Communicating in Biology
Communicating in biology covers the science process skills, the three types of variable, how to write a testable hypothesis, and how to design and report a scientific investigation.
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Science process and manipulative skills
Content standard 1.3 covers the skills used to carry out a scientific investigation. Science process skills include observing, classifying, measuring and using numbers, making inferences, predicting, communicating, and using space-time relationships.
Manipulative skills are the practical skills of handling apparatus and specimens correctly, taking accurate measurements, and carrying out a technique safely and in the right sequence.
Variables and hypothesis
- Manipulated variable, the factor you deliberately change in the investigation.
- Responding variable, the factor you measure or observe, which changes because of the manipulated variable.
- Constant (fixed) variable, every other factor that must be kept the same so the comparison is fair.
- Hypothesis, a statement predicting the relationship between the manipulated and responding variables, written so it can be tested by an experiment.
Designing and reporting an investigation
A full investigation is usually reported with these sections: aim (the question being investigated), variables (manipulated, responding, constant), hypothesis, list of apparatus and materials, a step-by-step procedure, tabulated results, and a conclusion that states whether the results support the hypothesis. Data is usually presented as a results table and, where appropriate, a line graph with the manipulated variable on the x-axis and the responding variable on the y-axis.
How it is examined
Exam questions describe an experimental scenario and ask you to identify the manipulated, responding and constant variables, to state a suitable hypothesis, or to complete a results table or graph. You may also be asked to state one precaution needed to make the investigation valid, such as repeating a reading or controlling a variable that was not mentioned.
Presenting data in tables and graphs
Results are recorded in a table with the manipulated variable in the first column and the responding variable beside it; each column heading names the quantity and its unit, for example 'Temperature (°C)'. Readings taken more than once are averaged, and the table is ruled so that every value sits in its own box.
Continuous numerical data is then plotted as a line graph, with the manipulated variable on the x-axis and the responding variable on the y-axis. The axes are labelled with quantity and unit, a sensible scale is chosen so the points fill most of the grid, and the points are plotted accurately and joined with a smooth curve or a straight line of best fit.
Discontinuous or categoric data is shown as a bar chart instead.
Key terms
- Hypothesis, a testable statement predicting how the responding variable changes with the manipulated variable.
- Manipulated variable, the one factor the investigator deliberately changes.
- Responding variable, the factor measured or observed as a result of the change.
- Controlled variable, a factor kept constant so the test stays fair.
- Inference, an early explanation drawn from an observation, which can later be tested.
Worked exam-style question
Question. A student investigated how the temperature of a water bath affects the time taken for the enzyme amylase to completely digest starch. She tested the reaction at five temperatures and used iodine solution to find the moment when no starch remained.
(a) State the manipulated variable and the responding variable. (b) State two variables she must keep constant to make the test fair.
(c) Write a suitable hypothesis for this investigation. (d) Suggest one way she could make her results more reliable.
Model answer. (a) The manipulated variable is the temperature of the water bath; the responding variable is the time taken for the starch to be completely digested. (b) Any two controlled variables, for example the concentration of amylase, the volume of starch solution, and the pH of the mixture.
(c) A suitable hypothesis: as the temperature increases, the time taken to digest the starch decreases, up to the optimum temperature. (d) Repeat the experiment at each temperature and calculate the average (mean) time, so that anomalous readings can be identified and ignored.
Practice question
A student placed a piece of pondweed in sodium hydrogencarbonate solution and counted the number of gas bubbles released in one minute at different distances from a lamp. (a) Identify the manipulated and responding variables.
(b) State one variable that must be kept constant.
Exam tip
Source:SRC-DSKP-EN
Frequently asked questions
What is the difference between the manipulated and responding variable?
How do I write a good hypothesis for a biology investigation?
What makes an investigation a fair test?
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