Water is split inside the lumen of a thylakoid in a mesophyll cell, and the oxygen gas must leave…
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Water is split inside the lumen of a thylakoid in a mesophyll cell, and the oxygen gas must leave the cell. The membranes to cross are: the thylakoid membrane, the inner membrane of the chloroplast, the outer membrane of the chloroplast, and the plasma membrane of the cell. (a) How many membranes does one oxygen molecule cross to reach the air space between cells? (b) A carbon dioxide molecule arrives from the air space and is fixed in the stroma. How many membranes does it cross? (c) In which phase is the carbon dioxide used?
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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 oxygen. From the lumen: thylakoid membrane, inner membrane, outer membrane, plasma membrane. That is membranes.
Step 2. The carbon dioxide. It crosses the plasma membrane, the outer membrane and the inner membrane. It is then in the stroma. That is membranes. It does not cross a thylakoid.
Step 3. The phase. The stroma holds the enzymes of the biosynthetic phase, so the carbon dioxide is used there.
Answer: (a) membranes; (b) membranes; (c) the biosynthetic phase.
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