GCSE Biology (AQA)

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Light Intensity & Photosynthesis

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Bioenergetics Photosynthesis

Light Intensity & Photosynthesis

2:08 Photosynthesis and Light Intensity, Carbon Dioxide and Chlorophyll
Spec 4.4.1.2
Previous Temperature & Photosynthesis Next Carbon Dioxide & Photosynthesis
  • Light intensity affects photosynthesis and can be thought of as how bright a light is.
  • Light energy typically comes from the sun but can also come from artificial sources like lamps.
  • The effect of light intensity on photosynthesis can be investigated by altering the distance of pondweed from a light source.
  • Changing the distance of the light from the pondweed alters the light intensity and affects the bubbles of oxygen released, which can be counted every minute.
  • The further away the light, the lower the light intensity; the closer the light, the higher the light intensity.
  • A stopwatch is used to calculate the number of oxygen bubbles released per minute as a measure of the rate of photosynthesis.
  • The rate of photosynthesis in relation to light intensity can be plotted on a graph, showing that the rate speeds up with increased light intensity and then plateaus.
  • On the graph, the X-axis represents light intensity, ranging from dim to bright light, and the Y-axis represents the rate of photosynthesis, from slow to fast.
  • At low light levels (point A on the graph), the rate of photosynthesis is low; at higher light levels (point B), the rate increases.
  • Between points B and C, the curve flattens, indicating no further increase in the rate of photosynthesis despite increased light intensity.
  • Beyond point C, other factors such as carbon dioxide concentration need to be increased to further enhance the rate of photosynthesis.
  • In summary, brighter light increases the rate of photosynthesis, while dimmer light slows it down.

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