CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Learner’s Book answers Unit 1 Respiration Topic 1.1 The human respiratory system Activity: Gases in and out 1 and 3 Getting started Respiration happens in all the cells in your body. Respiration releases energy from food. Respiration happens in all living things. green arrow Questions 1 nose or mouth, voicebox (larynx), windpipe (trachea), bronchus, bronchiole, air sacs 2 air sacs, bronchiole, bronchus, windpipe, voicebox, nose or mouth blue arrow Think like a scientist: Looking at lungs 1 Learners can give a basic description: they look big, soft and pink, for example. 2 2 The lungs feel spongy, because they are full of air sacs. Think like a scientist: Why are air sacs so small? 3 a trachea 1 b It has hard ridges on it, with softer areas between. The dye moving (diffusing) into the jelly is like oxygen moving (diffusing) into the blood. 2 Learners should find that the dye diffuses more quickly into the jelly when there are many small holes. Some learners may be able to relate this to surface area, and explain that many small holes have more surface in contact with the jelly than a few large holes. 3 Learners may or may not think this is a good model. Accept any sensible suggestions. For example, both the dye and oxygen move by diffusion; the dye is a liquid, whereas oxygen is gas; blood moves past the alveoli, but in this experiment the jelly does not move. c bronchi d The larynx or voicebox; it makes sounds. Topic 1.2 Gas exchange Getting started 1 diagram C 2 In a gas, the particles are far apart. In a gas, the particles move freely. 1 Two – one in the wall of the alveolus, and one in the wall of the capillary. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Think like a scientist: Comparing the carbon dioxide content of inspired air and expired air 1 Expired air bubbles through tube B. 2 Inspired air bubbles through tube A. 3 The one that expired air bubbles through. 4 carbon dioxide 5 The limewater went cloudy first in tube B. This is the limewater that expired air bubbles through. Think like a scientist: Using a model to represent breathing movements 1 lungs = balloons; trachea = hole through the bung; diaphragm = plunger; rib cage = syringe 2 As the plunger is pulled out, the volume of air inside the syringe increases. This makes the pressure decrease. As the air pressure outside the syringe is now higher than the air pressure inside, air moves into the syringe through the small hole in the bung. The only place for it to go is into the balloon, so the balloon inflates. 3 The movement of the plunger represents the movement of the diaphragm, which causes the pressure to reduce in the chest cavity when it moves downwards. This draws air through the trachea, inflating the lungs. 4 There are several points that learners could make. For example, the ‘rib cage’ in the model cannot move, as there is nothing to represent the intercostal muscles. There are no ‘air sacs’ in the balloons. There are no ‘blood capillaries’ around the balloons. Our results show that expired air contains more carbon dioxide than inspired air. Topic 1.3 Breathing Getting started Gas exchange is the movement of oxygen and carbon dioxide between the air in the lungs and the blood. It happens in the air sacs (alveoli). The air you breathe in contains more oxygen than the air you breathe out. There is a small quantity of carbon dioxide in the air you breathe in. Questions 1 There is still quite a lot of oxygen in the air you breathe out. Think like a scientist: Measuring the volume of air you can push out of your lungs 1 This will depend on the results the learners obtain. 2 Plans could include the following ideas. • The variable to be changed (the independent variable) is the type of musical instrument that the person plays. • The variable to be measured (the dependent variable) is the volume of water they can displace when they breathe out. • 2 Some attempt should be made to standardise other variables, but in practice this is almost impossible, so the experiment cannot really be a fair test. 2 Action What do the diaphragm muscles do? What do the intercostal muscles do? Breathing in contract contract Breathing out relax relax When we breathe in, the muscles in the diaphragm and between the ribs increase the volume of the chest. This makes air move into the lungs. When we breathe out, the muscles in the diaphragm and between the ribs decrease the volume of the chest. This makes air move out of the lungs. Topic 1.4 Respiration Getting started To make something happen, energy has to be transferred or transformed. Learners may be able to suggest a range of energy changes (e.g. energy in electricity to energy in light). Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Questions Activity: Thinking about a thermogram 1 1 The object with the highest temperature is the computer screen. Computers change electrical energy to other forms (e.g. light) and some energy is dissipated as heat. 2 About 30 °C (Note that this is the temperature of her skin surface, which is lower than her core temperature would be.) 3 The woman’s cells are respiring. Respiration releases some energy as heat, raising her temperature above the temperature of the non-living chair. 2 3 a The reactants are oxygen and glucose. b The products are carbon dioxide and water. The air we breathe out contains less of the reactants (because these have been used up by respiring cells) and, therefore, less oxygen. It contains more of the products and, therefore, more carbon dioxide. Topic 1.5 Blood Getting started Think like a scientist: Investigating respiration in peas Learners should recall that red blood cells are small, round and red with a dent on the surface. 1 The condition of the peas (alive or dead). 2 size of the flasks; quantity of peas; insulation on the flasks; temperature the flasks were kept at; position of the thermometer bulb in the flask Red blood cells transport oxygen, and contain haemoglobin that helps them to do this. They have no nucleus, to make space for more haemoglobin. 3 temperature 4 The live, germinating peas were respiring. In the mitochondria in their cells, oxygen combined with glucose and released energy. Some of this energy was dissipated as heat, causing the temperature to rise. The dead peas did not respire. 5 6 3 Neurones need a lot of energy to transfer electrical signals around the body. Cheek cells do not need much energy, as they just stay in place, forming a lining on the inside of the cheek. Mitochondria are where energy is released from glucose, through aerobic respiration, so neurones need a lot of them. It is very unlikely that exactly the same results would be obtained. Different peas might respire at a different rate – they might be different sizes, for example. Learners should appreciate that it is not always possible in biology experiments to standardise all the variables that might affect the results. Accept any suggestions that would improve this experiment. Do not accept any that would make it a different experiment – such as using beans or small animals instead of peas. Good suggestions would be: counting the number of peas in each flask to make sure they are the same; measuring the mass of the peas; taking steps to make sure the insulation on each flask is the same; taking readings on the thermometers at more frequent intervals; using three or more replicates of each flask and then calculating the mean temperature change. Questions 1 Roughly 30 to 40 times more. 2 Learners may mention differences in colour, in shape, and the knobbly surface of the white cell in contrast to the smooth red cell. 3 Aerobic respiration happens inside mitochondria, in which oxygen reacts with glucose to release energy. 4 Component Appearance Function of blood red blood cell 5 round with a transport dent in the oxygen middle; red; no nucleus white blood spherical; cell have a nucleus protect against pathogens plasma transport blood cells, nutrients and carbon dioxide liquid Red blood cells, white blood cells, dissolved glucose, dissolved carbon dioxide. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Check your progress d Arrow labelled C from the blood capillary into the air sac. 1.1 trachea, bronchus, bronchiole, alveolus (air sac) e Reference to haemoglobin which combines with oxygen in the lungs and releases it when it reaches respiring cells. 1.2 1.3 a A b B c C d B O wall of air sac C blood capillary 1.4 a Labels to cell membrane and cytoplasm both correct. b nucleus mitochondria a Blood capillary correctly labelled. c Description of how the cell takes in a pathogen; kills pathogen once it is inside the cell d They produce antibodies which are chemicals which attach to pathogens and kill them OR make it easier for other white cells to destroy them (by phagocytosis). Wall of air sac correctly labelled. b Two red cells drawn inside the capillary. c Arrow labelled O from the space inside the air sac into the blood capillary. Unit 2 Properties of materials Topic 2.1 Dissolving Questions Getting started 1 Water is the solvent; sugar is the solute. Most learners should be able to explain that an element is made of one type of atom, a compound is made of two or more different types of atom which a bonded together and that a mixture is different items, element and/or compounds that are mixed together but not chemically bonded. Illustrations should reflect this. Look for confusion and misunderstandings about compounds and mixtures especially the ideas of mixtures of compounds such as sugar and salt. 2 When something dissolves, such as sugar in tea, there are two substances involved. The sugar is the solute, which dissolves in the tea, which is the solvent. When something melts, such as ice cream on a hot day, only one substance is involved. 3 59 g; the mass of water is 50 g and the mass of the salt is 9 g so together it is 59 g. 4 No; a solution is transparent and if there are lumps and it is cloudy, it is not a solution. The green powder was insoluble. 5 Credit any sensible suggestions such as: Think like a scientist: Dissolving and mass 1–3 4 4 These will depend on the practical task. Credit an answer that explains that the solvent and solute both have mass so that, when the two are placed in the same beaker, none of the mass suddenly disappears. The salt is still present even though you cannot see the particles because they have dissolved. the choice of a suitable measuring cylinder (a 10 cm3 one if using small volumes); using a pipette to top up to the correct level; ensuring that the meniscus is read at eye level Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Topic 2.2 Solutions and solubility 5 mass of solute dissolved in grams up the vertical axis; a suitable scale used; bars drawn with pencil and ruler; bars labelled; space between bars 6 510 g 7 395 g (at 80 °C, 905 g of sugar could be dissolved in 250 cm3 water. So, 905 g − 510 g = 395 g) Think like a scientist: Making different concentrations of a solution 8 For all three salts: the higher the temperature of the water, the greater the solubility. 1 9 73 g/100 g water Getting started Most learners should be able to define the terms as: solvent such as water that a substance dissolves in; solute as the substance that dissolves solution as being what is produced when a solute dissolves in a solvent. The point here is to discuss the definitions and to look for any misunderstandings. Learners should notice the differences in the colour of the various solutions. They should also notice that they have the same volume. 2 The paler the colour, the more dilute the solution is. 3 No, because there is no colour to help you. The salt or sugar dissolves to give a clear, colourless solution. 4 So that you have the exact volumes you need to make the different solutions. 5 No, it would make the task very difficult because the small volume would be hard to measure in such a large measuring cylinder. The graduations on the scale would not be clear enough. 6 There would be more food dye particles in the most concentrated solution than in the most dilute solution. Think like a scientist: Solubility in water 1 and 2 Answers will depend on the solutes provided. 3 You could find the mass of the test tube of water and then find the mass of the solute added by using a top pan balance. This would be much more accurate than just counting the number of spatulas because they will not all carry the same quantity. 10 sodium nitrate 11 potassium nitrate Topic 2.3 Planning a solubility investigation Getting started Many learners find it difficult to understand that their results can be reliable but not accurate. Reliable means they get similar results every time but accurate means as near to the true answer/ measurement as possible. The point here is to discuss this and look for any misunderstandings. Questions 1 The students have identified the following variables: the volume of water used, the temperature of the water and the number of spatulas of the solute used. 2 If different volumes of water are used, then they will not be able to account for the change in the quantity of solute used. The change could be due to the volume of water or to the temperature; would not be able to tell which, so the results would be of no use. 3 temperature 4 The volume of water is a control variable. Another control variable is the size of the spatula and how full each spatula is. Questions 5 1 A saturated solution is one that cannot have any more solute dissolved in it. 5 The dependent variable is the number of spatulas of sodium chloride that will dissolve. 2 32 g 6 3 14 g The number of spatulas of sodium chloride that dissolves in 50 cm3 of water. 4 18 g Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Think like a scientist: Plan and carry out an investigation into the effect of water temperature on the amount of sodium chloride (common salt) that will dissolve in it 2 brown 3 blue 4 brown 5 There is one that is not permitted, substance C. 1 A line graph (which would be better as you can read off the solubility at intermediate temperatures) with the number of spatulas of sodium chloride dissolved in water up the vertical axis and the temperature along the horizontal axis. Credit: a suitable scale; axes labelled; points plotted accurately; pencil and ruler used; points joined appropriately as a line of best fit. 6 She repeats the investigation to ensure the results are reliable. 7 Substance D is the most soluble because it has been carried the furthest along the chromatography paper by the solvent. This will depend on the results; expect a simple statement such as the higher the temperature, the more salt dissolves. Specific comments on the results obtained should also be expected. 1 Ethanol was used because the green pigment is not soluble in water but is soluble in ethanol. 2 The pigment is not pure. The evidence for this is that the chromatogram shows there is more than one colour present. Allow answers that reflect the learner’s evidence from the investigation. If they do not get separation, this requires some discussion about why this may have been. Sometimes the colours are very faint and are difficult to see. 2 3 Yes, similar results should be expected. Topic 2.4 Paper chromatography Getting started These could include dissolving then filtering, evaporating off water and day to day ideas such as using a sieve, picking out the larger items. The idea is that the learners are reminded that chromatography is another way of separating a mixture. Think like a scientist: Separating the colours in ink 1 To show where the spot of dye was to be placed. Pencil is used because it will not dissolve and interfere with the results. 2 It was important not to let the ink spot go under the water so that the ink did not dissolve into the water in the beaker. 3 It was important to remove the strip of paper before the water level reached the end of the strip so that the different colours in the ink could be seen separated and the ink did not run off the end of the paper. 4 The answer will be based on learners’ results. They should get a separation into different colours of pigment so the answer should state that the pigment is not pure. Questions 1 6 Think like a scientist: Is the green colour in plant leaves pure? Check your progress 2.1 A solute is a solid that dissolves in a liquid. The liquid it dissolves into is called a solvent. Together they make a solution. A solid that does not dissolve in a liquid is called insoluble. The solubility of a solid measures how much of a solute will dissolve. When you measure the solubility of a solute you must use the same volume and type of solvent at a given temperature. 2.2 a zinc carbonate b colourless c Note: learners are asked to describe what they would do, so they do not need to explain the reasons for each step in the process. The information in brackets below does not need to be included in their answer. Place the mixture of copper carbonate and iron sulfate in water and stir. (The iron sulfate is soluble and will dissolve in the water. The copper carbonate will not dissolve.) blue and yellow Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Filter the mixture. (The copper carbonate will remain in the filter paper and the green iron sulfate solution will pass through.) 2.3 a b c The interval they used for the temperatures was 10 °C. d Heat the filtrate to concentrate the solution, which is then allowed to cool. (You will be left with iron sulfate crystals in the evaporating basin.) The learners should keep the volume of water used the same. e The independent variable is the temperature of the water. a saturated solution f The point at 60 °C should be identified. g The hotter the water, the more copper sulfate will dissolve in it. b i thrust ii lift i lift ii drag The range of temperatures the learners used was 20 °C to 80 °C. Unit 3 Forces and energy Topic 3.1 Forces and motion Getting started newton or N 2 Arrows: the length of the arrow shows the size of the force and the direction of the arrow shows the direction of the force. 3 True: weight or the force of gravity always acts on all objects on Earth; there may or may not be other forces acting on the objects. 4 a D b B c C Activity: Balanced or unbalanced forces? Questions These statements go in the balanced forces column: 1 a Forces that are equal in size and opposite in direction. This can be shown in an annotated force diagram. • a bowling ball rolling at constant speed in a straight line • a computer sitting on a desk b • a helicopter going straight upwards at a constant speed 2 3 7 c 1 i Box drawn on a surface; upward and downward arrows (coming from any position); arrows of approximately equal length; down arrow labelled weight or gravity; up arrow labelled contact force. ii Same diagram as in part i; two sideways arrows in opposite directions; length of sideways arrows approximately equal to each other (length relative to vertical arrows is not important); one sideways arrow labelled push and the other friction. a orces are balanced; force from Team A is F equal and opposite to the force from Team B. b Force from Team B increases; force from Team A decreases. a i Thrust and drag are equal and opposite. ii Lift and weight are equal and opposite. The others go in the unbalanced forces column. Think like a scientist: Measuring balanced and unbalanced forces 1 Opposite directions/away from each other. 2 Forces are balanced; forces have equal sizes and opposite directions. 3 a The string moves toward the side with the larger force. b 4 Force diagram showing opposite direction arrows of unequal lengths; forces that were used in the investigation written on the arrows with units, such as 8 N and 7 N. String moves faster/moves more suddenly (not moves further unless moves further in a shorter time). Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 5 Forcemeters should give the same reading when the same force is applied. 6 The forcemeters represent the teams/the people who are pulling. 4 a b Topic 3.2 Speed Getting started 1 2 Learners may not know what the speed limits are as they do not drive, but they could be prompted to find out. In some areas the speed limits for cars and motorcycles are different from the speed limits for heavier commercial vehicles – learners could be asked why this is so. In most countries, this will be in kilometres per hour or km/h; learners may see this written in some contexts as kmh, but this is scientifically incorrect as it represents kilometres multiplied by hours (distance × time), which is not the correct way to calculate speed. Questions 1 a b c 2 distance speed = ________ time m/s or metres per second (not sec for seconds) distance = speed × time d distance time = ________ speed a distance speed = ________ time 100 = ____ 10 = 10 m/s b 3 a b c 5 distance = speed × time = 800 × 6 = 4800 km distance time = ________ speed 7125 = _____ 950 = 7.5 h distance speed = ________ time 3 = __ 2 = 1.5 m/h Activity: Speed, distance and time Provide learners with distances if required. A range of different distances should be used and a range of different methods of travel used for calculation. Care should be taken where distances are in km because the unit of speed in the table is m/s. Distances should be converted from km to m rather than risking mistakes by converting m/s to km/h. Learners should be asked why some methods of travel are not suitable for certain distances in terms of the three variables time, distance and speed. For example, an aeroplane would not be suitable for 100 m distance as the aeroplane may need a longer distance than 100 m to take off. Think like a scientist: Calculating speed The speed of the runner changes over the 100 m distance. distance speed = ________ time 210 = ____ 6 = 35 m/s distance = speed × time = 35 × 14 = 490 m 1 The table should have columns for height in cm or m, time to travel 1 m in s, and space for repeat measurements. Averages and calculated speeds can be in the same table or a separate one. See answer for 2 below. 2 If the distance used on the horizontal surface is 1 m then we can divide 1 m by the time taken in seconds to obtain the speed in m/s. 3 The graph is not expected to be a straight line, so a curve should be drawn if the points look like they show a curve. Learners are not to know what the relationship between height and speed should be, so a straight line of best fit is acceptable if the points are not very obviously showing a curve. 4 a b distance time = ________ speed 1925 = _____ 35 = 55 s 8 c distance speed = ________ time 8100 = _____ 9 = 900 km/h Height of the ramp. Time taken to travel 1 m or speed. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 5 Any two from: same object, same method of release, same distance on the horizontal surface, same release point on the ramp/same distance travelled down the ramp. 6 To identify anomalous results and to calculate an average. 7 As the height of the ramp increases, the speed of the object increases. Topic 3.3 Describing movement Getting started The intention here is to allow learners to think about what the shape of the graph will be like, so that you can discover their reasoning, rather than for them all to get the correct answer. This activity will allow you to refine your planning about how to approach distance/time graphs. d e Think like a scientist: Walking and running The safety precautions should include: • • • • • ensure the surface is not slippery ensure there are no obstacles in the way ensure the area for slowing down is clear wear suitable shoes run at a sensible, comfortable speed. 1 a he average speed is calculated by T dividing the total distance in m by the total time in s. b The average speed is calculated in the same way and should be a value greater than that in part a. Questions 1 a, b and c faster distance 2 Axes should be labelled with distance in m on the vertical axis and time in s on the horizontal axis and a linear scale used to include zero on both axes; lines should be ruled and clearly labelled. 3 The line for running is steeper than the line for walking; when running, you are moving faster, so cover more distance in a fixed time; when walking, you are moving slower, so cover less distance in a fixed time. slower time 2 a and b first, faster part stopped distance from home last, slower part time 3 a 80 m b distance speed = ________ time 80 = ___ 40 = 2 m/s c 9 distance speed = ________ time time = 132 − 100 = 32 s 80 speed = ___ 32 = 2.5 m/s 132 s Topic 3.4 Turning forces Getting started This is an open-ended activity where learners could give many types of examples, such as bottle tops, control knobs, rotary switches, and so on. The object is for learners to think of forces being used to turn objects rather than the more obvious pushing and pulling effects of forces that they may have considered previously. 100 − 40 Questions = 60 s or 1 minute 1 a the turning effect of a force b moment = force × distance c N m, accept N cm Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 2 a A 5 Comment based upon their original prediction. b This force is furthest from the pivot; this force will make the object turn in the correct direction. 6 Improvements should refer to the equipment or the method and not how well the learner worked. Reference can be made to specific difficulties of their set-up, but also stopping the pivot from moving, keeping the metre rule aligned correctly and keeping the downward pull on the metre rule constant. 3 4 × 0.12 = 0.48 N m 4 moment = force × distance moment force = ________ distance 5 1.8 = ____ 0.09 = 20 N moment caused by Zara = force × distance = 450 × 1.5 = 675 N m To balance, the moments on both sides must be equal. Topic 3.5 Pressure between solids Getting started Learners should be able to give examples, such as knives, scissors, pins, and be able to link these to cutting or pushing into other objects. Questions 1 a b moment caused by Sofia = force × distance moment caused by Sofia distance = _____________________ force 675 = ____ 500 = 1.35 m 1 2 10 There should be reference to making sure the clamp stand supporting the metre rule is stable; making sure the elastic band is in good condition; not stretching the elastic band too far; ensuring that the loops of string do not break or come off their support. 3 x-axis labelled with distance in m; y-axis labelled with force in N; linear scale with zero on both axes so points cover at least half the grid; points plotted correctly; smooth curve or line of best fit drawn. 4 Trend description that matches the results. The line is not theoretically straight, but if learners have drawn a straight line, then they can describe this. The statement should be that as distance from the pivot increases, the force decreases. To make the area as large as possible, so the pressure is as small as possible. a N/m2 b N/cm2 c N/mm2 force pressure = _____ area 60 = ___ 0.5 = 120 N/m2 4 Total weight = 8000 N 8000 weight on each tyre = _____ 4 = 2000 N Table should have distance in m in the first column and forces in N in the following columns, with repeats if needed. There should be at least five distances, equally spaced. 3 i To make the area as small as possible, so the pressure is as large as possible. ii 2 Think like a scientist: Calculating moments force pressure = _____ area force pressure on each tyre = _____ area 2000 = _____ 150 = 13.3 N/cm2 5 force pressure = _____ area force = pressure × area = 40 × 0.5 = 20 N Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Think like a scientist: Calculating pressure a 1 A value should be given as a whole number of cm2. 2 The value from 1 should be doubled and given in cm2. 3 a From the method, learners should have a value of the person’s mass recorded in kg, converted to weight, and given in N. The pressure is the weight of the person divided by the value given in 2. The answer should be a pressure in N/cm2 b This is the weight of the person divided by the value given in 1. The answer should be a pressure in N/cm2, and should be double the answer to 3 a. 4 The pressure when standing on one foot is greater/double because the same weight is pressing on a smaller area / half the area. 5 A value should be given as a whole number of cm2 that is smaller than the answer to 1. 6 Walking / running / dancing etc. 8 a b Draw around the person when lying down. Then a workable method for finding the area of the shape. iThe pressure when lying down will be lower. iiThe weight or force remains the same, but the area is larger, meaning the pressure is smaller. Topic 3.6 Pressure in liquids and gasses Getting started Learners should recall the arrangements of particles in liquids and gases. The common misconception here is the particles in a liquid are not all touching at least one other particle. If these particles are not touching, they have drawn the particles in a high pressure gas. 11 Questions 1 2 a ressure increases with depth in water; P submarines must be very strong to withstand this pressure / not be damaged by the pressure. b Pressure increases with depth in water; the wall needs to be stronger at the bottom than at the top to withstand the greater pressure. a Pressure increases with depth / pressure is directly proportional to depth. b When the depth in the liquid doubles, the pressure in the liquid doubles. 3 C 4 a Particles in the air inside the ball colliding with the inside surface of the ball. This is calculated by dividing the person’s weight by the answer to 5. It should be a pressure in N/cm2 and be greater than the answer to 3 b. 7 b 5 b More particles inside the ball, so more collisions with the inside surface. c Particles move faster at higher temperature; collisions with the inside surface have more force and occur more frequently. a There are no particles to collide. b Particles in the air collide with the outside of the container; there are no particles colliding with the inside of the container; the forces on the container are not balanced and the force from the outside is greater. Think like a scientist: Observing the effects of pressure 1 The answer will depend on the prediction. 2 The diagram should show water coming out with increasing pressure from the lower holes; the water should be drawn in a curve from each hole and landing further from the bottle lower down. 3 Pressure increases with depth; water comes out faster through the lower holes; as water flows out, depth decreases, so the pressure at each hole slowly decreases. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 4 The bottle should appear to be its normal shape before; after being in the cold, the bottle should be dented or squeezed in. 5 The pressure inside decreased. 6 Particles in air move slower at lower temperature, so will collide less frequently and with less force with the inside surface of the bottle; the pressure on the outside of the bottle remains the same; the pressure of air in the bottle in the warm place was equal to atmospheric pressure because the lid was off; the pressure inside the bottle became less than atmospheric pressure in the cold place, so the forces on the sides of the bottle were not balanced. 7 The bottle would be pushed outwards/become harder; particles in air move faster at higher temperature, so will collide more frequently and with more force with the inside surface of the bottle; the pressure on the outside of the bottle remains the same; the pressure of air in the bottle in the cold would be equal to atmospheric pressure because the lid was off; the pressure inside the bottle would become greater than atmospheric pressure in the warm place, so the forces on the sides of the bottle would not be balanced. Topic 3.7 Particles on the move Getting started 1 2 Learners should be able to offer the idea that the smell of the food spreads outwards from the food. Learners should suggest that the orange mixes with the water and spreads throughout the water. Questions 1 2 3 a B b A Overall random movement of particles from an area of higher concentration to an area of lower concentration. a Gas; because the particles are not touching each other. b 12 The concentrations are the same because there are the same number of blue particles in the same space/volume. c 4 a By diffusion; particles move randomly and spread from an area of high concentration to an area of low concentration. b 5 The concentration is higher in B because there are more red particles in the same space than in A. Sofia is not correct; particles continue to move randomly even though the overall movement of the orange colour has stopped. A, C and D Activity: Watching diffusion 1 The method should be written in a logical order and be workable. 2 There should be a minimum of three drawings depicting the start of the process where colour has not yet begin to spread, an intermediate stage where colour is spreading and a final stage where colour is uniform in the water; the colour should be less intense each time. 3 The prediction should have the idea of the colour spreading more quickly. Think like a scientist: The effect of temperature on the speed of diffusion 1 The higher the temperature, the faster the colour spreads. 2 Diffusion happens faster at higher temperature because particles move faster. 3 The volume of water is a control variable / makes the investigation a fair test; it would take longer for the colour to diffuse through a larger volume. 4 Any two from: Do each temperature separately so that the stopwatch can be started at the correct time; keep each beaker at a constant temperature while diffusion happens; repeat the experiment; use a larger range of temperatures; use smaller temperature intervals. Check your progress 3.1 A and C (both required) 3.2 a b c The bicycle will slow down. The car will speed up/accelerate. The ball will change direction/curve/move in a circle. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 3.7 can be measured 3.3 B 3.4 Sketch graph with ‘distance run’ on the vertical axis and time on the horizontal axis (ignore units or scale); line sloping upward; second part of line sloping upward with shallower gradient. 3.5 a Graph with distance in m on the vertical axis, scaled from 0 to at least 550; time in s on the horizontal axis, scaled from 0 to at least 10; graph drawn to cover at least half the available grid; straight line ruled from (0, 0) to (10, 550). distance 550 = 55 m/s or ____ speed = ________ time [ 10 ] 3.6 a People’s feet are different lengths / 16 people may not be available / a rod is not a fixed length. b No special equipment is needed / one person could measure a rod using their own left foot. b must be calculated force moment length area time pressure speed 3.8 a moment = force × distance (Accept any correct arrangement) b Larger moment is created by increasing the distance of the force from the pivot. force 3.9 a pressure = _____ area (Accept any correct arrangement) b i ii B C 3.10 A 3.11 ny two from higher temperature; higher A concentration; smaller/lighter particles. Unit 4 Ecosystems Topic 4.1 The Sonoran Desert 2 Getting started Deserts are difficult for organisms, because there is little water available. Learners may also say that they are very hot, but this is not always true; there are cold deserts (e.g. the Gobi desert) and many deserts become very cold at night. Cacti are plants that have very reduced leaves – in many, the leaves have become spines. Instead of leaves, they use their green, thick stems for photosynthesis. This reduces the surface area of leaf that is exposed to the air, which reduces the loss of water vapour from the leaves. The spines also protect the plant from grazing animals, which would otherwise eat the plant to obtain water as well as food. The stems store water. Learners may also know about the root systems of cacti, which sometimes spread very widely just below the surface to catch rainwater almost as soon as it falls. Roots may also go very deeply into the ground to reach groundwater. Some species have both types of root. 13 4 5 Activity: How a species fits into the desert ecosystem 1–2 Answers will depend on the sources that learners used to find information, and how they selected the best. Topic 4.2 Different ecosystems Getting started Questions 1 3 The producers use energy from the Sun to make food by photosynthesis; this makes energy available for all other organisms in the food web. The arrows represent energy, in the form of chemical energy in food, passing from one organism to another. For example: Gila woodpeckers use saguaro cacti to make nests; fruit bats pollinate saguaro cacti. A habitat is a place where an organism lives. An ecosystem is a network of interactions between living and non-living things; an ecosystem contains many different habitats. prickly pear cactus and brittlebrush Sofia is correct. An ecosystem does include a place, but it also includes all of the interactions between the living and non-living things in that place. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Topic 4.3 Intruders in an ecosystem 4 The quantity of DDT in an animal’s body increases at each level of the food chain, because: • one animal eats a lot of other animals in its lifetime • all the DDT stays in the animal and does not break down. 5 Learners will differ in their views, so be prepared to accept any relevant suggestions. For example, the model does help to show that one animal eats many animals, or what happens over a long period of time, and it does not model a complex food web. Getting started Learners are likely to suggest that the introduced species ‘will take over’. Because it grows and reproduces more quickly than the native saguaro, there will be less light, water and space for the saguaros to grow. If the saguaros disappear, or are reduced in numbers, this would reduce the numbers of other species that depend on the saguaros, such as the Gila woodpecker, termites, sap beetles and so on. Questions Questions 1 A species that has always lived in that country; a species that ‘belongs’ in a country. 1 2 This will depend on the learner’s country. 3 Accept any sensible ideas. For example, individuals of the species will have spread all over the country, so it can be very difficult to find them all and kill them. People may become fond of the introduced species, and not want it to be killed. Minnow concentration is 0.50 ppm; cormorant concentration is 26.40 ppm. The cormorant concentration is 52.8 times greater than the minnow concentration. 2 4 It is an invasive species. DDT does not break down inside the cormorant’s body, so all the DDT that the cormorant eats in its lifetime builds up in its body. Cormorants eat a lot of minnows, so all the DDT from all the minnows accumulates in its body. 5 Answers will be partly determined by learner’s pictures in Topic 4.1. They are likely to suggest that native plants, including the saguaro, will not be able to grow. This will then affect other species that rely on the saguaro. Check your progress 4.1 a A tree branch; the pool in a bromeliad. b They get a lot of light; they are safe from being eaten by herbivores on the ground (Accept other correct ideas.) c It has a constant supply of water; it is protected from predators. d Any two from: An ecosystem is a network of interactions between organisms and non-living parts of their environment. A habitat is a place where an organism lives. An ecoystem contains many different habitats. Topic 4.4 Bioaccumulation Getting started 1 A decomposer is an organism that breaks down dead bodies or waste from animals and plants. 2 Organic substances – ones that have been made by living organisms. 3 Substances that have not been made by living organisms – for example: metal, glass, rock, most plastics. Think like a scientist: Modelling DDT in a food chain 1–2 Answers will depend on the results of the activity. 3 14 At each stage, there are fewer animals. So all the red tokens from many animals go into the body of one animal. 4.2 a There are many different habitats in the reef; these provide suitable habitats for many different species. b It is poisonous. c single-celled alga → herbivorous fish → carnivorous fish → human d bioaccumulation Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE e c The concentration of ciguatoxin is higher in the carnivorous fish because the concentration builds up along the food chain/reference to biomagnification. d It reduced the (mean) number of visits from 35 to 26 / by nine. There are fewer insect visits and fewer seeds produced; idea that seed production follows successful pollination. They could repeat it to check if the results are always the same; they could time insect visits for longer than 15 minutes because one 15-minute period may not be representative of what happens over a long period of time. (Accept other good suggestions and explanations.) 4.3 a A species that has been moved to a country/place/ecosystem where it does not naturally live. b To count visits to winged loosestrife with and without purple loosestrife, so they could compare the number of visits; this was how they changed their independent variable. e Unit 5 Materials and cycles on Earth Topic 5.1 The structure of the atom Getting started Most learners will identify the largest cup as being the heaviest. They cannot know this for certain. You should follow the instructions in the teacher's resource and, before the lesson, hide a piece of modelling material or a stone in the middle or smallest cup before filling them with water. Then ask the class to predict which is the heaviest. Then ask one learner to come and lift each cup, ask them if they want to change their mind about which is heaviest. Do not allow them to tell the class directly what they found out by lifting the cups. Challenge the class about this learner's decision. Is this result true? Is this classmate trying to trick you? The whole point of this exercise is to discuss the evidence you need in order to come to a conclusion. Questions 15 9 Ernest Rutherford discovered the proton in 1909 and the nucleus in 1911. 10 Rutherford’s model of the atom has a nucleus but it doesn’t have any neutrons in it because neutrons had not been proved to exist when his model was formed. Topic 5.2 Purity Getting started 1 It is made of only one thing. 2 oxygen; gold; potassium 3 Elements: oxygen; gold; potassium. Mixtures: sea water; orange juice; black ink; soil. Compounds: sodium chloride; copper oxide; silver nitrate. Questions 1 proton 2 electron 3 protons and neutrons 4 No charge; they balance each other out. 5 The individual atoms are held together by electrostatic attraction between the positively charge protons and the negatively charged electrons. 6 Thompson’s model of the atom has no nucleus, unlike the model we use today. 7 J. J. Thompson discovered the electron in the 1890s. 8 James Chadwick proved the neutron existed in 1932. 1 37.5% 2 90% 3 boron 4 nitrogen, nickel or hydrogen. 5 6 Salt Percentage sodium chloride 68.0 magnesium chloride 14.6 sodium sulfate 11.4 calcium chloride 3.1 other salts 2.9 14.6 ____ × 35 = 5.11 g 100 Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Think like a scientist: Finding the mass of salts in seawater 1–3 4 Questions 1 This will depend on their experiment. There should be some similarity between the results obtained and those suggested in the Learner’s Book. If not, suggestion might be: different seawater samples, spilling some of the seawater or other practical issues. Scotland: The weather is cold, there is snow on the ground. There is no precipitation. It is cloudy. 5 This is dependent on what they did and any attempts they made to address these difficulties. 6 • Wearing safety glasses. Namibia: The weather must have very little rain as there is only sparse vegetation. The sun is shining as you can see shadows. There are white clouds in the distance. • Care when heating in the evaporating basin as the solution may spit. New Zealand: The weather is wet; it is raining heavily. The sky is cloudy and dark. • Care when moving the hot evaporating basin or heating equipment. Canada: The sky is grey with low cloud or mist above the trees. Republic of Ireland: There are many white clouds in the sky but the sun is shining, you can see it on the grass. There is a rainbow. Think like a scientist: Reactions with more than one product 1 These should be specific to what the learners have done in the practical. Ensure word equations are written on one line. 2 Look for suggestions, such as where there is a solid and liquid formed, filtering (to obtain the liquid) and collecting and drying (to obtain the solid) for example silver nitrate and sodium chloride. Evaporating the solution; for example, in a neutralisation reaction. The suggestions are the important thing based on the knowledge they have. The suggestion does not need to be what you would do but it needs to be discussed in class. 3 Specific suggestions for each reaction or general suggestions, such as care with acids and alkalis; not spilling liquids; any spills cleared up at once; replacing bottle stoppers as soon as possible; bottle tops placed upside down on the work surface; any spills on the skin washed with water; wearing safety glasses. Bangladesh: It is very windy and the branches of the trees are bent over in the wind. The sky is grey. 2 So that we can use the information to build up a picture of what is likely to happen in the future. 3 This will depend on where you live. 4 Credit any correct answers, such as Mali, Chad, Oman, Saudi Arabia, and Yemen. 5 Credit any correct answers, such as S/SW Australia, central Chile, the Western Cape, SW of USA. 6 Credit any correct answers, such as Cameroon, Democratic republic of Congo, Uganda, Brazil, Columbia, Malaysia, Indonesia, Thailand, Costa Rica, Cuba and Jamaica. 7 The climate in the arid zone is hot and dry all year, whereas the climate in the tropical zone is hot and wet all year. 8 The climate in the temperate zone has cold winters and mild summers, whereas the Mediterranean zone has mild winters and hot, dry summers. Topic 5.3 Weather and climate Getting started Accept any relevant words such as rain, hail, snow, cloudy, hot, humid, monsoon, hurricane, storm; aim for a variety of terms and use a dictionary to help define the terms. 16 Credit answers that are correct and use the correct vocabulary even if they do not cover every aspect shown in the photograph. The following answers are examples only. Activity: Recording the weather 1 So that a comparison can be made. The temperature tends to be higher in the middle of the day, so if you took the temperature at 9 am and the next day at 2 pm you would not be comparing the same thing. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 2 3 So that they are not affected by direct sunlight. On one day it may be cloudy and the Sun not visible, and on another day, direct sunlight on the thermometer would affect the reading, so you would not be comparing the same thing. The report should reflect what learners have found and account for temperature, precipitation (even recorded as zero, if appropriate) wind speed and direction, cloud cover, humidity, visibility, and so on. The measurements and observations should be presented in an appropriate way. 4 The line graph should be drawn to an appropriate scale and accurately plotted to show the changes in temperature over the week. Temperature should be plotted on the vertical axis and the date along the horizontal axis. 5 In the comparisons, there are likely to be minor differences in the temperature readings, due mainly to where they were taken and how accurately they can use the thermometer. Other observations where it is a matter of opinion, such as cloud cover, are likely to show greater variation. Learners should recognise the difference between accurate measurements and the more descriptive assessments. They should question the method used by each group, the timing and whether they used the same apparatus. 6 Data should be available via the internet or local television. Comparisons are likely to be difficult as learners do not know exactly where the measurements or observations were taken and they are unlikely to be measured in the same way or at the same time. The measurements will be the averages of many readings taken at different sites and times. So the differences between the learners’ data and national data will be down to these factors as well as the more accurate measurements taken by professionals and the more accurate methods for taking the measurements and the standardisation of observations. Topic 5.4 Climate and ice ages Getting started Most learners will be able to understand that the body has been frozen for all that time. Some may find it difficult to believe that any part of the Earth has been frozen for that long. The reason why 17 her body was discovered in 1977 could lead to a discussion about rising temperatures on Earth. Activity: Where in the World is there ice? 1 Credit any correct country or area that can be identified by comparing a current world map with that in the Learner’s Book. 2 The parts of the world that are covered in ice are all either a long way from the equator or on the top of high mountains. Questions 1 five 2 Yes, because an ice age is when there is permanent ice somewhere on Earth and there is currently permanent ice at the poles and on some mountains and glaciers. 3 An ice age is when there is some permanent ice somewhere on the Earth. In an ice age, there are periods when most of the Earth is frozen, that is a glacial period. 4 No, we are in an interglacial period with ice only at the poles, on some mountains and glaciers. 5 Accept any glacier locations that are correct; answers will depend on your location. 6 Learners should provide evidence, such as marks on the rock, U-shaped valleys as opposed to the V-shaped valley a river would make, deposits of large boulders and other rocks. Topic 5.5 Atmosphere and climate Getting started Most learners will have some idea that an ice age was when the Earth was frozen but many understand this to be when the whole of the Earth was frozen. Some discussion around an ice age being when there is some part of the Earth that is permanently frozen will be needed. Some learners will be aware of fossils that indicate that parts of the Earth were very different in the past and will be able to recall the ideas about samples from ice cores and cores of soil from peat bogs. This is not about a set of correct answers but a discussion to help the teacher to learn how much the class have understood. Questions 1 The early atmosphere was formed from the gases that the many volcanoes produced. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 2 3 Any two differences, such as: there was very little oxygen in the early atmosphere, but today about 20% is oxygen; there is very little carbon dioxide in the atmosphere today (about 0.04%) but the early atmosphere was about 80% carbon dioxide; there was very little nitrogen in the early atmosphere (2.5%) now there is almost 80%. There was very little oxygen in the early atmosphere. It was not suitable for humans or other animals because they need oxygen to respire. 4 Fossil fuels are those that have been formed from plants and animals that did not rot when they died. They have carbon locked up in them. 5 Microorganisms and plants developed over many millions of years and they used the carbon dioxide to produce food. The plants produced their food by the process of photosynthesis. 6 As a control, to see how much hotter or cooler the ones with added carbon dioxide or water became. 5 This will depend on the results, but the expected temperature readings would be highest in extra carbon dioxide and lowest in normal air. The carbon dioxide and additional water vapour prevent the loss of thermal energy, so the bottle retains more of the energy from the Sun. 6 Credit any sensible suggestions including extending it over a longer period of time; taking more and more accurate readings, more accurate using digital technology; using larger containers; finding an easier way to attach the thermometer. Check your progress 5.1 a There is evidence that the oxygen levels increased because there are rocks where iron has combined with oxygen to form red iron oxide. These rocks date from about 2 billion years ago. 7 carbon and oxygen 8 calcium, carbon and oxygen 9 Limestone is formed when the shells of dead sea creatures fall to the bottom of the ocean and over millions of years these layers become compressed into rock. 10 About 3500 million years ago. Think like a scientist: The greenhouse effect 18 4 − neutron proton electron b i + + nucleus − proton ii neutron iii electron iv nucleus 5.2 C 5.3 Pure diamonds are colourless and translucent, whereas those with other elements in them are coloured. Answers are dependent on learners’ findings. 5.4 A→2; B→5; C→4; D→3; E→1 1 Learners should consider the likely temperature changes during the day; what time(s) of day to take the readings, and how often to take them. 5.5 a 2 Credit any suitable table with correct headings and units. 3 This depends on the learners’ results. It is likely that the bottles containing extra carbon dioxide and water vapour will have higher readings. 5.6 When the ice was formed, bubbles of gas from the atmosphere were trapped in the ice. These can be analysed. The deeper the ice that the gas came from, the older the sample. Scientists can also tell from the way the ice was formed what the weather conditions were like at that time. 10 °C b an ice age c 24 °C Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 5.7 Any two from shrinking ice caps, retreating glaciers, rising sea levels. 5.8 a false b true c true d false e true c 5.9 a Any three from solar, wind, tidal, hydroelectric, biofuels. b Earth, so that less of the thermal energy generated on Earth is dissipated into the atmosphere. Global warming is the term used to describe the fact that the average global temperature of the Earth is increasing. This effect is caused by an increase in the levels of gases, such as carbon dioxide, methane and water vapour. These gases act like a blanket around the The carbon contained in fossil fuels has been locked up for millions of years. When we burn them, this carbon combines with the oxygen in the atmosphere to produce more carbon dioxide. The more carbon dioxide there is in the atmosphere, the greater the greenhouse effect. The greater the greenhouse effect, the more the temperature rises, which adds to the problem of global warming. 5.10 An analogy is the use of one structure, idea or process to explain another. Accept any example from any discipline; such as the idea of the layer of greenhouse gases acting like a blanket around the Earth. Unit 6 Light Topic 6.1 Reflection 3 Diagram copied with light ray coming from the candle to the mirror; normal drawn; reflected ray going toward the eye; arrowheads on light rays should be in the correct direction (from candle to mirror and from mirror to eye); labels should be added for: the incident ray, the normal, the reflected ray, the angle of incidence, the angle of reflection. (Note – the question asks only about the reflection of light, so an image construction is not required). 4 Mirror drawn at the end of the incident ray that is provided; reflected ray drawn to eye with an arrowhead pointing away from the mirror; mirror at such an angle that angles of incidence and reflection are approximately correct (normal need not be included). Getting started 1 straight lines 2 Learners could quote evidence such as the three cards with holes activity where light can only be seen through the holes when they are lined up in a straight line; some may describe shadow formation or the fact that we cannot see around corners; some may have used ray boxes and describe the rays produced from these. Questions 19 1 C 2 Ray diagram completed correctly; the normal should be marked; the angle of incidence should be measured and recorded; the angle of reflection should be equal to the angle of incidence (as judged by eye); the reflected ray should have an arrowhead; the rays should meet each other and the normal at the surface but should not cross the surface (the tolerance for these is the thickness of the pencil line). Activity: Mirrors and reflections Examples of uses of mirrors include: in bathrooms for washing and grooming; in bedrooms for dressing; in vehicles for checking behind; in shops for security; in makeup bags for applying makeup; at a dentist’s for seeing inside the mouth. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Shiny surfaces that include glass, glazed tiles, ceramics, polished metal and painted surfaces produce reflections. Liquid surfaces such as water also produce reflections. 2 The surfaces that produce mirror-like reflections are all smooth, although not always flat. All objects that do not give out their own light and can be seen produce reflections, otherwise we would not be able to see them. Questions 1 2 The table should include column headers with units; the angle of incidence should be the first column and the values should be in ascending order, cover a good range and be in equal intervals; the angles of reflection should be equal to the angles of incidence. a b 3 4 5 2 3 ray of light angle of incidence air glass angle of reflection 4 As the angle of incidence increases, the angle of reflection increases; they are directly proportional; they are equal. a It is difficult to mark the exact position of the light rays as the pencil blocks the light and the light rays are wide; any other difficulties that are specific to their investigation such as the presence of bright sunlight. Methods for improvement linked to difficulties,such as using a narrower slit / narrower light ray and making the room darker. This is an open-ended question, but most learners should be able to offer suggestions such as glass (solid), water (liquid) and air (gas); some may suggest plastic for a solid as they may have transparent rulers, etc. but prompt whether all plastics are transparent. angle of refraction refracted ray angle of refraction air water normal refracted ray angle of incidence ray of light Activity: Refraction effects 1 The ray diagram should resemble the answer to question 4 from the Learner’s Book, with the light ray going from the coin toair the water surface closer to vertical than in the dashed line in the glass or water diagram. The refracted ray then goes to the eye. The possible misconception here is that light goes from the eye to the coin. Getting started 20 Refraction of light is when light changes direction because of a change in speed (accept medium). normal Topic 6.2 Refraction 1 Light travels faster in air than it does in glass. angle of incidence Graph with angle of incidence in degrees on the horizontal axis and angle of reflection in degrees on the vertical axis; both axes with linear scales starting from zero, scaled so that plotted points cover more than half the grid; all points plotted correctly; line of best fit drawn through the points. b a Light travels slower in water than it does in air. b Think like a scientist: Measuring angles of incidence and reflection 1 This, again, is an open-ended question intended to find out what learners may think about this; their responses will help you pick up on any misconceptions about the way that light travels; learners are not expected to know the term refraction at this stage. 2 The ray diagram in this case should be drawn as if looking at the glass from above. Any indication that the light ray is refracted more when passing from the water than passing from the glass only is sufficient; an image construction is not required. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 3 The pencil appears broken in two places: at the air-oil boundary and at the oil-water boundary. An indication that the speeds of light in oil and in water are different is sufficient (the speed of light in cooking oil is slower than that in water, and some learners may be able to work this out). Think like a scientist: Drawing accurate ray diagrams 1 2 The angle of incidence in air is equal to the angle of refraction in air; the angle of refraction in glass is equal to the angle of incidence in glass (provided a perfectly rectangular glass block has been used). 4 As the angle of incidence increases, the angle of refraction increases; if the learner’s graph has been drawn as a curve then that should be mentioned: the angle of refraction does not increase as much as the angle of incidence. The angle of refraction is also zero. This is the only angle of incidence where the angle of refraction is equal. Topic 6.3 Making rainbows Getting started 1 No, rainbows can only be seen in the daytime. 2 Yes, there needs to be sunshine or sunny intervals in order to see a rainbow. 3 Yes, there need to be water droplets of some form – a rain shower or spray from a hosepipe, fountain or waterfall. 4 Learners may have memorised the seven colours (red, orange, yellow, green, blue, indigo, violet), or be able to recall some of them, although not necessarily in the correct order at this stage. They may refer to the colours they see in the picture. Questions 1 21 C (triangular glass prism) 3 a A b A c spectrum 4 The water drops act as prisms; dispersion happens in the water; light is refracted going into / coming out of water. 5 Six: red, orange, yellow, green, blue and indigo-violet. Think like a scientist: Making a rainbow 1 Axes correctly labelled with units; linear scales on both axes including zero; all points plotted correctly; smooth curve or straight line drawn. The line is not actually straight, but a slight curve with decreasing gradient. Learners are not expected to know this, so if they interpret their points as being on a straight line, that is acceptable. 3 2 dispersion 2 3 a his varies from five to seven, depending T on the individual. b The list should include: red, orange, yellow, green, blue, indigo and violet. a red b violet a The colours get closer together; the colours get brighter. b The colours get further apart; the colours get dimmer. 4 The colours get dimmer; colours get further apart / easier to see separately. 5 Part 1 advantage: many people can view the spectrum at once. Part 1 disadvantage: need dark room/some colours may not be easy to see on the screen. 6 Strength: shows the colours of the rainbow (in the same order); shows how a rainbow forms; models the raindrops by using a prism. Limitations: does not show a complete, curved, rainbow; produces the spectrum on the screen rather than (what appears to be) in the air; spectrum looks much smaller than a ‘real’ rainbow. Topic 6.4 Colours of light Getting started This is an open-ended activity to allow learners to begin thinking about seeing colour. Some colours in the picture may be described differently. For example, some may name one of the flowers orange while others may consider it to be red. Learners may also refer to shades of colour. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE c Questions 1 red, green, blue 2 a magenta b yellow c white a yellow b orange a green, white b green, red c A, B, D 3 4 6 7 8 Think like a scientist: Identify the colour The answers will depend on the pens used and the filters used with the light source. Topic 6.5 Galaxies Getting started moon, planet, star, solar system, galaxy 1 spiral, elliptical and irregular 2 planet, star and stellar gas 3 gravity 4 They are the closest to us; other galaxies are much further away; if other galaxies can be seen, individual stars in them cannot easily be distinguished. Not all of them can be seen; new stars are forming; stars are reaching the end of their life; some objects that look like stars may not be stars. Think like a scientist: Estimating large numbers Topic 6.6 Rocks in space Getting started This is an open-ended activity, but most learners should recall stars, planets and moons; some may know about comets or asteroids and some may include dust and small particles that contribute to meteors. 1 Rocky object; part of the Solar System; smaller than a planet; can have an irregular shape. 2 They are much smaller than planets, the Sun or moons of planets. 3 Impacts with other asteroids/impacts with comets. 4 Formed during the formation of the Solar System; left over as they did not come together to form a planet. Activity: Making a model asteroid 1 It has an irregular shape. 2 140 000 _______ 3 1–3 The answers will vary according to the samples taken. 4 5 22 Use a similar method, but estimate the volume of the sand using the length, width and depth of the sand on the beach. Questions Questions 5 Count a larger sample; measure the mass / volume of the large sample more accurately with equipment reading to more decimal places. Different groups of scientists may study different regions of the sky; results from different groups are brought together for an overall result. This will be the time taken to count the small sample multiplied up in proportion to how many times more grains there are in the large sample. This should be correctly calculated from the answers to questions 1, 2 and 3. a This method is quicker. b Not all grains may have the same mass / volume; the mass / volume of the large sample cannot be determined to the accuracy of a single grain. = 700 times larger. 200 a A length recorded in cm or m. b Answer to part a × 700 (units included with answer). Think like a scientist: What happened at Tunguska? 1 Hypotheses 1 and 5 will probably be chosen as supported, and the others contradicted, or not supported; reasons should include facts such as an alien spacecraft crashing is not supported because no metal parts were found. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 2 a Hypotheses 1 and 5 will probably be chosen as the most likely, with 5 being even more likely than 1. b 3 6.8 a Hypotheses 2, 3 and 4 will probably be chosen as most unlikely. Arrow head on refracted ray pointing away from the surface. Idea that there is lack of evidence to fully support the more likely hypotheses and lack of evidence does not mean that the less likely hypotheses are impossible. Angle of incidence and angle of refraction marked between the rays and the normal. b Check your progress Arrow head on refracted ray pointing away from the surface. 6.2 The angle of reflection is equal to the angle of incidence. Angle of incidence and angle of refraction marked between the rays and the normal. 6.3 Ray diagram with: reflected ray at approximately the correct angle and labelled as reflected ray • arrowhead on the reflected ray pointing away from the mirror • angle of incidence and angle of reflection marked and labelled between the rays and the normal. 6.9 White light can be split into its component colours. This is called dispersion and can be done with a prism. The range of colours is called a spectrum The range starts with red and ends with violet. 6.4 Diagram showing: • mirror labelled • rider/eye • in incident ray with an arrow pointing toward to mirror • a reflected ray at approximately the correct angle going to the rider/eye with an arrow pointing away from the mirror. 6.10 a red b green c no light/none 6.11 a red b green c blue 6.5 refraction d black 6.6 • When light passes from air into glass, the light slows down. • • 6.7 F T T 23 Normal drawn and labelled. Refracted ray bent away from the normal and labelled. 6.1 flat • Normal drawn and labelled. Refracted ray bent toward the normal and labelled. 6.12 a magenta b cyan When light passes from air into water, the light slows down. When light passes from glass into air, the light speeds up. c yellow d white 6.13 a stellar dust; gas; stars; planets/solar systems b Milky Way 2 smaller; (many have) irregular shapes Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Unit 7 Diet and growth • • The foods that are best for energy are ones that contain carbohydrate and fat; in most countries there is a staple food that contains a lot of starch (bread, rice, potatoes, maize and so on) which is usually the food that provides most energy. Learners may know that food goes into the alimentary canal, where is it broken down so that is can be absorbed through the walls of the alimentary canal and get into the blood. The blood then transports it to our cells. They should remember that glucose is combined with oxygen in aerobic respiration inside mitochondria in cells, to release energy. Think like a scientist: Testing foods for starch 24 1 Starch from one food might get onto another that does not contain it, so you would get an incorrect result. 2 It makes it easier to see the colour that is produced after iodine solution has been added to the food. 3 The second column shows the results, and the third (last) column shows the conclusions. 4 Learners should find starch in some foods from plants. 5 Learners should not find starch in foods that come only from animals. 2 Nutrient 1 Examples of Why the body foods that contain needs this nutrient a lot of this nutrient Protein Getting started fish, meat, dairy products, eggs, milk, beans and peas to make new cells for growth and repair; to make haemoglobin and antibodies Carbohydrate Questions cereal grains (and foods made from them, such as bread and pasta), potatoes and sweet foods such as biscuits, chocolate and cakes for energy Fat Topic 7.1 Nutrients fatty meat, dairy products (milk, cheese, butter), coconut milk, oil used in cooking for energy; to make cell membranes; to store for long-term energy supplies and insulation Food refers to the things that we eat, such as chicken and rice. Nutrients are the substances contained in the food that the body uses, including protein, carbohydrate, fat, vitamins, minerals and water. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 3 Nutrient vitamin A 4 5 Examples of Why the body foods that needs this contain a lot nutrient of this nutrient green vegetables, carrots, squash, fruit, dairy products, fish to help the eyes to work well, especially in low light; to help white blood cells to destroy pathogens vitamin C citrus fruits, potatoes, berries to keep skin strong and able to heal quickly; keeps blood vessels and bones healthy vitamin D most is made in our skin when sunlight falls on it; oily fish helps calcium to be absorbed from food; for strong bones and teeth calcium dairy products, for strong seeds and nuts bones and teeth iron red meat, dark green vegetables, fish, shellfish, nuts, seeds 1 8 MJ per day 2 They may be very energetic and use up a lot of energy playing sport. They may be growing faster than normal. 3 They might not do much exercise, either because they cannot or because they choose not to. 4 The boy may do more exercise, and he is still growing. Making new cells for growth uses energy. 5 Girls are usually smaller. It takes less energy to move a small mass around than a larger mass. Girls might also be less active, on average, than boys. 6 a I need protein for growth. b There is a lot of protein in fish. c Starch and sugar are carbohydrates. d I get energy from carbohydrate and fat. a e should not eat too many of these, W because they contain a lot of sugar and fat. Too much of these foods can cause weight gain, and increase the risk of developing heart disease later in life. b They contain fibre, which helps the digestive system to work normally and reduces the risk of getting constipation. They also contain vitamin A, which helps with good vision. c You can eat pulses – peas, beans, and lentils – nuts, eggs and milk. a protein, fat, carbohydrate, calcium, iron b He needs fresh fruit and vegetables, to provide vitamins and fibre. c Answers should include reference to why too much fat in the diet is harmful to health. 7 to make haemoglobin (which is found in red blood cells and transports oxygen) If they have anaemia, not enough oxygen is transported to cells. So they cannot release enough energy from glucose by aerobic respiration. 8 The main nutrients are likely to be: protein in the lentils and cheese; fat in the cheese; Vitamin A, Vitamin D, calcium and iron in the lentils; Vitamin A in the colourful vegetables. Topic 7.2 A balanced diet Getting started The six nutrients are: protein, fat, carbohydrate, vitamins (A, C and D), minerals (calcium, iron) and water. Carbohydrate, fat and protein can provide energy. Vitamins and minerals are needed in only small amounts. 25 Questions Activity: Advice on a healthy diet 1 Eat a wide variety of foods... 2 Eat plenty of fresh fruit... 3 Don’t eat too much fast food. 4 Make sure you eat enough food... 5 Don’t eat too much food containing a lot of fat. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Topic 7.3 Growth, development and health 2 Getting started 1 Possible answers include: helps the heart to remain healthy; good for mental health; keeps muscles and bones strong. 2 Learners may know that smoking causes lung cancer, so not smoking reduces the risk of getting this disease; they may not know that it also increases the risk for most other types of cancer; smoking also increases the risk of heart disease and strokes. b Cells grow, and then divide to produce more cells, which in turn divide, and so on. 2 Protein is needed to make new cells. If there is not enough protein or energy, this slows down the growth of cells, so they don’t get big enough to divide. Ball-and-socket joints: hip joint and shoulder joint. 3 the radius 4 the scapula, the humerus and the ulna 5 It has three attachments at the top – one to the scapula and two to the humerus. 6 As the muscle contracts, it exerts a pulling force on the tendon, which transmits the force to the bone. If the tendon stretched, the bone would not move. Questions 1 a Hinge joints: elbow joint, knee joint. Learners may also mention the wrist; this is actually made up of many small bones which slide over one another, and is not a hinge joint. Think like a scientist: Using a model arm to investigate how the biceps muscle works 1 The forcemeter represents the biceps muscle. 3 About 3.6%. 2 The force decreased. 4 100 − the answer to question 3, so about 96.4%. 3 5 The more a mother smokes, the more likely it is that her baby will have a low birthweight. Smoking 15 or more cigarettes a day increases the chance from 3.6% to 9% – making it 2.5 times more likely. Learners need to remember the principle of moments. Turning forces (moments) are found by multiplying the force by the distance from the pivot. As the distance from the pivot increases, less force is needed to produce the same moment. 4 The force increased. 5 Again, learners need to think about the principle of moments. The clockwise moment is produced by the force pulling upwards on the forcemeter, and the anticlockwise moment by the masses on the hanger. Topic 7.4 Moving the body Getting started 1 Learners may be able to identify the cranium (protects the brain), ribs (heart and lungs) and pelvic girdle (abdominal organs). 2 leg and arm bones; shoulder and hip bones; vertebral column Questions 1 A joint is a place where two bones meet. clockwise moment = force on forcemeter × distance from pivot anticlockwise moment = force produced by masses on hanger (weight) × distance from pivot So, if distances do not change, and the weight on the hanger is greater, a greater force must be applied to the forcemeter to balance it. Learners could show these calculations as part of their answer. 26 Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 6 Position 1, closest to the pivot. 7 At this position, the muscle needs to produce the largest force to keep the radius horizontal, so it might be thought to be better if it was fixed at position 4. However, if it was fixed between position 4 and the scapula, the muscle would need to shorten by a much greater amount than when it is fixed between position 1 and the scapula. Muscles cannot shorten by much, so this would not work. (Learners may also think of what their arm would be like if the biceps was fixed between the scapula and the wrist – answers such as ‘you would not be able to put your shirt on’ and ‘you might be able to fly like a bat’ show that they are thinking.) 7.2 a b 33 − 12 = 21 kg c About 9 and 13 years (the steepest part of the graph). d No. The line is still sloping upwards at this age. 7.3 a B and C are hinge joints. A and D are ball-and-socket joints. b R and S c P and Q d antagonistic e Idea that muscles can only contract and pull, not push. So one muscle is needed to pull the bone in one direction, and another muscle is needed to pull it back again. f Calcium g From the bones of the animals they eat. Check your progress 7.1 a The weightlifter uses his muscles to lift weights. The muscles contract to make the weights move. This uses energy. The muscles get the energy by breaking down glucose in a reaction called respiration. b Protein is needed for making new cells. It is needed for growth. So building strong muscles requires protein. c Carbohydrate is needed for energy. The weightlifter needs energy for his muscles to contract, to lift the weights. d minerals (calcium and iron); vitamins (A, C and D); fats; water 12 kg Unit 8 Chemical reactions 2 An exothermic reaction is one in which more energy is given out than is put in. 3 Thermal energy is given off. Name a product: carbon dioxide. 4 Magnesium chloride and hydrogen. The number of atoms in a carbon dioxide particle is 3. 5 When the fizzing stopped. 6 Sofia’s idea was correct because in their reactions the increase in temperature is the same. 7 Safety glasses should be worn in case the acid spills or spits into the eyes. Topic 8.1 Exothermic reactions Getting started Name a reactant: carbon or oxygen. One of these atoms is carbon. Suggestions might be that it gets hot. Questions 1 27 A fuel, oxygen and energy to start off the reaction. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 8 Does adding more magnesium to hydrochloric acid increase the temperature in the reaction? Does adding a different metal to hydrochloric acid result in a different quantity of thermal energy being given off ? 2 Questions Does changing the acid used in the reaction with magnesium result in a different quantity of heat energy being given off ? 1 Think like a scientist: Planning and carrying out an investigation into the reaction between acid and magnesium 2 An endothermic reaction is one where heat energy from the environment is taken in. 3 Inside sherbet sweets there is a mixture of dry citric acid and sodium hydrogencarbonate. When you suck them, these substances dissolve in the water in your saliva, and react together. Your mouth feels cooler because this reaction is endothermic and takes energy in from its surroundings. 4 The ‘fizzy feeling’ is due to carbon dioxide being given off in the reaction. 5 When the ice melts, no new products are formed, so this is not a chemical reaction. The ice changes state. 6 Evaporation, when a liquid changes to a gas. 7 You feel cold because the water particles on your skin use energy from your skin to change to a gas and evaporate. This is an endothermic process. You lose heat energy so you feel colder. 8 When water freezes, energy from the water is lost to the environment, so this is an exothermic process. The particles of water in the liquid state have enough energy to move past one another. When ice is formed, the particles have lost energy and can only vibrate. 9 Self-heating cans are very expensive because they have to be made so that the chemicals used to warm the food or drink do not come into contact with it. Since the can and chemicals are only used once, this also makes it expensive. It should also include stating the variables to be changed, measured and kept the same. There should be an indication of repeating experiments and how they will ensure the results are more reliable. An outline results table is also needed. There should be some indication of how the results will be presented. 1 This will be based on the results obtained. 2 There should be some indication of a comparison and/or discussion of the other learners’ results. 3 Credit any sensible suggestions, such as a larger range of readings, more accurate methods of measuring the variables or changes in the method. Suggestions should result from the experience of the investigation. Topic 8.2 Endothermic reactions Getting started The target with the most accurate arrows is B, with the arrows at the centre. The targets B and C have precise arrows, they are close together. C has been precise but not accurate, arrows close together but not at the centre. A is neither precise nor accurate, arrows spaced out and not at the centre. B is accurate and precise with arrows close together and at the centre. The point here is to discuss what the learners think and to use this as an opportunity to assess their understanding rather than to mark this as right or wrong. Think like a scientist: Carrying out an endothermic reaction 1 Credit readings from the practical they have done. aSodium hydrogencarbonate and citric acid. b The plan should cover all the practical issues and safety requirements, such as an equipment list. 28 Heat energy should be transferred from the surroundings into the reaction, so a drop in temperature should be recorded, but credit what the students obtain in their practical. Sodium citrate, carbon dioxide and water. 10 The can is only able to be used once because, once the chemicals have reacted, they cannot produce any more heat. 11 The chemical ice pack has the advantage that it can be used when you do not have access to a fridge or freezer. The disadvantage is that it is more expensive and can only be used once. The freezer ice pack has the advantage that it is much cheaper and can be used many times. The disadvantage of this type of ice pack is that you must have access to a fridge or freezer. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Think like a scientist: Endothermic or exothermic? 1 A polystyrene cup is used rather than a glass beaker because it is a poor conductor of heat so the contents will lose less heat energy to the environment. 2–3 This will depend on the reactions you supply. 4 Learners may comment on the fact that some of the changes in temperature are very small. They may also comment that it was not possible to take the temperature with some of the processes, such as the steam and a cold surface to show condensation, or the melting ice cubes. To decide if it was an endothermic or exothermic process without taking the temperature, they might suggest using their knowledge of the changes of state and what happens. Accept any sensible suggestions. Topic 8.3 Reactions of metals with oxygen Getting started The answers will be dependent on what each learner can remember. Use this as an opportunity to revise the properties and to encourage cooperation between learners. Think like a scientist: Heating metals in air 1 2 This will depend on what was provided. The evidence for this should involve a practical observation. These should cover the use of safety glasses, holding the metal at arm’s length, not looking directly at the metal in case it reacts in a similar way to magnesium. 3 Learners should remember the reaction they have seen with sodium or potassium and water and suggest that these metals are very reactive and it might be dangerous. 4 Learners should know that these metals are expensive so unlikely to be provided in class. Questions 29 1 It is soft enough to be easily cut with a knife. 2 To protect themselves because the sodium is very reactive and may react with the moisture on the skin. 3 sodium + oxygen → sodium oxide 4 To prevent iron from rusting it should not be in the presence of air and water. The iron nail in dry air does not rust. 5 The nail in test tube 2 rusted most quickly. The conditions in this tube are water and air. 6 The same type of nail is used in all test tubes so that it is a fair test. The only variable that changes is the conditions. 7 The air in test tube 3 is dried by the calcium chloride inside absorbing moisture in the air. 8 The air in test tube 4 is kept away from the nail by having a layer of oil across the surface of the water. The water has also been boiled so that any air dissolved in it has been removed. Topic 8.4 Reactions of metals with water Getting started This will depend on what metals you were able to use, and what learners have remembered and understood. It will also encourage discussion and co-operation. The most reactive is likely to be magnesium but learners should base their discussion on the metals they have used or seen demonstrated. This is an opportunity for you to assess the learners' understanding. Think like a scientist: Reactions of metals with water 1 This will depend on which metals you provide but it is likely to be magnesium. The evidence for this will be the speed of reaction and/or the number of bubbles of hydrogen given off. 2 This will depend on the metals you provide. Accept the order based on the learners’ results. 3 Some metals that did not react in cold water may react in hot water because the particles in the hot water have more energy than those in cold water. The more energy particles have, the more they move. The more they move, the more likely they are to collide with the metal particles and to react. Questions 1 sodium + water → sodium hydroxide + hydrogen 2 Wear safety glasses; the metals should be moved using tongs not hands; only small pieces of the metals should be used; a safety screen should be used. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 3 These metals are stored under oil because they are so reactive that they react with the moisture in the air and could do so inside the container, causing an explosion. 3 When the magnesium is placed in the acid, bubbles of hydrogen are given off. The temperature increases as it is an exothermic reaction 4 Hydrogen; you could test for this gas by using a lighted splint. If the gas is hydrogen, it would cause a squeaky pop as it burns. 4 zinc + nitric acid → zinc nitrate + hydrogen 5 6 Measure which one produces the greater volume of hydrogen in a given time. The mass of calcium and magnesium used should be the same; the volume of water used should be the same; the temperature of the water used should be the same. 7 calcium + water → calcium hydroxide + hydrogen 8 The particles in the steam are able to move freely and have a lot more energy than the particles in the liquid water. The particles in the steam collide with the particles on the surface of the magnesium more frequently than the particles in the liquid water. This means that a reaction between steam and magnesium is more vigorous than between liquid water and magnesium. 9 Accept any correct answers, such as copper, gold, silver. Think like a scientist: An investigation into the reaction of metals in acid 1 The metals that should not be used are potassium, sodium and calcium. This is because they are so reactive that there would be an explosive and dangerous reaction. 2 The measuring cylinder that should be used is the one that is nearest in volume to the volume needed for the test tube or beaker. For example, if students need 25 cm3 of acid in a beaker then to measure this volume of acid, it would not be sensible to use a 100 cm3 measuring cylinder, as 25 cm3 is only a small proportion of the volume of this cylinder. It would not be very accurate to use a 10 cm3 measuring cylinder as they would have to use it three times and there is more opportunity for error. It is easier to get an accurate measure of 25 cm3 by using a 25 cm3 cylinder. Credit an appropriate response to the use of a 10 cm3 measuring cylinder, if students choose to use a test tube for the investigation. 10 That it does not react / is chemically inactive 3–4 These depend on the results obtained. Topic 8.5 Reactions of metals with dilute acids Getting started oxygen + sodium → sodium oxide oxygen + magnesium → magnesium oxide oxygen + iron → iron oxide water + potassium → potassium hydroxide + hydrogen water + calcium → calcium hydroxide + hydrogen magnesium + steam → magnesium oxide + hydrogen Questions 30 1 magnesium + sulfuric → magnesium + hydrogen sulfate acid 2 magnesium sulfate Activity: Reactivity order 1 This will depend on which metals they used, but is likely to be magnesium. 2 There should be some discussion of the fact that gold and silver are very unreactive, but that if silver is left in the air for a long time it goes black, as silver oxide is formed. Gold, however, stays shiny even if it is buried in the ground for hundreds of years. Check your progress 8.1 a magnesium ribbon placed in hydrochloric acid OR burning b sodium hydrogencarbonate added to citric acid c decreases d evaporation or melting ice e exothermic Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 8.2 a b c d 8.3 a b he type of fuel he uses in the T spirit burner. The volume of water used and the time he heats it for. He must take the temperature of the water before and after he heats it. He must do this for each of the fuels he uses. The fuel that produces the largest rise in temperature is the one that gives out the most energy. Credit comments about handling hot equipment with care. Credit wearing safety glasses. carbon + oxygen → carbon dioxide b The temperature would increase by about 5 °C. c Zara’s results, final column from top to bottom: 1, 2, 3, 4. Arun’s results, final column from top to bottom: 1, 1, 3, 4 d sodium sodium hydrochloric + → chloride + hydrogen hydroxide acid Mass of calcium Mean temperature added in g change in °C e magnesium + oxygen → magnesium oxide d potassium + water → potassium + hydrogen hydroxide 8.4 aThe more calcium you add, the greater the increase in temperature. 1 1 2 1.5 3 3 4 4 iMass of calcium added in g. c iiTemperature increase in oC. f They would not be able to use these results because the volume of water used will affect the temperature increase. Unit 9 Magnetism Topic 9.1 Magnetic fields Getting started Learners should be able to recall some examples such as fridge magnets, holding cupboard doors closed, holding paperclips or pins and in some toys. Questions 1 2 The area around a magnet where the effects of the magnet can be detected. Magnet A is stronger than magnet B. 3 S 4 N a b S N 31 S S Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE Activity: Showing a magnetic field pattern 1 2 3 a At the poles. b The iron filings are clustered together more at the poles (not ‘there are more iron filings at the poles’, unless the idea is more per unit area). a no b Both poles have equal strength; both poles attract the same number of iron filings. Some of them are piled up in vertical lines; they are attached end to end. Questions 1 (magnetic) compass 2 North, because the pole of the Earth’s magnetic field close to geographic north is a south pole; opposite poles attract. 3 The movement in that time will be so small it can be ignored. 4 a core b iron 5 a Think like a scientist: Detecting a magnetic field 1 Average value of d correctly worked out from their results. 2 The stronger the magnetic field, the larger the value of d. 3 The strength of both poles of the same magnet is the same. 4 a To reduce friction; make it easier for the paperclip to slide; so the force on the paperclip is not having to pull against friction. b 5 To be easier to pull (than a large paperclip); to detect the magnetic field as far from the magnet as possible. Use something that does not have to slide / is not affected by friction (so much), such as a steel ball that can roll; another method, such as hanging a paper clip on a string and seeing when it starts to move/move a magnetic compass closer until it starts to deflect. Topic 9.2 The Earth as a giant magnet b Think like a scientist: Detecting the Earth’s magnetic field 1 To show that the direction it will point is independent of objects in the room or position in the room. 2 a north b The Earth’s magnetic field has the south pole closer to geographic north. 3 Getting started 1 2 32 a Learners will refer to the pointed end or the end with the hole depending on how they magnetised their needle. b Learners should recall the north and south poles of the Earth, but they do not need to refer to geographic poles at this stage. Learners should understand the idea of navigation, although this can be expressed in different ways. A magnetic compass will point along the direction of the lines; the needle will point towards/close to geographic north. 4 The end of the needle that pointed towards north was a north pole. a–c Learners deduce how the needle was magnetised in terms of the pole that was used to stroke the needle and the direction; they link this to the direction their needle pointed. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 5 b Too fragile; easily damaged; difficult to carry; difficult to store. Topic 9.3 Electromagnets Getting started This is an open-ended activity, but learners may suggest applications that involve lifting objects and then dropping them again. Questions 1 iron and steel 2 Magnetic means to be attracted to a magnet. Magnetised means turned into a magnet. 3 An electromagnet works using electricity / flow of current, and a permanent magnet does not need electricity; an electromagnet can be switched on and off, but a permanent magnet works all the time. 4 5 Diagram showing wire coiled around a nail, with either end of the wire connected to a switch and a cell, which are also connected; circuit symbols should be used for the switch and cell. a xamples: lifting scrap metal, toaster, E controlling a fire door, electric bell. b Reason for each that includes the idea of the magnet being switched on or off as part of the function, e.g. scrap iron and steel can be lifted using the magnet and then dropped again as the magnet is switched off. Topic 9.4 Investigating electromagnets Getting started These are open-ended questions, where learners may express some different ideas, but the electromagnet used for scrap metal will be stronger than the one in a toaster; that used to hold open a door will be stronger than that in a bell (it may also be switched on for longer times). Questions 1 More force is needed to lift the metal than to hold the toast down. 2 Current in the coil; number of turns in the coil; the material of the core. 3 C 4 To make an electromagnet stronger, the current can be increased; stronger electromagnets will have a higher current. Think like a scientist: Investigating electromagnet strength 1 The table should have columns headed Number of turns and Number of paperclips. The number of turns should be in the first column and in ascending order. The number of paperclips should have columns for repeats. Activity: Making an electromagnet 33 It would change to be the opposite pole; reversing the cell will reverse the current; the magnetic field will be reversed when the current is reversed. 1 So that current does not flow through the nail; the nail is a conductor. 2 Averages correctly calculated (can be a column in the results table). 2 The ends of the nail are the poles; the magnetic field around a magnet is strongest at the poles; the magnetic field is weakest beside the middle of a magnet. 3 Graph with axes correctly labelled, with linear scale on both axes, scaled so points cover at least half the grid in both directions; all points plotted correctly; line of best fit drawn. 3 a Either: bring a magnetic compass close to the end; if the compass points towards the end of the nail, it is south; if the compass points way from the end of the nail, it is north. Or: bring the north pole of a bar magnet to the end of the nail; if they attract, it is south; if they repel, it is north. 4 As the number of turns increases, the number of paperclips that can be lifted increases. 5 The table should have columns headed Material of core and Number of paperclips; number of paperclips should have columns for repeats. 6 Averages correctly calculated (can be a column in the results table). Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 7 Bar chart with axes correctly labelled; linear scale on vertical axis, scaled so bars cover at least half the grid in both directions; all bars to correct height; bars not touching. 8 Comment on the best material and the worst; comments on any intermediate results. 9 In Part 1, the number of turns is a continuous variable (you can have any fraction of a turn); the material in the core is a discontinuous variable / discrete variable / variable with no intermediate values. 10 Line graph because current is a continuous variable. b S S • Lines curving outward from the poles. • Arrows on lines pointing to S. • Lines not touching or crossing each other. 9.4 N 11 Graph drawn according to answer in question 10; graph with axes correctly labelled; linear scale on both axes, scaled so points cover at least half the grid in both directions; all points plotted correctly; line of best fit drawn. 12 Comment that links their prediction with the trend shown in the graph. Check your progress 9.1 B S 9.2 N → S • Lines curving outward from the poles and going around the Earth top to bottom (ignore magnetic poles at same position as geographic poles). • Arrows on lines pointing from geographic south to geographic north. • Lines not touching or crossing each other 9.3 a 9.5 C 34 • Lines connecting the poles, may curve outward above and below the centre line. • Arrows on lines all pointing N to S. • Lines not touching or crossing each other. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021 CAMBRIDGE LOWER SECONDARY SCIENCE 8: TEACHER’S RESOURCE 9.6 a b Diagram to include: • 9.7 a b 35 iii electromagnet • cell or power supply (does not need to be labelled if conventional circuit symbol used) • switch (does not need to be labelled if conventional circuit symbol used) • coil • core, labelled as iron. it will increase /double i the current ii number of paperclips held / strength of the electromagnet •line sloping upward (ignore curve) c starting at origin i c urrent in the coil; number of turns in the coil ii D Science skills Questions 1 33 2 It does not fit the pattern. It is much larger than the other results for a distance of 40 cm. 3 Means are 28.0, 18.5, 13.0 and 9.3 for distances of 20, 40, 60 and 80 cm. Cambridge Lower Secondary Science 8 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth © Cambridge University Press 2021