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HKDSE Biology Paper 1 Mock Paper (2027): 20 MC and 6 Section B Questions with Answers
TUTORZONE ORIGINAL MOCK PAPER · HKDSE BIOLOGY PAPER 1
Written to the HKEAA 2027 framework: Paper 1 covers the Compulsory Part, 60% of the subject, 2 hours 30 minutes, with Section A multiple-choice at 18% of the subject mark and Section B (short, structured and essay questions) at 42%, all compulsory. This paper has 20 MC items and 6 Section B questions with answers and mark allocation.
What is in HKDSE Biology Paper 1?
Direct answer: Paper 1 covers the Compulsory Part, is 60% of the subject and lasts 2 hours 30 minutes, with every question compulsory. Section A is multiple-choice and takes 18% of the subject mark; Section B – short questions, structured questions and one essay – takes the remaining 42%. The Elective Part is Paper 2 (20%) and SBA is 20%.
Assessment at a glance (2027)
| Component | Content | Weighting | Duration |
|---|---|---|---|
| Section A (multiple-choice) | Compulsory Part; 18% of the subject mark | 18%（全科） | 35-40 min |
| Section B (short, structured, essay) | Compulsory Part; 42% of the subject mark, ending with an essay question | 42%（全科） | 100-110 min |
| Paper 1 total | All questions compulsory; Paper 2 (Electives) is another 20% in 1 hour (structured, choose two of four topics) plus SBA 20% (practical skills 8% and investigative report 12%) | 60% | 2 h 30 min |
Cut the 150 minutes as 38 for Section A, 105 for Section B and 7 to check. Section B marks come from three things: the right biological terms, the mechanism written out, and calculations with units on data questions. Conclusions alone rarely score.
How this paper was built
This is a TutorZone original mock paper: the questions follow the 2027 framework’s structure (Section A MC at 18% of the subject mark, Section B at 42%, all compulsory) and the answers and mark allocation are our own, not HKEAA past papers or marking references.
HKEAA publishes no fixed question count for Paper 1, so this paper sets its own: 20 MC items and 6 Section B questions, one of them an essay question. Numeric answers were recomputed programmatically.
Pacing
| Section | Marks | Suggested time | What to do first |
|---|---|---|---|
| Section A (multiple-choice) | 18%（全科） | 35-40 min | Definitions and comparisons; watch for NOT questions |
| Section B (short, structured, essay) | 42%（全科） | 100-110 min | Use biological terms; show calculations and units on data questions |
| Paper 1 total | 60% | 150 min (about 38 for A and 105 for B) | Keep 12-15 minutes for the essay |
How should the 150 minutes be split?
Direct answer: about 38 minutes on Section A, 105 on Section B and 7 to check. Section B scores on correct terms, complete mechanisms and calculations with units; give the essay 12-15 minutes.
Section A: multiple-choice (20 questions, 18% of the subject mark)
Aim for 35-40 minutes. Watch for NOT questions.
Question 1
Which structure is found in plant cells but not in animal cells?
A. 細胞膜B. 細胞核C. 葉綠體D. 線粒體
Question 2
Under a 40× objective and a 10× eyepiece the field of view is 8 mm across. A cell spans about 1/20 of it. What is the cell diameter?
A. 4 000 µmB. 0.4 µmC. 40 µmD. 400 µm
Question 3
Which observation best shows enzyme specificity?
A. 酶的活性受 pH 影響B. 澱粉酶只催化澱粉水解，不催化蛋白質C. 酶可重複使用D. 酶在高溫下失去活性
Question 4
An enzyme is heated to 80 °C and then cooled back to its optimum temperature. What happens to its activity?
A. 回復一半B. 完全回復C. 不會回復，因為酶已變性D. 活性反而提高
Question 5
In 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, how much CO₂ is needed to make 3 mol of glucose?
A. 18 molB. 36 molC. 3 molD. 6 mol
Question 6
How much CO₂ is produced when 1 mol of glucose is fully broken down in aerobic respiration?
A. 2 molB. 12 molC. 3 molD. 6 mol
Question 7
What does salivary amylase mainly break starch down into at first?
A. 甘油B. 葡萄糖C. 麥芽糖D. 氨基酸
Question 8
Which chamber of the heart has the thickest muscular wall?
A. 左心房B. 右心房C. 右心室D. 左心室
Question 9
Which statement about mature red blood cells is correct?
A. 沒有血紅蛋白B. 有細胞核，含血紅蛋白C. 沒有細胞核，含血紅蛋白D. 可進行有絲分裂
Question 10
Which is NOT a feature of alveoli that aids gas exchange?
A. 表面濕潤並有密集微血管B. 肺泡壁有豐富的肌肉組織C. 壁只有一層細胞厚D. 表面積大
Question 11
In urine formation, which process happens in the tubule?
A. 紅血球被製造B. 尿素被分解為氨C. 有用的物質被重吸收回血液D. 血液被過濾成濾液
Question 12
What is the order of a reflex arc?
A. 中樞 → 受體 → 感覺神經元 → 效應器B. 受體 → 運動神經元 → 中樞 → 感覺神經元 → 效應器C. 受體 → 感覺神經元 → 中樞 → 運動神經元 → 效應器D. 效應器 → 感覺神經元 → 中樞 → 運動神經元 → 受體
Question 13
What is the main action of insulin?
A. 提高血糖B. 促進蛋白質分解C. 加快心跳D. 降低血糖
Question 14
Two individuals of genotype Aa are crossed. What phenotype ratio is expected in the offspring?
A. 1:2:1B. 1:1C. 9:3:3:1D. 3:1
Question 15
In the offspring of Aa × Aa, what is the expected genotype ratio?
A. 1:2:1B. 1:1C. 2:1D. 3:1
Question 16
In humans, a sex chromosome pair of XY indicates which sex?
A. 兩者皆非B. 無法判斷C. 女性D. 男性
Question 17
If producers fix 20 000 kJ of energy, roughly how much reaches primary consumers at about 10% efficiency?
A. 2 000 kJB. 20 kJC. 200 kJD. 2 000 000 kJ
Question 18
What is the main role of decomposers in an ecosystem?
A. 把無機物合成有機物B. 把死去的生物體與排泄物分解為無機物C. 直接捕食生產者D. 固定大氣中的氮
Question 19
In genetic engineering, which enzyme cuts out the target gene?
A. 解旋酶B. 限制酶C. 連接酶D. 聚合酶
Question 20
Why does vaccination give immunity?
A. 身體產生抗體與記憶細胞（主動免疫）B. 直接殺死病原體C. 直接注入抗體（被動免疫）D. 改變基因
Section B: short, structured and essay questions (6 questions, 42% of the subject mark)
Aim for 100-110 minutes. Answer with biological terms, show calculations and units on data items, and keep 12-15 minutes for the essay.
Question 1 (7 marks)
A student places mixtures of amylase and starch solution in water baths at 10 °C, 37 °C and 80 °C, then tests with iodine solution after 10 minutes. (a) Predict and explain the three results; (b) why do 10 °C and 80 °C differ, even though both look “slow”?
Question 2 (8 marks)
A student counts bubbles per minute from pondweed in sodium hydrogencarbonate solution in sunlight to study the rate of photosynthesis. (a) Which gas are the bubbles, and how could you prove it? (b) Name two variables that should be kept constant; (c) what happens to the bubble count if the lamp is moved further away? Explain.
Question 3 (7 marks)
Both parents have genotype Aa (A dominant, a recessive). (a) Use a Punnett square to give the possible genotypes and their ratio; (b) find the probability of a recessive phenotype; (c) if a child shows the recessive phenotype, what must the parents’ genotypes be?
Question 4 (7 marks)
Compare inhaled and exhaled air and explain the differences. (a) Give two differences with reasons; (b) how would you demonstrate that exhaled air contains more carbon dioxide? (c) why does exhaled air still contain oxygen?
Question 5 (8 marks)
In a food chain – phytoplankton to small fish to large fish to a bird – the producers fix 20 000 kJ and energy transfer is about 10% efficient. (a) Work out the energy at each trophic level; (b) explain why energy falls at each level (two reasons); (c) why are top predators usually few?
Question 6 (8 marks) essay question
Discuss how the overuse of antibiotics leads to more antibiotic-resistant bacteria, and suggest two ways to reduce resistance.
Where are the answers, and do they show the steps?
Direct answer: each question is followed by an answer-and-marks block giving the answer, the key steps or mechanism and the marks each step earns (the enzyme question: 2 marks per temperature plus 1 for reversibility), plus the usual losses.
Section A answers and explanations
Question 1
Answer: C (葉綠體) Chloroplasts occur only in photosynthetic plant cells (and some algae).
Question 2
Answer: D (400 µm) 400× magnification, 8 mm field; 8 ÷ 20 = 0.4 mm = 400 µm.
Question 3
Answer: B (澱粉酶只催化澱粉水解，不催化蛋白質) Specificity means one enzyme acts on a particular substrate only.
Question 4
Answer: C (不會回復，因為酶已變性) Heat denatures the active site irreversibly; low temperature only slows it down, which is reversible.
Question 5
Answer: A (18 mol) The ratio is 6:1, so 3 × 6 = 18 mol.
Question 6
Answer: D (6 mol) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.
Question 7
Answer: C (麥芽糖) Starch to maltose (maltase then splits maltose into glucose).
Question 8
Answer: D (左心室) The left ventricle pumps blood around the whole body, so it needs the highest pressure.
Question 9
Answer: C (沒有細胞核，含血紅蛋白) Mature red cells lack a nucleus and most organelles, making room for more haemoglobin.
Question 10
Answer: B (肺泡壁有豐富的肌肉組織) Alveolar walls have no muscle; exchange relies on diffusion over a short distance, a large wet area and a gradient.
Question 11
Answer: C (有用的物質被重吸收回血液) The glomerulus filters; the tubule selectively reabsorbs glucose, some water and salts.
Question 12
Answer: C (受體 → 感覺神經元 → 中樞 → 運動神經元 → 效應器) The signal travels from receptor along the sensory neurone to the CNS, then out along the motor neurone to the effector.
Question 13
Answer: D (降低血糖) Insulin promotes glucose uptake and glycogen formation, lowering blood glucose; glucagon does the opposite.
Question 14
Answer: D (3:1) Aa × Aa gives AA : Aa : aa = 1 : 2 : 1, so the dominant phenotype takes 3/4.
Question 15
Answer: A (1:2:1) A Punnett square gives AA : Aa : aa = 1 : 2 : 1.
Question 16
Answer: D (男性) Males are XY and females XX; the Y chromosome comes from the father.
Question 17
Answer: A (2 000 kJ) Each trophic level keeps about 10%: 20 000 × 10%.
Question 18
Answer: B (把死去的生物體與排泄物分解為無機物) Decomposers break organic matter into inorganic nutrients, returning matter to the environment.
Question 19
Answer: B (限制酶) Restriction enzymes cut DNA at specific sequences; ligase joins the fragments.
Question 20
Answer: A (身體產生抗體與記憶細胞（主動免疫）) The vaccine supplies the antigen so the body makes antibodies and memory cells, allowing a fast response later.
Section B answers and mark allocation
Question 1
(a) 10 °C: starch likely remains (iodine turns blue-black) – cold only slows the enzyme, which is not denatured (2 marks); 37 °C: starch has gone (no blue-black) – near optimum, fastest (2 marks); 80 °C: starch remains (blue-black) – the enzyme is denatured (2 marks). (b) At 10 °C the structure is intact and activity returns on warming, whereas at 80 °C the active site is permanently destroyed (1 mark).
Question 2
(a) Oxygen (1 mark); a glowing splint relights in it (2 marks). (b) Any two of temperature, sodium hydrogencarbonate concentration, size or number of shoots, other apparatus conditions (2 marks). (c) Fewer bubbles (1 mark) – lower light intensity means less energy and reducing power from the light reaction, so the rate falls (2 marks).
Question 3
(a) The square gives AA, Aa, Aa, aa → AA : Aa : aa = 1 : 2 : 1 (3 marks); (b) only aa shows the recessive phenotype, so the probability is 1/4 (2 marks); (c) both parents must contribute a, so both carry a (in practice both Aa) (2 marks).
Question 4
(a) less oxygen, used up by respiration in the tissues (2 marks); more carbon dioxide, produced by respiration (2 marks); (b) bubble exhaled air through limewater and it turns milky (2 marks); (c) each breath exchanges only part of the air and respiration does not remove all the oxygen in the alveoli (1 mark).
Question 5
(a) 2 000 kJ in the small fish, 200 kJ in the large fish and 20 kJ in the bird (3 marks); (b) much of the energy is lost as heat in respiration (2 marks), and some leaves the chain in undigested material and excretory products (2 marks); (c) too little energy reaches the top, so the biomass and numbers it can support are small (1 mark).
Question 6
Mechanism (4 marks): a bacterial population already contains individuals resistant through gene mutation (1 mark); antibiotics kill the sensitive ones while the resistant ones survive and reproduce (1 mark), passing resistance to their offspring and even sideways to other bacteria through plasmids (conjugation) (1 mark); repeated use therefore amounts to natural selection that raises the resistant proportion (1 mark).
Measures (2 marks each): prescribe antibiotics only for confirmed bacterial infections and complete the full course rather than stopping early or self-medicating; and cut routine antibiotic use as growth promoters in farming while strengthening infection control and vaccination.
Marks go per mechanism step, measure and reason.
Where are Paper 1 marks most easily lost?
Direct answer: three places – a conclusion with no process (four words such as “the enzyme denatures”), everyday language instead of terms, and no units on data questions. An essay that says “harmful” without the mechanism scores nothing either.
Where these marks are usually lost
| Mistake | What it looks like | What it costs | Instead |
|---|---|---|---|
| Conclusions without the process | “because the enzyme is denatured” and nothing else | Structured items are marked per step, so a right conclusion can still earn one mark | Write high temperature, altered active site, irreversible |
| Everyday language instead of terms | “the vessel is blocked”, “the bacteria got stronger” | Markers require the correct term, not a description | Use atherosclerosis, or resistance rising through natural selection |
| No units on data questions | Bare numbers | Biology data items require units and significant figures too | Give the unit (kJ, µm, mol) with every number |
| Essays with no mechanism | “antibiotics are harmful” | The essay is marked on mechanism steps and recommendations | Follow mutation, selection, reproduction, then your measures |
How to use this paper
First sit: no references, the full 150 minutes, no textbook.
Mark it: work through the mark allocation item by item, checking terminology and steps rather than just the facts.
Second sit: redo Section B three to seven days later, aiming for accurate terms and complete mechanisms.
What should I do after this paper?
Direct answer: turn every imprecise answer into a glossary entry; drill past-paper questions by topic (cells, enzymes and metabolism, genetics, ecology, biotechnology); then redo Section B three to seven days later for accurate terms and complete mechanisms.
FAQ
Is this an HKEAA paper?
No. The questions, answers and mark allocation are TutorZone originals; only the framework figures (60%, 18%, 42%, 150 minutes) come from the HKEAA 2027 assessment framework.
How many questions does Paper 1 have?
HKEAA publishes no fixed count. This paper sets its own: 20 MC items and 6 Section B questions, proportioned to the 18/42 split.
What about Paper 2 and SBA?
Paper 2 covers the Elective Part: 20% in 1 hour, structured questions, answer two of the four topics. SBA is 20% (practical skills 8%, investigative report 12%) and compulsory for school candidates.
Official references
| Resource | What to check |
|---|---|
| HKEAA 2027 HKDSE Biology Assessment Framework | Confirm Paper 1’s 60%, 2 h 30 min, Section A 18% and Section B 42% |
| https://www.tutorzone.com.hk/en-dse-biology-paper-1-drill-guide/ | Paper 1 drilling guide: pacing and structured-question writing |
| https://www.tutorzone.com.hk/en-dse-biology-paper-2-electives-drill-guide/ | Paper 2 (Electives) drilling guide |
Related: practice area · Paper 2 electives guide · Chemistry Paper 1 mock
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