e calculations using the data in the table.","markscheme":"- Calculates the percentage mass change for 0% sucrose solution: $\\frac{13.8 - 12.5}{12.5} \\times 100 = +10.4\\%$ (or absolute change of $+1.3$ g) M1\n- Calculates the percentage mass change for 20% sucrose solution: $\\frac{11.4 - 12.5}{12.5} \\times 100 = -8.8\\%$ (or absolute change of $-1.1$ g) and notes $0\\%$ change for 10% sucrose A1\n- Explains that in 0% sucrose (distilled water), the external water concentration is higher than inside the egg, causing water to enter by osmosis down a concentration gradient B1\n- Explains that in 20% sucrose, the external water concentration is lower than inside the egg, causing water to leave by osmosis down a concentration gradient B1\n- Explains that in 10% sucrose, there is no net movement of water because the external solution is isotonic to the egg cytoplasm B1\n- Concludes that the solute concentration inside the egg cytoplasm is approximately equal to 10% B1","marks":6,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"calculate_and_explain","label":"Calculate then explain osmosis","steps":[{"type":"hyper_latex","block":{"nodes":[{"latex":"\\text{Percentage mass change}=\\frac{\\text{mass after 24 hours}-\\text{mass at start}}{\\text{mass at start}}\\times100"},{"latex":"\\text{Percentage mass change}=\\frac{13.8-12.5}{12.5}\\times100"},{"latex":"\\text{Percentage mass change}=+10.4\\%"}]},"order":0,"title":"Calculate the gain","description":"Percentage change gives a standard way to compare mass changes between eggs. Start with the distilled-water result. Substituting the measured masses into the percentage-change formula earns M1."},{"type":"hyper_latex","block":{"nodes":[{"latex":"\\text{For }10\\%\\text{ sucrose:}\\quad\\frac{12.5-12.5}{12.5}\\times100=0\\%"},{"latex":"\\text{For }20\\%\\text{ sucrose:}\\quad\\frac{11.4-12.5}{12.5}\\times100=-8.8\\%"}]},"order":1,"title":"Calculate other changes","description":"Use the same percentage-change calculation for the other two solutions. These results earn A1 when stated alongside the distilled-water calculation."},{"type":"text","order":2,"title":"Explain distilled water","content":"In $0\\%$ sucrose (distilled water), the water concentration outside the egg is higher than inside it. Water therefore enters the egg by **osmosis**: the net movement of water through a selectively permeable membrane from a higher to a lower water concentration. This explains the $+10.4\\%$ mass change and earns B1.","highlights":[{"text":"0 (Distilled water)","location":"specification"}]},{"type":"text","order":3,"title":"Explain concentrated sucrose","content":"In $20\\%$ sucrose, the water concentration outside the egg is lower than inside it. Water leaves the egg by osmosis, down the water-concentration gradient. This explains the $-8.8\\%$ mass change and earns B1.","highlights":[{"text":"20","location":"specification"}]},{"type":"text","order":4,"title":"Use the unchanged mass","content":"The $10\\%$ sucrose egg has $0\\%$ mass change, so there is no **net movement** of water: water molecules still move both ways, but at equal rates. The external solution is **isotonic**, meaning it has the same water concentration as the egg cytoplasm. This earns B1.","highlights":[{"text":"10","location":"specification"}]},{"type":"text","order":5,"title":"State the conclusion","content":"Because the egg's mass stays unchanged in $10\\%$ sucrose, its cytoplasm has approximately the same solute concentration as a $10\\%$ sucrose solution. Therefore, the solute concentration inside the egg cytoplasm is approximately $10\\%$. This earns the final B1.","highlights":[{"text":"10","location":"specification"}]}]}],"generatedAt":"2026-07-21T04:32:06.653Z","modelVersion":"gpt-5.6-terra","explanationVersion":"v3"},"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null}],"subjectCode":"gcse_biology","summaries":[{"id":"0054a117-c349-4607-a397-fb7bc5b697e3","difficultyBand":"easy","c

Transport in and out of cells

Question 1

Transport in and out of cells Questions

Transport in and out of cells

Question 1

Transport in and out of cells Questions