Control and coordination in plants
Cambridge A-Level Biology (9700) · Unit 15: Control and coordination · 7 flashcards
Control and coordination in plants is topic 15.2 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 15 — Control and coordination , alongside Control and coordination in mammals. In one line: Expansins are enzymes that loosen the bonds between cellulose microfibrils in the plant cell wall. This allows the cell wall to become more flexible and stretchable, facilitating cell expansion.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 7 flashcards — 2 definitions and 5 key concepts — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
The function of 'expansins' during cell elongation
Expansins are enzymes that loosen the bonds between cellulose microfibrils in the plant cell wall. This allows the cell wall to become more flexible and stretchable, facilitating cell expansion.
What the Cambridge 9700 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- describe the rapid response of the Venus fly trap to stimulation of hairs on the lobes of modified leaves and explain how the closure of the trap is achieved
- explain the role of auxin in elongation growth by stimulating proton pumping to acidify cell walls
- describe the role of gibberellin in the germination of barley (see 16.3.4)
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Control and coordination in plants
- › Always include charge symbols (Na+ and K+) for ions. Referring to them as 'sodium and potassium' implies the metal atoms, not the ions.
- › Use the term 'saltatory conduction' to describe the 'increased speed of transmission' of the impulse; the action potential itself is not faster.
- › Use precise language: ions pass 'through' or 'across' a membrane, and it is the 'membrane' (not the whole neurone) that becomes depolarised.
- › Note that endorphins bind to specific receptors on the presynaptic knob to inhibit the release of neurotransmitters.
Describe the mechanism by which the Venus flytrap rapidly closes upon stimulation.
Stimulation of trigger hairs causes an action potential that propagates across the leaf lobes. This triggers rapid turgor pressure changes in cells at the hinge, causing the lobes to snap shut, trapping the insect.
Explain how auxin promotes cell elongation in plant shoots.
Auxin stimulates proton (H+) pumps in the plasma membrane, acidifying the cell wall. This activates expansins, enzymes that loosen cellulose microfibrils, allowing the cell to expand due to turgor pressure.
What is the role of gibberellin in barley seed germination?
Gibberellin stimulates the aleurone layer to produce amylase. Amylase hydrolyzes starch stored in the endosperm into glucose, providing energy for the growing embryo.
What is the function of 'expansins' during cell elongation?
Expansins are enzymes that loosen the bonds between cellulose microfibrils in the plant cell wall. This allows the cell wall to become more flexible and stretchable, facilitating cell expansion.
Describe the sequence of events that lead to the closure of the Venus flytrap leaf lobes when a fly lands on it.
Fly lands, stimulating trigger hairs --> Action potential generated --> Turgor pressure change in hinge cells --> Rapid closure of trap.
Explain the relationship between acidification of the cell wall and cell elongation.
Acidification of the cell wall by proton pumps activates expansins. Expansins loosen cellulose microfibrils. This makes the cell wall more flexible, allowing it to expand under turgor pressure, resulting in cell elongation.
What cells are involved in the gibberellin-mediated breakdown of starch in a barley seed?
Gibberellin produced by the embryo stimulates the aleurone layer to synthesize and secrete amylase. Amylase then hydrolyzes starch in the endosperm.
More topics in Unit 15 — Control and coordination
Control and coordination in plants sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Control and coordination in plants deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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