Edexcel IGCSE Biology Independent Dependent and Control Variables Questions

Practise Edexcel IGCSE Biology investigation variables by naming what changes, what is measured and what must stay constant in practical work.

Exam points

Identify the independent variable, such as missing mineral, soil treatment or solution composition.
State the dependent variable, such as sweat rate, indicator colour or volume of gas released.
Give controlled variables such as temperature, time, buffer volume, light or sample size.

[Maximum number: 1]

A student uses this method to investigate the nitrogen cycle.
- take two samples of soil, each of mass 100 g
- sterilise one sample of soil by heating at $100^{\circ} \mathrm{C}$ for one hour
- place the sterilised and unsterilised samples into separate filter funnels
- pour $25 \mathrm{~cm}^{3}$ of water through each soil sample and collect the filtrate in a test tube
- test each filtrate for nitrates
- pour water through each soil sample for 5 minutes
- pour another $25 \mathrm{~cm}^{3}$ of water through each soil sample and collect the filtrate in a test tube
- test each filtrate for nitrates
- add $1 \mathrm{~cm}^{3}$ of a solution of ammonium salts to each soil and leave for three days
- pour $25 \mathrm{~cm}^{3}$ of water through each soil sample again and collect the filtrate in a test tube
- test each filtrate for nitrates

The diagram shows the student's apparatus.

Figure for Question Edexcel IGCSE Biology Independent Dependent and Control Variables Questions question 1 — Edexcel IGCSE Biology

The table shows the student's results.

Table for Question Edexcel IGCSE Biology Independent Dependent and Control Variables Questions question 1 — Edexcel IGCSE Biology

Give the independent variable in the investigation.

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Edexcel IGCSE Biology Independent Dependent and Control Variables Questions question 1