OCR A2 Biology F215: Plant Responses

Response

Plants need to respond to their environment to avoid abiotic stress (such as water shortage).

Tropism

Is...a directional growth response in which the direction of the response is determined by the direction of the external stimulus.
POSITIVE tropism grows toward the direction of the stimulus, and NEGATIVE tropism grows away from the stimulus.
Phototropism: Shoots grow towards light, to increase rate of photosynthesis.
Geotropism: Shoots grow upwards and roots grow downwards towards the pull of gravity.
Chemotropism: Pollen tubes grow towards chemicals given off by the ovary in a flower.
Thigmotropism: Shoots grow towards other plants by responding to touch.

Plant hormones

...coordinate plant growth. Hormones are produced in one part of a plant and are transported to target cells by active transport, diffusion and in the xylem/phloem.
Cytokinins - promote mitosis in the meristem
Auxins - promote cell elongation in shoots and inhibit growth of lateral buds and leaf fall.
Gibberellins - promote cell elongation in stems.
Abscisic acid - stimulates production of ethene, and causes stomatal closure when plants are stressed by low water availability.
Ethene - stimulates leaf fall and promotes fruit ripening.

Phototropism

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