A respirometer turns respiration into something you can read with a ruler: soda lime absorbs the carbon dioxide, so the coloured drop creeps towards the germinating seeds as they take up oxygen. By hand, turn the thermostat dial, leave both tubes in the water bath with their screw clips open until they reach its temperature, close the clips and use the syringes to bring each drop near the start of its scale. Read the thermometer and both drops, run the stopwatch for 5 minutes (its speed lever saves you the real minutes) and read the drops again. Do it at six temperatures, beside a control tube of glass beads. Then calculate the rates, plot rate against temperature and explain what you see. Every attempt uses a different batch of seeds. Allow about 35 minutes.
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Headings with quantity / unit, every temperature read from the thermometer to the nearest 0.5 °C at each of the six dial settings, every drop position read to the nearest millimetre at the start and at 5 minutes, distance moved = final - start, the control tube’s distance recorded, and a fair method: tubes at the bath temperature and both screw clips closed before the stopwatch starts, nothing touched for the 5 minutes.
Rate = distance moved ÷ 5 min to a consistent number of decimal places; temperature on the x-axis and rate on the y-axis with units, a scale that uses more than half the grid, and every point plotted to within half a small square.
The rate rises to an optimum and then falls, the highest rate and its temperature quoted from your own table, and the fall explained by the enzymes of respiration being denatured.
Soda lime absorbs carbon dioxide, so the drop measures oxygen uptake; the glass beads show that the seeds, not temperature or pressure changes, move the drop.
Control variables (mass, type and age of seeds, mass of soda lime), why the tubes equilibrate with the clips open, a real limitation (one reading per temperature) and its improvement (repeats and a mean), and the corrosive soda lime. Examiner reports on 0610 practical papers regularly note units in the table cells, inconsistent decimal places and conclusions with no data quoted.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.