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Levels  of organization :

1.       Body symmetry

2.       Nature of coelom ( cavity )

3.       Body plan

4.       Pattern of development

5.       Segmentation of the body

6.       Presence/absence of notochord

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.


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 

Chordates                                                        Non 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 ovoviviiparous – egg laying mammals (Platypus)

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

Ex. Canis macaca, Camelus, Dolphin.