Teacher Resource 1
Random sampling using quadrats
This is a paper-based activity looking at the process of taking random quadrat samples to
investigate the distribution and abundance of organisms on a field in two areas (sunny and shaded
or more/less trampling by foot). This activity is not a replacement for practical work, but could be
used if short on time, if the weather is not great or if the school lacks sampling equipment.
Preparation
Before the lesson teachers must:
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Print out copies of ‘field area 1’ and ‘field area 2’ worksheets, one set per group of 2 or 3
learners. The worksheets would benefit from being in colour if possible. It may also be useful to
have them laminated so they can be reused by other classes.
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Print out the ‘quadrat’ sheet onto acetate and cut out the ‘quadrats’ - one quadrat per group of
2 or 3 learners.
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Each group will also require two envelopes. One with cards each with a number from 1 to 5.
The other containing cards, each with a letter A to H.
The following websites give information and step by step instructions on how to carry out a random
sample of two areas. Although this activity covers the information required for learners to
understand how to carry out random sampling and the issues surrounding random sampling, if the
opportunity does arise, learners would benefit from completing the sampling technique outside. If
doing this, learners could use keys to identify the plants.
http://www.nuffieldfoundation.org/practical-biology/biodiversity-your-backyard
http://www.saps.org.uk/secondary/teaching-resources/260-questions-about-quadrats
Instructions
Learners work in groups of 2 or 3. Hand out a ‘field area 1’ and ‘field area 2’ worksheet to each pair
along with an acetate ‘quadrat’ and bag of coordinate cards. Each field area measures 5m by 8m
and the acetate quadrat represents 1m2.
There are two methods you can use for sampling two areas: number of plants/m2, which measures
density or total number of plants and percentage cover, which measures plant frequency, taking
into consideration size as well as number.
You can choose whether to do one or the other in class, or whether to do both and compare the
results.
Before the activity explain to the class how to sample a large area using a quadrat. Discuss with
learners how they might make the sample random (for this activity learners will pick cards out of a
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bag to use as coordinates for placing their quadrats) and how many sample quadrats they should
take to get a fair representation of the distribution and abundance of plants in the whole area.
If measuring the number of plants/m2 discuss with learners how they may deal with a plant that is
not fully inside the quadrat. Some groups may decide to count the plant only if more than half of it
is inside the quadrat, other groups may decide to count plants that touch the top and right edge of
the quadrat as ‘in’ and plants touching the bottom and left edge of the quadrat as ‘out’.
If measuring the percentage cover, if any part of a plant is in a square of the quadrat it is counted.
On the acetate squares in this activity each square is equivalent to 4%.
Once groups have decided how many samples to take etc. they take a number card out of one
envelope and a letter card out of the other envelope. They use these to place the left hand corner
of their quadrat on this coordinate on ‘field area 1’ worksheet. Learners make a note of how
many/percentage cover of each type of plant in that quadrat. The cards go back in the envelopes
and the process is repeated.
Number of plants/m2
As the acetate quadrats represent 1m2, learners can take an average of the number of each type
of plant in each quadrat and this will give them the average number of each plant/m2.
As the ‘field’ area is 40m2, learners can multiply their average for each plant to estimate the total
number of each plant in the ‘field’ (scaling up).
Learners use the data to draw a bar chart and analyse the density of plants in the two areas and
explain why this might be the case (abiotic and biotic factors).
Ask learners to count the actual number of each plant in the two ‘fields’ and compare this to their
results. Discuss why any differences may have arisen.
Percentage cover
Learners use the data to draw a bar chart and analyse the density of plants in the two areas and
explain why this might be the case (abiotic and biotic factors).
If learners have completed both types of measurements they can take it further and compare both
sets of results: similarities and differences between the data, why this may be the case and
advantages and disadvantages to each type of measurement.
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Answers
The number of each plant and the percentage cover of each plant will vary slightly from group to
group as they will have placed their ‘quadrats’ randomly.
Actual numbers of each plant:
Field area 1
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Clover – 21
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Daisy – 118
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Dandelion – 24
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Buttercup – 12
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Primrose – 3
Actual numbers of each plant:
Field area 2
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Clover – 18
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Daisy – 42
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Dandelion – 4
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Buttercup – 0
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Primrose – 0
Factors that may have caused the difference in distribution and abundance may include: light
intensity, temperature, water content of soil, more grazing animals in one area, more/less people
walking over the area, type of soil etc.
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