Biology Figures

Pondweed and lamp distance: bubbles of oxygen per minute against distance from the lamp

An example figure from the Photosynthesis Rate generator.

Graph of bubbles of oxygen per minute, 0 to 35, against distance from the lamp, 0 to 50 cm, on a grid: measured points scattered along a curve that stays level at about 27 bubbles a minute up to about 19 cm from the lamp, then falls, steeply at first and then more slowly, to about 4 bubbles a minute at 50 cm
The pondweed practical: bubbles of oxygen counted each minute with the lamp 5 to 50 cm away, at 20 °C with plenty of CO₂. Close to the lamp the rate stays level, because light isn’t limiting. Farther away the light intensity falls as 1/d², so the rate falls with it, steeply at first and then more slowly. The points are scattered a little around the curve, like real counts.
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Answer key

  • 0.1 % CO₂, 20 °C: levels off at 27 bubbles a minute closer than about 19 cm to the lamp; farther away light is limiting, and the rate falls as 1/d²

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