(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.

(a) Organs of the Human Excretory System

The human excretory system consists of the following organs:

1. A pair of kidneys: Located in the abdomen, one on either side of the backbone, which filter the blood.
2. A pair of ureters: Long muscular tubes that carry urine from each kidney to the urinary bladder.
3. A urinary bladder: A muscular sac that stores urine temporarily under nervous control.
4. A urethra: A canal through which urine is expelled from the body.

---

(b) Process of Urine Production

Urine is produced in the kidneys through three main sequential processes occurring in the functional units called nephrons:

1. Ultrafiltration (Glomerular Filtration):

• Blood flows into the kidney through the renal artery under high pressure.
• It enters a cluster of thin-walled capillaries called the glomerulus, which is nestled inside a cup-shaped structure called Bowman's capsule.
• Under high pressure, nitrogenous wastes (like urea and uric acid), glucose, amino acids, salts, and a large amount of water are filtered out of the blood into the Bowman's capsule as initial filtrate.

1. Selective Reabsorption:

• As the filtrate flows along the tubular part of the nephron, useful substances such as glucose, amino acids, essential salts, and a major portion of water are selectively reabsorbed back into the surrounding blood capillaries.
• The amount of water reabsorbed depends on how much excess water is present in the body and how much dissolved waste needs to be excreted.

1. Tubular Secretion and Collection:

• Certain waste ions and molecules are actively secreted from the blood capillaries into the tubular filtrate.
• The remaining concentrated fluid is urine, which flows into a collecting duct.
• From the collecting duct, urine enters the ureter, is carried to the urinary bladder, and is stored there until the pressure of the expanded bladder leads to the urge to pass it out through the urethra.