Response to Stimuli: Plants

Tropism

A growth response in plants to a stimulus

Phototropism

Growth response to light

Geotropism (gravitropism)

Growth response to gravity

Positive tropism

Growth towards a stimulus

Negative tropism

Growth away from a stimulus

Auxin

Plant hormone controlling growth responses

Shoot

Above‑ground part of plant that grows towards light

Root

Underground part of plant that grows towards water and gravity

Differential growth

Uneven growth on different sides of a plant organ

What is a tropism?

A directional growth response to a stimulus

What is phototropism?

Growth in response to light

What is geotropism?

Growth in response to gravity

What type of phototropism do shoots show?

Positive phototropism

Why do shoots grow towards light?

To maximise photosynthesis

What type of geotropism do roots show?

Positive geotropism

Why do roots grow downwards?

To anchor the plant and absorb water/minerals

What hormone controls plant growth responses?

Auxin

Where is auxin produced?

In the tips of shoots and roots

How does auxin cause shoots to bend towards light?

It accumulates on the shaded side, causing faster growth there

How does auxin affect root growth?

High auxin inhibits growth in roots

Why do roots grow away from light?

They show negative phototropism

Why do shoots grow away from gravity?

They show negative geotropism

What causes bending in plant organs?

Uneven distribution of auxin leading to differential growth