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AQA_A Level Biology Paper 3_Mark Scheme 2022 | Practice Paper 3

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AQA A Level Biology Paper 3 Mark Scheme 2022 Practice Paper 3 - - - - 1 (a) Introns; 1 (b) Ile Gly Val Ser; 1 (c) (i) Has no effect / same amino acid (sequence) / same 1 primary structure; ... Reject same amino acid formed or produced. Glycine named as same amino acid; 1 It still codes for glycine = two marks. (ii) Leu replaces Val / change in amino acid (sequence) / primary structure; Change in hydrogen / ionic bonds which alters tertiary structure / active site; Different amino acid formed or produced negates first marking point. Substrate cannot bind / no longer complementary / 3 no enzyme-substrate complexes form; Active site changed must be clear for third marking point but does not need reference to shape. (d) (i) Interphase / S / synthesis (phase); 1 (ii) DNA / gene replication / synthesis occurs / longest stage; 1 Allow ‘genetic information’ = DNA. Allow ‘copied’ or ‘formed’ = replication / synthesis [Total 9 marks] 2 (a) (i) where mitosis / division / growing / occurs 1 (reject growing cells) (ii) to distinguish chromosomes / chromosomes not visible without stain; 1 (iii) to let light through / thin layer; 1 to make a single layer of cells (b) (i) 74 + 18 / 982; 2 = 9.4% / 9%; (allow 1 mark for identifying prophase & metaphase i.e.92 or correct method using wrong figures) - - - [Show More]

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