Tropic responses Flashcards – Cambridge IGCSE (9–1) Biology 0970 (Extended) (2026–2028)

What is gravitropism?

Directional growth in response to gravity.

What is the difference between positive and negative gravitropism?

• Positive: growth towards gravity.
• Negative: growth away from gravity.

How do roots and shoots generally differ in their gravitropic growth?

• Roots: grow downwards, showing positive gravitropism.
• Shoots: grow upwards, showing negative gravitropism.

How should seedlings be positioned and lit to investigate gravitropism?

Place them horizontally under uniform lighting.

What should be observed over time in a seedling gravitropism investigation?

Whether new growth in each root and shoot bends towards or away from the direction of gravity.

What is phototropism?

Directional growth in response to light.

What is the difference between positive and negative phototropism?

Positive: growth towards a light source. Negative: growth away from a light source.

How do shoots generally grow in response to light?

Towards the light.

How can roots grow in response to light?

Away from the light.

How can phototropism be investigated using seedlings?

Illuminate seedlings from one side and observe their new shoot and root growth over time.

Why keep seedlings’ orientation relative to gravity unchanged during a phototropism investigation?

To distinguish a response to light from a response to gravity.

What is auxin?

A plant growth chemical.

Where is auxin made in a shoot?

In the shoot tip.

How does auxin move through a plant from the shoot tip?

It diffuses through the plant from the tip.

What effect does auxin have on shoot cells?

It stimulates shoot cells to elongate.

How does auxin cause a shoot to bend when light comes from one direction?

More auxin accumulates on the shaded side, causing greater cell elongation there. The shoot bends towards the light.

How does auxin cause a horizontal shoot to bend in response to gravity?

More auxin accumulates on the lower side, causing greater cell elongation there. The shoot bends upwards, away from gravity.