(a) Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain.

(b) Draw a diagram of human respiratory system and label – pharynx, trachea, lungs, diaphragm and alveolar sac on it.

OR

(a) Name the organs that form the excretory system in human beings.

(b) Describe in brief how urine is produced in human body.

(a) The aquatic organisms depend only on the oxygen present in the dissolved form in the water body. Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms.

(b)

Human Respiratory System

OR

a. The organs of the Human Excretory System are

1. A pair of Kidneys

2. A pair of Ureters

3. Urinary Bladder

4. Urethra

(b) The main excretory organ in human beings is the kidney that releases about 80% of liquid waste from the body. Urine formation occurs in the kidney in 3 parts-

1. Glomerular Filtration or Ultrafiltration

2. Selective Reabsorption

3. Tubular Secretion.

The afferent arteriole brings blood to the kidney and forms a bunch of capillaries in the Bowman’s capsule. Glomerular filtration occurs in the Bowman's capsule where glucose, salts, amino acids, urea enters the filtrate. Water and solutes that are smaller than proteins are forced into the renal tubule where reabsorption of water, glucose, amino acids and needed ions occurs and returns them back to the blood. Tubular secretion removes additional wastes from the blood and adds them to the filtrate. Further, water is removed from urine and returned to blood. Urine is sent to the collecting ducts.