(a) Two chambered heart is present in organisms like fishes. Only one atria and one ventricle is present which are not separated and hence mixing of oxygenated and deoxygenated blood blood occurs.

(b) Three chambered heart develops after the division of auricle into right and left halves as in amphibian. Mixing of oxygenated and deoxygenated blood occurs in ventricles.

(c) An intermidiary heart is present in reptiles in which ventricle get partially divided through a septum which is incomplete. e.g., Crocodiles, thus having four-chambered heart.

(d) In four chambered heart both the auricle and ventricle are divided into two halves and thus no mixing of oxgyenated and deoxygenated blood occurs. e.g., birds and mammals.

Excretion involves the elimination of metabolic waste products from the animal body.

Different organs are involved in the process of excretion in different animals.

(a) In Arthropods, the Malpighian tubules remove excretory products from haemolymph.

(b) In Annelids, the excretory organ occurs as segmentally arranged coiled tubules called nephridia

(c) In Molluscas, excretion occurs by paired structures called organ of Bojanus also called metanephridia.

(d) In Amphibians mesonephric kidneys are associated with excretion.

Blood circulation involves the circulation of blood and lymph along with oxygen, carbondioxide, hormones, blood cells, etc, within the body system for the nourishment of cells, fighting diseases, and for stabilising body temperature and pH .

Respiratory organs are involved in the exchange of gases from the atmosphere. Different respiratory organs are as follows

(a) Lungs/gills/tracheal system in arthropoda and molluscs.

(b) Skin in annelids.

(c) Lungs and skin in amphibians.

A. $\rightarrow$ (v) B. $\rightarrow$ (iii) C. $\rightarrow$ (ii) D. $\rightarrow$ (i) E. $\rightarrow$ (vi) F. $\rightarrow$ (iv)

A. Amphibians possess dual habitat, i.e., they are found in both aquatic and terrestrial habitat. Their larva is completely aquatic and adult lives in terrestrial as well as in aquatic habitat

B. Mammals have mammary glands which produce milk and feed their young ones. The mammary glands are enlarged exocrine modified sweat glands functional in female mammals.

C. Chondrichthyes have the cartilaginous rod (notochord) in the young stage which is gradually replaced by cartilage.

D. Osteichthyes have air bladder which is a vesicle or sac containing air,

E. Cyclostomes possess sucking and circular mouth without jaws which is surrounded by tentacles and the tongue bears teeth. e.g., lamprey and nagfish.

F. Aves have light weighted bones with internal spaces filled with air called pneumatic bones and aerodynamic lungs with specialised air sacs. These are the adaptations which enable birds to fly.

The endoparasites such as Taenia solium and Fasciola hepatica (liver fluke), etc., are found inside the host body, and survive due to the presence of certain characters.

Special characters present in by endoparasites are as folows

(i) The possess anaerobic respiration and the gaseous exchange is through general body surface.

(ii) These organisms bear additional organ for the attachment to the host. Fasciola hepatica possesses acetabulum or posterior sucker for the attachment. Taenia solium posses hooks and suckers for the attachment with the host.

(iii) Reproductive organs are well developed. They are generally, hermaphrodite and self fertilisation is common in them.

(iv) The thick tegument (body covering) is present which is resistant to the host's digestive enzymes and antitoxins.

(v) Absence of locomotary organs.

(vi) Tapeworms lack digestive organs because digested and semidigested food of the host is directly absorbed through their because body surface.

A. $\rightarrow(\mathrm{v})$ B. $\rightarrow$ (ii) C. $\rightarrow$ (iii) D. $\rightarrow$ (iv) E. $\rightarrow$ (ii) F. $\rightarrow$ (vi)

A. Pila-Presence of shell Shell in Pila is an elongated structure which consists of a tubular whorl coiled around a central axis called columella. The main function of shell is to provide protection from harsh conditions.

B. Cockroach-Jointed appendages Presence of jointed appendages along with segmented body is the characteristic feature of arthropods (e.g., spiders, bees, crabs etc).

C. Asterias-Water vascular system It is the unique and characteristic feature in echinoderms. This system acts as a hydraulic system, composed of canals connecting numerous tube feet. It is very important as it helps Asterias (sea star) to move as well as to catch food. Respiration also takes place, through, water vascular system.

D. Torpedo Electric organ. Torpedos are unique organisms, having two large kidney shaped electric organs. These organs are capable of generating high voltage electric shocks.

E. Parrot-Perching Birds with the feet adapted (to hold tree branches are perching birds. The Passeriform birds are true perching birds with four toes, three directed forward and one backward.

F. Dog fish-Placoid scales Placoid scales are tough scales that cover the skin of elasmobranchs (dog fish, sharks and rays). They are covered with hard enamel. The function of these scales is to protect against predators.