Answer the following about chemical control in organisms.
Generated by claude-sonnet-4-6 · 2026-06-15 06:50 · grounding rag
Model Answer
(a)
(i) The thyroid gland requires iodine to produce thyroxin hormone. Iodine deficiency reduces thyroxin production, causing the thyroid gland to enlarge abnormally — a condition called goitre (swollen neck).
(ii) The pituitary gland secretes growth hormone. If it secretes insufficient growth hormone during childhood, the person's growth is stunted, resulting in dwarfism (very short height).
(iii) At puberty (10–12 years), the testes begin secreting testosterone (male sex hormone). This hormone triggers the development of secondary sexual characters, including growth of thick facial hair in boys.
(b)
- Not all cells are connected by nerves — chemical hormones can reach every cell through the bloodstream, coordinating parts where nerve impulses cannot act directly.
- Long-term/slow responses are needed — some body functions like growth, reproduction, and metabolism require sustained regulation, which hormones provide more effectively than quick electrical impulses.
Source: Control and Coordination, Chapter 6
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Explanation
- For (a), name the specific gland, hormone, and condition in each case — examiners award marks for all three elements.
- For (b), two distinct reasons are required; focus on "why nerves alone are insufficient" (reach) and "type of response needed" (duration). Avoid vague answers like "hormones are important."
- Keyword terms: goitre, dwarfism, testosterone, thyroxin, growth hormone — use these for full marks.