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Exchange and Transport in Animals

Investigating the rate of respiration

  • 3 things to know
  • Paper 2

Overview

Using a respirometer with germinating peas or woodlice, soda lime and a glass bead control, the variables, airtightness, settling time, errors and safety, calculating means, ranges and uncertainty, anomalous results and range bars, and treating small animals ethically.

What you need to know

Answer each one before you reveal it.

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Key term

Name two organisms that are suitable for an investigation into the rate of respiration.

Key term

Explain why soda lime is placed in the tube with the organisms.

Key term

Explain why the coloured liquid in the capillary tube moves towards the organisms.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Name the apparatus used to measure how quickly small living organisms take up oxygen.

    Model answer

    A respirometer.

  2. 2

    Name two organisms that are suitable for an investigation into the rate of respiration.

    Model answer

    Germinating peas and small invertebrates such as maggots or woodlice are suitable.

  3. 3

    Explain why soda lime is placed in the tube with the organisms.

    Model answer

    Soda lime absorbs the carbon dioxide the organisms release, so any fall in gas volume is caused only by oxygen being used.

  4. 4

    Explain why the coloured liquid in the capillary tube moves towards the organisms.

    Model answer

    The organisms use up oxygen and their carbon dioxide is absorbed, so the gas volume and pressure inside fall.

  5. 5

    A respirometer is used to compare the rates of respiration of small living organisms. State what is measured.

    Model answer

    The distance the coloured liquid moves along the capillary tube in a set time is measured.

  6. 6

    Explain why a control tube containing glass beads is set up alongside the organisms.

    Model answer

    The beads take up the same space but do not respire, so the control reveals any liquid movement caused by changes in room temperature or pressure.

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