Exploring and designing practice questions.

Why are quadrat positions in a uniform field chosen using random coordinates rather than placed by eye?

• To reduce bias in where samples are placed
• To make the fieldwork take much less time
• To guarantee that every single species is recorded
• To remove the need for any repeats

Answer: To reduce bias in where samples are placed

Random sampling stops the investigator unconsciously choosing convenient or interesting spots, so the sample better represents the whole area; it does not guarantee catching every species.

Which is an essential ethical requirement when using live animals in an investigation?

• Minimising any pain or distress caused
• Using the largest possible number of animals
• Choosing animals that prove the hypothesis
• Keeping the animals in complete isolation

Answer: Minimising any pain or distress caused

Ethical practice requires minimising harm, pain and distress and using the fewest animals needed; the other options are wasteful, biased or harmful.

How many values of the independent variable should an investigation into a relationship use, and why?

• At least five across a range, so a trend can be seen
• Exactly two, so that the comparison stays uncomplicated
• As many as time allows, whatever range they happen to cover
• Three, since that is the minimum for a line of best fit

Answer: At least five across a range, so a trend can be seen

Two values reveal a difference but no shape, so an optimum or a plateau would be invisible. The values also have to span a wide enough range for the relationship to change over it, which is a separate requirement from the number of them.

Why is a small preliminary run carried out before the main investigation begins?

• To check that the range and the method actually work
• To provide a first set of results for the final report
• To let the experimenter practise until readings agree
• To establish the value that the results should confirm

Answer: To check that the range and the method actually work

It answers questions the main run cannot afford to get wrong: whether anything measurable happens across the chosen range, whether the intervals are sensible, and how long each reading takes. Its data are reported as part of the design rather than pooled with the results.

A student plans to test whether music improves plant growth by playing music to one tray on a sunny windowsill while the silent tray stands in a cupboard. What is the principal flaw?

• The two trays also differ in the light they receive
• Plants have no organs capable of detecting sound
• Only one tray of plants is used for each treatment
• Growth cannot be measured reliably over a short period

Answer: The two trays also differ in the light they receive

Whatever the trays end up doing, light explains it just as well as music does, and no amount of careful measurement can separate the two afterwards. Deciding in advance that plants cannot hear would prejudge the very question the investigation was set up to ask.

How should a student decide how many quadrats to place in a field survey?

• Plot species found against quadrats placed and stop when it levels
• Place as many quadrats as the time available in the session will allow
• Use the number recommended for that habitat in a textbook
• Place enough to cover about a tenth of the total area

Answer: Plot species found against quadrats placed and stop when it levels

The cumulative curve answers the question with data from the site itself: once further quadrats add nothing new, the sample describes the community. Time available is a constraint on what was possible, which is not the same as a justification for the number chosen.