Exam practice answers

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1 Chapter 1 Cells and movements across membranes 1 a) Active transport [1] b) The salt moves against a concentration gradient/from a low to high concentration c) Mitochondria perform respiration [1] which provides the energy needed for active transport d) The cells would shrivel/be damaged because water would be lost [1] by osmosis 2 a) Osmosis [1] b) / [1] = 26.2% [2 marks for correct answer even if working is not shown.] c) Between M the potato cell sap is more concentrated than the solution [1], so water enters by osmosis Above 0.4 M the solution is more concentrated than the cell sap [1], and water leaves by osmosis The movement of water causes the change in mass d) Any value greater than 0.2 M and less than 0.4 M Allow between 0.2 M and 0. 4 M. e) The potato cylinders had different initial masses Chapter 2 Respiration and the respiratory system in humans 1 a) Glucose Lactic acid [1] b) The exercise of the sprint increases demand for oxygen [1], because it is needed to provide energy for the run Breathing cannot supply enough oxygen c) Lactic acid would build up [1] and this would cause muscle fatigue/aching muscles d) To take in extra oxygen [1] to break down the lactic acid built up by anaerobic respiration/ to repay the oxygen debt 2 a) Carbon dioxide is produced at the same rate as oxygen is used The volume of the air in the apparatus would not change [1] so the liquid would not move b) To ensure that the starting volume of air is the same in both respirometers c) 103.8/10 [1] = 13.8 mm min -1 [1] d) Respiration is controlled by enzymes [1] and enzymes work best at warm temperatures Chapter 3 Digestion and the digestive system in humans 1 a) There was glucose present in the water [1] but no starch b) Add Benedict s solution [1] heat in a boiling water bath c) Starch inside the Visking tubing had been digested by the amylase [1] to form glucose The glucose can diffuse through the Visking tubing into the water surrounding it d) High temperatures might denature the amylase [1] so the starch would not be digested e) Increasing the concentration of the starch or the amylase (either) 2 a) The older males are no longer growing [1], which requires energy b) 2772/76 [1] = or 36.5 [1] c) Girls tend to be smaller than boys at that age [1] so have fewer cells requiring energy d) Using kcal/kg/day takes account of the different sizes/masses of a 5-year-old child and an adult Chapter 4 Circulatory system in humans 1 a) C, A, F, E, D, G, B. [All correct 3 marks; any 5 in correct sequence 2 marks; any 3 in correct sequence 1 mark] b) The pulmonary artery [1] c) The atria pump the blood a much shorter distance than either of the ventricles [1] so they do not need to contract with as much force d) To ensure one-way flow of the blood through the heart 2 a) The blood gets further away from the heart [1], which is where the pressure is applied OR 1

2 Contact with the blood vessel walls reduces the pressure The further the blood travels, the more the pressure is reduced b) There are a very large number of capillaries c) It allows time for materials to be exchanged d) They have very thick walls e) The valves ensure one-way flow in the veins Arteries do not need them because they have a pulse which pushes the blood in the right direction Chapter 5 Plants and photosynthesis 1 a) The disc is placed in boiling water [1], then into boiling alcohol It is rinsed in cold water [1], then iodine solution is added b) Blue-black [1] c) To remove any stored starch/to de-starch it d) The plant had carried out photosynthesis [1] to make sugar [1] which was then stored as starch e) The plant did not carry out photosynthesis [1], but used the glucose supplied and converted it into starch 2 Indicative content: Apparatus assembled under water. All joins sealed (with petroleum jelly). These are done to ensure no air enters the apparatus. Leaves dried. Air bubble introduced. Starting position of air bubble recorded. Position of bubble recorded again at set time intervals up to 30 minutes. Distance moved is calculated. Detailed account including all steps in setup and how readings are taken. There is a description which is coherent, relevant, and logically structured. The candidate uses appropriate scientific terminology and accurate spelling, punctuation and Account including most steps in setup and how readings are taken. There is a description which is partially coherent, largely relevant, and with some structure. The candidate uses mainly appropriate scientific terminology and some accurate spelling, punctuation and Basic account with only a vague account of setup and method of taking readings. There 3 a) Respiration [1] b) Photosynthesis [1] c) C the processes of respiration and photosynthesis [1] are balanced [1]; D the plant does not carry out photosynthesis because there is no light [1], but does respire d) To check/ensure that the colour changes seen were not due to changes in the atmosphere/air Chapter 6 Ecosystems, nutrient cycles and human impact on the environment 1 a) i) The animal waste contains ammonium ions. [1] ii) Bacteria will feed on the waste [1], their population will grow [1] and they will remove oxygen through respiration iii) Nitrifying bacteria [1] will convert the ammonium ions into nitrates iv) Some will settle to the bottom/some will be broken down by bacteria. [1] b) Moving water tends to churn up at the surface and incorporate oxygen (or words to that effect). [1] c) Eutrophication [1] 2 a) The sun/sunlight [1] b) Second/secondary consumer [1] c) The mouse will not eat the whole plant [1] and will not digest all that it eats. d) The eagle The heavy metal will accumulate/increase at each level in the food chain e) A [1] Chapter 7 The variety of life 1 Indicative content: Such species are called alien species. The organism may have no natural predators and so its population may grow out of control. The organism may out-compete native species and displace them. 2

3 The organism (animal) may eat native species and so reduce their population. Detailed account including all indicative content. spelling, punctuation and punctuation and 2 a) To avoid the confusion that might result in different countries with different languages/so that the same name is used all over the world b) Steep increase up to 12 weeks [1], followed by decline until 18 weeks [1] then a very slight rise between weeks c) The growth was reduced [1] and did not continue over the whole period/stopped after 15 weeks d) The growth of both species is reduced when they are grown together e) Each has some advantage over the other. T. fragiferum grows to be taller than T. repens, (which is an advantage) but more slowly (which is a disadvantage) Or converse argument. 3 a) /5 [1] = 8000 [2 marks for correct answer on its own.] b) To allow time for the first sample to mix back into the population. [1] c) If they were marked on top, they would be more noticeable to predators [1] and to the people taking the second sample d) It would be possible that none of the original sample would be recaptured [1], so no calculation could be made Chapter 8 Cell division and stem cells 1 a) 60 [1] b) Deoxyribose nucleic acid/dna [1] c) Mitosis [1] d) 30 [1] 2 a) Meiosis [1] b) The chromosomes are all different/the chromosomes are not paired This only happens in meiosis/does not happen in mitosis c) i) Meiosis [1] ii) Mitosis [1] iii) Mitosis [1] iv) Both [1] 3 Indicative content: A stem cell is an undifferentiated cell which is capable of developing into several types of cell. Stem cells could be changed into types of cell which could be used to repair damaged tissues. They could be used to treat cancer, diabetes, brain/nerve damage. Embryonic cells can develop into more types of cell than adult stem cells. Obtaining embryonic cells results in the death of the embryo. People object to the death of a human embryo. Detailed account with no significant omissions. spelling, punctuation and punctuation and 3

4 Chapter 9 DNA and inheritance 1 a) Poland [1] b) Males are formed from sperm carrying a Y chromosome [1] and females from sperm carrying an X chromosome The two types of sperm are formed in equal numbers c) (i) and (iv) [2] [Marks deducted for choosing ii ( 1) or iii ( 1)] d) The % of males is the same for children under 15 as it is at birth e) Women have a higher survival rate at 65+ / women live longer than men on average. [1] 2 a) Black coat colour is dominant to brown b) i) BB [1] ii) bb [1] iii) Bb [1] c) 11 [2] [If answer is wrong, 1 mark for 44/4.] d) The black mice which produced the brown offspring had the genotype Bb [1]; those producing only black had the genotype BB Chapter 10 Variation and evolution 1 Indicative content: Most mosquitos were exposed to DDT. Some would have a natural immunity to it. That immunity would have been caused by a mutation. Only the mosquitoes with immunity survived. Those mosquitoes bred and passed on the mutation to the next generation. Immunity would therefore be more common in the next generation. This process would have been repeated over many generations. Eventually (nearly) all mosquitoes would be immune to DDT. Detailed account with no significant omissions. spelling, punctuation and punctuation and 2 a) i) cc ii) Cc iii) Cc b) No they cannot Patsy may be a carrier [1], and it is possible Alexei is too If they are both carriers, there is a 25% chance of a child with cystic fibrosis Two children without the disease is not enough to eliminate the possibility that both are carriers c) 1 in 4 / 25% [1] Chapter 11 Response and regulation 1 a) 105 minutes b) 0.8 C [Must have units. 0.9 C also acceptable.] c) Without fluids he was unable to produce enough sweat [1], the evaporation of which would have cooled him down d) The body temperature had not risen enough to cause a significant increase in sweating. [1] e) If the air is warmer than the skin, the temperature gradient [1] will cause heat to go from the air into the skin f) The body is cooled by the evaporation of sweat In humid conditions, the sweat will not evaporate so the cooling mechanism will not work 2 a) The time between a stimulus and the response to that stimulus. [1] b) 297 ms [1] [Units essential.] c) The reaction time decreases over time Practice may decrease reaction time/james may be better able to anticipate when the shape will appear with experience d) The difference between the means is very small/the ranges of the right hand and left hand results overlap/not enough repeats e) It is not involuntary f) Motor neurone [1] 4

5 Chapter 12 The kidney and homeostasis 1 a) The renal artery [1] b) Blood enters at a faster rate than it leaves This causes a build-up of pressure inside the knot of capillaries [1], which forces fluid through the filter c) Cells [1] and proteins [1] d) 8 40 = 320 dm / [1] = 99.5% Alternatively 1.5/ = 0.5%, so = 99.5% 2 a) Osmosis [1] b) Diffusion [1] c) It maintains the concentration gradient between the blood and the dialysate. [1] d) Too much salt would pass out of the blood [1] because the concentration in the blood will always be higher than in the dialysate [1] OR water will pass into the blood rather than out of it [1] because the dialysate is more dilute than the blood e) It avoids frequent and regular attachment to a kidney machine Chapter 13 Microorganisms and disease 1 a) Lymphocytes [1] b) Pathogen [1] c) The level of antibodies has not stabilised at a level that gives immunity. d) The first vaccination has produced memory cells [1], which produce antibodies The second vaccination adds more memory cells e) High exposure [1] to a given antibiotic causes bacteria to evolve immunity to it [1], making the antibiotic ineffective 2 a) A chemical (used in medicine) to destroy bacteria. [1] b) i) To mix the nutrients throughout the fermenter ii) To test the ph so that it can be adjusted to optimum levels iii) Gas is being pumped into the fermenter [1] so pressure will build up [1] and must be released. c) Penicillium will respire [1] producing heat If this builds up, it will denature the enzymes of Penicillium d) To prevent contamination of the culture by other microorganisms. [1] 5

Cambridge IGCSE. BIOLOGY 0610/04 Paper 4 Theory (Extended) For examination from 2020 MARK SCHEME Maximum Mark: 80. Specimen

Cambridge IGCSE. BIOLOGY 0610/04 Paper 4 Theory (Extended) For examination from 2020 MARK SCHEME Maximum Mark: 80. Specimen Cambridge IGCSE BIOLOGY 0610/04 Paper 4 Theory (Extended) For examination from 2020 MARK SCHEME Maximum Mark: 80 Specimen This document consists of 8 printed pages. [Turn over 2 mark scheme abbreviations