▶️ Answer/Explanation
(a)(i) Urea is formed through deamination in the liver. This process involves the removal of the nitrogen-containing part of excess amino acids, which are converted into ammonia. Ammonia is then combined with carbon dioxide to form urea, a less toxic compound that can be safely transported in the blood and excreted by the kidneys.
(a)(ii) Plasma.
Explanation: Urea is dissolved in the plasma, the liquid component of blood, which transports it to the kidneys for excretion.
(a)(iii) Urea must be excreted because it is toxic and can harm the body if allowed to accumulate.
Explanation: High levels of urea can disrupt cellular functions and lead to serious health issues, so it must be removed from the body.
(a)(iv) Renal vein.
Explanation: The renal vein carries filtered blood, now with reduced urea levels, away from the kidney and back into the circulatory system.
(b) The glomerulus (K) filters blood under high pressure, allowing water, glucose, urea, and ions to pass into the nephron (L). The nephron then reabsorbs all glucose and some water and ions back into the blood through the capillary network (M). The remaining fluid, now called urine, flows through the collecting duct (N) and contains urea, excess water, and excess ions.
Explanation: This process ensures that essential substances are retained while waste products are efficiently removed from the body.
(c) Nitrate ions are essential for plants because they are a key component in the synthesis of amino acids, which are the building blocks of proteins. Proteins are vital for growth, repair, and various metabolic processes in plants.
Explanation: Without nitrate ions, plants would be unable to produce sufficient proteins, leading to stunted growth and poor development.
(d) Two precautions the farmer should take are:
- Apply the fertiliser in appropriate amounts to avoid excess runoff into the lake.
- Avoid applying fertiliser before heavy rain to prevent it from being washed into the lake.
Explanation: These precautions help minimise the risk of eutrophication, which occurs when excess nutrients in water bodies lead to algal blooms, oxygen depletion, and harm to aquatic life.
