Plant hormones

Plants have no nerves, so they send messages with chemicals. ICSE calls these plant growth regulators. Each has one main effect:

• Auxin is made at the shoot tip and makes cells grow longer. It bends a shoot towards light.
• Gibberellins make stems grow longer. They can make fruit form without seeds.
• Cytokinins make cells divide. They are found where cells divide fast, as in fruits and seeds.
• Abscisic acid slows growth. It keeps seeds dormant, and one of its effects is wilting of leaves.
• Ethylene is a gas that ripens fruit. ICSE lists it; NCERT names the first four.

A small example

A grape grower sprays gibberellins when the fruit is forming. The grapes grow longer, and they have no seeds. Fruit that forms without fertilisation, and so without seeds, is called parthenocarpic.

Where marks go

In CBSE, the Science syllabus for 2026-27 includes an introduction to plant hormones. The 2026-27 sample paper has no question on them. Learn each hormone with one clear effect, such as auxin making cells grow longer.

In ICSE, the 2025 Biology paper used the grape grower for 2 marks. The answers were gibberellins and parthenocarpy. CISCE's report on the 2025 ICSE Biology paper says some answers gave "ethylene", reading it as a question on ripening. For the second part it names "pollination" and "fertilisation" as answers given instead.

The 2027 specimen paper asks which hormone makes plants grow toward sunlight. Its draft marking scheme answers auxins, with the movement named as phototropism.

About the author

Deepti Sardana

Founder Member & Academic Lead

An IIT alumna (M.Sc., M.Phil.) with over 25 years in teaching, child psychology and learning assessment. As Academic Lead at EduBrahma, she leads the method TRUtesting uses to find where and why a child loses marks.

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