Bio 3.3 ,, Plant Space and Time

Trophic behaviours

Growth responses in plants. The plant responds to an abiotic factor in the environment, and growth occurs in a direction which results in a benefit for the plant.

Positive geotropism

When the root / radicle, which is grows towards the pull of gravity.

Negative geotropism

When the plumule /coleoptile, which grows away from the pull of gravity.

Positive phototropism

Occurs when the plumule coleoptile breaks the soil surface, and grows towards the light.

Hydrotropism

The radicle is the growth of the root towards a water source.

Positive Thigmotropism

Directional growth movement that causes the plant to bend as a result of touching / coiling around a support in the direction of the support.

Nastic response

Reversible movement of part of a plant to a diffuse environmental stimulus.

Nastic movements

A result of changing turgor pressure in cells, resulting in a reversible movement of a part of the plant.

Thigmonastic response

A non-directional stimulus, due to touch.

Auxin (or IAA)

Made in the shoot tip and is soluble, and migrates / moves down the shoot, accumulating in the cells on the opposite side to the stimulus.

Photoperiodism

The regulation of seasonal activity by day length or differing ratio of light and dark in a day.

Short-day plants

Will be induced to flower when the night is getting longer – longer than a critical period.

Long-day plants

Will be induced to flower when the night is getting shorter – shorter than a critical period. Critical periods differ in different species.

Phytochrome

A blue pigment/protein that helps the plant to measure day length.

Pfr

The active form of the phytochrome system. In long day plants, Pfr promotes flowering. In short day plants, Pfr inhibits flowering