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AQA GCSE Biology (9-1): Getting the most out of Required Practicals - Field Investigations

Posted by James Simms on November 20, 2019

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Specification location: AQA GCSE Biology Paper 2, Section 4.7 - Ecology

Note: this required practical consists of two parts: field Investigations of a population and investigating how an environmental variable affects the distribution of a species. As the second part is more complex, this guide will focus upon that. As the exact method followed will depend heavily on location, this guide will assume that the most common method will be followed.

Summary of method: A transect is determined upon across an area with varying levels of light intensity. The quadrat is periodically placed along this transect at regular intervals: the light levels and the distribution of plants are then measured (e.g. this could be percentage grass cover within the quadrat, for example). The results are then analysed to determine if there is a link between light levels and plant coverage.

For more detail on carrying out this experiment, watch our high-quality required practical tutorial on YouTube.

Field Investigations required practical variables:

Independent variable: Light intensity (changed by altering location along a transect line)

Dependent variable: Plant distribution (percentage cover within the quadrat, for example)

Control variables: Soil moisture, plant species surveyed

Common issues	Potential solutions
Equipment shortages	Some schools do not have access to light metres or do not have sufficient numbers of them to carry out this investigation. If this is the case, there are free apps available (EXAMPLE URL - https://play.google.com/store/apps/details?id=com.doggoapps.luxlight&hl=en_GB) which could be installed on to mobile phones and used instead.
Estimating	Depending on exactly which plants are being surveyed and how, it may be necessary for students to estimate distribution (e.g. percentage coverage of grass). Modelling this will be necessary for some students, especially if the quadrats used do not have an internal grid to aid with this.

Sample field investigations required practical results:

Transect line distance (m)	Percentage grass cover within quadrat	Light intensity (lux)
0	95	25,000
5	95	24,000
10	90	15,000
15	75	8,000
20	60	4,500
25	30	1,200
30	10	200

Source: The EverLearner Office Garden

AQA GCSE Science subject-specific terminology:

As a digital light meter will be used frequently in this experiment, this is an ideal opportunity to discuss resolution.
As total control of all variables apart from light intensity (soil depth, soil moisture, etc) is next to impossible, this may be a good time to discuss validity and valid conclusions.