Tropism, Taxis, Kinesis AQA BIOLOGY P2

Does a plant’s shoot grow away or towards the force of gravity?

Away from the force of gravity.

Does a plant’s root grow away or towards the force of gravity?

Towards the force of gravity.

What happens when light (eg. lamp) is placed near a plant?

The plant will grow towards the light whereas the root will grow away from the light.

What is tropism?

Part of a plant that has a directional growth response to a stimulus.

What is phototropism?

directional growth response of a plant to light.

What is positive phototropism?

Part of a plant grown towards light.

what is negative phototropism?

Part of a plant grows away from light.

What type of phototropism do the shoots and roots of a plant exhibit?

shoots - positive phototropism

roots - negative phototropism

What is gravitropism?

directional growth response of a plant to gravity.

What is positive gravitropism?

Part of a plant grows towards the force of gravity.

What is negative gravitropism?

Part of a plant grows away from the force of gravity.

How do plants respond to stimuli?

Plants produce specific chemicals which affect the direction of which the plant grows

Identify the name of the chemical which affect the direction of which the plants grow

Plant growth factors

What is the name of the plant growth factor which regulate phototropism and gravitropism?

Indoleacetic acid (IAA)

Which class do indoleacetic acids (IAA) belong to?

Auxins

Where is indoleacetic acids (IAA) synthesised?

Parts of plants which are actively growing. Eg. tip of shoots and tip of roots.

What is the function of indoleacetic acids (IAA)?

Stimulate cell elongation/ inhibit cell elongation

How does indoleacetic acids (IAA) coordinate positive phototropism in shoots.

1.IAA moves from the light side to the shade side

2.This means theres a greater concentration of IAA on the shaded side compared to the light side therefore cells elongate faster on the shaded side.

3.This causes the shoot to bend towards the light.

How does indoleacetic acids (IAA) coordinate positive gravitropism in roots.

1.Due to the force of gravity, IAA move towards the lower side of the root compared to upper side of the root.

2.When there is a high concentration of IAA in roots, this inhibits cell elongation

3.Therefore cells on the upper side of the root elongate faster

4.This causes the root to bend towards the force of gravity