Plant Responses To The Enviroment

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Plants Respond To Stimuli

Tropisms are the plants responses to external stimuli, these can be things such as:

  • Phototropism- growth towards light.
  • Geotropism- roots growth towards gravity pull.
  • Chemotropism- growth towards chemical stimuli.

What Controls Plant Responses

Plant responses are controled by hormones. Howerver these hormones aren't produced by endocrine glands and so are also known as plant growth regulators.

The hormones, when they reach their target cells/tissue, bind to receptors on the plasma membrane.

The hormones move around the plant by either:

  • active transport.
  • diffusion.


  • in phloem sap or xylem vessels.

However some hormones have an effect on the the effects of other hormones. Some amplify the effects (synergy), and some cancel the effects (antagonism).

Plant Growth

Plant growth is limited to particular regions caled meristems. These areas are made up of unspeaclised cells that can still divide, unlike the mature cells that make up the rest of the plant.

Cell division is promoted by hormones known as Auxins. These are produced the at apex and travel to the…


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