Development of practical skills in biology

A student repeats a measurement five times and gets very similar values that are all far from the true value. The results are:

Describe how you would investigate the effect of temperature on the permeability of beetroot cell membranes.

A spirometer trace showed 18 breaths in 1 minute, each with a tidal volume of 0.45 dm³. The oxygen chamber volume fell by 1.2 dm³ in 3 minutes. Calculate the ventilation rate and the rate of oxygen uptake.

A student measured the rate of respiration of maggots at five temperatures using a respirometer. Suggest how she could: (a) improve the validity of the results; (b) process the data to show the effect of temperature; (c) estimate the uncertainty in the volume readings.

Which statistical test is appropriate to compare the means of two independent sets of data?

Figure 1 shows the rate of oxygen uptake by germinating peas at different temperatures. Describe the trend shown.

Use Figure 1 to calculate the temperature coefficient, Q₁₀, between 20 °C and 30 °C.

Suggest three improvements to this investigation.

A student used an eyepiece graticule. At ×400, 1 epu = 2.5 µm. A cell measured 18 epu long and 12 epu wide. Calculate the actual dimensions and the area of the cell, assuming it is rectangular.

Give three rules for producing a scientific drawing from a microscope slide.

A student compared the length of ivy leaves growing in sunlight and in shade.

	Sun	Shade
Mean length / mm	42	58
Standard deviation / mm	5.1	6.3
Number of leaves	15	15

(a) Suggest a null hypothesis. (b) The student calculated t = 7.64. The critical value for 28 degrees of freedom at p = 0.05 is 2.05. What can she conclude? (c) Explain why a large sample size is important. (d) Suggest a biological explanation for the difference.