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Edexcel IGCSE Biology Observations and Variables

Practise Edexcel IGCSE Biology observations, measurements and variables by identifying independent, dependent and controlled variables in investigations.

Syllabus
Issue 3 (2024)
Course
Biology 4BI1

Exam points

  • Identify independent variables such as missing minerals, soil treatment or experimental condition.
  • State dependent variables such as sweating rate, indicator colour or gas volume released.
  • Choose controlled variables such as temperature, time, volume, light, species or sample size.

Covered syllabus points

Precise observations and measurementsIndependent, dependent and control variables

(c) Observations, measurements and variables question 1

[Maximum number: 2]

Pineapple juice contains a protease called bromelain.
A student uses this method to investigate the digestion of solid gelatine protein by bromelain.
- place solid gelatine protein into a test tube up to a height of 5 cm
- mix 5 cm35 \mathrm{~cm}^{3} pineapple juice with 1 cm31 \mathrm{~cm}^{3} of pH 4 buffer
- place 1 cm31 \mathrm{~cm}^{3} of the pineapple juice and buffer solution on top of the gelatine
- leave for one hour in a water bath set to 37∘C37^{\circ} \mathrm{C}
- measure the height of the solid gelatine and use it to calculate the volume of gelatine that has been digested

Repeat the method three more times.
The diagram shows part of the student's method.

Figure for Question (c) Observations, measurements and variables question 1 — Edexcel IGCSE Biology

The student repeats the investigation with different pH buffers.

The table shows their results.

Table for Question (c) Observations, measurements and variables question 1 — Edexcel IGCSE Biology

Give two variables the student should control.

1

2

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