Transport


  • Movement of molecules from high concentration to low concentration without semi-permeable membrane.
  • Slow process
  • No expenditure of energy
  • Diffusion depends upon: Concentration gradient, Permeability of the membrane, Temperature, Pressure and Size of the substance.

Facilitated Transport

  • In facilitated diffusion, the membrane proteins are involved. They provide a site for hydrophilic molecules to pass through the membrane and no energy is required.
  • Proteins involved in the process form channels which may always be opened or controlled. Facilitated diffusion is very specific.
  • Porins: Proteins that forms huge pores in the outer membranes of plastids, mitochondria, etc. They are different kinds;
  • Aquaporins: Proteins that facilitate diffusion of water molecules
  • Transport can be of 3 types:
    • Symport − both molecules move in the same direction
    • Antiport − both molecules move in opposite directions
    • Uniport − independent movement of molecules
  • When all proteins involved are saturated, it leads to maximum transport.
Active transport

  • Requires special proteins which are very specific and sensitive to inhibitors.
  • Requires energy to pump molecules against the concentration gradient.
  • When all proteins involved are saturated, it leads to maximum transport.
Water Potential (ψW)

  • Greater the concentration of water in a system, greater is its kinetic energy and greater is the water potential.
  • It is measured in Pascal (Pa)
  • If two systems are in contact, then there is movement of water from the solution with greater water potential to lower water potential.
  • Solute potential (ψs) − Magnitude of lowering of water potential when a solute is added to the water
  • Pressure Potential (ψp) − Magnitude of increase of water potential when pressure greater than atmospheric pressure is applied to pure water or a solution
  • Water potential of pure water is zero.
  • Solute potential is always negative and water potential is always positive.
  • ψw = ψs + ψp

  • Water diffuses from region of its higher concentration to its lower concentration through semi-permeable membrane.
  • Diffusion of water across a semi-permeable membrane
  • Direction and rate of osmosis depends upon pressure gradient and concentration gradient.
  • Osmotic pressure − External pressure applied to prevent the diffusion of water
    It depends upon solute concentration.
  • Numerically, osmotic pressure is equal to osmotic potential
  • Osmotic pressure has positive sign.  Osmotic potential has negative sign.
Types of Solutions:

  • Isotonic solution
    • Concentration of external solution is equal to Concentration in cytoplasm
    • There is no net gain, hence No change in cell size.
  • Hypotonic solution
    • Concentration in cytoplasm is greater than the Concentration of external solution.
    • So water enters into the celsl and Cells swell.
  • Hypertonic solution
    • Concentration of external solutions is greater than the Concentration in cytoplasm.
    • Hence water moves from cells to external solution and Cells shrink.

  • Plasmolysis
    • It occurs when cell is placed in hypertonic solution, because water moves out from cytoplasm and vacuole. Hence Cell membrane shrinks away from the cell wall.
    • As water moves in, cytoplasm builds up a pressure against the cell wall. This pressure is called turgor pressure and cells enlarge.

  • Diffusion in which water is absorbed by solids, causing them to enormously increase in volume.
  • Imbibition is along the concentration gradient and depends upon affinity between adsorbent and liquid being adsorbed.
  • Examples − Imbibition of water by seeds that causes seeding to emerge out of soil, swelling of wooden door during rainy season, swelling of raison when soaked in water.
Long Distance Transport of Water: It occurs by three processes, Diffusion, Mass flow system and Translocation through conducting vascular tissues. There are two types of conducting tissues, namely;

Xylem: Transports water, salts, nitrogen and hormones. From roots to the other parts and it is unidirectional.

Phloem: Transports organic and inorganic solutes.  It occurs from the source (leaves) to the sink (storage part) and it is multidirectional.

Absorption of Water by Plants

  • Water is absorbed through roots by diffusion.
  • Root hairs (slender, thin-walled extensions of root epidermal cells) increase the surface area for absorption.
  • Once absorbed by root hairs, water moves into deeper layers by 2 pathways − Apoplast Pathway or Symplast Pathway.
Apoplast Pathway:

  • Movement occurs through the intercellular spaces or walls of the cells, without entering the cytoplasm.  Movement is fast.  Most of the water flow in roots occurs via apoplast, except at the casparian strip.

Symplast pathway:

·         Water enters the cell through the cell membrane and travels intracellularly through plasmodesmata. Movement is slow. At the casparian strip region, water moves through the symplast.

·         Most of the water enters through apoplast pathway, endodermis has casparian strips which are made of suberin, it is impervious to water, so water enters the symplast.

There are two forces which are responsible for transporting the water up in a plant; they  are root pressure and transpiration pull.

Root Pressure

  • Water molecules enter from soil to root hair, then to cortical cells and finally reach xylem vessels.
  • Positive pressure created inside the xylem when water transported along the concentration gradients into the vascular system
  • Guttation − Loss of water in its liquid phase from special openings near tip of grass blades and leaves of herbaceous plants.
Transpiration pull

  • Transpiration is a process of loss of water in the form of water vapours from the surface of leaves.
  • Transpiration accounts for loss of 99% of water taken by the plant. Loss is mainly through stomata.
  • Pull of water as a result of tension created by transpiration is the major driving force of water movement upwards in a plant.
  • There are three physical properties of water which affect the ascent of xylem sap due to transpiration pull.
    • Cohesion − Mutual attraction between water molecules
    • Adhesion − Attraction of water molecules to polar surface
    • Surface tension − Attraction of water to each other in liquid phase to a greater extent than to water in gaseous phase

  • It occurs manly through openings called stomata. Transpiration provides the transpirational pull which is responsible for the upward movement of water in tall plants.
  • Stomata:
    • Open in the day and close during the night
    • Also contribute in the exchange of O2 and CO2
    • Opening and closing of stomata is influenced by the turgidity of the guard cells.
Factors affecting transpiration:

  • External factors: Temperature, Light, Humidity and Wind speed.
  • Plant factors / Internal factors: Number of stomata, distribution of stomata, water status in plants.
Importance of Transpiration

  • Creates transpirational pull for transport
  • Supplies water for photosynthesis
  • Transports minerals from soil to all parts of a plant
  • Cools the surface of the leaves by evaporation.
  • Keeps the cells turgid; hence, maintains their shape
Uptake of Mineral Nutrients

  • Minerals are absorbed from the soil by active transport. They cannot follow passive transport because of two factors;
    • They are charged. Hence, they cannot cross the cell membranes.
    • Concentration of minerals in soil is lesser than the concentration of minerals in roots. Hence, concentration gradient is not present.
  • Certain proteins in the membranes of root hair cells actively pump ions from soil to cytoplasm of epidermal cells.
Transport of Mineral Nutrients

  • Unloading of mineral ions occur at fine vein endings of the leaves through diffusion.
  • Some minerals are also remobilised from old senescing parts N, P K, S. Minerals forming structural components (example Ca) are not remobilised.
  • Phloem transports food from source to sink, but this source-sink relationship is reversible depending upon the season. Therefore, phloem transport is bi-directional.
Mass flow Hypothesis:

  • This is the well accepted mechanism used for translocation of sugars from the source to the sink.
  • Glucose prepared at the source is converted into sucrose. Sucrose is moved to the companion cells, and then to the living phloem sieve tube cells by active transport. This process of loading creates a hypertonic condition in the phloem.
  • Water in the adjacent xylem moves into the phloem by osmosis. Osmotic pressure builds phloem sap.
  • As hydrostatic pressure on the phloem sieve tube increases, pressure flow begins and sap moves through the phloem to the sink and stored as complex carbohydrates (starch).

In 1860, Julius von Sachs, a prominent German botanist, demonstrated, for the first time, that plants could be grown to maturity in a defined nutrient solution in complete absence of soil. This technique of growing plants in a nutrient solution is known as hydroponics

Criteria for the essentiality of an element are:
  • The element must be absolutely necessary for supporting normal growth and reproduction. In the absence of the element the plants do not complete their life cycle or set the seeds.
  • The requirement of the element must be specific and not replaceable by another element. In other words, deficiency of any one element cannot be met by supplying some other element
  • The element must be directly involved in the metabolism of the plant
Categories of Essential Elements
  • Essential elements are 17.
  • Basically categorized according to:
Their requirements:

  • Macronutrients – Present in large amounts in tissues (C, H, O, N, P, S, K, Mg, Ca).
  • Micronutrients – Present in small amounts in tissues (Fe, Mn, Cu, Mo, Zn, B, Cl, Ni)
Functions performed in a plant:
  • Components of bio-molecules (C, H, O, N)
  • Components of energy-related chemical compounds (Mg – chlorophyll ; P – ATP)
  • Activation / Inhibition of enzymes – Mo (enzyme nitrogenase)
  • Elements that activates osmotic potential of cell – K (opening and closing of stomata)
Deficiency Symptoms of Essential Elements
·         If essential elements are below their Critical concentration (amount of nutrients required for normal growth and development of plants), plants show certain morphological and observable characters. Those characters are called as Deficiency symptoms.

Deficiency symptoms:

·         Chlorosis (Loss of Chlorophyll) - leads to yellowing of leaves - N, K, Mg, S, Fe, Mn, Zn, Mo.

·         Necrosis (Death of Tissue) - Ca, Cu, K, Mg

·         Delayed flowering - N, S, Mo

·         Inhibition of Cell Division - N, K, S, Mo

Toxicity of Micronutrients

  • Any mineral ion concentration that reduces the dry weight of tissues by 10% is considered toxic.
  • Toxicity of one element may lead to deficiency of other elements since the former may inhibit the uptake of latter.
  • For example; Mn competes with Fe, Mg for uptake and also inhibits Ca translocation to shoot apex. Therefore, Mn toxicity symptoms are actually same as deficiency symptoms of Fe, Mg, and Ca.
Nitrogen Metabolism

Nitrogen Cycle:

  • Nitrogen fixation: The process of conversion of nitrogen (N2) into ammonia (NH3)
  • Ammonification: The process of decomposition of organic nitrogen of plants and animals into ammonia.
  • Nitrification: The ammonia so formed may volatilise and re-enter the atmosphere, or some of the ammonia may be converted into nitrate by soil bacteria.

  • These are the steps involved in nitrification.
    The nitrate so formed can be easily absorbed by the plants, and transported to leaves. In leaves, nitrate is reduced to ammonia to form the amine group of amino acids.
  • Denitrification: Process of reduction of the nitrate present in soil to nitrogen. Carried out by bacteria like Pseudomonas and Thiobacillus.

Biological Nitrogen Fixation

  • Reduction of nitrogen to ammonia by living organisms is called Biological Nitrogen Fixation.
  • Certain prokaryotes (bacteria) are able to fix nitrogen because the enzyme nitrogenase is present exclusively in them.
    N ≡ N NH3
  • Nitrogen-fixing microbes can be classified as follows:
    • Free living : Aerobic (Azotobacter), Anaerobic (Rhodospirillum), Cyanobacteria (Nostoc, Anabaena).
    • Symbiotic – with leguminous plants (Rhizobium), with non-leguminous plants (Frankia).
·         It needs three biological components :

o    A reducing agent to transfer hydrogen atom to dinitrogen (N ≡ N)

o    ATP to provide energy

o    Enzyme system , Nitrogenase, Mo- Fe protein and leghaemoglobin.

·         Leg haemoglobin: It is a pink colour pigment similar to haemogolobin of vertebrates and functions as an oxygen scavanger and protects nitrogenase from oxygen.

N2 + 8e− + 8H+ + 16ATP → 2NH3 + H2 + 16ADP + 16Pi

Nodule Formation

·         Root hair comes in contact with Rhizobium. It becomes curved and deformed due to the chemical secretion.

·         Plant forms an infection thread, grows inside and delivers bacteria to the cortical  tissue.

·         Bacteria produce cytokinin and auxin which is produced by the plant to stimulate cell division and enlarge to form nodules.

·         Nodules form contact with vascular tissues and get food.

·         Formation of root nodules and nitrogen fixation occur under the control of nod genes of legumes and nod, nif and fix genes of bacteria.

Synthesis of amino acids


·         Ammonia formed by nitrogen fixation is used for the synthesis of amino acids.

·         There are 2 processes by which amino  acids are synthesized

o    Reductive amination

§  NH4+ reacts with  - ketoglutaric  acid and forms glutamic acid.

§  It is catalysed by glutamate dehydrogenase enzyme.

o    Transamination

§  Amino group of one amino acid is transferred to keto group of a keto – acid.

§  Glutamic acid is the main amino acid which transfers its amino group (NH2) to form 7 other amino acids by the enzyme transaminase.

o    Amides

§  By the replacement of OH- of the amino acid by NH2 radical.

§  Asparagine  and glutamine   are amines formed from aspartic acid and glutamic acid In the presence of enzyme asparagines synthetase  and glutamine synthetase.

Photosynthesis: Photosynthesis is an enzyme regulated anabolic process of manufacture of organic compounds inside the chlorophyll containing cells from carbon dioxide and water with the help of sunlight as a source of energy.

Site for photosynthesis :
  • Photosynthesis takes place only in green parts of the plant, mostly in leaves.
  • Within a leaf, photosynthesis occurs in mesophyll cells which contain the chloroplasts.
  • Chloroplasts are the actual sites for photosynthesis.
  • The thylakoids in chloroplast contain most of pigments required for capturing solar energy to initiate photosynthesis.
  • The membrane system (grana) is responsible for trapping the light energy and for the synthesis of ATP and NADPH. Biosynthetic phase (dark reaction) is carried in stroma.

Pigments involved in photosynthesis:
  • Chlorophyll a : (Bright or blue green in chromatograph). Major pigment, act as reaction centre, involved in trapping and converting light into chemical energy.
  • Chlorophyll b : (Yellow green)
  • Xanthophylls : (Yellow)
  • Carotenoid : (Yellow to yellow-orange)
  • In the blue and red regions of spectrum shows higher rate of photosynthesis.

What is light reaction?
Light reactions or the 'Photochemical 'phase includes light absorption, splitting of water, evolution of oxygen and formation of high energy compound like ATP and NADPH.
Light Harvesting Complexes (LHC) : The light harvesting complexes are made up of hundreds of pigment molecules bound to protein within the photosystem I (PSI) and photosystem II (PSII).
Each photosystem has all the pigments except one molecule of chlorophyll 'a' forming a light harvesting system (antennae).
The reaction centre (chlorophyll a) is different in both the photosystems.
Photosystem I (PSI) : Chlorophyll 'a' has an absorption peak at 700 nm (P700).
Photosystem II (PSII) : Chlorophyll 'a' has absorption peak at 680 nm (P680).

different chlorophyll pigments

Process of photosynthesis :
It includes two phases - Photochemical phase and biosynthetic phase.
Photochemical phase (Light reaction) : This phase includes - light absorption, splitting of water, oxygen release and formation of ATP and NADPH.
Biosynthetic phase (Dark reaction) : It is light independent phase, synthesis of food material (sugars).

The electron transport :
In photosystem centre chlorophyll a absorbs 680 nm wavelength of red light causing electrons to become excited and release two electrons from the atomic nucleus.
These electrons are accepted by primary electron acceptor i.e. ferredoxin.
The electron from the ferredoxin passed to electron transport system consisting cytochromes.
The electron moved in down hill in terms of redox potential by oxidation-reduction reactions.
Finally the electron reached photosystem-I.
Simultaneously electron released from photosystem-I is accepted by electron acceptor.
Electron hole created in PS-I is filled up by the electron from PS-II.
Electron from PS-I passed down hill and reduce NADP into NADPH+ + H+.

Photolysis of water :
PS-II loose electrons continuously, filled up by electrons released due to photolysis of water.
Water is split into H+, (O) and electrons in presence of light and Mn2+ and Cl-.
This also creates O2 the bi-product of photosynthesis.
Photolysis takes place in the vicinity of the PS-II.
2H2O → 4H+ + O2 + 4e-

Photophosphorylation :

The process of formation of high-energy chemicals (ATP and NADPH).

Non Cyclic photophosphorylation :
Two photosystems work in series – First PSII and then PSI.
These two photosystems are connected through an electron transport chain (Z. Scheme).
ATP and NADPH + H+ are synthesized by this process. PSI and PSII are found in lamellae of grana, hence this process is carried here.

Cyclic photophosphorylation :
Only PS-I works, the electron circulates within the photosystem.
It happens in the stroma lamellae (possible location) because in this region PS-II and NADP reductase enzyme are absent.
Hence only ATP molecules are synthesized.

Chemiosmotic Hypothesis :
Chemiosmotic hypothesis explain the mechanism of ATP synthesis in chloroplast.
In photosynthesis, ATP synthesis is linked to development of a proton gradient across a membrane.
The protons that are produced by the splitting of water are accumulated inside of membrane of thylakoids (in lumen).
As the electron moves through the photosystem, protons are transported across the membrane.
NADP reductase enzyme is located on the stroma side of the membrane, along with electrons from the acceptor it removes H+ from the stroma during reduction of NADPH + H+.
This creates proton gradients across the thylakoid membrane as well as a measurable decrease in pH in the lumen.
ATPase has a channel that allows diffusion of protons back to stroma across the membrane.
This releases energy to activate ATPase enzyme that catalyses the formation of ATP.

Biosynthetic phase in C3 plants : ATP and NADH, the products of light reaction are used in synthesis of food. The first CO2 fixation product in C3 plant is 3-phosphoglyceric acid or PGA. In some other plants the first stable product is an organic acid called oxaloacetic acid a 4-C compound hence is called C4 plants.

The Calvin cycle :
The Calvin cycle

The CO2 acceptor molecule is RuBP (Ribulose bisphosphate).
The cyclic path of sugar formation is called Calvin cycle on the name of Melvin Calvin, the discoverer of this pathway. Calvin cycle proceeds in three stages:

Carboxylation :
Carboxylation is the fixation of CO2 into a stable organic intermediate.
CO2 combines with Ribulose 1, 5 bisphosphate to form 3 PGA in the presence of RuBisCo enzyme.

Reduction :
These are a series of reactions that lead to the formation of glucose.
2 molecules of ATP for phosphorylation and two of NADPH for reduction per CO2 molecule fixed.
The fixation of six molecules of CO2 and 6 turns of the cycle are required for the formation of one molecule of glucose.

Regeneration :
Regeneration of the CO2 acceptor molecule RuBP is crucial if the cycle is to continue uninterrupted.
Regeneration steps required one ATP for phosphorylation to form RuBP.
Hence for every CO2 molecule entering the Calvin cycle, 3 molecules of ATP and 2 molecules of NADPH are required.

In and out of calvin cycle

The C4 pathway :
Plants that are adapted to dry tropical regions have the C4 pathway.
C4 oxaloacetic acid is the first CO2 fixation product.
These plants have special type of leaf anatomy, they tolerate higher temperatures.
The leaf has two types of cells: mesophyll cells and Bundle sheath cells (Kranz anatomy).
Initially CO2 is taken up by phosphoenol pyruvate (PEP) in mesophyll cells and changed to oxaloacetic acid (OAA) in the presence of PEP carboxylase.
Oxaloacetate is reduced to malate/asparate that reaches into bundle sheath cells.
In the bundle sheath cells these C4 acids are broken down to release CO2 and a 3-carbon molecule i.e. pyruvic acid.
The CO2 released in the bundle sheath cell enters the C3 cycle because these cells are rich in enzyme Ribulose bisphosphate carboxylase-oxygenase (RuBisCO).
The pyruvate formed in the bundle sheath cell transported back to the mesophyll cell, get phosphorylated to form phosphoenol pyruvate.

C4 pathway

The light induced respiration (evolution of CO2) in green plants is called photorespiration.
Active site of RuBisCO has active site for both O2 and CO2.
In C3 plants some O2 binds with RuBisCo and hence CO2 fixation is decreased.
In this process RuBP instead of being converted to 2 molecules of PGA, binds with O2 to form one molecule of PGA and phosphoglycolate.
In the photorespiratory pathway there is neither synthesis of sugar, nor of ATP. Rather it results in the release of CO2 with utilization of ATP.
In the photorespiratory pathway there is no synthesis of ATP or NADPH.
Therefore photorespiration is a wasteful process.
In C4 plant photorespiration does not occur:
RuBisCO enzyme is present in the bundle sheath cells.
Primary carboxylation is takes place in the mesophyll cell by PEP carboxylase.
CO2 supplied to bundle sheath cell by C4 acid intermediate.
Hence C4 plants are photosynthetically more efficient than C3 plant.

Law of Limiting Factors : If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value. It is the factor which directly affects the process if its quantity is changed.

  • The breaking of C-C bonds of complex compounds through oxidation within the cells, leading to release of considerable amount of energy is called respiration.
  • The compound that oxidized during this process is known as respiratory substrates.
  • In the process of respiration the energy is released in a series of slow step-wise reactions controlled by enzymes and is trapped in the form of ATP.
  • ATP acts as the energy currency of the cell.

Glycolysis : 

Gycolysis:Respiration in plants
  • The term has originated from the Greek word, glycos =glucose, lysis = splitting or breakdown means breakdown of glucose molecule.
  • It is also called Embeden-Meyerhof-Paranus pathway. (EMP pathway)
  • It is common in both aerobic and anaerobic respiration.
    anaerobic respiration.
  • It takes place outside the mitochondria, in the cytoplasm.
  • One molecule of glucose (Hexose sugar) ultimately produces two molecules of pyruvic acid through glycolysis.
  • Glucose and fructose are phosphorylated to give rise to glucose-6-phosphate, catalyzed by hexokinase.
  • This phosphorylated form of glucose is then isomerizes to produce fructose-6-phosphate.
  • ATP utilized at two steps:
    • First in the conversion of glucose into glucose-6-phosphate
    • Second in fructose-6-phosphate→fructose 1, 6-diphosphate.

  • The fructose-1, 6-diphosphate is split into dihydroxyacetone phosphate and 3-phosphoglyceraldehyde (DPGA).
  • In one step where NADH + H+ is formed form NAD+; this is when 3-phosphogleceraldehyde (PGAL) is converted into 1, 3-bisphophoglyceric acid (DPGA).
  • The conversion of 1, 3-bisphophoglyceric acid into 3-phosphoglyceric acid is also an energy yielding process; this energy is trapped by the formation of ATP.
  • Another ATP synthesized when phosphoenolpyruvate is converted into pyruvic acid.
  • During this process 4 molecules of ATP are produced while 2 molecules of ATP are utilized. Thus net gain of ATP is of 2 molecules.


  • There are three major ways in which different cells handle pyruvic acid produced by glycolysis:
    • Lactic acid fermentation.
    • Alcoholic fermentation.
    • Aerobic respiration.

  • Alcoholic fermentation :
    • The incomplete oxidation of glucose to achieved under anaerobic conditions by sets of reactions where pyruvic acid is converted into CO2 and ethanol.
    • The enzyme pyruvic acid decarboxylase and alcohol dehydrogenase catalyze these reactions.
    • NADH + H+ is reoxidised into NAD+.

  • Lactic acid fermentation:
    • Pyruvic acid converted into lactic acid.
    • It takes place in the muscle in anaerobic conditions.
    • The reaction catalysed by lactate dehydrogenase.
    • NADH + H+ is reoxidised into NAD+.

  • Aerobic respiration:
    • Pyruvic acid enters into the mitochondria.
    • Complete oxidation of pyruvate by the stepwise removal of all the hydrogen atoms, leaving three molecules of CO2.
    • The passing on the electrons removed as part of the hydrogen atoms to molecular oxygen (O2) with simultaneous synthesis of ATP.


  • The overall mechanism of aerobic respiration can be studied under the following steps :
  • Glycolysis (EMP pathway)
  • Oxidative Decarboxylation
  • Krebs’s cycle (TCA-cycle)
  • Oxidative phosphorylation

Oxidative decarboxylation:

  • Pyruvic acid formed in the cytoplasm enters into mitochondria.
  • Pyruvic acid is converted into Acetyl CoA in presence of pyruvate dehydrogenase complex.
  • The pyruvate dehydrogenase catalyses the reaction require several coenzymes, including NAD+ and Coenzyme A.
  • During this process two molecules of NADH are produced from metabolism of two molecules of pyruvic acids (produced from one glucose molecule during glycolysis).
  • The Acetyl CoA (2c) enters into a cyclic pathway, tricarboxylic acid cycle.

Tri Carboxylic Acid Cycle (Krebs cycle) or Citric acid Cycle :

Citric acid cycle

  • This cycle starts with condensation of acetyl group with oxaloacetic acid and water to yield citric acid.  This reaction is catalysed by citrate synthase.
  • Citrate is isomerised to form isocitrate.
  • It is followed by two successive steps of decarboxylation, leading to formation of α-ketoglutaric acid and then succinyl-CoA.
  • In the remaining steps the succinyl CoA oxidized into oxaloacetic acid.
  • During conversion of succinyl CoA to succinic acid there is synthesis of one GTP molecule.
  • In a coupled reaction GTP converted to GDP with simultaneous synthesis of ATP from ADP.
  • During Krebs cycle there production of :
    • 2 molecule of CO2
    • 3 NADH2
    • 1 FADH2
    • 1 GTP.
  • During the whole process of oxidation of glucose produce:
    • CO2
    • 10 NADH2
    • 2 FADH2
    • 2 GTP.( 2 ATP)

Electron transport system and oxidative phosphorylation :

  • The metabolic pathway, through which the electron passes from one carrier to another, is called Electron transport system.
  • it is present in the inner mitochondrial membrane.
  • ETS comprises of the following:
    • Complex I – NADH Dehydrogenase.
    • Complex II – succinate dehydrogenase.
    • Complex III – cytochromes bc1
    • Complex IV – Cytochromes a-a3 (cytochromes c oxidase).
    • Complex V – ATP synthase.

  • NADH2 produced in the citric acid cycle oxidized by NADH Dehydrogenase, and electrons are then transferred to ubiquinone located in the inner membrane.
  • FADH2 is oxidized by succinate dehydrogenase and transferred electrons to ubiquinone.
  • The reduced ubiquinone is then oxidized with transfer of electrons to cytochrome c via cytochromes bc1 complex.
  • Cytochrome c is small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for transfer electrons from complex III and complex IV.
  • When electrons transferred from one carrier to another via complex I to IV in the electron transport chain, they are coupled to ATP synthase for the synthesis of ATP from ADP and Pi.
  • One molecule of NADH2 gives rise to 3 ATP.
  • One molecule of FADH2 gives rise to 2ATP.
  • Oxygen plays a vital role in removing electrons and hydrogen ion finally production of H2O.
  • Phosphorylation in presence of oxygen is called oxidative phosphorylation.

Total ATP Production -

Process Total ATP produced :

  • Glycolysis 2ATP + 2NADH2 (6ATP) = 8ATP
  • Oxidative decarboxylation 2NADH2  (6ATP) = 6ATP
  • Krebs’s Cycle 2GTP (2ATP) + 6NADH2 (18ATP) + 2FADH2 (4ATP) = 24 ATP
  • Energy production in prokaryotes during aerobic respiration = 38 ATP
  • Energy production in eukaryotes during aerobic respiration = 38 − 2 = 36 ATP
  • (2ATP are used up in transporting 2 molecule of pyruvic acid in mitochondria.)

Abbreviations :

ATP −          Adenosine tri phosphate

ADP −         Adenosine di phosphate

NAD −         Nicotinamide Adenine dinucleotide

NADP −       Nicotinamide Adenine dinucleotide Phosphate

NADH −       Reduced Nicotinamide Adenine dinucleotide

PGA −          Phosphoglyceric acid

PGAL −        Phospho glyceraldehyde

FAD −          Flavin adenine dinucleotide

ETS −          Electron transport system

ETC −          Electron transport chain

TCA −          Tricarboxylic acid

OAA −          Oxalo acetic acid

FMN −          Flavin mono nucleotide

PPP −          Pentose phosphate pathway

Plant Growth and Development
  • An irreversible permanent increase in size of an organ or its parts or even of an individual cell.
  • Growth is accompanied by metabolic process that occurs at the expense of energy.

Plant growth is generally is indeterminate :

  • Plants retain the capacity of unlimited growth throughout their life.
  • This ability is due to the presence of meristems at certain locations in their body.
  • The cells of such meristems have capacity to divide and self-perpetuate.
  • The product eventually looses the capacity to divide and differentiated.
  • Apical meristems responsible for primary growth of the plants and principally contribute to the elongation of the plants along their axis.
  • The lateral meristem, vascular cambium and cork cambium appears later and responsible for the increase in the girth.

Phases of growth :

  • The period of growth is generally divided into three phases
    • Meristematic.
    • Elongation.
    • Maturation.

  • Root apex and shoot apex represent the meristematic phase of growth.
  • The cells of this region are rich in protoplasm, possesses large conspicuous nuclei.
  • Their cell walls are primary in nature, thin and cellulosic with abundant plasmodesmatal connection.
  • The cells proximal to that region are the phase of elongation.
  • Increased vacuolation, cell enlargement and new cell wall deposition are the characteristic of the cells in this phase.
  • Further away from the zone of elongation is the phase of maturation.
  • The cells of this zone attain their maximal size in terms of wall thickening and protoplasmic modifications.

Condition of growth :

  • Water, oxygen and nutrients as very essential element for growth.
  • Turgidity of cells helps in extension growth.
  • Water also provides the medium for enzymatic activities needed for growth.
  • Oxygen helps in releasing metabolic energy essential for growth activities.
  • Nutrients are required by plants for synthesis of protoplasm and act as source of energy.

Differentiation, dedifferentiation and redifferentiation :

  • The cells derived from root apical and shoot apical meristems and cambium differentiate and mature to perform specific functions.
  • This act of maturation is termed as differentiation.
  • During differentiation major changes takes place in their cell wall and protoplasm.
  • Differentiated tracheary element cells loose their protoplasm, develop a very strong, elastic lignocellulosic secondary cell walls.
  • The living differentiated cells, that by now have lost the capacity to divide can regain the capacity of division under certain condition is dedifferentiation.
  • Development of interfascicular cambium and cork cambium from fully differentiated parenchymatous cells is the example of dedifferentiation.
  • Cells produced by the dedifferentiated tissues again loose the capacity to divide and mature to perform specific function is called redifferentiation.


Characteristics :

  • The plant growth regulators are small, simple molecules of diverse chemical composition.
  • They could be:
    • Indole compounds (indole-3-acetic acid, IAA);
    • adenine derivatives (N6-furfurylamino purine, kinetin)
    • derivatives of carotenoids (abscisic acid,ABA)
    • terpenes (gibberellic acid, GA2)
    • Gases (ethylene, C2H4)

  • One group of PGRs are involved in growth promoting activities such as cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting and seed germination. These are called plant growth promoters, e.g. auxin, gibberellins and cytokinin.

  • Another group of PGRs play important role in plant responses towards to wounds and stresses of biotic and abiotic origin. They involved in inhibitory responses like dormancy and abscission, e.g. abscisic acid.

Discovery of plant growth regulators :

  • Auxin was isolated by F.W. Went from tips of oat seedlings.

  • The ‘bakane’ (foolish seedling) a disease of rice seedlings, was caused by a fungal pathogen Gibberalla fujikuroi.

  • E. Kurosawa reported the appearance of the symptom of the disease in uninfected rice seedlings when treated with sterile filtrate of the fungus. The active substance was later identified as Gibberellic acid.

  • Skoog and Miller identified and crystallized the cytokinesis promoting active substance that they termed as kinetin.

  • During mid 1960s three different kinds of inhibitors purified, i.e. inhibitor-B abscission II and dormin. Later all the three proved to be chemically identical and named as Abscisic acid (ABA).

  • Cousinsdiscovered a gaseous PGR called ethylene from ripened orange.

Physiological effect of plant growth regulators :

Auxin :

  • The term auxin is applied to indole-3-acetic acid
  • Generally produced by growing apices of the stems and roots.
  • IAA and IBA have been isolated from plants.
  • NAA and 2, 4-D (2, 4-dichlorophenoxyacetic acid) are synthetic auxin.
  • Promote rooting in stem cutting.
  • Promote flowering.
  • Inhibit fruit and leaf drop at early stages.
  • Promote abscission of older mature leaves and fruits.
  • The growing apical bud inhibit the growth of lateral bud, the phenomenon is called apical dominance.
  • Auxin induces parthenocarpy.
  • Used as herbicides.
  • Controls xylem differentiation.
  • Promote cell division.

Gibberellins :

  • Ability to cause an increase in length of axis is used to increase the length of grapes stalks.
  • Gibberellins cause fruits like apple to elongate and improve its shape.
  • Delay senescence
  • GA3 is used to speed up the malting process in brewing industry.
  • Gibberellins promote to increase length of stem in sugar cane.
  • Promote early seed production.
  • Promote bolting (internodes elongation) in beet, cabbages.

Cytokinins :

  • Cytokinins have specific effects on cytokinesis.
  • Zeatin isolated from corn-kernels and coconut milk.
  • Promote cell division.
  • Help to produce new leaves, chloroplast in leaves, lateral shoot growth
  • Promote formation of adventitious shoot.
  • Cytokinins help to overcome apical dominance.
  • Promote nutrient mobilization.
  • Delay senescence.

Ethylene :

  • Ethylene is a simple gaseous PGR.
  • Synthesized in the tissue undergoing senescence and ripening fruits.
  • Promote horizontal growth of seedling.
  • Promote swelling of axis and apical hook formation in dicot seedlings.
  • Promote senescence and abscission of plant organs like leaf and flower.
  • Increase rate of respiration during ripening of fruits, called respiratory climactic.
  • Breaks seed and bud dormancy.
  • Initiate germination.
  • Promote rapid internodes elongation.
  • Promote root growth and root hair formation.
  • Used to initiate flowering and for synchronizing fruit-set.
  • Induce flowering in mango.
  • The source of ethylene is ethephon.
  • Promote female flower in cucumbers thereby increasing the yield.

Abscisic acid :

  • Regulates abscission and dormancy.
  • Acts as general plant growth inhibitor and an inhibitor of plant metabolism.
  • Inhibit seed germination.
  • Stimulates the closure of stomata and increases the tolerance of plants to various kinds of stresses, hence called as stress hormone.
  • Important role in seed development, maturation and dormancy.
  • Inducing dormancy, ABA helps seeds to withstand desiccation and other factors unfavourable for growth.
  • Acts as antagonist to Gas.


  • Some plants require a periodic exposure to light to induce flowering.
  • Response of plants in terms of day/night in relation to flowering is called photoperiodism.
  • Long day plant: plant requires the exposure to light for a period exceeding critical period.
  • Short day plant: plant requires the exposure to light for a period less than critical period.
  • Day neutral plant: there is no such correlation between exposure to light duration and induction of flowering response.
  • The site of perception of light/dark duration is the leaves.


  • Vernalisation: There are plants for which flowering is either quantitatively or qualitatively dependent on exposure to low temperature.
  • It prevents precocious reproductive development late in the growing season.
  • Vernalisation refers to the promotion of flowering by a period of low temperature.

In short
Growth is one of the most conspicuous events in any living organism. It is an irreversible increase expressed in parameters such as size, area, length, height, volume, cell number etc. It conspicuously involves increased protoplasmic material. In plants, meristems are the sites of growth. Root and shoot apical meristems sometimes alongwith intercalary meristem, contribute to the elongation growth of plant axes. Growth is indeterminate in higher plants. Following cell division in root and shoot apical meristem cells, the growth could be arithmetic or geometrical.
geometric and arithmetic growth
Growth may not be and generally is not sustained at a high rate throughout the life of cell/tissue/organ/organism. One can define three principle phases of growth – the lag, the log and the senescent phase. When a cell loses the capacity to divide, it leads to differentiation. Differentiation results in development of structures that is commensurate with the function the cells finally has to perform. General principles for differentiation for cell, tissues and organs are similar. A differentiated cell may dedifferentiate and then redifferentiate. Since differentiation in plants is open, the development could also be flexible, i.e., the development is the sum of growth and differentiation. Plant exhibit plasticity in development. Plant growth and development are under the control of both intrinsic and extrinsic factors. Intercellular intrinsic factors are the chemical substances, called plant growth regulators (PGR). There are diverse groups of PGRs in plants, principally belonging to five groups: auxins, gibberellins, cytokinins, abscisic acid and ethylene. These PGRs are synthesised in various parts of the plant; they control different differentiation and developmental events. Any PGR has diverse physiological effects on plants. Diverse PGRs also manifest similar effects. PGRs may act synergistically or antagonistically. Plant growth and development is also affected by light, temperature, nutrition, oxygen status, gravity and such external factors. Flowering in some plants is induced only when exposed to certain duration of photoperiod. Depending on the nature of photoperiod requirements, the plants are called short day plants, long day plants and day-neutral plants. Certain plants also need to be exposed to low temperature so as to hasten flowering later in life. This treatement is known as vernalisation.

All the living organisms require the presence of energy to do various functions of life.  They get this energy from the food they eat.  Food is also needed for growth and development of the body.  Nutrition is defined as, the substance in total from which an organism derives its energy to do work and other materials for its growth, development and maintenance of life.   

Human Digestion System

The breaking down of complex and insoluble organic substances such as carbohydrates, proteins and fats into simpler and soluble substances like glucose, amino acids and fatty acids respectively so that they can be easily absorbed into the body is known as digestion.  This is a hydrolytic process and is carried out by various enzymes.”
Alimentary or Digestive system:

Alimentary canal is a tube present in all higher animals starting from mouth and reaching up to anus.  Various glands located on its wall produce digestive juices that help in the process of digestion.  Two glands namely liver and pancreas are also associated with it.  They also produce the digestive juices.  The digested food is also absorbed into the alimentary canal and undigested and indigestible food is passed out of the body through anus.

Mammalian Alimentary System
             In man the total length of alimentary canal is about 21 feet and consists of the following parts:
 Mouth leads into a buccal cavity.  The opening of the mouth is provided with lips.  At the floor of the buccal cavity a muscular tongue is present.  It helps in the ingestion, mastication and swallowing of food.  It has got taste buds on its surface.  Most of the mammals possess teeth on both the jaws.  They are present in the cavity or socket of gums (thecodont dentition).  The number and types of teeth vary in mammals.  In man, there are 32 teeth of four different types namely incisors, canines, premolars and molars. 
Arrangement of different types of
teeth in the jaws on one side and
the sockets on the other side
This type of dentition is known as heterodont dentition.  Their number can be represented by the dental formula: In each half of jaw;

Upper jaw    I(2);  C(1);  PM(2);  M(3)

-----------------------------------------------       = 32

Lower jaw I (2); C (1); PM (2); M (3)           


The incisor teeth are chisel-shaped and have sharp cutting edges.  Canines are dagger-shaped and pierce the food.  They are very large and well developed in predatory animals.  Premolars and molars are broad and strong crushing teeth.  Thus the incisors are used for biting; the canines for tearing the food; and premolars and molars for grinding the food.  With the help of the teeth, tongue and jaw movements, food is chewed and mixed with saliva in the mouth.

Salivary glands:

  There are three pairs of salivary glands namely parotids, submaxillary (submandibular) and sublingual glands.  Their secretion is collectively known as saliva that is poured into the buccal cavity.  Saliva usually contains enzymes and mucin.  The enzyme present in saliva is known as ptyalin that helps in the digestion of carbohydrates; while mucin helps to lubricate the food for swallowing.   


The mouth leads to a funnel-shaped pharynx, which communicates with a long muscular tube called oesophagus.  The oesophagus opens into a muscular sac like structure called as stomach. 
Human Stomach
In man, it is somewhat J-shaped and occupies the left side of the abdomen. The stomach opens into the small intestine.  The stomach has many glands on its wall. Stomach wall produces gastric juice, which chiefly contains HCl, mucin and two protein digesting enzymes – rennin and pepsin.  The muscles of the stomach wall churn and mix the food with gastric juice.  Stomach through its pyloric region opens into small intestine. It is differentiated into three regions viz., duodenum, jejunum and ileum.  Duodenum is U-shaped and gets the common bile duct and pancreatic duct from the gall bladder and pancreas. Jejunum is longer and more coiled.  Ileum is the last part of small intestine and opens into the large intestine.  Its wall has numerous long, finger-like projections called villi, which enhance absorption.  Small intestine is the main region where digestion and absorption of food occurs.  It has large number of tubular glands that produce the intestinal juice containing a number of enzymes, which digest various types of food.  Digestion of different nutrients is completed in the small intestine by the action of pancreatic juice, intestinal juice and bile juice.  The end products of digestion are then absorbed from the small intestine. 

The small intestine opens into the large intestine.  It is comparatively much shorter and wider than the small intestine.  It does not have villi.  It is also differentiated into three regions:  caecum, colon and rectum.  Caecum is a small pouch-like structure and its main part is vermiform appendix.  However, caecum is very well developed in herbivorous animals like horse and ass.  The colon is longest and has four parts; ascending colon, transverse colon, descending colon and pelvic colon.  The pelvic colon opens into the rectum.  Rectum is the last part of large intestine.  Both in colon and rectum most of the water is reabsorbed back while the undigested food is removed from the body as faecal matter through anus.  This is known as Egestion.


Glands associated with alimentary canal:


Pancreas:  It is located in between the loops of duodenum.  It is the second largest gland of the body.  It secretes pancreatic juice that contains large number of digestive enzymes for digesting starch, lipids, proteins and nucleic acids.  The pancreatic juice is released into the pancreatic duct, which joins with the common bile duct. 

It is the largest gland of the body lying immediately below the diaphragm in the right upper part of abdomen.  The cells of the liver (hepatic cells) produce bile juice that contains bile pigments and bile salts.  These bile salts help in the digestion and absorption of fats.  Bile juice does not contain any enzyme.  Bile juice flows out of the liver through hepatic ducts forming the common bile duct that opens into the duodenum (when the food is present in the duodenum).  When there is no food in the duodenum, then bile juice is stored in the gall bladder.  The gall bladder is a small elongated, muscular sac below the liver.  When the food comes into duodenum, it contracts to release the bile juice. 


Digestion of Carbohydrates:

             Carbohydrates are of three types: polysaccharides, disaccharides and monosaccharides.  During the process of digestion both poly-and disaccharides are broken down to monosaccharides and in this form they can be absorbed into the body.  Some of these complex carbohydrates are starch and cellulose, present in cereal grains, potato, fruits and tubers; sucrose present in cane sugar; lactose present in milk etc.  Enzymes that act on carbohydrates are collectively known as carbohydrases.


In the mouth cavity, the food is mixed with saliva.  It contains an enzyme called salivary amylase or ptyalin. Salivary amylase acts on starch and convert it into maltose, isomaltose and small dextrins or `limit dextrin’(disaccharides).  Chewing and mastication of food increases the action of salivary amylase on starch by increasing the surface area of food on which the enzyme acts.  About 30 percent of starch present in food is hydrolysed in the mouth.  The action of salivary amylase continues for sometime even in the stomach but soon HCl present in the gastric juice destroys the entire enzyme.


                        Starch  --------------> Maltose + Isomaltose + Dextrin



Pancreatic juice and intestinal juice also contain carbohydrates digesting enzymes.  Pancreatic juice contains pancreatic amylase that acts on starch to digest it into maltose, isomaltose and dextrin.  Intestinal juice contains number of carbohydrates like maltase, isomaltase and sucrase and lactase.  Maltase and isomaltase act on maltose, isomaltose and dextrins and convert into glucose; sucrase acts on sucrose to convert it into glucose and fructose; and lactase acts on lactose to convert it into glucose and the galactose. 


                        Starch  ------------> Maltose + Isomaltose + Dextrin



                        Maltose + Isomaltose + Dextrin ------------> Glucose



                        Sucrose ------------> Glucose  + Fructose


                        Lactose  -----------> Glucose  +  Galactose


Only human being can digest lactose present in the milk.  But with advancing age, they also cannot digest milk.  This is because less of lactase is produced.  In them,  lactose remains undigested and gets fermented in the intestine producing gases and acids. This results in intestinal disorder and diarrhoea.  So these persons must consume curd or yoghurt (sweetened curd) as lactase is fermented to lactic acid in them.  This will not pose any digestive problem to them. 

Many of the herbivorous animals can digest cellulose by the microorganisms (bacteria and protozoa) present in their alimentary canal.  These microbes ferment cellulose into short chain fatty acids such as acetic acid and propionic acid.  These acids are then absorbed and utilized by the animal. This is, thus, an example of symbiotic digestion.  Microbes may be present in the rumen and reticulum part of stomach (cow and buffaloes); or in the large intestine (horse and donkeys).


 Digestion of proteins:


Proteins are complex organic compounds made up of single units called amino acids.  In the process of digestion, proteins are broken down to amino acids.  Enzymes that hydrolyze protein are collectively known as proteases or peptides.  Many of these enzymes are secreted in their inactive form or proenzymes.  These inactive enzymes are converted to their active form only at the site of action.


Protein digestion starts in the stomach.  The gastric glands of stomach produce a light coloured, thin and transparent gastric juice.  It contains hydrochloric acid and pepsinogen. The H+ ions present in HCl converts pepsinogen into pepsin.  The presence of HCl makes the medium highly acidic so that pepsin can act on proteins to convert them into peptones.  HCl also helps to kill bacteria and other harmful organisms that may be present along with the food.  Calf gastric juice contains another milk coagulating protease, called rennin.  It is secreted as inactive pro-rennin.  In the presence of HCl, the inactive prorennin is converted into their active form, i.e., rennin.  Rennin acts on the casein protein of milk and converts it into paracasein, which in the presence of calcium ions forms calcium paracaseinate (curdling of milk). The function of rennin is then taken over by pepsin and other milk-coagulating enzymes.  Adult cows or human infants do not produce rennin.


Both pancreatic juice and intestinal juice are poured into small intestine.  Pancreatic juice contains trypsinogen, chymotrypsinogen, carboxypeptidases, lipases, amylases, DNAases and RNAases.  All these enzymes of pancreatic juice can act only in the alkaline medium.  This change in the medium of food, from acidic to alkaline, is done by the bile juice.  Therefore, bile juice acts on the food before the action of pancreatic juice.  In the intestinal lumen, pancreatic and intestinal juices mix together. Then a protease of intestinal juice, called Enteropeptidase or Enterokinase acts in coordination with pancreatic proteases. This enterokinase converts inactive trypsinogen into active trypsin.   In predatory animals, trypsins can hydrolyse fibrinogen of blood into fibrin leading to blood coagulation.  But it is unable to bring about coagulation of milk.  The inactive Chymotrypsinogen is activated to chymotrypsin by trypsin.  Chymotrypsins can hydrolyse casein into paracasein, which then coagulates to form calcium paracaseinate.  But it acts in the alkaline medium.  Chymotrypsin acts on other proteins and converts them into peptides.  Carboxypeptidase hydrolyses the terminal carboxyl groups from peptide bonds to release the last amino acids from the peptides thus making the peptide shorter.


The intestinal juice contains aminopeptidases and dipeptidases; and enterokinase or enteropeptidase.  Out of these enterokinase activates the trypsinogen. Aminopeptidase hydrolyses the terminal amino group from peptide bonds to release the last amino acid from the peptides thus making the peptide shorter.  Dipeptidase acts on dipeptides to release the individual amino acids.


Digestion of fats:


Fat digestion starts only when the food reaches the small intestine.  It starts with the action of bile juice from liver.  Bile juice contains bile salts, which are secreted by the liver in the bile.  Bile salts break down the bigger molecules of fat globules into smaller droplets by reducing the surface tension of fat droplets.  This process is known as emulsification of fats. 


Lipase is the enzyme that acts on emulsified fats.  It is present both in the pancreatic juice and intestinal juice.  Lipase converts emulsified fats into diglycerides and monoglycerides releasing fatty acids at each step.  At the end of digestion, all fats are converted into fatty acids, glycerol and monoglycerides.

Absorption Summary

During the process of digestion proteins are changed to amino acids, carbohydrates to glucose, fructose and galactose, fats to fatty acids, glycerol and monoglycerides.  These end products of digestion are finally absorbed in small intestine.  So absorption can be defined as a process by which nutrient molecules are taken into the cells of the body.  For this purpose, intestine has vast surface area of absorption by the presence of numerous villi.  Further, this area is increased by microvilli present on the free surface of epithelial cells.

Passive absorption: When the nutrients are absorbed by simple diffusion, then it is known as passive absorption.  Various amino acids and monosaccharides diffuse into the blood capillaries of villi.  This is dependent on the fact that these nutrients are more in concentration in the intestine than in the cells.  Further, these molecules are small and water soluble.  All the amino acids and monosaccharides are not absorbed in this way. 


Water is absorbed from the intestine to the intestinal cells and finally to the blood by the process of osmosis.  This occurs when the solute concentration in the blood is higher (hypertonic).  Thus, whenever any solute is absorbed from the intestine, it also results in the absorption of water.


Active absorption: This process occurs against the concentration gradient, i.e., nutrients may be more in intestinal cells than in the lumen of intestine.  It requires the expenditure of energy i.e., ATP.  Various nutrients like amino acids, glucose, galactose, Na+ ions can be absorbed by active transport.  After their passive absorption, they are completely absorbed by active transport.  For the active absorption of Na+ ions, a mechanism of sodium pump operates in the cell membranes.



Micelles in fat absorption/Role of bile juice in the absorption of  fats:

As the fatty acids and glycerol are insoluble in water, the intestine cannot directly absorb them. So they cannot reach the blood stream directly.  Instead, they are passed into lymph capillaries of the villi called lacteals.  Digested fats are first incorporated into small, spherical droplets called micelles with the help of bile salts and phospholipids in the intestinal lumen.  In the lacteals, fats are resynthesised into very small fat molecules called chylomicrons.  An obstruction in the bile duct may prevent the entry of bile juice into the small intestine (obstructive jaundice) as a result unabsorbed fats are removed from the body along with the faecal matter.  Thus bile plays an important role in the absorption of fats. 


Balanced diet:  To maintain normal functioning of our body, we need varieties of food so that all the systems are well maintained.  A diet, which contains adequate amount of all the essential nutrients, is known as balanced diet.  It varies according to age and occupation.  A balanced diet should have the following three qualities:

·         It must be rich in various essential nutrients like vitamins, minerals and some amino acids.

·         It should provide enough raw materials needed for the growth and development, repair and replacement of cells, tissues and organs of the body.

·         It should provide the necessary energy required by the body.


Disorders of Digestive System:

1.      Jaundice: The liver is affected; skin and eyes turn yellow due to the deposit of bile pigment.

2.      Vomiting: It is the ejection of stomach contents through the mouth and controlled by the centre in the medulla oblongata.

3.      Diarrhoea: Abnormal bowel movement and the faecal discharge with more liquidity, which leads to dehydration.

4.      Constipation: the feces are retained within the rectum due to irregular bowel movement.

5.      Indigestion: food is not properly digested leading to a feeling of fullness due to inadequate enzyme secretion, anxiety, food poisoning, over eating nd spicy food.