Practical skills

Question 1

What is the purpose of a control?

Answer 1

• Allows a comparison to be made
• Shows what would normally happen so comparison can be made when independent
  variable is changed

Question 2

Common ways of improving an investigation:

Answer 2

• Ensure equal sizes/volumes of samples are used
• Calculate standard deviation
• Repeat the experiment at least 3 times and calculate the mean
• Test a wider range of values for the independent variable
• Replicate experiment using different samples/species
• Use larger sample size
• Use random sampling method (e.g. random number generator)

Question 3

How to make an investigation more reliable:

Answer 3

• Repeat experiment at least three times to increase number of observations
• Identify anomalous results
• Calculate mean
• Compare results with values provided by other

Question 4

How to make an investigation more accurate:

Answer 4

• Carry out more tests within existing range
• Introduce method to ensure no double counting occurs
• Use a narrower range (if appropriate)

Question 5

How to increase the validity of an investigation:

Answer 5

• Make sure equal volumes/concentrations are used each time
• Use buffer solutions (if appropriate)

Question 6

When analysing practical results:

Answer 6

• Calculate the mean and standard deviation of results
• Use the correct statistical test
• e.g. Student’s t-test, chi-squared test, correlation coefficient
• Include a sensible number of significant figures (i.e. 2-3)
• Draw scientifically correct graphs

Question 7

When answering ‘describe’ questions:

Answer 7

• Write what the data is showing e.g. trends, changes in rate, increases and decreases etc
• If describing a graph, break the graph down into sections
• Each section should be a describable feature
• e.g. constant rate from A to B, increasing rate from B to C…
• Use data points provided in the question to illustrate description

Question 8

When answering ‘explain’ questions:

Answer 8

• Say why the results have come about
• Use scientific knowledge to explain any patterns and trends
• Make sure explanation is specific to the question

Question 9

When answering ‘evaluate’ questions:

Answer 9

• Provide both positive and negative responses to the statement
• Use the data given and scientific knowledge to agree with conclusion
• Use methodological errors (e.g. no statistical test performed, small range of samples etc) or
  other untested factors that could be involved in the process

Question 10

When answering ‘compare’ questions:

Answer 10

Each statement should include both pieces of data
- e.g. Both A and B remained constant for 2 hours
- e.g. The rate of increase of A was greater than that of B from 2 to 4 hours

Question 11

When answering ‘conclude’ questions:

Answer 11

Only give conclusions that the evidence supports

Question 12

When drawing diagrams:

Answer 12

• Include a title
• Use a sharp pencil
• Labels should be outside the diagram
• Use ruled label lines
• Do not cross label lines
• Include a scale bar
• State magnification
• Do not use shading
• Use at least 50% of the available space

Question 13

To create a calibration curve (e.g. when using a colorimeter)

Answer 13

• Calibrate colorimeter using distilled water
• Create serial dilutions of known concentrations of product
• Plot absorbance against product concentration to create calibration curve
• Use graph to read off concentration of experimental results