0610/11 Oct/Nov 2025 Worked Answers (IGCSE Biology 0610 Core)
40 questions · 40 marks · 45 minutes
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Worked answers for 33 questions
- Step 1: Every living organism excretes waste, moves at least part of itself, and respires to release energy. Step 2: Photosynthesis is carried out only by plants and some other organisms, so it is not shown by all organisms. Step 3: Egestion is the removal of undigested food and is not a characteristic of all organisms, so the correct set is excretion, movement and respiration.Method:Test each process against whether every living organism carries it out.Examiner tips
- Use MRS GREN, but remember photosynthesis and egestion are not shared by every organism.
- Step 1: In the binomial system the first part of the scientific name is the genus and the second part is the species. Step 2: In Turdus philomelos the first word is Turdus. Step 3: So the genus of the song thrush is Turdus.Method:Identify the first word of the scientific name as the genus.Examiner tips
- The first word of a binomial name (with a capital letter) is the genus.
- Step 1: Arachnids are a group of arthropods that includes spiders and scorpions. Step 2: Arachnids have four pairs of jointed legs, giving eight legs in total. Step 3: Insects have three pairs of legs and myriapods have many pairs, so the arachnid has four pairs only.Method:Recall the number of leg pairs that defines arachnids.Examiner tips
- Arachnids have four pairs of legs; insects have three pairs.
- Step 1: A plasmid is a small circular ring of extra DNA found floating in bacterial cytoplasm. Step 2: Animal cells do not contain plasmids. Step 3: Both cells have a cell membrane, the cell wall lies outside the cytoplasm, and animal cells have a nucleus, so the plasmid is the structure unique to the bacterial cytoplasm.Method:Compare the contents of bacterial and animal cytoplasm to find the structure unique to bacteria.Examiner tips
- Plasmids are rings of extra DNA found only in bacterial cytoplasm.
- Step 1: Palisade mesophyll cells are packed with chloroplasts and carry out photosynthesis, which makes glucose that is stored as starch. Step 2: So the palisade mesophyll cell is correctly matched with the production of starch. Step 3: Ciliated cells move mucus, white blood cells defend against disease, and oxygen is carried by red blood cells, so the other rows are wrong.Method:Check each cell against its true function and find the correctly matched row.Examiner tips
- Palisade cells photosynthesise and store starch; red cells carry oxygen.
- Step 1: Diffusion is faster when the concentration gradient is steeper, so the gradient should increase. Step 2: It is also faster across a thinner membrane, over a larger surface area, and at a higher temperature. Step 3: Only the row with a larger gradient, a thinner membrane, a larger surface area and a higher temperature improves all four factors at once.Method:Choose the row where all four factors change in the direction that speeds up diffusion.Examiner tips
- Improve every factor at once: steeper gradient, thinner membrane, larger area, warmer.
- Step 1: A red Benedict’s result shows reducing sugar and a blue-black iodine result shows starch, so both carbohydrates are present. Step 2: The biuret test staying blue shows no protein, and the ethanol test staying clear shows no fat. Step 3: So this food contains carbohydrates only, while the other rows show protein, fat or both as well.Method:Read each test result and keep the row positive only for carbohydrate tests.Examiner tips
- Benedict red = sugar, iodine blue-black = starch, biuret purple = protein, ethanol cloudy = fat.
- Step 1: A catalyst speeds up a chemical reaction without being used up. Step 2: Enzymes are biological catalysts that speed up the reactions of metabolism. Step 3: Hormones are chemical messengers, mitochondria are the site of respiration, and ribosomes make proteins, so enzymes are the catalysts.Method:Recall the definition of a biological catalyst and match it to enzymes.Examiner tips
- Enzymes are biological catalysts that speed up reactions in cells.
- Step 1: Chlorophyll is the green pigment that absorbs light energy. Step 2: Plant nutrition is photosynthesis, which uses chlorophyll to capture light to make food. Step 3: Fertilisation, movement and respiration do not need chlorophyll, so the process requiring chlorophyll is nutrition.Method:Link chlorophyll to capturing light for photosynthesis, which is plant nutrition.Examiner tips
- Plant nutrition is photosynthesis, which needs the green pigment chlorophyll.
- Step 1: Proteins are made of amino acids, which all contain nitrogen as well as carbon, hydrogen and oxygen. Step 2: Fats, glucose and starch contain only carbon, hydrogen and oxygen. Step 3: So the molecule that contains nitrogen is protein.Method:Recall that nitrogen is found in proteins (amino acids) but not in carbohydrates or fats.Examiner tips
- Only proteins contain nitrogen; carbohydrates and fats do not.
- Step 1: Rickets is a disease of soft, weak bones caused by a lack of calcium or vitamin D. Step 2: Calcium is needed to harden bones and vitamin D helps the body absorb calcium. Step 3: Vitamin C prevents scurvy and iron is needed for haemoglobin, so the nutrients that prevent rickets are calcium and vitamin D.Method:Link rickets to bones and pick the nutrients that strengthen bone.Examiner tips
- Calcium plus vitamin D build strong bones and prevent rickets.
- Step 1: Physical digestion breaks food into smaller pieces, for example by chewing with the teeth. Step 2: Smaller pieces have a larger total surface area, so enzymes can act on them faster. Step 3: Absorption, active transport and respiration do not increase the surface area of food, so the answer is physical digestion.Method:Recall that breaking food into smaller pieces is physical digestion.Examiner tips
- Chewing is physical digestion; it increases the surface area for enzymes.
- Step 1: During transpiration water first evaporates from the wet surfaces of the mesophyll cells into the air spaces, which is process 2. Step 2: The water vapour in the air spaces then diffuses out through the stomata, which is process 4. Step 3: Water moves into, not out of, the mesophyll cells overall, and the loss through the stomata is by diffusion of vapour, so the correct processes are 2 and 4.Method:Trace the water from the wet cell surfaces to the air, then out of the stomata.Examiner tips
- Transpiration = evaporation from mesophyll surfaces, then diffusion of vapour through stomata.
- Step 1: Blood in the capillaries collects into veins that carry it back towards the heart. Step 2: The heart then pumps the blood out into the arteries. Step 3: So, starting from the capillaries, the order is capillaries, veins, heart and then arteries.Method:Use the direction of flow in veins and arteries to order the parts from the capillaries.Examiner tips
- Capillaries to veins to heart to arteries: veins return, arteries leave.
- Step 1: Treating sewage stops pathogens in human waste from reaching water and food. Step 2: Washing hands regularly removes pathogens before they are passed on, and clean drinking water prevents waterborne diseases. Step 3: All three measures reduce the spread of disease, so the correct statement is the one that includes all three.Method:Check each public-health measure; all three reduce the spread of disease.Examiner tips
- Sewage treatment, hand washing and clean water are all measures that reduce disease spread.
- Step 1: Limewater turns from clear to milky (cloudy) when carbon dioxide is bubbled through it. Step 2: So limewater is used to test for carbon dioxide. Step 3: Benedict’s solution tests for reducing sugar, biuret reagent for protein, and DCPIP for vitamin C, so none of these tests for carbon dioxide.Method:Recall the chemical test for carbon dioxide and match it to limewater.Examiner tips
- Limewater goes milky with carbon dioxide.
- Step 1: Yeast respire anaerobically when there is no oxygen, breaking down glucose into alcohol and carbon dioxide. Step 2: The carbon dioxide gas produced collects and inflates the balloon. Step 3: Combining carbon dioxide and water is photosynthesis, the aerobic equation makes water not gas in a balloon this way, and lactic acid is the product in muscle, so the correct equation is glucose to alcohol and carbon dioxide.Method:Identify that yeast without oxygen ferment glucose, producing the gas that inflates the balloon.Examiner tips
- Yeast fermentation: glucose to alcohol and carbon dioxide; the carbon dioxide inflates the balloon.
- Step 1: Healthy urine contains water, urea and excess ions (mineral salts) removed from the blood by the kidneys. Step 2: So the third component X is ions. Step 3: Platelets are blood fragments that are not filtered into urine, and starch and sucrose are not normally present in the urine of a healthy person.Method:Recall the normal composition of urine and identify the missing component as ions.Examiner tips
- Urine is water, urea and excess ions (salts).
- Step 1: Adrenaline is released from the adrenal glands when a person is frightened or excited. Step 2: It prepares the body for action, including widening the pupils. Step 3: Insulin controls blood glucose, while oestrogen and testosterone are sex hormones, so the fight or flight hormone is adrenaline.Method:Match the fight or flight response and wider pupils to adrenaline.Examiner tips
- Adrenaline is the fight or flight hormone; it widens the pupils.
- Step 1: Roots grow downwards in the direction of gravity, so they show positive gravitropism. Step 2: Roots grow away from light, so they show negative phototropism. Step 3: This anchors the plant and helps the roots find water, so the root response is positive gravitropism and negative phototropism.Method:Recall the directions roots grow relative to gravity and light.Examiner tips
- Roots: positive gravitropism (towards gravity), negative phototropism (away from light).
- Step 1: Asexual reproduction produces offspring that are genetically identical to the parent, forming a clone. Step 2: The tuber grew from the parent by asexual reproduction, and the shoots grow from the tuber by asexual reproduction, so all of them are genetically identical. Step 3: So the tuber is identical to the shoots and the parent is also identical to the shoots.Method:Apply the rule that asexual reproduction gives identical genotypes throughout.Examiner tips
- Asexual reproduction = clones = all genetically identical.
- Step 1: Wind-pollinated flowers are adapted to catch pollen blown in the air. Step 2: They have long, feathery stigmas that hang outside the flower to trap drifting pollen. Step 3: Large bright petals, nectar and anthers held inside attract insects, so they are features of insect-pollinated flowers, not wind-pollinated ones.Method:Pick the feature that helps catch wind-blown pollen rather than attract insects.Examiner tips
- Wind-pollinated: feathery stigmas and dangling anthers; insect-pollinated: bright petals and nectar.
- Step 1: Fertilisation is the fusion of a male gamete with a female gamete. Step 2: The important event is that the nucleus of the male gamete fuses with the nucleus of the female gamete, combining their genetic material. Step 3: So it is the nuclei of the gametes that fuse during fertilisation.Method:Recall that fertilisation is defined by the fusion of the nuclei of two gametes.Examiner tips
- Fertilisation = fusion of the gamete nuclei.
- Step 1: Testosterone is the male sex hormone that controls male secondary sexual characteristics. Step 2: It promotes the development of stronger muscles (statement W) and causes the voice to deepen at puberty (statement X). Step 3: Breast tissue development is caused by oestrogen and the pancreas produces insulin and glucagon, so the correct statements are W and X.Method:Select the statements describing male secondary sexual characteristics.Examiner tips
- Testosterone deepens the voice and builds muscle at male puberty.
- Step 1: AIDS is caused by the human immunodeficiency virus, HIV. Step 2: HIV is a virus, so the organism that causes the infection leading to AIDS is a virus. Step 3: Amphibians and myriapods are animals, and a bacterium is a different type of pathogen, so none of these causes AIDS.Method:Recall that AIDS is caused by HIV, which is a virus.Examiner tips
- HIV is a virus, and it is the cause of AIDS.
- Step 1: A gene is a length of DNA that carries the instructions for making a particular protein. Step 2: So a gene codes for a protein. Step 3: Amino acids are the building blocks that make up proteins, while carbohydrates and fats are not coded for directly by genes.Method:Recall the definition of a gene as a length of DNA that codes for a protein.Examiner tips
- A gene is a length of DNA coding for a protein.
- Step 1: In humans, females have two X chromosomes, written XX. Step 2: Males have one X and one Y chromosome, written XY. Step 3: So the correct statement is that a female has the sex chromosomes XX, while the other options give the wrong pairings.Method:Recall the sex chromosome combinations for human females and males.Examiner tips
- Female = XX, male = XY.
- Step 1: The TT parent can only pass on a T allele, while the Tt parent passes on T or t. Step 2: Combining these gives offspring that are TT (from T and T) or Tt (from T and t), each equally likely. Step 3: So the expected genotypes are 50% TT and 50% Tt.Method:Work out the gametes from each parent and combine them to find the genotype ratio.Examiner tips
- Cross TT with Tt: gametes T x (T or t) give TT and Tt only, 50% each.
- Step 1: Because each student falls into one of a few separate, distinct categories with no in-between values, this is discontinuous variation. Step 2: Blood group is determined only by the genes inherited, not by the environment. Step 3: So blood groups show discontinuous variation caused by genes only.Method:Decide the type of variation from the distinct categories and rule out environmental effects.Examiner tips
- Discrete categories = discontinuous; gene-only means the environment has no effect.
- Step 1: Between 1600 and 2000 the population rises very rapidly and steeply. Step 2: A period of rapid increase in numbers is the exponential, or log, phase of population growth. Step 3: The slow early period is the lag phase, a levelling off is the stationary phase, and a fall would be the death phase, so the rapid rise is the exponential phase.Method:Match the steep, rapid rise in numbers to the exponential phase.Examiner tips
- Rapid, steep growth = exponential (log) phase.
- Step 1: A sustainable resource is one that can be removed from the environment and replaced at the same rate, so it does not run out. Step 2: This means it is produced as rapidly as it is removed. Step 3: Needing no conservation, using genetic modification, or causing habitat destruction do not define sustainability, so the correct statement is that it is produced as fast as it is removed.Method:Choose the statement that describes a resource being replaced at the rate it is used.Examiner tips
- Sustainable = replaced as fast as it is removed, so it does not run out.
- Step 1: Conservation works better when people understand why species need protecting. Step 2: Education helps people change their behaviour and support conservation, so it increases the chance of conserving species. Step 3: Climate change, hunting and introducing new species all threaten species, so they reduce the chance of conservation.Method:Pick the measure that protects species rather than the threats that harm them.Examiner tips
- Education supports conservation; hunting and invasive species harm it.
- Step 1: Genetic modification can make crops that need less herbicide and less insecticide and that resist pest damage, which are all benefits (statements 1, 2 and 3). Step 2: Reducing the nutritional quality of a crop (statement 4) is a disadvantage, not a reason to use genetic modification. Step 3: So the reasons for using genetic modification are statements 1, 2 and 3.Method:Keep the statements that are benefits and reject the one describing a drawback.Examiner tips
- GM crops are used to cut chemical use and pest damage, not to lower food quality.
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