Both plants and animals use chemical signals for coordination, yet animals also possess a nervous system. Explain why chemical signalling is indispensable in animals even though it is slower than nerve impulses. How does the nature of chemical signalling in plants differ from that in animals in terms of the structural requirements and speed of response?
Generated by claude-sonnet-4-6 · 2026-06-26 01:03 · grounding rag
Model Answer
Chemical signalling in animals: Even though nerve impulses are fast, they can only reach tissues connected by nerves. Chemical signals (hormones) are secreted into the blood and reach all cells of the body, enabling wide-ranging, coordinated responses — for example, adrenaline prepares the entire body for fight or flight by affecting the heart, muscles, and breathing simultaneously. Such body-wide coordination is impossible through nerve impulses alone.
Difference between plants and animals:
- Plants have no specialised conducting tissue for chemical signals; information passes cell to cell by electrical-chemical means, and response is relatively slow (e.g., cells change shape by altering water content).
- Animals have a specialised endocrine system; hormones travel rapidly via the bloodstream to specific target organs, giving a faster and more directed response.
Source: Chapter 6, Sections 6.2 / 6.2.1 / 6.3
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Explanation
- The key examiner expectation is two distinct parts: (i) why chemical signalling is indispensable in animals (reach all cells / blood-borne / wide-ranging effect — adrenaline is the textbook example), and (ii) the structural difference (no specialised tissue in plants vs. endocrine system in animals) and consequent speed difference.
- Avoid writing a long essay; 3 marks = ~3 clear points.
- Always anchor to textbook examples: adrenaline/adrenal gland for animals; sensitive plant / cell water change for plants.