Chemical Coordination in Plants — ICSE Class 10 Biology Important Questions
13 hand-picked ICSE Class 10 Biology important questions for Chemical Coordination in Plants, each with a full model answer — the formats and topics most likely to appear in your board exam.
- 13
- Questions
- 6
- Question types
- 32
- Total marks
- ₹0
- With answers
High-yield ICSE Chemical Coordination in Plants questions cover the five plant hormones (auxins, gibberellins, cytokinins, abscisic acid, ethylene) with their functions, tropic movements (phototropism, geotropism, hydrotropism, chemotropism) versus nastic movements, and the classic auxin experiments on coleoptiles that prove auxin causes bending toward light.
About Chemical Coordination in Plants
In the ICSE Class 10 Biology chapter Chemical Coordination in Plants you study how plants coordinate their activities using chemical messengers called phytohormones (plant hormones) instead of a nervous system. The chapter covers auxins, gibberellins, cytokinins, abscisic acid and ethylene and their roles, the difference between tropic (directional, growth) movements and nastic (non-directional) movements, and the experiments showing that auxin, produced at the shoot tip, controls a plant's response to light and gravity.
Key concepts & formulas
Chemical substances produced in small amounts that regulate growth and responses. Growth-promoting: auxins, gibberellins, cytokinins. Growth-inhibiting: abscisic acid (ABA). Ripening/ageing: ethylene.
A directional growth movement of a plant part in response to an external stimulus. It is positive if towards the stimulus and negative if away. Examples: phototropism (light), geotropism (gravity), hydrotropism (water), chemotropism (chemicals).
Auxin is made at the shoot tip and diffuses down. In unilateral light, auxin accumulates on the shaded side, which elongates faster, so the shoot bends towards the light (positive phototropism).
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Important questions with answers
Try each on paper first, then reveal the model answer to check your method.
| Question type | Count | Marks |
|---|---|---|
| MCQ | 4 | 1 |
| Assertion–Reason | 1 | 1 |
| Very Short | 2 | 2 |
| Short Answer | 3 | 3 |
| Long Answer | 2 | 5 |
| Case-based | 1 | 4 |
Multiple-choice questions (1 mark)
The plant hormone chiefly responsible for cell elongation and phototropism is:
- (a)
Abscisic acid
- (b)
Cytokinin
- (c)
Auxin
- (d)
Ethylene
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Answer: (c) Auxin.
Auxin, produced at the shoot tip, promotes cell elongation and causes the bending of shoots towards light (positive phototropism).
The downward growth of a root in response to gravity is called:
- (a)
Positive phototropism
- (b)
Positive geotropism
- (c)
Negative geotropism
- (d)
Hydrotropism
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Answer: (b) Positive geotropism.
Roots grow towards gravity (downwards), which is positive geotropism; shoots grow away from gravity, which is negative geotropism.
Which hormone promotes the ripening of fruits and is used commercially for this purpose?
- (a)
Gibberellin
- (b)
Ethylene
- (c)
Auxin
- (d)
Cytokinin
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Answer: (b) Ethylene.
Ethylene is a gaseous hormone that hastens the ripening of fruits and the ageing/abscission of leaves.
The tip of a coleoptile is cut off and replaced with a tiny agar block that had earlier been in contact with a tip. When lit from one side, the coleoptile still bends towards the light. This best shows that:
- (a)
Light itself bends the coleoptile mechanically
- (b)
The stimulus is a diffusible chemical (auxin) made at the tip
- (c)
The tip is not needed for a response
- (d)
Bending is due to loss of water on the lit side
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Answer: (b) The stimulus is a diffusible chemical (auxin) made at the tip.
Because the agar block (which absorbed the tip's chemical) can substitute for the tip, the response must be caused by a diffusible substance — auxin — not by the tip itself or by light acting directly.
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Practise free with the AI tutor →Assertion–Reason questions (1 mark)
Assertion (A): A shoot growing on a windowsill bends towards the window.
Reason (R): Auxin accumulates on the shaded side of the shoot, causing that side to elongate more.
- (a)
Both A and R are true and R is the correct explanation of A
- (b)
Both A and R are true but R is not the correct explanation of A
- (c)
A is true but R is false
- (d)
A is false but R is true
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Answer: (a) The shoot shows positive phototropism. Auxin moves to the darker side, which elongates faster, bending the shoot towards the light. R correctly explains A.
Very short answer questions (2 marks)
Define tropism. How does it differ from a nastic movement?
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A tropism is a directional growth movement of a plant part in response to an external stimulus, where the direction of movement is determined by the direction of the stimulus.
A nastic movement is a non-directional movement (e.g. folding of Mimosa leaves on touch) that is independent of the direction of the stimulus and is usually due to changes in turgor, not growth.
Name the plant hormones responsible for (i) breaking of seed dormancy and stem elongation, and (ii) closing of stomata and inhibition of growth during water stress.
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(i) Gibberellins — promote stem elongation and help break seed and bud dormancy (they also induce bolting).
(ii) Abscisic acid (ABA) — a growth inhibitor that closes stomata during water stress and promotes dormancy; it is called the 'stress hormone'.
Short answer questions (3 marks)
Distinguish between phototropism, geotropism and hydrotropism, giving one example of a plant part showing each.
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Phototropism — growth movement in response to light. Example: a shoot bends towards light (positive phototropism).
Geotropism — growth movement in response to gravity. Example: a root grows downwards towards gravity (positive geotropism).
Hydrotropism — growth movement in response to water. Example: a root grows towards a source of moisture (positive hydrotropism).
In each case the response direction is set by the direction of the stimulus.
State one important function each of auxins, cytokinins and abscisic acid in plants.
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Auxins: promote cell elongation of the shoot, control apical dominance and cause phototropic bending.
Cytokinins: promote cell division (cytokinesis), delay ageing of leaves and help break dormancy of buds.
Abscisic acid (ABA): inhibits growth, promotes closure of stomata during water shortage and induces seed/bud dormancy.
Explain, with a labelled sketch, how a shoot responds when exposed to light coming from only one side.
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When light falls on one side only, the shoot shows positive phototropism — it bends towards the light.
Auxin from the tip accumulates on the shaded side; those cells elongate more than the lit side, so the shoot curves towards the light.
Long answer questions (5 marks)
Describe an experiment using oat/canary-grass coleoptiles to demonstrate that (a) the tip is the region that perceives light and (b) a diffusible chemical from the tip causes the bending. State the observations and conclusion.
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Aim: To show that the coleoptile tip perceives unidirectional light and produces a diffusible chemical that causes bending.
Part (a) — perception is in the tip:
- Take several coleoptiles. Leave one intact; from another cut off the tip; on a third place an opaque cap over the tip; on a fourth cover the base with an opaque sleeve.
- Expose all to light from one side.
Observations: The intact coleoptile and the one with only the base covered bend towards light; the one with its tip removed or its tip capped does not bend.
Conclusion: The tip is the region that perceives the light stimulus.
Part (b) — a diffusible chemical causes bending:
- Cut off a tip and place it on a small agar block for some time, then discard the tip.
- Place this agar block off-centre on the cut stump of a decapitated coleoptile, kept in the dark.
Observation: The coleoptile bends away from the side carrying the block, because that side, receiving more auxin, elongates faster.
Conclusion: A diffusible chemical (auxin) made at the tip moves down and, by promoting elongation on one side, causes the bending. Thus phototropism is chemically controlled by auxin.
Tabulate the five major plant hormones with one site of production and two functions of each, and explain why plants can coordinate without a nervous system.
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| Hormone | Where produced | Two functions |
|---|---|---|
| Auxin | Shoot tip, young leaves | Cell elongation; apical dominance / phototropism |
| Gibberellin | Young leaves, seeds | Stem elongation; breaking seed dormancy |
| Cytokinin | Root tips, developing fruits | Cell division; delaying leaf ageing |
| Abscisic acid | Leaves, seeds | Closing stomata in stress; inducing dormancy |
| Ethylene | Ripening fruits, ageing tissues | Fruit ripening; leaf and fruit fall (abscission) |
Coordination without nerves: Plants have no nervous system, yet they respond to stimuli through these chemical messengers (phytohormones). The hormones are made in one region, diffuse or are transported to target tissues, and there they alter growth (e.g. rate of cell elongation or division). Because plant responses are mostly slow growth movements rather than rapid actions, this chemical coordination is sufficient for their needs.
Case-based questions (4 marks)
A potted plant is laid on its side in the dark. After two days the shoot has curved upward and the root has curved downward.
(i) Name the stimulus and the type of tropism shown by the shoot and by the root.
(ii) State whether each response is positive or negative to that stimulus.
(iii) Explain the role of auxin in producing these two opposite responses.
(iv) What advantage do these responses give the plant?
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(i) The stimulus is gravity; both responses are geotropism (gravitropism).
(ii) The shoot growing upward, away from gravity, is negatively geotropic; the root growing downward, towards gravity, is positively geotropic.
(iii) When the plant lies on its side, auxin accumulates along the lower side of both organs. In the shoot, this extra auxin makes the lower side elongate more, so the shoot bends upward. In the root, a high auxin concentration inhibits elongation, so the lower side grows less than the upper side and the root bends downward. The same hormone thus gives opposite effects because roots and shoots have different auxin sensitivities.
(iv) The shoot grows up towards light and air for photosynthesis, while the root grows down into the soil for anchorage, water and minerals — improving the plant's survival.
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Yes — they are aligned to the CISCE latest syllabus syllabus for ICSE Class 10 Biology, so nothing here is outside the current course.How should I practise the Chemical Coordination in Plants important questions?
Attempt each question on paper first, then reveal the model answer to check your method — not just the final result. Re-do anything you got wrong the same day.What types of questions are covered for Chemical Coordination in Plants?
A full mix — multiple-choice questions, assertion–reason questions, very short answer questions, short answer questions, long answer questions, case-based questions — so every format in the ICSE paper is covered.
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