October/November 2025 Paper 12 Worked Answers (IGCSE Biology 0610 Core)
40 questions · 40 marks · 45 minutes
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Worked answers for 30 questions
- Step 1: Growth is a permanent increase in size and dry mass as an organism makes new cells and materials. Step 2: Digestion breaks down food and respiration releases energy, neither of which permanently adds dry mass. Step 3: Reproduction makes new organisms rather than increasing the dry mass of the parent, so growth is the correct process.Method:Match the definition of each life process to a permanent increase in dry mass.Examiner tips
- Growth is the permanent increase in size and dry mass of an organism.
- Step 1: The genus is the first word of a scientific name. Step 2: Pinus glabra and Pinus resinosa both begin with Pinus, so they share the same genus. Step 3: The other pairs share only their second word (the species name) or no word, so they are not in the same genus.Method:Compare the first word of each name and group the two that match.Examiner tips
- Two organisms are in the same genus only if the first word of their names is identical.
- Step 1: Insects have a body in three parts (head, thorax and abdomen), three pairs of legs and one pair of antennae. Step 2: These exact features match the organism described. Step 3: Arachnids have four pairs of legs and no antennae, crustaceans have more legs and two pairs of antennae, and myriapods have many body segments, so none of these fit.Method:Match the number of legs, body parts and antennae to the features of each arthropod group.Examiner tips
- Insects: three body parts, three pairs of legs, one pair of antennae.
- Step 1: A leaf is made of several different tissues, such as palisade, spongy and vascular tissue, working together. Step 2: A structure made of different tissues working together for a function is an organ. Step 3: A cell is a single building block, a tissue is one type of cell, and an organism is a whole living thing, so a leaf is an organ.Method:Place a leaf on the cell-tissue-organ-organism scale by what it is made of.Examiner tips
- Order of organisation: cell, tissue, organ, organ system, organism.
- Step 1: Actual length equals the image length divided by the magnification. Step 2: Dividing 150 mm by 20 gives 7.5 mm. Step 3: So the actual length of the insect is 7.5 mm.Method:Divide the drawing length by the magnification to find the real length.Examiner tips
- Rearrange magnification = image / actual to get actual = image / magnification.
- Step 1: Osmosis is the diffusion of water molecules, so diffusion is involved. Step 2: Osmosis needs a partially permeable membrane to let water through while holding back solutes. Step 3: It does not need a cell wall, because osmosis also happens in animal cells, which have no cell wall.Method:Recall the definition of osmosis and test each of the three features against it.Examiner tips
- Osmosis = diffusion of water through a partially permeable membrane; no cell wall needed.
- Step 1: Enzymes are proteins. Step 2: Proteins are built from many amino acids joined together. Step 3: Fatty acids build fats, sugars build carbohydrates, and carbon dioxide and water are raw materials for photosynthesis, so enzymes are made from amino acids.Method:Identify enzymes as proteins, then recall that proteins are made from amino acids.Examiner tips
- Enzymes are proteins, and all proteins are made from amino acids.
- Step 1: An enzyme works because the substrate fits into the active site like a key fits a lock. Step 2: This means their shapes are complementary, so the substrate fits neatly into the active site. Step 3: They do not have the same shape, and temperature or kinetic energy does not explain the fit, so complementary shapes is correct.Method:Use the lock-and-key model to explain how the substrate fits the active site.Examiner tips
- Lock and key: the active site and substrate have complementary shapes.
- Step 1: Photosynthesis absorbs light energy and stores it as chemical energy in glucose. Step 2: Respiration releases energy already stored in glucose; it does not use light. Step 3: So only photosynthesis transfers light energy into energy in chemicals.Method:Decide which process uses light as its energy input.Examiner tips
- Photosynthesis traps light energy as chemical energy; respiration only releases it.
- Step 1: The stomach churns food with its muscular walls, which is physical digestion. Step 2: The stomach also makes protease enzymes that chemically break down protein, which is chemical digestion. Step 3: The gall bladder only stores bile, and the liver and pancreas make secretions but do not physically churn food, so the stomach is correct.Method:Find the organ that both moves food mechanically and secretes enzymes.Examiner tips
- The stomach both churns food (physical) and releases protease (chemical).
- Step 1: Water enters the plant through the root hair cells, which have a large surface area. Step 2: It then passes across the root cortex cells to the xylem in the centre of the root. Step 3: The xylem carries the water up to the leaves, where it reaches the mesophyll cells, giving the order root hair, cortex, xylem, mesophyll.Method:Trace water from where it enters the root to where it is used in the leaf.Examiner tips
- Entry to exit: root hair cells, cortex, xylem, then mesophyll in the leaf.
- Step 1: Red blood cells contain haemoglobin, which binds to oxygen. Step 2: They carry oxygen from the lungs to the rest of the body. Step 3: Antibodies are made by white blood cells, and glucose and hormones are carried dissolved in the plasma, so the function of red blood cells is transport of oxygen.Method:Recall what haemoglobin in red blood cells carries.Examiner tips
- Red blood cells carry oxygen using haemoglobin.
- Step 1: A pathogen is any organism that causes disease. Step 2: Bacteria and viruses are only particular types of pathogen, so neither word covers them all. Step 3: Decomposers break down dead material and do not generally cause disease, so the general term is pathogens.Method:Choose the general term that includes all disease-causing organisms.Examiner tips
- Pathogen is the umbrella term for any disease-causing organism.
- Step 1: Respiration in the body uses oxygen and produces carbon dioxide. Step 2: So expired air has gained carbon dioxide, making its carbon dioxide concentration higher. Step 3: Expired air has lost oxygen, making its oxygen concentration lower, so carbon dioxide is higher and oxygen is lower.Method:Use respiration (uses oxygen, makes carbon dioxide) to compare the two gases.Examiner tips
- Expired air: more carbon dioxide, less oxygen than inspired air.
- Step 1: Anaerobic respiration in human muscles breaks down glucose without oxygen. Step 2: This produces lactic acid. Step 3: Alcohol is the product of anaerobic respiration in yeast, carbon dioxide is a product of aerobic respiration, and urea is made in the liver, so the answer is lactic acid.Method:Recall the product of anaerobic respiration in human muscle.Examiner tips
- Muscle anaerobic respiration makes lactic acid; yeast makes alcohol.
- Step 1: A ureter joins a kidney to the bladder, so it is attached to the kidney. Step 2: A urethra joins the bladder to the outside, so it is not attached to a kidney. Step 3: Both tubes carry urine, which contains urea, mineral ions and water, and both connect to the bladder, so only the attachment to the kidney sets the ureter apart.Method:Track the start and end of each tube to find the true comparison.Examiner tips
- Ureter: kidney to bladder. Urethra: bladder to outside.
- Step 1: Being chased triggers the release of adrenaline, which prepares the body for action. Step 2: Adrenaline increases the breathing rate and the heart rate to supply more oxygen and glucose to the muscles. Step 3: It also widens the pupils, so the breathing rate, heart rate and pupil diameter all increase.Method:Recall the fight-or-flight effects of adrenaline on the body.Examiner tips
- Adrenaline (fight or flight) increases breathing rate, heart rate and pupil diameter.
- Step 1: Shoots grow upwards, away from the pull of gravity, which is negative gravitropism. Step 2: Shoots also grow towards a light source, which is positive phototropism. Step 3: Both of these together make the shoot grow up and towards the window, so the shoot grows away from gravity and towards the light.Method:Combine the shoot responses to gravity and to light.Examiner tips
- Shoots: away from gravity (up) and towards light.
- Step 1: The mean before coffee is (0.25 + 0.30 + 0.20 + 0.35 + 0.15) divided by 5 = 1.25 / 5 = 0.25 s. Step 2: The mean after coffee is (0.20 + 0.15 + 0.10 + 0.20 + 0.10) divided by 5 = 0.75 / 5 = 0.15 s. Step 3: Since 0.25 s is greater than 0.15 s, the mean reaction time before drinking coffee is longer than after.Method:Calculate both means and compare them to judge each statement.Examiner tips
- Mean = total of the values divided by how many values there are.
- Step 1: Germinating seeds need water to activate their enzymes and mobilise their food store. Step 2: They need oxygen for aerobic respiration to release energy for growth. Step 3: They need warmth so that the enzymes can work, so most seeds require oxygen, warmth and water together.Method:Recall the three conditions needed for most seeds to germinate.Examiner tips
- Germination needs water, oxygen and warmth together (not light).
- Step 1: HIV is carried in body fluids, so it spreads through exchange of blood and through unprotected sex. Step 2: It can also pass from an infected mother to her fetus during pregnancy. Step 3: HIV is not spread by eating contaminated food or by insect bites, so the correct routes are blood exchange, mother to fetus, and unprotected sex.Method:Keep the fluid-borne routes and rule out food and insect bites.Examiner tips
- HIV spreads through body fluids: blood, sexual contact and mother to fetus.
- Step 1: A gene is a length of DNA that carries the instructions to make a particular protein. Step 2: The order of bases in the gene determines the order of amino acids in that protein. Step 3: Carbohydrates and fats are not coded directly by genes, and DNA is what genes are made of, so a gene codes for a protein.Method:Recall the definition of a gene as a code for a protein.Examiner tips
- A gene is a length of DNA that codes for one protein.
- Step 1: The cross is Hh multiplied by hh. Step 2: The Hh parent gives H or h, and the hh parent gives h, so the offspring are Hh, Hh, hh, hh. Step 3: Half the offspring (Hh) are short-haired and half (hh) are long-haired, giving 50% short-haired and 50% long-haired.Method:Use a Punnett square for Hh x hh and read off the phenotype ratio.Examiner tips
- Hh x hh gives a 1:1 ratio of short-haired to long-haired offspring.
- Step 1: Discontinuous variation gives distinct categories with no in-between values and is usually caused by genes only. Step 2: ABO blood groups fall into separate categories (A, B, AB, O), so they are an example of discontinuous variation. Step 3: Continuous variation, such as body mass, is caused by both genes and the environment, so only the statement about discontinuous variation and blood groups is fully correct.Method:Match the type of variation to its cause and to a correct example.Examiner tips
- Discontinuous = distinct groups, genes only (e.g. blood groups). Continuous = a range, genes + environment.
- Step 1: The primary consumers receive 5000 kJ from the producers. Step 2: They lose 4500 kJ of this to the environment. Step 3: The energy passed on to the secondary consumers is 5000 minus 4500 = 500 kJ.Method:Subtract the energy lost by the primary consumers from the energy they received.Examiner tips
- Energy passed on = energy received minus energy lost to the environment.
- Step 1: A new population starts slowly in the lag phase while it adjusts. Step 2: It then grows rapidly in the log phase when resources are plentiful. Step 3: Finally it levels off in the stationary phase as limiting factors take effect, giving the order lag, log, stationary.Method:Order the phases from the slow start to the final levelling-off.Examiner tips
- Sigmoid curve order: lag, log (exponential), then stationary.
- Step 1: Weeds compete with crops for light, water and nutrients. Step 2: A herbicide is a chemical that kills weeds, reducing this competition. Step 3: Fertiliser adds nutrients, insecticide kills insects, and deforestation clears trees, so the chemical that controls weeds is a herbicide.Method:Match the chemical to the pest it controls: herbicide for weeds.Examiner tips
- Herbicide kills weeds; insecticide kills insects.
- Step 1: Removing trees means less photosynthesis and more carbon dioxide left in the atmosphere. Step 2: Without tree roots to hold the soil, it is washed away, so soil is lost. Step 3: Deforestation reduces biodiversity and increases flooding, so the correct effects are more carbon dioxide and loss of soil.Method:Keep the true effects (more carbon dioxide, soil loss) and reject the false ones.Examiner tips
- Deforestation: more carbon dioxide, soil erosion, less biodiversity, more flooding.
- Step 1: Greenhouse gases trap heat in the atmosphere and include carbon dioxide and methane. Step 2: Methane is released from sources such as cattle and rice fields and is a greenhouse gas. Step 3: Herbicide and insecticide are farming chemicals, and oxygen is not a greenhouse gas, so the answer is methane.Method:Recall the named greenhouse gases and pick methane.Examiner tips
- Carbon dioxide and methane are the greenhouse gases to remember.
- Step 1: Oil is a fat, so an oil stain is broken down by the enzyme that digests fats. Step 2: Lipase is the enzyme that breaks down fats into fatty acids and glycerol. Step 3: Amylase breaks down starch and protease breaks down protein, so the enzyme that removes an oil stain is lipase.Method:Identify the stain as a fat and choose the fat-digesting enzyme.Examiner tips
- Lipase digests fats and oils; protease digests protein; amylase digests starch.
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