Plant hormones

Tropisms

The growth of a plant in response to an external stimulus.

Positive tropism

If a plant grows towards the stimulus.

Negative tropism

If a plant grows away from a stimulus.

Phototropism

Directional growth of a plant in response to light.

Auxin

The master hormone that controls growth patterns in plants, produced in small quantities in the tip of the shoot.

Apical dominance

Auxin produced in the apical bud at the top of the plant will inhibit the development of side branches.

Hydrotropism

Roots grow towards water.

Thigmotropism

Growth response to the stimulus of touch.

Cytokinins

Promotes cell division and cell differentiation in growing tips, roots, and fruits.

Gibberellins

Initiate seed germination, flowering, and fruit enlargement.

Ethylene gas

Stimulates the ripening of fruit and can cause stunted growth in plant stems.

Photoperiod

The response of plants to particular periods of light and dark.

Geotropism

Response to gravity.

Bending in plants

If the light is on one side of the tip, the auxin moves to the darker side, causing curvature towards the light as cells elongate

Bushier growth

Pruning is used to produce bushier growth as many new buds will replace the original apical bud.

Short day plants

Plants that require long nights to flower, such as poinsettias and chrysanthemums.

Long day plants

Plants that require long periods of uninterrupted light to flower, such as petunias and hibiscus.

Circadian Rhythms

Daily cycles, such as plants opening their flowers in the day and closing them at night.

Circannual Rhythms

Yearly cycles, such as plants losing their leaves in Autumn and flowering in Spring.