Quadrats, transects, capture–recapture and collecting equipment — how to choose and use the right sampling method.
7 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
How could you count every crab on a mangrove shore without catching them all? You sample.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Copy these into your notebook in your own words — that is how they stick.
A small representative part of a habitat studied to estimate the whole. Must be random and repeated.
Square frame (usually 1 m²) for plants and slow-moving animals. Measures density, frequency or % cover.
Line across a habitat along an environmental gradient. Line transect records touches; belt transect uses quadrats at intervals. Shows zonation.
N = (first sample × second sample) ÷ marked recaptured. For mobile animals.
Harmless marks; marked animals mix evenly; no births, deaths or migration; marks stay on.
Container sunk level with soil to catch ground-dwelling invertebrates. Check it often; add a cover against rain.
Nets for flying insects in vegetation / small organisms in water.
Heat and light from a lamp drive small soil animals down into alcohol or a jar.
The kind of support a teacher gives after the lesson: worked examples to attempt first, a board illustration, key terms, common misconceptions and memory aids.
Try it in your notebook first, then reveal the solution one step at a time.
Try it in your notebook first, then reveal the solution one step at a time.
| Method / apparatus | Used to sample | Key precaution |
|---|---|---|
| Quadrat | Plants and slow-moving animals in an area | Place randomly; use many quadrats |
| Line / belt transect | Change in organisms along a gradient (shore, pond edge) | Record at regular intervals along the line |
| Pitfall trap | Ground-crawling invertebrates | Rim level with the soil; cover against rain; check often |
| Sweep net | Insects in long grass | Same number of sweeps at each site |
| Plankton net | Tiny organisms in water | Tow at the same speed and depth |
| Tullgren funnel | Small animals in leaf litter or soil | Do not overheat the sample |
| Capture–recapture | Mobile animals (snails, woodlice, fish) | Marks must be harmless and permanent |
Match the method to the organism: fixed or slow organisms → quadrats and transects; fast-moving animals → traps and capture–recapture.
Lincoln index: “First times Second, over Marked-in-second” — F × S ÷ M.
Fisheries officers across the Caribbean use sampling and mark–recapture data to estimate stocks of fish and spiny lobster, and use those estimates to set closed seasons and catch limits.
Make a 0.5 m × 0.5 m quadrat from string and four sticks. Throw it ten times on a lawn, count one type of plant in each throw, and estimate how many there are on the whole lawn.
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Write full answers, then reveal the mark scheme and tick the points you earned (14 marks in total). Your answers are saved on this device.
Question 1 [7 marks]
Jacob found many wood lice near his home. He caught 20, marked each with a small dot of paint and released them. One week later he caught 50 wood lice, of which 10 were marked.
(a) Apart from capture–recapture, list THREE methods used by ecologists to study organisms in an ecosystem. [3]
(b) Using a suitable equation, estimate the number of wood lice in the area. [2]
(c) Suggest TWO assumptions Jacob made when using this method. [2]
Question 2 [7 marks]
A class wants to compare the plants growing near a pond with those on a dry hillside 30 m away.
(a) Name a suitable sampling method and describe how it would be carried out. [4]
(b) State TWO precautions the students should take. [2]
(c) Suggest ONE abiotic factor that could explain the differences in plants. [1]
Find these in your own past-paper booklets for extra timed practice. The practice above is adapted from them.