NCERT Class 11-Biology: Chapter –4 Animal Kingdom

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Question 2:

What is the relationship between germinal layers and the formation of body cavity in case of coelomate, acoelomates and pseudocoetomates?

Answer:

All adult multicellular organisms typically possess a concentric arrangement of tissues in the body. These tissues are derived from the three embryonic cell layers called germinal layers.

(i) The outer layer is the ectoderm, the middle layer is the mesoderm and the inner most layer is the endoderm.

(ii) Endoderm layer is associated with the formation of the stomach, colon, liver, pancreas, urinary bladder and other vital organs in an organism.

(iii) Mesoderm forms the main structural components of the body like the skeletal muscles, the skeleton, the dermis of the skin connective tissue, etc.

(iv) Ectoderm is associated with the formation of CNS, eye lens, ganglia, nerves and glands.

(v) The body cavity that is lined by mesoderm is called coelom, and the animals possessing coelom are called as coelomates. e.g., phylum-Annelida, Mollusca, Arthropoda, Echinodermata, Hemichordata and Chordata.

(vi) In some organisms, body cavity is not lined by mesoderm, instead mesoderm is present in the form of scattered pouches in between ectoderm and endoderm, Such body cavity is called pseudocoelom and animals possessing there stusturs are referred to as pseudo coelomates e.g. Ascaris.

(viii) The animals in which there is complete absence of body cavity are called acoelomates. e.g., Platyhelminthes. Called acoelomates. e.g., Platyhelminthes.

Platyhelminthes

Platyhelminthes

Platyhelminthes

Question 3:

Comment upon the habitats and external features of animals belonging to class, amphibia and reptilia.

Answer:

Amphibians (i) They possess dual life as they can live in aquatic as well as terrestrial habitat. They are ectothermic (cold blooded).

(ii) They are tetrapods (4 limbs) which facilitate movement land.

(iii) Their limbs are evolved from the pectoral and pelvic fins.

(iv) Skin is thin, covered by mucus and mostly remain moist, also serves as an accessory source oxygen.

(v) They are both gill and lung breathers; usually gills appear in the larval stage, replaced by lungs in the adults stage.

(vi)They possess three chambered heart with two atria and one ventricle. (vii) The fertilization is mostly external, females are oviparous.

(viii) Larva is a tadpole, which metamorphosis into adult thus shaving metamorphosis. e.g., Ranafrog, Nectureus (mud puppy), Salamandera (salamander).

Salamandera

Salamandera

Salamandera

Frog

Frog

Frog

Reptiles (i) In reptiles, creeping and crawling mode of locomotion is found.

(ii) They are mostly terrestrial animals and their body is covered by dry, and cornified skin, epidermal scales or scutes.

(iii) Lungs are well developed and present in all stages of life.

(iv) Toes possess claws.

(v) Appendages are well adapted for the movement on land.

(vi) Heart possesses a partially divided ventricle and 2 atria.

(vii) They lay amniotic eggs which are incubate on land.

(viii) They are poikilothermic or cold blooded animals. Temperature is regulated mechanically and not metabolically by moving in and out; heat source is usually the sun.

(ix) Fertilization is internal they are oviparous and development of young ones is direct. e.g., Chelone (turtle), Naja (cobra), Crocodicus (crocodile).

Crocodicus

Crocodicus

Crocodicus

Chelone

Chelone

Chelone

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