Animal A can live on land as well as in water and can respire through lungs as well as moist skin. The animal is frog.
Animal B lives in water and respires through a specific organ called gills. These are found in the tadpoles besides fishes.
The animal B is a fish. Animal C is also an aquatic animal which lives in sea water and respires through nostrils and lungs not by the gills. The animal is whale.

Kidney is the major excretory organ which consists of thousands of tiny filters called nephrons.
The major functions of nephron are
(i) To filter blood at high pressure which helps in the separation of nitrogenous waste such as urea from the blood.
(ii) It helps in selective re-absorption of some substances (from the initial filtrate which is filtered at a very high pressure). These substances include glucose, amino acid, salts and a major amount of water.

The blood clot is formed due to the presence of the cells called platelets in the blood. If there were no platelets in the blood, then bleeding caused by a cut from an injury would not stop. This may cause loss of too much blood from the body of a person leading to death.

Electric fuse is required in all electrical appliances to prevent damage from excessive current flow and during short circuit.

Lenticels

Diaphragm is known as the floor of chest cavity

Stethoscope.

A cockroach has small opening on the side of its body. These openings are called spiracles. Insects have a network or air tubes called tracheae for gas exchange, oxygen rich air rushes through spiracles into the tracheal tubes, diffuses into the body tissues and reaches every cell of the body. Similarly carbon dioxide from the cells goes into the tracheal tubes and moves out through spiracles. These air tubes or tracheae are found only in insects

Electric circuit: The path along which an electric current can flow is called electric circuit. The components of an electric circuit are
(i) The cell or battery-The source of electrical energy,
(ii) The connecting wires or conductors,
(iii) The bulb-that uses the current,
(iv) Switch-to close or open the circuit.
The simplified circuit diagram is given below with components and their symbols:

Blood is a fluid which flows in blood vessels.
(a) Functions of blood :
(i) It transports digested food from small intestine to all parts of the body. 
(ii) It carries oxygen from lungs to cell.
(b) Components of blood:
(i) Fluid: Plasma
(ii) Cells: RBC,WBC, Platelets.