IGCSE Biology Formula Sheet – Key Equations, Processes & Must-Know Facts (Cambridge 0610)

Biology at IGCSE level is less about long calculations and more about knowing the right equation, the right sequence and the right explanation at the right moment. This sheet gathers the essentials for Cambridge 0610 in syllabus order, so you can work through it topic by topic and spot the gaps in your revision before you open a past paper. It is a memory aid, not a replacement for your notes: use it to test yourself, then go back to the full explanation for anything you cannot recall confidently.

How to use this sheet: Cover the bullet points and try to rebuild each one from memory, starting with the boxed equation or relationship. Learn the equations exactly as written, including units, and practise turning word equations into symbol equations and back again. Return to weak topics in short, repeated sessions rather than reading the whole sheet through once.

1. Characteristics and Classification of Living Organisms

Key relationship: scientific name = genus + species

Memory aid: MRS GREN — Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition

All living things show the same seven life processes, even though they carry them out in very different ways.
A species is a group of organisms that can breed together and produce fertile offspring.
Classification groups organisms by shared features, and the groups are arranged in a hierarchy from kingdom down to species.
The five kingdoms are animals, plants, fungi, prokaryotes and protoctists; viruses sit outside this scheme because they have only a protein coat around genetic material and cannot carry out life processes on their own.
Dichotomous keys work by offering a pair of opposite choices at each step until only one organism fits.
Vertebrates are split into mammals, birds, reptiles, amphibians and fish, while arthropods include insects, arachnids, crustaceans and myriapods.

2. Organisation of the Organism

Key equation: magnification = image size ÷ actual size

Rearranged: image size = magnification × actual size | actual size = image size ÷ magnification

Unit conversion: 1 mm = 1,000 µm

Animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes; plant cells also have a cell wall, chloroplasts and a large permanent vacuole.
Bacterial cells have a cell wall, cell membrane, cytoplasm, ribosomes and circular DNA, sometimes with small extra loops called plasmids, but no true nucleus.
Each structure has a job: the nucleus holds genetic material, mitochondria release energy, ribosomes build proteins, chloroplasts trap light energy, and the vacuole helps keep a plant cell firm.
Specialised cells suit one task well: root hair cells absorb, palisade cells photosynthesise, red blood cells carry oxygen, ciliated cells move mucus, neurones carry impulses, and gametes are built for reproduction.
Organisation builds up in steps: cells form tissues, tissues form organs, organs work together in organ systems, and systems make up the organism.
Always convert image size and actual size to the same unit before using the magnification equation.

3. Movement Into and Out of Cells

Key equation: percentage change = (change in value ÷ original value) × 100

Key relationship: faster diffusion comes from a larger surface area, a steeper concentration difference and a shorter distance to travel.

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.
Osmosis is the net movement of water molecules through a partially permeable membrane, from a dilute solution to a more concentrated one.
Active transport moves substances against their concentration gradient, so it needs energy from respiration.
In osmosis experiments, a gain in mass shows net water uptake and a loss in mass shows net water loss; percentage change lets you compare samples that started at different masses.
Large surface areas, thin exchange surfaces and a good blood supply all speed up movement into and out of cells.
Turgor pressure is the outward push of cell contents against the cell wall in a plant cell full of water; loss of turgor makes the cell flaccid and the plant wilt.

4. Biological Molecules

Key relationship: carbohydrates, fats and proteins are built from smaller units joined together.

Food tests to remember: Benedict’s test for reducing sugars, iodine test for starch, biuret test for proteins, ethanol emulsion test for fats.

Carbohydrates, fats and proteins are the three main food groups, and each has a different role: carbohydrates supply energy, fats store energy and insulate, and proteins build and repair body structures.
Starch is the main storage carbohydrate in plants, glycogen is the storage carbohydrate in animals, and glucose is the sugar most often used directly in respiration.
DNA is a double helix made of two strands, and its base sequence carries the instructions for making proteins.
Water matters for life because it acts as a solvent, helps transport substances, and takes part in many chemical reactions in cells.
A positive Benedict’s result turns from blue to brick red on heating, iodine turns blue-black with starch, biuret turns purple with protein, and fats leave a milky emulsion with ethanol and water.

5. Enzymes

Key relationship: enzyme + substrate → enzyme-substrate complex → enzyme + products

Rate reminder: rate can be followed as amount changed ÷ time taken, or as 1 ÷ time taken when only the time to a visible change is measured.

Enzymes are proteins that act as biological catalysts: they speed up reactions without being used up themselves.
Each enzyme has an active site whose shape fits one substrate, so an enzyme usually works on only one type of reaction.
Rate rises with temperature up to an optimum, then falls sharply as the enzyme denatures and its active site loses its shape.
Each enzyme also has an optimum pH; moving far from it changes the active site and slows or stops the reaction.
Denaturation is a permanent change in shape, not a change in the enzyme’s chemical identity, and a denatured enzyme can no longer fit its substrate.
When you plot rate against temperature or pH, describe the rise, the peak and the fall, and always name the optimum.

6. Plant Nutrition

Word equation: carbon dioxide + water → glucose + oxygen (needs light energy and chlorophyll)

Balanced symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Photosynthesis takes place mainly in the leaves, inside chloroplasts, where chlorophyll absorbs light energy.
Glucose made in photosynthesis can be used in respiration, converted to starch for storage, used to build cellulose for cell walls, or changed into other substances the plant needs.
Nitrate ions are needed to make amino acids and therefore proteins, while magnesium ions are needed to make chlorophyll.
Leaves are adapted for photosynthesis: they are broad and thin, with many chloroplasts in the palisade layer, stomata for gas exchange, and veins for transport.
The rate of photosynthesis is limited by whichever factor is in shortest supply: light intensity, carbon dioxide concentration or temperature.
A leaf that has made starch turns blue-black with iodine solution after testing, which is how photosynthesis can be shown experimentally.

7. Human Nutrition

Key sequence: ingestion → digestion → absorption → assimilation → egestion

Key relationship: large food molecules must be broken into small, soluble molecules before they can be absorbed.

A balanced diet supplies carbohydrates, fats, proteins, vitamins, minerals, fibre and water in the right proportions for age, activity and health.
Mechanical digestion breaks food into smaller pieces, while chemical digestion uses enzymes to break large molecules into small ones.
Amylase breaks starch into sugars, proteases break proteins into amino acids, and lipases break fats into fatty acids and glycerol.
Bile from the liver emulsifies fats, giving lipases a larger surface area to work on, and it also neutralises stomach acid.
Absorption happens in the small intestine, where villi provide a large surface area, a thin wall and a rich blood supply.
After absorption, food molecules are used in assimilation: glucose in respiration, amino acids in protein building, and excess glucose stored as glycogen.

8. Transport in Plants

Key relationships: xylem carries water and mineral ions upwards; phloem carries sucrose and amino acids in both directions.

Transpiration rate rises with: higher light intensity, higher temperature, lower humidity and faster wind.

Transpiration is the loss of water vapour from leaves, mainly through open stomata, and it pulls water up the plant in the transpiration stream.
Xylem vessels are dead, hollow tubes strengthened by lignin, which lets them carry water without collapsing.
Phloem is living tissue, and translocation is the movement of dissolved food substances, mainly sucrose and amino acids, to where they are needed.
Root hair cells increase the surface area for absorbing water and mineral ions from the soil.
Water moves into root hairs by osmosis, then across the root and up the xylem to the leaves.
A potometer measures water uptake, which is used as an estimate of transpiration rate, and closing stomata reduces water loss when water is scarce.

9. Transport in Animals

Key sequence (double circulation): heart → lungs → heart → body → heart

Key relationship: arteries carry blood away from the heart, veins carry blood towards it, and capillaries link the two in tissues.

The heart has four chambers: two atria on top and two ventricles below, with valves that stop blood flowing backwards.
The left side of the heart pumps oxygenated blood around the body, while the right side pumps deoxygenated blood to the lungs.
Arteries have thick, elastic walls to cope with high pressure, veins have valves and thinner walls, and capillaries have walls one cell thick for fast exchange.
Red blood cells carry oxygen using haemoglobin, white blood cells defend against disease, platelets help blood clot, and plasma carries dissolved substances.
Coronary arteries supply the heart muscle itself with oxygen and glucose, which is why a blockage there is so serious.
Tissue fluid forms when plasma leaks from capillaries, and it bathes cells so substances can be exchanged before most fluid drains back.

10. Diseases and Immunity

Key sequence: pathogen enters → white blood cells respond → antibodies made → memory cells kept for faster future defence

Key distinction: immunity from infection or vaccination is specific to one pathogen.

Pathogens are disease-causing organisms, and they can be spread by direct contact, droplets, contaminated food or water, or by vectors such as insects.
The body’s first defences include skin, mucus, stomach acid and blood clotting at a wound.
White blood cells defend the body by engulfing pathogens and by producing antibodies that lock onto matching antigens.
Antibiotics kill bacteria or stop them growing, but they do not work against viruses, which is why they must not be used for viral infections.
Vaccination introduces a harmless form of a pathogen so the body makes memory cells, giving a fast, strong response if the real pathogen appears later.
Controlling disease also means clean water, good hygiene, safe food handling and controlling vectors.

11. Gas Exchange in Humans

Key relationship: oxygen moves into the blood and carbon dioxide moves out, both down their concentration gradients.

Key features of alveoli: large surface area, thin walls, moist lining, rich blood supply.

Air enters through the nose or mouth, passes down the trachea, through the bronchi and bronchioles, and reaches the alveoli.
Rings of cartilage hold the trachea open, mucus traps dust and microbes, and cilia sweep the mucus upwards away from the lungs.
In the alveoli, oxygen diffuses into the blood and carbon dioxide diffuses out, helped by the short diffusion distance and the constant blood flow.
Inspired air has more oxygen and less carbon dioxide than expired air, and expired air is warmer, wetter and contains more carbon dioxide.
Breathing in uses the intercostal muscles and diaphragm to increase chest volume and lower air pressure inside the lungs.
Smoking damages the lungs: tar, nicotine and carbon monoxide harm the lining, reduce oxygen transport and raise the risk of lung disease.

12. Respiration

Aerobic, word: glucose + oxygen → carbon dioxide + water + energy

Aerobic, balanced: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

Anaerobic in animals, word: glucose → lactic acid + energy (much less energy than aerobic)

Anaerobic in yeast, word: glucose → ethanol + carbon dioxide + energy

Anaerobic in yeast, balanced: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy

Respiration is a set of chemical reactions in cells that breaks down nutrient molecules and releases energy for metabolism.
Aerobic respiration uses oxygen and releases far more energy per glucose molecule than anaerobic respiration.
Anaerobic respiration in muscles produces lactic acid, which can cause fatigue and must later be broken down using oxygen.
Yeast carries out anaerobic respiration, called fermentation, which is used in bread making and brewing.
Energy from respiration powers muscle contraction, active transport, cell division, growth and keeping warm.
Do not confuse respiration with breathing: breathing moves air in and out, while respiration is a chemical process inside cells.

13. Excretion in Humans

Key sequence in the kidney: blood filtered in the glomerulus → useful substances reabsorbed in the nephron → urine passed to the bladder

Key distinction: excretion removes metabolic waste, while egestion removes undigested food that never entered the body’s cells.

The main excretory organs are the kidneys, which remove urea and excess salts and water, while the lungs excrete carbon dioxide and the skin loses salts in sweat.
Urea is made in the liver when excess amino acids are deaminated, and the kidneys then remove that urea from the blood.
In the nephron, filtration under pressure forces small molecules out of the blood, then selective reabsorption returns glucose, ions and most water to the blood.
The amount of water reabsorbed changes with the body’s needs, so urine volume and concentration vary with water intake and temperature.
Dialysis can stand in for failed kidneys by filtering the blood artificially, while a transplant replaces the organ itself.
Excretion questions often test the difference between filtration, which is not selective, and reabsorption, which is.

14. Coordination and Response

Reflex arc sequence: stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response

Key distinction: nervous responses are fast and short-lived; hormonal responses are slower and longer-lasting.

The central nervous system is the brain and spinal cord, and it links sense organs to effectors such as muscles and glands.
A reflex action is fast, automatic and does not involve conscious thought, which protects the body from harm.
Synapses pass impulses from one neurone to the next using chemicals, and impulses travel in one direction only.
The eye focuses light with the lens, detects it with the retina, and sends the signal to the brain through the optic nerve; the iris and pupil control how much light enters.
Hormones travel in the blood: insulin lowers blood glucose, glucagon raises it, and adrenaline prepares the body for action by raising heart rate and blood glucose.
Plants respond to light and gravity through growth movements called tropisms, controlled by plant hormones such as auxin.

15. Drugs

Key distinction: a medicinal drug treats or prevents illness; drug misuse means using a drug in a harmful way or for a non-medical purpose.

Key relationship: repeated misuse can lead to tolerance, dependence and addiction.

Medicinal drugs include antibiotics, painkillers and insulin, and they should be used at the right dose for the right condition.
Alcohol is a depressant: it slows reactions, impairs judgement and coordination, and long-term heavy use damages the liver.
Other misused drugs can overstimulate or depress the nervous system, distort perception and change behaviour, making everyday tasks unsafe.
Addiction means a person feels unable to stop using a drug, and withdrawal symptoms can appear when use stops.
Drug misuse carries social costs as well as health costs, including accidents, broken relationships and crime.
Exam answers should name the effect on the body and on behaviour, not just say a drug is harmful.

16. Reproduction

Key distinction: asexual reproduction produces genetically identical offspring from one parent; sexual reproduction produces varied offspring from two parents.

Key sequence in flowering plants: pollination → fertilisation → seed formation → dispersal → germination

In flowering plants, pollen is transferred to a stigma, a pollen tube grows to the ovule, and fertilisation joins the male and female gametes.
Insect-pollinated flowers tend to be bright, scented and sticky, while wind-pollinated flowers tend to be small, dull and produce large amounts of light pollen.
Seeds are dispersed by wind, water, animals or explosive mechanisms, which reduces competition with the parent plant.
In humans, fertilisation happens in the oviduct, the embryo implants in the uterus wall, and the placenta transfers nutrients and oxygen while removing waste.
Puberty brings the sex hormones into play: testosterone in males and oestrogen in females, driving the changes of adolescence.
The menstrual cycle is controlled by hormones and prepares the uterus for a possible pregnancy each month.

17. Inheritance

Key symbols: dominant allele shown with a capital letter (for example, T); recessive allele with the matching small letter (t).

Key ratio: a cross between two heterozygous parents gives a 3:1 ratio of dominant to recessive phenotypes in the offspring.

Genes are sections of DNA that code for proteins, and alleles are different versions of the same gene.
An organism with two identical alleles is homozygous, while one with two different alleles is heterozygous.
The genotype is the combination of alleles an organism carries, and the phenotype is the observable result.
A dominant allele shows its effect even when only one copy is present, while a recessive allele only shows when two copies are present.
Punnett squares predict the possible genotypes and phenotypes of offspring, but they give probabilities, not certainties, for any one child.
Sex is determined by chromosomes: females carry two X chromosomes and males carry one X and one Y, so a child’s sex depends on which chromosome comes from the father.

18. Variation and Selection

Key distinction: continuous variation shows a range of values (for example, height); discontinuous variation falls into clear groups (for example, blood group).

Key sequence for natural selection: variation exists → organisms compete → best adapted survive and reproduce → useful alleles become more common

Variation can be caused by genes, by the environment, or by both acting together.
Genetic variation arises from mutation and from the shuffling of alleles during sexual reproduction.
Mutations are changes in genes or chromosomes; most are harmful or neutral, and a few can be useful in a particular environment.
Natural selection is not a choice made by organisms: individuals with features that suit their environment are simply more likely to survive and pass those features on.
Over long periods, natural selection can lead to new species forming when populations become separated and can no longer interbreed.
Selective breeding, by contrast, is humans choosing parents with wanted features, as in farm animals and crop plants.

19. Organisms and Their Environment

Key sequence: producer → primary consumer → secondary consumer → tertiary consumer

Key relationship: energy enters a food web through producers and only part of it reaches each next level, because much is lost at every step.

Producers, usually green plants, make their own food by photosynthesis, while consumers eat other organisms and decomposers break down dead material.
Food chains show one feeding route, while food webs show the many linked routes in a habitat.
Arrows in a food chain point in the direction energy flows, from the food to the feeder.
Pyramids of numbers, biomass and energy summarise feeding levels, and pyramids of energy always narrow towards the top because energy is lost.
Energy is lost through respiration, excretion, egestion and movement, and as heat to the surroundings.
The carbon cycle and the water cycle both depend on living things: photosynthesis and respiration move carbon, while evaporation, condensation and precipitation move water.

20. Human Influences on Ecosystems

Key sequence for eutrophication: fertiliser run-off → algae grow rapidly → light blocked → plants die → decomposers use up oxygen → aquatic animals die

Key distinction: a renewable resource can be replaced naturally; a non-renewable resource cannot be replaced on a human timescale.

Deforestation removes habitats, reduces biodiversity, increases soil erosion and adds carbon dioxide to the atmosphere.
Burning fossil fuels releases carbon dioxide and other gases that increase the greenhouse effect and change the climate.
Pollution harms ecosystems in different ways: sewage and fertilisers feed algal blooms, pesticides can build up through food chains, and plastic waste harms wildlife.
Overfishing and hunting can push populations down faster than they can recover, sometimes to extinction.
Conservation works by protecting habitats, setting up reserves, controlling hunting and fishing, and breeding endangered species.
Sustainable development means meeting human needs today without destroying the resources future generations will need.

21. Biotechnology and Genetic Modification

Key sequence for insulin production: human insulin gene inserted into bacteria → bacteria multiply in a fermenter → insulin collected and purified

Key distinction: genetic modification moves a gene from one organism to another; selective breeding only crosses organisms of the same species.

Biotechnology uses living organisms or their products, such as enzymes and microbes, to make useful substances.
Fermenters give microbes the conditions they need: a food supply, the right temperature and pH, oxygen where needed, and stirring to mix everything evenly.
Penicillin is made by fungi in fermenters, mycoprotein is made from fungi as a meat alternative, and enzymes are used in washing powders and food production.
Genetic modification can give crops herbicide resistance, insect resistance or extra nutrients, and can let bacteria produce human insulin.
Genetically modified crops have possible benefits, such as higher yields, and possible concerns, such as effects on wild plants and dependence on seed suppliers.
Genetic modification raises ethical questions as well as scientific ones, so exam answers should weigh both sides rather than giving one-sided claims.

Keep Revising

Work through this sheet one topic at a time and write out the boxed equations from memory before checking them. For every process, practise saying the steps in order without looking, then test the order backwards to make sure you truly know the sequence rather than just recognising it. Mix topics as you get stronger, so your brain has to choose the right equation instead of guessing from the heading above it. Finish each session with a few past-paper questions on the topics you just covered, and keep a short list of the facts you missed so your next session starts exactly where revision will help most. Little and often beats one long read-through, and steady recall practice is what turns a formula sheet into marks.

More revision on this site: Biology MCQs hub.

IGCSE Biology Section MCQs

Topic-wise practice questions for Cambridge IGCSE Biology 0610 — 30 MCQs per topic with answers and explanations.