Biology Required Practicals and Data Analysis
The GCSE Biology required practicals are the ten investigations every student must carry out, covering microscopy, culturing microorganisms, osmosis, food tests, the effect of pH on amylase, the rate of photosynthesis, reaction time, plant responses, field sampling with quadrats and transects, and decay. Roughly 15 percent of the marks on the papers test practical skills such as naming variables, justifying repeats, identifying anomalies and drawing conclusions that go no further than the data allows.
Before you start
No specific prerequisites - this is a good place to start.
Method
- Name the three variable types before anything else: the independent variable is the one you change, the dependent variable is the one you measure, and control variables are everything you keep the same so the comparison is fair.
- Describe a method in numbered steps a stranger could repeat: state the apparatus, the quantities, the range and interval of the independent variable, how long each run lasts, and exactly what you measure and when.
- Justify repeats: repeating and taking a mean reduces the effect of random error and lets you spot anomalies. Repeats do not fix a systematic error, such as a balance that reads 0.2 g high, which is why zeroing equipment is a separate point.
- Process the data before drawing conclusions: identify anomalous results, exclude them from the mean and say that you have, then calculate the mean to the same number of decimal places as the raw readings.
- Calculate a rate as change divided by time, and always state the unit (for example cubic centimetres of oxygen per minute, or bubbles per minute). For a graph, the rate is the gradient, so read off two clear points and divide the change in y by the change in x.
- Write conclusions in three parts: state the pattern, quote a pair of figures from your own data as evidence, and explain it with biology. Then evaluate, naming one specific improvement (better resolution, wider range, more repeats) rather than 'be more accurate'.
Worked example
A student investigates the effect of light intensity on the rate of photosynthesis by counting bubbles of oxygen released by pondweed. At a lamp distance of 20 cm the student counts 36, 40 and 38 bubbles in two minutes, and one run of 62 bubbles. Calculate the mean rate in bubbles per minute, and state how the anomaly should be treated.
- Identify the anomaly: 62 is far outside the cluster of 36, 40 and 38, so it is anomalous and should be excluded from the mean, with that exclusion stated in the answer.
- Add the remaining results: 36 + 40 + 38 = 114 bubbles.
- Divide by the number of results: 114 / 3 = 38 bubbles in two minutes.
- Convert to a rate per minute: 38 / 2 = 19 bubbles per minute.
- State the treatment of the anomaly: it is excluded from the mean but not deleted from the results table, and the likely cause (for example a bubble released from a previous run, or the lamp being moved) is given.
- Final answer: mean rate = 19 bubbles per minute, with the 62-bubble result identified as an anomaly and excluded.
Practice questions
Try each question, then tap to reveal the answer.
Q1Define the independent variable.Show answer
Answer: The variable that the experimenter deliberately changes.
Q2Why does taking repeat readings and calculating a mean improve the data?Show answer
Answer: It reduces the effect of random error and allows anomalies to be identified. It does not remove systematic error.
Q3State the difference between resolution and accuracy.Show answer
Answer: Resolution is the smallest change an instrument can detect (a balance reading to 0.01 g has a higher resolution than one reading to 0.1 g); accuracy is how close a measurement is to the true value.
Q4A student measures 24 cubic centimetres of gas in 3 minutes. Calculate the rate.Show answer
Answer: 24 / 3 = 8 cubic centimetres per minute.
Q5Why must the same volume of solution be used in every tube in an enzyme investigation?Show answer
Answer: It is a control variable: changing the volume would change the number of enzyme or substrate molecules, so any difference in rate could not be attributed to the independent variable.
Q6Name the apparatus used to estimate the population of a slow-moving or non-moving species in a field.Show answer
Answer: A quadrat, placed using random number coordinates for a population estimate, or along a transect line to study how distribution changes with distance.
Q7In the microbiology practical, why are agar plates incubated at 25 degrees Celsius in schools rather than at 37 degrees Celsius?Show answer
Answer: To reduce the risk of growing pathogens that are adapted to human body temperature.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
A student investigates how temperature affects the rate at which amylase breaks down starch. Describe how the student should control the pH of the reaction, and explain why pH must be controlled.
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A student measures the mass of five potato cylinders before and after 30 minutes in sugar solutions. One cylinder is not dried before its final mass is taken. Explain the effect this has on the result, and state whether it is a random or a systematic error.
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A student claims: 'My results prove that light intensity is the only factor that limits photosynthesis.' Evaluate this claim, and describe two improvements to the investigation.
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See real GCSE Science past-paper questions, with official mark schemes →
Free printable worksheet
Want more practice on paper? Download the biology required practicals and data analysis worksheet pack - 18 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 8 of GCSE Biology Workbook, the whole course as one free printable PDF.
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