1. Anchoring in the Mark Scheme—Bottom-Up or Top-Down?
Bottom-Up Approach:
- Assume a script is Level 1
- If it clearly ticks all Level 1 boxes, check for Level 2 elements
- Only award Level 3 if all advanced requirements (method, detail, analysis, language) are fully present and correct
Top-Down Check:
- Could the answer possibly get full marks?
- If not, what is missing? Move one level down until the descriptor is satisfied
2. Levels Explained: What You're Actually Awarding
Level 3 (5–6 marks) – AO1, AO2, AO3 clearly evident:
- All equipment and steps precise; method is clear, sequential, reproducible
- Measurement and variables fully specified (independent, dependent, controls)
- Correct, logical explanation linking to key science; high-level terms (e.g. denature, optimum, lock and key)
- Data/graph described with specific values and trends referenced
- Safety covered
- Clear, coherent, near-flawless writing
Level 2 (3–4 marks) – Mostly AO1, some AO2/AO3, missing depth or detail:
- Method present but less detail or clarity, or missing some variables/controls
- Partial analysis of data/graph OR basic explanation (e.g., describes trend but not full science)
- Some science terms used
Level 1 (1–2 marks) – Just AO1, mostly recall/list:
- Gist of the practical; little or no sequencing/structure
- Minimal analysis, lots of gaps, basics only
3. Useful Framework: EMMAS With AO Coding
You can use EMMAS to structure both students' answers and your marking:
| EMMAS Element | AO Code | What to Look For |
|---|---|---|
| Equipment | AO1 | All necessary items named: test tube, beaker, water bath, buffer, iodine, etc. |
| Method | AO2 | Logical, step-by-step sequence, repeats, controls |
| Measurements | AO2 | Specific timings/readings; equipment like stopwatch, thermometer |
| Analysis | AO3 | Trends from data, use of graph, quotes actual values, correct science explained |
| Safety | AO2 | Eye protection, using water baths, handling glass safely |
4. Model Student Snippets by AO (with Bullet-Point Examples)
AO1 (Knowledge—recall and facts)
- "Amylase breaks down starch into maltose in the presence of water."
- "Enzymes are proteins that have a specific active site (lock and key model)."
- "The independent variable in my experiment is the temperature. The dependent variable is the speed the starch disappears."
- "A water bath is used to keep the temperature of the reaction mixture constant."
AO2 (Application—using knowledge logically)
- "Add 5 cm³ of starch solution to a test tube, then add 1 cm³ of amylase and 1 cm³ of buffer solution at pH 7."
- "Place the test tube in a water bath set to 37°C for 2 minutes to allow everything to reach temperature."
- "Every 30 seconds, use a pipette to take a sample from the mixture and add it to iodine solution on a spotting tile."
- "Repeat the experiment at 5 different temperatures: 20°C, 30°C, 40°C, 50°C, and 60°C in each case with at least 3 repeats per temperature."
- "Make sure to keep the concentration of starch solution and amylase and the pH the same in all experiments, to control variables."
- Measurement precision: "Use a digital stopwatch to time how long it takes for the iodine to remain brown (indicating all starch is gone)."
AO3 (Analysis—graph/data, explanation, reasoning)
- "I would plot a graph of temperature (x-axis, the independent variable) against rate of starch breakdown (y-axis, calculated as 1/time)."
- "The graph should be a bell-shaped curve, rising to a maximum rate (optimum) at 37°C, then falling sharply at higher temperatures."
- "For example, at 30°C, the mean rate is 0.25 s⁻¹, but at 60°C, the mean rate drops to almost zero."
- "At high temperatures, the rate decreases as the enzyme denatures—the active site changes shape, so substrate can no longer bind."
- "This shows how the protein structure is altered by heat, supporting the lock and key model of enzyme action."
5. Gold Standard 6-Mark Model Answer (AO1, AO2, AO3, EMMAS)
Question: Describe how you would accurately investigate the effect of temperature on the action of amylase on starch and analyse your results. [6 marks]
Model Answer:
"First, collect all equipment: test tubes, beakers, water baths at set temperatures (e.g., 20°C, 37°C, 60°C, 80°C), pipette, digital stopwatch, starch solution, amylase solution, buffer at pH 7, and iodine solution. (AO1—equipment)
To begin the method, add 5 cm³ starch solution and 1 cm³ buffer to a test tube, then place in the 37°C water bath for 2 minutes. (AO2—method)
Add 1 cm³ of amylase, stir, and start the stopwatch. Every 30 seconds, remove a small sample with a pipette and add it to iodine solution on a spotting tile. Record the time taken for the iodine to remain brown (showing all starch has broken down). Repeat this process for at least five different temperatures, such as 20°C, 30°C, 40°C, 50°C, 60°C, making sure the volume and concentration of all solutions and the pH are the same each time. (AO2—control, repeats, stepwise)
Measurement is done using a graphical approach; plot temperature (independent variable, x-axis) against rate of reaction (y-axis, calculated as 1/time for starch breakdown at each temperature). (AO2/3—measurement and analysis)
The data should show the rate increases with temperature until around 40°C, reaching a peak or optimum (e.g., 0.5 s⁻¹ at 40°C), then decreases at higher temperatures due to denaturation of the enzyme's active site (AO3—using data from the graph, correct science explanation).
Amylase is a protein that works on a "lock and key" model. High temperatures, above 50°C, cause enzyme denaturation where the active site changes shape and can no longer bind substrate; this results in a much lower rate. (AO1/AO3—key science explanation)
Wear safety goggles and handle hot water baths with care to prevent scalding. (AO2—safety)"
[EMMAS ticks: ✓ Equipment ✓ Method ✓ Measurement ✓ Analysis ✓ Safety. AO1/2/3 all covered.]
6. Lower-Level Answers for Comparison & Boundary Marking
Level 2 (4 marks):
"Use water baths at different temperatures and test tubes with amylase and starch. Use a timer and record how long it takes for the starch to disappear with iodine. Plot a graph to show the result. Keep everything else the same."
Missing: "lock and key", no mention of denaturation, doesn't explicitly say what's on axes or how variable is controlled, no specific numbers from graph.
Level 1 (2 marks):
"Mix enzyme and starch and warm it. Time how long it takes. Try higher temperature."
Issues: Gist only—not enough detail, no science vocabulary, no steps, no graph, no measured variables, no safety.
Feedback Example:
"To access the highest marks, clearly state your variables, describe all...""