Top 200 Secondary 4 Biology Vocabulary

Secondary 4 Biology becomes easier when the words describe mechanisms rather than isolated facts. This guide explains 200 biology terms in ten groups: cells, enzymes, digestion, respiration, homeostasis, infection, plants, ecosystems, genetics and reproduction. Each group tells you what the vocabulary helps you understand, followed by examples, a four-week plan and answers to common questions.

The 2026 GCE O-Level Biology subject code is 6093. The corresponding 2027 Singapore-Cambridge SEC G3 Biology subject code is K325. The separate Combined Science Biology pathways have different codes and content depth. This is an independent curated learning glossary, not an official or compulsory 200-word list, and a few extension words are included to clarify important ideas.

What you can do with this page:

Read all 200 key terms immediately, with definitions in accessible language.
Understand why diffusion differs from osmosis, and why breathing differs from respiration.
Link cellular structures to whole-body systems and ecological relationships.
Practise simple biological interpretation using original examples and a four-week recall routine.
Check your exact examination syllabus and other eduKate science guides.

Top 200 Secondary 4 Biology Vocabulary Words with Simple Meanings

Vocabulary is useful when it connects a feature to a function or a process to an observable result. Try drawing each idea, explaining it aloud and applying it to a question you have not seen before.

1. Cells, microscopy and biological organisation — words 1–20

Biology grows from the cell to whole systems. When describing a specialised cell, connect a feature to the function it makes possible.

cell — The smallest unit capable of carrying out life processes.
cell membrane — The selectively permeable boundary of a cell.
cell wall — A supporting outer layer in plants and certain other organisms.
cytoplasm — Cell contents outside the nucleus where many reactions occur.
nucleus — The compartment containing most genetic material in eukaryotic cells.
mitochondrion — An organelle where much aerobic respiration occurs.
ribosome — The cellular structure that builds proteins from amino acids.
chloroplast — The organelle in plants where photosynthesis occurs.
vacuole — A membrane-bound compartment used for storage and other functions.
cellulose — A structural carbohydrate forming much of plant cell walls.
organelle — A specialised structure carrying out a function within a cell.
unicellular — Consisting of one cell.
multicellular — Consisting of many cooperating cells.
cell differentiation — The development of specialised cell structure and function.
specialised cell — A cell adapted to perform a particular task.
tissue — A group of similar cells working together.
organ — A structure made from tissues performing particular functions.
organ system — Organs working together in a broader life function.
magnification — Apparent image size divided by actual object size.
resolution — Ability to distinguish two nearby points as separate.

2. Molecules, enzymes and movement of substances — words 21–40

Enzymes are catalysts, not fuel. Membrane movement is about gradients and transport mechanisms; distinguish diffusion, osmosis and active transport.

carbohydrate — An organic molecule used in energy supply and other functions.
protein — A molecule made of amino-acid chains with diverse functions.
lipid — An organic class including fats and oils.
amino acid — A building block of proteins.
glucose — A simple sugar commonly used by cells in respiration.
starch — A plant storage carbohydrate made from glucose units.
glycogen — An animal storage carbohydrate made from glucose units.
enzyme — A biological catalyst that accelerates a reaction.
active site — The enzyme region where a substrate binds.
substrate — The substance an enzyme acts upon.
denaturation — Loss of a protein’s functional three-dimensional structure.
optimum temperature — The temperature at which a process has its highest measured rate under stated conditions.
diffusion — Net movement of particles down a concentration gradient.
osmosis — Net movement of water through a partially permeable membrane down its water-potential gradient.
active transport — Energy-dependent movement of substances across membranes against a gradient.
concentration gradient — A difference in concentration between two locations.
partially permeable membrane — A membrane allowing some particles through more readily than others.
surface area-to-volume ratio — The area exposed relative to the volume enclosed.
turgor pressure — Pressure of plant cell contents against the cell wall.
plasmolysis — Shrinkage of plant cell contents away from the cell wall after water loss.

3. Food, nutrition and human digestion — words 41–60

Food must be broken down, absorbed and used. Different verbs refer to different stages, and not all digestion occurs in the stomach.

nutrition — Obtaining and using substances needed for living processes.
balanced diet — A diet supplying suitable amounts of required nutrients.
ingestion — Taking food into the digestive tract.
digestion — Breaking food into smaller substances for absorption.
mechanical digestion — Physical breakdown of food into smaller pieces.
chemical digestion — Enzyme-driven breakdown of food molecules.
absorption — Movement of digested nutrients into blood or lymph.
assimilation — Using absorbed nutrients in body tissues.
egestion — Removal of undigested material from the digestive tract.
peristalsis — Muscular waves moving food through the alimentary canal.
oesophagus — The muscular tube carrying food from throat to stomach.
stomach — The digestive organ that churns food and begins significant protein digestion.
small intestine — The main site of digestion and nutrient absorption.
large intestine — The region absorbing water and forming faeces.
villus — A finger-like projection increasing intestinal absorption area.
bile — A liver-produced fluid involved in fat emulsification.
emulsification — Breaking fat into smaller droplets to increase surface area.
amylase — An enzyme catalysing starch breakdown.
protease — An enzyme catalysing protein breakdown.
lipase — An enzyme catalysing fat breakdown.

4. Respiration, gas exchange and circulation — words 61–80

Breathing is moving air; respiration is a cellular chemical process. Use these exact meanings rather than treating the words as synonyms.

aerobic respiration — Cellular release of energy from substances using oxygen.
anaerobic respiration — Cellular energy release without oxygen involvement.
ventilation — Movement of air into and out of the lungs.
gas exchange — Movement of respiratory gases between surfaces or compartments.
alveolus — A tiny air sac in the lung where gas exchange occurs.
diaphragm — A muscle important in changing chest volume during breathing.
intercostal muscle — A muscle between ribs involved in ventilation.
breathing rate — Number of breathing cycles per unit time.
heart — A muscular organ that pumps blood.
artery — A blood vessel carrying blood away from the heart.
vein — A blood vessel carrying blood towards the heart.
capillary — A narrow blood vessel enabling exchange with tissues.
plasma — The liquid part of blood carrying dissolved materials.
red blood cell — A cell specialised for transporting respiratory gases.
white blood cell — A blood cell involved in immune defence.
platelet — A blood component involved in clot formation.
haemoglobin — An oxygen-binding protein inside red blood cells.
oxygenated blood — Blood containing relatively more oxygen.
deoxygenated blood — Blood containing relatively less oxygen.
double circulation — A circulatory system moving blood through lung and body circuits.

5. Homeostasis, excretion and coordination — words 81–100

Negative feedback is about returning a variable towards a suitable range. It does not mean that every biological change is bad.

homeostasis — Maintaining internal conditions within suitable ranges.
negative feedback — A control response that opposes a detected deviation.
stimulus — A change detected by a receptor.
receptor — A structure that detects a particular stimulus.
coordinator — A system or centre that integrates information and directs responses.
effector — A muscle or gland carrying out a response.
response — An action or change resulting from a stimulus.
nervous system — A network that detects information and coordinates rapid responses.
neuron — A cell specialised for transmitting nerve impulses.
synapse — A junction where a signal passes between neurons or to a target.
reflex action — A rapid involuntary response to a stimulus.
hormone — A chemical messenger carried to target cells.
endocrine gland — A gland releasing hormones into the bloodstream.
blood glucose — The amount or concentration of glucose in blood.
insulin — A hormone that helps lower raised blood glucose.
glucagon — A hormone that helps raise low blood glucose.
kidney — An organ filtering blood and regulating water and solutes.
urea — A nitrogen-containing waste product formed in the liver.
excretion — Removal of metabolic waste products and excess substances.
osmoregulation — Control of water and dissolved-solute balance.

6. Infection, defence and public-health vocabulary — words 101–120

Different pathogens and defences work differently. Antibiotics are not drugs for treating viruses, and public-health claims need sound evidence.

pathogen — A biological agent able to cause disease.
infectious disease — A disease caused by an infectious agent that can spread.
transmission — Passing an infectious agent between hosts.
infection — Entry and multiplication of a disease-causing agent in a host.
bacterium — A single-celled prokaryotic organism.
virus — An infectious particle that reproduces only in suitable host cells.
fungus — A eukaryotic organism including yeasts and moulds.
parasite — An organism living on or in another and obtaining resources from it.
host — An organism harbouring another organism or infectious agent.
vector — An organism carrying an infectious agent between hosts.
immune system — Cells and molecules that recognise and respond to threats.
antigen — A molecular feature recognised by immune defences.
antibody — A protein that binds a specific antigen.
phagocytosis — Engulfing particles or microbes by certain cells.
vaccination — Administration of a vaccine to stimulate protective immunity.
immunisation — A process that develops protection against a disease.
herd immunity — Population-level indirect protection arising when sufficient transmission is prevented.
antibiotic — A medicine active against susceptible bacteria.
antibiotic resistance — The ability of bacteria to withstand a previously effective antibiotic.
hygiene — Practices that reduce spread of harmful contaminants and pathogens.

7. Plants: photosynthesis and transport — words 121–140

A plant is an interacting system: leaf structure affects photosynthesis, roots absorb resources and transport tissues connect locations.

photosynthesis — Conversion of light energy into chemical energy in organic compounds.
chlorophyll — A green pigment absorbing light for photosynthesis.
light intensity — Light power received per unit area.
limiting factor — A factor restricting a process when others are sufficient.
carbon dioxide fixation — Incorporation of carbon dioxide carbon into organic compounds.
stomata — Small pores in plant surfaces controlling gas exchange.
guard cell — A specialised cell that regulates stomatal opening.
palisade mesophyll — Leaf tissue containing many chloroplasts.
spongy mesophyll — Leaf tissue with air spaces supporting gas exchange.
xylem — Plant transport tissue carrying water and dissolved mineral ions.
phloem — Plant transport tissue carrying sugars and other organic solutes.
transpiration — Loss of water vapour from plant aerial surfaces.
transpiration stream — Movement of water through a plant driven largely by evaporation.
root hair cell — A root epidermal cell adapted for absorption.
mineral ion — An inorganic charged nutrient absorbed by roots.
translocation — Movement of organic solutes through phloem.
phototropism — Directional growth in response to light direction.
gravitropism — Directional growth in response to gravity.
auxin — A plant hormone involved in growth regulation.
starch test — A chemical test using iodine solution to detect starch.

8. Organisms, populations and ecosystems — words 141–160

Biomass and usable energy are not recycled in the same way. Nutrients cycle through ecosystems; energy flows and is dissipated.

habitat — The natural environment where an organism lives.
population — Members of one species living in a defined area.
community — Populations of different species living together.
ecosystem — Organisms and their physical environment interacting.
biotic factor — A living component affecting an ecosystem.
abiotic factor — A non-living environmental condition.
producer — An organism that makes organic food from inorganic materials.
consumer — An organism that obtains energy by feeding on other organisms.
decomposer — An organism that breaks down dead material and wastes.
food chain — A sequence showing transfer of energy through feeding.
food web — Connected food chains within an ecosystem.
trophic level — A feeding position in an ecosystem.
pyramid of biomass — A diagram showing biomass at successive trophic levels.
energy flow — Transfer of usable energy through biological systems.
carbon cycle — Movement of carbon between organisms and environments.
nitrogen cycle — Movement and transformation of nitrogen among environmental reservoirs.
biodiversity — Variety of organisms, species and ecosystems.
conservation — Protection and responsible management of species and habitats.
competition — Interaction where organisms seek the same limited resource.
predation — An interaction in which a predator captures and eats prey.

9. DNA, molecular genetics and variation — words 161–180

DNA, genes, chromosomes, genotype and phenotype are related but different. A trait’s expression can also depend on its environment.

DNA — The molecule storing hereditary information in living cells.
nucleotide — A building block of DNA and RNA.
double helix — The twisted two-strand structure of DNA.
gene — A DNA sequence contributing to a functional product.
chromosome — A DNA-containing structure carrying many genes.
allele — An alternative version of a gene.
genome — The complete genetic material of an organism.
genotype — The genetic makeup at a specified locus or loci.
phenotype — Observable characteristics resulting from genes and environment.
mutation — A change in DNA sequence.
gene expression — Use of genetic information to produce a functional product.
transcription — Production of RNA using a DNA template.
translation — Production of a protein using an RNA sequence.
messenger RNA — RNA carrying sequence information used in protein synthesis.
complementary base pairing — Specific matching between nucleic-acid bases.
protein synthesis — Cellular construction of proteins according to genetic information.
inherited variation — Differences passed to offspring through genetic information.
environmental variation — Differences arising from environmental conditions.
genetic engineering — Deliberate modification of genetic material.
biotechnology — Use of biological systems to make products or solve problems.

10. Reproduction, inheritance and investigation skills — words 181–200

Use simple crosses for the inheritance patterns specified by your course. A single-gene model must not be assumed to explain every trait.

asexual reproduction — Production of offspring without fusion of gametes.
sexual reproduction — Production of offspring involving fusion of gametes.
gamete — A reproductive cell that fuses at fertilisation.
fertilisation — Fusion of gametes to form a zygote.
zygote — A cell formed by fusion of gametes.
mitosis — Nuclear division producing genetically similar daughter nuclei.
meiosis — Division producing cells with half the original chromosome number.
dominant allele — An allele expressed in a heterozygote.
recessive allele — An allele whose effect may be masked in a heterozygote.
homozygous — Having two copies of the same allele at a gene locus.
heterozygous — Having two different alleles at a gene locus.
Punnett square — A diagram showing possible allele combinations in offspring.
genetic cross — A prediction of offspring genotypes from parental alleles.
probability — A numerical measure of how likely an outcome is.
hypothesis — A testable explanation proposed before an investigation.
sampling — Selecting observations or organisms from a wider population.
standardised method — A procedure carried out consistently across trials.
repeatability — Agreement when a method is repeated under similar conditions.
correlation — A relationship in which measured quantities vary together.
causation — A relationship in which a factor produces an effect.

Seven Worked Biology Examples: From Vocabulary to Understanding

1. Cell structures need a function, not a label alone

Students often memorise that a red blood cell is shaped like a flattened disc with a depression on both sides. The useful explanation is that this biconcave form creates a large surface area relative to volume, helping gas exchange. Its flexibility helps movement through narrow capillaries. When asked about an adaptation, connect each feature to a physiological advantage rather than reciting shape words.

2. Diffusion versus osmosis

Imagine a drop of food colouring spreading in a glass of water. Its dye particles diffuse as they disperse down their concentration gradient. Now consider a plant cell placed in a more concentrated sugar solution: water may leave the cell across a partially permeable membrane by osmosis, causing reduced turgor and potentially plasmolysis. Osmosis specifically refers to water movement across a suitable membrane; the two concepts are not synonyms.

3. The journey of a starch-rich meal

Starch is a large carbohydrate. Digestion breaks it into smaller carbohydrates and ultimately absorbable sugars through enzyme actions. Ingestion starts when food is taken in; digestion breaks it down; absorption moves products into the body’s transport systems; assimilation involves using the absorbed substances. A student who uses “absorption” to describe chewing has misplaced the process, even if other facts are correct.

4. Breathing is not the same as respiration

During ventilation, air moves into and out of the lungs as the chest volume changes. Oxygen may diffuse across the alveolar surface into the blood. In cells, aerobic respiration uses oxygen to release usable energy from substrates, producing carbon dioxide and water under the usual school-level model. The ventilation process supplies gas; it is not itself the chemical process releasing energy.

5. Negative feedback and blood glucose

After a meal, blood glucose may rise. Insulin helps body cells take up glucose and supports storage, tending to lower elevated levels. When blood glucose falls, glucagon helps increase it. The important idea is negative feedback: opposing deviations so internal conditions remain within a functional range. This explanation describes the physiological model, not medical advice for someone experiencing symptoms.

6. Xylem, phloem and a leaf exposed to sun

Leaves lose water by transpiration, especially through stomata. Water can move up xylem from the roots, while the products of photosynthesis move through phloem to sinks such as growing tissues. A common mistake is to say that xylem carries food and phloem carries only water. Ask what is transported, where it comes from, and why the plant needs it.

7. Why a genetic cross is a probability model

Consider a hypothetical single-gene trait with dominant allele A and recessive allele a. Two heterozygous parents (Aa × Aa) can produce offspring genotypes AA, Aa, Aa, aa, in expected proportions of 1:2:1 under ordinary Mendelian assumptions. The chance of the aa genotype is 1/4 for each offspring; the result is not a guarantee that exactly one of four real children will show that genotype. Real characteristics may involve many genes and environmental factors.

How the 200 Words Fit Together: Structure, Function, Process, Evidence

Biology terms frequently belong in chains. For example, cell membrane → concentration gradient → diffusion → exchange → tissue function. If the student can explain the connections, unfamiliar questions become less intimidating.

Take the small intestine. Its many villi increase the surface area for absorption. Blood flow carries absorbed substances away, helping maintain gradients. The word villus alone is not an explanation; the chain of reasoning is what gives it meaning.

Or take a food web. Producers store energy from light in organic compounds; consumers obtain energy by feeding, and decomposers break down dead material. Nutrients may be recycled, but not all energy remains available to later trophic levels. The explanation requires separating the two words energy and nutrient.

Three quick diagnostic prompts: What exactly moves during osmosis? What is the job of the mitochondrion? What can a Punnett square predict, and what can it not guarantee? If the student can answer in plain language before using technical terminology, the foundation is improving.

Biology in Daily Life, Without Overstating What Science Says

Food choices: Nutrients have different functions. A “balanced diet” refers to an adequate pattern over time, not any single perfect ingredient. Biological vocabulary can help distinguish energy content, digestion and health claims without treating a label as a complete judgement.

News about infections: The words virus, bacterium, vaccine, immunisation, antibiotic and resistance describe different mechanisms. A treatment useful against some bacteria is not necessarily useful against a viral infection. For any personal medical decision, consult a qualified professional rather than using a school glossary as clinical guidance.

Urban nature: A garden or mangrove ecosystem involves producers, consumers, decomposers, abiotic factors and species interactions. Observing biodiversity can make ecological ideas real, but one quick visit cannot establish every trend in a population.

Genetics and media: A gene associated with a trait is not automatically a complete explanation of the trait. Inheritance patterns, expression and environment matter. Claims about “the gene for” a complex human behaviour deserve careful scrutiny.

Repair Common Examination Mistakes

Describe instead of explain: “The stomata were open” is an observation; “open stomata allow gas exchange, with effects on water loss” begins an explanation.
Memorise organ functions without the pathway: Trace material into, through and out of a system, identifying which step is responsible.
Confuse immunity with infection: Immunity is an aspect of protection, not the mere presence of a pathogen.
Swap units in microscopy: If an image is 20 mm long and the actual object is 0.2 mm, magnification is 20 ÷ 0.2 = 100×; first convert quantities to the same units.
Use cause where only correlation exists: A change in one measured factor associated with another does not alone prove a causal mechanism.
Describe each part but not the whole mechanism: For a cycle or process, include starting material, transformation, movement and result.

Four-Week Biology Vocabulary Plan

Week 1 — Foundations: Learn words 1–50. Draw a cell, explain a membrane movement and identify how a structure supports a function.
Week 2 — Humans: Learn words 51–100. Build a pathway for digestion, circulation, respiration and homeostatic feedback using arrows.
Week 3 — Disease, plants and ecology: Learn words 101–150. Distinguish one pathogen mechanism and one plant transport mechanism, then interpret a small food web.
Week 4 — Genetics and reasoning: Learn words 151–200. Explain one genotype–phenotype question, one simple inherited pattern and one experimental limitation.

Review missed terms after a day, several days and a week. Mark success only when the student can explain and apply an idea without the original sentence in front of them. Keep the workload realistic alongside school requirements.

Frequently Asked Questions

Are these official 200 Biology vocabulary words required by SEAB?

No. These are 200 editorially selected words and phrases. The official Biology syllabus defines assessable content, and certain enrichment terms on this page may be outside the assessed minimum.

Does Secondary 4 Biology become SEC Biology in 2027?

The 2027 G3 subject is SEC Biology K325, while the 2026 O-Level subject is Biology 6093. Always use the subject code and school or private candidate route for the year being taken.

Does Combined Science (Chemistry, Biology) cover the same topics?

Not necessarily at the same depth. For 2027 G3, Science (Chemistry, Biology) is K328 and Science (Physics, Biology) is K327. Their syllabuses are not interchangeable with pure Biology K325.

Why is understanding more important than reciting definitions?

Many Biology questions ask students to connect evidence with a mechanism. Explaining why villi increase absorption or why feedback stabilises a variable demonstrates more useful understanding than naming an organ alone.

What should I do if a student struggles with diagrams?

Start with a blank version of the diagram, then have the student label structures, trace the movement of substances and state one reason for every major step. Do this before adding extra worksheets.

Should learners use this glossary to make health decisions?

No. It is secondary-school learning material. Personal symptoms, treatments, vaccination decisions and other clinical questions require appropriate up-to-date medical guidance.

Official Syllabus and Further eduKate Reading

Updated 7 November 2026. This independent reference does not replace the SEAB syllabus, supervised practical work or professional medical guidance.

Top 200 Vocabulary for Secondary 4 Biology | O-Level and SEC 2027 Cells, Human Systems, Genetics and Ecology