VS 2021 O Level Pure Biology P1+2 MS w Feedback

2021 Biology 6093 Suggested Answers Paper 1 1 2 3 4 5 6 7 8 9 10 C B D D A D C A D A 11 12 13 14 15 16 17 18 19 20 B A B B A D C A C D 21 22 23 24 25 26 27 28 29 30 A A D D D C B C C C 31 32 33 34 35 36 37 38 39 40 B C C B A C D B A D Paper 2

Section A Q No Suggested Answers Marks Feedback 1(a) P: vena cava Q: right atrium 1 1 Some candidates confused the vena cava with pulmonary vein. 1(b) Transport blood rich in oxygen and glucose from aorta to muscles of the heart 1 1 Many correctly summarised the role of the coronary arteries 1(c) Oxygenated blood from pulmonary vein; enter heart through the left atrium; passes through bicuspid valves / AV valve into left ventricle; ventricular systole , pushing blood out of left ventricle, passes through the semi-lunar valves to the aorta; enters the kidney via the renal artery 1 1 1 Many candidates included unnecessary detailed info abt the oxygenation of the blood in the lungs as an intro Describe route to the kidney, ref to renal artery 1(d) platelets and damaged tissue release thrombokinase; thrombokinase converts prothrombin to thrombin thrombin converts soluble fibrinogen to insoluble fibrin threads, which entrap RBCs, forming a mesh to plug the wound 1 1 Blood clotting was well understood by most candidates, with many demonstrating extensive knowledge not required for answering the question. Many candidates had a good knowledge of the role of platelets and the role of fibrin in forming the clot. 2(a)(i) energy used for growth = 6 x 2.5 1

= 15 au / year 2(a)(ii) heat 1 2(a)(iii) 20 x 2.5 = 50 au / year 1 2 (b) percentage = 15 / (15 + 25 + 50) x 100% = 16.7% 1 2(c) For animals to move, they have to break down more digested food to release more energy through respiration. By reducing movement, less energy is used by the animal and hence lost as heat to the environment. There will be more excess energy to be used for growth → increase in mass increases profit for farmers. 1 1 1 3(a) B, salivary amylase C, lipase A, pepsin 2 2 2 The vast majority of candidates demonstrated an excellent knowledge of enzymes in different parts of the digestive system. Occasional errors occurred when trypsin and pepsin were ascribed to the incorrect areas, or ligase enzyme was confused with lipase enzyme. 3(b) Enzyme acts as a lock while the substrate acts as a key. The substrate has a complementary shape to the active site of the enzyme . 1 A significant number of candidates did not follow the instruction to ‘explain the mode of action’ of enzymes and instead listed a range of digestive enzymes including their associated substrates and products with

Substrate binds to the active site, forming an enzyme-substrate complex . This allows the enzyme to break the bonds in the substrate easily, lowering the activation energy for the reaction. Substrate which the large, complex food molecule e.g. protein is broken down by protease into products which are small, simple food molecules e.g. amino acids. 1 1 occasional references to optimal pH values and possible denaturation. Candidates who did correctly address the question demonstrated a good level of understanding 4(a) Nn X Nn N n N n NN Nn Nn nn normal normal normal affected 1 1 1 1 Most candidates correctly completed the genetic cross. Candidates who performed less well used the term ‘carrier’ for the phenotype of ‘Nn’, which is a genotype not a phenotype. 4(b) 25% / 0.25 1 The majority of candidates gave the correct probability, although some candidates who correctly completed the genetic cross went on to give an incorrect probability of 0.5 or gave a ratio answer of 3:1. 4(c) The mother does not have PKU and thus can produce the enzyme to break down phenylalanine. Mother will not accumulate phenylalanine in the blood, which will not be passed to the foetus in excess through the placenta. 1 1 Many candidates identified that the mother possessed the enzyme that would break down phenylalanine, but they did not develop their answer fully to describe the consequences of this. Candidates who performed less well referred to the mother’s enzyme diffusing to the baby. 4(d) Down syndrome 1 The vast majority of candidates provided a correctly

named disease. Incorrect suggestions included ‘cancer’ or ‘autism’. 5(a) Excretion is the removal of metabolic waste products, toxic substances and excess substances from the body. For example, carbon dioxide from respiration is excreted via lungs, urea from deamination of excess amino acids is excreted via kidneys. 1 1 This question was well answered. a very large proportion of candidates could describe the origin of the waste products. 5(b)(i) From glomerulus to Bowman’s capsule 1 Most candidates knew the site of ultrafiltration and drew their arrow in the correct vicinity. Some, however, only indicated the position (usually within the glomerulus) of the process and did not indicate the direction of ultrafiltration. 5(b)(ii) From proximal convoluted tubule to peritubular capillaries 1 Origin of their arrow showing reabsorption within the nephron, sometimes did not reach the capillaries. Others only drew arrows along the nephron or within the tubule showing the direction of flow. 5(c) ADH causes walls of V to be more permeable to water Increases reabsorption of water from V into surrounding blood capillaries 1 1 5(d)(i) Both similarities and differences required 3

Similarities: 1. Both contain digested food substances e.g. amino acids, glucose. 2. Both contain mineral salts 3. Both contain dissolved gasses e.g oxygen, carbon dioxide. 4. Both are maintained at body temperature Differences 1. Unlike plasma, dialysis fluid contains no metabolic waste products e.g. urea. 2. Unlike plasma, dialysis fluid contains no hormones e.g. insulin, glucagon. 5(d)(ii) Dialysis fluid is a medium that creates a steep concentration gradient for a high rate of diffusion of metabolic waste e.g. urea and excess substances e.g. salt, water, from blood. This effectively removes metabolic waste and excess substances from the patient’s blood. 1 1 6 Isolation idea: Scientists isolate the human DNA containing insulin gene from a pancreatic cell, and a bacterial plasmid. Restriction enzyme: Insulin gene is cut using a suitable restriction enzyme. T he plasmid is cut using the same restriction enzyme. This produces complementary sticky ends on the human DNA fragment and the bacterial plasmid. 1 1

DNA ligase: The human DNA fragment containing insulin gene is mixed with the bacterial plasmid and inserted into it using DNA ligase forming recombinant plasmid. Transformation : Recombinant plasmid/DNA is inser