The big idea: Every part of a chloroplast's structure helps it carry out photosynthesis.
The points to remember
- A double membrane (envelope) makes the chloroplast a separate compartment.
- Thylakoids stacked into grana give a large surface area of membrane holding the photosystems, so a lot of light is absorbed.
- The fluid inside each thylakoid has a small volume, so a proton gradient builds up quickly.
- The stroma holds the enzymes and substrates of the Calvin cycle, concentrated together.
Remember it as: Stacks to catch light, a tiny inside for protons, a stroma for the Calvin cycle.
Real example: leaves in the shade: Leaves that grow in deep shade have chloroplasts with taller grana, more thylakoids per stack, so they catch as much as possible of the little light that reaches them.
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How it is asked: Expect a Paper 1A item on a labelled chloroplast (where the Calvin cycle or the light-dependent reactions happen), or an Explain on how the structure suits photosynthesis.
IB-style questionExplain[3 marks]
Explain how the structure of a chloroplast is adapted for photosynthesis.
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See the answer broken into clear points, with guidance on how each point earns marks.