Required Practical 12 - Sampling

Question 1

Explain why it is important to use a statistical test in analysing the results of an investigation

Answer 1

• results may be due too chance
• confirm difference is significant
• in order to accept or reject null hypothesis

Question 2

Describe how you would place quadrats at random

Answer 2

• random number generator on calculator

- to determine coordinates to place quadrat in a gridded area

Question 3

Describe how you would decide the number of quadrats to use in order to collect representative data

Answer 3

• enough to carry out a statistical test
• large enough to be reliable and collect in available time
• calculate running mean

Question 4

Explain why biologists collect data randomly

Answer 4

• avoid bias
• to collect representative data
• so statistical tests can be calculated

Question 5

Explain why it is important to check the repeatability of measurements

Answer 5

• increases reliability of measurements

- differences less likely to be due to measurement error / anomalies

Question 6

Describe how you could use a scatter diagram to check the repeatability of measurements made by two observers

Answer 6

• plot one set of results against the other
• expect to see points lying close to line
  OR
• plot both sets against variable
• look for overlapping/ corresponding points

Question 7

Suggest precautions taken when carrying out sampling

Answer 7

• allow sufficient time to elapse before taking further samples so vegetation can recover from trampling
• study organisms in situ or take minimum number and return

Question 8

Evaluate density in measuring abundance of a species

Answer 8

• most accurate
• time consuming
• not suitable when there are too many individuals / individuals are difficult to identify

Question 9

Evaluate percentage cover (% area of quadrat) in measuring abundance of a species

Answer 9

• more accurate than frequency but less time consuming compared to density
• subjective so unreliable
• does not consider overlapping individuals

Question 10

Evaluate frequency (% squares in quadrat) in measuring abundance of a species

Answer 10

• quick, basic overview
• inaccurate
• does not consider overlapping individuals

Question 11

Draw a conclusion using data provided

Answer 11

Give BALANCED Argument

• correlation data shows
• state if correlation is weak or strong
• give anomalous examples
• sample size small so unreliable
• other factors not considered
• cannot be sure since no statistical analysis

Question 12

Suggest precautions taken when sampling

Answer 12

• avoid trampling on vegetation
• allow sufficient time to elapse before further studies
• study organisms in situ / remove and return and minimum amount

Question 13

State when to use quadrats and transects

Answer 13

Quadrats - uniform distribution

Transects - distribution changes over an area

Question 14

Suggest why a certain number of samples is taken

Answer 14

• too many would be too time-consuming

- too few would be unreliable and insufficient to eliminate anomalies