","explanationVersion":"v3"},"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"864979b2-9f95-40f5-8b8c-ae639046bb2b","revisionId":"0990a02d-4fc3-47a6-b2b0-a1829d8558b5","questionNumber":null,"questionType":"LA","specification":"","difficulty":4,"difficultyBand":"medium","totalMarks":8,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"0c0d980d-82ee-4e4b-a5df-767df3147836","label":"a","content":"Describe the processes of simple diffusion and facilitated diffusion.","markscheme":"- Simple diffusion involves non-polar/lipid-soluble molecules, whereas facilitated diffusion transports polar or charged molecules/ions B1\n- Both are passive processes moving substances down a concentration gradient B1\n- Simple diffusion occurs directly through the phospholipid membrane bilayer, while facilitated diffusion requires transport proteins (channel or carrier proteins) B1","marks":3,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"compare_membrane_diffusion","label":"Compare the two processes","steps":[{"type":"text","order":0,"title":"State the shared idea","content":"Start with what both processes have in common: they are **passive**, so no ATP is required. In each case, particles move **down a concentration gradient**, meaning from a region of higher concentration to a region of lower concentration.\n\nThis earns one mark because it applies to **both** named processes.","highlights":[{"text":"Describe the processes of simple diffusion and facilitated diffusion.","location":"specification"}]},{"type":"text","order":1,"title":"Compare molecule types","content":"Simple diffusion is used by non-polar or lipid-soluble molecules. Facilitated diffusion is used by polar molecules or charged ions.\n\nThis molecule-type contrast earns **one mark**.","highlights":[{"text":"Describe the processes of simple diffusion and facilitated diffusion.","location":"specification"}]},{"type":"text","order":2,"title":"Compare membrane routes","content":"For the membrane-route comparison, non-polar/lipid-soluble molecules pass directly through the phospholipid bilayer in simple diffusion. Polar molecules and ions need transport proteins in facilitated diffusion: these may be channel proteins or carrier proteins.\n\nStating the direct bilayer route **and** the protein requirement as a comparison gains the third mark.","highlights":[{"text":"Describe the processes of simple diffusion and facilitated diffusion.","location":"specification"}]}]}],"generatedAt":"2026-07-21T04:44:04.668Z","modelVersion":"gpt-5.6-terra","explanationVersion":"v3"},"options":[]},{"id":"a63347a8-5ec2-4b1f-8052-c6b535e04e2d","label":"b","content":"State what microvilli are in terms of cell structure.","markscheme":"- Microvilli are highly folded cell-surface (plasma) membranes of epithelial cells B1","marks":1,"order":1,"markingRubric":null,"explanation":{"methods":[{"id":"recall_cell_structure","label":"Recall the cell-surface adaptation","steps":[{"type":"text","order":1,"title":"State the definition","content":"State the structural definition directly: microvilli are **highly folded cell-surface (plasma) membranes of epithelial cells**. This covers the full B1 mark.","highlights":[{"text":"State what microvilli are in terms of cell structure.","location":"specification"}]}]}],"generatedAt":"2026-07-21T04:45:48.632Z","modelVersion":"gpt-5.6-terra","explanationVersion":"v3"},"options":[]},{"id":"8d5e47cc-c57d-450f-93fa-88b5179f6c56","label":"c","content":"Vitamin D is a fat-soluble substance. Micelles are involved in the absorption of vitamin D.\nDescribe the process of vitamin D absorption into the epithelial cells lining the ileum.","markscheme":"- Vitamin D associates/mixes with bile salts to form micelles B1\n- This makes the molecules soluble in water B1\n- Micelles carry the molecules to the epithelial cells and break down close to the cell-surface membrane, maintaining a high concentration gradient B1\n- Vitamin D, being

Digestion and absorption

Question 8

Digestion and absorption Questions

Digestion and absorption

Question 8

Digestion and absorption Questions