Cambridge IGCSE Combined and Co-ordinated Sciences Answers to end-of-chapter questions Answers to end-of-chapter questions All sample answers were written by the authors 5 a A cell wall; Biology B chloroplast; b they have cell walls; [2] [2] Chapter B1 Cells 1 a movement, growth, nutrition, sensitivity, excretion b reproduction, respiration 2 a chloroplast b mitochondrion c cell membrane d nucleus vacuole e cell wall 3 a A chloroplast is an organelle that contains the pigment chlorophyll (A chloroplast is surrounded by two membranes Folded membranes inside the chloroplast have molecules of chlorophyll on them.) Photosynthesis takes place inside chloroplasts, with the help of chlorophyll, which absorbs energy from light b All cells have a cell membrane, which is a thin layer of protein and lipid that surrounds the cell and controls what enters and leaves it Plant cells (and bacterial cells) also have a thicker layer surrounding them In plant cells, this is made of cellulose Cell membranes are partially permeable Cell walls are fully permeable a they have chloroplasts; c i Measured diameter on image = 20.5 mm [1] (Note: the measurement depends on where the outer limit of the cell is considered to be It should be the middle point of the two cell walls around the adjacent cells If the measurement has been made from cell membrane to cell membrane, it will be 19.1 mm If it has been made from the midpoints of the triangle of extracellular space at each corner, it will be 21.1 mm.) ii actual size = image size ÷ magnification = 20.5 ÷ 250 = 0.082 mm or 82 µm [2] Chapter B2 Movement in and out of cells 1 a Osmosis Water is at a high water potential (dilute solution) in the soil and at a lower water potential (concentrated solution) inside the root cells It moves through the partially permeable cell membrane, down its water potential gradient b Neither In this case, all the molecules in the saliva move as one, like water flowing in a river Both diffusion and osmosis involve the random, individual movement of molecules or ions c Diffusion The ink particles move randomly, bumping into each other and into the water particles, gradually spreading throughout the water • be drawn with unbroken lines (no gaps in the line) • have the correct proportions • show each structure accurately and clearly [5] b Measured diameter on diagram = 36.5 mm actual size = image size ÷ magnification = 36.5 ÷ 0.6 = 60.8 mm (or 6.08 or 6.1 cm) d Diffusion The carbon dioxide particles move randomly, and some will ‘bump into’ a stoma in the underside of the plant leaf There is a low concentration of carbon dioxide inside the leaf, because the plant uses it up very quickly in photosynthesis The carbon dioxide diffuses down its concentration gradient, from the air into the leaf 2 a The sugar solution as a whole does not anything We need to think about the individual particles in the sugar solution – the water molecules and the sugar molecules Both of these move about randomly The water molecules can get through the tiny holes in the tubing, but the sugar molecules are too big What will happen is that the water molecules will move © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences If Visking tubing containing a sugar solution is put into a beaker of water, water will move from the water into the sugar solution, by osmosis b It is true that plant cells not burst in pure water, but this is because the cell wall is strong enough to prevent this happening The cell wall is fully permeable, and cannot stop water molecules going through it So the corrected sentence could be: Plant cells not burst in pure water because, although water enters the cell by osmosis, the strong wall prevents the cell from bursting c It is true that water will move out of a plant cell by osmosis, if the cell is placed in a concentrated sugar solution However, the cell wall is not partially permeable – it is fully permeable So the corrected sentence could be: When a plant cell is placed in a concentrated sugar solution, water moves out of the cell by osmosis, through the partially permeable cell membrane d Plasmolysis is the result of placing a plant cell in a concentrated sugar solution So much water moves out of the cell by osmosis that the contents shrink, and the cell membrane pulls away from the cell wall As animal cells not have a cell wall, they cannot undergo plasmolysis So the corrected sentence could be either: Animal cells shrink when placed in a concentrated sugar solution OR Plant cells plasmolyse in a concentrated sugar solution 3 a Diffusion is a result of the random movement of molecules or ions At higher temperatures, these have more kinetic energy and move faster, so diffusion happens faster b During daylight, plants photosynthesise They produce oxygen in their leaves, so the oxygen concentration inside the leaf is higher than the oxygen concentration in the air outside Oxygen therefore diffuses down its concentration gradient, from the leaf and into the air c Visking tubing is a partially permeable membrane It has tiny, molecule-sized holes in it Water molecules are even smaller than the holes, so they can pass through Sugar molecules are much bigger than the holes, so they cannot pass through d When it is placed in pure water, an animal cell absorbs water by osmosis This is because there is a higher water potential outside the cell than inside it The extra water makes the cell swell, until it bursts e Plant cells are held in shape by their full vacuoles, which push outwards against the strong cell wall, producing a very firm structure A plant cell like this is said to be turgid Turgid cells pressing against each other make plant tissues strong and firm When the cells are not full of water, they are no longer turgid, and their contents not press outwards on the cell wall The cells, and the tissues in the leaves that they make up, become soft and floppy This is why the plant wilts 4 a the movement of molecules / ions, down a concentration gradient / from a high concentration to a low concentration; as a result of their random movement; [2] b i 70 Time for litmus to go blue / s randomly back and forth through the holes Because there are more of them in the water than in the sugar solution, their net movement will be into the tubing So the corrected sentence could be: Answers to end-of-chapter questions 60 50 40 sample A 30 20 sample B 10 0 10 12 Distance along tube / cm 14 16 all points correctly plotted; lose one mark for any incorrect point neat best-fit line drawn; [3] ii ammonium hydroxide is alkaline; [1] iii A; [1] iv C’s concentration was between A and B; specific evidence quoted to support this statement, e.g it took less time for it to travel 10 cm than A and more time than B.[2] 5 a the pH is greater than 8; [1] b table is drawn with a ruler and has rows and columns for dimensions of block and time taken to go colourless; headings for both quantities include correct units – including time / s; times to go colourless are correctly recorded as 128 and 72 (with no units); [3] © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences c i diffusion; [1] ii hydrochloric acid neutralised the alkaline substance in the agar / the pH became less than 8; [1] d block B had a greater surface area to volume ratio / the distance for diffusion to the centre of the block was smaller in block B;[1] Chapter B3 Biological molecules 1 a monosaccharide, found in both plants and animals, used as fuel in respiration b polysaccharide, found in plants only, used as an energy store in plant cells c polysaccharide, found in plants only, used to make cell walls d polysaccharide, found in animals only, used as an energy stores in (liver) cells 2 a nitrogen (or sulfur) b amino acids c Benedict’s d lipid (fat) sucrose e sucrose f metabolism or metabolic reactions Measure equal volumes of each solution into two identical test tubes Add equal volumes of Benedict’s solution to each one Place both tubes into a water bath at about 80 °C Do this at exactly the same time Watch carefully The one that changes to green or orange first, or the one that is the darkest orange after a set length of time, is the one that has the most concentrated solution of reducing sugar Substance Elements Carbohydrate, How to One it contains fat or protein? test for it function haemoglobin C, H, O, N protein biuret test carries oxygen in the blood glucose C, H, O carbohydrate Benedict’s to provide test energy starch C, H, O carbohydrate iodine test stores energy in plant cells enzyme C, H, O, N protein biuret test speeds up reactions Answers to end-of-chapter questions 5 a a protein catalyst, which speeds up the rate at which metabolic reactions take place b a term used to describe the state of a protein molecule that has lost its shape – often caused by high temperature or extremes of pH; a denatured enzyme molecule is unable to catalyse its reaction because the substrate no longer fits into its active site c the substance that is changed into products by an enzyme; the substrate fits into the enzyme’s active site d a new substance formed in an enzyme-catalysed reaction e the part of an enzyme molecule into which a substrate molecule fits 6 a About 37 °C – human body temperature b About – hydrochloric acid has a very low pH c At low temperatures, molecules have low kinetic energy and move slowly This means that the frequency of collisions between enzyme molecules and substrate molecules is also low d Above the enzyme’s optimum temperature, the enzyme molecule begins to lose its shape – it is denatured This means that the substrate molecule does not fit into the active site, so the enzyme cannot catalyse the change of the substrate into products 7 a calcium; b water; c they both contain protein; d orange-brown; it does not contain starch; [1] [1] [1] [2] e protein, fat and carbohydrate; [1] 8 a blue-black; b the blue-black colour would have disappeared from parts of the plain paper. c i Time / Number of new Total number of minutes areas where there areas where there had been a reaction had been a reaction 14 14 28 42 18 60 12 72 6 78 [1] [1] [2] © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences Number of new areas where there had been a reaction ii 30 20 10 0 Time / minutes time on x-axis and number of new areas on y-axis; scales on both axes go up in even steps (e.g 1, 2, etc on x-axis, 10, 20, 30 etc on y-axis); both axes fully labelled including units; all points accurately plotted with small, neat crosses or circles with a ring around them; straight lines drawn between the points / good best-fit line drawn; [5] iii any two sensible suggestions about differences between the goats, e.g different ages, different genders, different breeds, different concentrations of enzyme in their saliva, how hungry they were when the saliva was collected; [2] d continue for longer; take readings more often than one minute intervals; include some discs that have no enzyme in them / have boiled enzyme in them; repeat the experiment two more times; [max 3] 9 a sucrose molecules and enzyme molecules move randomly; sucrose molecule collides with enzyme’s active site; enzyme causes sucrose molecule to split into glucose and fructose; reference to involvement of water in this reaction; products / glucose and fructose, leave the active site; [max 3] b i optimum temperature for enzymes; temperature kept constant because, pH is the independent variable / temperature is a control variable; [2] ii no activity below pH 3; optimum / greatest activity, is at pH 7; no activity above pH 11; [3] Chapter B4 Plant nutrition Obtained from Used for Nitrates the soil making amino acids and proteins Water the soil photosynthesis, maintaining turgor / supporting tissues, transporting substances Magnesium the soil making chlorophyll Carbon dioxide the air photosynthesis Answers to end-of-chapter questions 2 a A chloroplast is an organelle that contains the pigment chlorophyll Photosynthesis takes place inside chloroplasts, with the help of chlorophyll, which absorbs energy from light b The palisade mesophyll is closer to the upper surface of the leaf than the spongy mesophyll The cells in the palisade mesophyll are tall and thin, while the cells in the spongy mesophyll are more rounded The palisade cells contain more chloroplasts than the spongy cells More photosynthesis takes place in palisade cells than in spongy cells There are larger air spaces in the spongy mesophyll than in the palisade mesophyll c Organic substances have been made by living organisms, e.g carbohydrates, proteins, vitamins Inorganic substances have not been made by organisms, e.g magnesium ions, water d Guard cells are pairs of sausage-shaped cells found in the epidermis of leaves (usually in the lower epidermis) The hole in between the pair of guard cells is a stoma 3 a carbon dioxide + water → glucose + oxygen b Carbon dioxide enters the leaf through stomata, by diffusion from the air Water enters the root hairs, by osmosis from the soil and is then transported up the xylem to the leaf c Glucose is used to make starch, or to provide energy by respiration Oxygen diffuses out of the leaf into the air, through the stomata 4 a Carbon dioxide diffuses through the stoma and then through the air spaces, allowing it to reach the cells in the palisade layer Oxygen diffuses in the opposite direction when photosynthesis is taking place (When you have learnt about transport in plants, you will also find out that the air spaces are important for allowing the movement of water vapour out of the leaf.) b This means that light can pass straight through these cells, so little light is lost before it reaches the palisade cells, where it is used in photosynthesis c The larger the surface area, the more sunlight will hit the leaf This means that more energy can be absorbed by chlorophyll, so more photosynthesis can take place d The veins bring water from the soil to the leaf cells By branching, they can bring water close to every cell The cells need water for photosynthesis, and to maintain their turgor, helping the leaf to be held out straight 5 a sucrose This is a soluble sugar, which can dissolve in water for transport It is not too reactive © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences b starch This is an insoluble polysaccharide, which can be stored as solid grains in cells and will not interfere with the reactions that take place in the cell (It also does not affect the water potential of the cell; if sucrose was stored, this would tend to draw excess water into the cell by osmosis.) 6 a Leaf from plant A: all orange-brown; Leaf from plant B: uncovered part blue-black; covered part orange-brown; [3] b i to break down the cell membranes so that iodine solution and starch can come into contact; [1] ii to remove the chlorophyll; [1] c i cover other areas with a simlar material that is transparent (so that the only difference is whether light can reach the leaf); [1] ii it controls a significant variable – having different plants could affect the results / because one plant might respond differently from another; [1] d use a plant with variegated leaves; destarch it; then leave in the light long enough for it to make starch; test a leaf for starch; would expect green parts to go blue-black, white parts to be orange-brown; [max 3] 7 a i F; [1] ii A; [1] iii D. [1] b i little light is lost before it reaches the palisade cells, where it is used in photosynthesis; [1] ii the waxy cuticle prevents water loss through this surface of the leaf; [1] iii bring water to the leaf; take sucrose away from the leaf; help to support the leaf. [max 2] c i carbon dioxide; water [2] ii some is used in respiration to release energy; some is converted to starch for storage; some is used to make cellulose cell walls for new cells; some is converted to sucrose for transport to other parts of the plant; some is converted, with the addition of nitrogen, to amino acids; some is converted to, fats / lipids [max 4] Chapter B5 Animal nutrition 1 a i calcium, vitamin D ii carbohydrate, fat, protein Answers to end-of-chapter questions iii protein iv fibre v protein, iron vi vitamin D b There is a very wide range of possible answers Images B5.02 to B5.04, and Tables B5.02 and B5.03, provide some examples Answers can also be checked against a table of nutrient values of foods Search on the internet for: 'food nutrient content table' and select one that covers foods commonly eaten in the relevant country 2 a Digestion is the breaking down of large food molecules into small ones Absorption is the movement of these small molecules through the wall of the small intestine and into the blood b The small intestine is longer and narrower than the large intestine It is made up of the duodenum and ileum, whereas the large intestine is made up of the colon and rectum Digestion and absorption of all types of food molecules – including water – takes place in the small intestine Only water absorption takes place in the large intestine c Enamel is the exceptionally hard outer layer of a tooth Dentine is a softer layer beneath the enamel. Dentine contains living cells, but enamel does not d Bile is a greenish liquid made in the liver and stored in the gall bladder, whereas pancreatic juice is made in the pancreas Both liquids flow along ducts into the duodenum Bile contains bile salts, which are not enzymes but which help to emulsify fats (break large droplets into small ones) Pancreatic juice contains several different digestive enzymes that digest fats, proteins and carbohydrates Both bile and pancreatic juice also contain sodium hydrogencarbonate, which neutralises the acid from the stomach 3 a A salivary gland B oesophagus C stomach D pancreas E duodenum F ileum G colon H rectum I anus J liver b i A and D ii C and D © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences Answers to end-of-chapter questions iii D diagram shows a molar tooth; correct labels to: enamel; dentine; pulp cavity; nerves and blood vessels; crown / root; iv C v F and G vi I 4 ingestion amylase starch mucus oesophagus hydrochloric proteins duodenum small pancreas gall fatty acids glycerol 5 a vitamin C and vitamin D; [1] b they all already are small molecules; which can pass through the walls of the ileum; [2] c any two dairy foods, bread; [1] d helps calcium to be absorbed; needed for making, bones / teeth; [2] e anaemia; lack of energy; iron is needed to make haemoglobin; which transports oxygen around the body; lack of oxygen means less respiration; [max 3] 6 a A incisor; B canine; C molar; [3] b tooth A: cut off pieces of food; to help with ingestion; tooth C: crush / grind, food; to increase surface area for enzyme action; [4] c [6] 7 a i blue-black; [1] ii starch is present; [1] iii rows 2, and show sugar absent, starch absent and sugar absent; rows 5, 6, and show starch absent, sugar present, starch absent, sugar present; b i breaks down starch to sugar; [2] [1] ii results show there is sugar in the water in the beaker; so sugar molecules have moved through the membrane; sugar molecules are small enough to pass through the holes in the membrane; c i small intestine / duodenum / ileum; [2] [1] ii blood / blood plasma / capillaries; [1] d its molecules are too big to be absorbed / to pass through the wall of the small intestine; [1] 8 a breakdown of large / insoluble molecules; to small / soluble molecules; [2] b amylase; [1] c i at the beginning; [1] ii maltose; [1] iii line is of similar shape; line is above the 35 ºC line; [2] d to produce molecules that are small enough to be absorbed / because starch molecules are too large to be absorbed; [1] Chapter B6 Transport in plants 1 a xylem vessel b xylem vessel c root hair d transpiration e stoma f potometer © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences b so plants can make more amino acids / proteins; a and b root hairs liquid root cortex cells liquid xylem liquid gas stomata gas b, c and d 4 a 20; [1] b as wind speed increases, water uptake increases; any use of manipulated figures (e.g doubling of wind speed from to metres per second results in 1.7 times the rate of water uptake); [2] c light intensity; temperature; humidity; [max 2] 5 a i more root hairs; shorter root hairs; decrease in length of root hairs is (much) greater for plant B;[2] iii less surface area; so less uptake of mineral ions / water; so less photosynthesis; less glucose / starch / carbohydrate synthesised; so less fuel for respiration / less energy available; less nitrate reduces protein synthesis; [2] 2 a Arteries take blood away from the heart; veins take blood towards the heart Arteries have thick, elastic walls; veins have thinner walls Arteries have a narrow lumen; veins have a wider lumen Arteries not have valves; veins have valves b Oxygenated blood contains a lot of oxygen (combined with haemoglobin inside the red blood cells) and is bright red Deoxygenated blood contains less oxygen, and is a duller purplish-red c An atrium is one of the upper chambers of the heart, which receives blood and which has thin walls A ventricle is one of the lower chambers of the heart, which has thick walls that pump blood out of the heart d A red blood cell is a small cell with no nucleus, indented, and containing a large amount of haemoglobin Its function is to transport oxygen There are several types of white blood cells, but most are larger than red blood cells and they all have a nucleus They not contain haemoglobin Their function is to fight pathogens 3 a plasma b white cells c red cells d platelets and plasma e plasma [2] ii both show same increase in number of root hairs (per unit area); to make more cells for growth; 1 a vena cava, right atrium, right ventricle, pulmonary artery, lungs, pulmonary vein, left atrium, left ventricle, aorta b vena cava, right atrium, right ventricle, pulmonary artery 3 a a section cut across something Chapter B7 Transport in animals leaf mesophyll cells liquid air spaces in leaf Answers to end-of-chapter questions [max 3] • Arteries: thick walls to withstand high-pressure blood; elastic walls to withstand pulsing blood; narrow lumen so blood moves through fast • Veins: valves to keep low-pressure blood moving in one direction; wide lumen to provide least resistance to blood flow • Capillaries: very narrow, so red blood cells have to squeeze through and are brought close to cells that require oxygen; very thin walls with gaps, so substances can easily move between blood and tissue fluid • Xylem vessels: dead and hollow so nothing in the way of water movement; narrow, so a tall column of water © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences can be supported without breaking; lignin in walls to make them waterproof and to provide strength; pits in walls to allow water to move sideways • Phloem tubes: living but with no nucleus and only a small amount of cytoplasm, so sap can flow through; perforated end walls to allow sap to flow through 5 a contains haemoglobin that combines with oxygen; collects oxygen in lungs, releases it in body tissues; [2] b protects against, disease / pathogens; takes in and kills micro-organisms / bacteria / pathogens;[2] c to deliver requirements to body cells; e.g oxygen / glucose / other named nutrient; to remove waste products from body cells; e.g carbon dioxide / other named waste product; [max 2] Answers to end-of-chapter questions b E vena cava; F aorta; [2] c coronary (arteries); plaques / cholesterol / fat deposit, in artery wall; partly blocks artery; less blood can flow through; less oxygen carried to heart muscle; increased likelihood of blood clotting; [max 3] d to keep the blood moving; to keep the blood oxygenated; to remove carbon dioxide from the blood; [max 2] e has a septum dividing the two sides of the heart; oxygenated blood on the left and deoxygenated on the right; both sides contract at the same time; more muscle on the left side; so more pressure produced on the left side; high pressure to most of body; low pressure to lungs; [max 4] 6 a Red cell in diagram measures 23 mm; Chapter B8 Gas exchange and respiration = × 3285. b it has no nucleus; it has a depression in the centre / is a biconcave disc; it contains haemoglobin. 1 a protein synthesis, cell division, growth, movement, passage of nerve impulses, maintaining a constant body temperature b respiration c glucose + oxygen → carbon dioxide + water so magnification = 23 / 0.007; [3] [3] c i transporting oxygen; ii it contains haemoglobin; which combines reversibly with oxygen; it has a large surface area to volume ratio; which speeds up the movement of oxygen into and out of the cell; it is small; which allows it to squeeze through very small capillaries; it has no nucleus; which makes more room for haemoglobin. [max 3] 7 a 2; [1] b i about 0.75 s; [1] ii explanation of measuring time between two equivalent points; [2] c ventricle volume decreasing; because the muscle is contracting;[2] d when the ventricle contracts, the valve shuts; because of the pressure of the blood pushing upwards on it; when ventricle relaxes, valve opens; [3] e line follows the same pattern as the first, at the same times, but does not rise to such a high volume; [2] 8 a A left atrium; B bicuspid valve / atrioventricular valve; C semilunar valve; D right ventricle; [4] 2 a inspired air has more oxygen; inspired air has less carbon dioxide; inspired air usually has less water vapour b Oxygen is used by body cells in respiration Carbon dioxide is produced by body cells in respiration Water evaporates from the lining of the lungs into the air, so it is breathed out in expired air 3 a the movement of oxygen into the body and the loss of carbon dioxide b the alveoli in the lungs b any three of: large surface area; thin; good supply of air containing oxygen; good blood supply 4 a anaerobic b both c aerobic only in humans; both in yeast d both The following sequence should be shown, in a diagram or words: down trachea, bronchus, bronchiole, into alveolus (by mass flow of air), across wall of alveolus into the blood, by diffusion into a blood capillary into a red blood cell, combines with haemoglobin, carried along the pulmonary vein to the left atrium of the heart then to the left ventricle, pumped out of the heart into the aorta, then to a capillary in the arm muscle, diffuses out of the red blood cell, diffuses out of the capillary, diffuses into the muscle cell © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences 6 a i to make sure all the carbon dioxide had been removed;[1] ii clear; Answers to end-of-chapter questions most of the graph paper provided; each bar drawn neatly and precisely; [4] b the more cigarettes smoked per day, the greater the chance of dying between the ages of 40 and 60 years old; [1] b i to see if any carbon dioxide had been produced;[1] ii cloudy; [1] c have another apparatus in which flask has no insects;[1] the younger a person is when they start smoking, the greater the chance of dying between the ages of 40 and 60 years old; the number of cigarettes smoked per day seems to increase the chance of dying between 40 and 60 more than the age at which smoking started; [3] d i red / orange; [1] ii carbon dioxide present; Chapter B9 Coordination and homeostasis dissolves / reacts with water; to produce an acidic solution; e respiration ; [3] [1] 7 a 12; [1] b 21; [1] c 0.5 dm ;[1] d 1.1 dm3;[1] e more rapid breathing brings fresh air into the lungs more often; deeper breathing brings a larger volume of fresh air into the lungs; more oxygen can diffuse into the blood more quickly; supplying more oxygen to the muscles; so they can respire faster; releasing more energy from glucose; [max 4] f brain senses the pH of blood; pH decreases during exercise; because more carbon dioxide is dissolved in the blood plasma; brain responds by sending more frequent impulses to the breathing muscles; so they contract harder and more frequently; [max 4] 8 a 12.5 breaths per minute at start, 25 breaths per minute during exercise; so increase is 12.5 breaths per minute; [2] b from just before 11 minutes to just before 16 minutes; minutes; [2] c during exercise not enough oxygen was supplied to muscles; so they respired anaerobically (as well as aerobically); producing lactic acid; which was broken down by combining with oxygen (when exercise finished); reference to paying back the oxygen debt ; [max 4] d would follow a pattern similar to that of breathing rate; heart pumps oxygenated blood to the muscles; more oxygen required by muscles as they exercise; so that they can respire faster; more carbon dioxide needs to be removed from the muscles; continuing need for more oxygen after exercise to pay off oxygen debt; [max 4] 9 a axes correctly labelled; x-axis scale uses the ranges from the table; good scale on both axes that uses 1 a a reflex action b The stimulus from the sharp object is detected by a receptor in the foot This sends an electrical impulse along a sensory neurone to the brain or spinal cord The impulse is passed along a relay neurone and then to a motor neurone This transmits the impulse to an effector, the muscles in your leg, and makes them contract 2 a motor and relay b sensory c sensory d motor, relay e relay 3 a motor neurone b receptor c cornea d retina e contraction f circular 4 a Keeping the body temperature constant is just one part of homeostasis, which is the maintenance of a constant internal environment Homeostasis also involves the regulation of blood glucose concentration, as well as the water content of the body b The hairs stand on end when the body is too cold, but in humans we not have enough hair for this to help to keep us warm In other hairier mammals, the raised hairs trap a layer of insulating air next to the skin c Air of any kind cannot get into the body through the skin The fat layer prevents heat leaving the body by conduction, as it is an insulator d The sweat glands secrete sweat onto the surface of the skin when we are too hot, but this liquid is not cold It cools the body because the water in the sweat evaporates, and this process takes heat energy from the skin © Cambridge University Press 2017 Cambridge IGCSE Combined and Co-ordinated Sciences e The blood capillaries not move at all The arterioles that supply the blood capillaries near the surface of the skin get wider (dilate) when you are too hot This allows more blood to flow through these capillaries, allowing heat to radiate from the blood into the air f Insulin is a hormone, not an enzyme Enzymes catalyse reactions, but insulin is not a catalyst Insulin causes enzymes in liver cells to convert glucose to glycogen 5 a A 37.4 °C; B 37.5 °C. [2] b homeostasis; humans are endothermic; body produces more heat to maintain body temperature; shivering; vasoconstriction; [max 4] c air is more insulating than water; heat lost more easily from the body in water than in air; by conduction; [max 2] d person A was moving but person B remained still; idea that ‘new’ cold water was constantly coming into contact with A’s skin; water around B’s body warms up (as heat is lost from his body to the water); heat transfers from hot object to cold object; so more heat lost from A’s body than B’s body; [max 3] 6 a for respiration; by combining it with oxygen to provide energy; (not ‘produce’ energy) for named function (e.g movement, active transport); [max 3] b pancreas; [1] c i starch digested to glucose; by enzymes / amylase and maltase; absorbed into the blood from, the small intestine / ileum; [3] ii insulin secreted; causes liver to take up glucose from the blood; liver converts glucose to glycogen; (also) glucose used by body cells in respiration; [max 3] d negative feedback is a process that brings concentration back to normal when it gets too high or too low; when blood glucose concentration rises too high, insulin is secreted and reduces it to normal; when blood glucose concentration drops too low, glucagon is secreted and raises it to normal; [3] 7 a ability to detect changes in the environment; and respond to them; b i gravitropism; firm anchorage in the soil; leaves have more light; 10 for photosynthesis; [2] iii builds up on the lower side; causes cells in stem to elongate more; causes cells in root to elongate less; [3] Chapter B10 Reproduction in plants 1 a gamete b zygote c asexual d pollination e seed f fertilisation g sexual Asexual reproduction Sexual reproduction only one parent involved all offspring genetically identical one or two parents involved involves gametes involves fertilisation zygote formed genetic variation among offspring 3 a i age of seeds; [1] ii water; oxygen; warm temperature; [3] (if light also given, max marks) b i young plants will get light for photosynthesis; [1] ii D;[1] 4 a i a sex cell; joining together of nuclei of male and female gametes;[2] ii A – sepal; B – produces pollen; iii wall of ovary; b B and C; [2] [1] they have water; they have a suitable temperature; they not need light; [max 3] c i tropism; [2] [1] ii better photosynthesis; ii better access to water; Answers to end-of-chapter questions [2] negative gravitropism; because leaves can get more light; flowers held up higher; where insects can access them; [2] [max 3] © Cambridge University Press 2017 ... hydrogen atoms [1] b i many ethene molecules join together to make a long chain; draw a series of units joined together [2] Chapter C11 Petrochemicals and polymers Answers to end- of- chapter questions. .. Co-ordinated Sciences Chemistry Answers to end- of- chapter questions Chapter C2 The nature of matter 1 a Both ways of categorising substances have their use to a chemist Chapter C1 Planet Earth 1 a i... addition of nitrogen, to amino acids; some is converted to, fats / lipids [max 4] Chapter B5 Animal nutrition 1 a i calcium, vitamin D ii carbohydrate, fat, protein Answers to end- of- chapter questions