n time interval. A bigger fall in pH per hour means lactic acid is being produced faster.\n\nTherefore, the readings allow them to calculate the **rate of fermentation** (or the rate of enzyme activity). This earns the second mark.","highlights":[{"text":"at regular intervals over 48 hours.","location":"specification"}]}]}],"generatedAt":"2026-07-22T07:43:18.213Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]},{"id":"e5f20f68-7a8e-4c50-b669-a979509ec1dc","label":"b","content":"Describe how the students should display their results in a graph.","markscheme":"- Draw a line graph or scatter graph (do not allow a bar chart or histogram) B1\n- Plot time (in hours) on the horizontal $x$-axis and pH on the vertical $y$-axis B1\n- Plot three separate curves/lines (one for each temperature) B1","marks":3,"order":1,"markingRubric":null,"explanation":null,"options":[]},{"id":"b40cd2bb-fd19-4802-b409-3a23b8e72337","label":"c","content":"Explain the effect of increasing the temperature on the rate of lactic acid production in this experiment.","markscheme":"- Increasing temperature increases the rate of lactic acid production B1\n- Higher temperature increases the kinetic energy of the molecules/enzymes/substrates M1\n- This results in more frequent successful collisions / more enzyme-substrate complexes formed A1","marks":3,"order":2,"markingRubric":null,"explanation":{"methods":[{"id":"particle_collision_explanation","label":"Particle collision explanation","steps":[{"type":"text","order":1,"title":"Compare the pH changes","content":"The starting pH was $7.0$ in every tube. Over $48$ hours, pH fell by $1.0$ at $20^\\circ\\text{C}$, $1.8$ at $30^\\circ\\text{C}$ and $2.6$ at $40^\\circ\\text{C}$.\n\nA larger pH fall in the same time means more lactic acid has been produced, so increasing temperature increases the rate of lactic acid production. This is the **B1** point.","highlights":[{"text":"* Keep each test tube in a water bath at a different temperature: $20^\\circ\\text{C}$, $30^\\circ\\text{C}$, and $40^\\circ\\text{C}$.","location":"specification"},{"text":"* Measure the pH of the solution at regular intervals over 48 hours.","location":"specification"}]},{"type":"text","order":2,"title":"Explain particle energy","content":"Temperature is a measure of how much kinetic energy particles have. **Kinetic energy** is the energy of moving particles.\n\nAt a higher temperature, the glucose molecules and the bacterial enzymes have more kinetic energy, so they move faster. This earns the second marking point (M1)."},{"type":"text","order":3,"title":"Link collisions to rate","content":"Faster-moving glucose molecules collide with enzyme active sites more often. More of these collisions are successful, meaning more enzyme-substrate complexes form each second.\n\nThe enzymes can therefore convert glucose to lactic acid more quickly. This completes the final marking point (A1)."}]}],"generatedAt":"2026-07-22T08:33:22.636Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]},{"id":"ea75473e-e241-4d05-a70a-c005be7ba86a","label":"d","content":"The students plan a further experiment where they boil the bacterial culture first before adding it to the glucose solution.\nPredict what effect this would have on the pH of the solution. Explain your answer.","markscheme":"- Prediction: pH would remain constant / would not decrease / remains at $7.0$ B1\n- Explanation: Boiling kills bacteria or denatures enzymes, changing the shape of the active site so glucose can no longer fit B1","marks":2,"order":3,"markingRubric":null,"explanation":{"methods":[{"id":"predict_boiled_culture","label":"Predict from enzyme activity","steps":[{"type":"text","order":1,"title":"State the pH change","content":"The pH would **remain at $7.0$** (so it would not decrease).\n\nThis clear prediction earns the **B1** mark.","highlights":[{"text":"boil the bacterial culture first before adding

What happens in cells (and what do cells need)?

Question 17

What happens in cells (and what do cells need)? Questions

What happens in cells (and what do cells need)?

Question 17

What happens in cells (and what do cells need)? Questions