Light and photosynthesis sim
Move the lamp: light falls with the inverse square law and the pondweed bubbles slow.
Photosynthesis: limiting factors · covers the GCSE, O-Level topic
What the sim shows
d is measured from the lamp to the pondweed. The lamp's light at the plant falls with the inverse square of distance, I = (10/d)², so moving it from 10 cm to 20 cm leaves a quarter of the light. The inverse square law treats the lamp as a point source, so it is only approximate close to the tube. The bubble rate follows a limiting-factor curve, rate = 60 · I/(I + 0.35) per minute: 44.4 at 10 cm, 25.0 at 20 cm, 6.2 at 50 cm. At high light the curve levels off towards 60 because something else, such as carbon dioxide or temperature, becomes the limiting factor. Sodium hydrogencarbonate solution supplies carbon dioxide, so CO₂ is kept constant. The beaker of water absorbs much of the lamp's heat, helping keep the temperature constant (check it with the thermometer). Counting bubbles only estimates the oxygen given off: bubbles vary in size, some oxygen dissolves, and the gas is not pure oxygen. These numbers come from a model, not measured data. Bubbles and the stopwatch run in real time.
- Gas bubbles (mostly oxygen) from the cut stem
- Pondweed (Elodea) in NaHCO₃ solution
- Lamp on a carriage; d from lamp to pondweed
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