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All 12 Flashcards — Measuring respiration rate
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Question
What does 'respiration rate' mean?
Answer
How **fast** an organism respires — usually the **oxygen used** (or **CO₂ produced**) **per unit time**.
Question
What is a respirometer?
Answer
Apparatus that measures respiration rate by detecting the **change in gas volume** (usually the **oxygen used up**) as organisms respire.
Question
In a respirometer, why does the coloured liquid move towards the seeds?
Answer
The seeds **use up oxygen**, lowering the gas volume, so the liquid is **drawn in**.
Question
Why is potassium hydroxide (KOH) added to a respirometer?
Answer
To **absorb the carbon dioxide** released, so the **only** gas change measured is the **oxygen used up**.
Question
Why include a tube of dead (boiled) seeds in a respirometer experiment?
Answer
As a **control** — dead seeds don't respire, so the liquid shouldn't move; this proves any movement is caused by **respiration**, not temperature or pressure.
Question
Name four quantities that can be used to measure respiration rate.
Answer
**Oxygen used**, **carbon dioxide produced**, **temperature rise**, and **mass lost**.
Question
Which gas does aerobic respiration use up, and which does it release?
Answer
It **uses up oxygen** and **releases carbon dioxide**.
Question
How does respiration cause a measurable temperature rise?
Answer
Respiration **releases some energy as heat**, so in an insulated flask the temperature climbs — faster respiration gives a faster rise.
Question
Why does respiring tissue lose mass over time?
Answer
Carbon leaves the organism as **carbon dioxide gas**, so its **dry mass falls**.
Question
How would an inhibitor such as cyanide affect a respirometer reading?
Answer
It **slows or stops** respiration, so **less oxygen is used** and the coloured liquid moves **less** (or not at all).
Question
Why do we measure respiration indirectly?
Answer
You can't watch a cell respire, but you **can** measure the gases, heat or mass it changes — so measuring one of these gives the rate.
Question
Why must a respirometer experiment be a fair test?
Answer
So any change in the liquid is caused by **respiration alone** — the dead-seed control rules out temperature and pressure effects.
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Topic 3.2 hub
Cell respiration
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