Limiting Factors In Photosynthesis

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There are Optimum Conditions for Photosynthesis

Ideal conditions for UK-like plants

As well as a constant supply of water (oo little photosynthesis stops, too high the soil becomes water-logged reducing mineral uptake) plants also need a:

High light intensity of a certain wavelength

  • Light provides energy for the light dependant reaction - the higher the intensity the more energy it provides.
  • Only certain wavelengths are used for photosynthesis, the photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorb red and blue lights in sunlight (green is reflected)

Temperature of about 25°C

  • Photosynthesis involves enzymes (like ATP synthase, rubisco) so if the temperature falls below 10°C the enzymes become inactive, if more than 45°C they can denature.
  • At high temperatures, the stomata can close to avoid water loss, so photosynthesis can slow down because less CO2 enters the leaf

Carbon Dioxide at 0.4%

  • Carbon dioxide makes up about 0.04% of the gases in the atmosphere
  • Increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata can start to close

Light, Temperature and CO2 can all Limit


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