the place where an organism lives. A pond is the habitat of a frog.

Why are quadrats placed at random?

to avoid bias. Choosing where to put them would skew the results.

Which is an abiotic factor?

temperature. Abiotic means non-living.

What is biodiversity?

the variety of species in an area. An area with many species has high biodiversity.

Ecosystems and sampling · Edexcel IGCSE Science (Double Award)

In plain words

You can't count every daisy on a football pitch. Instead you count the daisies in a few small squares, placed at random, and scale up. That's sampling, and it's how ecologists find out what lives where.

Three things to know

Population: all of one species in an area. Community: all the populations of different species in an area. Habitat: the place where an organism lives. Ecosystem: the community together with the non-living environment.
A quadrat is a square frame. Place several at random, count the organisms in each, find the mean, and multiply up to the whole area. Biodiversity is the variety of species in an area.
Abiotic factors are non-living (light, temperature, water, soil pH). Biotic factors are living (predators, competition, disease, food).

Worked example

Ten quadrats, each 1 m², are placed at random in a 500 m² field. They contain 40 daisies in total. Estimate the number of daisies in the field.

Mean per quadrat = 40 ÷ 10 = 4 daisies per m².
Multiply by the area of the field: 4 × 500.
= 2000 daisies.

Tips and tricks

Quadrats must be placed at random (use random numbers for coordinates) to avoid bias, and there must be enough of them to be reliable.
Abiotic: A for "absent of life". Light, temperature, water. Biotic: anything alive.

5 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Ecosystems and sampling: 5 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What is a habitat?
- a group of animals
- the place where an organism lives (the answer)
- a food chain
- a type of quadrat
A pond is the habitat of a frog.
Why are quadrats placed at random?
- to save time
- to avoid bias (the answer)
- to find the most plants
- because it is easier
Choosing where to put them would skew the results.
Which is an abiotic factor?
- predators
- disease
- temperature (the answer)
- competition
Abiotic means non-living.
Five 1 m² quadrats contain 2, 4, 3, 5 and 6 plants. What is the mean per square metre?
- 3
- 4 (the answer)
- 5
- 20
20 ÷ 5.
What is biodiversity?
- the number of one species
- the variety of species in an area (the answer)
- the size of a habitat
- the mass of living things
An area with many species has high biodiversity.

5 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

3 questions, 7 marks. Write your answers on paper, then check them.

Ecosystems and sampling

Edexcel International GCSE Science (Double Award) 4SD0 · 7 marks · papermunch.org

Name ______________________________ Date ______________

State the difference between a population and a community.[2]
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A population is all the organisms of one species in an area; a community is all the populations of all the species living there.
I got this one
Describe how to use quadrats to estimate the number of dandelions in a field.[3]
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Place quadrats at random (using random coordinates). Count the dandelions in each and calculate the mean per quadrat. Multiply by the number of quadrats that would fit into the field (the total area ÷ the quadrat area).
I got this one
Give two abiotic factors that affect where a plant can grow.[2]
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Any two: light intensity, temperature, water (soil moisture), soil pH, mineral ions, wind.
I got this one

Answers: Ecosystems and sampling

1. A population is all the organisms of one species in an area; a community is all the populations of all the species living there.
2. Place quadrats at random (using random coordinates). Count the dandelions in each and calculate the mean per quadrat. Multiply by the number of quadrats that would fit into the field (the total area ÷ the quadrat area).
3. Any two: light intensity, temperature, water (soil moisture), soil pH, mineral ions, wind.