ze)** for both samples. Larger discs contain more photosynthesising tissue, so they could produce oxygen differently and affect the time taken to rise.\n\nThis is a second valid control variable and earns **B1**.","highlights":[{"text":"Cut 10 leaf discs from a sun leaf.","location":"specification"},{"text":"Repeat this using 10 leaf discs from a shade leaf.","location":"specification"}]},{"type":"text","order":3,"title":"Control the temperature","content":"Keep the **temperature** the same for both syringes. Temperature affects the rate of photosynthesis, so a difference in temperature could change the time taken for the discs to rise.\n\nThis is a third valid control variable and earns **B1**.","highlights":[{"text":"two different environmental conditions","location":"specification"}]}]}],"generatedAt":"2026-07-22T12:16:18.356Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]},{"id":"97193776-1e54-4431-83e6-e00e6d06ca3c","label":"b","content":"Explain why the leaf discs rise to the top of the syringes.","markscheme":"- Oxygen gas ($O_2$) is produced as a product of photosynthesis M1\n- The gas is trapped in the intercellular air spaces of the leaf tissue (spongy mesophyll), making the discs less dense (buoyant) so they rise A1","marks":2,"order":1,"markingRubric":null,"explanation":{"methods":[{"id":"photosynthesis_buoyancy","label":"Link photosynthesis to rising","steps":[{"type":"text","order":0,"title":"Identify the gas","content":"The leaf discs carry out photosynthesis. Oxygen is made as a product of this process.\n\n**Examiner point (M1): oxygen is produced as a product of photosynthesis.**","highlights":[{"text":"Explain why the leaf discs rise to the top of the syringes.","location":"specification"}]},{"type":"text","order":1,"title":"Explain the rise","content":"The oxygen becomes trapped in the intercellular air spaces of the spongy mesophyll (the leaf tissue with air spaces). This makes each disc less dense than the solution, so it is buoyant and rises.\n\n**Examiner point (A1): oxygen is trapped in intercellular air spaces in the spongy mesophyll, making the discs less dense and buoyant so they rise.**","highlights":[{"text":"rise to the top of the syringes","location":"specification"}]}]}],"generatedAt":"2026-07-22T08:25:01.958Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]},{"id":"dbbc2e63-b173-49f9-8f63-268bea9a285a","label":"c","content":"Describe how the student could adapt this method to investigate the effect of carbon dioxide concentration on the rate of photosynthesis for the sun leaves.","markscheme":"- Prepares several different concentrations of sodium hydrogen carbonate solution M1\n- Places 10 sun leaf discs into each syringe and measures the time taken for the discs to rise at each concentration A1\n- Controls other variables by keeping the light source at a fixed distance or maintaining temperature constant (e.g., using a water bath) M1","marks":3,"order":2,"markingRubric":null,"explanation":{"methods":[{"id":"vary_carbon_dioxide","label":"Vary carbon dioxide","steps":[{"type":"text","order":1,"title":"Vary the concentration","content":"Prepare several different concentrations of sodium hydrogen carbonate solution. This changes the carbon dioxide concentration available to the sun leaf discs.\n\n**This earns M1.**","highlights":[{"text":"effect of carbon dioxide concentration on the rate of photosynthesis for the sun leaves","location":"specification"}]},{"type":"text","order":2,"title":"Time the discs","content":"Put $10$ sun leaf discs into each syringe, using one concentration in each syringe. Measure and record the time taken for the discs to rise at every concentration.\n\n**This earns A1.** Keeping the number and type of leaf discs the same makes the comparison valid.","highlights":[{"text":"Record the time it takes for the leaf discs to rise to the top of each syringe.","location":"specification"}]},{"type":"text","order":3,"title":"Control

Photosynthesis

Question 14

Photosynthesis Questions

Photosynthesis

Question 14

Photosynthesis Questions