A-LevelBiologyCell membranes and transportMay/June 2020Paper 4 Q48 Marks
Lung epithelial cells have a thin layer of watery mucus on their surface. The normal allele of the CFTR gene codes for a transport protein that transports chloride ions out of epithelial cells. Fig. 4.1 is a diagram of part of the cell surface membrane and the mucus layer of an epithelial cell with normal CFTR proteins. [Figure 4.1] Cystic fibrosis (CF) is a genetic disorder caused by having two recessive alleles of CFTR. In severe cases of CF, the transport proteins are not added to the cell surface membrane. This causes the mucus layer to be thick and sticky.
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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