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.

Ornithine cycle takes place in liver. The amino acid arginine and citrulline are formed during this cycle. Therefore it is referred as ornithine, arginine cycle and also Kreb-Henseleit cycle. The products of this cycle are urea and ornithine. The substances excreted through this cycle are CO₂ and NH₂

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.

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.

Lysosomes or suicidal bags are bounded by single unit membrane. It contains hydrolytic enzymes which help to digest the nucleic acids, proteins and polysaccharide etc. (i.e., extracellular material). It also helps in autolysis.

Ventricles are related to both heart and brain. Mammalian heart is four chambered. The upper two chambers known as right and left auricle and the lower as right and left ventricles. In brain there are four ventricles. Ventricle Ist and II (lateral ventricles) are cavities of two cerebral hemispheres. IIIrd ventricle (diocoel) is cavity of diencephalon and IV ventricle (metacoel) is cavity of medulla oblongata.

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.

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.

Arachidonic acid is polyunsaturated (i.e., have more than one double bond) and essential fatty acids. Essential fatty acids cannot be synthesised by the body of animal and has to be taken from outside to fulfil the body requirement. Linoleic acid and linolenic acid are also essential fatty acids.

In ruminants (e.g., cow, goat and camel) the stomach is 4 chambered as follows

(a) Rumen (cellulose is digested)

(b) Reticulum (cellulose is digested)

(c) Omasum (absorb water)

(d) Abomasum (true stomach)