RP9: Required practical activity 9: Field investigations

Independent variable: none — this is a sampling method, not a manipulated experiment.

Dependent variable: number of the target organism counted per quadrat; used to calculate an estimated total population.

Quality controls:

use random coordinates to place quadrats (not throwing — this introduces bias)

same quadrat size (0.25 m × 0.25 m)

consistent counting criteria (e.g. only count whole plants fully inside the quadrat)

at least 10 quadrats for a reliable estimate

Your teacher will set up a survey area (e.g. 20 m × 20 m) with two tape measures laid at right angles.

Work in groups of three. One person picks a random number from one bag (0–20) and moves to that point along one tape. A second person picks from the other bag and moves along the other tape.

The third person places the 0.25 m × 0.25 m quadrat at the intersection of those two positions.

Count and record the number of the target species (e.g. plantain) inside the quadrat.

Return numbers to the bags. Repeat until 10 quadrats have been sampled.

Calculate the estimated population using:

Estimated population = (total area of habitat ÷ area of one quadrat) × mean count per quadrat

Independent variable: distance along the transect line (m), used as a proxy for a changing abiotic factor (e.g. light intensity under a tree canopy).

Dependent variable: number of organisms (or % cover) per quadrat at each position along the transect.

Quality controls:

same quadrat size

consistent counting criteria

measure the abiotic factor (e.g. light intensity using a light meter) at each quadrat position

Lay a 30 m tape measure in a straight line from one habitat type to another (e.g. from the base of a tree to open ground).

Place the 0.25 m × 0.25 m quadrat with one corner at the 0 m mark. Count and record the number of the target species inside the quadrat. Record any abiotic measurements (e.g. light intensity).

Move the quadrat to 5 m, then repeat. Continue at 5 m intervals to 30 m.

Pool class data. Plot a graph of plant number (or % cover) on the y-axis against distance or abiotic factor on the x-axis.

Survey area check — the teacher must inspect the area beforehand for hazards (broken glass, dog mess, or items hidden in long grass).

Wet conditions — do not carry out this practical on very wet grass due to the risk of slipping.

Tape measures — take care when rewinding retractable tape measures as they can recoil suddenly and cause injury.

Quadrats — carry quadrats carefully; do not throw them near other students.

Hand hygiene — wash hands thoroughly after the practical to remove soil, plant material and allergens.