- Plants need to respond to their environment to avoid abiotic stress (such as water shortage).
- 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.
- ...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.
- A shoot will grow towards a light stimulus because cells in…
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