Edexcel as level biology paper 1 mark sche me june 2023

Question Number Answer Additional Guidance Mark 1(a) The only correct answer is B A is incorrect because Down’s syndrome is an example of polysomy not monosomy C is incorrect because Down’s syndrome is caused by a chromosome mutation not a gene mutation D is incorrect because Down’s syndrome is caused by a chromosome mutation not a gene mutation (1) Question Number Answer Additional Guidance Mark 1(b) An answer that makes reference to the following: • birth order has no effect on the incidence (1) • the incidence increases with the age (of the mother) (1) • credit use of manipulated figures to support answer (1) ACCEPT no pattern e.g. approx. 80 times greater chance if over 40 than under 20 approx. 4 times greater chance if over 40 than between 35 and 39 approx. 500 per 100 000 more if over 40 than between 35 and 39 (3) Question Number Answer Additional Guidance Mark 2(a) A description that makes reference to the following: • to {digest / breakdown} the {egg cell / ovum / secondary oocyte} membrane (1) • so that the sperm {nucleus / genetic material} can enter the {egg cell / ovum / secondary oocyte} (1) ACCEPT zona pellucida (2) Question Number Answer Additional Guidance Mark 2(b) A description that makes reference to three of the following: • transcription of the genes coding for the (acrosome) enzymes (1) • translation (of the mRNA) (to synthesise the enzymes) (1) • transported in the RER (to the Golgi) (1) • {modification / processing / packaging} (of the enzymes) in the Golgi (1) • packaging (by the Golgi of the enzymes) into {the membrane / vesicles} (of the acrosome) (1) ACCEPT description of transcription e.g. mRNA copy of gene coding for enzyme made ACCEPT description of translation e.g. amino acids joined by peptide bonds DO NOT ACCEPT for exocytosis (3) Question Number Answer Additional Guidance Mark 3(a) A description that makes reference to the following: • glucose and galactose (1) • joined by a (1-4) glycosidic bond (1) (2) Question Number Answer Additional Guidance Mark 3(b) • tangent drawn as a straight line touching at 2 hours, on the outside of the curve (1) • rate calculated (1) ACCEPT value between 0.034 and 0.052 to 2 or 3 dps Correct answer gains 2 marks 0.08 / 0.075 gains 1 mark (2) Question Number Answer Additional Guidance Mark 3(c) A description that makes reference to the following: • (2.5 % and 7.5 %) lactose stimulates growth of pollen tubes (1) • the effect is dose-dependent / growth depends on the concentration (1) • high concentrations inhibit pollen tube growth (1) ACCEPT pollen tubes can grow in lactose increases pollen tube growth ACCEPT pollen tube did not grow in high concentrations 10% was too concentrated for growth (3) Question Number Answer Additional Guidance Mark 3(d) An answer that makes reference to the following: • because sucrose is {produced / secreted / used} by the {stigma / carpel / plant} (1) • because lactose is {found in milk / not {produced by / found in} plants}