Biology Figures

CO₂ concentration in a closed chamber in the dark, dim and bright light

An example figure from the Photosynthesis Rate generator.

Graph of CO₂ concentration (%) against time (minutes) with no numbers on the axes: from one starting point, a solid blue line labeled Dark rises steadily, a dashed red line labeled Dim light (compensation point) stays level, and a dotted green line labeled Bright light falls and levels off near the bottom, with a key under the graph
The CO₂ around a plant in a closed chamber over an hour, starting from the 0.04 % in air. In the dark (solid blue) the plant only respires, so the CO₂ rises in a straight line. In dim light at the compensation point (dashed red), photosynthesis uses just as much CO₂ as respiration gives off, so it stays level. In bright light (dotted green) it falls, then levels off at the CO₂ compensation point.
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Answer key

  • Dark: CO₂ rises in a straight line, by 0.054 % in 60 minutes: respiration only
  • Dim light (compensation point): CO₂ stays level, as photosynthesis just keeps up with respiration (the compensation point)
  • Bright light: CO₂ falls and levels off at about 0.0083 %, the CO₂ compensation point

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