CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Exam-style questions and sample answers have been written by the authors. In examinations, the way marks are awarded may be different. ractical Workbook P answers Chapter 1 Practical investigation 1.1 Exam-style questions 1 1 2 3 4 5 6 Suitable drawing made of the organism chosen by the student, with clear lines drawn in pencil, drawing larger than the original, correct shape and proportion, main features observable, main features correctly labelled. Main features of student’s drawing correctly identified. Correct group identified for the organism chosen. Student should use magnification = image size / actual size to calculate a number greater than 1 if the image is correctly larger than the original. Student’s own checklist matches that of their drawing. To ensure that the drawing is clear and that the student can demonstrate their understanding. Reflection a b c d e Student draws a diagram that satisfies each of the marking points: clear lines drawn in pencil [1] ; drawing larger than the original [1] ; correct shape and proportion [1] ; main features observable [1] ; main features correctly labelled [1] ; 17 mm or 1.7 cm (accept +/– 1 mm) [1] ; magnification = image size / actual size [1] ; correct calculation = magnification = measured size / actual size; magnification = student’s own measurement of their wing diagram / 17 mm; answer should be greater than 1 if diagram is larger, and given to three significant figures [1] ; Musca domestica (student answer should [1] be in italics, or underlined). ; Any two from: two pairs of wings (but not visible in flies); body divided into head, thorax and abdomen; three pairs of [Max. 2] jointed legs. ; Student correctly identifies the points not done correctly in the diagram. 1 Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 2 Practical investigation 2.1 Practical investigation 2.3 1 1 2 3 4 5 6 7 Suitable drawing made, with clear lines drawn in pencil, drawing larger than the original, correct shape and proportion, main features observable, main features correctly labelled. Any observable features labelled (such as cell wall). Cell wall provides strength and support, cytoplasm is the site of cell reactions, the nucleus controls the activity of the cell. Accept any sensible answer, such as mitochondria, cell membrane, chloroplast etc. The resolution is not high enough to distinguish between the smaller parts of the cell. To see the cells in a single layer; clearer to see the cells. You might see the same structures but they might not be as clear or obvious without the staining solution. Practical investigation 2.2 1 2 3 4 5 Student’s drawings of cells, with clear lines drawn in pencil, drawing larger than the original, correct shape and proportion, main features observable, main features correctly labelled. Limited to cell membrane, nucleus, cytoplasm. Cell membrane controls what enters and leaves the cell, cytoplasm is the site of cell reactions, the nucleus controls the activity of the cell. Site of cellular respiration. Health and safety, to protect against airborne pathogens being released. 2 3 4 Student’s drawings of cells, with clear lines drawn in pencil, drawing larger than the original, correct shape and proportion, main features observable, main features correctly labelled, magnification included. Student’s answer should include the calculation for objective lens × eyepiece lens. Student’s answer should match the specimens viewed. To show understanding and so that the viewer knows what they are looking at. Reflection Student’s own reflection. Exam-style questions 1 a b c d Drawing larger than original [1] ; clear lines [1] drawn in pencil [1] ; main features labelled [1] ; correct shape and proportion [1] ; 50 mm or 5.0 cm (accept +/– 2 mm) ; [1] Student’s measurement matches that of the drawing. ; [1] Magnification = image size / actual size [1] ; correct numbers substituted [1] ; correct answer given based on answers to parts b and c [1]. ; Reflection Use a microscope with greater resolution or magnification. 2 Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 3 Practical investigation 3.1 Practical investigation 3.3 1 2 1 2 3 4 5 6 Time stated in seconds. Student sketch shows diffusion of colours towards the centre. The colours / dyes dissolved into the water and diffused towards an area of lower concentration. The diffusion would happen faster because the warmer water would allow for faster diffusion of the colours. Method should include a range of water temperatures for the independent variable, suggestion that the time taken to reach the centre can be measured, and some attempt to control all other variables such as sweet size, volume of water, room temperature, etc. The reaction will happen faster. Any sensible suggestion such as using a pipette or a way of adding the water slowly. Practical investigation 3.2 2 3 4 4 5 Reflection Reflection 1 3 Colour change stated with time in seconds as observed. The colour diffused out of the gelatine into the water as it moved down the concentration gradient. Use an acid of higher molarity / strength. Repeat the readings and take an average. Unlikely to be able to add at the same time so therefore the results might be less valid as some of the beetroot could have been in the solution for longer than others. Practical investigation 3.4 1 2 3 4 3 Data recorded by student. Add the two lengths together before dividing by two. Student should divide the difference by the original length, before multiplying by 100. Student’s answer should refer to water moving into the beetroot by osmosis where there has been an increase of length. The water moves into the beetroot when water concentration is higher outside of the beetroot. If there is no change in length, then the water concentration inside and outside of the beetroot must have been similar. Method should refer to measuring the mass of the beetroot, using a measuring balance to either 2 or 3 decimal places. Student’s drawing should show water moving into the tubing and becoming bloated / larger. The tube becomes more filled / larger/ more bloated or similar wording. As the water potential inside the tubing was lower than outside, the water moved down the concentration gradient by osmosis, into the tubing. Any sensible answer, such as increase the concentration gradient, or by using warmer water. Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 3 continued Exam-style questions 1 a Three correct answers for distilled water [1] ; three correct answers for sucrose solution [1] ; Mass of potato / g Solution c d 4 After Change 1.30 1.79 +0.49 1.31 1.71 +0.40 1.21 1.66 +0.45 20% sucrose solution 1.51 1.45 –0.06 1.60 1.53 –0.07 1.69 1.43 –0.26 40% sucrose solution 1.40 Distilled water b Before 1.40 1.40 For distilled water: (0.49 + 0.40 + 0.45) / 3 = 0.45 g; for 20% sucrose solution: (−0.06 + −0.07 + −0.26) / 3 = −0.13 g [1] ; for calculating total change in mass, [1] ; for dividing by 3, and [1] for the correct answers with units. ; Water molecules move down their concentration gradient from an area where there are more to an area where there are fewer [1]. ; Therefore, in the potato placed in the distilled water, the water moved from the high concentration of water molecules outside of the potato [1] ; into the lower concentration of water molecules inside [1] ; by osmosis, which caused an increase in the mass of potato [1]. ; (Accept opposite argument for potato placed in 20% sucrose solution.) Any sensible answers between 1.40 g and 0.80 g [1] ; with correct ‘change’ calculations completed [1]. ; Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 4 Practical investigation 4.1 Recording data 1 3 2 3 4 5 Student’s table should include types of orange / fruit used in the first column. The next columns should record the amount of juice / ml required to turn the DCPIP colourless. Student’s answer should match their data. Student data should be described with reference to figures from their own table. Student should also state any obvious pattern or relationship. Repeat the investigation. Any sensible suggestion, such as different prices of orange, different origins of orange, organic vs non-organic, raw vs cooked orange. Use equipment that can measure the colour of the solutions, or any other sensible suggestion along these lines. Reflection No, as different people might have different opinions on when it turned colourless. This means that we might get different results and the results might not be as valid. 2 5 5 Reflection Students are likely to say that it was difficult to crush each food for testing with a solution or that it was difficult to keep the mass the same when adding water. Any sensible suggestion for improvement, such as making a large sample of crushed food that can then be used for multiple tests. This ensures that the samples are the same for each test. Use the large sample to remove the exact mass required. Practical investigation 4.3 1 2 3 Practical investigation 4.2 1 4 Any two sensible safety suggestions: wear safety spectacles, wash hands. Student outlines the correct test for three different foods, any from: • Reducing sugar: heat with Benedict’s solution and observe the colour change (from blue to orange-red) • Protein: add biuret’s solution and observe the colour change (from blue to purple / mauve) • Starch: add iodine solution and observe the colour change (from brown to blue-black) • Fats / lipids: add ethanol and water in equal quantity and observe the change (cloudy layer forms) Student’s table completed and correct food group identified. Student’s answer should include the correct colour change for the foods tested. Repeating the investigation more than once, or multiple times. 4 Student’s own drawing of the suspended DNA. Student may answer either way here but if they can see the twisted nature of the DNA then they may be able to link this to the double helix structure of DNA. Breaks down the membrane to release the DNA from the nucleus. Some students may not have followed the method correctly, or with enough care. Exam-style questions 1 2 a b c d e Biuret reagent ; [1] Protein ; [1] From blue to purple / mauve ; [1] A and C ; [1] Because there was a colour change [1] ; from blue to purple [1] ; Method should include: • Grind the sample of food and add water [1] ; • Add the food to a test-tube [1] ; • Add a few drops of Benedict’s solution [1] ; • Place the test-tube with Benedict’s and food into a water-bath [1] ; with description or drawing of the water-bath [1] ; • Leave for a few minutes and observe the colour change [1] ; • The solution will turn from blue to green or to an orange-red colour [1] ; in the presence of a reducing sugar [1] ; Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 5 Practical investigation 5.1 Practical investigation 5.2 1 1 Student’s table should be similar to: Test -tube Solutions added Testing agent used Colour change A Starch Iodine From brown to blue-black B Starch + amylase Iodine None C Starch Benedict’s None D Starch + amylase Benedict’s From blue to orangered 2 3 4 5 2 The starch has been broken down into reducing sugars which turn orange-red when tested with Benedict’s solution. Reducing sugar / glucose / any named sugar There is no colour change; the iodine solution remains brown. To break down the starch into smaller molecules / sugars 3 4 5 6 6 Testtube Solutions added Testing agent used Colour change A Starch Iodine From brown to blue-black B Starch + amylase Iodine From brown to blue-black C Starch Benedict’s None D Starch + amylase Benedict’s None 6 7 Student’s own table should include the temperature of the water-bath in the first column, with space for readings taken for the time that the solution became colourless in the other columns, with units included in column headings (°C for temperature and s or min for time). Student’s line graph should match the results gathered and include: • Axes drawn using a pencil and ruler • Axes labelled with correct units • Points plotted using a sharp pencil • Points joined by straight lines that do not extend past the final point Student’s answer should match the graph. Student’s answer should match the data, using conditional sentences that include the IV and the DV. Such as, ‘as the temperature increased, the rate of reaction of the amylase increased’. The enzyme denatured and so the physical nature of the enzyme changed. This means that substrates can no longer bind to the enzyme and reactions cannot take place. In this investigation, the amylase was not able to break down the starch. Any sensible range such as: 10, 20, 30, 40, 50 oC. Repeat the experiment at least twice. Reflection Sensible ideas such as: work as a team, plan which team member will be responsible for each stage and annotate the method to that effect. Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 5 continued Practical investigation 5.3 1 H2O2 concentration / % Volume of oxygen collected every 30 seconds / cm3 0 30 60 90 120 150 180 210 240 270 60 40 20 0 Student data included in table. 2 Student’s own calculations from the data in Q1. 3 Student’s answer should refer to the data gathered: As the concentration of hydrogen peroxide increases from (student data to student data), the rate of reaction increases from (student data to student data). This is because the catalase acts as a catalyst and allows the reaction to happen at a faster rate. 4 To compare the effect of hydrogen peroxide. Reflection Student’s own reflection but may include assigning specific roles to each team member. Exam-style questions 1 a Any three from: • temperature ; • pH ; • enzyme concentration ; • type / source of enzyme ; • quantity / volume of solutions ; • same equipment used. ; [Max. 3] b i Enzyme activity Temperature / °C [1] ; pH [1] ; Substrate concentration [1] ; ii Enzyme activity iii Enzyme activity 7 Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 5 continued 2 a Temperature / oC Time taken for starch to be broken down / s Attempt 1 Attempt 2 Attempt 3 10 250 240 280 Average 257 20 240 240 271 250 30 65 55 63 61 40 72 70 69 70 50 110 120 131 120 60 247 278 271 265 70 300 301 312 304 [1] b 350 300 250 Time taken 200 for starch to break 150 down / s 100 50 0 c 8 0 10 20 30 40 50 Temperature / °C 60 70 Correct axis drawn [1] ; units added to labelled axis [1] ; appropriate size and scale of graph (at least half of the graph paper) [1] ; plotted correctly [1] ; lines joined together [1] ; Reference to: as the temperature increases from 10 to 20 oC, the time taken remains stable [1] ; but between 20 and 50 oC, the time taken falls to as low as 61 seconds [1] ; before increasing again from 50 oC upwards [1] ; Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 6 Practical investigation 6.1 Exam-style questions 1 1 2 3 4 Student’s drawing of epidermal peel should include labelled stomata, with clear lines drawn in pencil, drawing larger than the original, correct shape and proportion, main features observable, main features correctly labelled, magnification included. Student’s own data. Student’s explanation linked to conditions from where leaf was obtained. For example, if the leaf was gathered from a plant in warm, dry conditions then it may be that more stomata were closed to prevent loss of water. Student’s answer should identify the independent variable as named locations or conditions (such as in shade, direct sunlight, range of temperatures, etc.). The dependent variable should be the number of open / closed stomata. Controlled variables should include species of plant, surface area of leaf, any equipment named, same microscope, etc. a b c Reflection Student’s own reflections. Practical investigation 6.2 1 2 3 4 5 6 9 d Student’s own data. Student correctly calculates the average from own data (combined with that of peers if required). More oxygen bubbles produced indicates higher rate of photosynthesis. Student’s own data but expected results will be similar to: red / blue/ green / other. Light intensity. Student states method but includes an independent variable that alters the light intensity. This can be done by making the light source brighter / dimmer, or by moving the light source towards / away from the leaf. Accept any sensible named suggestion. Student’s method should include six from: • Place leaf into boiled water for 30 seconds ; • Remove leaf and place into ethanol solution ; • Place ethanol and leaf into water-bath to keep warm ; • Remove leaf after 15 minutes ; • Wash leaf with water and place onto white tile ; • Add iodine solution ; • Starch is present where iodine turns blue / black ; • Any safety point mentioned ; [Max. 6] Positive result (blue/black) in the green parts of the leaf [1] ; but no colour change from yellow iodine in the white parts of the leaf [1]. ; Where there is no chlorophyll in the white areas there will not be any photosynthesis [1] ; and so there will be no stores of starch in those areas [1]. ; 6CO2 + 6H2O ➞ C6H12O6 + 6O2 correct reactants [1] ; correct products [1] ; balanced equation [1] ; e Leaves contain many veins Leaves are wide and flat Leaves are thin Leaves have stomata on the underside Any three from: • wide, flat leaf ; • thin leaf ; • presence of veins ; • stomata. ; [Max. 3] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 7 Practical investigation 7.1 Exam-style questions 1 2 1 3 4 Student’s own data. a and b Student correctly uses Q = mc ∆T to calculate the energy transferred in joules for each food in their table. a Student correctly identifies the food with the highest energy value. b This food heated the water to the highest temperature and so transferred the most energy to the water. Using the same size / mass of food, holding the food the same distance from the water, using the same starting temperature for the water, using the same equipment for each trial, allowing the food to burn for same time, or to completion of burning. Reflection Student identifies possible improvement and makes sensible suggestions. For example, for the food burning at the same distance from the water, an improvement would be a second boss clamp and stand to hold the food in place. Practical investigation 7.2 1 2 3 4 5 10 Student’s diagram of the eggs drawn with clear pencil lines. Student’s own observations of the eggs. One of these should be smooth and one should be cracked and shrivelled. Fizzy drinks contain sugars that combine with bacteria to form acids. This acid attacks the teeth and weakens the protective enamel that surrounds them. The amount of solution should be the same for valid results. The eggs should be from the same source and this can be verified by taking from the same carton of eggs. The quality and validity of results might be affected as you cannot be sure any change is due to the type of solution. It might not be possible, or safe, to use real teeth and so using the eggshells allows us to model the effect of acids. a b c d Q = mc ∆T [1] ; Q = 30 × 4.2 × 27 [1] ; Q = 3402 J or 3.4 kJ [1] ; Any two sensible safety precautions from: safety spectacles ; use Bunsen burner safely with yellow flame ; dispose of food safely after burning ; do not handle hot equipment ; [Max. 2] Carbohydrates, fats, vitamins, minerals, water, protein, fibre (all correct for one mark) ; [1] Any correct food stated that is rich / known for that nutrient. (One mark for each food per food group.) Common examples include: • Carbohydrates: bread, pasta, rice, potatoes ; • Fats: oils, dairy products, fatty meats, chocolate ; • Vitamins: oranges, fruit, oily fish, eggs ; • Minerals: milk, broccoli, fruit, vegetables ; • Water: water ; • Protein: eggs, milk, meat, fish ; • Fibre: cereals, bread, nuts ; [Max. 7] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 8 Practical investigation 8.1 Practical investigation 8.3 1 2 Method 3 4 5 6 Student’s own results in the table. The correct temperature chosen to match the data in the table. The difference correctly calculated between the furthest and the shortest distances in the student’s table. Xylem. Five would be ideal but accept any answer between four and ten. Students may have used different plants, or differently sized stems. Students may also suggest natural variation between different plants and parts of plants. 4 Recording data 1 Reflection Student’s own reflection. 2 Practical investigation 8.2 1 2 3 4 5 Water vapour / condensation / water collected inside the bag. Turns blue. Water. Condensation. Investigation should outline a similar method to Practical investigation 8.2 but by using two different types of plant. Answer may identify differences between the leaves as a factor, control variables should be identified such as plant size, surrounding conditions, and size and type of polythene bag. Student’s method should be similar to: • Ensure that there are no air gaps between the plant and the potometer tubing. • Open the clip and fill the tubing with the water, close the clip immediately. • Record the position of the water meniscus. 3 4 5 Student’s table should have the independent variable in the left column (either surface area of leaf or number of stomata) and the distance travelled by the bubble should be in the right-hand column. The table should include the time taken for the recordings. Student uses own data. Transpiration rate = distance travelled by the meniscus / time taken. Units should be correct (for example cm/min). Student correctly identifies variable with greatest transpiration rate. Student makes reasonable suggestion. For example, the greater the surface area of the leaf, or the greater the number of stomata, will both result in higher rates of transpiration. This is because more water can be lost from the leaf. Type of plant, size of plant, temperature, humidity, or any other named variable. To make the experiment valid and to be sure that any change in rate was as a result of the independent variable. Reflection Any sensible suggestion such as using graph paper with smaller squares, or technology to help count the number of stomata. 11 Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 8 continued Exam-style questions 1 a b Any two from: • time the plant was observed for ; • time intervals ; • temperature of the room ; • leaves taken from the same plant ; • same equipment used each time ; [Max. 2] i all four averages correct ; [1] ii correctly dividing the average distance by time [1] ; time converted into minutes [1] ; Leaf Distance moved by air bubble / mm 1 c d 12 2 3 Average Transpiration rate / mm / minute 1 120 101 72 97.7 1.6 2 109 115 154 126 2.1 3 70 61 80 70.3 1.2 darkness 0 1 1 0.7 0.01 The temperature of the room could have been varied [1] ; improve by keeping the temperature the same and not adjusting the heating throughout the day [1]. ; Some of the water is used up by the plant / stored by the plant. ; [1] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 9 Practical investigation 9.1 Practical investigation 9.3 1 1 2 3 2 Student’s own drawing should be in pencil and have structures labelled (this may include aorta, pulmonary vein, atrial wall, valve tendons, ventricle wall, valve flaps). a To prevent bacteria from coming into contact with skin or clothes. b To destroy or remove any bacteria that may be on the hands or skin. c To destroy any bacteria that remain on the surface and prevent coming into contact with anyone who touches the work surface. d To prevent airborne pathogens from being ingested. 4 5 Reflection Student’s own reflections. 6 Practical investigation 9.2 1 2 3 4 5 6 7 8 Student completes the table using their own data. Beats per minute (or BPM) in columns 2, 3, and 4. Correct calculation from student’s own data. Correct calculation from student’s own data. It is most likely that there will be a small decrease in the heart rate. Accept any answer that matches the student data as results may vary between different people. Sportsperson or athlete may be able to use the techniques to help them relax and perform better in high-intensity or high-pressure competitions. Any sensible suggestion such as heart monitor, wearable activity tracker, or other electronic pulse measuring device. Not all members will be of the same sex, fitness, age, diets, etc. This means that results might vary a lot within the group. Reflection Student’s own reflections. 13 Student completes the table using their own data. Correct calculation from student’s own data. Student’s graph should contain: • graph covers at least half of the grid • x-axis contains the treadmill speed • y-axis contains the average heart rate • correct units shown (km/h and beats per minute) • points plotted correctly • points joined together using pencil and ruler. As treadmill speed increases, the heart rate increases. The body requires more oxygen and glucose to be pumped around the body for cells to carry out respiration. The differences in participants – they might have been different ages, sexes, fitness levels, diets, etc. Reflection Student’s own reflections. Exam-style questions 1 a b c d Any three from • age, sex, fitness, weight / mass, height, diet of the participants ; • Accept any sensible named variable not stated. [Max. 3] Improve the validity of his results / the investigation. ; [1] Health of participant / ability to stop the exercise if feeling ill or dizzy. ; [1] Method should include any six from: • at least 3 male and 3 female participants ; • of similar age and fitness ; • description of measuring heart rate before and after exercise ; • time stated for length of exercise ; • attempt to control the variables of temperature, equipment, type of participant, etc. ; • one valid safety point ; • repeat each reading at least once and find the mean ; [Max. 6] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 10 Practical investigation 10.1 Exam-style questions 1 1 2 3 4 5 6 7 8 Student’s drawings should include bacterial growth or spores on the dish. Description of counting a smaller area and multiplying to estimate the total number of spores. Student’s answer matches their Petri dish. Incubation at 25 oC, use of nutrient broth, sealed contained, away from agents that destroy or inhibit bacterial growth, or any other sensible suggestion. Bacteria would not grow. To provide a sterile environment for the investigation. The bacteria would multiply too quickly which is dangerous / hazardous. The airborne bacteria that would be released would be very dangerous for those that ingest or inhale them. Reflection a b Any eight from: Prepare two agar plates [1] ; heat an inoculating loop in a hot Bunsen burner flame [1] ; Using the loop, collect bacteria from the door handle and from the keyboard [1] ; add the bacteria to the agar plates [1] ; and seal the Petri dishes with tape [1]. ; Place the Petri dishes in an incubator [1] ; between 20 oC and 30 oC [1]. Count the number of bacterial spores in the dishes [1] ; after a named time period [1]. ; Allow one mark for safety [1]. ; [Max. 8] 60 mm (accept 59 to 61 mm) ; [1] i ii Convert mm to μm (60 × 1000 = 60 000 μm) [1] ; Actual length = image length / magnification [1] ; = 60 000 μm / 12 000 [1] ; answer = 5 μm [1] ; Student’s own reflections. Practical investigation 10.2 1 2 3 4 5 6 7 14 Student states correct names of solutions. Suitable biological drawing of the dish, with clear lines drawn in pencil, correct shape and proportion, main features observable, main features correctly labelled. Student’s answers match their Petri dish, units provided (mm). Student’s answer matches the results of the dish. The antibacterial agent was the most effective and was able to destroy more of the bacteria. They destroy bacteria in the mouth that may otherwise attack our teeth. This prevents infection and tooth decay. To observe if it was the antibacterial mouthwash that had an effect on the bacterial growth, as a control for the investigation. Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 11 Practical investigation 11.1 Practical investigation 11.3 1 1 2 3 4 5 6 7 Student’s own table contains acceptable results. Student’s answer should be the difference between the two answers given in Question 1. Heat energy released during respiration. Collate results and calculate the mean / average. To reduce heat loss to the surroundings. They act as a control so that the results can be compared. This will allow any change in temperature to be attributed to the independent variable. To observe the temperature change and link this to the germination of the seed, so that any temperature change was not due to growth/ respiration of bacteria/fungi. 2 3 Reflection Student’s own reflections. 4 Practical investigation 11.2 1 2 3 4 5 15 Student’s diagram correctly labelled. Possible structures include the trachea, the C-shaped tracheal rings, the bronchi, the bronchioles, the pleural membrane and possibly some of the blood vessels that travel to and from the heart. The lung floated / did not sink. The density of the lung is less than the density of water, due to the amount of air and air space in the lung, even when deflated. Compare the surface area of the lung before / after the inflation. The most suitable method might be to compare the displacement of water when the lung is submerged but accept any sensible suggestion. Clean / sterilise with disinfectant to remove unwanted bacteria. 5 6 7 8 9 Student’s method should be similar in style and structure to the method in the experiment in 11.3 of the Coursebook. The student should state how the breathing rate is achieved and measured, the type and length of exercise, and how the breathing rate will be measured every minute after exercise until the rate returns to the resting rate. The table should include the following headings for each student tested: Breathing rate at rest / breaths per minute, breathing rate for every minute after exercise (this may go up to 5 to 10 minutes depending on activity and student fitness). Student’s graph should match data from the table with Time / minutes on the x-axis, and Breathing rate / breaths per minute on the y-axis. The graph should be drawn to an appropriate scale and the plots joined pointto-point with a ruler. Students should describe the increase in maximum breathing rate during exercise, before describing the gradual decrease in breathing rate after the exercise has finished. To provide oxygen required to break down the lactic acid produced during exercise Lactic acid The time taken for the body to break down the lactic acid and return to the normal breathing rate. This is the time taken to repay the oxygen debt. By selecting participants of similar age / sex / fitness / diets / lifestyle The results might have varied because of the differences and cast doubt on whether the independent variable made a difference. Reflection Student’s own reflections related to possible issues in their own method, such as time available to carry out the exercise, the different types of participant, or other sensible answers. Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 11 continued Practical investigation 11.4 1 2 3 a–d Student observations. a Temperature of air increases as it passes through the respiratory system. b Water vapour will turn the white (anhydrous) copper sulfate crystals from white to blue. c Limewater turns cloudy/milky in the presence of carbon dioxide. d Oxygen relights a glowing splint. Suggestion of use of technology or data logger or probe. Exam-style questions 1 2 3 16 a Student’s graph shows breathing rate on the y-axis [1] ; against time on the x-axis [1] ; with appropriate units [1]. ; Curve sketched showing breathing rate at rest for 3 minutes, before rising to a peak at 10 minutes, falling back to the resting rate at 14 minutes [1]. ; b Breathing rate increases gradually from 3 to 10 minutes [1] ; before decreasing back to the resting rate at 14 minutes [1]. ; c Muscles had produced lactic acid during exercise [1] ; which requires oxygen to break down into carbon dioxide and water [1]. ; Breathing rate remains high [1] ; until this oxygen debt [1] ; has been paid off. d Any two sensible variables such as height / mass / weight / fitness / age / sex of the person, same environmental conditions. ; [Max. 2] Breathing rate is ‘normal’ before running [1]. ; Breathing rate increases gradually as she runs [1]. ; Breathing rate reaches a maximum level [1]. ; Breathing rate increases to take in more oxygen for respiration [1]. ; Allow student credit if their answer includes reference to breathing deeper as part of the increase in oxygen uptake. C6H12O6 + 6O2 ➞ 6CO2 + 6H2O correct reactants [1] ; correct products [1] ; a balanced equation [1] ; Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 12 Practical investigation 12.1 Practical investigation 12.3 1 1 2 2 3 4 5 6 7 Student’s table includes readings from each attempt and a column to calculate the mean. Student’s answer matches the corresponding value in Table 12.1. Yes, a combination of anticipation, and the body reacting faster to the stimulus. Student’s prediction should be that the reaction time was faster as they can feel the ruler moving. Outline of method similar to original method but with the ruler touching the hand before release Accept suggestions such as use of data loggers to remove human error or the use of video footage to capture and check exact distances. Suggestion of method involving blindfold and reaction to a sound stimulus, such as a bell attached to the ruler. 5 Student’s table completed with answers. Student’s answer matches that in the table. Student’s answer matches that in the table. More receptors in those parts of the body so the two pins could be detected separately. Each person is different and might have different numbers of receptors in one area than other people might have. Reflection Any sensible ethics concern such as religious preferences for exposed skin, being respectful of each other and being aware that testing on ‘live’ subjects requires sensitivity. 17 Reflection Student’s own reflections. Exam-style questions 1 Practical investigation 12.2 1 2 3 4 3 Completed table. The pupil becomes smaller to prevent excessive light damaging the eyes; the reaction of the heel and the knee are involuntary actions useful for walking; and the eyelids close and open quickly to prevent foreign objects from entering the eye. The double vision occurs because the pressure on the eyelid distorts the signal sent to the brain. Each person is different and reacts in different ways; some students might not have the stimuli carried out in the same way. For example, some students might have tapped the heel or the knee in the wrong place. a b c Axes labelled with units [1] ; even scale and graph occupying half the grid [1] ; all four bars plotted correctly [1] ; with gaps between bars [1]. ; does not allow for any anomalies [1] ; as each student might have different results with more attempts [1] ; Drawing should include: sensory neurone connected to some sort of stimulus [1] ; relay neurone and CNS connecting sensory neurone [1] ; to motor neurone [1] ; motor neurone connected to effector [1] ; response shown, such as muscle contraction [1]. ; Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 13 Practical investigation 13.1 1 2 3 4 Student records correct data with units for mass and length. Student’s diagram includes all labelled parts, such as the medulla and the cortex areas; with clear lines drawn in pencil, drawing larger than the original, correct shape and proportion, main features observable. Correct formula shown (magnification = image size/actual size), student’s answer greater than 1 and given to three significant figures. Student correctly identifies one of the internal structures and links this to the appropriate function. These may include: medulla is where filtration takes place, or the cortex where water levels are regulated. Any sensible suggestion such as using a microscope or magnification instrument. 6 7 8 Reflection Student refers to possible heat loss before taking the starting temperature and suggests ways to minimise this effect. Examples include practising the technique to minimise the time, or having the materials partly placed and using a funnel to add the water through a small gap. Practical investigation 13.3 1 2 Reflection Student’s own reflections. Practical investigation 13.2 1 2 3 4 5 18 Student’s table includes columns for starting temperature, end temperature and temperature change. Table headings include units and the different materials are named in the first column. Student’s calculations match data from the table. Student describes, using data from the table, how the temperature decreases for all of the tests and identifies which materials caused the most/least change. The material prevents the heat energy from escaping and keeps it trapped inside the beaker or cup. The hairs on the outside of the skin become erect, causing an insulating layer of air to be trapped. This, along with a layer of fat and any clothes that the person may be wearing minimises the heat energy escaping from the body. To make the investigation (more) valid. The same volume of water at the same starting temperature could be used. This is a control to see that the materials did have an effect on the rate of cooling of the beakers/cups. 3 4 5 6 Student’s table includes suitable headings and units. Student’s answer describes the different changes, using data from the table to support that the cotton wool ball soaked in acetone showed the greatest drop in temperature, followed by the cotton wool ball soaked in water. The dry cotton wool ball showed no (or negligible) change in temperature. The alcohol in the aftershave evaporates quickly, having a pronounced cooling effect on the skin. As the water evaporates, the heat energy leaves the skin and lowers the internal body temperature. This results in feeling cooler. Student’s table is similar to the table in the investigation but shows an extra column for repeat readings and the calculation of the mean change in temperature. All headings and units are included. To compare what happens when no solution is added to the cotton wool. Reflection The data logger will record the temperature change more accurately and eliminate human error. The data logger will also record the temperature change at more regular intervals. Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 13 continued Exam-style questions 1 a b c d 19 Line graph [1] ; with sensible scale covering at least half of the paper [1] ; correctly plotted [1] ; axes labelled with units [1] ; points joined together by a line going through each of the points [1]. ; As time passes [1] ; body temperature decreases [1]. ; Shivering (rapid contraction and relaxation of the muscles) [1] ; hairs at the skin become erect [1] ; and trap an insulating layer of air [1] ; description of vasoconstriction [1] ; to reduce blood flow and heat loss from the blood [1]. ; The maintenance of a constant internal environment. ; [1] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 14 Practical investigation 14.1 Practical investigation 14.3 1 1 2 3 Student’s drawings of flower, with clear lines drawn in pencil, drawing larger than the original, correct shape and proportion, main features observable. Student correctly identifies the main features and functions of the flower: stigma (collects pollen), anther (produces pollen), sepal (protects flower), stamen (male part and includes anther), petals (attract insects), ovary (produces female sex cells). Student shows formula (magnification = image size/actual size), working and correct answer with units. The answer should be greater than 1.0 as the drawing should be larger than the petal. 2 3 4 5 Reflection Student’s own reflections. Practical investigation 14.2 1 2 3 4 5 6 a–d Student’s predictions and observations. Student describes the difference in growth – boiling tube A shows normal growth, boiling tube B shows little or no growth at all. The removal of oxygen from the surroundings prevents germination as oxygen is required to do so. As a control, to show that the removal of oxygen was a factor in the different results. Caustic substances are extremely harmful to the body and must be handled by a fully trained professional. The seeds would begin to grow as the removal of oxygen would not have killed the seeds while in boiling tube B. Reflection Any valid comparison between student methods (such as range of temperatures, or attempts to control variables). Exam-style questions 1 a b c d e Reflection Student’s own reflections. Student’s method includes three different temperatures and a way of measuring the growth of the seeds. Method should also include an attempt to control any variables such as humidity, same species, etc. Student’s table includes headings and units. Student’s calculations match data from the table. Student uses data from their table to describe the differences in growth. Student explains that the cress seeds will grow best within the range of room temperature as that is when the enzymes involved in breaking down molecules that supply the seeds with the nutrients used for growth are most active. Mustard seeds and cress seeds might have different rates of germination as they are different species. 2 a b c d 20 Stamen ; [1] Contains the filament/anther [1] ; and is the male reproductive organ of a flower [1]. ; Petal ; [1] Student drawing larger than the carpel in the practical workbook [1] ; labelled as the carpel (or stigma, style and ovary) [1] ; smooth outline drawn in pencil [1] ; shape and size in proportion [1] ; drawn with sharp pencil [1]. ; The carpel stigma/style/ovary [1] ; is the female reproductive organ of a flower [1]. ; Any sensible range that includes at least three different temperatures [1] ; around the 30 oC mark [1] ; such as 10, 20, 30, 40, 50. At least three times, accept any answer between three and five. ; [1] wear safety spectacles, wash hands, any other sensible precaution ; [1] % change = (change / original) × 100 [1] ; = (7 / 4) × 100 [1] ; = 175% [1] ; Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 15 Practical investigation 15.1 1 2 3 4 5 Egg in water: no breakage; egg without water: egg breaks. Amniotic fluid Fetus The fluid protects against external forces and knocks that the fetus may experience. As a control/to compare what would happen if the water was not there to protect the egg. Reflection Improve reliability by repeating more than once, improve validity by making sure that the eggs come from the same chicken and are the same age, improve engagement by trying with different eggs from different species or birds. Exam-style questions 1 a b c d e 2 a b c d 21 Pituitary gland. ; [1] The egg is released / Ovulation. ; [1] Oestrogen [1] ; and progesterone [1]. ; The egg has not been fertilised and progesterone ceases being secreted [1] ; so the uterus wall breaks down [1] ; and menstruation begins [1]. ; The concentration of progesterone would not decrease [1] ; as progesterone will continue to be secreted until the fertilised egg [1] ; is fully sunken into the wall of the uterus [1]. ; Amniotic fluid. ; [1] To support the embryo/fetus [1] ; and to protect it from external forces [1]. ; The fetus has developed limbs [1] ; and the placenta is joined to the umbilical cord [1]. ; Any three from: • named nutrients/food materials ; • oxygen ; • carbon dioxide ; • waste materials ; [Max. 3] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 16 Practical investigation 16.1 1 2 3 2 Observations of cloned cauliflower: a After one week: a few mm of growth. b After two weeks: a full floret should be visible. a DNA would be identical. b The cauliflower asexually reproduced by mitosis to produce new cells that are genetic copies of the original sample. Contamination will lead to growth of bacteria and fungi, link to potential safety and health hazards if this happens. More importantly, the experiment will fail due to death of the plant if this was allowed to occur. a b i [1] ; ii [1] ; iii [1] ; iv [1] ; i Description Number of people Male 9 Female 6 Student’s own reflections. Male with Marfan syndrome 2 Exam-style questions Female with Marfan syndrome 2 Homozygous dominant 0 Homozygous recessive 11 Reflection 1 a b c d e 22 (One mark for each correct answer.) ; Observable feature [1] ; of an organism. Has two identical alleles [1] ; of a particular gene [1]. ; i A version of a gene. ; [1] ii An allele that is always expressed if present in the genotype. ; [1] iii An allele that is present in the genotype but is not expressed in the presence of a dominant allele. ; [1] Genotypes stated as BB and bb [1] ; genetic cross drawn [1] ; possible genotypes shown [1] ; correct answer stated as 0% [1]. ; B B b Bb Bb b Bb Bb 100% ; Heterozygous 4 [6] ii If individual B was homozygous dominant [1] ; then all of her offspring would be sufferers of Marfan syndrome [1]. ; [1] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 17 Practical investigation 17.1 Practical investigation 17.2 1 1 2 3 4 5 6 7 8 Student’s table matches the data collected with correct headings and units. a Students correctly tally the number of students in each category. Categories should be evenly split across the range of data for that characteristic. Tally should use the correct tally method and have the final number in bracket next to the tallies. b Histogram drawn to show data from tally chart (hand size and units on the x-axis, number of students on the y-axis), bars drawn touching each other in order of increasing or decreasing magnitude. Bar chart drawn to show the number of students with each eye colour (eye colour on the x-axis, number of students on the y-axis), blocks should not be touching. Student describes the pattern for the data of their data/chart/histogram. Continuous Height, hand size, eye colour, hair colour, arm span. Increase the sample size and survey more students, i.e. the idea that the more students that are surveyed, the more reliable the data will be. No, because the sample size is very small and does not account for older / younger people, different race and origins, etc. 2 3 4 5 Student’s diagrams showing that the leaf in sunlight will have more stomata open than the leaf in darkness but this will vary on leaf type, environmental conditions and magnification used. Student accurately counts the number of stomata shown for each leaf – student should have more open stomata on the leaf in sunlight. Student describes the difference in open stomata and links this to the need for the plant to prevent water loss and/or to take in more carbon dioxide. More reliable test, to compare the effect of the amount of sunlight. Use the same leaf, place in sunlight and take a varnish sample. Then, place the same leaf into darkness and repeat the observation. The leaf must not be removed from the plant and it must be fed and watered as normal. Exam-style questions 1 a b c Reflection If no, it is because of human error. Students often miscount, or miss people out. 23 d Continuous ; [1] Histogram drawn [1] ; blocks touching [1] ; blocks drawn in increasing or decreasing magnitude [1] ; suitable axis labels [1] ; Similar pattern described for boys, girls or both, of few students at the extreme [1] ; and most students gathered around the mean [1]. ; Large sample of the population gathered. ; [1] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 18 Practical investigation 18.1 Practical investigation 18.2 1 1 • Four-week date and observation: soil drying out, food breaking down, some evidence of mould, any growth of bacteria or life noted. • Eight-week date and observation: food broken down, biodegradable waste starting to break down, any growth of bacteria or life noted. • Twelve-week date and observation: all/ most of food/kitchen waste decomposed completely and most biodegradable waste broken down. Non-biodegradable waste still evident. 2 Organic waste decomposes quickly; other waste will not decompose in the time allowed. 3 The layer that contains the organic kitchen waste as nitrates from the food would be released back into the soil. 4 Decomposition. 5 The rate would increase as the worms help to decompose some types of waste. 2 3 4 5 6 7 8 Student’s table should include ‘organism type’ and ‘number of organisms counted’ for each sample of the quadrat. Student’s bar chart, axes correctly labelled, bars not touching, key to label bars if necessary. Student describes the pattern of data gathered. Student makes comparison between two different areas that have different population sizes for the same species. Student refers to factors such as light, water or available food. Student may also refer to factors such as human footfall or the presence of predators. To improve the reliability of the data taken. To reduce bias and improve validity of the method. This would take too long and there may be change over the time taken anyway. Reflection Student’s own reflections but will likely involve carrying out more repeats to increase reliability. Exam-style questions 1 a b c d e f 2 a b c 24 Lag phase ; [1] Log or exponential phase ; [1] Stationary phase ; [1] Death phase ; [1] The conditions for growth are ideal [1] ; large number of cells reproducing quickly at the same time [1]. ; Lack of food or reduction in the ideal conditions [1] ; so some cells begin to die [1] ; the death rate exceeds the birth rate [1]. ; total number of caterpillars added together / number of gardens [1] ; 28 / 7 [1] ; answer = 4 caterpillars [1]. ; average number of caterpillars (4) × total number of gardens (32) [1] ; = 128 caterpillars [1]. ; Any sensible answer from: • natural variation in populations of different gardens ; • some gardens have more / fewer predators or prey ; • some gardens have greater resources and food available ; • some caterpillars might not have been counted / human error ; [1] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 19 Practical investigation 19.1 Reflection 1 Student’s answer should qualify that humans might make errors / have subjective views of colour changes / methods carried out differently / any other sensible named example. Scientists can remove the subjective views by measuring known quantities. 2 3 4 5 6 Completed student table with accurate observations for each Petri dish. Student describes the pattern of data from their investigation/table. The pH will affect the activity of enzymes, thus affecting growth. The pH may also affect the availability of nutrients. Student explains the effect of acid rain on soil pH and that the optimum pH for most plant/ crop growth is around pH 7. The acid used represents acid rain and the growth of the cress seeds shows what might happen to crops/ plant life if acid rain falls and reduces the pH of the soil. Acid rain has a significant impact on the growth of crops if the rain becomes too acidic. The height/mass of the cress could be measured to compare the growth under different acidic conditions. By taking more readings / repeats. Practical investigation 19.2 1 2 3 4 5 25 Student’s diagram should show the cotton wool turning brown / black and the universal indicator turning orange / pink / red. a Cotton wool turned brown/black. b Universal indicator turned orange/ pink/red. Shows that the gases produced are acidic. These gases dissolve in water vapour and condense in the air as clouds before falling as acidic rain. Limewater turns cloudy as the burning of coal produces carbon dioxide. Limewater turning cloudy is a positive test for carbon dioxide. Student outlines an investigation that burns different quantities of coal. The coal is heated until completion and the pH of the gases produced are measured using a pH probe or a pH scale. Exam-style questions 1 2 B ; [1] a garden area A ; [1] b soil closer to neutral pH (7) would be best for growing most plants ; [1] c pH probe would have greater accuracy [1] ; and removes the subjective nature of judging a colour change [1] ; d Different areas of the garden will have different conditions [1] ; such as garden area C might receive more rainwater [1] ; than the other areas. Accept any other valid point to explain why the soil might be more acidic [1]. ; e Any two from: • same type of plant ; • same species of plants ; • same temperature ; • humidity ; • other named conditions ; • same amount of water ; [Max. 2] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 20 Practical investigation 20.1 1 2 3 4 5 6 Student’s results in table with correct headings and units. Student’s graph includes correct axis drawn, units added to labelled axis, appropriate size and scale of graph (at least half of the graph paper), plotted correctly, both lines joined together and labelled accordingly. The pectinase caused more juice to be released from the apple than from the apple that was in water only. Pectinase broke down the pectin in the cell walls, releasing the juice more easily and faster. This allows a greater yield to be produced for commercial gain. As a control, to compare the effect of pectinase, to confirm that it was pectinase that caused the release of the juice from the pulp. Results might be different due to differences in the type of apple. One apple is different from another, certainly if from different species or types of apple. Reflection 5 6 7 8 Practical investigation 20.3 1 2 3 4 5 Student’s own reflections. Practical investigation 20.2 1 2 3 4 26 Two safety precautions, such as wash hands after touching the apple, consult safety information, clean surfaces. Student’s method – should contain the range of variables used (at least three temperatures around 45 oC, i.e. 30 oC, 40 oC, 50 oC), as well as how to measure the dependent variable (how to measure the volume of juice produced, i.e. by mass, or with a measuring cylinder). Credit should be given for any attempt to control the variables and for a safety point. Student’s temperatures should be sensible and safe, such as any three between 10 oC and 60 oC. Student’s table should include at least three different temperatures and units, with correct headings. Student’s answer of the best temperature. Produced the most juice. This is close to the optimum temperature for most enzymes. The enzyme will carry out more reactions at this temperature and in the case of pectinase; will break down more pectin and release more juice from the fruit. Repeat the investigation and take a mean for the volume of juice produced; ensure that all variables are constant. Student’s drawings should be drawn in pencil and include a label to show where the stains had / had not been removed. Student describes the difference between the stains drawn in their notes. The biological washing powder contains enzymes that break down the stains faster so that more stain was removed compared to the non-biological washing powder. Protease; accept other option used in washing powders, such as lipase. Student’s method suggests washing materials with similar stains at different temperatures for comparison. Some effort made to identify and control the variables, safety points should be noted. Exam-style questions 1 a b C ; [1] Any six from: • named use of pectinase, such as commercial fruit juice, skin peeling ; • protease, lipase used in washing powders, detergents, baby food ; • enzymes used to catalyse reactions involved ; • faster reactions ; • lower temperatures required ; • higher yield ; • any other sensible point related to common use of the enzymes ; [Max. 6] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021 CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK Chapter 20 continued c d 27 Any five from: • suitable equipment identified ; • fruit named ; • fruit chopped into small pieces and pectinase added ; • repeated at different pH levels for the enzyme ; • enzyme and fruit pulp incubated at optimum temperature ; • fruit pulp filtered into measuring cylinder ; • comparison of volume of fruit juice collected ; • safety points mentioned ; • repeat testing for reliability ; [Max. 5] Any two from: • same temperature ; • same quantity of pectinase ; • same equipment ; • same source of pectinase ; • same apples / species ; • any other valid point ; [Max. 2] Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021