CSEC Biology • Lesson 2 of 2Ecological Sampling · Myers Science Hub Student Centre
CourseCSEC Biology
Practice formatMCQ • Structured • Experimental
Your progress0% complete
Learning objectives
- Distinguish habitat, population, community and species.
- Select suitable sampling methods for organisms in a habitat.
- Use quadrat data to calculate mean count and density.
- Plan a valid field investigation with random sampling and controlled procedure.
Core notes
Habitat
The place where an organism lives, including biotic and abiotic features that affect survival.
Quadrat
A frame of known area used mainly for organisms that are stationary or slow-moving, such as plants.
Random sampling
Sampling positions should be selected without favouring any visible patch. Coordinates or a random-number method can reduce bias.
Density
Density = number of individuals ÷ area sampled. Repeated quadrats give a more reliable estimate than a single quadrat.
Worked example: Five 0.25 m² quadrats contain 4, 6, 5, 3 and 7 daisies. Total = 25 daisies; total area = 1.25 m²; estimated density = 25 ÷ 1.25 = 20 daisies m⁻².
Video lesson
Paper 01-style MCQ
1. Which organism is MOST appropriately sampled using a quadrat?UK • 1
2. Why should a quadrat be placed at random positions?UK • 1
Paper 02-style structured question
3. A 0.5 m² quadrat is placed at six random points. Counts of a plant species are 2, 5, 3, 4, 1 and 3. Calculate (a) the mean number per quadrat and (b) the estimated density per m².UK • 4
Total = 18 (1); mean = 18/6 = 3 plants per quadrat (1); total sampled area = 6 × 0.5 = 3 m² (1); density = 18/3 = 6 plants m⁻² (1).
CXC experimental planning
4. Plan a field investigation to determine whether grass density changes with distance from a frequently used footpath.XS/PD • 10
State testable hypothesis (1); independent variable = distance from path (1); dependent variable = grass count/percentage cover/density (1); use a line transect with quadrats at stated intervals or repeated random quadrats within distance bands (2); keep quadrat area/counting rule consistent (1); repeat samples at each distance (1); record in table and calculate means/density (1); graph mean grass density against distance (1); conclusion linked to trend and acknowledge relevant environmental factors/limitations (1).