5.3.7Topic 5 · On the Wild Side

Practical- Temperature and Development of Organisms — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

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5.3.7 Practical- Temperature and Development of Organisms — Edexcel A Level Biology A (SNAB) 9BI0 notes: Plan, carry out and evaluate an investigation into the effect of temperature on the development of an organism, with correct controls, variables and analysis.This core practic…

Independent variable
Control variables
Reliability
Precision and validity
Improvements
Exam-style question 1

Section 1 of 9Aim and biological background

This core practical investigates how temperature affects the rate of development of a small organism.

Aim and biological background

Common choices are the time taken for brine shrimp (Artemia) eggs to hatch, the rate of seed germination, or the time for fruit fly (Drosophila) or Daphnia development.

As an ectotherm, the organism has a rate of development that depends on the activity of its enzymes (see the previous lesson).

Over the tolerated range, a higher temperature increases the rate until it approaches the upper limit, where development fails.

Section 2 of 9Variables

Independent variable

Independent variable temperature, for example 10, 15, 20, 25 and 30 °C, set using water baths, incubators or temperature-controlled rooms. Monitor with a thermometer in a control tube.

Dependent variable

Dependent variable a measure of development, such as the percentage of eggs hatched after a set time, the mean time to hatch, or the number of seeds germinated per day (radicle emerged).

Control variables

Control variables number and source of eggs or seeds, volume and salinity of water, light, oxygen supply (aeration), size of container and the time of observation.

Section 3 of 9Method outline

Prepare a salt solution of constant concentration, and put equal volumes in labelled containers.

Equilibrate containers at each temperature.

Add the same number of eggs (for example 50) or seeds to each container.

Return each to its temperature for a fixed period or observe at regular intervals.

Count the number hatched or germinated, using a hand lens or low-power microscope where needed.

Repeat at least three times at each temperature, and calculate the mean.

Ethical and safety points

treat living organisms humanely, wash hands after handling, use only the stated number of organisms, and dispose of them as instructed.
Avoid stressing animals with extreme temperatures.

Section 4 of 9Processing and presenting results

Calculate the mean percentage hatching or the mean rate (1 / time to hatch) for each temperature.

Plot temperature on the x-axis and the dependent variable on the y-axis, with units, and join points with straight lines or a smooth curve.

Include error bars if data are replicated, or use standard deviation to compare variability.

You can also calculate the Q₁₀ between pairs of temperatures.

The expected pattern is an increase in rate with temperature to an optimum, followed by a fall at high temperatures when enzymes are denatured or conditions are lethal.

Use a statistical test when appropriate, for example a correlation test or a t-test between two temperatures.

Section 5 of 9Evaluation

Reliability

Reliability repeats and mean values reduce the effect of anomalies; identify anomalies and exclude or repeat them.

Precision and validity

Precision and validity eggs vary in viability, so use a large number from the same batch. Temperatures may drift, so monitor them.

Improvements

Improvements more temperatures near the optimum, blind counting, using a thermostatic water bath, and a longer observation period.

Section 6 of 9Choosing a suitable organism and range and statistical analysis

The temperatures chosen must be within the range that the organism can tolerate, determined by a preliminary trial.

Choosing a suitable organism and range and statistical analysis

For brine shrimp eggs the useful range is about 15 to 30 °C.

For seeds, such as mustard or cress, a germination test in damp conditions between 5 and 35 °C is suitable.

In a preliminary test you also decide how long to observe and what counts as hatched or germinated: define the end point clearly, for example radicle at least 2 mm long.

Use equal intervals of temperature so a graph can be plotted evenly, and include a range that surrounds the expected optimum. Record temperatures at the start and end of the experiment, and report the mean.

The results can be tested for correlation using a Spearman rank test to see whether the increase in the rate of development with temperature is significant, with the null hypothesis that there is no relationship between temperature and rate.

Choosing a suitable organism and range and statistical analysis

A calculated value above the critical value at p = 0.05 allows the null hypothesis to be rejected.

Remember that the test shows only that a correlation is unlikely to be due to chance; explaining the cause requires the biology of enzyme activity.

Safety and ethics also deserve a sentence in a plan.

Choosing a suitable organism and range and statistical analysis

Brine shrimp should be returned to suitable saltwater or disposed of as directed, hands should be washed, and electrical equipment such as a heated water bath must be kept away from spilt water.

Any use of animals should follow the principle of using the smallest number of organisms needed to get reliable results.

Section 7 of 9Exam-style questions

Describe how you would investigate the effect of temperature on the hatching of brine shrimp eggs. [5]5 marks
Mean times to hatch were 60 h at 15 °C, 36 h at 20 °C and 24 h at 25 °C. Calculate the rate of development (1/time) at each temperature and describe the trend. [3]3 marks
Explain why it is important to use the same number and batch of eggs at each temperature. [2]2 marks

Section 8 of 9Key terms

Term	Meaning
Independent variable	The variable deliberately changed.
Dependent variable	The variable measured as the response.
Control variable	A variable kept constant to make the test fair.
Reliability	Whether repeated measurements give consistent results.
Anomaly	A result that does not fit the pattern.
Water bath	Apparatus that holds a liquid at a constant temperature.
Viability	The ability of an egg or seed to develop.

Section 9 of 9Exam technique

Allowing more than one variable to change, for example putting some containers in the light and others in the dark.

Taking a single measurement per temperature and calling the result reliable. Repeats are needed.

Plotting time to hatch as the rate. A rate is the reciprocal of time.

Describing the effect without explaining it in terms of enzyme activity.

Last updated: 13 October 2026

Section 1 of 9Aim and biological background

Section 2 of 9Variables

Section 3 of 9Method outline

Section 4 of 9Processing and presenting results

Section 5 of 9Evaluation

Section 6 of 9Choosing a suitable organism and range and statistical analysis

Section 7 of 9Exam-style questions

Describe how you would investigate the effect of temperature on the hatching of brine shrimp eggs. [5]5 marks

Mean times to hatch were 60 h at 15 °C, 36 h at 20 °C and 24 h at 25 °C. Calculate the rate of development (1/time) at each temperature and describe the trend. [3]3 marks

Explain why it is important to use the same number and batch of eggs at each temperature. [2]2 marks

Section 8 of 9Key terms

Section 9 of 9Exam technique

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