Chapter summary
Photosynthesis and energy capture, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Chloroplasts and light absorption
Why does an absorption spectrum differ from an action spectrum?
Key idea and reminders
Pigments absorb selected wavelengths; an action spectrum measures how effectively those wavelengths support photosynthesis.
- Absorption spectrum: light absorbed.
- Action spectrum: photosynthetic response.
- Thylakoids and stroma support different stages.
Keep in mind: It measures the effectiveness of wavelengths in driving photosynthesis under the assay conditions.
02
Light-driven electron transfer
Where do the replacement electrons and released oxygen come from?
Key idea and reminders
Light excites electrons; water supplies replacements, electron transfer supports ATP formation, and NADP accepts reducing power.
- Water supplies electrons and releases oxygen.
- Electron transfer helps create a proton gradient.
- NADP is reduced on the stromal side.
Keep in mind: It is produced by water oxidation in the light-dependent reactions.
03
Use a proton gradient to make ATP
Why must thylakoid membranes remain intact?
Key idea and reminders
A proton gradient across the thylakoid membrane drives ATP synthase as protons return from lumen to stroma.
- High proton concentration: thylakoid lumen.
- Return through ATP synthase: lumen to stroma.
- Cyclic flow adds ATP without net NADPH or O2 production.
Keep in mind: ATP synthesis depends on their controlled downhill return through ATP synthase.
04
Fix, reduce and regenerate carbon
Why do most triose phosphates stay in the Calvin cycle?
Key idea and reminders
Rubisco fixes CO2; ATP and reduced NADP support reduction; most carbon regenerates RuBP so fixation can continue.
- Fixation: CO2 plus RuBP, catalysed by rubisco.
- Reduction uses ATP and reduced NADP.
- Regeneration uses most triose phosphate and more ATP.
Keep in mind: Five are needed to regenerate three RuBP; only one is net output in that accounting.
05
Identify a limiting factor
What does a plateau reveal, and what further comparison tests it?
Key idea and reminders
A limiting factor is identified by changing it and observing a response while other conditions are controlled.
- A plateau signals a limit but does not name it.
- Change one candidate factor to test the explanation.
- Net gas exchange includes respiration.
Keep in mind: Once the curve plateaus, another condition may limit further response.