Zoology MCQs for NEET — Practice Questions with Answers

Increase in aldosterone levels cause an increase in sodium reabsorption is DCT. It is secreted by outer, layer of adrenal gland when aldosterone is present in the blood, all the Na⁺ in the filterate is reabsorbed. Retaining Na⁺ raises the osmotic pressure of the blood and reduces the water loss from the body.

Convoluted tubule is the highly convoluted segments of nephron in the renal labyrinth of the kidney. It is made up of the proximal tubule leading from the Bowmans capsule to the descending limb of Henle's loop and the distal tubule leading from the ascending limb of Henle's loop to a collecting tubule.

Reptile, birds, land snails and insects excrete nitrogenous waste as uric acid in the form of pellet of paste with a minimum loss of water and are called uricotelic animals.

The plasma fluid that filters out from glomerular capillaries into Bowman's capsule of nephron is called glomerular filtrate. A comparison of the volume of the filtrate formed per day (180 L/day) with that nearly 99 percent of filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption.

In humans, the principal nitrogenous excretory compound (i.e., urea) is synthesized in liver by ornithine cycle. In liver, one molecule of CO₂ is activated by biotin and combines with two molecules of NH₃ in the presence of carbamoyl phosphate synthetase enzyme and 2ATP to from carbamoyl phosphate and one molecule of H₂O is released. Carbamoyl phosphate reacts with ornithine and forms citrulline. Citrulline combines with another molecule of ammonia and form arginine that is broken into urea and ornithine in the presence of an enzyme arginase and water.

$2{\mathrm{NH}}_3 + {\mathrm{CO}}_2\stackrel{\mathrm{Arginase}}{\to } {\mathrm{NH}}_2-\mathrm{CO}-{\mathrm{NH}}_2+{\mathrm{H}}_2\mathrm{O}$
urea is eliminated mostly through kidney as nitorogenous excretory product.

Cockroach excretes uric acid as the chief nitrogenous excretory product.

Man excretes urea as the chief nitrogenous excretory product.

Earthworm excretes 40% urea, 20% ammonia and 40% amino acids.

Frog excretes urea as the chief nitrogenous product.

Due to a long hunger strike and survival on water, a person will have less urea in his urine because urea comes to kidney as a waste product from liver which is formed after the breakdown of protein fat, carbohydrate during hunger. It is not synthesized but the synthesized ones are catabolized. 

Angiotensinogen is a plasma protein produced and secreted by the liver cells. It is the precursor of angiotensin I, which is further converted to angiotensin II, a potent vasoconstrictor involved in the regulation of blood pressure and fluid balance in the body.

(c) : Uricotelic animals ( living in dry conditions) are those animals which excrete uric acid as their
excretory product e.g lizard and crow. These animals conserve water in their bodies and synthesize crystals of uric acid from ammonia. These crystals can be retained in the body (in solid form ) for a considerable time before being discharged from the body. 

(b) Vasopressin or ADH secreted from posterior pituitary stimulates reabsorption of water by the distal convoluted tubule and the collecting renal tubules and thus regulates urine volume. It has no such important effect on glucose metabolism. Therefore, a person whose blood glucose level is normal, but passes much urine and drinks much water has a reduction in vasopressin secretion which ultimately leads to diabetes insipidus.