Bean seeds are put in a closed jar, in the dark, with damp cotton wool…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Bean seeds are put in a closed jar, in the dark, with damp cotton wool. After some days they have sprouted.
- Where did the energy for the growth come from?
- Could the seeds have made food by photosynthesis in the jar?
- What happens to the oxygen and the carbon dioxide in the jar?
- A green leaf in bright light seems to take in carbon dioxide and not to give any out. Does it respire? Explain.
Need a reminder? The key ideaShow
Plants exchange gases through stomata, lenticels and roots, and each part looks after itself. Cellular respiration breaks food down in steps and traps energy in ATP. One mole of glucose holds kJ, and one mole of ATP holds about kJ. The share kept in ATP is the energy kept divided by the energy of the glucose.
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. (a) The energy came from the food stored in the seeds. Respiration broke it down and trapped the energy in ATP.
Step 2. (b) No. There was no light, so there was no photosynthesis.
Step 3. (c) The seeds take in oxygen and release carbon dioxide. The oxygen falls and the carbon dioxide rises.
Step 4. (d) Yes, it respires. In bright light, photosynthesis uses the carbon dioxide of respiration, and more besides, and it makes the oxygen that the cells use. So respiration is hidden, but it does not stop.
Answer: (a) stored food; (b) no, there is no light; (c) oxygen falls, carbon dioxide rises; (d) yes, photosynthesis hides it.
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