(b) Investigation planning and methods
- Syllabus
- 2024
- Topic
- —
- Level
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Learning objectives
—Devise and plan investigationsDevise and plan investigations, using scientific knowledge and understanding when selecting appropriate techniques.—Appropriate and safe experimental methodsDemonstrate or describe appropriate experimental and investigative methods, including safe and skilful practical techniques.
Build an investigation that answers the question
A valid investigation plan is a connected chain: change one relevant condition, measure a response that answers the question, keep other influential conditions consistent, repeat the comparison, and state exactly how the evidence will be collected.
| Planning move | Decision to record |
|---|---|
| 1 define the outcome | translate the question into a measurable response, such as gas volume per minute, mass lost in a fixed time, or number of visits in ten minutes |
| 2 choose the change | use a sensible range or clear comparison for the condition being investigated; include a reference condition when it makes the effect interpretable |
| 3 select the technique | choose apparatus and a measurement that genuinely indicate the biological process, with units and a stated time interval |
| 4 control other influences | keep relevant biological material and environmental conditions the same so they cannot provide a rival explanation |
| 5 make evidence dependable | repeat each condition using independent samples and calculate a representative result such as a mean |
| 6 specify the comparison | state which results will be compared to answer the original question |
For decomposition at different temperatures, use equal masses and the same type of plant material and decomposer. Keep moisture, pH and oxygen availability consistent. Measure carbon dioxide volume produced in the same time at each stated temperature, repeat each temperature, then compare mean volumes per unit time.
A list of apparatus is not a plan. Each item must have a purpose, and the measured response must connect to the biological process. Changing several conditions together prevents the result from showing which condition caused the difference.
Choose an appropriate and safe practical method
An experimental method is appropriate when its apparatus, sequence and measurement produce evidence that answers the aim. It is safe when each real hazard is identified and controlled without preventing the method from working.
| Experimental need | Appropriate technique and reason |
|---|---|
| measure gas production | collect gas in a gas syringe or inverted measuring cylinder; this gives a volume rather than an uncertain bubble count |
| measure a rate | record a defined change and divide by a stated time, or measure the time taken for a defined change |
| maintain temperature | use a thermostatically controlled water bath, check with a thermometer and allow samples to reach the set temperature before timing |
| compare biological samples | use the same species and matched starting size, mass, age or condition where these could affect the response |
| handle measured quantities skilfully | zero the instrument, read scales at eye level where relevant, use suitable units and apply the same timing and endpoint to every condition |
Plan safety as hazard → possible harm → specific control. For hot apparatus, use a heatproof mat and suitable handling tools and allow equipment to cool; for irritant solutions, wear eye protection and avoid skin contact; for microorganisms, use clean technique, keep cultures contained and wash hands. Use only controls relevant to the stated method.
Writing 'be careful' or listing gloves and goggles for every investigation is not a safety method. A precaution is useful only when it reduces an identified risk. Likewise, precise apparatus cannot rescue a method that measures the wrong outcome or changes its procedure between conditions.