Nitrogenous waste substances such as ammonia, urea and uric acid are produced during protein metabolism according to the species. Amino acids are the breakdown products of proteins in the body. Ammonia is the most toxic and requires large amount of water for its excretion. It is excreted as waste product in protozoans, e.g. amoeba, paramecium, sponges, hydra, liver fluke, earthworm, etc. Uric acid is also excreted as waste product by the most insects (e.g. cockroach), land snails (e.g. helix), land reptiles (e.g. lizards), snakes and birds. 

Ureters are long tubes which connect the kidneys with the urinary bladder. Urinary bladder is a muscular sac where urine is stored until the pressure of the expanded bladder leads to urge to pass it out through the urethra.

Plasma from which fibrinogen has been removed is called serum.

Red blood cells in humans are devoid of mitochondria.

Neutrophils: Phagocytosis Eosinophils: Detoxify germs Basophils: Produce histamine Lymphocytes: Produce antibodies

Mature RBC lacks nucleus and its life span is 120 days.

The gaseous exchange occurs over the area, which is thin and moist, and has a huge surface area and is richly supplied by blood. These are the properties of alveoli. On the contrary, trachea, bronchi and bronchioles are passages of the respiratory system, which lead to the alveoli. But, exchange of gases cannot occur here because they are not thin and are not richly supplied with blood to allow quick diffusion of gases for exchange.

Transportation of oxygen in humans is carried out by haemoglobin, which is stored in RBC’s. Haemoerythrin pigment is present in lower organisms while leghaemoglobin is present inside the root nodules of leguminous plants, e.g. pulses. Haemolysin is not a pigment. Thus, option (3) is correct.

Four chambered heart is present in mammals and birds. Four chambers are left atrium, left ventricle, right atrium and right ventricle. Oxygenated blood passes from the left atrium into the left ventricle. Deoxygenated blood passes from the right atrium into the right ventricle. The hearts of mammals and birds are four chambered to prevent the oxygenated blood from mixing with blood containing carbon dioxide (deoxygenated blood).

Capillaries are the smallest vessels; in fact they are microscopic vessels which are in close contact of the body tissue.

White fur provides camouflage due to white snow.

Penguins have streamlined body and their feet have webs, making them good swimmers.

Large ears of the elephant help it to hear even very soft sounds. They also help the elephant to keep cool in the hot and humid climate of the tropical rainforest.