Understanding how to approach exam questions helps to boost exam performance. Question types will include multiple choice, structured, mathematical and practical questions.

You will complete 21 required practical activities if you are studying GCSE combined science: Trilogy. You could be asked questions about the apparatus, methods, safety precautions, results, analysis and evaluation of these experiments.

In this Bioenergetics topic, you should have undertaken one required practical activity before your exam:

Required Practical Activity 6 - Investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism.

There will be a number of different types of practical based questions. Some will be on the set required practicals, some will cover the working scientifically terms and some will be on other science practicals which you might have done in class. Use all the information given in the question particularly any diagrams to help you understand what the question is about.

*These questions have been written by Bitesize consultants as suggestions to the types of questions that may appear in an exam paper.*

- Question
Describe an experiment to investigate the effect of the presence of chlorophyll on photosynthesis.

**[6 marks]**Marking points are made from:

- use a plant with variegated leaves
- kill and preserve a leaf by dipping it in boiling water
- decolorize/remove chlorophyll from the leaf by immersing it in hot alcohol
- dip it in water to soften it
- place in a Petri dish and flood with iodine solution
- a blue-black colour indicates the presence of starch
- the parts of the leaf that contained chlorophyll will stain blue-black, indicating that chlorophyll is required for photosynthesis

- Question
A student investigated the effect of different parts of the spectrum on photosynthesis. She covered three test tubes containing pond weed with plastic filters.

She counted the bubbles produced over one minute intervals.

Suggest how the student could check the repeatability of her results.

**[2 marks]**Marking points are made from:

- by carrying out the experiment/repeating it several times
- the student can see how close they are together, ie repeatable

Note that this question is worth two marks, so it isn't sufficient to just say, 'repeat them'.

The question includes the word 'how', so you have to link the term, repeatability, to how repeating the results enables the student to check this.

- Question
Suggest why checking the reproducibility of her results would be difficult.

**[2 marks]**Marking points are made from:

- reproducibility means how consistent the results from different groups carrying out the same experiment are
- this would not be possible to achieve unless other groups were using the same plant, or an identical mass of plant, or went on to work out a measurement that was comparable, eg the rate of photosynthesis per gram of plant tissue

- Question
The student's graph of her results is shown below.

Explain why the student drew a bar chart and not a line graph.

**[2 marks]**The variable on the x-axis - part of the spectrum - is not continuous.

Bar charts are used when variables are not continuous - line graphs for continuous data.

- Question
Use the bar chart to complete the student's table of results.

**[3 marks]**Colour of light Number of bubbles Blue Green Red Colour of light Number of bubbles Blue 78 Green 9 Red 74

A student was investigating the effect of light intensity on the rate of photosynthesis.

She positioned an LED lamp at different distances from a boiling tube containing a piece of pondweed.

She measured the volume of oxygen produced.

- Question
Suggest why she used an LED lamp.

**[1 mark]**To provide the illumination necessary, but she used an

*LED*lamp so that the temperature would not be raised/stay constant [1].

- Question
Tungsten or halogen bulbs would cause the temperature to rise. Temperature is one of the variables that needs to be controlled.

What variables need to be controlled?

**[4 marks]**Marking points are made from:

- temperature
- concentration of carbon dioxide
- type of light source
- same light source
- duration of the experiment

- Question
Plot a graph of volume of oxygen produced over distance of the pondweed from the lamp.

**[4 marks]**The student's results are shown below.

Distance to LED Rate 5 cm 160 μl 10 cm 41 μl 15 cm 18 μl 20 cm 10 μl 25 cm 6 μl Axes and scales correct and labelled [1].

All points plotted correctly [2], or two to three points plotted correctly [1].

Points joined together correctly [1].

Follow the instructions on the exam paper when connecting points on a graph.

Join points dot-to-dot when told to do so, or draw lines of best fit to illustrate trends.

- Question
Complete the middle column of the table by calculating the inverse square, , for the distances used to investigate the effect on light intensity on photosynthesis of pondweed.

**[4 marks]**Distance Rate 5 cm 160 μl 10 cm 41 μl 15 cm 18 μl 20 cm 10 μl 25 cm 6 μl Distance Rate 5 cm 0.0400 160 μl 10 cm 0.0100 41 μl 15 cm 0.0044 18 μl 20 cm 0.0025 10 μl 25 cm 0.0016 6 μl Example calculation:

For instance, for the lamp 5 cm away from the plant:

You would be awarded 4 marks for all five answers correct, or 3 marks for 3-4 correct. All of your results should be to the same number of decimal places in order to avoid dropping a mark. Since the distances of 20 cm and 25 cm give the inverse square of the distance value as requiring four decimal places, the other values need to reflect the same number of decimal places - as the answer table shows.

- Question
Plot a graph of the volume of oxygen produced against .

**[4 marks]**Axes and scales correct and labelled [1].

All points plotted correctly [2], or two to three points plotted correctly [1].

Appropriate line - linear - of best fit [1].

Make sure that you use equal divisions on the x-axis - the scale you use must be linear.

Note that there is a linear relationship between the inverse square of distance and volume of oxygen produced or rate of oxygen production.