Edexcel IGCSE Biology C Observations Measurements and Variables Questions

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

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 measurements Independent, dependent and control variables

[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 $5 \mathrm{~cm}^{3}$ pineapple juice with $1 \mathrm{~cm}^{3}$ of pH 4 buffer
- place $1 \mathrm{~cm}^{3}$ of the pineapple juice and buffer solution on top of the gelatine
- leave for one hour in a water bath set to $37^{\circ} \mathrm{C}$
- 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 1 — Edexcel IGCSE Biology

The student repeats the investigation with different pH buffers.

The table shows their results.

Table for Question 1 — Edexcel IGCSE Biology

Give two variables the student should control.

1

2

[Maximum number: 3]

Catalase is an enzyme found in many cells.
This enzyme controls the breakdown of hydrogen peroxide into water and oxygen.

2 \mathrm{H}_{2} \mathrm{O}_{2} \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}

hydrogen water oxygen peroxide

A teacher uses this method to investigate the effect of pH on catalase.
Step 1 cut a cylinder of potato tissue into six equal sized discs
Step 2 measure $10 \mathrm{~cm}^{3}$ of hydrogen peroxide solution and place into a boiling tube
Step 3 add a pH buffer solution to the tube to keep the pH at 7
Step 4 add the six potato discs to the boiling tube
Step 5 collect the gas given off by the reaction in an inverted $20 \mathrm{~cm}^{3}$ measuring cylinder

Step 6 measure the total volume of gas collected after five minutes
Repeat steps 1 to 6 using four different pH buffers ( pH 4, pH 5, pH 6 and pH 8 ).
The diagram shows the teacher's apparatus.

Figure for Question 2 — Edexcel IGCSE Biology

(a)

Give the dependent variable in this experiment.
1

2

[ 1 ]

(b)

The teacher controls the time for gas collection and also the volume of hydrogen peroxide used.

State two other abiotic variables the teacher should control in this experiment.

1

2

[ 2 ]

[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 3 — Edexcel IGCSE Biology

The table shows the student's results.

Table for Question 3 — Edexcel IGCSE Biology

Give the independent variable in the investigation.

All question bank results loaded

Covered syllabus points

Question 1

Question 2

Question (a)

Question (b)

Question 3