Effect of Temperature on the Rate of Amylase Digestion of Starch

How to Write a 12-Mark Investigation Plan

In the BTEC Applied Science Unit 3 exam, learners are asked to write a scientific plan for an investigation. This question is worth 12 marks, so it is important to write clearly, logically, and include all required sections.

This blog post explains how to structure your plan using the example investigation:

the effect of temperature on the rate of digestion of starch by the enzyme amylase.

1. Writing a Clear Hypothesis

A hypothesis is a testable prediction that links the independent variable (temperature) to the dependent variable (rate of starch digestion). A strong hypothesis should:

• Mention temperature

• Refer to enzyme activity

• Predict a trend

This shows understanding of enzyme structure and function and scores well.

2. Selection and Justification of Equipment and Techniques

You must name equipment and explain why it is suitable. Simply listing equipment is not enough for higher marks. Equipment and justification:

• Test tubes – to hold starch and amylase solutions

• Water baths – to maintain constant temperatures

• Thermometer – to check the exact temperature of each reaction

• Stopwatch – to measure the time taken for starch digestion

• Iodine solution – to test for the presence of starch

• Spotting tile – to safely observe colour changes

3. Health and Safety Considerations

You must show awareness of risks and control measures. Health and safety points:

• Wear eye protection when handling iodine solution

• Take care when using hot water baths to avoid burns

• Clean spills immediately to prevent slips

• Wash hands after handling biological materials

These points show safe laboratory practice.

4. Step-by-Step Method for Data Collection

This is the largest section and should be written in logical steps.

Method:

1. Set water baths to a range of temperatures (e.g. 20 °C, 30 °C, 40 °C, 50 °C).

2. Add a fixed volume of starch solution to labelled test tubes.

3. Place test tubes in water baths and allow them to reach the correct temperature.

4. Add the same volume of amylase solution to each tube and start the stopwatch.

5. Every 30 seconds, remove a small sample and add it to iodine on a spotting tile.

6. Record the time when iodine no longer turns blue-black.

7. Repeat each temperature at least three times to improve reliability.

5. Quantities Measured

You must clearly state what is measured. Examples:

• Time taken for starch to disappear (seconds)

• Temperature of reaction (°C)

• Volume of starch and amylase solutions (cm³)

6. Number and Range of Measurements

This demonstrates planning for reliability. Example:

• Temperatures tested: 20 °C–50 °C at 10 °C intervals

• Each temperature repeated three times

• Mean time calculated for each temperature

7. Control Variables

Control variables are factors kept constant to ensure a fair test. Examples include:

• Concentration of starch solution

• Concentration of amylase

• pH of the reaction mixture

• Total volume of solution

• Method of mixing

Each control variable should be mentioned briefly with a reason.

8. Brief Method of Data Analysis

You must explain how results will be processed, not just collected. Example:

• Calculate the mean time for starch digestion at each temperature

• Convert time into rate of reaction

• Plot a graph of rate vs temperature

• Identify the optimum temperature for amylase activity

Exam Tip for Full Marks

High-scoring answers:

• Use subheadings or clear paragraphs

• Link enzyme structure to temperature effects

• Include justification, not just description

• Cover every bullet point in the question

Final Takeaway

This type of planning question is not about memorising a method — it’s about showing that you can design, justify, and evaluate a scientific investigation. Using clear structure and scientific language is the key to accessing the higher mark bands.

Model answer -  Plan to Investigate the Effect of Temperature on the Rate of Digestion of Starch by Amylase

Hypothesis

As the temperature increases, the rate of digestion of starch by the enzyme amylase will increase up to an optimum temperature, after which the rate will decrease because the enzyme becomes denatured.

Selection and justification of equipment and techniques

Test tubes will be used to contain the starch and amylase solutions. Water baths set to different temperatures will be used to ensure the reactions occur at constant, controlled temperatures. A thermometer will be used to check that each solution reaches the correct temperature before the reaction starts. A stopwatch will be used to measure the time taken for starch digestion. Iodine solution will be used to test for the presence of starch, as iodine turns blue-black in the presence of starch but remains brown when starch has been fully digested to maltose. A spotting tile will be used to safely observe colour changes.

Health and safety

Eye protection will be worn when handling iodine solution, as it is an irritant. Care will be taken when using hot water baths to avoid burns. Any spills will be cleaned immediately, and hands will be washed after completing the investigation.

Method for data collection

A fixed volume of starch solution will be placed into labelled test tubes. Water baths will be set to a range of temperatures, such as 20 °C, 30 °C, 40 °C and 50 °C. The test tubes will be placed in the water baths and allowed to equilibrate. The same volume of amylase solution will then be added to each tube, and the stopwatch started. At regular intervals, a sample will be tested with iodine on a spotting tile. The time taken for iodine to no longer turn blue-black will be recorded as the time for starch digestion. The experiment will be repeated three times at each temperature.

Quantities, range, and repeats

The quantities measured will include temperature (°C) and time taken for starch digestion (seconds). Temperatures between 20 °C and 50 °C will be tested, and each temperature will be repeated three times to improve reliability.

Control variables

The concentration and volume of starch and amylase will be kept constant, as well as the pH of the reaction mixture. The same method of mixing and sampling will be used throughout to ensure a fair test.

Data analysis

Mean times will be calculated for each temperature. These values will be used to calculate reaction rate, and a graph of rate of reaction against temperature will be plotted to identify the optimum temperature for amylase activity.

Why this would score full marks

✔ Clear hypothesis linked to enzyme theory

✔ Justified choice of equipment and technique

✔ Appropriate health and safety considerations

✔ Logical, step-by-step method

✔ Quantities, ranges, repeats, and control variables included

✔ Clear explanation of how data will be analysed