Edexcel as level biology paper 1 mark scheme june 2023 salters nuffield

Question Number Answer Additional Guidance Mark 1 (a)(i) An answer that makes reference to the following: • inverted DNA nucleotide (1) • {2 / 3} hydrogen bonds (1) Example of diagram: (2) Question Number Answer Additional Guidance Mark 1 (a)(ii) An answer that makes reference to the following: • phosphodiester (1) • hydrogen (1) (2) Pearson Education Limited. Registered company number 872828 with its registered office at 80 Strand, London, WC2R 0RL, United Kingdom Question Number Answer Additional Guidance Mark 1 (b) An answer that makes reference to one of the following: • DNA (nucleotide) has no double bonds whereas CeNA has a double bond (1) • DNA (nucleotide) has {pentose / deoxyribose / 5 carbon} sugar whereas CeNA does not (1) ALLOW only CeNA has a double bond ALLOW DNA nucleotide has an oxygen atom in the ring whereas CeNA does not (1) ALLOW CeNA has an additional carbon atom ALLOW DNA (nucleotide) has {pentose / deoxyribose / 5 carbon} sugar whereas CeNA has {hexose / 6 carbon} (sugar) IGNORE reference to sugar in CeNA (1) Pearson Education Limited. Registered company number 872828 with its registered office at 80 Strand, London, WC2R 0RL, United Kingdom Question Number Answer Mark 2 (a)(i) The only correct answer is A - P B is incorrect because the atrioventricular valve is already closed at this point C is incorrect because the atrioventricular valve is already closed at this point D is incorrect because the atrioventricular valve is opening at this point (1) Question Number Answer Mark 2 (a)(ii) The only correct answer is B - Q A is incorrect because the atrio-ventricular valve would open at P C is incorrect because the semi-lunar valve would be closed D is incorrect because the semi-lunar valve would be closed (1) Pearson Education Limited. Registered company number 872828 with its registered office at 80 Strand, London, WC2R 0RL, United Kingdom Question Number Answer Additional Guidance Mark 2 (a)(iii) An answer that makes reference to two of the following: • atria and ventricles relax (1) • blood enters the atria (1) • semilunar valves close / atrioventricular valves open (1) ALLOW {cardiac / heart / myocardium} muscle {relaxes / no longer contracts} ALLOW atrium singular ALLOW pressure inside the {atria / ventricles} decreases (2) Question Number Answer Additional Guidance Mark 2(b)(i) • correct measurement of width of XY divided by magnification value (1) • correct calculation of lumen width in mm to two significant figures (1) Example of calculation {99 / 100 / 101} ÷18= 5.5 or 5.6 One mark for 0.55 or 0.56 Correct answer with no working gains full marks