Why Plants Respond to the Environment

Plants Respond to Stimuli
1. Tropisms are directional growth responses of plants
  1. Phototropism - Shoots grow towards the light which enables them to photosynthesise
  2. Geotropism - Roots grow towards the pull of gravity. Helps them take up water.
  3. Chemotropism - On a flower , pollen tubes grow down the style, attracted to chemicals, towards the ovary for fertilisation
  4. Thigmotropism - Shoots of climbing plants wind around other plants or sold structures to gain support
What Controls Plant Responses?
1. Hormones coordinate plant responses to environmental stimuli.
2. Plant hormones are chemical messengers that can be transported to act in other parts of the plant.
  1. They are often referred to as plant growth regulators because they are not produced in endocrine glands but by cells in a variety of tissues
3. When hormones reach their target cells, they bind to receptors on the plasma membrane.
4. Specific hormones have specific shapes which can only bind to specific receptors with complementary shapes.
  1. This specific binding makes sure the hormones only act upon the correct tissues.
5. Hormones move around using:
  1. Active Transport
  2. Diffusion
  3. Mass flow in the phloem sap or xylem vessels
What Certain Hormones Do?
1. Auxin - Promote cell elongation; inhibit growth of side shoots and leaf abcission
2. Cytokinis - Promote cell division
3. Gibberellins - Promote seed germination and growth of stems
4. Abscisic acid - Inhibits seed germination and growth of stems
5. Ethene - Promote fruit ripening

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Why Plants Respond to the Environment

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	Created by kirareynolds over 10 years ago