Top 200 Vocabulary for Secondary 3 Biology (MOE G3 Syllabus) | Cells, Human Body, Ecology and Genetics

What are the most useful Secondary 3 Biology words? This guide defines 200 terms about cells, osmosis, enzymes, digestion, blood circulation, respiration, homeostasis, plants, ecology and inheritance. Each group explains not only the words but how structures and processes support life, with mini-practice prompts to test understanding.

The 2027 Singapore-Cambridge SEC G3 syllabus index identifies full Biology as K325 (the earlier code was 6093). Its official syllabus is organised around cells and the chemistry of life, maintaining the human body, plants and ecosystems, and continuity of life. This independent 200-term glossary covers the wider upper-secondary pathway; it is not a compulsory MOE-issued word list or a claim that every section is taught in Secondary 3.

• Start: identify the biological structure or process named in the question.
• Explain: connect a structure to what it does and why its features matter.
• Compare: separate terms that sound similar, such as diffusion versus osmosis or excretion versus egestion.
• Practise: use labelled diagrams, short explanations and provided data.
• Check scope: match the school’s actual chapter and subject level.
• For parents: ask students to teach one mechanism rather than recite twenty definitions without understanding.

Top 200 Secondary 3 Biology terms and clear definitions

These are teaching definitions designed for recall and correct application. For an examination answer, the important step is to explain the specific biological mechanism described by the question. Multiword entries are treated as one scientific concept.

1. Cells and living organisation

Biology becomes clearer when one structure is connected to one job. A thin exchange surface supports short diffusion distance; a red blood cell’s form supports oxygen transport. Magnification describes image size relative to actual size, not the actual size of the structure. Diagrams should label function as well as shape.

1. cell — the basic structural and functional unit of living organisms.
2. cell membrane — a selectively permeable boundary surrounding a cell.
3. cytoplasm — the region where many cellular reactions occur.
4. nucleus — the cell compartment holding most genetic material.
5. mitochondrion — an organelle where much aerobic respiration occurs.
6. ribosome — the cellular structure assembling proteins.
7. cell wall — a rigid outer support layer in plant cells.
8. chloroplast — a plant organelle containing chlorophyll for photosynthesis.
9. vacuole — a membrane-bound compartment for water or materials.
10. chlorophyll — a pigment absorbing light used for photosynthesis.
11. organelle — a specialised component within a cell.
12. tissue — a group of similar cells performing a particular function.
13. organ — a structure combining tissues to perform functions.
14. organ system — organs working together for a larger function.
15. organism — an individual living entity.
16. specialisation — development of features suited to a task.
17. differentiation — the process by which cells become specialised.
18. surface-area-to-volume ratio — the amount of exposed surface relative to an object’s volume.
19. microscope — an instrument used to magnify small structures.
20. magnification — image size divided by actual object size.

Test understanding: Draw a plant cell and an animal cell; label three structures that both share and two that differ.

2. Movement through membranes

Diffusion does not necessarily require cellular energy, but active transport moves material against a relevant concentration gradient using energy. Osmosis is specifically net water movement through a partially permeable membrane. Asking which substance crosses and what barrier is present prevents vague explanations.

21. diffusion — net movement of particles from higher to lower concentration.
22. osmosis — net water movement across a partially permeable membrane down water potential.
23. active transport — movement of substances against a concentration gradient using energy.
24. concentration gradient — difference in concentration across a distance.
25. water potential — a measure predicting direction of water movement.
26. partially permeable membrane — a barrier allowing some particles through more readily than others.
27. selectively permeable — allowing some substances to cross more easily than others.
28. passive transport — movement without direct cellular energy input.
29. carrier protein — a membrane protein involved in moving particular substances.
30. channel protein — a membrane protein forming a route for selected particles.
31. equilibrium — a state with no net change in opposing processes.
32. net movement — overall change after movement in both directions is considered.
33. turgid — swollen and firm from water uptake in a plant cell.
34. flaccid — not firm because of low internal water pressure.
35. plasmolysis — retraction of the cell membrane from the wall after water loss.
36. hypotonic — having a lower effective solute concentration than the comparison solution.
37. hypertonic — having a higher effective solute concentration than the comparison solution.
38. isotonic — having the same effective osmotic concentration as a comparison.
39. absorption — uptake of substances into cells or body tissues.
40. exchange surface — a structure adapted for transfer of substances.

Test understanding: Predict how a plant cell changes in a much more concentrated surrounding solution, and name the water movement.

3. Biological molecules and enzymes

An enzyme changes the rate of a reaction without being used up overall. Conditions such as temperature and pH affect shape and reaction rate, but higher temperature does not always mean faster activity: excessive heat can denature many enzymes. Interpret a graph rather than memorising a single optimum as universal.

41. carbohydrate — an organic substance class including sugars and starch.
42. glucose — a simple sugar used in cellular respiration.
43. starch — a storage polysaccharide made of glucose in plants.
44. glycogen — a storage polysaccharide common in animals.
45. cellulose — a structural polysaccharide in plant cell walls.
46. protein — a large molecule made from amino acids.
47. amino acid — a building block of proteins.
48. lipid — a group of mainly water-insoluble biological molecules.
49. fat — a lipid used for energy storage and other functions.
50. enzyme — a biological catalyst commonly made from protein.
51. substrate — the substance an enzyme acts on.
52. active site — the region of an enzyme where its substrate binds.
53. enzyme-substrate complex — a temporary association formed during enzyme action.
54. denaturation — loss of protein shape and function under disruptive conditions.
55. optimum temperature — the temperature supporting greatest rate under stated conditions.
56. optimum pH — the acidity at which an enzyme functions best under stated conditions.
57. catalyst — a substance speeding reaction without being consumed overall.
58. hydrolysis — breakdown of a chemical bond using water.
59. condensation reaction — a joining reaction that removes a small molecule such as water.
60. food test — a standard chemical procedure identifying certain nutrients.

Test understanding: Explain why an enzyme might work more slowly after being heated far beyond its optimum.

4. Human nutrition and digestion

Digestion is the breakdown of food substances; absorption brings the resulting small molecules into the body. Egestion removes undigested material, not metabolic waste removed by excretion. A balanced diet is not a single magic food but an overall pattern of adequate nutrients and energy.

61. ingestion — taking food into the digestive system.
62. digestion — breaking large insoluble food molecules into smaller soluble forms.
63. mechanical digestion — physical breakup of food without changing its chemical identity.
64. chemical digestion — enzymatic breakdown of food molecules.
65. peristalsis — wave-like gut muscle contractions moving contents onward.
66. saliva — fluid in the mouth that moistens food and contains enzymes.
67. oesophagus — the tube carrying swallowed food to the stomach.
68. stomach — the organ mixing food and beginning protein digestion.
69. small intestine — the main site of final digestion and nutrient absorption.
70. large intestine — the region where water and salts are absorbed from gut contents.
71. villus — a finger-like projection increasing intestinal absorption area.
72. microvillus — a microscopic surface projection increasing cell surface area.
73. bile — a liver-produced fluid that assists fat emulsification.
74. emulsification — division of fat into small droplets without hydrolysis.
75. pancreas — an organ releasing digestive enzymes and hormones.
76. liver — an organ involved in bile production and nutrient processing.
77. assimilation — use of absorbed nutrients by cells for growth or activity.
78. balanced diet — food intake providing suitable nutrients and energy.
79. malnutrition — poor health caused by insufficient excessive or unbalanced nutrients.
80. defaecation — the expulsion of faeces from the digestive tract.

Test understanding: Describe the difference between food digestion in the gut and nutrient absorption at intestinal villi.

5. Blood transport and respiration

The heart moves blood through circuits; blood cells and plasma carry different substances. Arteries are defined by direction away from the heart, not by always carrying oxygenated blood. Gas exchange at alveoli is distinct from cellular respiration, which releases energy inside living cells.

81. heart — a muscular pump driving blood circulation.
82. atrium — an upper chamber of the heart receiving blood.
83. ventricle — a lower heart chamber pumping blood out.
84. artery — a blood vessel carrying blood away from the heart.
85. vein — a vessel returning blood toward the heart.
86. capillary — a microscopic vessel allowing exchange with tissues.
87. red blood cell — a blood cell specialised for transporting oxygen.
88. white blood cell — a blood cell involved in immune defence.
89. platelet — a cell fragment involved in clot formation.
90. plasma — the liquid component of blood.
91. haemoglobin — a protein that binds oxygen in red blood cells.
92. alveolus — an air sac where gases exchange with blood.
93. trachea — the airway leading toward the lungs.
94. bronchus — one of the main airways entering a lung.
95. bronchiole — a smaller airway branching within a lung.
96. diaphragm — a muscle helping change thoracic volume during breathing.
97. aerobic respiration — release of energy from glucose using oxygen.
98. anaerobic respiration — release of energy from glucose without oxygen.
99. gas exchange — transfer of oxygen and carbon dioxide across surfaces.
100. oxygen debt — additional oxygen uptake after anaerobic exercise to aid recovery.

Test understanding: Explain why pulmonary arteries carry blood away from the heart even though the blood is relatively deoxygenated.

6. Excretion and homeostasis

Excretion and egestion have different mechanisms. Kidney filtration removes small substances from blood, while useful materials can be selectively reabsorbed. Homeostasis means regulation within a workable range through feedback, not that every body measurement remains absolutely constant.

101. excretion — removal of metabolic waste and certain excess substances.
102. egestion — expulsion of undigested food through the digestive tract.
103. kidney — an organ filtering blood and controlling water and solute balance.
104. nephron — the functional filtration and reabsorption unit of a kidney.
105. glomerulus — a capillary network involved in filtering blood.
106. Bowman’s capsule — a structure receiving filtrate from the glomerulus.
107. ultrafiltration — pressure-driven passage of small solutes and water into a kidney tubule.
108. selective reabsorption — return of useful filtered substances to blood.
109. ureter — the tube carrying urine from kidney to bladder.
110. urinary bladder — the organ temporarily storing urine.
111. urethra — the tube carrying urine out of the body.
112. urea — a nitrogen-containing waste product from protein metabolism.
113. homeostasis — maintenance of relatively stable internal conditions.
114. negative feedback — a response that counteracts a deviation from a set range.
115. osmoregulation — control of water and dissolved-solute balance.
116. thermoregulation — control of body temperature.
117. vasodilation — widening of blood vessels.
118. vasoconstriction — narrowing of blood vessels.
119. sweating — release of fluid on skin for evaporative cooling.
120. dialysis — a treatment removing wastes and some excess fluid when kidneys cannot.

Test understanding: Compare egestion and excretion, with one correct human example of each.

7. Coordination, hormones and disease

A reflex is a quick neural response; hormonal messages travel by blood and can act over different timescales. Infection and symptoms are not interchangeable. Antibiotics target susceptible bacteria, so they should not be assumed to cure a viral illness.

121. stimulus — a change detected by a living system.
122. receptor — a structure detecting a particular stimulus.
123. sensory neurone — a nerve cell carrying signals from receptors inward.
124. relay neurone — a nerve cell connecting pathways within the central nervous system.
125. motor neurone — a nerve cell delivering signals to effectors.
126. effector — a muscle or gland producing a response.
127. reflex action — a rapid automatic response through a neural pathway.
128. synapse — a junction where signals pass between neurones.
129. hormone — a blood-borne chemical signal affecting target cells.
130. endocrine gland — a gland releasing hormones directly into the bloodstream.
131. insulin — a hormone helping lower elevated blood glucose.
132. glucagon — a hormone helping raise low blood glucose.
133. adrenaline — a hormone supporting an immediate stress response.
134. hypothalamus — a brain region helping coordinate body temperature and other functions.
135. infection — entry and multiplication of a disease-causing organism in a host.
136. pathogen — an organism or agent capable of causing disease.
137. transmission — movement of an infectious agent from one host or route to another.
138. immunity — the body’s ability to resist a particular infection.
139. vaccination — administration intended to train immune protection.
140. antibiotic — a medicine acting against susceptible bacteria rather than viruses.

Test understanding: Describe the path from a skin receptor through a neurone pathway to a muscle response.

8. Plant nutrition and transport

Leaves exchange gases and capture light while vascular tissues transport water, ions and organic products. Xylem and phloem perform different functions. Water loss through transpiration can be useful for transport but excessive loss may lead to wilting; link conditions to mechanisms.

141. photosynthesis — conversion of light energy to chemical energy in organic matter.
142. stomata — pores in leaves controlling gas exchange.
143. guard cells — specialised cells controlling stomatal openings.
144. xylem — plant tissue transporting water and mineral ions.
145. phloem — plant tissue moving sucrose and other products.
146. transpiration — loss of water vapour mainly from aerial plant surfaces.
147. translocation — movement of organic nutrients through phloem.
148. root hair cell — an adapted cell increasing the surface for uptake.
149. palisade mesophyll — a leaf tissue rich in chloroplasts.
150. spongy mesophyll — a leaf tissue with air spaces supporting exchange.
151. cuticle — a waxy covering reducing water loss.
152. epidermis — the outer cell layer of plant organs.
153. mineral ion — a charged inorganic nutrient required in small amounts.
154. nitrate — a nitrogen-containing ion used in protein production.
155. magnesium ion — a plant nutrient used in chlorophyll formation.
156. limiting factor — a condition that restricts the rate of a process.
157. light intensity — light energy received per unit area or another stated measure.
158. carbon dioxide concentration — the amount of carbon dioxide per volume of air.
159. chlorosis — yellowing of leaf tissue through loss or shortage of chlorophyll.
160. wilting — drooping when water loss exceeds sufficient replacement.

Test understanding: Explain the role of guard cells in changing water loss from a leaf.

9. Ecology and environmental systems

A food web shows connections that a single chain omits. Energy enters ecosystems through producers and decreases in the amount available at higher trophic levels; matter is recycled through ecological processes. An ecological observation does not automatically prove the cause of a population change.

161. ecosystem — organisms and their physical environment interacting together.
162. population — members of one species in a particular area.
163. community — populations of different species living together.
164. habitat — the natural place where an organism lives.
165. niche — the ecological role and resources used by a species.
166. producer — an organism forming organic matter using external energy.
167. consumer — an organism obtaining organic matter by feeding.
168. decomposer — an organism breaking down dead organic matter.
169. food chain — a simplified sequence of feeding relationships.
170. food web — interconnected food chains within an ecosystem.
171. trophic level — the feeding position of an organism.
172. energy flow — movement of energy through feeding relationships.
173. biomass — the mass of living biological material.
174. biodiversity — variety of living organisms at different levels.
175. competition — struggle for limited resources.
176. predation — one organism killing and consuming another.
177. mutualism — an interaction benefiting both species.
178. carbon cycle — movement of carbon among organisms atmosphere and environment.
179. conservation — protection of organisms habitats and biological diversity.
180. sustainability — meeting needs without undermining future ecological resources.

Test understanding: Build a three-organism food chain and explain why it does not capture the whole food web.

10. DNA, reproduction and inheritance

A gene, allele and chromosome are not synonyms. A simple dominant-recessive model can explain some traits but not every inherited characteristic. Mitosis and meiosis support different biological outcomes; a diagram and the chromosome number reveal why.

181. DNA — the molecule storing genetic information.
182. gene — a DNA sequence contributing to a functional product.
183. chromosome — a long DNA molecule packaged with proteins.
184. allele — an alternative form of a gene.
185. genotype — the genetic combination carried by an organism.
186. phenotype — observable traits resulting from genotype and environment.
187. dominant allele — an allele expressed in a heterozygous individual under simple inheritance.
188. recessive allele — an allele expressed only without a dominant counterpart in simple inheritance.
189. homozygous — having two identical alleles at a locus.
190. heterozygous — having two different alleles at a locus.
191. mitosis — cell division producing genetically identical daughter nuclei in usual cases.
192. meiosis — cell division that reduces chromosome number for gamete formation.
193. gamete — a reproductive sex cell with half the usual chromosome set.
194. fertilisation — fusion of male and female gametes.
195. zygote — the cell formed when gametes fuse.
196. sexual reproduction — reproduction involving fusion of gametes.
197. asexual reproduction — reproduction without gamete fusion.
198. variation — differences among members of a species.
199. mutation — a change in the DNA sequence.
200. inheritance — transfer of genetic information between generations.

Test understanding: Use B and b in an illustrative single-gene model to distinguish genotype from phenotype.

Five worked examples: Biology is more than memorising labels

Example 1: what osmosis really describes

Imagine a plant cell placed in a solution with lower water potential than its cell sap. Water moves across the partially permeable cell membrane from a region of higher water potential to a region of lower water potential. The plant cell loses water and becomes less turgid. With substantial loss, the membrane may pull away from the wall and the cell may become plasmolysed.

The word osmosis is not simply a fancy synonym for diffusion of any substance. It refers to the net movement of water through an appropriate membrane. Students should identify the membrane, the water-potential difference and the direction of net water movement before explaining what happens to the cell.

Example 2: enzyme action and temperature

For a typical enzyme, raising temperature from a low level can increase collision frequency and reaction rate until an optimal range is approached. At much higher temperature, the enzyme’s protein structure may be disrupted, altering the active site and reducing its catalytic function. This loss of structure is called denaturation.

Do not conclude that every enzyme has the same optimum temperature or that denaturation occurs at one universal number. Use the actual graph or conditions supplied in the question. “More heat always makes enzymes work faster” is a common oversimplification that the vocabulary helps correct.

Example 3: digestion, absorption and assimilation

Suppose a person eats starch-containing food. The starch is broken down through digestive reactions into smaller sugars, ultimately yielding molecules such as glucose that can be absorbed. The small intestine has villi that increase the absorptive surface area, and microvilli provide additional area at the cell level.

After absorption, body cells may use glucose in respiration or transform it into other substances. This use within the body is part of assimilation. Digestion happens in the digestive system, absorption brings material into the body’s transport systems, and assimilation describes the use or incorporation of absorbed substances. Keeping these stages distinct strengthens explanations.

Example 4: blood flow and respiratory processes

The pulmonary artery carries blood away from the heart toward the lungs, even though that blood is relatively low in oxygen. The pulmonary vein returns oxygenated blood from the lungs to the heart. This shows why the definition of artery or vein is based on direction relative to the heart, not always on oxygen content.

At the alveoli, oxygen moves across a short exchange distance into the blood. Red blood cell haemoglobin helps transport it. Cells later use oxygen in aerobic respiration to release energy from glucose. Breathing, gas exchange, transport and respiration are connected processes but not interchangeable labels.

Example 5: a simple inheritance probability

Take an illustrative gene with alleles B and b, where B is completely dominant to b. If two heterozygous parents (Bb × Bb) reproduce, the four equally likely allele combinations under a simple Punnett-square model are BB, Bb, bB and bb. The genotype ratio is 1 BB : 2 Bb : 1 bb, and the dominant phenotype occurs in three of four combinations under the stated assumptions.

This is a probability model, not a prediction that exactly three of any four children will show one trait. Each event has uncertainty; many human characteristics involve multiple genes, environments or other complexities. The model is useful because it teaches the meanings of allele, genotype, phenotype, heterozygous and dominant without pretending all inheritance is simple.

Reading a biological diagram or experiment in the right order

Start by naming the whole organism or system and then the level shown: organ, tissue, cell or molecule. Identify arrows and labels before explaining processes. If a diagram shows the movement of a substance, ask what drives the movement: a concentration gradient, water-potential difference, pressure or energy-dependent transport. An answer using the right term for the wrong mechanism is still incorrect.

With a graph, check the axes, units, scale and experimental controls. A measured rise in rate might be associated with a changed temperature or light intensity, but an observation alone does not prove a unique cause if other factors varied. Record the actual pattern first, provide the biological explanation second, and separate limitations from conclusions.

School Biology practical activities require proper hygiene, handling and teacher supervision. For independent study at home, use supplied data, labelled microscopy images, approved models and diagrams rather than unfamiliar biological specimens or experiments that present avoidable risks.

Seven frequent misunderstanding patterns and repairs

Cell structure without function: a correct label is given but the required adaptation is missing. Repair: explain one feature and how it helps perform the stated job.

Diffusion confused with osmosis: water, membrane and direction are not identified. Repair: draw the concentration or water-potential relationship.

Enzyme rates described mechanically: students say temperature “kills the enzyme”. Repair: explain effects on enzyme shape, active site and reaction rate where applicable.

Digestion mixed with egestion: the breakdown and movement of food are treated as identical. Repair: place each process at the correct stage of the digestive pathway.

Artery defined by oxygen content: pulmonary vessels appear to contradict the memory phrase. Repair: define arteries as vessels that carry blood away from the heart.

Homeostasis interpreted as unchanging: students assume body temperature and glucose never vary. Repair: explain feedback mechanisms working within regulated ranges.

Inheritance presented as certainty: probability ratios are treated as guaranteed outcomes in a small family. Repair: state model assumptions and the random nature of gamete combinations.

A four-week Secondary 3 Biology vocabulary plan

Week 1 — cells, transport and enzymes

Learn groups 1–3 in daily sets of eight to ten terms. Use one labelled diagram and one explanation of structure-function per day. Contrast diffusion and osmosis in a two-column comparison, then apply the difference to a new example.

Week 2 — digestion, blood and homeostasis

Study groups 4–6. Draw a human system at each level and narrate what changes along the pathway. Explain digestion versus absorption, oxygen transport versus respiration, and excretion versus egestion. Retest the exact distinctions the learner missed rather than copying the entire textbook.

Week 3 — coordination, plant transport and ecology

Use groups 7–9. Trace one reflex pathway; then draw a leaf and identify xylem, phloem and stomata. Explain an ecosystem food web with more than one connection and discuss what a single observation can or cannot prove.

Week 4 — genetics, evidence and transfer

Use group 10 and mixed questions relevant to the current school lessons. Construct a simple Punnett square, explain what the ratio represents and write a limitation. End with two unfamiliar structured questions, one data interpretation and one short explanation. Revise only the words that still cause mistakes.

Parent checkpoint: ask the student “What is the mechanism?” and “Which part of your explanation is evidence and which part is inference?” If the student can transfer the idea to a changed example, the vocabulary is useful.

Frequently asked questions

Is this MOE’s official list of 200 Secondary 3 Biology words?

No. It is an independently curated glossary informed by the broader upper-secondary syllabus. MOE and SEAB do not identify this exact list as a compulsory set.

Does this list cover combined Science Biology?

The central reference is full G3 Biology K325. Combined Science (Physics, Biology) K327 and Science (Chemistry, Biology) K328 have their own syllabuses. Use the subject document matching the student’s enrolment.

Will a Secondary 3 student be assessed on every topic now?

Not necessarily. Different schools sequence upper-secondary lessons differently. Follow the immediate school assignments first and use later groups as a reference for future study.

What is the quickest way to answer “explain” in Biology?

State what happens, identify the relevant structure or process, and connect the cause to its effect. Avoid an isolated term that does not actually answer the question.

Why is practical data analysis important?

Biological investigations must distinguish observation, variable control, uncertainty and inference. Real evidence can challenge an attractive explanation, so students need both precise terminology and disciplined reasoning.

Is Biology just memorising 200 definitions?

No. Biological understanding depends on explanations of systems, structures and functions, and evidence about how organisms respond. Small application exercises are more useful than copying definitions without context.

When can additional help be useful?

When repeated mistakes reveal a specific gap in a mechanism or interpretation that the student cannot repair through ordinary practice. First identify the starting position and teach the missing link.

Official references and connected learning

Read the official SEAB G3 Biology K325 syllabus for 2027 and the 2027 G3 SEC subject index. For connected chemical concepts see Secondary 3 Chemistry: 200 terms. For the foundation-first learning method see the eduKate Clementi teaching guide.

Remember: name the structure, state its function, explain the mechanism and check that the evidence supports the claim. This is what biological vocabulary is for.