How Plants Respond to the Environment

Plant Growth
1. The cell wall around a plant cell limits the cell's ability to divide and expand.
2. Growth only happens in particular places in the plant where there are groups of cells cable of dividing (meristems)
3. Apical Meristems - located at the tips or apices of roots and shoots and are responsible for them getting longer
4. Lateral Bud Meristems - found in the buds. These could give rise to side shoots
5. Lateral Meristems - are found in a cylinder near the outside of roots and shoots and are responsible for them getting wider.
What causes phototropisms?
1. In a phototropic response, a shoot bends towards a light source
  1. This happens because the shaded side elongates faster than the illuminated side which pushes the end of the shoot towards the light
2. How the light causes redistribution of auxin is still uncertain.
3. Two enzymes have been identified as phototropin 1 and phototropin 2.
  1. Their activity is promoted by blue light hence there is a lot of phototropin 1 activity on the light side.
    1. The gradient is thought to cause the redistribution of auxins
Shedding Leaves
1. Cytokinins stop the leaves of deciduous trees senescing by making sure the leaf acts as a sink for phloem transport.
  1. This means the leaf is guaranteed a good supply of nutrients.
2. If cytokinin productions drops senescence begins
  1. Causes auxin production at the top of the leaf to drop
    1. Makes cells in the abscission zone more sensitive to ethene.
    2. Causes an increase in ethene production
      1. Increases production of the enzyme cellulose which digests the walls of the cells in the abscission zone, eventually separating the petiole from the stem

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How Plants Respond to the Environment

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