C.

distal convoluted tubules

The vasopressin hormone, secreted by neurohypophysis of pituitary gland promotes the reabsorption of water from the distal convoluted tubules of nephrons, reducing excretion of water in urine (diuresis). Hence, it is called Antidiuretic Hormone (ADH). Its release in blood is controlled by an 'osmoregulatory centre' located in hypothalamus. Hyposecretion of ADH causes diabetes incipidus.

A.

increase in number

At altitude the partial pressure of the oxygen decreases in atmosphere so there is less oxygen available to carry out respiration. In order to compensate the cellular oxygen demand, the body increases the amount of RBC present to trap as many oxygen molecules as possible.

C.

virus

Virus is without necessary metabolic enzymes, hence, free virus are inert particles incapable of any vital activities and uses host machinery. Virus is regarded as obligate parasite and have characteristic of both living and non-livings.

A.

N-acetyl glucosamine

The chitin (polyglycosamine) is an acetate of mucopolysaccharide called glycosamine which is formed by the combination of polysaccharide with small peptide molecules. The basic unit (monomer) of chitin is N-acetylglucosamine, monomers are joined by 1-4 $\beta$ linkages.

D.

syncytial

Striped (striated or skeletal or voluntary) muscles are syncytial. Nuclei are spindle shaped, peripheral in position and lie near the sarcolemma. They are multi nucleate because each fibre is formed by the fusion of a number of embryonic stem cells (myoblasts), hence, regarded multicellular syncytial body.