Tick off each objective as you master it. These are the exact learning objectives from the Cambridge 0610 syllabus (2026-2028).
In IGCSE Biology, you need to know the seven characteristics that define all living organisms. These characteristics separate life from non-life โ and they're tested heavily in Paper 1 and Paper 6.
1. Movement: An action by an organism or part of an organism causing a change of position or place. This includes movement of the entire organism (a rabbit hopping) or movement of parts (your heart beating, plants bending toward light). Movement is powered by energy from respiration.
2. Respiration: The chemical reactions in cells that break down nutrient molecules and release energy for metabolism. Note: This is cellular respiration (a chemical process inside cells), NOT breathing. A bacterium respires but does not breathe. Respiration happens in every living cell all the time and is essential for life.
3. Sensitivity: The ability to detect and respond to changes in the internal or external environment. A plant growing toward light shows sensitivity. Your pupil dilating in darkness shows sensitivity. A bacterium moving toward a nutrient source shows sensitivity. Organisms detect stimuli using receptors and respond using effectors.
4. Growth: A permanent increase in size AND dry mass. This is important โ growth is not just getting bigger, it's actually adding more living material. A balloon gets bigger when inflated but doesn't grow. A plant growing new leaves is growing because it's adding organic matter through photosynthesis and respiration.
5. Reproduction: The processes that make more of the same kind of organism. This can be sexual (producing genetically different offspring) or asexual (producing genetically identical clones). Viruses don't reproduce on their own โ they need to invade a host cell, which is why many scientists argue viruses aren't truly alive.
6. Excretion: The removal of the waste products of metabolism and substances in excess of requirements. This is NOT the same as defecation (which is egestion โ removing undigested food). Excretion includes removing COโ (from respiration), urea (from protein breakdown), and excess water. If an organism cannot excrete toxic waste, it dies.
7. Nutrition: The taking in of materials for energy, growth, and development. This includes both autotrophs (plants making their own food) and heterotrophs (animals eating other organisms). All organisms need materials for energy and building new cells.
There are millions of species on Earth. Classification systems organize them by shared characteristics. The main ranks (from largest to smallest groups) are:
| Rank | Example (Lion) | Key Point |
|---|---|---|
| Kingdom | Animalia | Broadest grouping; defines basic body plan and nutrition method |
| Phylum | Chordata | Major structural features (e.g., presence of backbone) |
| Class | Mammalia | Mammals: have hair, produce milk, have a diaphragm |
| Order | Carnivora | Carnivores: meat-eating mammals with specialized teeth |
| Family | Felidae | Cats: retractable claws, flexible spine |
| Genus | Panthera | Big cats that can roar |
| Species | leo | African/Asian lion; can interbreed with lion (the species level) |
The binomial naming system uses the genus and species. The lion is Panthera leo (genus + species). The first letter of the genus is capitalized, the species is lowercase, and both are italicized. This system was invented by Carl Linnaeus and is used worldwide โ it's why a scientist in Japan and a scientist in Brazil can talk about the same organism using the same name.
A species is defined as: a group of organisms that can reproduce to produce fertile offspring. This is crucial. A lion and a tiger can produce a liger, but ligers are usually sterile โ they cannot produce fertile offspring. Therefore, lions and tigers are different species. If two organisms are the same species, they can interbreed and produce fertile offspring.
Animals: Heterotrophic, usually mobile, no cell wall, store energy as glycogen, ingest food.
Plants: Autotrophic (produce own food via photosynthesis), have cell walls made of cellulose, store energy as starch, chloroplasts present.
Fungi: Heterotrophic, digest food externally (secrete enzymes into food), have cell walls made of chitin, store energy as glycogen. Examples: mushrooms, yeasts, molds.
Prokaryotes: No nucleus (single-celled bacteria and archaea), no membrane-bound organelles, DNA in a nucleoid region, much smaller (0.1โ5 ฮผm). Examples: E. coli, Streptococcus.
Protoctists: Have a nucleus and membrane-bound organelles, mostly single-celled, can be plant-like (algae, which photosynthesize) or animal-like (amoeba, which engulf food). This is a "catch-all" kingdom for organisms that don't fit the other four.
Vertebrates have a backbone (spine made of vertebrae). The five main groups of vertebrates are:
1. Fish: Aquatic, scales, gills, fins, cold-blooded (ectothermic), lay eggs. Examples: salmon, shark.
2. Amphibians: Can live on land and in water, moist skin, lay eggs in water, tadpoles transform into adults. Examples: frogs, newts, salamanders.
3. Reptiles: Dry, scaly skin, laid on land, cold-blooded, internal fertilization. Examples: snakes, lizards, turtles, crocodiles.
4. Birds: Feathers, wings, hollow bones, lay eggs with hard shells, warm-blooded (endothermic), have a four-chambered heart. Examples: eagle, chicken, sparrow.
5. Mammals: Hair/fur, produce milk to feed young, warm-blooded, have a diaphragm, four-chambered heart, most give birth to live young. Examples: humans, dogs, whales, bats.
Arthropods are the largest invertebrate group (insects, spiders, crustaceans) and have jointed legs and an exoskeleton. Key groups:
โข Insects: 6 legs, 3 body segments (head, thorax, abdomen), some have wings. Examples: beetles, butterflies, ants.
โข Arachnids: 8 legs, 2 body segments (cephalothorax + abdomen), no wings. Examples: spiders, scorpions, ticks.
โข Crustaceans: Many legs, hard exoskeleton, mostly aquatic. Examples: crabs, shrimp, lobsters.
โข Myriapods: Many legs (centipedes have 30+, millipedes have 100+), one pair of antennae.
Ferns: No flowers, no seeds, have roots/stems/leaves, reproduce via spores. Examples: bracken fern, tree fern.
Flowering Plants (Angiosperms): Reproduce via seeds (inside a fruit), have flowers, have roots/stems/leaves. Split into two groups:
โข Monocotyledons (Monocots): One seed leaf, parallel leaf veins, flower petals in multiples of 3. Examples: grasses, wheat, maize, lilies.
โข Dicotyledons (Dicots): Two seed leaves, net-like leaf veins, flower petals in multiples of 4 or 5. Examples: beans, roses, apples, humans (yes, we eat dicot fruits and seeds).
Viruses have only two features: a protein coat (capsid) and genetic material (DNA or RNA inside). They do NOT have: cytoplasm, ribosomes, or the ability to reproduce independently. Viruses can only replicate by invading a host cell and hijacking its machinery. For this reason, most biologists do NOT classify viruses as living organisms. They're on the borderline between life and chemistry.
A dichotomous key is a tool for identifying organisms. At each step, you choose between two statements and follow the instruction. Example:
1a. Has feathers โ Go to 2
1b. Has fur โ It's a mammal
2a. Can fly โ It's a bird
2b. Cannot fly โ Go to 3
3a. Lays eggs โ It's a flightless bird (penguin, kiwi)
3b. Gives birth to live young โ Not a bird
Dichotomous keys use observable features. Examiners expect you to be able to both use a key AND create one from a set of organisms.
These definitions use exact wording expected in Cambridge mark schemes. Click each term to reveal.
Amoeba is a single-celled organism. Explain why Amoeba is classified as a living organism by referring to the seven characteristics of life.
โ Amoeba can move by using pseudopodia (false feet) to change position [1 mark]
โ Amoeba respires โ it breaks down nutrients to release energy for metabolism [1 mark]
โ Amoeba is sensitive โ it can detect food particles and move toward them [1 mark]
โ Amoeba grows, reproduces by binary fission, excretes waste, and takes in nutrition by engulfing food particles [1 mark โ any one of these additional characteristics]
The scientific name of the domestic dog is Canis lupus familiaris. Explain why it is classified as a mammal and not as a bird.
โ A dog has hair/fur, whereas birds have feathers [1 mark]
โ A dog produces milk to feed its young, whereas birds do not [1 mark]
Use the dichotomous key below to identify organism A (described as: has 6 legs, has wings, cannot fly).
1a. Has more than 4 legs โ Go to 2
1b. Has 4 or fewer legs โ Go to 3
2a. Has 6 legs and wings โ Go to 4
2b. Has more than 6 legs โ It is a myriapod
3a. Has 8 legs โ It is an arachnid
3b. Has fewer than 8 legs โ It is a vertebrate
4a. Can fly โ It is an insect
4b. Cannot fly โ It is a flightless bird
โ Start at 1. Has 6 legs (more than 4) โ Go to 2 [1 mark]
โ At 2. Has 6 legs and wings โ Go to 4 [1 mark]
โ At 4. Cannot fly โ Organism A is a flightless bird [1 mark]
Lions and tigers can produce offspring called ligers, but ligers are sterile (cannot produce offspring). Explain why lions and tigers are classified as separate species.
โ A species is defined as organisms that can interbreed to produce fertile offspring [1 mark]
โ Ligers are sterile, so lions and tigers do not produce fertile offspring together, so they are separate species [1 mark]
Which of the following is NOT a characteristic of all living organisms?
Which kingdom includes organisms that digest food externally and have cell walls made of chitin?
Classify a domestic cat (Felis catus) as: (a) a vertebrate or invertebrate, and (b) state two characteristics that support this classification.
Explain why respiration is a characteristic of living organisms but photosynthesis is not.
In binomial naming, which part of the name is capitalized?
A moss plant and a flowering plant both have roots, stems, and leaves. Explain why the flowering plant is classified in a different group.
Construct a dichotomous key to identify three organisms: a spider (8 legs, no wings), an insect (6 legs, has wings), and a fish (no legs, has scales).
Which of the following is a feature of monocotyledonous plants?
Explain the difference between movement and sensitivity as characteristics of living organisms, using an example for each.
Explain why DNA base sequences are used to classify organisms and relate this to evolutionary relationships.
Characteristics and Classification typically appear in Paper 1 (MCQ + short answer) and Paper 2 (structured long answer). Budget 15โ20 minutes total. These are foundational questions โ get them right and you have momentum.
Paper 1 (MCQ): 3โ5 questions on the seven characteristics, kingdom identification, vertebrate vs. invertebrate, binomial naming.
Paper 2 (Long Answer): 1 structured question (e.g., "Explain why organism X is classified as Y" or "Construct a key to identify these three organisms").
Paper 6 (Practical): Rarely tested in this topic, but if there's a practical on classifying organisms or using keys, know how to do it.
"State" โ Brief factual answer (e.g., "State two features of mammals").
"Describe" โ Give details (e.g., "Describe the seven characteristics of living organisms").
"Explain" โ Say WHY (e.g., "Explain why lions and tigers are separate species").
"Classify" โ Put into a group with reasons (e.g., "Classify this organism as a vertebrate because...").
โข Remember the seven characteristics: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition (MRS GRE-N)
โข Always compare features when classifying (e.g., "feathers vs. fur," "scales vs. skin")
โข Practice dichotomous keys โ draw or write them out to get comfortable with the logic
โข Binomial naming: Always check your capitalization and italics
โข Know the five kingdoms and one key feature of each
Tick off each objective as you master it. These are the exact learning objectives from the Cambridge 0610 syllabus (2026-2028).
All living organisms are made of cells. The cell is the smallest unit that can carry out all the functions of life. You cannot have a living organism smaller than a cell (though some organisms like bacteria ARE single cells). In IGCSE, you must know three types of cells in detail: plant cells, animal cells, and bacterial cells.
Structures found in BOTH plant and animal cells:
Cell membrane (partially permeable membrane): Surrounds the cytoplasm. Controls what enters and leaves the cell. In plant cells, it's inside the cell wall.
Cytoplasm: A jelly-like substance filling the cell. Contains many organelles (tiny structures inside the cell). Chemical reactions happen here, including respiration and photosynthesis. It's not just empty space โ it's where most cellular work occurs.
Nucleus: Contains genetic material (DNA) organized into chromosomes. Controls the cell's activities and growth. NOT present in bacterial cells.
Ribosomes: Tiny structures where proteins are made (protein synthesis). Found in all cells including bacteria. They're not membrane-bound organelles.
Mitochondria (plural; singular: mitochondrion): The "power station" of the cell. Site of aerobic respiration, where glucose is broken down to release energy. ALL cells (plant, animal, bacteria) have mitochondria because all cells need energy. Animal cells typically have more mitochondria than plant cells because animals are generally more active.
Structures found ONLY in plant cells:
Cell wall: A rigid layer outside the cell membrane, made of cellulose. Provides structural support and protection. Plant cells would burst without it. Animal cells do NOT have cell walls (though bacterial cells do, made of different material).
Chloroplasts: Where photosynthesis happens. Contains chlorophyll (the green pigment). Only in plant cells (and some protoctists) because only these organisms photosynthesize. NOT found in animal cells or bacteria.
Large permanent vacuole: Filled with cell sap (water + dissolved ions and sugars). Maintains turgor pressure (firmness of the plant). When a plant wilts, water has left the vacuole. Animal cells have small, temporary vacuoles. Bacterial cells have no vacuoles.
Bacteria are MUCH smaller than plant or animal cells (bacteria: 0.5โ5 ฮผm; animal cell: 20โ30 ฮผm). Key features:
No nucleus: Genetic material (circular DNA) is in a region called the nucleoid, not enclosed by a membrane.
Plasmids: Small, circular pieces of DNA separate from the main chromosome. Used in genetic engineering (scientists can insert genes into plasmids).
Cell wall: Made of peptidoglycan (NOT cellulose like plants). Rigid, provides structure.
Ribosomes: Smaller than eukaryotic ribosomes (prokaryotic vs. eukaryotic โ this detail is supplementary).
No membrane-bound organelles: No mitochondria, no chloroplasts (but some bacteria photosynthesize using structures called thylakoids, not enclosed in chloroplasts).
Cells are too small to see with the naked eye. We use microscopes. The magnification formula is:
Magnification = Image size รท Actual size
Example: If a cell's actual diameter is 0.05 mm and the image under a microscope is 5 mm, then magnification = 5 รท 0.05 = 100ร
When converting units, remember: 1 mm = 1000 ฮผm (micrometres). Always convert to the same unit before calculating.
Cells in multicellular organisms become specialized (adapted for specific functions). You must know six examples:
1. Ciliated cells (in the trachea and bronchi): Have cilia (tiny, hair-like projections). Beat in coordinated waves to move mucus up the trachea, trapping pathogens. Hundreds of cilia per cell.
2. Root hair cells (in plant roots): Elongated, with a large surface area. Absorb water and mineral ions from soil. The "hair" extension greatly increases surface area for absorption.
3. Palisade mesophyll cells (in leaves): Packed with chloroplasts. Narrow and tall to maximize light absorption. Site of most photosynthesis in the leaf. Positioned just below the leaf's upper epidermis where light is strongest.
4. Neurones (nerve cells): Have a cell body, axon (long extension), and dendrites (branched extensions). Conduct electrical impulses over long distances. Adapted for rapid communication.
5. Red blood cells (mammalian): Biconcave disc shape maximizes surface area for oxygen absorption. NO nucleus in mature red blood cells (unusual!), so more space for hemoglobin. Deformable, so they can squeeze through tiny capillaries.
6. Sperm and egg cells (gametes): Have half the chromosomes of other cells. Sperm have a flagellum (tail) for movement and many mitochondria for energy. Eggs are large, packed with nutrients for the developing embryo.
Cell: The basic unit (e.g., a muscle cell).
Tissue: A group of similar cells with the same function (e.g., cardiac muscle tissue = many cardiac muscle cells working together).
Organ: A structure made of different tissues working together (e.g., the heart = cardiac muscle tissue + connective tissue + nervous tissue).
Organ system: Multiple organs working together (e.g., the circulatory system = heart + blood vessels + blood).
Organism: A complete living individual made of many organ systems (e.g., a human).
A plant cell has a cell wall, but an animal cell does not. Explain why a plant cell has a cell wall and state two functions of the cell wall.
โ Plants are stationary (do not move around) and need rigid structure to support their stems and leaves against gravity [1 mark]
โ Function 1: Provides structural support and rigidity [1 mark]
โ Function 2: Protects the cell / prevents excessive water loss / maintains shape [1 mark โ accept any one]
A cell is observed under a microscope. The image is 8 mm wide. The actual cell is 0.04 mm wide. Calculate the magnification.
Magnification = Image size รท Actual size
Magnification = 8 รท 0.04
โ Magnification = 200ร [1 mark for method, 1 mark for correct answer]
Root hair cells are adapted for absorption of water. Describe two adaptations and explain how each adaptation helps water absorption.
โ Adaptation 1: Long, thin extension (hair). Explanation: Increases surface area for water absorption [1 mark]
โ Adaptation 2: Many mitochondria. Explanation: Produce ATP for active transport of mineral ions, which lowers water potential and causes water to move in by osmosis [1 mark]
โ Alternative: Thin cell wall and cell membrane close to root hair surface for rapid water uptake [1 mark]
Compare a plant cell and a bacterial cell. State four ways in which they are different.
โ Plant cell has a nucleus; bacterial cell does not / bacterial cell has nucleoid region [1 mark]
โ Plant cell has chloroplasts; bacterial cell does not [1 mark]
โ Plant cell has large vacuole; bacterial cell has no vacuole [1 mark]
โ Plant cell has mitochondria in cytoplasm (in organelle); bacterial cell has no mitochondria / bacterial cell has smaller ribosomes [1 mark โ accept difference in ribosome size or any other valid difference]
Which organelle is responsible for releasing energy in all cells?
Which of the following is found in a bacterial cell but NOT in an animal cell?
An image of a cell under a microscope is 5 mm. The actual cell is 0.02 mm. Calculate the magnification.
State two features of the nucleus and explain their importance to the cell.
Convert 50 micrometres (ฮผm) into millimetres (mm).
Palisade mesophyll cells contain many more chloroplasts than other plant cells. Explain why.
Describe the levels of organization in a multicellular organism, starting from the cell, using the human circulatory system as an example.
Which cell structure controls which substances can enter and leave a cell?
Red blood cells do not have a nucleus, but they still function. Explain how a red blood cell can function without a nucleus.
Compare and contrast plant cells and bacterial cells. State three differences.
Cell structure questions appear heavily in Paper 1 (MCQ identifying organelles) and Paper 2 (structured questions on specialised cells). Budget 20โ25 minutes total. This is foundational โ every other topic builds on cell structure knowledge.
You MUST be able to: (1) Label a plant cell diagram, (2) Label an animal cell diagram, (3) Label a bacterial cell diagram. In the exam, you'll be given an unlabeled diagram and asked to identify structures. Practice this repeatedly until you can do it without thinking.
Magnification calculations appear in every exam. Remember: units must be the same before dividing. Practice converting mm โ ฮผm repeatedly.
โข Know the organelles and their ONE main function each
โข Remember plant cells have Wall and Chloroplasts (W+C = Green & rigid)
โข Bacteria = no nucleus, no mitochondria, no chloroplasts (except some)
โข All cells need mitochondria for energy
โข All cells have ribosomes for protein synthesis
Tick off each objective as you master it.
In IGCSE, you MUST understand three mechanisms: diffusion, osmosis, and active transport. They're tested in every exam and are crucial to understanding how organisms work.
Definition: The net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e., down a concentration gradient), as a result of their random movement.
Key points:
โข Particles are ALWAYS moving randomly (due to kinetic energy from heat)
โข More particles are in the high-concentration region, so statistically more cross the boundary toward the low-concentration region than the reverse
โข Net movement continues until concentration is equal everywhere (equilibrium)
โข DOES NOT require ATP (energy) โ it uses kinetic energy from random motion
โข Examples: Oxygen diffusing from air into blood in lungs; COโ diffusing out of cells into blood
Factors speeding up diffusion:
โข Higher temperature โ particles move faster
โข Larger surface area โ more space for particles to cross
โข Steeper concentration gradient โ bigger difference on each side
โข Shorter distance โ particles reach destination faster
Definition (Core): Water diffuses through partially permeable membranes by osmosis.
Definition (Supplement): The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.
Key points:
โข Osmosis is JUST diffusion of water molecules
โข The cell membrane is selectively permeable โ water and some small molecules cross, but large dissolved molecules (like glucose) do NOT
โข Water potential is a measure of how many water molecules are "free" to move. A dilute solution has higher water potential (more free water); a concentrated solution has lower water potential (fewer free water molecules because they're surrounded by dissolved particles)
โข Water always moves toward the concentrated solution (lower water potential)
โข Does NOT require energy
In plant cells: When a plant cell is placed in a dilute solution (or pure water), water enters by osmosis. The vacuole fills, pushing the cytoplasm and cell membrane against the cell wall. This pressure is called turgor pressure. The cell becomes firm and rigid โ this is how plants stand up.
Plant cell in concentrated solution: Water leaves the vacuole. The cytoplasm shrinks away from the cell wall. This is called plasmolysis. The cell becomes flaccid (limp). If left too long, the cell dies.
Animal cell in different solutions: Animal cells have no cell wall, so osmosis has different effects:
โข In dilute solution (hypotonic): Water enters faster than it leaves. The cell swells and bursts (lyses) โ cell destruction.
โข In concentrated solution (hypertonic): Water leaves faster than it enters. The cell shrivels (crenation).
โข In isotonic solution: Water moves in and out at equal rates. The cell is balanced.
Definition: The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (against a concentration gradient), using energy from respiration.
Key points:
โข Moves substances UP the concentration gradient (opposite of diffusion)
โข REQUIRES ATP from respiration
โข Requires protein carriers in the cell membrane
โข Much slower than diffusion but essential for life
Why is active transport important?
โข Cells need to absorb specific ions even when they're scarce outside (e.g., plants absorb nitrogen from soil by active transport)
โข Glucose is absorbed in the small intestine against the concentration gradient
โข Nerve cells use active transport to maintain ion gradients needed for electrical signals
โข Root hair cells actively transport mineral ions from soil solution
Water dissolves many substances, making it the "solvent of life." This is critical for:
โข Digestion: Enzymes work on dissolved food
โข Excretion: Urea and excess ions dissolve in water and are removed
โข Transport: Glucose and oxygen dissolve in blood for transport
A plant cell is placed in pure water. Describe what happens and explain in terms of osmosis.
โ The cell absorbs water / becomes turgid / becomes firm [1 mark]
โ Water has higher water potential than the cell sap inside the vacuole [1 mark]
โ Water moves by osmosis across the partially permeable cell membrane into the vacuole [1 mark]
Explain why root hair cells have many mitochondria.
โ Root hair cells carry out active transport to absorb mineral ions / move ions against the concentration gradient [1 mark]
โ This requires ATP / energy from respiration, which mitochondria produce [1 mark]
A potato chip is placed in a concentrated salt solution. Describe and explain what happens to the potato tissue.
โ The potato becomes soft / limp / floppy [1 mark]
โ The salt solution has a lower water potential than the cell sap [1 mark]
โ Water moves out by osmosis, the cell becomes plasmolyzed / loses turgor [1 mark]
Distinguish between diffusion and active transport.
โ Diffusion is movement down a concentration gradient (high to low) without energy; active transport is movement against the concentration gradient (low to high) using energy [1 mark]
โ Diffusion is passive (random motion); active transport requires ATP from respiration [1 mark]
Which of the following requires energy (ATP) from respiration?
Water moves into a plant cell placed in pure water. Which of the following best describes this movement?
Name the process by which oxygen enters red blood cells and carbon dioxide leaves them.
Explain why a plant wilts when the soil is very dry.
Which statement about diffusion is correct?
Explain why glucose absorption in the small intestine often requires active transport.
Describe the effect of temperature on the rate of diffusion and explain why.
What does the term "plasmolysis" describe in a plant cell?
Compare what happens to an animal cell and a plant cell when placed in pure water.
Explain why root hair cells are adapted for active transport of mineral ions.
Transport processes are tested in Paper 1 (MCQ, practical reasoning) and Paper 2 (long-answer explanations). Budget 20โ25 minutes total. This topic is fundamental โ it explains how ALL substances enter and leave cells.
"Describe" = State what happens (e.g., "Describe what happens when a plant cell is placed in concentrated salt solution").
"Explain" = Give reasons (e.g., "Explain why active transport is needed in root hair cells").
"Distinguish" = State differences between two processes (e.g., "Distinguish between diffusion and osmosis").
โข Diffusion & osmosis = passive (no ATP); active transport = active (requires ATP)
โข Always mention "concentration gradient" or "water potential" when explaining
โข Remember: water moves toward LOWER water potential
โข Know the four factors affecting diffusion rate: temperature, concentration gradient, surface area, distance
โข Plasmolysis happens in plants (hypertonic solution); lysis happens in animals (hypotonic solution)
Tick off each objective as you master it.
All living things are made of billions of cells, but cells are made of just four types of macromolecules: carbohydrates, lipids (fats), proteins, and nucleic acids. You must know their building blocks, functions, and how to test for them.
Chemical elements: Carbon (C), Hydrogen (H), Oxygen (O). Always in a ratio of roughly C:H:O = 1:2:1. Example: glucose is CโHโโOโ.
Monomers (small molecules): Simple sugars like glucose and fructose.
Polymers (large molecules):
โข Starch: In plants, stores glucose as a compact polymer for energy (found in potatoes, grains).
โข Glycogen: In animals, stores glucose for quick energy (found in liver and muscles).
โข Cellulose: In plants, structural component of cell walls. Very strong because the glucose units are linked differently than in starch, making it insoluble and rigid.
Test for starch: Add iodine solution โ blue-black color = starch present (orange/brown = starch absent).
Test for reducing sugars (glucose, fructose): Add Benedict's solution and heat โ brick-red precipitate = reducing sugar present (stays blue = absent).
Chemical elements: Carbon (C), Hydrogen (H), Oxygen (O) โ same elements as carbohydrates, but in different proportions. Lipids have much more C and H, less O.
Building blocks: Fatty acids + glycerol. A fat molecule has one glycerol backbone attached to three fatty acids (a "triglyceride").
Functions:
โข Energy storage (9 kcal per gram โ more than twice that of carbohydrates at 4 kcal/g)
โข Insulation (subcutaneous fat in mammals)
โข Cell membrane (phospholipids form the bilayer)
โข Hormone signaling (some hormones are lipid-based)
Test for fats/oils: Add ethanol, shake, then add water โ white emulsion = fat present (stays clear = absent).
Chemical elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N). Some proteins also contain Sulfur (S).
Building blocks: Amino acids (20 different types). Amino acids link together in chains via peptide bonds.
Functions (this is tested heavily):
โข Enzymes โ catalyze (speed up) chemical reactions
โข Antibodies โ fight infections
โข Hemoglobin โ carries oxygen in blood
โข Muscle (actin, myosin) โ enable movement
โข Collagen โ provides strength in skin and bone
โข Hormones (some) โ regulate body processes
Test for proteins: Add biuret test (alkaline copper(II) solution) โ purple/violet color = protein present (blue = absent).
For Core, you just need to know structure. For Supplement, you need detail.
DNA (Deoxyribonucleic Acid):
โข Two strands coiled together in a double helix (like a twisted ladder)
โข Each strand is made of nucleotides joined together
โข The "sides" of the ladder are made of sugar (deoxyribose) and phosphate
โข The "rungs" of the ladder are made of base pairs
โข Four bases: A (adenine), T (thymine), G (guanine), C (cytosine)
โข Base pairing rule: A always pairs with T; G always pairs with C
โข This base pairing allows DNA to copy itself and pass genetic information to offspring
Vitamins are small organic molecules needed in tiny amounts for health:
โข Vitamin C (ascorbic acid): In fruits/vegetables, prevents scurvy (bleeding gums, slow healing).
โข Vitamin D: Helps calcium absorption; deficiency causes rickets (weak bones).
Test for Vitamin C: Add DCPIP (a blue dye) โ DCPIP decolorizes (turns clear) = Vitamin C present (stays blue = absent).
A food sample is tested with iodine solution and turns blue-black. What does this indicate and which molecule is present?
โ The sample contains starch / carbohydrate [1 mark]
โ Iodine reacts with starch molecules to form a blue-black color [1 mark]
Fats have a higher energy content than carbohydrates. Explain why this is important for animals.
โ Fats provide 9 kcal per gram; carbohydrates provide only 4 kcal per gram [1 mark]
โ Animals can store more energy in less mass (space and weight saving) [1 mark]
โ This is important for movement, insulation, and survival during periods of food scarcity [1 mark]
Describe the structure of a DNA molecule.
โ DNA consists of two strands coiled together to form a double helix [1 mark]
โ Each strand contains bases that pair together: A with T, and G with C, held by hydrogen bonds [1 mark]
Proteins have many different functions in organisms. State the chemical elements present in all proteins and name two different functions.
โ Chemical elements: Carbon, Hydrogen, Oxygen, and Nitrogen [1 mark โ may also mention Sulfur]
โ Function 1: Enzymes catalyze chemical reactions [1 mark]
โ Function 2: Antibodies defend against pathogens / Hemoglobin carries oxygen / Muscle proteins enable movement / Structural support [1 mark โ accept any two]
Which of these elements is present in proteins but NOT in carbohydrates?
Which molecule is used to store energy in animal cells?
A food sample is heated with Benedict's solution. The solution turns brick-red. What does this indicate?
Explain why fats are described as having twice the energy density of carbohydrates.
Which test would you use to identify the presence of protein in a food sample?
Explain how DNA is able to pass genetic information from one generation to the next.
Describe the functions of three different proteins in the human body.
Which test would you use to confirm that a liquid contains vitamin C?
Explain why cellulose cannot be digested by humans, even though it is made of glucose units.
A food sample is tested with several reagents. Iodine turns blue-black, Benedict's solution produces a brick-red precipitate when heated, and biuret solution turns purple. What organic molecules are present?
Biological molecules are tested in Paper 1 (MCQ on tests and molecule identification) and Paper 4 (practicals with food testing). Budget 15โ20 minutes total. Most questions are straightforward if you know the tests.
Iodine โ STARCH (blue-black) | Benedict's โ SUGAR (brick-red, heated) | Biuret โ PROTEIN (purple) | Ethanol โ FAT (white emulsion) | DCPIP โ VITAMIN C (decolorizes)
โข Know which macromolecule contains which elements (C,H,O = carbs/fats; +N = protein)
โข Starch (energy) vs. cellulose (structure) โ different glucose types, different functions
โข Fats = 9 kcal/g; carbs = 4 kcal/g (memorize this ratio)
โข DNA = double helix with A-T, G-C pairing
โข Proteins are made of 20 amino acids linked by peptide bonds
Tick off each objective as you master it.
Life exists because of enzymes. Without enzymes, chemical reactions in cells would be too slow to sustain life. An enzyme is a protein that speeds up (catalyzes) a chemical reaction WITHOUT being changed by the reaction itself. Enzymes are REUSABLE โ one enzyme molecule can catalyze thousands of reactions per second.
At body temperature (37ยฐC), most chemical reactions that keep us alive happen too slowly. For example, breaking down glucose into energy should take days without an enzyme, but with the enzyme glucose oxidase, it happens in milliseconds. Enzymes lower the activation energy โ the energy barrier that molecules must overcome to react.
Without enzymes:
โข Digestion would take weeks
โข Photosynthesis would not happen
โข Respiration would be too slow to provide energy
โข DNA copying would fail
โข We would be dead
Think of an enzyme like a lock and its substrate (the molecule being acted on) like a key.
The active site is the region on the enzyme where the substrate binds. It has a specific 3D shape that is COMPLEMENTARY to the substrate's shape (like a key fitting into a lock).
The process:
1. Substrate approaches the enzyme and binds to the active site
2. An enzyme-substrate complex forms (substrate + enzyme together)
3. The enzyme catalyzes the reaction
4. Products are released
5. The enzyme is unchanged and ready for another reaction
Each enzyme catalyzes only ONE reaction. Amylase breaks down starch, but not cellulose. Lactase breaks down lactose, but not sucrose. This specificity comes from the unique 3D shape of the active site โ only the right substrate "key" fits. If the shape doesn't match, no reaction happens. This is why a person who is lactose-intolerant lacks the enzyme lactase โ they cannot digest milk sugar.
1. Temperature: As temperature increases from 0ยฐC to the enzyme's optimum (usually ~37ยฐC in humans), enzyme activity INCREASES. Substrate molecules move faster, collisions increase, and more reactions occur per second.
BUT if temperature rises ABOVE the optimum, enzyme activity DROPS sharply. Why? The heat breaks the 3D structure of the enzyme (denaturation). The active site loses its shape, and substrates no longer fit. Denaturation is irreversible โ once an enzyme is denatured, it cannot recover.
2. pH: Each enzyme has an optimum pH. Pepsin (works in stomach acid) has an optimum pH of 2. Trypsin (works in small intestine) has an optimum pH of 8. Outside the optimum, enzyme activity falls because the pH denatures the protein structure.
3. Substrate Concentration: If you increase substrate concentration while enzyme concentration stays constant, the reaction rate increases โ until all enzyme active sites are occupied. Beyond this point, adding more substrate has no effect (the enzyme is saturated).
4. Enzyme Concentration: More enzyme molecules = more active sites = faster reaction (assuming substrate is plentiful).
Explain how an enzyme catalyzes a reaction, referring to the active site and substrate.
โ The substrate has a shape complementary to the enzyme's active site [1 mark]
โ The substrate binds to the active site, forming an enzyme-substrate complex [1 mark]
โ The enzyme catalyzes the reaction to form a product, which is released; the enzyme is unchanged and can catalyze another reaction [1 mark]
Describe the effect of temperature on enzyme activity and explain what happens above the optimum temperature.
โ Between 0ยฐC and the optimum (~37ยฐC), enzyme activity increases / molecules move faster and collisions increase [1 mark]
โ At the optimum, enzyme activity is at maximum [1 mark]
โ Above the optimum, enzyme activity decreases sharply because the enzyme is denatured / the active site loses its shape and can no longer bind substrate [1 mark]
Explain why each enzyme can only catalyze one specific reaction.
โ Each enzyme has an active site with a specific 3D shape [1 mark]
โ Only the correct substrate (with a complementary shape) can fit into the active site and bind, so only one type of reaction can be catalyzed [1 mark]
Why are enzymes important for maintaining life in organisms?
โ Enzymes speed up metabolic reactions so they occur fast enough to sustain life [1 mark]
โ Without enzymes, reactions like digestion, respiration, and photosynthesis would be too slow and life could not be maintained [1 mark]
Which of the following best describes an enzyme?
Why can enzymes only catalyze one specific reaction?
Describe what happens to an enzyme when it is heated above its optimum temperature.
Explain why enzymes are essential for life.
A student says "This enzyme is destroyed when heated to 60ยฐC." What term should be used instead?
Explain why pepsin (an enzyme in the stomach) works best at pH 2, while trypsin (an enzyme in the small intestine) works best at pH 8.
Describe the process by which an enzyme catalyzes a reaction, using the terms "active site," "substrate," and "product."
Why are enzymes not consumed in the reactions they catalyze?
A person cannot digest milk because they lack the enzyme lactase. Explain why lactase is necessary.
A student investigates how temperature affects enzyme activity. Explain why enzyme activity increases from 0ยฐC to 37ยฐC but then decreases above 37ยฐC.
Enzymes are tested across all papers: Paper 1 (MCQ on enzyme properties), Paper 2 (long-answer explanations of specificity and denaturation), Paper 4 (enzyme kinetics practicals). Budget 20โ25 minutes total. This is one of the most-tested topics in IGCSE Biology.
1. Enzymes speed up reactions without being changed (they're catalysts). 2. Each enzyme is specific because its active site shape fits only one substrate. 3. Temperature and pH affect enzyme shape โ above optimum, denaturation makes the enzyme non-functional.
โข Enzyme = protein that catalyzes reactions (always mention both "protein" and "catalyst")
โข Active site = the part where substrate binds (mention "complementary shape" or "lock and key")
โข Denaturation = irreversible loss of 3D structure (NOT temporary)
โข Optimum temperature for humans = 37ยฐC
โข Always explain enzyme specificity by mentioning the active site shape
Tick off each objective as you master it. These are the exact learning objectives from Cambridge IGCSE Biology 0610 (2026-2028).
Photosynthesis is the most important biochemical reaction in the biosphere. Plants use sunlight energy to convert simple inorganic molecules (COโ and HโO) into glucose, a complex organic compound. This process feeds nearly all life on Earth.
Understanding the concept of light-dependent and light-independent reactions helps retention:
Photosynthesis is limited by whichever factor is in shortest supply:
Every structure in a leaf is an adaptation:
Write the word equation for photosynthesis and state the conditions needed.
carbon dioxide + water โ glucose + oxygen
Marking: 1 mark reactants, 1 mark products, 1 mark conditions. Don't forget conditions โ they're worth a mark.
Explain how the large surface area of a leaf is an adaptation for photosynthesis.
Always link structure to function to function outcome for full marks.
A graph shows photosynthesis rate vs. light intensity. The curve plateaus at high light intensity. Explain why.
An aquatic plant is placed in hydrogencarbonate indicator. In light, solution turns orange/red; in darkness, turns yellow. Explain.
Indicator key: Yellow = high COโ, Orange/Red = low COโ
Memorise which colour means what: light=orange (less COโ), dark=yellow (more COโ).
Always link structure to function to outcome. Don't just state facts โ explain WHY they matter.
Physical: Teeth chew, stomach churns. Molecules unchanged, just broken into pieces. Increases surface area for enzymes.
Chemical: Enzymes break chemical bonds. Produces small soluble molecules that can be absorbed.
Contains correct proportions of carbs (energy), fats (energy, insulation), proteins (growth/repair), vitamins (functions vary), minerals (functions vary), fibre (gut health), water (transport). Proportions depend on age, sex, activity, metabolism.
Describe the role of amylase in digestion. Where is it secreted and where does it work?
Always give complete answer: where made AND where it acts.
Describe the function of the stomach in physical digestion.
This question asks about physical digestion only, not chemical.
Describe the structure of a human tooth and explain how teeth are adapted for different digestion types.
Structure: Enamel (outer), dentine (middle), pulp (nerves/blood), cement (anchors to bone); embedded in gums
Adaptations:
Explain the causes of scurvy and rickets and suggest prevention.
Scurvy: Vitamin C deficiency โ collagen can't be made โ connective tissue weak. Prevent with citrus/berries
Rickets: Vitamin D deficiency โ calcium not absorbed โ bones weak. Prevent with sunlight/oily fish
Scurvy = C, Rickets = D. Don't confuse them โ this is a common exam error.
Describe how the structure of a villus is adapted for absorption of nutrients.
Wrong: "Amylase breaks down starch"
Right: "Amylase, secreted by salivary glands and pancreas, breaks down starch in mouth and small intestine"
| Vitamin | Source | Function | Deficiency |
|---|---|---|---|
| C | Citrus, berries | Collagen synthesis | Scurvy |
| D | Sunlight, oily fish | Calcium absorption | Rickets |
Root hair cells have large surface area for absorption of water (by osmosis) and mineral ions (by active transport). Water travels: root hair โ root cortex cells โ xylem vessels โ stem xylem โ leaf mesophyll cells.
Plants constantly lose water as water vapour through stomata (transpiration). This isn't waste โ it drives water uptake from roots (transpiration pull). Water evaporates from mesophyll cell surfaces into air spaces, then diffuses out through stomata as vapour.
Sucrose and amino acids made in leaves (sources) are transported through phloem to regions that use them (sinks: roots, flowers, fruits, young leaves). Some parts act as source AND sink at different times (e.g., a potato tuber is a sink when storing, a source when sprouting).
Describe the functions of xylem and phloem and explain why they are separate systems.
Explain how the structure of a root hair cell is adapted for water and mineral ion absorption.
Explain the mechanism by which water vapour is lost from leaves during transpiration.
Key: evaporation โ diffusion through stomata. Both steps needed for full mark.
Explain how increased temperature increases the rate of transpiration.
Explain why a potato tuber can act as both a source and a sink in translocation.
| Feature | Xylem | Phloem |
|---|---|---|
| What | Water + minerals | Sucrose + amino acids |
| Direction | Upwards only | Both directions |
| Cells | Dead (hollow) | Living |
| Transport type | Passive | Active |
High temperature/wind/low humidity โ faster water evaporation โ larger concentration gradient โ faster diffusion through stomata โ faster transpiration rate
Be familiar with potometers (measure water uptake as proxy for transpiration). Variables: temperature, wind speed, humidity affect rate. Typical exams ask you to interpret graphs showing these effects.
Single circulation (fish): Heart โ body โ heart (blood passes through capillaries once before returning)
Double circulation (mammal): Heart โ lungs โ heart โ body โ heart (two separate circuits). Advantage: blood reaches body at higher pressure (more oxygen delivery); allows for greater metabolic rate needed by mammals.
Atherosclerosis (buildup of cholesterol/plaque) narrows coronary arteries โ blood flow blocked โ heart muscle oxygen-starved โ chest pain (angina) or heart attack. Risk factors: high cholesterol diet, smoking, lack of exercise, stress, genetic predisposition, age, sex (higher in males).
Compare the structure and function of single and double circulation systems. Explain the advantage of double circulation.
Single (fish): One circuit. Blood passes through capillaries once before returning.
Double (mammal): Two circuits. Blood passes through lungs first, returns to heart, then goes to body.
Describe the function of the atrioventricular valves in the heart.
Always mention both functions: allow forward flow AND prevent backflow.
Explain how the structure of a capillary is adapted for exchange of substances between blood and tissues.
Describe the functions of red blood cells, white blood cells, platelets, and plasma.
Each one needs a distinct function. Don't say "plasma carries blood cells" AND white blood cells are in plasma โ they're separate things.
Explain what coronary heart disease is and list three risk factors. Suggest how diet and exercise can reduce risk.
Risk factors (list 3 of 7): High cholesterol diet, smoking, lack of exercise, stress, genetic predisposition, age, male sex
Prevention: Diet: reduce cholesterol/saturated fat. Exercise: strengthens heart, improves circulation, reduces stress.
| Vessel | Wall Thickness | Lumen | Valves | Pressure |
|---|---|---|---|---|
| Artery | Thick | Narrow | No | High |
| Vein | Thin | Wide | Yes | Low |
| Capillary | Very thin | Very narrow | No | Medium |
Don't say "all arteries carry oxygenated blood." The pulmonary ARTERY carries deoxygenated blood to lungs. It's PRESSURE (not oxygen) that defines an artery.
Bacteria, viruses, fungi, and parasites can cause disease. They are transmitted directly (blood, saliva, sexual contact) or indirectly (contaminated food/water, surfaces, air droplets, insect vectors). Not all bacteria are pathogens โ most are harmless or beneficial.
Weakened or inactive pathogen/antigens injected โ immune response โ memory cells produced โ future exposure triggers fast immune response โ disease prevented. This is WHY vaccination is effective: memory cells exist before infection.
Antibodies received from another individual (through placenta, breast milk, blood transfusion, antivenom). Provides immediate protection BUT no memory cells โ lasts weeks/months only. Useful for newborns (breast milk) or post-exposure (antitoxins, antivenoms).
Bacterium (Vibrio cholerae) transmitted via contaminated water. Produces toxin in small intestine โ causes chloride ion secretion โ osmotic movement of water into gut โ severe watery diarrhoea โ dehydration and ion loss.
Explain the difference between direct and indirect transmission of pathogens. Give one example of each.
Describe five non-specific body defences against pathogen entry and explain how each works.
Compare active and passive immunity. Explain how vaccination generates active immunity and why this provides long-term protection.
Active immunity: Antibodies made by your own immune system โ long-term (memory cells persist)
Passive immunity: Antibodies acquired from external source โ short-term (no memory cells)
Vaccination:
This is why booster shots sometimes needed: memory cells fade over decades. But one vaccination provides years of protection.
Describe how cholera toxin causes diarrhoea and dehydration. How is cholera transmitted?
Transmission: Vibrio cholerae bacterium in contaminated water
Mechanism:
Key: it's the TOXIN, not the bacteria itself, that causes symptoms. Antibiotics kill bacteria but don't remove toxin already produced.
Explain the importance of breast-feeding for passive immunity in infants.
| Feature | Active | Passive |
|---|---|---|
| Source of antibodies | Your own body | Another individual |
| Memory cells? | Yes (long-term) | No (short-term) |
| Duration | Years/lifetime | Weeks/months |
| Examples | Infection, vaccination | Breast milk, antivenom |
Memorise this. It comes up every year in slightly different wording.
If asked about cholera mechanisms, follow this path:
Always mention the osmotic gradient โ that's the key to understanding why water is lost.
These appear in almost every exam year. Cambridge loves testing public health knowledge.