Net gas exchange of a leaf in bright light, dim light and darkness.
Reveal answer
Bright: CO₂ in, O₂ out. Compensation point: no net exchange. Dark: O₂ in, CO₂ out.
Key words: compensation point
2(g) GAS EXCHANGE · RECALL
2.44B Net gas exchange in light and dark
15 recall questions · Biology only (B): not in Science (Double Award). Answer from memory, reveal the answer, then rate yourself. Ratings stay on this device.
Ratings are saved in this browser on this device, under a KS4 key kept separate from International A Level recall. Written answers are temporary and cleared when you leave the page. Use Reset to clear the ratings on this device.
What is meant by the term carbon sink?
Reveal answer
A system taking up more carbon than it releases over a stated interval.
Key words: carbon sink
What is meant by the term carbon source?
Reveal answer
A system releasing more carbon than it takes up over a stated interval.
Key words: carbon source
Light intensity and net exchange: for Darkness, give the relative rates and the net exchange.
Reveal answer
Relative rates: Respiration only. Net exchange: O₂ in; CO₂ out.
Key words: Darkness
Light intensity and net exchange: for Below compensation point, give the relative rates and the net exchange.
Reveal answer
Relative rates: Respiration > photosynthesis. Net exchange: O₂ in; CO₂ out.
Key words: Below compensation point
Light intensity and net exchange: for At compensation point, give the relative rates and the net exchange.
Reveal answer
Relative rates: Respiration = photosynthesis. Net exchange: No net exchange.
Key words: At compensation point
Light intensity and net exchange: for Above compensation point, give the relative rates and the net exchange.
Reveal answer
Relative rates: Photosynthesis > respiration. Net exchange: CO₂ in; O₂ out.
Key words: Above compensation point
True or false, and why? “Plants stop respiring during the day.”
Reveal answer
False. Respiration continues while photosynthesis also occurs.
True or false, and why? “No net exchange means the leaf is inactive.”
Reveal answer
False. Photosynthesis and respiration may be occurring at equal rates.
True or false, and why? “Any light causes net carbon-dioxide uptake.”
Reveal answer
False. Below compensation intensity, respiration can still exceed photosynthesis.
Why does a plant give out carbon dioxide in darkness?
Reveal answer
Only respiration happens → CO₂ is produced and none is used.
Key words: respiration
Why does a plant give out oxygen in bright light?
Reveal answer
Rate of photosynthesis is greater than rate of respiration → more O₂ produced than used.
Key words: photosynthesis
As dawn light gets brighter, how does a leaf’s net carbon dioxide uptake change?
Reveal answer
It increases: from net release, through zero at the compensation point, to net uptake.
Key words: increases
Suggest why the carbon dioxide concentration in a closed glasshouse is lowest in the late afternoon.
Reveal answer
Photosynthesis has been faster than respiration all day → hours of net uptake of CO₂.
Key words: net uptake
A leaf takes in 6 units of CO₂ per hour for photosynthesis and gives out 2 units per hour from respiration. What is its net CO₂ exchange?
Reveal answer
4 units per hour taken in (6 − 2).
Key words: 4