Why is random sampling used when estimating the abundance of a plant in a field?

It removes bias in choosing where to sample, so the samples represent the whole area and the estimate is reliable.

What is a belt transect and when would it be the better sampling method?

A line across a habitat along which quadrats are placed at set intervals, used where a factor changes gradually, such as from the sea up a rocky shore.

A student places 10 quadrats each of 0.25 m² at random in a field of 2000 m² and counts 30 daisies in total. Estimate the number of daisies in the field.

The quadrats cover 2.5 m², so the mean density is 12 daisies per m² and the estimate is 24000 daisies.

In a capture-recapture study 40 woodlice are caught, marked and released. The next day 50 are caught and 10 of them are marked. Estimate the size of the population.

The estimate is 40 × 50 ÷ 10, which is 200 woodlice.

OCR GCSE Combined Science Biology J250

Cell Level Systems

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Field investigations, and human impact on ecosystems

3 things to know
Paper 8 (Biology)

Overview

Random sampling with quadrats and belt transects, estimating plant numbers from quadrat counts and animal populations by capture-recapture with its assumptions, collecting with pooters and sweep nets, using a dichotomous key, how land use, monoculture and hunting reduce biodiversity, captive breeding, nature reserves and habitat conservation, positive human interactions, and the mean, median, mode and percentiles of survey results.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

What is a pooter and how does it work?

Key term

How can random positions for quadrats be chosen in a grassy field?

Key term

What is a quadrat and what is it used to measure?

Questions from this subtopic

Each one with the model answer underneath.

1
Why is random sampling used when estimating the abundance of a plant in a field?
Model answer
It removes bias in choosing where to sample, so the samples represent the whole area and the estimate is reliable.
2
How can random positions for quadrats be chosen in a grassy field?
Model answer
The field is divided into a numbered grid and pairs of random numbers are used as coordinates for each quadrat.
3
What is a quadrat and what is it used to measure?
Model answer
A square frame of known area placed on the ground, used to count the number of organisms or estimate the percentage cover in that area.
4
What is a belt transect and when would it be the better sampling method?
Model answer
A line across a habitat along which quadrats are placed at set intervals, used where a factor changes gradually, such as from the sea up a rocky shore.
5
A student places 10 quadrats each of 0.25 m² at random in a field of 2000 m² and counts 30 daisies in total. Estimate the number of daisies in the field.
Model answer
The quadrats cover 2.5 m², so the mean density is 12 daisies per m² and the estimate is 24000 daisies.
6
In a capture-recapture study 40 woodlice are caught, marked and released. The next day 50 are caught and 10 of them are marked. Estimate the size of the population.
Model answer
The estimate is 40 × 50 ÷ 10, which is 200 woodlice.

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