AQA_A-level_Biology_Paper_3_MARK SCHEME 2021

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A-LEVEL BIOLOGYMARK SCHEME 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 produ... ced. 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. [Show More]

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