Which two gases are excreted by leaves?
Reveal answer
Oxygen (from photosynthesis) and carbon dioxide (from respiration).
Key words: oxygen · carbon dioxide
3(i) EXCRETION · RECALL
3.20 Carbon dioxide and oxygen lost from a leaf
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How do waste gases leave a leaf?
Reveal answer
Diffuse from cells → air spaces → out through stomata.
Key words: stomata
What is meant by the term excretory product?
Reveal answer
Waste product of metabolism that is removed from an organism.
Key words: excretory product
Metabolic gases in a leaf: for Aerobic respiration, give the gas produced and the likely net effect.
Reveal answer
Gas produced: Carbon dioxide. Likely net effect: CO₂ may leave in darkness.
Key words: Aerobic respiration
Metabolic gases in a leaf: for Photosynthesis, give the gas produced and the likely net effect.
Reveal answer
Gas produced: Oxygen. Likely net effect: O₂ may leave in sufficient light.
Key words: Photosynthesis
Metabolic gases in a leaf: for Bright light overall, give the gas produced and the likely net effect.
Reveal answer
Gas produced: Both processes occur. Likely net effect: Net CO₂ uptake and O₂ loss are common.
Key words: Bright light overall
Metabolic gases in a leaf: for Darkness overall, give the gas produced and the likely net effect.
Reveal answer
Gas produced: Respiration only. Likely net effect: Net O₂ uptake and CO₂ loss.
Key words: Darkness overall
True or false, and why? “Plants only excrete oxygen.”
Reveal answer
False. Respiration produces carbon dioxide, and net exchange changes with conditions.
True or false, and why? “Oxygen is always harmful waste to a plant.”
Reveal answer
False. It is a photosynthetic product and is also used in aerobic respiration.
True or false, and why? “Stomata actively pump gases out.”
Reveal answer
False. Gases diffuse through stomata down concentration gradients.
Why is oxygen described as an excretory product of a plant?
Reveal answer
It is a waste product of metabolism (photosynthesis) that the plant removes.
Key words: metabolism
Why does a leaf excrete carbon dioxide in dim light?
Reveal answer
Respiration makes CO₂ faster than photosynthesis uses it → the excess diffuses out.
Key words: diffuses out
Name a plant organ that excretes carbon dioxide but never oxygen.
Reveal answer
The roots (no chloroplasts, so only respiration).
Key words: roots
Suggest why a plant excretes more oxygen on a sunny day than on a cloudy day.
Reveal answer
Higher light intensity → faster photosynthesis → more O₂ made than respiration uses.
Key words: photosynthesis
Name the excretory organs of a flowering plant and of a human.
Reveal answer
Plant: leaves. Human: lungs, kidneys and skin.
Key words: leaves · lungs · kidneys