Chapter summary
Photosynthesis and respiration, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Capture light and make usable chemical energy
Where does the oxygen released by photosynthesis come from?
Key idea and reminders
In chloroplasts, light-dependent reactions use light and water to supply ATP and reduced NADP; oxygen is released from water.
- Photosynthesis occurs in chloroplasts.
- Light-dependent outputs include ATP, reduced NADP and oxygen.
- Water is the source of released oxygen.
Keep in mind: Released oxygen comes from water. Carbon dioxide is the carbon input to carbohydrate synthesis.
02
Use carbon dioxide to build carbohydrate
What returns to the light-dependent reactions?
Key idea and reminders
The light-independent stage uses carbon dioxide, ATP and reduced NADP to form carbohydrate, returning ADP, phosphate and oxidised NADP for reuse.
- Inputs: carbon dioxide, ATP and reduced NADP.
- Outputs include carbohydrate and regenerated ADP, phosphate and NADP.
- Matter and energy have different sources.
Keep in mind: They are named for not requiring light directly. They can operate in light and depend on ATP and reduced NADP from the light-dependent stage.
03
Begin respiration in the cytoplasm
What happens before pyruvate reaches a mitochondrion?
Key idea and reminders
Glycolysis occurs in the cytoplasm and converts glucose to pyruvate, with a net ATP gain and reduction of NAD.
- Glycolysis: cytoplasm, glucose to pyruvate.
- Net ATP and reduced NAD are produced.
- Glycolysis does not directly require oxygen.
Keep in mind: Glycolysis occurs in the cytoplasm. The link reaction, Krebs cycle and oxidative phosphorylation occur in mitochondria under aerobic conditions.
04
Release carbon dioxide and reduce carriers
Where does pyruvate carbon go under aerobic conditions?
Key idea and reminders
The link reaction converts pyruvate to acetyl-CoA, releasing carbon dioxide and reducing NAD. The Krebs cycle oxidises acetyl groups, releasing more carbon dioxide and reduced carriers.
- Link reaction: pyruvate to acetyl-CoA, carbon dioxide and reduced NAD.
- Krebs cycle: carbon dioxide, reduced NAD, reduced FAD and ATP-equivalent output.
- Both occur in the mitochondrial matrix.
Keep in mind: Glucose-to-pyruvate conversion occurs in glycolysis in the cytoplasm. The Krebs cycle receives acetyl groups via acetyl-CoA in the mitochondrion.
05
Use oxygen at the end of electron transfer
Why does oxygen availability affect ATP supply?
Key idea and reminders
Reduced carriers are oxidised, oxygen accepts electrons to form water, and energy transfer supports ATP formation from ADP and phosphate.
- Location: inner mitochondrial membrane.
- Oxygen accepts electrons and contributes to water.
- NAD and FAD are regenerated as ATP is formed.
Keep in mind: Oxygen acts as the final electron acceptor and forms water. Carbon dioxide is released from carbon-containing respiratory substrates in earlier stages.
06
Keep glycolysis going without oxygen
Why do yeast and muscle release different products?
Key idea and reminders
Anaerobic pathways regenerate NAD so glycolysis can continue. Yeast produces ethanol and carbon dioxide; mammalian muscle produces lactate. Less energy is released per glucose than aerobically.
- Yeast: ethanol and carbon dioxide.
- Muscle: lactate.
- Aerobic conditions release more energy per glucose.
Keep in mind: Yield per substrate and rate per time are different. H1 compares the amount of energy released per glucose, not a universal ranking of instantaneous rates.