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Grades 9 and 10 Intermediate About 20 min Version 1 Awaiting review Premium

Respiration in germinating seeds

Respiration is the release of energy from food inside every living cell. In aerobic respiration, glucose reacts with oxygen to give carbon dioxide, water and energy. Germinating seeds respire quickly because they need energy to grow. In a respirometer, soda lime absorbs the carbon dioxide the seeds give out, so as they use oxygen the gas in the tube shrinks and a coloured drop in the capillary tube moves towards them. A second tube of the same seeds is joined to limewater, which turns milky with carbon dioxide. Respiration is controlled by enzymes, so it speeds up as it gets warmer, until the enzymes start to be damaged.

What you will learn

  • Show that germinating seeds use oxygen and give out carbon dioxide.
  • Use controls to show that only living seeds respire.
  • Describe the effect of temperature on the rate of respiration.

Before you start

  • Know that living things need energy.

Materials

  • Germinating and dry bean or pea seeds, boiled seeds, limewater, coloured water

Equipment

  • Boiling tubes, bungs, capillary tube with a scale, gauze, water bath, thermometer

Procedure

  1. Set up the respirometer with germinating seeds in a water bath at 20 °C. Record how far the drop moves after 10, 20 and 30 minutes.
  2. Repeat with boiled seeds (killed) and dry seeds, recording after 30 minutes.
  3. Repeat the germinating seeds at 10 °C, 30 °C and 40 °C, recording after 30 minutes.

How this simulation is simplified

  • Germinating seeds at 20 °C use enough oxygen to move the drop 0.8 mm a minute; dry seeds respire at a tenth of that rate.
  • The rate doubles for every 10 °C rise up to 30 °C; at 40 °C enzyme damage brings it back to the 20 °C rate.