0610/13 Oct/Nov 2025 Worked Answers (IGCSE Biology 0610 Core)
40 questions · 40 marks · 45 minutes
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Worked answers for 36 questions
- Step 1: The hairs bending over to trap the insect is a movement of part of the plant. Step 2: The hairs only bend when they detect an insect, which is a response to a stimulus, so this is sensitivity. Step 3: No waste is removed and no increase in size happens here, so excretion and growth are not shown; the answer is movement and sensitivity.Method:Identify the bending of the hairs as movement and the response to the insect as sensitivity.Examiner tips
- Sensitivity is detecting and responding to a stimulus; here the response is a movement.
- Step 1: Insects are the arthropods that have three pairs of legs (six legs in total). Step 2: Arachnids have four pairs of legs, and crustaceans have many pairs. Step 3: Myriapods have a very large number of legs along a long body, so an arthropod with three pairs of legs is an insect.Method:Recall the number of legs typical of each arthropod group and match three pairs to insects.Examiner tips
- Three pairs of legs (six legs) is the key feature of insects.
- Step 1: To reach Z the animal has no fur, no feathers, no dry skin and no scales. Step 2: A vertebrate with moist skin and no scales, fur, feathers or dry skin is an amphibian. Step 3: Fish have scales, mammals have fur and reptiles have dry skin, so each of those leaves the key earlier; Z is an amphibian.Method:Trace the no branch of each question in turn to identify the animal at endpoint Z.Examiner tips
- Work through a key one step at a time, choosing yes or no for each feature.
- Step 1: A plasmid is a small circular piece of DNA found in bacterial cells, separate from the main loop of DNA. Step 2: It carries extra genes that the bacterium can use. Step 3: The liquid part of blood is plasma, aerobic respiration happens in mitochondria, and protein synthesis happens at the ribosomes, so none of those describe a plasmid.Method:Recall that a plasmid is the small circular DNA of a bacterial cell.Examiner tips
- Plasmid = small circular DNA in bacteria; do not confuse it with blood plasma.
- Step 1: A typical plant cell has a cellulose cell wall, a large permanent vacuole and chloroplasts as well as the usual nucleus, cytoplasm and membrane. Step 2: A cell with a cell wall, large vacuole and chloroplasts is therefore a plant cell. Step 3: A rounded cell with no wall is an animal cell, a biconcave cell with no nucleus is a red blood cell, and a small cell with a loop of DNA but no nucleus is a bacterium.Method:Pick the cell that has the three plant-cell features: cell wall, large vacuole and chloroplasts.Examiner tips
- Plant cells have a cell wall, a large permanent vacuole and often chloroplasts.
- Step 1: Actual size = image size divided by magnification. Step 2: The image size is 90 mm and the magnification is 225, so actual size = 90 ÷ 225 = 0.40 mm. Step 3: So the alveolus is 0.40 mm across.Method:Divide the image size by the magnification to find the actual size of the alveolus.Examiner tips
- Actual size = image size ÷ magnification.
- Step 1: A longer diffusion distance means particles have further to travel, so diffusion is slower. Step 2: Increasing temperature, surface area or concentration gradient all speed diffusion up. Step 3: So the factor that decreases the rate of diffusion is an increased diffusion distance.Method:Identify the change that makes particles travel further, which slows diffusion.Examiner tips
- A greater distance slows diffusion; higher temperature, area and gradient all speed it up.
- Step 1: A cell membrane is partially permeable, letting water through but holding back larger molecules. Step 2: Dialysis (Visking) tubing is partially permeable, so it behaves like a cell membrane. Step 3: Filter paper lets everything through, while a measuring cylinder and a test-tube are containers, not membranes.Method:Choose the material that is partially permeable, like a cell membrane.Examiner tips
- Dialysis (Visking) tubing models a partially permeable cell membrane.
- Step 1: Oxygen moves from a higher concentration in the soil to a lower concentration inside the cell. Step 2: Movement of a gas down its concentration gradient is diffusion. Step 3: Osmosis is the movement of water, respiration is a chemical reaction inside the cell, and ventilation is the movement of air in breathing, so the process is diffusion.Method:Recognise that a gas moving down its concentration gradient is moving by diffusion.Examiner tips
- Movement of a gas down a concentration gradient is diffusion.
- Step 1: The biuret test turns from blue to purple when protein is present, so a protein-containing food gives a purple result. Step 2: Blue DCPIP is decolourised (turns colourless) by vitamin C, so a food with vitamin C turns DCPIP colourless. Step 3: With both protein and vitamin C present, the biuret test is purple and the DCPIP test is colourless.Method:Recall the positive result of each test and apply it to a food with protein and vitamin C.Examiner tips
- Positive biuret = purple; positive DCPIP = colourless.
- Step 1: Amylase is an enzyme, and enzymes are biological catalysts. Step 2: A catalyst speeds up a reaction without being used up. Step 3: The product is what is made, the substrate is what is broken down, and a solvent is a liquid that dissolves things, so amylase acts as a catalyst.Method:Recall that enzymes are catalysts and apply this to amylase.Examiner tips
- All enzymes are catalysts that speed up reactions without being used up.
- Step 1: The sugar can be stored as starch, used in respiration to release energy, and used to make cellulose for cell walls, so all three of these are yes. Step 2: Photosynthesis is the process that makes the sugar, so the plant does not use sugar for photosynthesis. Step 3: So the correct row is starch yes, photosynthesis no, respiration yes, cellulose yes.Method:Check each use in turn, remembering that photosynthesis produces the sugar rather than using it.Examiner tips
- Photosynthesis makes glucose; the plant then stores, respires or builds with it.
- Step 1: The stomach produces hydrochloric acid, so its contents are acidic. Step 2: The muscular wall of the stomach churns and squeezes the food, which is physical digestion. Step 3: The mouth is not acidic, and the small and large intestines are not acidic, so food is physically digested in acidic conditions in the stomach.Method:Find the organ that is both acidic and physically churns the food.Examiner tips
- The stomach is acidic and churns food, combining acid conditions with physical digestion.
- Step 1: Each stoma is a small pore in a leaf, controlled by a pair of cells on either side. Step 2: These cells are guard cells, which change shape to open and close the stoma. Step 3: Ciliated cells move mucus, egg cells are female sex cells, and mesophyll cells carry out photosynthesis, so the cells around a stoma are guard cells.Method:Recall which specialised cells control the stomata and pick the guard cell.Examiner tips
- Guard cells surround each stoma and control its opening and closing.
- Step 1: Direct contact means the pathogen passes straight from one person to another. Step 2: Exchanging body fluids passes the pathogen directly between people, so it is direct contact. Step 3: Air, food and contaminated surfaces all pass the pathogen through the environment first, so they are indirect transmission.Method:Separate direct (person-to-person) from indirect (through the environment) transmission.Examiner tips
- Direct contact = pathogens passing straight between people, for example through body fluids.
- Step 1: The body uses oxygen in respiration, so expired air has less oxygen than inspired air. Step 2: Respiration produces carbon dioxide, so expired air has more carbon dioxide than inspired air. Step 3: So expired air has a lower oxygen concentration and a higher carbon dioxide concentration.Method:Use respiration to decide that oxygen falls and carbon dioxide rises in expired air.Examiner tips
- Expired air: less oxygen, more carbon dioxide than inspired air.
- Step 1: Aerobic respiration uses glucose and oxygen as its raw materials, so both are used. Step 2: It produces carbon dioxide and water, so both of these are produced. Step 3: So carbon dioxide is produced, glucose used, oxygen used and water produced.Method:Split the four substances into reactants (used) and products (produced) using the respiration equation.Examiner tips
- Glucose + oxygen are used; carbon dioxide + water are produced.
- Step 1: Alveoli are tiny air sacs found at the ends of the air passages in the chest. Step 2: These air sacs make up the lungs, where oxygen and carbon dioxide are exchanged with the blood. Step 3: The heart pumps blood, the liver makes bile and the kidneys make urine, so alveoli are found in the lungs.Method:Link alveoli (air sacs) to the breathing organ, the lungs.Examiner tips
- Alveoli are the air sacs of the lungs.
- Step 1: The central nervous system is the brain and spinal cord. Step 2: The relay neurone lies entirely within the spinal cord, so it is found only in the central nervous system. Step 3: The receptor is in the skin, while the sensory and motor neurones run between the body and the spinal cord, so they are not found only in the central nervous system.Method:Identify the neurone that lies wholly inside the spinal cord, which is the relay neurone.Examiner tips
- The relay neurone sits inside the spinal cord, so it is wholly within the central nervous system.
- Step 1: Light first passes through the cornea, the clear curved layer at the front of the eye. Step 2: The curved cornea bends (refracts) the light, changing its direction as it enters. Step 3: The iris controls how much light enters, the pupil is the gap that light passes through, and the retina detects light, so the cornea changes the light direction.Method:Recall that the cornea is the curved front of the eye that bends entering light.Examiner tips
- The curved cornea does most of the bending of light entering the eye.
- Step 1: Endocrine glands secrete hormones directly into the blood. Step 2: Insulin is a hormone made by the pancreas, so it is secreted by an endocrine gland. Step 3: Glucose is a sugar, lactic acid is made in muscles during anaerobic respiration, and starch is a storage carbohydrate, so none of these is a hormone.Method:Recall that endocrine glands release hormones and pick the hormone from the list.Examiner tips
- Endocrine glands secrete hormones such as insulin and adrenaline.
- Step 1: Antibiotics work by attacking structures found in bacteria. Step 2: Viruses do not have these structures, so antibiotics do not kill viruses. Step 3: Antibiotics therefore kill bacteria only, not viruses or all microorganisms.Method:Recall that antibiotics act on bacteria only and rule out the options that include viruses.Examiner tips
- Antibiotics kill bacteria but have no effect on viruses.
- Step 1: The new plants come from one parent and are genetically identical to it. Step 2: Producing genetically identical offspring from a single parent is asexual reproduction. Step 3: Fertilisation and pollination are steps in sexual reproduction, which involves two parents and produces variation, so this is asexual reproduction.Method:Recognise that identical offspring from a single parent is asexual reproduction.Examiner tips
- One parent plus identical offspring equals asexual reproduction.
- Step 1: Germinating seeds need water to activate their enzymes and start growth. Step 2: They also need oxygen for aerobic respiration to release energy. Step 3: So seeds will only germinate when both oxygen and water are present.Method:Recall that both water and oxygen are required for seeds to germinate.Examiner tips
- Germination needs water and oxygen (and a suitable temperature).
- Step 1: Seminal fluid is the liquid that carries and nourishes the sperm. Step 2: It is produced by the prostate gland and other glands. Step 3: The penis passes semen out of the body, the scrotum holds the testes, and the testes make sperm, so seminal fluid is produced by the prostate gland.Method:Recall the function of each part and pick the gland that makes seminal fluid.Examiner tips
- The prostate gland produces seminal fluid that nourishes the sperm.
- Step 1: Secondary sexual characteristics develop at puberty under the control of sex hormones. Step 2: The growth of the sexual organs happens in both males and females. Step 3: Fat on the hips and thighs and widening hips develop mainly in females, while facial hair develops mainly in males, so the change shared by both is the growth of the sexual organs.Method:Pick the characteristic that develops in both sexes rather than in only males or only females.Examiner tips
- Some secondary sexual characteristics are shared; growth of the sexual organs occurs in both sexes.
- Step 1: HIV is spread through infected blood and body fluids. Step 2: Screening blood used for transfusions removes infected blood, so more screening reduces the number of new infections. Step 3: More illegal drug use, reusing needles and unprotected sexual contact would all increase transmission, so only increased blood screening explains a fall.Method:Match the fall in infections to the one change that reduces transmission of HIV.Examiner tips
- To explain a fall in infections, look for a measure that blocks a route of transmission.
- Step 1: A gene can exist in different versions that give different forms of a feature. Step 2: Each of these versions is called an allele, so an allele is an alternative form of a gene. Step 3: A sequence of amino acids is a protein, an observable feature is a phenotype, and the genotype is the full set of alleles, so none of those describes a single allele.Method:Recall the definition of an allele as one alternative form of a gene.Examiner tips
- Allele = an alternative form of a gene (for example, the allele for red or for white flowers).
- Step 1: The offspring show about three red to one white (93 to 28), which is the 3 : 1 ratio. Step 2: A 3 : 1 ratio comes from crossing two heterozygous parents, Rr and Rr. Step 3: White offspring (rr) need an r allele from each parent, and both parents are red, so both must be Rr.Method:Recognise the 3 : 1 ratio and work out that both red parents must be Rr.Examiner tips
- A 3 : 1 offspring ratio means both parents are heterozygous.
- Step 1: Almost all food chains start with the energy captured by plants in photosynthesis. Step 2: The hazel trees capture light energy from the Sun, and this energy then passes to the truffle and the deer. Step 3: So the original source of energy for the food chain is the Sun.Method:Follow the energy back through the food chain to the original source, the Sun.Examiner tips
- The Sun is the principal source of energy for nearly all food chains.
- Step 1: Every organism in the chain respires to release energy from its food. Step 2: Much of this energy is eventually released to the surroundings as heat, so it is lost from the food chain. Step 3: Ingestion is taking in food, photosynthesis captures energy rather than releasing it, and transpiration is water loss, so the energy is lost through respiration.Method:Identify respiration as the process in every organism that releases the energy lost from the chain.Examiner tips
- Energy is lost from food chains mainly as heat from respiration.
- Step 1: Weeds are unwanted plants growing among the crop. Step 2: A herbicide is a chemical designed to kill plants such as weeds. Step 3: A fertiliser and magnesium ions help plants grow, and an insecticide kills insects, so the weeds are killed with a herbicide.Method:Choose the chemical designed to kill plants, which is a herbicide.Examiner tips
- Herbicides kill plants (weeds); insecticides kill insects.
- Step 1: Pathogens are microorganisms that cause disease. Step 2: Untreated sewage contains human waste with many pathogens, so it pollutes water with disease-causing microbes. Step 3: An antibiotic treats infections, chlorophyll is a plant pigment, and methane is a gas, so none of those is a source of pathogens in water.Method:Pick the waste that contains disease-causing microorganisms, which is untreated sewage.Examiner tips
- Untreated sewage carries pathogens that pollute water and spread disease.
- Step 1: Level 4 is the producer (a plant) and level 3, which eats the producer, is the herbivore (primary consumer). Step 2: Carnivores are animals that eat other animals, so they are found above the herbivore. Step 3: Levels 2 and 1 eat the animals below them, so both are carnivores; only levels 1 and 2 contain carnivores.Method:Identify the producer and herbivore, then mark the levels above the herbivore as carnivores.Examiner tips
- Producer at the bottom, then herbivore, then carnivores at the higher levels.
- Step 1: In 90 minutes there are 90 ÷ 15 = 6 divisions, and the number doubles at each division. Step 2: Starting from 1 bacterium, after 6 doublings there are 2 to the power 6 = 64 bacteria. Step 3: The increase in number is 64 − 1 = 63 bacteria.Method:Find the number of divisions, double from 1 that many times, then subtract the starting bacterium.Examiner tips
- Number of divisions = total time ÷ division time; the count doubles each division.
- Step 1: Intensive farming uses large areas for a single crop or for housing many animals together. Step 2: This removes hedges and wild areas, so there are fewer habitats for wildlife, which is a disadvantage. Step 3: Lower cost, fewer workers needed and less land needed are advantages of intensive farming, not disadvantages.Method:Pick the option that harms the environment; the loss of habitats is the disadvantage.Examiner tips
- Intensive farming raises yields but reduces habitats and biodiversity.
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