33:I[196793,["/_next/static/chunks/1k7mhi2mpecuo.js?dpl=nogit-1791040192","/_next/static/chunks/2_6olli-sutu3.js?dpl=nogit-1791040192","/_next/static/chunks/0zcakt1-boe_f.js?dpl=nogit-1791040192","/_next/static/chunks/0yuh9obhrf6py.js?dpl=nogit-1791040192","/_next/static/chunks/3mz725-y91ph6.js?dpl=nogit-1791040192","/_next/static/chunks/2x_dbpl3b_l2r.js?dpl=nogit-1791040192","/_next/static/chunks/13_9hjun60hj-.js?dpl=nogit-1791040192","/_next/static/chunks/2bxmml65nu49g.js?dpl=nogit-1791040192","/_next/static/chunks/0zkcxwtbsqliz.js?dpl=nogit-1791040192","/_next/static/chunks/1dxqjl8rol78e.js?dpl=nogit-1791040192","/_next/static/chunks/2gjyu-jrwu-fu.js?dpl=nogit-1791040192","/_next/static/chunks/3jpl-42mbad5n.js?dpl=nogit-1791040192","/_next/static/chunks/3ml3vooxhiupb.js?dpl=nogit-1791040192","/_next/static/chunks/3kzt2piec6aoa.js?dpl=nogit-1791040192","/_next/static/chunks/19ijf68pshdcn.js?dpl=nogit-1791040192","/_next/static/chunks/40lyu17d590zu.js?dpl=nogit-1791040192","/_next/static/chunks/04zr-wqafvwoa.js?dpl=nogit-1791040192","/_next/static/chunks/38w1x0vrld4-w.js?dpl=nogit-1791040192","/_next/static/chunks/2wqr_qa524410.js?dpl=nogit-1791040192","/_next/static/chunks/2os7nxouq91eq.js?dpl=nogit-1791040192","/_next/static/chunks/1u0-4r35vefxo.js?dpl=nogit-1791040192","/_next/static/chunks/0v4byuex1x38h.js?dpl=nogit-1791040192","/_next/static/chunks/2tp0p_5fc9uvf.js?dpl=nogit-1791040192","/_next/static/chunks/26m8evoiza4ec.js?dpl=nogit-1791040192","/_next/static/chunks/2mv9l1xl_aa4j.js?dpl=nogit-1791040192","/_next/static/chunks/1coblm1-go81_.js?dpl=nogit-1791040192","/_next/static/chunks/1_p5v4n7583_r.js?dpl=nogit-1791040192","/_next/static/chunks/1ku-vdy4ggo41.js?dpl=nogit-1791040192","/_next/static/chunks/2dx-vzwyw9a3g.js?dpl=nogit-1791040192","/_next/static/chunks/32egb6-l4niwe.js?dpl=nogit-1791040192","/_next/static/chunks/1-n779e9yi4l0.js?dpl=nogit-1791040192","/_next/static/chunks/0llqhg6-bxn_b.js?dpl=nogit-1791040192","/_next/static/chunks/2a2shu5fsom14.js?dpl=nogit-1791040192","/_next/static/chunks/0k-y_4mcfub-p.js?dpl=nogit-1791040192","/_next/static/chunks/3795z2r1x82vp.js?dpl=nogit-1791040192","/_next/static/chunks/1s6j_7_p0ugo9.js?dpl=nogit-1791040192","/_next/static/chunks/33z1jiacs_jrz.js?dpl=nogit-1791040192","/_next/static/chunks/2leuonyicz6gk.js?dpl=nogit-1791040192","/_next/static/chunks/2rsljb77wejav.js?dpl=nogit-1791040192","/_next/static/chunks/075i0tnxt4not.js?dpl=nogit-1791040192","/_next/static/chunks/12za0kzs9m-b_.js?dpl=nogit-1791040192","/_next/static/chunks/1p8omo2zft7gp.js?dpl=nogit-1791040192","/_next/static/chunks/13gj59kzq50t_.js?dpl=nogit-1791040192","/_next/static/chunks/34lw53983v4li.js?dpl=nogit-1791040192","/_next/static/chunks/3pb98vwyysfzu.js?dpl=nogit-1791040192","/_next/static/chunks/1lsxkfxy262n-.js?dpl=nogit-1791040192","/_next/static/chunks/1ksyn9m68446d.js?dpl=nogit-1791040192","/_next/static/chunks/1hnuhh5t7cfaj.js?dpl=nogit-1791040192","/_next/static/chunks/2uzea6b173htc.js?dpl=nogit-1791040192","/_next/static/chunks/2s8s2tbh7ie54.js?dpl=nogit-1791040192","/_next/static/chunks/2u1q43gtwo_9f.js?dpl=nogit-1791040192","/_next/static/chunks/12bb60zmzpft7.js?dpl=nogit-1791040192","/_next/static/chunks/29gkme7_x75oo.js?dpl=nogit-1791040192","/_next/static/chunks/3wqp-h5xnebw9.js?dpl=nogit-1791040192","/_next/static/chunks/3ybwgs28on6c8.js?dpl=nogit-1791040192","/_next/static/chunks/1csf-qhroertu.js?dpl=nogit-1791040192","/_next/static/chunks/1d7tjnrc0fv5y.js?dpl=nogit-1791040192","/_next/static/chunks/0zg1om_k0m5zv.js?dpl=nogit-1791040192"],"Gingerbread"] 35:I[647935,["/_next/static/chunks/1k7mhi2mpecuo.js?dpl=nogit-1791040192","/_next/static/chunks/2_6olli-sutu3.js?dpl=nogit-1791040192","/_next/static/chunks/0zcakt1-boe_f.js?dpl=nogit-1791040192","/_next/static/chunks/0yuh9obhrf6py.js?dpl=nogit-1791040192","/_next/static/chunks/3mz725-y91ph6.js?dpl=nogit-1791040192","/_next/static/chunks/2x_dbpl3b_l2r.js?dpl=nogit-1791040192","/_next/static/chunks/13_9hjun60hj-.js?dpl=nogit-1791040192","/_next/static/chunks/2bxmml65nu49g.js?dpl=nogit-1791040192","/_next/static/chunks/0zkcxwtbsqliz.js?dpl=nogit-1791040192","/_next/static/chunks/1dxqjl8rol78e.js?dpl=nogit-1791040192","/_next/static/chunks/2gjyu-jrwu-fu.js?dpl=nogit-1791040192","/_next/static/chunks/3jpl-42mbad5n.js?dpl=nogit-1791040192","/_next/static/chunks/3ml3vooxhiupb.js?dpl=nogit-1791040192","/_next/static/chunks/3kzt2piec6aoa.js?dpl=nogit-1791040192","/_next/static/chunks/19ijf68pshdcn.js?dpl=nogit-1791040192","/_next/static/chunks/40lyu17d590zu.js?dpl=nogit-1791040192","/_next/static/chunks/04zr-wqafvwoa.js?dpl=nogit-1791040192","/_next/static/chunks/38w1x0vrld4-w.js?dpl=nogit-1791040192","/_next/static/chunks/2wqr_qa524410.js?dpl=nogit-1791040192","/_next/static/chunks/2os7nxouq91eq.js?dpl=nogit-1791040192","/_next/static/chunks/1u0-4r35vefxo.js?dpl=nogit-1791040192","/_next/static/chunks/0v4byuex1x38h.js?dpl=nogit-1791040192","/_next/static/chunks/2tp0p_5fc9uvf.js?dpl=nogit-1791040192","/_next/static/chunks/26m8evoiza4ec.js?dpl=nogit-1791040192","/_next/static/chunks/2mv9l1xl_aa4j.js?dpl=nogit-1791040192","/_next/static/chunks/1coblm1-go81_.js?dpl=nogit-1791040192","/_next/static/chunks/1_p5v4n7583_r.js?dpl=nogit-1791040192","/_next/static/chunks/1ku-vdy4ggo41.js?dpl=nogit-1791040192","/_next/static/chunks/2dx-vzwyw9a3g.js?dpl=nogit-1791040192","/_next/static/chunks/32egb6-l4niwe.js?dpl=nogit-1791040192","/_next/static/chunks/1-n779e9yi4l0.js?dpl=nogit-1791040192","/_next/static/chunks/0llqhg6-bxn_b.js?dpl=nogit-1791040192","/_next/static/chunks/2a2shu5fsom14.js?dpl=nogit-1791040192","/_next/static/chunks/0k-y_4mcfub-p.js?dpl=nogit-1791040192","/_next/static/chunks/3795z2r1x82vp.js?dpl=nogit-1791040192","/_next/static/chunks/1s6j_7_p0ugo9.js?dpl=nogit-1791040192","/_next/static/chunks/33z1jiacs_jrz.js?dpl=nogit-1791040192","/_next/static/chunks/2leuonyicz6gk.js?dpl=nogit-1791040192","/_next/static/chunks/2rsljb77wejav.js?dpl=nogit-1791040192","/_next/static/chunks/075i0tnxt4not.js?dpl=nogit-1791040192","/_next/static/chunks/12za0kzs9m-b_.js?dpl=nogit-1791040192","/_next/static/chunks/1p8omo2zft7gp.js?dpl=nogit-1791040192","/_next/static/chunks/13gj59kzq50t_.js?dpl=nogit-1791040192","/_next/static/chunks/34lw53983v4li.js?dpl=nogit-1791040192","/_next/static/chunks/3pb98vwyysfzu.js?dpl=nogit-1791040192","/_next/static/chunks/1lsxkfxy262n-.js?dpl=nogit-1791040192","/_next/static/chunks/1ksyn9m68446d.js?dpl=nogit-1791040192","/_next/static/chunks/1hnuhh5t7cfaj.js?dpl=nogit-1791040192","/_next/static/chunks/2uzea6b173htc.js?dpl=nogit-1791040192","/_next/static/chunks/2s8s2tbh7ie54.js?dpl=nogit-1791040192","/_next/static/chunks/2u1q43gtwo_9f.js?dpl=nogit-1791040192","/_next/static/chunks/12bb60zmzpft7.js?dpl=nogit-1791040192","/_next/static/chunks/29gkme7_x75oo.js?dpl=nogit-1791040192","/_next/static/chunks/3wqp-h5xnebw9.js?dpl=nogit-1791040192","/_next/static/chunks/3ybwgs28on6c8.js?dpl=nogit-1791040192","/_next/static/chunks/1csf-qhroertu.js?dpl=nogit-1791040192","/_next/static/chunks/1d7tjnrc0fv5y.js?dpl=nogit-1791040192","/_next/static/chunks/0zg1om_k0m5zv.js?dpl=nogit-1791040192"],"RecordResourceResume"] 36:I[830476,["/_next/static/chunks/1k7mhi2mpecuo.js?dpl=nogit-1791040192","/_next/static/chunks/2_6olli-sutu3.js?dpl=nogit-1791040192","/_next/static/chunks/0zcakt1-boe_f.js?dpl=nogit-1791040192","/_next/static/chunks/0yuh9obhrf6py.js?dpl=nogit-1791040192","/_next/static/chunks/3mz725-y91ph6.js?dpl=nogit-1791040192","/_next/static/chunks/2x_dbpl3b_l2r.js?dpl=nogit-1791040192","/_next/static/chunks/13_9hjun60hj-.js?dpl=nogit-1791040192","/_next/static/chunks/2bxmml65nu49g.js?dpl=nogit-1791040192","/_next/static/chunks/0zkcxwtbsqliz.js?dpl=nogit-1791040192","/_next/static/chunks/1dxqjl8rol78e.js?dpl=nogit-1791040192","/_next/static/chunks/2gjyu-jrwu-fu.js?dpl=nogit-1791040192","/_next/static/chunks/3jpl-42mbad5n.js?dpl=nogit-1791040192","/_next/static/chunks/3ml3vooxhiupb.js?dpl=nogit-1791040192","/_next/static/chunks/3kzt2piec6aoa.js?dpl=nogit-1791040192","/_next/static/chunks/19ijf68pshdcn.js?dpl=nogit-1791040192","/_next/static/chunks/40lyu17d590zu.js?dpl=nogit-1791040192","/_next/static/chunks/04zr-wqafvwoa.js?dpl=nogit-1791040192","/_next/static/chunks/38w1x0vrld4-w.js?dpl=nogit-1791040192","/_next/static/chunks/2wqr_qa524410.js?dpl=nogit-1791040192","/_next/static/chunks/2os7nxouq91eq.js?dpl=nogit-1791040192","/_next/static/chunks/1u0-4r35vefxo.js?dpl=nogit-1791040192","/_next/static/chunks/0v4byuex1x38h.js?dpl=nogit-1791040192","/_next/static/chunks/2tp0p_5fc9uvf.js?dpl=nogit-1791040192","/_next/static/chunks/26m8evoiza4ec.js?dpl=nogit-1791040192","/_next/static/chunks/2mv9l1xl_aa4j.js?dpl=nogit-1791040192","/_next/static/chunks/1coblm1-go81_.js?dpl=nogit-1791040192","/_next/static/chunks/1_p5v4n7583_r.js?dpl=nogit-1791040192","/_next/static/chunks/1ku-vdy4ggo41.js?dpl=nogit-1791040192","/_next/static/chunks/2dx-vzwyw9a3g.js?dpl=nogit-1791040192","/_next/static/chunks/32egb6-l4niwe.js?dpl=nogit-1791040192","/_next/static/chunks/1-n779e9yi4l0.js?dpl=nogit-1791040192","/_next/static/chunks/0llqhg6-bxn_b.js?dpl=nogit-1791040192","/_next/static/chunks/2a2shu5fsom14.js?dpl=nogit-1791040192","/_next/static/chunks/0k-y_4mcfub-p.js?dpl=nogit-1791040192","/_next/static/chunks/3795z2r1x82vp.js?dpl=nogit-1791040192","/_next/static/chunks/1s6j_7_p0ugo9.js?dpl=nogit-1791040192","/_next/static/chunks/33z1jiacs_jrz.js?dpl=nogit-1791040192","/_next/static/chunks/2leuonyicz6gk.js?dpl=nogit-1791040192","/_next/static/chunks/2rsljb77wejav.js?dpl=nogit-1791040192","/_next/static/chunks/075i0tnxt4not.js?dpl=nogit-1791040192","/_next/static/chunks/12za0kzs9m-b_.js?dpl=nogit-1791040192","/_next/static/chunks/1p8omo2zft7gp.js?dpl=nogit-1791040192","/_next/static/chunks/13gj59kzq50t_.js?dpl=nogit-1791040192","/_next/static/chunks/34lw53983v4li.js?dpl=nogit-1791040192","/_next/static/chunks/3pb98vwyysfzu.js?dpl=nogit-1791040192","/_next/static/chunks/1lsxkfxy262n-.js?dpl=nogit-1791040192","/_next/static/chunks/1ksyn9m68446d.js?dpl=nogit-1791040192","/_next/static/chunks/1hnuhh5t7cfaj.js?dpl=nogit-1791040192","/_next/static/chunks/2uzea6b173htc.js?dpl=nogit-1791040192","/_next/static/chunks/2s8s2tbh7ie54.js?dpl=nogit-1791040192","/_next/static/chunks/2u1q43gtwo_9f.js?dpl=nogit-1791040192","/_next/static/chunks/12bb60zmzpft7.js?dpl=nogit-1791040192","/_next/static/chunks/29gkme7_x75oo.js?dpl=nogit-1791040192","/_next/static/chunks/3wqp-h5xnebw9.js?dpl=nogit-1791040192","/_next/static/chunks/3ybwgs28on6c8.js?dpl=nogit-1791040192","/_next/static/chunks/1csf-qhroertu.js?dpl=nogit-1791040192","/_next/static/chunks/1d7tjnrc0fv5y.js?dpl=nogit-1791040192","/_next/static/chunks/0zg1om_k0m5zv.js?dpl=nogit-1791040192"],"FlashcardAccessBranch"] 37:I[315438,["/_next/static/chunks/1k7mhi2mpecuo.js?dpl=nogit-1791040192","/_next/static/chunks/2_6olli-sutu3.js?dpl=nogit-1791040192","/_next/static/chunks/0zcakt1-boe_f.js?dpl=nogit-1791040192","/_next/static/chunks/0yuh9obhrf6py.js?dpl=nogit-1791040192","/_next/static/chunks/3mz725-y91ph6.js?dpl=nogit-1791040192","/_next/static/chunks/2x_dbpl3b_l2r.js?dpl=nogit-1791040192","/_next/static/chunks/13_9hjun60hj-.js?dpl=nogit-1791040192","/_next/static/chunks/2bxmml65nu49g.js?dpl=nogit-1791040192","/_next/static/chunks/0zkcxwtbsqliz.js?dpl=nogit-1791040192","/_next/static/chunks/1dxqjl8rol78e.js?dpl=nogit-1791040192","/_next/static/chunks/2gjyu-jrwu-fu.js?dpl=nogit-1791040192","/_next/static/chunks/3jpl-42mbad5n.js?dpl=nogit-1791040192","/_next/static/chunks/3ml3vooxhiupb.js?dpl=nogit-1791040192","/_next/static/chunks/3kzt2piec6aoa.js?dpl=nogit-1791040192","/_next/static/chunks/19ijf68pshdcn.js?dpl=nogit-1791040192","/_next/static/chunks/40lyu17d590zu.js?dpl=nogit-1791040192","/_next/static/chunks/04zr-wqafvwoa.js?dpl=nogit-1791040192","/_next/static/chunks/38w1x0vrld4-w.js?dpl=nogit-1791040192","/_next/static/chunks/2wqr_qa524410.js?dpl=nogit-1791040192","/_next/static/chunks/2os7nxouq91eq.js?dpl=nogit-1791040192","/_next/static/chunks/1u0-4r35vefxo.js?dpl=nogit-1791040192","/_next/static/chunks/0v4byuex1x38h.js?dpl=nogit-1791040192","/_next/static/chunks/2tp0p_5fc9uvf.js?dpl=nogit-1791040192","/_next/static/chunks/26m8evoiza4ec.js?dpl=nogit-1791040192","/_next/static/chunks/2mv9l1xl_aa4j.js?dpl=nogit-1791040192","/_next/static/chunks/1coblm1-go81_.js?dpl=nogit-1791040192","/_next/static/chunks/1_p5v4n7583_r.js?dpl=nogit-1791040192","/_next/static/chunks/1ku-vdy4ggo41.js?dpl=nogit-1791040192","/_next/static/chunks/2dx-vzwyw9a3g.js?dpl=nogit-1791040192","/_next/static/chunks/32egb6-l4niwe.js?dpl=nogit-1791040192","/_next/static/chunks/1-n779e9yi4l0.js?dpl=nogit-1791040192","/_next/static/chunks/0llqhg6-bxn_b.js?dpl=nogit-1791040192","/_next/static/chunks/2a2shu5fsom14.js?dpl=nogit-1791040192","/_next/static/chunks/0k-y_4mcfub-p.js?dpl=nogit-1791040192","/_next/static/chunks/3795z2r1x82vp.js?dpl=nogit-1791040192","/_next/static/chunks/1s6j_7_p0ugo9.js?dpl=nogit-1791040192","/_next/static/chunks/33z1jiacs_jrz.js?dpl=nogit-1791040192","/_next/static/chunks/2leuonyicz6gk.js?dpl=nogit-1791040192","/_next/static/chunks/2rsljb77wejav.js?dpl=nogit-1791040192","/_next/static/chunks/075i0tnxt4not.js?dpl=nogit-1791040192","/_next/static/chunks/12za0kzs9m-b_.js?dpl=nogit-1791040192","/_next/static/chunks/1p8omo2zft7gp.js?dpl=nogit-1791040192","/_next/static/chunks/13gj59kzq50t_.js?dpl=nogit-1791040192","/_next/static/chunks/34lw53983v4li.js?dpl=nogit-1791040192","/_next/static/chunks/3pb98vwyysfzu.js?dpl=nogit-1791040192","/_next/static/chunks/1lsxkfxy262n-.js?dpl=nogit-1791040192","/_next/static/chunks/1ksyn9m68446d.js?dpl=nogit-1791040192","/_next/static/chunks/1hnuhh5t7cfaj.js?dpl=nogit-1791040192","/_next/static/chunks/2uzea6b173htc.js?dpl=nogit-1791040192","/_next/static/chunks/2s8s2tbh7ie54.js?dpl=nogit-1791040192","/_next/static/chunks/2u1q43gtwo_9f.js?dpl=nogit-1791040192","/_next/static/chunks/12bb60zmzpft7.js?dpl=nogit-1791040192","/_next/static/chunks/29gkme7_x75oo.js?dpl=nogit-1791040192","/_next/static/chunks/3wqp-h5xnebw9.js?dpl=nogit-1791040192","/_next/static/chunks/3ybwgs28on6c8.js?dpl=nogit-1791040192","/_next/static/chunks/1csf-qhroertu.js?dpl=nogit-1791040192","/_next/static/chunks/1d7tjnrc0fv5y.js?dpl=nogit-1791040192","/_next/static/chunks/0zg1om_k0m5zv.js?dpl=nogit-1791040192"],"TopicFlashcardRunner"] 24:[["$","$L33",null,{"feature":"flashcards"}],"$L34",["$","$L35",null,{"href":"/a-level/biology/edexcel/a/gas-exchange-and-diffusion/flashcards","label":"Gas exchange and diffusion","subjectCode":"a_level_biology__edexcel_a","surface":"flashcards"}],["$","$L36",null,{"runner":["$","div",null,{"className":"min-h-0 flex-1 overflow-hidden bg-background","children":["$","$L37",null,{"decks":[{"id":"20e7a753-98cc-4039-8b53-0193f359aea6","title":"Gas exchange and diffusion Flashcards","topicId":"b361a33f-7cee-5c4d-ad2a-b1ee85d2b716","topicSlug":"gas-exchange-and-diffusion","cards":[{"id":"b3df213a-2f55-40d9-993a-c81061975b55","cardType":"cloze","points":null,"front":"A concentration gradient is a [ ] between two regions.","back":"A concentration gradient is a difference in concentration between two regions.","mcqOptions":[{"text":"difference in concentration","correct":true,"explanation":"A concentration gradient exists when the concentration of a substance differs between two regions. This difference drives net diffusion from higher concentration to lower concentration."},{"text":"difference in volume","correct":false,"explanation":"Volume describes the space occupied, not the relative amount of a substance. The correct term is difference in concentration, which provides the gradient driving diffusion."},{"text":"difference in surface area","correct":false,"explanation":"Surface area affects the rate of diffusion but does not define a concentration gradient. The gradient is a difference in concentration between two regions."},{"text":"difference in pressure","correct":false,"explanation":"Pressure differences can drive bulk flow, but a concentration gradient specifically means a difference in concentration. For gases, partial pressure may instead represent the diffusion gradient."}]},{"id":"ce33f2ab-1df7-44da-a2d3-225509787507","cardType":"cloze","points":null,"front":"Diffusion is net movement from [ ] to [ ].","back":"Diffusion is net movement from higher concentration to lower concentration.","mcqOptions":[{"text":"Diffusion is net movement from higher concentration to lower concentration.","correct":true,"explanation":"Random particle movement produces an overall, or net, movement down the concentration gradient. Particles therefore diffuse from higher concentration to lower concentration."},{"text":"Diffusion is net movement from lower concentration to higher concentration.","correct":false,"explanation":"This reverses the direction of diffusion and describes movement against the concentration gradient. Diffusion produces net movement from higher concentration to lower concentration."},{"text":"Diffusion is net movement from higher concentration to higher concentration.","correct":false,"explanation":"Two regions at the same higher concentration do not create the stated gradient for directional net movement. Diffusion occurs from a region of higher concentration to lower concentration."},{"text":"Diffusion is net movement from lower concentration to lower concentration.","correct":false,"explanation":"Equal lower concentrations do not produce a concentration gradient, so there is no net movement in one direction. Diffusion requires movement from higher concentration to lower concentration."}]},{"id":"c5bcae2a-bbfa-423a-b7b4-588ef79c0782","cardType":"basic","points":1,"front":"Why is diffusion classed as a passive process?","back":"It does not require ATP.","mcqOptions":[{"text":"It does not require ATP.","correct":true,"explanation":"Diffusion is driven by the random kinetic movement of particles down a concentration gradient. It does not require energy supplied directly by ATP."},{"text":"It requires ATP from respiration.","correct":false,"explanation":"Requiring ATP is characteristic of active transport, not passive diffusion. Diffusion uses particles’ existing kinetic energy and therefore does not require ATP."},{"text":"It moves substances against a gradient.","correct":false,"explanation":"Movement against a concentration gradient requires an energy-dependent process such as active transport. Diffusion is passive because particles move down a gradient without requiring ATP."},{"text":"It is controlled by metabolic enzymes.","correct":false,"explanation":"Enzyme control is associated with metabolic reactions, not the definition of passive transport. Diffusion is passive because it does not require ATP."}]},{"id":"a3741ab7-75ea-4a2f-b35d-8ef26172189f","cardType":"cloze","points":null,"front":"For gases, biologists often describe a diffusion gradient using [ ] rather than concentration.","back":"For gases, biologists often describe a diffusion gradient using partial pressure rather than concentration.","mcqOptions":[{"text":"partial pressure","correct":true,"explanation":"A gas’s partial pressure measures its contribution to the total pressure of a gas mixture. Gases diffuse down their partial pressure gradients."},{"text":"total pressure","correct":false,"explanation":"Total pressure combines the contributions of all gases and does not show the gradient for one particular gas. Biologists use that gas’s partial pressure."},{"text":"gas volume","correct":false,"explanation":"Gas volume does not directly describe the diffusion gradient of an individual gas in a mixture. Its partial pressure indicates the direction in which it diffuses."},{"text":"mass density","correct":false,"explanation":"Mass density is mass per unit volume and is not normally used to express a gaseous diffusion gradient. The appropriate measure is partial pressure."}]},{"id":"c18d4550-c059-43e5-b418-5f150d8b2fe5","cardType":"basic","points":1,"front":"Alveolar air has $p_{\\text{O}_2}=13.0\\ \\text{kPa}$ and incoming blood has $p_{\\text{O}_2}=5.3\\ \\text{kPa}$. Which way does oxygen diffuse?","back":"From alveolus to blood.","mcqOptions":[{"text":"From alveolus to blood.","correct":true,"explanation":"Oxygen diffuses down its partial pressure gradient. Its partial pressure is higher in alveolar air at 13.0 kPa than in incoming blood at 5.3 kPa."},{"text":"From blood to alveolus.","correct":false,"explanation":"This reverses the partial pressure gradient. Oxygen moves from alveolar air at 13.0 kPa into blood at 5.3 kPa, so it diffuses from alveolus to blood."},{"text":"No net diffusion occurs.","correct":false,"explanation":"No net diffusion would occur only if oxygen partial pressures were equal. Here, the higher alveolar value creates net diffusion from alveolus to blood."},{"text":"From blood to body tissues.","correct":false,"explanation":"Oxygen later moves from systemic blood into respiring tissues, but this question concerns alveolar exchange. Here, oxygen diffuses from alveolus to blood."}]},{"id":"78d4c97e-4874-43a8-9c30-6bff85801213","cardType":"basic","points":1,"front":"Alveolar air has $p_{\\text{CO}_2}=5.3\\ \\text{kPa}$ and incoming blood has $p_{\\text{CO}_2}=6.1\\ \\text{kPa}$. Which way does carbon dioxide diffuse?","back":"From blood to alveolus.","mcqOptions":[{"text":"From blood to alveolus.","correct":true,"explanation":"Carbon dioxide diffuses down its partial pressure gradient. Its partial pressure is higher in incoming blood at 6.1 kPa than in alveolar air at 5.3 kPa."},{"text":"From alveolus to blood.","correct":false,"explanation":"This reverses the partial pressure gradient. Carbon dioxide moves from blood at 6.1 kPa into alveolar air at 5.3 kPa."},{"text":"No net diffusion occurs.","correct":false,"explanation":"No net diffusion would require equal carbon dioxide partial pressures. The blood has the higher value, so carbon dioxide diffuses from blood to alveolus."},{"text":"From alveolus to body tissues.","correct":false,"explanation":"Alveolar carbon dioxide is exhaled rather than transported directly to body tissues. During gas exchange, carbon dioxide diffuses from blood to alveolus."}]},{"id":"2b47f2e3-64df-4098-8639-b6ee6dd9e415","cardType":"cloze","points":null,"front":"As an object gets larger, [ ] increases faster than surface area, so SA:V [ ].","back":"As an object gets larger, volume increases faster than surface area, so SA:V decreases.","mcqOptions":[{"text":"As an object gets larger, volume increases faster than surface area, so SA:V decreases.","correct":true,"explanation":"For similarly shaped objects, surface area increases with length squared while volume increases with length cubed. Volume therefore grows faster, causing SA:V to decrease."},{"text":"As an object gets larger, volume increases faster than surface area, so SA:V increases.","correct":false,"explanation":"Although volume does increase faster than surface area, the conclusion is reversed. Faster volume growth makes the denominator proportionally larger, so SA:V decreases."},{"text":"As an object gets larger, surface area increases faster than surface area, so SA:V decreases.","correct":false,"explanation":"The first term has been confused with surface area. Volume increases with length cubed and therefore grows faster than surface area, causing SA:V to decrease."},{"text":"As an object gets larger, surface area increases faster than surface area, so SA:V increases.","correct":false,"explanation":"Surface area cannot increase faster than itself, and the scaling relationship is reversed. Volume grows faster than surface area, so SA:V decreases as size increases."}]},{"id":"57e289c4-e460-41d1-ae34-8f34fcf8440b","cardType":"basic","points":2,"front":"Why is diffusion across only the outer surface too slow in large organisms?","back":"

Low SA:V gives less exchange surface per tissue.
Longer diffusion distances slow particle movement.

","mcqOptions":[{"text":"

Low SA:V gives less exchange surface per tissue.
Longer diffusion distances slow particle movement.

","correct":true,"explanation":"Large organisms have relatively little outer surface available for each unit of tissue, while internal cells lie farther from that surface. Both factors make diffusion alone too slow."},{"text":"

High SA:V gives less exchange surface per tissue.
Shorter diffusion distances slow particle movement.

","correct":false,"explanation":"Both relationships are reversed. Large organisms have a low SA:V, providing less exchange surface per tissue, and their longer diffusion distances slow exchange."},{"text":"

Low SA:V gives more exchange surface per tissue.
Shorter diffusion distances slow particle movement.

","correct":false,"explanation":"Low SA:V means less, not more, exchange surface per tissue, while shorter distances speed diffusion. Large organisms instead have less relative surface and longer diffusion distances."},{"text":"

High SA:V gives less exchange surface per tissue.
Longer diffusion distances speed particle movement.

","correct":false,"explanation":"A high SA:V provides more relative exchange surface, and longer distances slow rather than speed diffusion. Large organisms have low SA:V and long diffusion pathways."}]},{"id":"522cf63f-10f5-4fff-b0dd-da893bfb5dfb","cardType":"cloze","points":null,"front":"At A-Level, diffusion rate is proportional to [ ].","back":"At A-Level, diffusion rate is proportional to $\\frac{A \\times \\Delta C}{d}$.","mcqOptions":[{"text":"$$\\frac{A \\times \\Delta C}{d}$","correct":true,"explanation":"Diffusion rate increases with exchange surface area and concentration gradient, but decreases as diffusion distance increases. These factors combine as $\\frac{A \\times \\Delta C}{d}$."},{"text":"$$\\frac{A \\times d}{\\Delta C}$","correct":false,"explanation":"This reverses the effect of diffusion distance and concentration gradient. The correct relationship is $\\frac{A \\times \\Delta C}{d}$ because a larger gradient increases diffusion, while a greater distance reduces it."},{"text":"$$\\frac{d \\times \\Delta C}{A}$","correct":false,"explanation":"This places diffusion distance and surface area in the wrong parts of the relationship. The correct expression is $\\frac{A \\times \\Delta C}{d}$, with area and gradient increasing rate and distance reducing it."},{"text":"$$\\frac{A + \\Delta C}{d}$","correct":false,"explanation":"Adding surface area and concentration gradient is not how the factors combine in Fick’s law. The correct relationship multiplies them: $\\frac{A \\times \\Delta C}{d}$."}]},{"id":"ed454684-6fbf-4219-8470-7df960448181","cardType":"basic","points":1,"front":"With surface area and gradient unchanged, what happens if diffusion distance triples?","back":"Diffusion rate falls to one third.","mcqOptions":[{"text":"Diffusion rate falls to one third.","correct":true,"explanation":"Diffusion rate is inversely proportional to diffusion distance. Tripling the distance therefore makes the rate one third as large when surface area and concentration gradient stay constant."},{"text":"Diffusion rate falls to one ninth.","correct":false,"explanation":"This applies an inverse-square relationship, which is not used for diffusion distance. Since rate is inversely proportional to distance, tripling the distance makes the rate one third."},{"text":"Diffusion rate triples.","correct":false,"explanation":"This reverses the inverse relationship between distance and diffusion rate. A longer pathway slows diffusion, so tripling diffusion distance reduces the rate to one third."},{"text":"Diffusion rate remains unchanged.","correct":false,"explanation":"Diffusion distance directly affects rate even when surface area and gradient are unchanged. Tripling the distance increases resistance to diffusion, reducing the rate to one third."}]},{"id":"2aceaa4a-77e7-46b7-8085-b79398fe6290","cardType":"basic","points":1,"front":"Where does mammalian gas exchange mainly occur in the lungs?","back":"In the alveoli.","mcqOptions":[{"text":"In the alveoli.","correct":true,"explanation":"Alveoli are the specialised air sacs where oxygen and carbon dioxide cross between the air and surrounding capillary blood, providing a large, thin exchange surface."},{"text":"In the bronchi.","correct":false,"explanation":"The bronchi mainly conduct air towards the lungs and are not the main exchange surface. Mammalian gas exchange mainly occurs across the thin walls of the alveoli."},{"text":"In the trachea.","correct":false,"explanation":"The trachea is an airway that carries air towards the bronchi and contains cartilage and ciliated epithelium. Gas exchange mainly occurs in the alveoli, not the trachea."},{"text":"In the diaphragm.","correct":false,"explanation":"The diaphragm is a muscle that changes thoracic volume to ventilate the lungs. It does not provide an exchange surface; gas exchange mainly occurs across alveolar walls."}]},{"id":"063c5c27-4f41-4416-a40c-1d445144d73c","cardType":"basic","points":1,"front":"Which process is the bulk movement of air into and out of the lungs?","back":"Ventilation.","mcqOptions":[{"text":"Ventilation.","correct":true,"explanation":"Ventilation is the bulk movement of air into and out of the lungs. It continually replaces alveolar air, helping maintain concentration gradients for gas exchange."},{"text":"Diffusion.","correct":false,"explanation":"Diffusion is the net movement of gases down concentration gradients across the alveolar and capillary surfaces. The bulk movement of air into and out of the lungs is ventilation."},{"text":"Perfusion.","correct":false,"explanation":"Perfusion refers to blood flowing through the pulmonary capillaries, not air movement. The bulk movement of air into and out of the lungs is called ventilation."},{"text":"Inspiration.","correct":false,"explanation":"Inspiration is only the process of breathing air into the lungs. The combined bulk movement of air into and out of the lungs is ventilation."}]},{"id":"21643a82-776f-4a1b-b16f-c1c34eeaba04","cardType":"cloze","points":null,"front":"Many alveoli give a total surface area of about [ ] in an adult human.","back":"Many alveoli give a total surface area of about 70 square metres in an adult human.","mcqOptions":[{"text":"70 square metres","correct":true,"explanation":"The numerous alveoli provide a very large total exchange surface, commonly given as about 70 square metres in an adult human, increasing the potential diffusion rate."},{"text":"7 square metres","correct":false,"explanation":"This is a common factor-of-ten underestimate of the alveolar surface area. The extensive number of alveoli gives an adult human a total area of about 70 square metres."},{"text":"700 square metres","correct":false,"explanation":"This is a factor-of-ten overestimate, often caused by misreading the scale of the measurement. The approximate total alveolar surface area is 70 square metres."},{"text":"0.7 square metres","correct":false,"explanation":"This value is far too small for the combined surface of millions of alveoli. Their large total exchange area is approximately 70 square metres in an adult human."}]},{"id":"8067fbae-c969-4203-914e-b82172f171a0","cardType":"basic","points":1,"front":"How does having both alveolar epithelium and capillary endothelium one cell thick affect diffusion?","back":"It creates a short diffusion distance.","mcqOptions":[{"text":"It creates a short diffusion distance.","correct":true,"explanation":"Both the alveolar epithelium and capillary endothelium are only one cell thick, so gases cross a very short pathway, increasing the rate of diffusion."},{"text":"It creates a long diffusion distance.","correct":false,"explanation":"One-cell-thick layers minimise rather than increase the distance gases must cross. Together, the alveolar epithelium and capillary endothelium create a short diffusion distance."},{"text":"It creates a large diffusion gradient.","correct":false,"explanation":"Layer thickness affects the distance across which gases diffuse, not the concentration gradient itself. One-cell-thick barriers create a short diffusion distance and speed exchange."},{"text":"It creates a small surface area.","correct":false,"explanation":"The thickness of the two cell layers does not determine the total surface area. Their one-cell thickness creates a short diffusion distance, while numerous alveoli provide a large area."}]},{"id":"6a5c5019-1ed2-485e-a7ad-2a0dcfcefb7d","cardType":"cloze","points":null,"front":"The total diffusion pathway across the alveolar exchange surface is around [ ].","back":"The total diffusion pathway across the alveolar exchange surface is around 0.5 µm.","mcqOptions":[{"text":"0.5 µm","correct":true,"explanation":"The alveolar epithelium and capillary endothelium together form a very thin exchange barrier. The total diffusion pathway is approximately 0.5 µm, allowing rapid gas exchange."},{"text":"5 µm","correct":false,"explanation":"This is ten times thicker than the typical exchange pathway and would substantially slow diffusion. The total diffusion pathway across the alveolar exchange surface is around 0.5 µm."},{"text":"0.05 µm","correct":false,"explanation":"This is ten times thinner than the accepted approximate value, likely from misplaced decimal places. The alveolar exchange pathway is around 0.5 µm."},{"text":"0.5 mm","correct":false,"explanation":"Millimetres are 1,000 times larger than micrometres, so this would represent an excessively thick barrier. The correct diffusion pathway is around 0.5 µm."}]},{"id":"3b1d9908-8150-4af9-a5cb-04b3ffac62b1","cardType":"basic","points":1,"front":"Why does a moist alveolar surface help oxygen and carbon dioxide diffuse?","back":"Gases dissolve before diffusing.","mcqOptions":[{"text":"Gases dissolve before diffusing.","correct":true,"explanation":"The moist alveolar lining allows oxygen and carbon dioxide to dissolve first. Dissolved gas molecules can then move across the exchange surface by diffusion."},{"text":"Gases react before diffusing.","correct":false,"explanation":"Moisture does not make the gases react before crossing the surface. It allows them to dissolve, which is necessary before they diffuse through the exchange barrier."},{"text":"Gases evaporate before diffusing.","correct":false,"explanation":"Evaporation is a change from liquid to gas and is not the relevant process here. Moist alveolar surfaces help gases dissolve before they diffuse across the membrane."},{"text":"Gases condense before diffusing.","correct":false,"explanation":"Condensation forms a liquid from a gas and would not facilitate normal alveolar exchange. The moist surface allows oxygen and carbon dioxide to dissolve before diffusing."}]},{"id":"c6a85c5e-ab44-467a-baac-9eb0b2c1b9d3","cardType":"basic","points":2,"front":"How does a dense capillary network keep alveolar diffusion rapid?","back":"It maintains blood flow, keeping gradients steep.","mcqOptions":[{"text":"It maintains blood flow, keeping gradients steep.","correct":true,"explanation":"A dense capillary network continually carries oxygenated blood away and brings deoxygenated blood towards the alveoli, preventing equilibrium and maintaining a steep concentration gradient."},{"text":"It maintains air movement, keeping gradients steep.","correct":false,"explanation":"Air movement is maintained by ventilation, not the capillary network. Capillaries maintain rapid exchange by continuously replacing the blood at the alveolar surface, preserving the gradient."},{"text":"It creates a thicker barrier, keeping gradients steep.","correct":false,"explanation":"A thicker barrier would increase diffusion distance and slow gas exchange. The capillary network instead maintains blood flow, continually replacing blood and keeping the concentration gradient steep."},{"text":"It reduces blood flow, keeping gradients steep.","correct":false,"explanation":"Reducing blood flow would allow oxygen and carbon dioxide concentrations to approach equilibrium, weakening diffusion. Continuous blood flow is needed to maintain steep gradients across the alveolar wall."}]},{"id":"15d4030c-644b-420b-89b5-c0001b330964","cardType":"basic","points":2,"front":"How does haemoglobin help maintain the oxygen gradient in alveoli?","back":"It binds oxygen after it enters blood.","mcqOptions":[{"text":"It binds oxygen after it enters blood.","correct":true,"explanation":"Haemoglobin binds oxygen as it diffuses into the blood, reducing the concentration of free oxygen and helping maintain a steep oxygen gradient from the alveoli into the capillaries."},{"text":"It releases oxygen before it enters blood.","correct":false,"explanation":"Haemoglobin does not release oxygen before it enters the blood. It binds oxygen after diffusion into the blood, lowering free oxygen concentration and sustaining the gradient."},{"text":"It binds carbon dioxide after it enters blood.","correct":false,"explanation":"Carbon dioxide transport involves haemoglobin to some extent, but this does not maintain the oxygen gradient. Oxygen binding by haemoglobin removes oxygen from solution and supports its continued diffusion."},{"text":"It converts oxygen into carbon dioxide after it enters blood.","correct":false,"explanation":"Haemoglobin does not chemically convert oxygen into carbon dioxide. It binds oxygen reversibly, reducing free oxygen concentration in the blood and maintaining diffusion from the alveoli."}]},{"id":"145a36d3-c9f6-4a7e-a2e8-4c17e86ed216","cardType":"basic","points":2,"front":"How does ventilation maintain oxygen diffusion into the blood?","back":"It brings oxygen-rich air into alveoli.","mcqOptions":[{"text":"It brings oxygen-rich air into alveoli.","correct":true,"explanation":"Ventilation replaces air in the alveoli with oxygen-rich air, keeping alveolar oxygen concentration higher than in the incoming deoxygenated blood and maintaining diffusion into the capillaries."},{"text":"It brings oxygen-poor air into alveoli.","correct":false,"explanation":"Oxygen-poor air would reduce the oxygen concentration gradient between alveoli and blood. Ventilation maintains diffusion by bringing oxygen-rich air into the alveoli."},{"text":"It brings carbon dioxide-rich air into alveoli.","correct":false,"explanation":"Carbon dioxide-rich air would not maintain a high alveolar oxygen concentration and could reduce oxygen diffusion. Fresh ventilation brings oxygen-rich air into the alveoli."},{"text":"It keeps stale air inside alveoli.","correct":false,"explanation":"Retaining stale air would lower alveolar oxygen concentration as oxygen is absorbed. Ventilation replaces this air with oxygen-rich air, preserving the gradient into the blood."}]},{"id":"0701771b-e44e-4b9d-ad9a-a5f329f4d88e","cardType":"basic","points":2,"front":"How does blood flow maintain oxygen diffusion into the blood?","back":"It brings deoxygenated blood with lower $p_{\\text{O}_2}$.","mcqOptions":[{"text":"It brings deoxygenated blood with lower $p_{\\text{O}_2}$.","correct":true,"explanation":"Deoxygenated blood arriving at the alveoli has a lower oxygen partial pressure than alveolar air. This difference maintains the gradient needed for oxygen to diffuse into the blood."},{"text":"It brings oxygenated blood with higher $p_{\\text{O}_2}$.","correct":false,"explanation":"Oxygenated blood already has a high oxygen partial pressure, so it would reduce the gradient from alveolar air into blood. Deoxygenated blood is required to sustain oxygen diffusion."},{"text":"It brings deoxygenated blood with higher $p_{\\text{O}_2}$.","correct":false,"explanation":"Deoxygenated blood has a lower, not higher, oxygen partial pressure than alveolar air. Its low $p_{\\text{O}_2}$ creates the gradient that drives oxygen into the blood."},{"text":"It brings deoxygenated blood with lower $p_{\\text{CO}_2}$.","correct":false,"explanation":"The relevant gradient for oxygen uptake depends on blood $p_{\\text{O}_2}$, not blood $p_{\\text{CO}_2}$. Deoxygenated blood has lower $p_{\\text{O}_2}$ than alveolar air."}]},{"id":"4bd4787c-4b6e-45ee-a568-2bdd32719ceb","cardType":"basic","points":2,"front":"How does ventilation maintain carbon dioxide diffusion out of the blood?","back":"It removes carbon dioxide from alveoli during exhalation.","mcqOptions":[{"text":"It removes carbon dioxide from alveoli during exhalation.","correct":true,"explanation":"Exhalation removes carbon dioxide from the alveoli, keeping alveolar carbon dioxide concentration lower than in the arriving blood and maintaining diffusion out of the blood."},{"text":"It removes oxygen from alveoli during exhalation.","correct":false,"explanation":"Removing oxygen does not directly maintain carbon dioxide diffusion. Exhalation must remove carbon dioxide from the alveoli so its concentration remains lower than in the blood."},{"text":"It adds carbon dioxide to alveoli during exhalation.","correct":false,"explanation":"Adding carbon dioxide would reduce the concentration gradient from blood to alveoli and slow diffusion. Exhalation removes carbon dioxide, preserving a low alveolar concentration."},{"text":"It keeps carbon dioxide in alveoli during exhalation.","correct":false,"explanation":"Retaining carbon dioxide would cause its alveolar concentration to rise, reducing the diffusion gradient. Ventilation maintains diffusion by removing carbon dioxide during exhalation."}]},{"id":"1a7bec3c-9626-416a-9e54-91bbefd3d32a","cardType":"basic","points":2,"front":"How does blood flow maintain carbon dioxide diffusion out of the blood?","back":"It brings carbon dioxide-rich blood to the lungs.","mcqOptions":[{"text":"It brings carbon dioxide-rich blood to the lungs.","correct":true,"explanation":"Blood arriving from respiring tissues contains a high carbon dioxide concentration. Bringing it to the lungs maintains a gradient for carbon dioxide to diffuse into the alveoli."},{"text":"It brings carbon dioxide-poor blood to the lungs.","correct":false,"explanation":"Carbon dioxide-poor blood would provide little concentration difference for diffusion into the alveoli. Blood flow brings carbon dioxide-rich blood from tissues to maintain the gradient."},{"text":"It brings oxygen-rich blood to the lungs.","correct":false,"explanation":"Oxygen-rich blood is not the condition that maintains carbon dioxide diffusion. Blood flow delivers carbon dioxide-rich blood, ensuring its concentration is higher than in the alveoli."},{"text":"It brings carbon dioxide-rich air to the lungs.","correct":false,"explanation":"Blood flow transports blood, not air. Carbon dioxide-rich blood arrives at the lungs from respiring tissues, maintaining the gradient for carbon dioxide to diffuse into the alveoli."}]},{"id":"2fbd6826-bfb7-44de-a97f-c9ef99706ca2","cardType":"basic","points":2,"front":"In cystic fibrosis, sticky mucus mainly reduces alveolar gas exchange by doing what?","back":"It blocks airways, reducing ventilation to alveoli.","mcqOptions":[{"text":"It blocks airways, reducing ventilation to alveoli.","correct":true,"explanation":"In cystic fibrosis, abnormally viscous mucus can obstruct the bronchioles and airways. Less air reaches affected alveoli, reducing ventilation and therefore limiting gas exchange."},{"text":"It thins airways, reducing ventilation to alveoli.","correct":false,"explanation":"The mucus does not thin the airways; it becomes thick and sticky, causing obstruction. This blockage reduces ventilation to alveoli and limits the replacement of respiratory gases."},{"text":"It blocks capillaries, reducing ventilation to alveoli.","correct":false,"explanation":"The primary effect is obstruction of airways, not capillaries. Reduced airflow prevents adequate ventilation of alveoli, weakening the concentration gradients needed for gas exchange."},{"text":"It increases ventilation, reducing diffusion to alveoli.","correct":false,"explanation":"Sticky mucus generally decreases ventilation by obstructing airways. Reduced airflow limits gas exchange because less oxygen reaches the alveoli and less carbon dioxide is removed."}]},{"id":"a190ba04-8249-44ed-bf98-ea65597fde28","cardType":"basic","points":2,"front":"Why are smaller agar cubes penetrated more completely in a fixed time?","back":"

Higher SA:V exposes more surface per volume.
Shorter diffusion distance to the centre.

","mcqOptions":[{"text":"

Higher SA:V exposes more surface per volume.
Shorter diffusion distance to the centre.

","correct":true,"explanation":"Smaller cubes have a greater surface area relative to volume and a shorter path to the centre. More cells are near the surface, so diffusion penetrates a greater proportion."},{"text":"

Lower SA:V exposes more surface per volume.
Shorter diffusion distance to the centre.

","correct":false,"explanation":"Smaller cubes have a higher, not lower, surface-area-to-volume ratio. Their shorter diffusion distance is correct, but the reduced surface relative to volume would not explain better penetration."},{"text":"

Higher SA:V exposes less surface per volume.
Longer diffusion distance to the centre.

","correct":false,"explanation":"A higher surface-area-to-volume ratio exposes more surface per volume, and smaller cubes have shorter diffusion distances. Reversing both relationships gives the wrong explanation."},{"text":"

Lower SA:V exposes less surface per volume.
Longer diffusion distance to the centre.

","correct":false,"explanation":"Both relationships are reversed: smaller cubes have higher surface area relative to volume and shorter distances to their centres. These features allow diffusion to penetrate more completely."}]},{"id":"781a6fe3-a00f-4579-bbf0-65f4aef3c72d","cardType":"basic","points":1,"front":"Which agar-cube limitation means it cannot model cellular oxygen demand?","back":"Agar does not use oxygen in respiration.","mcqOptions":[{"text":"Agar does not use oxygen in respiration.","correct":true,"explanation":"Agar cubes are inert and do not respire, so they cannot reproduce the continual oxygen consumption of living cells. Real cells maintain an oxygen concentration gradient by using oxygen during aerobic respiration."},{"text":"Agar does not contain a concentration gradient.","correct":false,"explanation":"A concentration gradient develops when oxygen diffuses into the agar cube, so this is not the relevant limitation. The correct answer is that agar does not use oxygen in respiration like living cells do."},{"text":"Agar does not contain haemoglobin.","correct":false,"explanation":"Haemoglobin transports oxygen in blood but is not required for oxygen to diffuse through an agar cube. The key limitation is that agar does not use oxygen in respiration to model cellular demand."},{"text":"Agar does not produce oxygen in photosynthesis.","correct":false,"explanation":"Oxygen production by photosynthesis is unrelated to modelling oxygen demand in respiring cells. The correct limitation is that agar does not use oxygen in respiration, so it cannot continuously remove oxygen."}]}]}],"examCountdown":{"examDate":"2027-06-07","paperLabel":"Paper 1"},"heading":"Gas exchange and diffusion","title":"Gas exchange and diffusion Flashcards","topbar":{"backHref":"/a-level/biology/edexcel/a/flashcards"},"topicSidebar":"$L38"}]}],"topicId":"b361a33f-7cee-5c4d-ad2a-b1ee85d2b716","walled":"$L39"}],"$L3a","$L3b"]