ZIMSEC Prac exam questions.

• There are usually three questions on Paper 4.
• The examiners will take care to set questions that are not exactly the same as any you have done before.
• It is very important that you do exactly what the question asks you to do.
• Candidates often lose marks by doing something they have already practiced, rather than doing what the question actually requires.

 

Question type 1

• This is likely to be a ‘wet practical’. For example, it could be:
  • an investigation into the activity of an enzyme;
  • an osmosis experiment;
  • tests for biological molecules;
• This question will often ask you to investigate the effect of one factor on another for
  example:
  • the effect of enzyme concentration on rate of reaction;
  • the effect of substrate concentration on rate of reaction

Types of variables

• The factor that you change or select is called the independent variable.
• The factor that is affected is the dependent variable.
• If you are investigating the effect of one variable on another, make sure that there are no other variables that might be affecting the results eg temperature — keep them constant.

Candidates should be able to

• Identify the independent and dependent variable
• decide the range to use for an independent variable and decide how to change its values, including:
  • concentration (using simple or serial dilution)
  • temperature (selected from above freezing to 100 oC)
  • pH (using buffers)
• Describe an appropriate control which removes the effect of the independent variable (including
  replacing a solution with the same volume of water or denaturing an enzyme by boiling)

Tips

During your course:

• Every time you do an experiment, identify and write down the independent variable and the dependent variable.
• learn how to make up dilutions from a solution of a given concentration

In the exam:

• Read the question carefully, then identify the independent variable and the dependent
  variable (even if the question does not ask you to do this).

 

Producing a range of concentrations from a standard solution.

Question type 2

• This question is likely to involve making drawings from a specimen.
• This could be a real specimen, or it could be a photograph.
• You may be asked to use a microscope, a stage micrometer and eyepiece graticule, to work out the magnification or size of the specimen.

Tips

During your course:

Every time you do a practical during your lower and upper sixth course, time yourself. Are you making
quickly enough? You will probably find that you are very slow to begin with, but as the
course progresses try to work a little faster as your confidence improves.

In the exam:

• Do exactly what the question asks you to do.
  • This is unlikely to be exactly the same as anything you have done before.
• leave yourself enough time to do each question, spending an appropriate number of minutes on each one.