Sampling a habitat
You cannot count every plant on a shore or every beetle in a field, so ecologists sample: they count a few small areas chosen at random and scale up. This square frame, a quadrat, marks one sample. Choosing the right tool for the habitat is half of the CSEC practical.
By the end of this page you can
- Describe quadrats, pooters and mark-release-recapture
- Choose the right equipment for a habitat and an organism
- Estimate population density with quadrats, step by step
- Define habitat, population, density and random sampling
- Calculate density and mark-release-recapture estimates
Goals tick themselves off as you try the activities below.
Photo: Marie-Noelle de Casamajor, CC BY 4.0, via Wikimedia Commons. Cropped, JPEG q64.
A quadrat on a rocky shore, used by marine scientists to count the seaweeds and animals inside it.
How often it shows up in past papers
Paper 1 counts come from our past-paper bank of CSEC Biology Paper 1s. Paper 2 is not included yet.
Count a part, estimate the whole
Each method suits a different kind of organism. Tap each card.
Match the tool to the organism
Examiners often describe a habitat and ask which equipment to use.
What does it sample?
Tap a tool to see what it is for.
Place quadrats at random, but a transect at fixed intervals along a line. Repeat, and take a mean.
Use a quadrat
Find the density of a weed on the school field. Drag or tap each card into its slot.
How do you decide where the first quadrat goes?
Seven terms to know cold
Say what each term means before you flip the card. Practical questions use these words exactly.
Six quick questions, then a real one
Pick an answer to see why it’s right or wrong.
Five quadrats, each 0.25 m², hold 4, 6, 3, 5 and 2 plants. What is the density?
40 snails are marked and released. Later 30 are caught, and 10 of them are marked. What is the estimated population?
Which equipment is best for collecting insects living in tall grass?
Why should quadrats be placed at random?
A student wants to see how seaweeds change from the low-tide line up to the top of a rocky shore. She should use a
A pitfall trap is used to catch
exam style · 3 marks
Describe how you would estimate the number of a particular weed per square metre on a school field.
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Practice questions are written by My V.I.P. Academy. They are not official CXC papers.