You will complete ten required practical activities if you are studying GCSE Biology and twenty-one if you are studying GCSE Combined Science. You could be asked questions about the methods, safety precautions you might take, results and conclusions of these experiments.
Lugworms (Arenicola marina) live in burrows in the sand on beaches. At one end of the burrow is a hole and at the other end is a mound of sand, called the cast, which the lugworm has removed from the burrow. Each burrow is occupied by one lugworm only.
Owen was asked by his teacher to estimate the number of lugworms, on a section of Whiteford Beach on Gower, by counting the number of casts. Owen decided to use 1 m2 quadrats to estimate the number of lugworms present in an area of the beach measuring 80 × 40 m.
These questions have been written by Bitesize consultants as suggestions to the types of questions that may appear in an exam paper.
Which of the following methods would be the correct way for Owen to use the quadrats to sample the number of lugworms? [1 mark]
Tick (✓) the correct answer.
|Place the quadrats where there are lots of casts|
|Place the quadrats randomly within the sample area|
|Place the quadrats carefully so as not to damage the casts|
Place the quadrats randomly within the sample area 
Owen counted the number of casts in 10 quadrat samples. The table below shows his results.
|Quadrat number||Number of casts|
(i) Calculate the mean number of casts per quadrat. [1 mark]
(ii) Estimate the number of lugworms in the section of the beach using the following equation. [2 marks]
(i) Mean = 6.2 
(ii) Estimated number of lugworms = 6.2 × 3200  = 19,840 
HINT- In most calculation questions there is a mark available for writing out the equation used and then another for the answer. The correct answer will get both marks automatically but just in case a calculation error is made it is always good practice to write out the workings.
Suggest why this sampling method would not be suitable for estimating the population of earthworms in an area of grassland. [1 mark]
Any one from:
Two students visited two locations and measured the number of lichens on nine trees in each location. Their results are below.
|Location||Tree 1||Tree 2||Tree 3||Tree 4||Tree 5||Tree 6||Tree 7||Tree 8||Tree 9|
Calculate the mean for each location. Give your answer to one decimal place. [2 marks]
London mean = 5.8
North Wales mean = 12.9
One of the students said "This definitely proves that there are more lichens in North Wales than London."
Suggest why the second student might not have been so sure. [2 marks]
The have only looked at nine trees in one location in North Wales and London. They would need to sample many, many more trees in many different locations to prove anything.
Describe the method used to investigate the effect of changing light intensity on the rate of photosynthesis. [6 marks]
In order to investigate how nitrogen is recycled by bacteria in soil, the apparatus shown in the diagram was kept at 25°C for two days.
At the start, the indicator paper in both tubes was yellow. After two days, the indicator paper in tube A was green but the indicator paper in tube B was still yellow.
A word equation representing the reaction in tube A is:
What can you conclude about the results obtained from tube A? [2 marks]
What can you conclude about the results obtained from tube B? [3 marks]