On a hot, dry afternoon, the stomata of a wheat leaf close…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
On a hot, dry afternoon, the stomata of a wheat leaf close. (a) What happens to the carbon dioxide and the oxygen inside the leaf? (b) What does RuBisCO then do with RuBP? (c) Name the three organelles of the pathway that follows. (d) Say three things that this pathway does not make, and one thing it releases.
Need a reminder? The key ideaShow
Photorespiration: RuBisCO binds oxygen when carbon dioxide is low and oxygen is high. RuBP and oxygen give one PGA and a 2-carbon compound. It involves the chloroplast, peroxisome and mitochondrion. It makes no sugar, no ATP and no NADPH, and it releases carbon dioxide. C4 plants lack it. Blackman's law of limiting factors: the factor nearest its minimum sets the rate. Light saturates at about 10 percent of full sunlight; carbon dioxide is the major limiting factor; temperature, water also matter.
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. The gases. The leaf cannot take in carbon dioxide, and its photosynthesis keeps making oxygen. Carbon dioxide falls and oxygen rises.
Step 2. RuBisCO. It binds oxygen and acts as an oxygenase. RuBP is oxidised to one PGA and one 2-carbon compound.
Step 3. The organelles. The chloroplast, the peroxisome and the mitochondrion.
Step 4. The products. It makes no sugar, no ATP and no NADPH, and it releases carbon dioxide.
Answer: (a) carbon dioxide falls and oxygen rises; (b) it binds oxygen; (c) chloroplast, peroxisome, mitochondrion; (d) no sugar, ATP or NADPH; it releases carbon dioxide.
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