Coordination & Response in Plants

Stimulus

A change in the environment that is detected by an organism and causes a response

Response

The action or change in behaviour of an organism as a result of a stimulus

Plant responses to stimuli

Plants respond to stimuli such as light and gravity by growing in a particular direction

Tropism

A directional growth response of part of a plant to a stimulus

Geotropism

A growth response of a plant to gravity

Positive geotropism

Growth of a plant part towards gravity

Negative geotropism

Growth of a plant part away from gravity

Geotropic response of roots

Roots grow downwards into the soil towards gravity, showing positive geotropism

Geotropic response of stems

Stems grow upwards away from gravity, showing negative geotropism

Phototropism

A growth response of a plant to light

Positive phototropism

Growth of a plant part towards light

Positive phototropism in stems

Stems grow towards light so leaves receive more light for photosynthesis

Why positive phototropism is beneficial

It increases the amount of light absorbed, increasing the rate of photosynthesis