Control and coordination Flashcards – AQA GCSE Biology - Foundation (8461)

What is gravitropism?

A directional growth response to gravity.

How is IAA distributed when a root or shoot is placed horizontally?

IAA becomes more concentrated on the lower side.

How does IAA cause a horizontal shoot to show negative gravitropism?

IAA promotes greater elongation on the lower side, bending the shoot upwards, away from gravity.

How does IAA cause a horizontal root to show positive gravitropism?

IAA inhibits elongation on the lower side relative to the upper side, bending the root downwards, towards gravity.

What is indoleacetic acid (IAA), and what aspect of plant growth does it affect?

IAA is a plant growth factor that affects cell elongation.

Where is IAA produced, and where is it transported?

It is produced in growing regions and transported to other tissues.

What two factors determine IAA’s effect on cell elongation?

Its concentration and the tissue responding.

How do roots and shoots differ in their sensitivity to IAA?

Roots are more sensitive: an IAA concentration that promotes shoot cell elongation can inhibit root cell elongation.

How can differences in IAA concentration across a growing organ cause it to bend?

They cause unequal growth across the organ, producing bending.

What is phototropism?

A directional growth response to light.

How is IAA distributed in a shoot illuminated from one side?

More IAA accumulates on the shaded side.

How does higher IAA on the shaded side affect a shoot’s growth?

It promotes greater cell elongation there, bending the shoot towards the light. This is positive phototropism.

What is negative phototropism in roots?

Growth away from light.

How can an uneven IAA distribution cause a root to bend away from light?

Greater IAA on the shaded side inhibits elongation there relative to the illuminated side, bending the root away from light.