Describe the common causes and methods of preventing blindness.

Here's the answer to Biology 2016 GCE question 6:

6. a) Describe the process of excretion in human beings.
Excretion is the process by which metabolic waste products and excess substances are removed from the body. The main excretory organs are the kidneys, which remove urea, excess water, and salts as urine; the lungs, which excrete carbon dioxide and water vapor; and the skin, which removes water, salts, and a small amount of urea as sweat. The liver also plays a crucial role by converting toxic substances into less harmful forms for excretion.

6. b) Describe the role of the kidney in maintaining the balance of water and salt ions in the blood.
The kidneys are vital for osmoregulation, which is the maintenance of water and salt balance in the blood. They achieve this through filtration, reabsorption, and secretion in the nephrons. Water balance is regulated by the hormone ADH (Antidiuretic Hormone), which controls the permeability of the collecting ducts to water, allowing more or less water to be reabsorbed into the blood. Salt ion balance is maintained through selective reabsorption of ions like sodium and chloride in the renal tubules, influenced by hormones such as aldosterone, ensuring that the blood's osmotic pressure remains stable.