0610/32 May/June 2025 Worked Answers (IGCSE Biology 0610 Core)
45 questions · 80 marks · 75 minutes
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Worked answers for 40 questions
- Step 1: Photosynthesis needs the green pigment chlorophyll, which is held inside the chloroplasts. Step 2: So the chloroplast is the structure where photosynthesis takes place. Step 3: The nucleus controls the cell, the mitochondrion is for respiration, and the vacuole stores cell sap, so none of these carry out photosynthesis.Method:Recall which green cell structure holds chlorophyll for photosynthesis.Examiner tips
- Chloroplasts contain chlorophyll and are the site of photosynthesis.
- Step 1: The green colour of a chloroplast comes from the pigment chlorophyll. Step 2: Chlorophyll absorbs light energy for photosynthesis. Step 3: Haemoglobin is in red blood cells, cellulose makes the cell wall, and glucose is a sugar, so none of these is the green pigment.Method:Name the green light-absorbing pigment of the chloroplast.Examiner tips
- Chlorophyll is the green pigment in chloroplasts that absorbs light.
- Step 1: Each square measures 1 cm by 1 cm, so its area is 1 cm². Step 2: Counting 35 such squares gives an area of 35 cm². Step 3: Centimetres measure length, cubic centimetres measure volume, and millimetres measure length, so the correct unit for area is cm².Method:Recognise that an area made of cm × cm squares is measured in cm².Examiner tips
- Area = length × length, so the unit is cm² for squares measured in cm.
- Step 1: A large, flat surface gives more area for light to fall on. Step 2: More light absorbed by the chlorophyll means a faster rate of photosynthesis. Step 3: Losing water and reducing carbon dioxide entry would not help photosynthesis, and surface area does not protect against animals, so the benefit is greater light absorption.Method:Link the broad shape of the leaf to absorbing more light.Examiner tips
- A large surface area lets the leaf absorb more light for photosynthesis.
- Step 1: A leaf vein carries water and dissolved substances through the leaf. Step 2: Water and mineral ions travel in the xylem, while dissolved sugars travel in the phloem. Step 3: So the vein is made of xylem and phloem; the other pairs are leaf cell layers or surface features, not transport tissues.Method:Recall the two transport tissues that form a vascular bundle.Examiner tips
- A leaf vein (vascular bundle) is made of xylem and phloem.
- Step 1: Guard cells change shape to open and close the stomata. Step 2: When the stomata are open, carbon dioxide can diffuse into the leaf. Step 3: This carbon dioxide is a raw material for photosynthesis, so by opening the stomata the guard cells let in the gas the leaf needs; they do not make chlorophyll, carry water or store glucose.Method:Explain how opening the stomata supplies carbon dioxide for photosynthesis.Examiner tips
- Guard cells open the stomata so carbon dioxide can enter for photosynthesis.
- Step 1: Work out each range: carrot 22, corn 19, pea 20, pepper 17, tomato 14 °C. Step 2: The largest range is the carrot (22 °C) and the smallest is the tomato (14 °C). Step 3: Not all species germinate at 18 °C (peas only reach 24, but a pea germinates at 18; however tomato needs 21 so it would not), so the only correct pair is carrots largest and tomatoes smallest.Method:Calculate each temperature range, then identify the largest and smallest.Examiner tips
- Range = highest − lowest temperature; compare the ranges to draw conclusions.
- Step 1: Germinating seeds need oxygen for respiration and water to start growth, as well as a suitable temperature. Step 2: Only tube D supplies both oxygen (the gas present) and water (the wet cotton wool). Step 3: Tubes A and C lack oxygen (they have carbon dioxide), and tube B lacks water (dry cotton wool), so only the seeds in tube D germinate.Method:Match the requirements for germination to the tube that provides them all.Examiner tips
- Seeds need oxygen, water and a suitable temperature to germinate.
- Step 1: Within the germination range, a higher temperature speeds up the chemical reactions and respiration in the seed. Step 2: Because 25 °C is warmer than 10 °C but still below 29 °C, the seeds germinate faster. Step 3: They will still germinate (25 °C is in range), so they do not stop or slow down, and the rate is not the same as at the cooler 10 °C.Method:Apply the idea that warmth within the range speeds up germination.Examiner tips
- Higher temperatures within the range make seeds germinate faster.
- Step 1: A shoot grows towards light, a response called phototropism. Step 2: A root grows downwards towards gravity, a response called gravitropism. Step 3: Root hairs increase the surface for absorbing mineral ions and water, so the correct set is light; phototropism; gravity; gravitropism; mineral ions.Method:Match each direction of growth to the correct tropism and the substances absorbed.Examiner tips
- Phototropism = response to light; gravitropism = response to gravity; roots absorb mineral ions and water.
- Step 1: Gastric juice in the stomach contains hydrochloric acid. Step 2: This strong acid kills many of the pathogens that are taken in with food. Step 3: Gastric juice is acidic, not alkaline, and does not carry oxygen or feed pathogens, so its defence is that the acid kills the pathogens.Method:State what gastric juice contains and what the acid does to pathogens.Examiner tips
- Gastric juice = hydrochloric acid that kills pathogens in food.
- Step 1: All the percentages must add up to 100 %. Step 2: The three named routes total 54 + 11 + 9 = 74 %. Step 3: So direct contact = 100 − 74 = 26 %.Method:Subtract the sum of the three given percentages from 100 %.Examiner tips
- Percentages add to 100 %, so direct contact = 100 − (54 + 11 + 9).
- Step 1: Find 11 % of 300. Step 2: 11 % = 11/100, so 11/100 × 300 = 33. Step 3: Therefore 33 of the 300 people caught the virus from contaminated water.Method:Multiply 300 by 11 and divide by 100.Examiner tips
- Number = percentage ÷ 100 × total = 11/100 × 300.
- Step 1: Indirect transmission happens through contaminated water, food, surfaces and hands. Step 2: Washing hands, using clean water, cooking food and cleaning surfaces all remove or destroy the virus before it reaches a new person. Step 3: The other options either spread the virus (sharing bottles, raw food) or are irrelevant (antibiotics do not kill viruses; diet or exercise do not stop transmission).Method:Pick hygiene measures that break the indirect routes of transmission.Examiner tips
- Stop indirect spread with hand-washing, clean water, cooked food and clean surfaces.
- Step 1: The airways are lined with mucus made by goblet cells, and tiny hairs called cilia. Step 2: Mucus traps viruses and dust, and the cilia sweep the mucus away, stopping pathogens reaching the lungs. Step 3: Hydrochloric acid is made in the stomach, red blood cells carry oxygen, and insulin controls blood glucose, so none of these defends the airways.Method:Recall the trapping defence that lines the airways.Examiner tips
- Mucus and cilia in the airways trap and remove airborne pathogens.
- Step 1: White blood cells both make antibodies and carry out phagocytosis. Step 2: Dissolved substances such as the hormone oestrogen are carried in the liquid plasma. Step 3: Red blood cells contain haemoglobin, which carries oxygen, so the correct matches are white blood cells (antibodies, phagocytosis), plasma (oestrogen) and red blood cells (oxygen).Method:Assign each function to the blood component that performs it.Examiner tips
- White blood cells: antibodies + phagocytosis; plasma: dissolved substances; red blood cells: oxygen.
- Step 1: Iron is needed to make haemoglobin in red blood cells. Step 2: Good dietary sources of iron include red meat and green leafy vegetables. Step 3: Lemons supply vitamin C, vegetable oil supplies fat, and yoghurt supplies calcium, so they are not the best iron sources.Method:Recall which foods supply the iron needed for haemoglobin.Examiner tips
- Iron-rich foods include red meat and green leafy vegetables.
- Step 1: When a blood vessel is cut, platelets help form a clot. Step 2: The clot seals the wound, which reduces the loss of blood. Step 3: The clot also forms a barrier that stops pathogens entering the body, so clotting reduces blood loss and prevents pathogen entry.Method:Recall the two protective roles a blood clot has at a wound.Examiner tips
- Clotting reduces blood loss and blocks the entry of pathogens.
- Step 1: The largest artery leaving the heart carries blood to the whole body. Step 2: This vessel is the aorta. Step 3: The vena cava returns blood to the heart, the pulmonary artery goes to the lungs, and the pulmonary vein returns blood from the lungs, so the main body vessel is the aorta.Method:Name the main artery that leaves the heart for the body.Examiner tips
- The aorta is the main artery carrying blood from the heart to the body.
- Step 1: Air flows from the trachea into the bronchi, which branch into smaller tubes. Step 2: These smallest tubes are the bronchioles, and they end in the air sacs called alveoli. Step 3: So the bronchioles are connected directly to the alveoli, while the larynx and trachea are higher up the airway.Method:Trace the air path to the smallest tubes ending at the alveoli.Examiner tips
- Bronchioles are the smallest air tubes and connect to the alveoli.
- Step 1: Gas exchange happens in millions of tiny air sacs called alveoli. Step 2: These alveoli are found in the lungs. Step 3: The heart pumps blood, the liver processes substances, and the kidney filters blood, so the organ containing the alveoli is the lung.Method:Name the breathing organ that holds the air sacs.Examiner tips
- Alveoli are found in the lungs.
- Step 1: Blood returning to the lungs carries waste carbon dioxide, so its concentration is higher in the capillary than in the air sac. Step 2: Carbon dioxide diffuses down its concentration gradient from the capillary into the alveolus. Step 3: From the alveolus it is breathed out, so the net movement of carbon dioxide is from the capillary into the alveolus, not the reverse.Method:Follow the waste gas from the blood into the air sac.Examiner tips
- Carbon dioxide diffuses from the blood (capillary) into the alveolus to be breathed out.
- Step 1: A large surface area gives more space for gases to diffuse across. Step 2: Thin walls give a short distance for gases to diffuse. Step 3: A good blood supply keeps a steep concentration gradient, so a large surface area, thin walls and a good blood supply make the alveoli efficient.Method:List the adaptations that increase the rate of diffusion of gases.Examiner tips
- Alveoli: large surface area + thin walls + good blood supply (+ moist lining).
- Step 1: Aerobic respiration uses glucose and oxygen as the reactants. Step 2: It releases energy and produces carbon dioxide and water as products. Step 3: So the equation is glucose + oxygen → carbon dioxide + water; the reverse is photosynthesis, and glucose → lactic acid is anaerobic respiration.Method:Recall the reactants and products of aerobic respiration.Examiner tips
- Aerobic respiration: glucose + oxygen → carbon dioxide + water (+ energy).
- Step 1: Aerobic respiration needs oxygen and releases energy from glucose. Step 2: This process happens mainly inside the mitochondria. Step 3: Chloroplasts carry out photosynthesis, the nucleus controls the cell, and the cell wall supports plant cells, so respiration occurs in the mitochondria.Method:Name the energy-releasing structure of the cell.Examiner tips
- Aerobic respiration takes place in the mitochondria.
- Step 1: Diffusion is the net movement from a region of higher concentration to a region of lower concentration, that is down a concentration gradient. Step 2: The energy comes from the kinetic energy of the molecules. Step 3: This movement of molecules is random, so the correct set is higher; lower; gradient; kinetic; random.Method:Recall the definition of diffusion and the source of its energy.Examiner tips
- Diffusion: high → low concentration, down a gradient, using the kinetic energy of random movement.
- Step 1: Starch is a carbohydrate, made of many glucose units joined together. Step 2: Carbohydrates contain only the elements carbon, hydrogen and oxygen. Step 3: Nitrogen and sulfur are found in proteins, not carbohydrates, so starch is made of carbon, hydrogen and oxygen.Method:Recall the three elements that make up carbohydrates.Examiner tips
- Carbohydrates (including starch) contain carbon, hydrogen and oxygen.
- Step 1: Glucose is a small sugar that plant cells can build into larger carbohydrates. Step 2: As well as starch, plants make cellulose (for the cell wall) and sucrose (for transport) from glucose. Step 3: Proteins are built from amino acids, fats from fatty acids and glycerol, and water is not made from glucose, so cellulose is the correct answer.Method:Name a carbohydrate plants build from glucose besides starch.Examiner tips
- Plants make cellulose and sucrose from glucose, as well as starch.
- Step 1: Dialysis tubing lets small molecules through but holds back large ones, so it is partially permeable. Step 2: The part of a cell that controls what enters and leaves in this way is the partially permeable cell membrane. Step 3: The nucleus, cytoplasm and chloroplast do not act as the partially permeable boundary, so the tubing represents the cell membrane.Method:Match the partially permeable tubing to the cell’s partially permeable boundary.Examiner tips
- Partially permeable dialysis tubing represents the cell membrane.
- Step 1: Dialysis tubing is partially permeable, letting only small molecules through. Step 2: Glucose is a small molecule, so it diffuses out into the water, which is why glucose is detected outside. Step 3: Starch is a large molecule that cannot pass through the tubing, so none is found outside, explaining the results.Method:Link molecule size to whether it can cross the partially permeable tubing.Examiner tips
- Small glucose diffuses through partially permeable tubing; large starch cannot.
- Step 1: Starch is a carbohydrate that must be digested into smaller sugars. Step 2: The enzyme that breaks starch down into reducing sugars (maltose/glucose) is amylase. Step 3: Protease digests proteins, lipase digests fats, and catalase breaks down hydrogen peroxide, so the enzyme for starch is amylase.Method:Recall the enzyme that acts on starch.Examiner tips
- Amylase breaks starch down into reducing sugars.
- Step 1: In the binomial system the first word is the genus and the second is the species. Step 2: In Elephas maximus the first word, Elephas, is the genus name. Step 3: maximus is the species name, the full two-word name is the binomial name, and "elephant" is the common name, so the genus is Elephas.Method:Take the first word of the two-part scientific name as the genus.Examiner tips
- Binomial name: genus (first, capital) then species (second).
- Step 1: Mammals have several features, including hair (fur) and external ears (pinnae). Step 2: Hair on the body is a visible mammal feature that the elephant shows. Step 3: Feathers belong to birds, dry scales to reptiles, and moist bare skin to amphibians, so hair identifies the elephant as a mammal.Method:Identify the mammal-specific body covering visible on the animal.Examiner tips
- Mammals have hair (fur) and external ears (pinnae).
- Step 1: A producer is followed by the primary consumer, then the secondary consumer, then the tertiary consumer. Step 2: Here the jackfruit tree is the producer, the orangutan the primary consumer, the bearded pig the secondary consumer, and the tiger the tertiary consumer. Step 3: So the tertiary consumer is the tiger, not the producer or the earlier consumers.Method:Count the trophic levels from the producer to find the tertiary consumer.Examiner tips
- Tertiary consumer = the fourth step (producer → primary → secondary → tertiary).
- Step 1: A producer makes its own food by photosynthesis, usually a green plant. Step 2: The fig tree and jackfruit tree are green plants that photosynthesise, so they are producers. Step 3: The orangutan, tiger and bearded pig are all consumers that feed on other organisms, so the producer is the fig tree.Method:Identify the photosynthesising plant in the web.Examiner tips
- Producers are green plants that photosynthesise, such as the fig and jackfruit trees.
- Step 1: Arthropods have an exoskeleton and jointed legs; insects are one group of arthropods. Step 2: A stick insect is an insect, so it is an arthropod. Step 3: The tiger and orangutan are mammals and the python is a reptile, all with internal skeletons, so the arthropod is the stick insect.Method:Pick the insect, which is a member of the arthropod group.Examiner tips
- Insects such as the stick insect are arthropods (exoskeleton + jointed legs).
- Step 1: In a food chain each arrow points from the food to the organism that eats it. Step 2: The jackfruit tree (producer) is eaten by the orangutan, so the first arrow goes from the tree to the orangutan. Step 3: The orangutan is then eaten by the tiger, so the chain is jackfruit tree → orangutan → tiger.Method:Order the producer, then the orangutan, then its predator with correct arrows.Examiner tips
- Start a food chain with the producer; arrows show the direction energy flows.
- Step 1: An ecosystem is more than just the organisms; it includes their surroundings. Step 2: It is a unit made up of the community of organisms together with the non-living environment. Step 3: These living and non-living parts interact, so the best description is the community of organisms and their environment interacting; one species alone is a population, not an ecosystem.Method:Combine the living community with the non-living environment in your definition.Examiner tips
- Ecosystem = community of organisms + their environment, interacting.
- Step 1: The number falls from 1850 in 2010 to 1500 by 2015, a decrease of 350 elephants. Step 2: From 2015 to 2016 the number stays at 1500, so the population is then stable. Step 3: So the population decreases by 350 and then levels off, rather than increasing or staying the same throughout.Method:State the overall fall and the later stable period from the figures.Examiner tips
- Describe both the size of the decrease and where it levels off.
- Step 1: Organisms become endangered when their numbers fall towards extinction. Step 2: Habitat loss from deforestation, hunting and pollution all reduce a species’ numbers. Step 3: The other options describe conservation measures or improved conditions, which help a species recover rather than endanger it.Method:Pick the pressures that drive a species towards extinction.Examiner tips
- Endangerment causes: habitat loss, hunting, pollution, disease, climate change, introduced species.
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