A student sections a maize leaf and sees a ring of large cells round each vein, full of…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student sections a maize leaf and sees a ring of large cells round each vein, full of chloroplasts, with thick walls and no spaces between them. (a) What is the ring called, and what is this leaf arrangement called? (b) Name the cells outside the ring. (c) Where does the Calvin cycle run in this leaf? (d) Which enzyme is absent from the cells outside the ring?
Need a reminder? The key ideaShow
C4 plants (maize, sugarcane, sorghum): Kranz anatomy (large bundle sheath cells with many chloroplasts, thick walls, no intercellular spaces, round the veins). In a mesophyll cell, PEP (3C) plus carbon dioxide gives OAA (4C) with PEP carboxylase. OAA becomes malic acid or aspartic acid. It goes to a bundle sheath cell, where carbon dioxide is set free. Pyruvate (3C) goes back to the mesophyll to become PEP with ATP. RuBisCO and the Calvin cycle work in the bundle sheath cells and are absent from the mesophyll cells. C4 plants lack photorespiration, have a high temperature optimum and high productivity.
The worked solution
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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 ring. The ring is the bundle sheath, and the arrangement is Kranz anatomy.
Step 2. Outside the ring. The mesophyll cells.
Step 3. The cycle. It runs in the bundle sheath cells, where RuBisCO is found.
Step 4. The absent enzyme. RuBisCO is absent in the mesophyll cells. They use PEP carboxylase.
Answer: (a) the bundle sheath; Kranz anatomy; (b) mesophyll cells; (c) in the bundle sheath cells; (d) RuBisCO.
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