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

Posted by James Simms on November 20, 2019

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Specification location: AQA GCSE Biology Paper 2, Section 4.5 - Homeostasis and Response

Summary of method: Cress seedlings are germinated and then are grown in different environments. One set of seedlings should be grown in an entirely dark environment; another should be grown with strong light direction overhead; another should be grown with the sole source of light to the side. These will show the effects of phototropism. To show the effects of geotropism, some seedlings are grown as normal, while another set are grown perpendicular to the ground. If equipment permits, a third set can be grown on a clinostat perpendicular to the ground (continually rotating them with regard to gravity). Results should be collected by sketching the seedlings and the effects of tropisms on them and by carefully measuring the height of the seedlings.

For more detail on the set-up of this experiment, watch our high-quality required practical tutorial on YouTube.

Plant responses required practical variables (these will vary, based on approach):

Independent variable: Light direction/light levels/direction of gravity

Dependent variable: Seedling height/direction of growth

Control variables: Plant species, time, source of moisture, light intensity (except in the case of seedlings grown in the dark

Common issues	Potential solutions
Equipment availability	Some schools have access to a clinostat to ensure rotation with regards to gravity or light source; others do not. In terms of fulfilling the stipulations of the required practical: Phototropism - Growing some seedlings in an environment where the light source is directly overhead, one where it is from the side and another set in darkness will suffice. Geotropism - Growing one set of seedlings as normal and another where the seed tray is orientated perpendicular to the ground will show strong geotropism.
Student mathematical skills	When comparing the seedlings grown in the dark with those grown in the light, a mean will need to be calculated. My experience has been that some students who are heavy calculator-uses often make BIDMAS errors with mean calculations, e.g. 1+2+3+4÷4 = 6 rather than (1+2+3+4)÷4=2.5.
Student literacy skills	Students will need to describe and sketch the tropisms that they are investigating. Students with weak literacy skills may need appropriate descriptive language to be modelled before attempting to write their own description.

Sample plant responses required practical results:

Seedling height (mm)	1	2	3	4	5	Mean height (mm)
Light	7	8	6	6	7	7
Dark	11	12	11	16	13	13

Source: The EverLearner Balcony

AQA GCSE Science subject-specific terminology:

As students will be allowing seeds to germinate in a variety of environments and analysing the results, this is an ideal opportunity to discuss predictions and hypotheses.
As part of the analysis, students will be measuring the height of the seedlings with a 15 or 30cm ruler, which makes a discussion of the idea of resolution worthwhile here.