14.5

Tropic responses

Cambridge IGCSE Biology (0610)  · Unit 14: Coordination and response  · 10 flashcards

Tropic responses is topic 14.5 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 14 — Coordination and response , alongside Coordination and response, Sense organs and Hormones.  In one line: Gravitropism is a plant's growth response to gravity. Roots show positive gravitropism (grow downwards), while shoots show negative gravitropism (grow upwards).

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 record 6 explicit questions on this topic — though the concept underpins many adjacent topics, so it is tested far more often than that figure suggests.

The deck below contains 10 flashcards — 2 definitions, 3 key concepts and 5 process cards — 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 application cards to handle explain, describe and compare questions.

Key definition

Gravitropism

Gravitropism is a plant's growth response to gravity. Roots show positive gravitropism (grow downwards), while shoots show negative gravitropism (grow upwards).

Example: A seed germinating underground sends its shoot up and root down.

What the Cambridge 0610 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. Describe Describe gravitropism as a response in which parts of a plant grow towards or away from gravity
  2. Describe Describe phototropism as a response in which parts of a plant grow towards or away from the direction of the light source
  3. Investigate Investigate and describe gravitropism and phototropism in shoots and roots
  4. Explain Explain phototropism and gravitropism of a shoot as examples of the chemical control of plant growth Supplement
  5. Explain Explain the role of auxin in controlling shoot growth, limited to: (a) auxin is made in the shoot tip (b) auxin diffuses through the plant from the shoot tip (c) auxin is unequally distributed in response to light and gravity (d) auxin stimulates cell elongation Supplement
Definition Flip

Define gravitropism.

Answer Flip

Gravitropism is a plant's growth response to gravity. Roots show positive gravitropism (grow downwards), while shoots show negative gravitropism (grow upwards).

Example: A seed germinating underground sends its shoot up and root down.
Definition Flip

Define phototropism.

Answer Flip

Phototropism is a plant's growth response to a light source. Shoots show positive phototropism (grow towards light), while roots usually show negative phototropism (grow away from light).

Example: A plant on a windowsill bends towards the sunlight.
Key Concept Flip

How would you investigate phototropism in shoots?

Answer Flip

Place several seedlings in a box with a hole on one side, allowing light to enter from that direction. Observe the shoots bending towards the light source over a few days. Use a control group in normal light conditions for comparison.

Key Concept Flip

How would you investigate gravitropism in shoots and roots?

Answer Flip

Place germinating seeds horizontally on moist filter paper in a Petri dish. Observe the roots growing downwards (positive gravitropism) and the shoots growing upwards (negative gravitropism). Keep one set upright as a control.

Key Concept Flip

Where is auxin produced in a plant?

Answer Flip

Auxin is primarily produced in the shoot tip (apical bud) of a plant. From there, it diffuses to other parts of the plant, influencing growth.

Example: Removing the shoot tip reduces auxin and lateral bud growth.
Key Concept Flip

How does auxin travel through the plant?

Answer Flip

Auxin diffuses from the shoot tip through the plant tissues. The distribution of auxin is influenced by factors like light and gravity, leading to uneven growth.

Example: Auxin moves down the shaded side of a shoot.
Key Concept Flip

How does light affect the distribution of auxin in a shoot?

Answer Flip

Light causes auxin to concentrate on the shaded side of a shoot. This unequal distribution causes cells on the shaded side to elongate more, resulting in the shoot bending towards the light.

Example: The stem of *Arabidopsis thaliana* bends towards light due to increased auxin on the shaded side.
Key Concept Flip

How does gravity affect the distribution of auxin in a horizontal shoot?

Answer Flip

Gravity causes auxin to accumulate on the lower side of a horizontal shoot. The higher concentration of auxin on the lower side stimulates cell elongation, causing the shoot to bend upwards (negative gravitropism).

Example: A bent tomato plant stem turning upwards.
Key Concept Flip

What is the role of auxin in shoot growth?

Answer Flip

Auxin promotes cell elongation in shoots. Higher concentrations of auxin stimulate cell elongation, leading to growth towards a stimulus (light or against gravity).

Example: Increased auxin in coleoptiles bending towards light.
Key Concept Flip

What happens to root growth in response to high concentrations of auxin?

Answer Flip

High concentrations of auxin inhibit root growth. While auxin promotes cell elongation in shoots, it has the opposite effect in roots at higher concentrations.

Example: If a root is placed horizontally, auxin accumulates on the lower side slowing the growth which allows the upper side to grow faster, making the root bend down.

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14.4 Homeostasis 15.1 Drugs

Key Questions: Tropic responses

Define gravitropism.

Gravitropism is a plant's growth response to gravity. Roots show positive gravitropism (grow downwards), while shoots show negative gravitropism (grow upwards).

Example: A seed germinating underground sends its shoot up and root down.
Define phototropism.

Phototropism is a plant's growth response to a light source. Shoots show positive phototropism (grow towards light), while roots usually show negative phototropism (grow away from light).

Example: A plant on a windowsill bends towards the sunlight.

Tips to avoid common mistakes in Tropic responses

More topics in Unit 14 — Coordination and response

Tropic responses sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

14.1 Coordination and response

10 flashcards
14.2 Sense organs

12 flashcards
14.3 Hormones

10 flashcards
14.4 Homeostasis

11 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

tropism phototropism geotropism gravitropism auxin growth plant hormone shoot root positive negative

Key terms covered in this Tropic responses 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.

Gravitropism
Phototropism

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How to study this Tropic responses deck

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