In clear sea water, take it that red light falls to half every 2 m, and blue-green light every 12 m.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In clear sea water, take it that red light falls to half every m, and blue-green light every m.
- What per cent of the red light is left at m?
- What per cent of the blue-green light is left at m?
- Use these to explain why a red alga can grow at m but a green alga struggles.
Need a reminder? The key ideaShow
Chlorophyceae: chlorophyll a and b, starch in pyrenoids, cellulose wall, 2 to 8 equal flagella at the tip. Phaeophyceae: chlorophyll a and c with fucoxanthin, laminarin or mannitol, algin, 2 unequal lateral flagella. Rhodophyceae: chlorophyll a and d with r-phycoerythrin, floridean starch, no flagella, oogamous. Red light is absorbed near the surface; blue-green light goes deeper.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Red light. halvings: .
Step 2. Blue-green light. halvings: .
Step 3. Why. At m almost no red light is left, but a quarter of the blue-green light is. Chlorophyll uses red and blue light best. Phycoerythrin absorbs the blue-green light, so red algae still trap enough energy.
Answer: ; ; red algae use the blue-green light that reaches the depth.
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