What is meant by the term leaf disc?
Reveal answer
A standardised circular sample of leaf tissue.
Key words: leaf disc
2(g) GAS EXCHANGE · RECALL
2.45B Light and net gas exchange
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.
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What is meant by the term net photosynthesis?
Reveal answer
Photosynthetic gas effect remaining after respiration is accounted for.
Key words: net photosynthesis
What is meant by the term indicator-only control?
Reveal answer
A control experiment: a matched tube without leaf tissue.
Key words: indicator-only control
Predicted indicator outcomes: for Dark, give the likely colour direction and the interpretation.
Reveal answer
Likely colour direction: Toward yellow. Interpretation: Respiration raises CO₂.
Key words: Dark
Predicted indicator outcomes: for Low light, give the likely colour direction and the interpretation.
Reveal answer
Likely colour direction: Yellow/red depending on balance. Interpretation: Respiration may equal or exceed photosynthesis.
Key words: Low light
Predicted indicator outcomes: for Compensation intensity, give the likely colour direction and the interpretation.
Reveal answer
Likely colour direction: Remains near red/orange. Interpretation: No net CO₂ exchange.
Key words: Compensation intensity
Predicted indicator outcomes: for Bright light, give the likely colour direction and the interpretation.
Reveal answer
Likely colour direction: Toward purple. Interpretation: Photosynthesis removes CO₂ faster than respiration releases it.
Key words: Bright light
Predicted indicator outcomes: for No-leaf control experiment, give the likely colour direction and the interpretation.
Reveal answer
Likely colour direction: Little change. Interpretation: Checks indicator stability and environmental effects.
Key words: No-leaf control experiment
True or false, and why? “Purple indicator proves oxygen was released.”
Reveal answer
False. It indicates reduced carbon dioxide concentration, not oxygen directly.
True or false, and why? “A lamp-distance experiment changes only light.”
Reveal answer
False. The lamp may also change temperature.
True or false, and why? “Red indicator means no respiration.”
Reveal answer
False. Respiration and photosynthesis may have equal net carbon-dioxide effects.
True or false, and why? “More leaf discs always improve validity.”
Reveal answer
False. Unequal tissue area changes respiration and photosynthesis capacity between treatments.
Which indicator shows changes in carbon dioxide concentration around leaves?
Reveal answer
Hydrogencarbonate indicator.
Key words: hydrogencarbonate
Why is one tube wrapped in foil in the hydrogencarbonate indicator experiment?
Reveal answer
Darkness → only respiration → CO₂ rises → indicator turns yellow.
Key words: yellow
Why put a water bath or heat shield between the lamp and the leaf tubes?
Reveal answer
Keeps temperature the same (a control variable), so only light intensity changes.
Key words: temperature