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Limiting factors in photosynthesis
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The rate of photosynthesis is limited by whichever factor is in shortest supply.
Limiting factors
Light intensity, carbon dioxide concentration and temperature.
Increasing the limiting factor speeds up the rate, until another factor becomes limiting. Then the graph levels off.
Increasing the limiting factor speeds up the rate, until another factor becomes limiting. Then the graph levels off.
The inverse square law (Higher)
Light intensity is inversely proportional to the square of the distance from the light.
light intensity ∝ 1distance2
Double the distance, and intensity falls to a quarter.
light intensity ∝ 1distance2
Double the distance, and intensity falls to a quarter.
The practical
Pondweed in water, with a lamp at different distances. Count the oxygen bubbles, or measure the gas volume, in a set time.
Keep the temperature and carbon dioxide constant for a fair test.
Keep the temperature and carbon dioxide constant for a fair test.
A lamp is moved from 10 cm to 20 cm away. What happens to the light intensity?
- The distance doubles.
- Intensity ∝ 1 ÷ distance2, so it falls by 22 = 4.
Answer: It becomes a quarter.
Light, carbon dioxide and temperature limit photosynthesis. When one is increased, the rate rises until another becomes limiting. Light intensity follows the inverse square law.
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