BY4.7 Plant Responses

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Plant Responses

  • plant responses are slow beacuse coordination is achieved by hormones
  • plans don't have a nervous system
  • growth is coordinated by plant growth substances

photoperiodism: flowering in repsonse to relative periods of light and darkness


photoreceptors responsible for absorbing light

found in 2 forms

Pr: has an absorption peak of 660nm - red light

Pfr: has an absorption peak of 730nm - far red light

the forms absorb light and convert it from one form into the other

  • sunlight has more red light so in daytime Pr is converted into Pfr
  • Pfr is unstable and in darkness it is converted slowly into Pr
  • pleants measure day lenght/lenght of darkness by the amount…


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