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Gas Exchange · Paper 1 — Free Biology HL Practice Questions

What this topic covers

This theme is built on one repeated argument: structure exists because it does a job, and you can predict the job from the structure. Examiners test this exact logic at every scale — a motor protein's shape tells you which way it walks a microtubule, a red blood cell's missing nucleus tells you why it can pack more haemoglobin, a gill's countercurrent geometry tells you why it out-performs a lung-style parallel flow. Several chunks here — muscle and motility, enzyme kinetics, endosymbiotic theory, detailed phloem loading — exist only on the HL paper, and they're flagged below. Get the mechanism words right (troponin, not tropomyosin; ATP-binding, not hydrolysis) because that's where the marks actually sit.

Read the full Form and Function lesson notes →

1FoundationMCQRespiratory structures in animals and plants1 markPaper 1~2 min

In insects, a network of internal tubes branches repeatedly into finer tubes called tracheoles, delivering oxygen directly to respiring cells without the involvement of a circulatory pigment. Which term describes the larger branching tubes that form the main conducting portion of this system?

Solutions

2FoundationMCQRespiratory structures in animals and plants1 markPaper 1~2 min

In a fish, oxygen concentration in water entering the gills is

9.1 \text{ mg dm}^{-3}

and in water leaving the gills is

3.8 \text{ mg dm}^{-3}

. Which mechanism moves oxygen from the water into the blood, and what property of oxygen makes this possible?

Solutions

3MasteryMCQRespiratory structures in animals and plants1 markPaper 1~2 min

A locust (Schistocerca gregaria) is sealed in a chamber fitted with a CO₂ sensor at 25°C. When CO₂ concentration is recorded every minute over 10 minutes, the total increase is 0.15%. Which pattern of CO₂ release is most likely observed, and what is its cause?

Solutions

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