Biology / Unit 3: Cellular Energy
3.3 The Two Stages of Photosynthesis
Notes
Photosynthesis happens in two connected stages.
- Light-dependent reactions occur in the thylakoid membranes. Light splits water, releasing oxygen, and makes ATP and NADPH.
- Calvin cycle (light-independent reactions) occurs in the stroma. It uses ATP, NADPH and $\text{CO}_2$ to build sugar.
- The oxygen released by plants comes from water, not from $\text{CO}_2$.
- Factors that affect the rate: light intensity, $\text{CO}_2$ concentration, and temperature.
Practice
The oxygen gas released during photosynthesis comes from:
Light reactions split water molecules, releasing O2.
Where does the Calvin cycle take place?
The Calvin cycle uses CO2 in the fluid stroma.
An aquarium plant is moved closer to a lamp and starts giving off more oxygen bubbles. Which factor increased the rate?
More light speeds up the light-dependent reactions, up to a limit.
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