28 WJEC Biology AS Level - Marianne Izen - 2nd Edition

Question 1

Independent variable

Answer 1

The variable that the experimenter purposely changes in order to test the dependent variable.

Question 2

Dependent variable

Answer 2

Experimental reading, count, measurement or calculation from them, the value of which depends on the value of the Independent variable.

Question 3

Controlled variable

Answer 3

Factor that is kept constant throughout an experiment, to avoid affecting the dependent variable.

Question 4

Describe the design for plotting the standard curve for the practical test to determine glucose concentration?

Answer 4

Question 5

Describe the apparatus needed for the practical test to determine glucose concentration?

Answer 5

Question 6

Describe the method for the practical test to determine glucose concentration?

Answer 6

Question 7

What are the three parts of a risk assessment?

Answer 7

Hazard - why an object or chemical is potentially harmful

Risk-the action in the experiment that could cause harm

Control measure - how to minimise or prevent harm.

Question 8

Describe the rationale of the practical test to determine glucose concentration?

Answer 8

The Benedict’s test detects the presence or absence of reducing sugars so it is qualitative.

It can indicate relative concentrations of different solutions so it is semi-quantitative.

It can be made quantitative using a calibration curve: the absorption of red copper (1) oxide is measured in a colorimeter for glucose solutions of known concentration.

A plot of absorbance against concentration produces a calibration or standard curve.

The test is repeated with a solution of unknown concentration, and from its absorbance, the glucose concentration can be read from the graph.