IGCSE Biology Key Definitions: Essential Revision Sheet

Most students lose definition marks for one reason. They understand the biology but write it in their own words instead of the exact phrasing examiners want. A vague answer often scores zero even when the idea is right.

This page is your one-stop reference for IGCSE biology key definitions. You get exam-accurate wording, the terms grouped by topic, and a proven method to remember them before test day.

What are IGCSE biology key definitions?

IGCSE biology key definitions are the syllabus-standard, exact-wording explanations of core terms. Examiners mark them against a fixed phrasing, so a synonym or loose paraphrase often earns nothing.

Cambridge sets the wording in its 0610 and 0970 syllabus glossary, and your answer must match it closely.

Precise wording beats paraphrasing because mark schemes list required key phrases. Miss the phrase "net movement" or "partially permeable membrane" and the mark is gone.

A definition is not the same as a broad concept. A definition is one tight sentence you can recite. A concept, like natural selection, needs a fuller explanation. Both belong in your IGCSE revision hub from the start.

Which key terms must you know by topic?

The essential terms cluster into about eight syllabus topics. The highest-yield ones are diffusion, osmosis, active transport, respiration, and photosynthesis.

Learn these first, because they appear across many exam papers. The full glossary below is your printable biology vocabulary list.

The table below lists the most tested IGCSE biology terms in clean Cambridge wording. According to Cambridge International, answers must match the syllabus phrasing, so learn them exactly as written.

Term	Definition
Diffusion	The net movement of particles from a higher to a lower concentration, down a gradient.
Osmosis	Net movement of water across a partially permeable membrane, down a water potential gradient.
Active transport	Movement of particles against a gradient, using energy from respiration.
Respiration	Chemical reactions in cells that break down nutrients and release energy.
Photosynthesis	How plants make carbohydrates from carbon dioxide and water using light energy.
Excretion	Removal of the waste products of metabolism and substances in excess.

Learn each definition word for word. The osmosis and active transport wordings above carry the extra detail Extended (Supplement) candidates must include. For deeper practice, see our IGCSE subject guides.

Characteristics of living organisms (MRS GREN)

All living things share seven life processes: movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition. The mnemonic MRS GREN helps you recall them. Learn one clear definition for each process.

Cells and movement in and out of cells

Key terms here are diffusion, osmosis, and active transport. Also define the cell wall, cell membrane, and what a partially permeable membrane means. These wordings appear often in mark schemes.

Enzymes

An enzyme is a protein that works as a biological catalyst. A catalyst speeds up a reaction without being used up. Learn the terms substrate, active site, and denatured too.

Nutrition, transport and respiration

Define aerobic respiration, anaerobic respiration, and photosynthesis in full. For transport, know terms like transpiration and translocation. Precise energy wording matters most here.

Coordination, reproduction and inheritance

This topic asks for definitions of hormone, gene, allele, and mitosis. Genetics terms such as dominant and recessive appear often. Keep each one to a single sentence.

Organisms and their environment (ecology)

Ecology definitions include ecosystem, population, community, habitat, and food chain. Know producer, consumer, and decomposer as well. These short terms are easy marks when learned precisely.

Which biology definitions do students confuse most?

Students confuse a few pairs most. Excretion is losing metabolic waste, while egestion is removing undigested food. Diffusion moves any particle down a gradient, osmosis moves only water, and active transport uses energy to move particles the other way.

This table shows the pairs that cost the most marks and the one detail that separates each. Learn the difference, not just the two terms.

Term A	Term B	Key difference
Excretion	Egestion	Metabolic waste versus undigested food.
Diffusion	Osmosis	Any particle moves versus only water.
Diffusion	Active transport	No energy needed versus respiration energy used.
Respiration	Breathing	Energy release versus air movement.
Sensitivity	Response	Detecting a change versus reacting to it.

A tutor can drill these pairs with you using worked examples. Our Cambridge IGCSE Biology tutors focus on the exact wording examiners expect.

How many definitions do you need to learn?

You need roughly 100 or more key terms across the whole syllabus. Core candidates learn a large subset. Extended candidates cover the full set, including Supplement-only terms. Focus first on the terms that appear most often in past papers.

The gap between Core and Extended is scope, not a different subject. Extended adds detail to definitions like osmosis and includes topics Core students skip. Check your tier before you plan revision.

A realistic timeline helps. Cover one topic of terms each week and you finish the whole glossary in about eight weeks, with time left to review.

How do you memorize IGCSE biology key definitions?

The most effective method is active recall with spaced repetition. You test yourself on the term instead of rereading notes.

Short sessions spread across several days beat one long cram. Turn your biology vocabulary list into flashcards for exam prep.

According to research by psychologist Hermann Ebbinghaus, we forget most new information within days unless we review it. His "forgetting curve" is why spaced repetition works. Apps like Anki and Quizlet handle the spacing for you.

Follow these five steps to lock in every definition:

• Write each term as a flashcard question.
• Cover the answer and recall it aloud.
• Sort cards into known and unsure.
• Review the unsure cards more often.
• Test against past-paper wording weekly.

If recall still feels shaky, work with a tutor who can quiz you live and correct your phrasing on the spot.

How are key definitions tested in exams?

Definitions appear through command words. "Define" and "state" expect the exact term wording. "Describe" and "explain" expect you to apply it. The marks available tell you how much detail to give, so match your answer length to the mark value.

Mark schemes award credit for specific key phrases inside a definition. Drop a required clause, such as "partially permeable membrane" in osmosis, and you lose that mark.

A common slip is answering a "define" question with an example instead of the meaning. Practise with real IGCSE past papers to see the exact phrases mark schemes reward.

How should you start revising definitions now?

Precise, syllabus-worded definitions are some of the easiest marks in IGCSE Biology. But only if you learn the exact wording and reinforce it with active recall, not last-minute rereading.

Start this week. Load the terms into flashcards, review them in short sessions, and test yourself against real IGCSE past papers. For targeted help, a Cambridge IGCSE Biology tutor can check your wording and close the gaps.