What is short-sightedness? Explain the causes, symptoms, correction methods, and prevalence in different countries based on the provided data. Also, briefly describe osmoregulation in a dehydrated per

3.4.2 Two structural defects of the eye that cause short-sightedness as seen in the diagram are:

• The eyeball is too long.
• The lens is too convex (or too powerful/curved).

3.4.3 A person who suffers from short-sightedness can see near objects clearly, but distant objects appear blurry or out of focus.

3.4.4 The type of lens used to correct the visual defect is a concave lens.

3.4.5 To draw a bar graph to represent the data in the table:

• X-axis: Label with "Name of Country" and list the countries: Singapore, Hong Kong, China, United States of America, India.
• Y-axis: Label with "12-year-old children with short-sightedness (%)" and scale it from 0% to at least 70%.
• Draw a bar for each country corresponding to its percentage:
  • Singapore: 62%
  • Hong Kong: 53%
  • China: 50%
  • United States of America: 20%
  • India: 10%
• Ensure all bars are of equal width and are separated by equal spaces.
• Provide a clear title for the graph, e.g., "Prevalence of Short-Sightedness in 12-Year-Old Children Across Five Countries".

3.5 The homeostatic mechanism that maintains the correct level of water in the blood (osmoregulation) in a dehydrated person involves the following steps:

• When the person is dehydrated, the water content in their blood decreases, leading to an increase in blood osmotic pressure.
• Osmoreceptors in the hypothalamus detect this increase in osmotic pressure.
• The hypothalamus stimulates the posterior pituitary gland to release more Antidiuretic Hormone (ADH) into the bloodstream.
• ADH travels to the kidneys and increases the permeability of the collecting ducts and distal convoluted tubules to water.
• This causes more water to be reabsorbed from the filtrate back into the blood, reducing water loss through urine.
• As a result, the urine produced is more concentrated, and the blood water level returns to normal.
• The hypothalamus also triggers the sensation of thirst, prompting the person to drink water, which further helps to restore water balance.