PLMGSS 2024 4E ScBio P4 Ans

1 Ans: 2024 Secondary 4 Science Bio 5088_Prelim Paper 4 Qn Ans Marks Remarks LO 1a for absorption + (become soluble) + small enough, for diffusion / active transport ; 1 4 (a) describe the functions of the various parts of the digestive system: mouth, salivary glands, oesophagus, stomach, duodenum, pancreas, gall bladder, liver, ileum, colon, rectum, anus, in relation to ingestion, digestion, absorption, assimilation and egestion of food, as appropriate 1bi Enzyme – protease / pepsin Substrate – protein Product – polypeptides 1 R product as amino acids R substrate as polypeptide 4 (b) describe the functions of enzymes (e.g. amylase, maltase, protease, lipase) in digestion, listing the substrates and end-products 1bii 1 Biological catalyst +speed up rate of reaction; 2 without being chemically unchanged; 3 can be reused; 4 Provide alternative pathway with lower activation energy; 2 1 must be in answer 3 (d) explain the mode of action of enzymes in terms of an active site, enzyme-substrate complex and enzyme specificity using the ‘lock and key’ hypothesis

2 1ci Lipase 1 4 (b) describe the functions of enzymes (e.g. amylase, maltase, protease, lipase) in digestion, listing the substrates and end-products 1cii any two from: enzymes are specific OR idea of, one type removes protein and one removes fats / AW ; protein (stains/substrate) will not fit into the active site of lipase / AW ora ; enzyme and substrate have complementary shapes ; 2 3 (d) explain the mode of action of enzymes in terms of an active site, enzyme-substrate complex and enzyme specificity using the ‘lock and key’ hypothesis 1ciii compare with tubes A, B and C to assess effect of lipase and / or bile + quote time taken to turn colourless bile, does not (chemically) digest fats / does not make solution acidic ; lipase / enzyme, is required (for breakdown of fats in milk) ; bile help speed up digestion of fats + emulsify fats; 3 4(b) describe the functions of enzymes (e.g. amylase, maltase, protease, lipase) in digestion, listing the substrates and end-products 4 (d) state the role of the liver in: • fat digestion Total 10m

3 2a 1.25 – 1.32 / 1.32 *100% = -5.3 1 R if not in one DP Ig if no working shown but warn students 3. manipulate numerical and other data; Calculate is used when a numerical answer is required. In general, working should be shown, especially where two or more steps are involved. 2bi 1m scale 1m plot 1m best fit 3 See last page (in words or by using symbolic, graphical and numerical forms of presentation) to translate information from one form to another. 2bii 0.44 / mol dm-3; where graph intersects X-axis 1 2c potato (cube) in 0.8 (mol dm –3 solution) loses (percentage) mass / ora + potato in 0.4 mol dm –3 solution gain mass/ora + quote data; water molecules moves from an area of high water potential to an area of low water potential / AW + osmosis; water potential of 0.8 (mol dm –3 solution) is lower than potato cell + the water potential of the 0. 4 (mol dm –3 solution) is higher than potato cell; movement of water molecules out / loss of water / into cell/gain water + cause of mass loss/gain; 3 2 (b) define osmosis, investigate and describe the effects of osmosis on plant and animal tissues 2d The cell from a potato cube will be turgid + red blood cell burst; 2 2(b) define osmosis, investigate and describe the effects of osmosis on plant and animal tissues

4 Red blood cell no cell wall to maintain shape of cell + rigid structure + prevent cell from bursting Total 10m 3ai A Pulmonary arteries D (Inferior) Vena cava 2 5 (a) identify the main blood vessels to and from the heart, lungs, liver and kidney 3aii Left ventricle 1 5 (d) describe the structure and function of the heart in terms of muscular contraction and the working of valves (histology of the heart muscle, names of nerves and transmitter substances are not required) 3aiii Pump blood to all parts of body through the (aorta); Generate force for blood + greatest distance 2 3aiv Semi-lunar valve; Prevent backflow of blood + ensure blood flows from right ventricle to pulmonary arteries 2 Allow ecf for wrong vessel 3bi 1 0 to 2 minutes pH decreases from 7.07 to 6.55 during vigorous exercise 2 anaerobic respiration + lactic acid production +extra energy required for vigorous exercise 3 After vigorous exercise + pH increases from 6.55 to 7.07 from 2 to 40 min 4 oxygen debt + time taken for lactic acid to be transported to liver 2 Students to quote figures 1 and 2 to get 1m 3 and 4 to get 1m 6 (f) explain why cells respire anaerobically during vigorous exercise resulting in an oxygen debt that is removed by rapid, deep breathing after exercise 3bii Longer time taken for pH to increase back to 7.07/ ora; Lower pH reached during the 2 minutes; AVP 3 6 (f) explain why cells respire anaerobically during vigorous exercise resulting in an oxygen debt that is

5 Less blood is sent to the lungs to be oxygenated; Less oxygenated blood sent to all parts of body for vigorous exercise; More anaerobic respiration + more lactic acid produced; Longer time required to repay oxygen debt removed by rapid, deep breathing after exercise Total 12m 4a A Palisade mesophyll B Spongy mesophyll C Intercellular air space 3 8 (a) identify the cellular and tissue structure of a dicotyledonous leaf, as seen in transverse section using the light microscope and describe the significance of these features in terms of their functions, such as the • distribution of chloroplasts for photosynthesis • stomata and mesophyll cells for gaseous exchange • vascular bundles for transport 4b any 2 from: many (air spaces) / large (air spaces) ; reduces density (of the leaf) ; allowing it to float /  be on water / be near surface of water ; (so) accessible, to light / carbon dioxide / gas exchange / AW, for photosynthesis ;) 2 4ci Guard cells 1 4cii comparison - max 1 from: 1 water lily has more stomata on upper epidermis than tomato ; ORA 2 water lily has more stomata (per mm2) than tomato ; ORA 2

6 any use of comparative manipulated figures from table including unit (at least once in the answer) ; explanation: 3 idea that tomato needs to reduce, water loss / transpiration / evaporation ; 4 water lily (floats on water so) only upper surface is exposed to air ; 5 (water lily has large number of stomata) as water does not need to be conserved ; Total 8m 5a Carnivore – 3 Consumer – 6 Herbivore – 3 Producer -1 2m 2 correct 1 m 9 (b) describe the roles of producers, consumers and decomposers in food chains and food webs 5b Dogwhelks will decrease as there would be more competition for limpets as food; Algae – increase as less limpet will consume the algae 2m 9 (b) describe the roles of producers, consumers and decomposers in food chains and food webs 5c Decomposers 1 9 (b) describe the roles of producers, consumers and decomposers in food chains and food webs Total 5m

7 6ai 2 1 6aii Individual 1 and 2 give birth to offspring 5 who do not have the disease; This means that Individual 1 and 2 are heterozygous; They display the trait though they are heterozygous; 2 12 (c) explain the terms dominant, recessive, homozygous, heterozygous, phenotype and genotype 6aiii 5 1m phenotype + genotype of parents 1m gametes 1m correct cross 1m genotype of offspring + phenotype of offspring of offspring 1m ratio 12 (f) use genetic diagrams to solve problems involving monohybrid inheritance 6bi Gene is a unit of unit of inheritance made up a sequence of nucleotide that codes for polypeptides 1 10 (d) state that each gene: • is a sequence of nucleotides, as part of a DNA molecule Huntington’s disease Hu