Exam Questions for Sampling Techniques

Question 1

Describe the techniques you would use ot obtain RELIABLE DATA in order to compare the sizes of the population of the snail in the muddy area and in the area covered by vegetation.

Answer 1

1. Use of LARGE numbers of quadrats in each area ( if no. mentioned then 10+)
2. Random sampling METHOD (e.g. grid + random no.s) OR systematic sampling METHOD
3. Counting
   OR
4. Mark and release
5. Recapture
6. Calculate proportion of marked snails in teh second sample

Question 2

Describe how you would measure the pH of a sample of the mud.

Answer 2

1. Use of indicator OR meter OR probe

2. Detail e.g. obtaining soil solution (dampl soil is neutral)

Question 3

Snails burrow into the mud when the tide is out.

Suggest 2 advantages to the snails of this behaviour.

Answer 3

1. Hidden from predators

2. Prevents dessication/keeps moist

Question 4

Describe how you would use quadrats to determine whether a particular plant species has a clustered or random distribuition.

Answer 4

1. Use of random nos. to place quadrats
2. No of individuals counted in LARGE nos of quadrats.
3. Little variation- random, large variation- clustered

Question 5

Explain why vegetative propagation(reproduction) in plants often results in a clustered distribution. (1 mark)

Answer 5

New plants grow attached to parent.

Question 6

Some plants in a hot, dry desert have a uniform distribution and are widely spread. Suggest how this type of distribution is an advantage to the plants. (2 marks)

Answer 6

1. Less competition

2. For water/nutrients

Question 7

Describe a practical technique which you could use to find the mean population density of daisies on a lawn. (3 marks)

Answer 7

1. Random sampling method
2. Use of large nos./ many / at least 10 quadrats in each area
3. Counting daisies and dividing by the area

Question 8

Give the null hypothesis for the statistical test on the population density of daisies. (1 mark)

Answer 8

The cutting has no effect.

Question 9

Some plants have adaptations that enable them to grow on lawns that are cut regularly. Suggest 2 of these adaptations and explain the advantage of each. (2 marks)

Answer 9

1. Grows from base not the tips
2. Growing point not affected
3. Rapid seed production
4. Dispersed between cuttings

Question 10

They decided to lay quadrats every 10 metres rather than use random sampling. Explain the advantage of this. (2 marks)

Answer 10

1. Regular measurements/systematic sampling

2. To establish pattern/detect changes in nos/ detect trends.

Question 11

Suggest an explanation for placing 5 quadrats, rather than just 1, at each sampling point.

Answer 11

1. Increases sample size
2. More representative sample/reduces impact of anomalies
3. Increases reliability

Question 12

Explain importance of the method of selecting the nettle plant ( 2 marks)

Answer 12

1. Random no. table avoids bias in placing of quadrat

2. Nearest centre avoids bias in choosing plant to measure.

Question 13

Explain the importance of measuring the 6th leaf. ( 2 marks)

Answer 13

1. To allow valid comparison/so as not to introduce another variable
2. Reduces/avoids influence of growth/age
3. Reduces/avoids influence of light/shading.

Question 14

Explain why standard deviation is more useful than range as a measure of variation within a population. (4 marks)

Answer 14

1. Definition of range + SD/ effect of outliers on range + SD
2. Ranges are similar in both areas
3. Suggests that variation within population is similar.
4. SD smaller in area of high light intensity
5. Shows that area of high light intensity is a more unifrom population.

Question 15

What other statistic could be calculated from the standard deviation that would give an indication of how the mean leaf length might vary in other samples form the same population of nettles? (1 mark)

Answer 15

Standard error (of the mean)

Question 16

Explain how a colony of genetically-identical Pleurococcus cells could develop from a single original cell ( 2 marks)

Answer 16

1. Mitosis
2. Followed by7 cytokinesis/ cells divide into 2 cells
3. Repeated many times

Question 17

Suggest how this 10 cm * 10 cm quadrat was used to obtain the percentage cover of Pleurococcus at each point. (2 marks)

Answer 17

1. Each small square represents 1 %
2. Count no of squares containing Pleurococcus
3. Credit an indication of percntge was calculated

Question 18

Suggest how more evidence for the relationship between light intensity and the distribution of Pleurococcus could be obtained. (3 marks)

Answer 18

1. Obtain more data outside
2. Processing the data e.g. plotting a scatter graph, correlation test.
3. Interpolation of graph
4. Extended study e.g. lab experiments
5. Looking at results of previous studies

Question 19

Suggest advantages to lichens of being able to reproduce both sexually and asexually (2 marks)

Answer 19

1. Advantage of sexual reproduction (genetically different/greater gene poo/greater genetic diveresityl)
2. Advantage of asexual reproductin: fasater/one o feach organism needed/conserves advantagous alleles)

Question 20

Suggest how percent cover of lichens can be determined (3 marks)

Answer 20

1. use quadart
2. Idea of random/systematic campling
3. Count no. of squares/determine area containing lichen
4. Credit an indication of how the percentage was calculated.

Question 21

Explain how light intensity could be measured at the surface of the wall. (2 marks)

Answer 21

1. Use of light probe/sensor

2. Taking several measurements

Question 22

Suggest how data collected could be used to show whether there is a relationship between the abundance of lichen and light intensity. (3 marks)

Answer 22

1. Plot a scatter graphy of light intesity against lichens
2. Look for a correlation.
3. Ref to use of stats test
4. Appropriate naamed test, e.g. Spearman’s rank

Question 23

Suggest why quadrats were divided into 25 smaller sections. (2 marks)

Answer 23

1. Make it easier to estimate/count
2. More precise
3. Each section will be 4%.