VS 2023 O Level Pure Biology P2 MS w Feedback

2023 / 6093 Biology Paper 1 25 A The most popular choice was to select the lens and the ciliary muscles, thereby neglecting the role played by the cornea. A considerable number selected the cornea and the lens, which infers that they do not appreciate that the lens can only change shape by the action of the ciliary muscles Paper 2 Answer Scheme Section A Qn No Answer Mark Feedback 1(a) X: pulmonary artery Y: right ventricle Z: tricuspid valve 1 1 1 Most candidates found this a straightforward, accessible question. Some candidates misapplied the letters to the structures and named correct structures but with the incorrect letter. Weaker responses referred to the wrong side of the heart, identifying X as the aorta or Z as the bicuspid valve. 1(b) During atrial systole, right atrium wall contracts and is emptied of blood. During ventricular systole, right ventricle wall contracts and pressure in RV exceeds RA. Tricuspid valves close to prevent backflow to RA. Pressure in RV exceeds pulmonary artery. Semi-lunar valves open to allow blood to flow into pulmonary artery towards the 1 1 1 1 Many candidates had a good appreciation of the cardiac cycle. Several candidates did not appreciate that the AV valve in the right atrium is open before atrial contraction, and that the ventricle fills passively. Stronger responses described how the ventricle muscle or wall contracted, increasing the pressure. Some candidates thought the pressure increased due to the ventricle filling with blood. Weaker

lungs. responses confused the left and right sides of the heart, sometimes indicating that blood was pumped from one side of the heart into the other. 1(c) Blood from right ventricle moves into the pulmonary artery and towards the lungs. Blood returns to left atrium via the pulmonary vein. Blood flows past the bicuspid valves into left ventricle. Left ventricle contracts, blood flows past the semi-lunar valves and enters aorta. Aorta branches into smaller arteries, including renal arteries, and then into capillaries. Blood flows into the kidneys. 1 1 1 1 There were many good accounts, with a clear and accurate sequence described. However, some candidates thought that the hepatic artery, hepatic portal vein, and hepatic vein take blood to the kidneys. Weaker responses indicated that the blood entered these vessels straight from the right ventricle, with no reference to the lungs at all. 2(a)(i) Both chromosomes are the same shape and length. Both are chromosome 9, which means they have the same gene sequence/ loci. 1 1 Candidates generally understood the question but often answered without correct use of scientific terminology. They referred to the chromosomes being the same size rather than being the same length. Candidates who performed well knew that they had the same genes, gene loci or centromere positions, but some just talked about a single gene or alleles being the same. 2(a)(ii) A body cell contains two copies of each chromosome / homologous pairs while a gamete contains only 1 copy. 1 1 Many candidates correctly used the terms haploid and diploid, although some thought the terms referred to the chromosomes themselves rather than the cells. Weaker responses made vague references to the number of chromatids,

or chromosomes coming from each parent. 2(a)(iii) Characteristic V-shape Spindle fibres attached to centromere, pulling towards opposite poles 1 1 Several candidates did not follow the instructions in the question to only draw one pair of homologous chromosomes. There was also some confusion between the first and second division of meiosis. Only stronger responses included the V shape as the chromosomes were pulled by the centromeres, but some were pointing in the wrong direction away from the poles. 2(b) I A I B I O I O I A I B I O I O I A I O I A I O I B I O I B I O A A B B 1 1 1 1 This question was well answered by the majority of candidates, suggesting a good understanding of how to represent genetic crosses. 3(a)(i) Mesophyll cells oxidise glucose during aerobic respiration to release energy for cellular processes Like synthesising high numbers of enzymes involved in photosynthesis 1 1 Most candidates were aware of the role of mitochondria in respiration, although some did not specify that this was ‘aerobic’. Many candidates went on to explain how energy might be used in a mesophyll cell. 3(a)(ii) Any two from: 1. Carbon dioxide 2. Water 3. Ions 4. ATP 1 1 The majority of candidates correctly named carbon dioxide and water as the substances leaving the mitochondrion. Weaker responses most commonly included ‘oxygen’ and ‘glucose’, indicating that products and reactants were confused, or that candidates mistook mitochondria for chloroplasts.

3(b)(i) As cell diameter increases from 10 to 80 um, mean number of mitochondria increases from 80 to 700, by 620. 1 The vast majority of candidates described the relationship correctly. 3(b)(ii) Root hair cell; Require a lot of energy to take in mineral salts by active transport; Xylem cell; No/ reduced protoplasm to have a hollow lumen to minimise resistance to flow of water and mineral salts. 1 1 1 1 Many candidates correctly named a cell that would have a greater density of mitochondria, for example, root hair cells and companion cells, and went on to make a correct reference to ‘active transport’ as the reason. Weaker responses incorrectly thought that water was moved by active transport. Candidates could also correctly name a cell with a lower density of mitochondria, although knowledge of reasons why fewer mitochondria might be required was less secure. Some candidates suggested that sieve tubes have ‘no cytoplasm’ or that epidermal cells require ‘no energy’. Weaker responses gave the cell types the other way round, such as root hair cells having fewer mitochondria, or suggested non-cellular components such as ‘stomata’ or ‘cuticle’ instead of types of cells. 4(a) Liver: all except last option Pancreas: 3rd and last option 5 This question was well answered by the majority of candidates. 4(b) Running: Adrenaline released → liver converts glycogen stores to glucose. Blood glucose concentration rises. Glucose is oxidised during aerobic respiration to release 2 Many candidates could correctly identify the secretion of appropriate hormones in each situation. The most common error was to state

energy for muscular contractions. Resting: More glucagon released. Low blood glucose after running is detected by receptors in pancreas. Pancreas secretes more glucagon and less insulin. Liver converts glycogen stores to glucose. Blood glucose rises. 3 or imply that the hormone itself was directly responsible for the formation or breakdown of glycogen, e.g. ‘insulin converts glucose to glycogen’. Most candidates gave the