Edexcel a level biology paper 2 mark scheme june 2023 salters nuffield

Question Number Answer Mark 1 (a)(i) The only correct answer is C metaphase A is incorrect as centromeres and spindle fibred do not join in anaphase B is incorrect as centromeres and spindle fibres do not join in interphase D is incorrect as centromeres and spindle fibres do not join in telophase [1] Question Number Answer Mark 1 (a)(ii) The only correct answer is C prophase A is incorrect as the nuclear envelope does not start to break down in interphase B is incorrect as the nuclear envelope does not start to break down in metaphase D is incorrect as the nuclear envelope does not start to break down in telophase [1] Question Number Answer Mark 1 (a)(iii) The only correct answer is C prophase A is incorrect as chromatids are not first visible in interphase B is incorrect as chromatids are not first visible in metaphase D is incorrect as chromatids are not first visible in telophase [1] Question Number Answer Additional Guidance Mark 1 (b) An explanation that makes reference to three of the following: • swapping of {alleles / genetic material} (1) • between non-sister chromatids (1) • of a {homologous pair of chromosomes/ bivalent} (1) • resulting in different combinations of alleles (1) ALLOW swapping {sections of DNA / genetic information } ALLOW between maternal and paternal chromosomes [3] Question Number Answer Mark 2(a) The only correct answer is - D the sugar in both eukaryotic and prokaryotic DNA is deoxyribose A is incorrect prokaryotic DNA is not linear and human DNA is not circular B is incorrect prokaryotic DNA is not located in a membrane-bound nucleus C is incorrect the base thymine is not replaced by uracil in the prokaryotic DNA [1] Question Number Answer Additional Guidance Mark 2 (b)(i) A description that makes reference to the following: • a group of genes / a section of DNA (1) • (controlled by a single) {operator/ promotor} / that are transcribed together (1) ALLOW two marks for operator and group of genes associated with it