Why keywords matter in IGCSE Science

Cambridge and Edexcel mark schemes reward syllabus terminology. Examiners look for specific scientific terms when awarding marks. Using everyday language or the wrong term often means partial or no credit—even if your understanding is correct. This applies to Biology, Chemistry and Physics across both exam boards.

Mark schemes also state that keywords must be used correctly in context. A correct term used incorrectly (e.g. “osmosis” for diffusion) does not receive credit. For Chemistry, spellings must allow clear separation from other terms (e.g. ethane vs ethene).

Biology keywords that earn marks

Cell and transport

Keyword	Use when	Alternative that may not score
Mitochondria	Site of aerobic respiration	”Battery” / “powerhouse”
Ribosome	Protein synthesis	”Protein factory”
Osmosis	Water; partially permeable membrane	”Water diffusion”
Concentration gradient	Diffusion	”Difference”
Active transport	Against gradient; energy; carrier	”Pumping”
Partially permeable membrane	Selective; osmosis	”Semi-permeable” (less preferred)

Enzymes and digestion

Keyword	Use when	Alternative that may not score
Optimum	Best pH or temperature	”Ideal”
Denature	Shape change; enzyme fails	”Destroy”
Substrate	Molecule enzyme acts on	”Chemical”
Absorption	Into blood	Assimilation
Assimilation	Into cells/tissues	Absorption
Lock and key	Substrate fits active site	”Fits”

Systems

Keyword	Use when	Alternative that may not score
Kidney	Excretes urea	Bladder
Villus	Absorption in small intestine	”Finger”
Alveolus	Gas exchange	”Lungs” (when structure asked)
Capillary	Exchange surface	”Blood vessel”

Inheritance

Keyword	Use when	Alternative that may not score
Allele	Form of a gene	”Gene”
Genotype	Genetic makeup (e.g. Bb)	Phenotype
Phenotype	Observable characteristic	Genotype
Dominant	Expressed with one allele	”Stronger”
Recessive	Need two alleles	”Weaker”

Chemistry keywords that earn marks

Structure and bonding

Keyword	Use when	Alternative that may not score
Ionic bond	Electrostatic attraction between ions	”Shared electrons”
Covalent bond	Shared pair of electrons	”Transfer” for covalent
Ion	Charged particle	Atom
Molecule	Covalent; shared electrons	”Particle”
Electrolyte	Conducts when molten/dissolved	Solid crystal
Delocalised electrons	In metals	”Free electrons”

Organic

Keyword	Use when	Alternative that may not score
Alkane	Saturated; C–C single bonds	Alkene
Alkene	Unsaturated; C=C double bond	Alkane
Ethane	C₂H₆; single bond	Ethene
Ethene	C₂H₄; double bond	Ethane
Combustion	Reaction with oxygen	”Burning”
Cracking	Breaking long chains	”Splitting”
Addition	Single product (e.g. alkene + Br₂)	Substitution
Substitution	One atom replaced	Addition

Acids and electrochemistry

Keyword	Use when	Alternative that may not score
Oxidation	Loss of electrons	”Gain of oxygen” only
Reduction	Gain of electrons	”Loss of oxygen” only
Oxidising agent	Accepts electrons	”Oxidises”
Reducing agent	Donates electrons	”Reduces”
Neutralisation	Acid + base → salt + water	Incomplete
Catalyst	Speeds up; unchanged	”Used up”
Exothermic	Releases energy	”Hot”
Endothermic	Takes in energy	”Cold”

Physics keywords that earn marks

Mechanics

Keyword	Use when	Alternative that may not score
Velocity	Vector; direction matters	Speed
Acceleration	Change in velocity / time	”Getting faster”
Weight	Force; N	Mass (kg)
Mass	kg	Weight (N)
Resultant force	Net force	Single force
Work done	F × d; J	”Effort”
Power	Energy / time; W	”Strength”
Efficiency	(useful / total) × 100%	Wrong formula

Energy and waves

Keyword	Use when	Alternative that may not score
Kinetic energy	½mv²	Wrong formula
Gravitational potential energy	mgh	Wrong formula
Conduction	Through solids	Convection
Convection	In fluids	Conduction
Radiation	Infrared; no medium	Conduction
Amplitude	Max displacement	”Height”
Frequency	Hz	”Speed”
Wavelength	m; one cycle	”Length”
Refraction	Change in speed; bending	”Bending” only
Critical angle	Angle for 90° refraction	Wrong angle
Total internal reflection	Angle > critical	Incomplete

Electricity and nuclear

Keyword	Use when	Alternative that may not score
Current	A	”Flow”
Potential difference	V	”Voltage” (Pd preferred)
Resistance	V/I; Ω	Wrong formula
e.m.f.	Energy per unit charge from source	Pd
Alpha	⁴₂He	Beta
Beta	⁰₋₁e	Alpha
Gamma	EM wave	Particle
Half-life	Time for half to decay	”Half the time”
Irradiation	Exposed to radiation	Contamination
Contamination	Radioactive material on/in body	Irradiation

How to use keywords effectively

1. Learn the syllabus terms—check your subject syllabus and past mark schemes.
2. Use in context—correct term + correct application.
3. Avoid confusion pairs—absorption/assimilation, ethane/ethene, weight/mass, speed/velocity.
4. Spelling—must allow clear separation (e.g. ethane vs ethene in Chemistry).
5. Don’t overuse—one correct use is enough; repetition doesn’t add marks.
6. Past papers + mark schemes—see exactly which terms are credited.

How Tutopiya helps

Tutopiya tutors use past papers and mark schemes to teach the keywords that earn marks in each science subject. Explore IGCSE resources or book a free trial.

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Based on Cambridge and Edexcel IGCSE science syllabuses and mark schemes. Check the latest syllabus for your exam series.