A chloroplast splits 24 water molecules in non-cyclic photophosphorylation…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A chloroplast splits water molecules in non-cyclic photophosphorylation. Each water gives two electrons. Two electrons make one NADPH. Each electron is lifted once at each photosystem, by one photon each. (a) How many oxygen molecules are released? (b) How many NADPH molecules are made? (c) How many photons are absorbed? (d) How many protons does the splitting of water release into the lumen?
Need a reminder? The key ideaShow
Non-cyclic: water, PS II (P680), acceptor, PQ, cytochrome b6-f, PC, PS I (P700), acceptor, NADP+ to NADPH. It gives ATP, NADPH and oxygen. Each electron is lifted twice, so 2 photons. Two water give 4 electrons, so one oxygen and 2 NADPH. Cyclic: PS I only, the electron returns to PS I, only ATP, in the stroma lamellae, in far-red light beyond 680 nm.
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.
Given. water molecules. From , two water molecules give one oxygen molecule, four protons and four electrons.
Step 1. Oxygen. molecules.
Step 2. Electrons. electrons.
Step 3. NADPH. molecules.
Step 4. Photons. Two for each electron, so photons.
Step 5. Protons. Each water gives two protons, so protons.
Check. The oxygen is half the water, the NADPH equals the water, and the photons are four times the water.
Answer: (a) ; (b) ; (c) ; (d) .
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