BiologyICSE Class 10 · Chemical Coordination in Plants

Abscisic Acid and Ethylene: Growth Inhibitor and Ripening Hormone (ICSE Class 10 Biology)

Updated 16 October 2026 · Fact-checked

Abscisic acid (ABA) is a growth inhibitor: it induces dormancy of seeds and buds, closes stomata during water shortage (so it is called the stress hormone) and promotes the fall of leaves and fruits. Ethylene is a gaseous hormone that ripens fruits such as banana and mango and speeds up ageing and abscission.

ABA is the inhibitor that pauses and protects the plant in stress; ethylene is a gas that ripens fruit and speeds ageing.

Illustration drawn for QuestionBuddy.

Understand Abscisic Acid and Ethylene in Plants

Two kinds of regulators. Growth regulators either promote growth (auxins, gibberellins, cytokinins) or inhibit it (abscisic acid). Ethylene, the fifth regulator in the syllabus, chiefly controls ripening and ageing. A plant needs both kinds: promoters to grow in good seasons, inhibitors to pause and survive bad ones.

Abscisic acid (ABA).

Dormancy: induces dormancy of seeds and buds, so they do not sprout before winter or a dry season.
Closing of stomata: during water shortage, ABA builds up in leaves and makes stomata close, cutting transpiration. Because it helps the plant cope with stress such as drought, it is called the stress hormone.
Abscission: promotes the falling of leaves, flowers and fruits (abscission = separation by a layer of cells at the base of the stalk).
Opposes promoters: it counteracts gibberellins, for example by keeping seeds dormant where gibberellins would break dormancy.

Ethylene.

A gas at ordinary temperatures; it spreads through air and between fruits.
Ripening of fruits: banana, mango, tomato, papaya; ripening fruits release more ethylene, which speeds up ripening of nearby fruits.
Abscission and senescence: speeds up ageing and falling of leaves and flowers.

Five regulators at a glance.

Regulator	Group	Signature effect
Auxin	promoter	cell elongation, apical dominance
Gibberellin	promoter	internode elongation, larger grapes
Cytokinin	promoter	cell division, delays ageing
Abscisic acid	inhibitor	dormancy, closes stomata
Ethylene	gaseous hormone	fruit ripening

Opposite pairs worth remembering.

Process	Promoted by	Opposed by
Seed germination	gibberellin	abscisic acid
Ageing of leaves	ethylene, ABA	cytokinin
Leaf and fruit fall	ABA, ethylene	auxin

Uses in daily life. Traders ripen bananas and mangoes evenly with ethylene; storing fruit in cool, ventilated places slows ripening by removing ethylene. ABA's natural role keeps seeds in storage from sprouting.

Flow chart: drought response. Soil dries → leaves lose water → ABA rises in leaves → guard cells lose K⁺ and water → stomata close → transpiration falls → plant survives the dry spell (photosynthesis also slows).

Draw-and-label checklist: abscission (simple sketch). A twig with a leaf stalk; a narrow band of cells at the base of the stalk labelled 'abscission layer'; arrow labelled 'ABA and ethylene promote'; the falling leaf; the scar left on the twig.

Abscisic Acid and Ethylene in Plants: key facts

Abscisic acid: Growth inhibitor
Induces dormancy of seeds and buds
Closes stomata in water shortage (stress hormone)
Promotes abscission
Opposes gibberellin; The only inhibitor in the syllabus.
Ethylene: Gaseous hormone
Ripens fruits
Promotes ageing and abscission; Ripening, not fruit size.
Promoters versus inhibitor: Promoters auxin, gibberellin, cytokinin
Inhibitor abscisic acid
Ripening ethylene; Useful for odd-one-out questions.

Promoters	auxin, gibberellin, cytokinin
Inhibitor	abscisic acid
Ripening	ethylene

How to answer Abscisic Acid and Ethylene in Plants questions

ICSE asks you to name the hormone from an effect, give its functions, classify regulators as promoters or inhibitors, and explain cases such as ripening in closed boxes or plant survival in drought.

1Spot the clue: ripening or a gas = ethylene; dormancy, drought, stomata closing, leaf fall = abscisic acid.
2Name the hormone and state its effect in one sentence.
3For classification, list the three promoters and the one inhibitor.
4For a case, follow cause → hormone → effect on the plant or fruit.
5Check you have not written ethylene for fruit size (that is gibberellin).

Abscisic Acid and Ethylene in Plants in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

One bad apple

Suppose one bruised, over-ripe apple is left in a crate of firm apples, and within a few days the apples touching it and near it have gone soft.

Explain why the other apples over-ripened.

Try it first, then show the solutionSolution

A bruised, over-ripe apple gives off a lot of ethylene gas.
Being a gas, ethylene spreads through the crate to the nearby apples.
Ethylene speeds up ripening and ageing: softening and changes in colour and taste.
Removing the damaged apple early protects the rest.

Answer: Ethylene gas from the over-ripe apple spread through the crate and hastened ripening of the others.

Memory hook: One bad apple gasses the barrel.

Wilting on a hot afternoon

Suppose during a dry May week a gardener notices that his marigold plants droop at noon but recover by evening even without watering.

How does abscisic acid help these plants survive?

Try it first, then show the solutionSolution

Water loss by transpiration exceeds absorption at noon.
Abscisic acid builds up in the leaves under this water stress.
It makes the stomata close, so transpiration drops sharply.
With less water lost, the cells regain turgor in the cooler evening.

Answer: ABA closes stomata during water stress, reducing transpiration so the plant recovers.

Memory hook: ABA = Anti-drought Brake Applied.

Tricks to remember Abscisic Acid and Ethylene in Plants

Short memory aids. Say each one aloud once, then use it on a question the same day.

ABA = Always Bad times Agent
ABA works in bad times: winter (dormancy), drought (stomata shut), autumn (leaf fall).
Use it when: Recalling all ABA effects.
Ethylene = Eat-ready
Ethylene makes fruit ready to eat.
Use it when: Linking ethylene to ripening.
Three promote, one stops
A-G-C go; ABA says no.
Use it when: Classifying regulators.

Abscisic Acid and Ethylene in Plants: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: The gaseous hormone · 1 mark · MCQBoard level

Which statement about ethylene is correct?
(a) It is a gas that hastens fruit ripening. (b) It is a liquid that delays ageing of leaves. (c) It breaks the dormancy of seeds. (d) It is the growth inhibitor that closes stomata.

Try it first, then show the solutionSolution

Ethylene is a gaseous hormone that promotes ripening; delaying ageing is cytokinin, breaking dormancy is gibberellin, and closing stomata is abscisic acid.

Answer: (a) It is a gas that hastens fruit ripening.

Example 2: The stress hormone · 2 marks · Short answerBoard level

Why is abscisic acid called the 'stress hormone'? Give one more effect of it.

Try it first, then show the solutionSolution

During water shortage it causes stomata to close, reducing water loss, helping the plant survive stress (1 mark).
It also induces dormancy of seeds and buds (or promotes abscission of leaves and fruits) (1 mark).

Answer: It closes stomata under water stress; it also induces dormancy (or abscission).

Example 3: Not a growth hormone · 2 marks · Short answerHarder board level

A student lists abscisic acid with auxin, gibberellin and cytokinin as 'hormones that make plants grow'. Correct the student, and give one effect of abscisic acid that shows the difference.

Try it first, then show the solutionSolution

Auxin, gibberellin and cytokinin are growth promoters, but abscisic acid is a growth inhibitor (1 mark).
For example, it induces dormancy of seeds and buds (or closes stomata, or promotes abscission) (1 mark).

Answer: Abscisic acid is a growth inhibitor, not a promoter; it induces dormancy (or closes stomata, or causes abscission).

Example 4: Seeds in a store · 2 marks · Short answerHarder board level

Wheat grains stored in a dry godown do not germinate for months, but sprout quickly if soaked and kept warm. Name the hormone that keeps them dormant and the hormone that breaks dormancy.

Try it first, then show the solutionSolution

Abscisic acid keeps the seeds dormant (1 mark).
Gibberellin breaks dormancy and promotes germination when conditions are suitable (1 mark).

Answer: Dormancy: abscisic acid. Germination: gibberellin.

Example 5: Banana trial · 3 marks · Case-basedHOTS / competency

Suppose a fruit seller finds that raw bananas kept alone take 8 days to ripen, but bananas kept in a closed carton with ripe apples take 3 days. (a) How many days are saved? (b) By what percentage is the ripening time cut? (c) Name and explain the cause.

Try it first, then show the solutionSolution

(a) 8 − 3 = 5 days (1 mark).
(b) 5 ÷ 8 × 100 = 62.5% (1 mark).
(c) Ethylene gas from the ripe apples collects in the closed carton and speeds up ripening (1 mark).

Answer: (a) 5 days. (b) 62.5%. (c) Ethylene from ripe apples.

Example 6: Drought trial · 3 marks · Case-basedHOTS / competency

Suppose in a drought experiment 80% of a leaf's stomata are open before treatment and only 20% are open an hour after the leaf is sprayed with abscisic acid. (a) By what percentage did the number of open stomata fall? (b) What happens to transpiration? (c) Why might growth slow down if the spray is repeated for weeks?

Try it first, then show the solutionSolution

(a) (80 − 20) ÷ 80 × 100 = 75% fall (1 mark).
(b) Transpiration falls, saving water (1 mark).
(c) Closed stomata let in less CO₂, so photosynthesis and growth slow; ABA is also a growth inhibitor (1 mark).

Answer: (a) 75%. (b) Transpiration decreases. (c) Less CO₂ enters, so photosynthesis and growth fall.

Where students lose marks in Abscisic Acid and Ethylene in Plants

The slips examiners see most often, and what to write instead.

Mistake: Ethylene given for fruit size
CISCE examiners' comments (2025): for a hormone sprayed to elongate grapes, candidates wrote ethylene, linking it to fruit ripening.
Do this: Ethylene ripens; gibberellin enlarges and elongates fruit.
Usually costs: 1 mark.
Mistake: Calling abscisic acid a promoter
Its name sounds like 'abscission' only, so students forget it is the growth inhibitor in the list.
Do this: ABA is the inhibitor: dormancy, stomatal closing, abscission.
Usually costs: 1 mark.
Mistake: Forgetting ethylene is a gas
The gaseous nature explains why ripe fruits ripen others in a closed space; omitting it weakens the explanation.
Do this: Write 'ethylene gas released by ripe fruit'.
Usually costs: 1 mark.

Exam tips

ABA: dormancy, closes stomata, abscission; the stress hormone.
Ethylene: gas, ripening, ageing.
Grapes bigger = gibberellin; fruit softer and sweeter = ethylene.
Three promoters, one inhibitor.

Practice questions on Abscisic Acid and Ethylene in Plants

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The plant hormone that induces dormancy in buds is:
(a) auxin (b) gibberellin (c) abscisic acid (d) cytokinin
Hint
The inhibitor.
Answer
(c) abscisic acid.
Q2 · 1 mark · Very short answerBoard level
What is abscission?
Hint
Leaves and fruits.
Answer
The shedding (falling) of leaves, flowers or fruits from the plant.
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Farmers spray ethylene on grapes to make the berries longer.
Reason (R): Ethylene promotes fruit ripening.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Hint
Which hormone enlarges grapes?
Answer
(b). Gibberellin, not ethylene, elongates grapes.
Q4 · 2 marks · Short answerHarder board level
Give two functions of ethylene.
Hint
Fruits and leaves.
Answer
Ripening of fruits; promotes ageing and abscission of leaves and flowers.
Q5 · 2 marks · Short answerHarder board level
Name the hormone that opposes each: (a) cytokinin's delay of ageing; (b) gibberellin's breaking of seed dormancy.
Hint
Opposite pairs.
Answer
(a) Ethylene (or abscisic acid) (b) Abscisic acid.
Q6 · 2 marks · Short answerHarder board level
Why do traders store mangoes in cool, well-ventilated rooms when they want to delay ripening?
Hint
What does ventilation remove?
Answer
Ventilation carries away the ethylene gas released by the fruits, and low temperature slows ripening, so the mangoes stay unripe longer.
Q7 · 2 marks · Short answerHarder board level
How does abscisic acid help a deciduous tree survive winter?
Hint
Buds and leaves.
Answer
It promotes the shedding of leaves, reducing water loss, and induces dormancy of buds so they do not open until conditions improve.
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose cut lettuce kept in water stays green for 3 days, while lettuce kept in a dilute cytokinin solution stays green for 7 days.
(a) How many extra days did cytokinin give? (1)
(b) Name the process that cytokinin delayed. (1)
(c) Name one hormone that would make the lettuce yellow faster. (1)
Hint
Opposing hormones.
Answer
(a) 7 − 3 = 4 days. (b) Senescence (ageing) of leaves. (c) Ethylene (or abscisic acid).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Which hormone is called the stress hormone?Show answer
Abscisic acid.
2.Name the gaseous plant hormone.Show answer
Ethylene.
3.Which hormone closes stomata during drought?Show answer
Abscisic acid.
4.Name a fruit commonly ripened with ethylene.Show answer
Banana (or mango, tomato, papaya).
5.Is abscisic acid a promoter or an inhibitor?Show answer
An inhibitor.

Abscisic Acid and Ethylene in Plants: frequently asked questions

Is ethylene a growth promoter or an inhibitor?

For ICSE, treat it separately as the ripening hormone; it mainly promotes ripening, ageing and abscission rather than growth.

Is artificial ripening with calcium carbide the same as ethylene?

Carbide releases a gas that acts like ethylene, but its use is banned in India because of harmful impurities; ethylene itself is the natural ripening hormone.

Does abscisic acid always slow a plant down?

Yes, it is an inhibitor, but that pause protects the plant during winter or drought.

How much detail do I need?

A brief idea of the physiological effects, as listed on this page, is enough.