中文（繁體）
中文（简体）
English
HKDSE Biology Paper 1 Section A (Multiple Choice) Practice Paper | 36 questions, 36 marks, 60 minutes
HKDSE Biology Paper 1
HKDSE Biology Paper 1 MCQ practice: 36 questions, 36 marks across the four compulsory topics, each with an answer and short explanation. Full Paper 1 is 2h30 (MCQ 18%, written 42%); this paper practises the MCQ section only.
Download Question paper PDF | Answer key PDF
Paper details Level: S6 (HKDSE) | Subject: Biology | Time: 60 minutes | Marks: 36 | Questions: 36
Section A – Cells and Molecules of Life / Genetics and Evolution (12 marks)
1 mark each. Choose the best answer.
| # | Question | Answer and marking notes |
|---|---|---|
| 1 | A cell structure measures 60 mm on a micrograph; its real length is 0.05 mm. What is the magnification? A. x120 B. x1200 C. x12 000 D. x12 | Answer: B | Magnification = image length / actual length = 60 / 0.05 = x1200. |
| 2 | Which structure is present in a bacterial cell? A. Nuclear envelope B. Mitochondrion C. Ribosome D. Chloroplast | Answer: C | Bacteria are prokaryotes: they have no membrane-bound organelles, but they do have ribosomes for protein synthesis. |
| 3 | An enzyme and its substrate are mixed. Above 6 mmol/dm3 substrate the rate stays at 3.2 per minute. What now limits the rate? A. Substrate concentration B. Temperature C. pH D. Enzyme concentration | Answer: D | All active sites are saturated, so the rate has reached its maximum and extra substrate has no effect; the enzyme concentration becomes limiting. |
| 4 | Agar cubes of side 1, 2 and 4 cm are placed in an indicator solution. Which cube is stained at the centre first? A. 1 cm cube B. 2 cm cube C. 4 cm cube D. All at the same time | Answer: A | The surface area to volume ratios are 6, 3 and 1.5, so the 1 cm cube has the largest ratio and the shortest diffusion path. |
| 5 | Potato strips are placed in sucrose solutions of 0.0, 0.1, 0.2, 0.3, 0.4 mol/dm3; the mass changes are +6, +4, +2, +0, -3%. Which concentration is closest to the cell sap? A. 0.0 B. 0.1 C. 0.3 D. 0.4 mol/dm3 | Answer: C | No change in mass means no net water movement, so the solution is isotonic with the cell sap, about 0.3 mol/dm3. |
| 6 | Two tall pea plants (Tt x Tt) produce 400 seeds. About how many should be tall? A. 100 B. 200 C. 267 D. 300 | Answer: D | Tt x Tt gives 1 TT : 2 Tt : 1 tt, so three quarters are tall: 400 x 3/4 = 300 seeds. |
| 7 | In a DNA sample adenine (A) is 30% of the bases. What percentage is guanine (G)? A. 30% B. 20% C. 30% D. 40% | Answer: B | A pairs with T, so A = T = 30% and together they take 60%. The remaining 40% is shared equally by G and C, so G = 20%. |
| 8 | A body cell of an organism has 24 chromosomes (2n = 24). How many chromosomes are in its gamete? A. 48 B. 24 C. 12 D. 6 | Answer: C | Meiosis halves the chromosome number, so the haploid gamete has 24 / 2 = 12 chromosomes. |
| 9 | A tall pea plant crossed with a dwarf plant gives only tall offspring. What is the genotype of the tall parent most likely to be? A. TT B. Tt C. tt D. Cannot be decided | Answer: A | No dwarf offspring appear, so the parent carries no recessive allele t and is most likely homozygous TT. |
| 10 | How many chromosomes are usually found in the body cells of a person with Down syndrome, and why? A. 46; one chromosome missing from pair 21 B. 47; one extra chromosome 21 C. 45; a sex chromosome missing D. 48; two extra chromosomes in pair 21 | Answer: B | Down syndrome is trisomy 21: there is one extra copy of chromosome 21, giving 47 chromosomes. |
| 11 | A root hair cell takes up nitrate from dilute soil solution into a more concentrated cell sap. Which transport is this and what does it need? A. Diffusion; no energy B. Osmosis; a water potential gradient C. Facilitated diffusion; carrier proteins only D. Active transport; energy from respiration | Answer: D | Movement against the concentration gradient requires active transport, which needs carrier proteins and ATP supplied by respiration. |
| 12 | 100 divisions of an eyepiece graticule equal 1.0 mm. A cell covers 25 divisions. What is its real length? A. 0.25 um B. 25 um C. 250 um D. 2 500 um | Answer: C | One division = 1.0 mm / 100 = 10 um, so 25 divisions = 250 um. |
Section B – Organisms and Environment (12 marks)
1 mark each. Choose the best answer.
| # | Question | Answer and marking notes |
|---|---|---|
| 13 | As light intensity rises the rate of photosynthesis increases and then levels off. What most likely limits the rate at that point? A. Light intensity B. Carbon dioxide concentration C. Oxygen concentration D. Number of leaves | Answer: B | Once the rate stops rising with light, light is no longer limiting; carbon dioxide concentration or temperature has become the limiting factor. |
| 14 | A shoot loses 3.0 cm3 of water per 10 minutes in still air and 9.0 cm3 per 10 minutes in front of a fan. By what factor does wind increase transpiration? A. 2 B. 6 C. 3 D. 12 | Answer: C | 9.0 / 3.0 = 3: wind removes the humid layer around the leaf, steepening the water potential gradient. |
| 15 | Producers hold 20,000 kJ, primary consumers 2,000 kJ and secondary consumers 200 kJ. What is the efficiency of energy transfer from primary to secondary consumers? A. 10% B. 20% C. 1% D. 50% | Answer: A | 200 / 2,000 x 100% = 10%; the rest is lost as heat from respiration, in excreta and in uneaten parts. |
| 16 | Which process returns carbon from living things to atmospheric carbon dioxide? A. Photosynthesis B. Nitrification C. Protein synthesis D. Respiration of decomposers | Answer: D | Decomposers respire as they break down dead matter, oxidising organic carbon to carbon dioxide. |
| 17 | Heavy nitrate fertiliser run-off enters a lake. What is the most likely sequence of events? A. Less algae, more oxygen, more fish B. Algal bloom, then decay and oxygen depletion, killing fish C. More oxygen, algae die, water clears D. Clearer water, more photosynthesis, more fish | Answer: B | Excess nutrients cause an algal bloom; when the algae die, decomposers multiply and use up dissolved oxygen, so fish suffocate. |
| 18 | Ten 1 m2 quadrats thrown at random in a 500 m2 field hold a mean of 4 plants each. Estimate the number of plants in the field. A. 500 B. 2,000 C. 2 500 D. 50 | Answer: B | 500 / 1 x 4 = 2,000 plants; random sampling avoids bias. |
| 19 | A single large tree supports thousands of insects. What shape is the pyramid of numbers based on this tree as the first trophic level? A. Upright B. Diamond C. Inverted D. It cannot be drawn | Answer: C | One producer supports many primary consumers, so the pyramid is narrow at the base and wider above: inverted. |
| 20 | During vigorous exercise muscle cells respire anaerobically. Which statement is correct? A. Lactate is formed and less energy is released than in aerobic respiration B. Ethanol and carbon dioxide are formed with the same energy yield C. No energy is released D. Lactate is formed and more energy is released than in aerobic respiration | Answer: A | Human muscle converts glucose to lactate without full oxidation, so far less energy is released than in aerobic respiration. |
| 21 | Which feature does NOT help alveoli exchange gases? A. Large surface area B. Thin walls, one cell thick C. Moist surface D. Many muscle fibres in the wall | Answer: D | Gas exchange needs a thin, moist, large surface; muscle fibres play no part in diffusion and would thicken the wall. |
| 22 | Leaf litter kept at 25 °C decomposes faster than litter at 10 °C. What is the most direct reason? A. The litter holds more water B. Decomposer enzymes work faster C. The litter has a larger surface area D. The oxygen concentration is lower | Answer: B | Decomposition depends on microbial enzymes, whose activity rises towards the optimum as temperature increases. |
| 23 | Which measure would best raise biodiversity on a farm? A. Keeping the original hedgerows and ditches B. Growing a single crop all year C. Spraying broad-spectrum insecticide everywhere D. Clearing all weeds | Answer: A | Hedgerows and ditches provide habitats and food for many species, whereas monoculture and insecticides reduce diversity. |
| 24 | A marine fish has body fluid less salty than sea water. How does it keep its water balance? A. Drinks much sea water and passes dilute urine B. Drinks nothing and passes concentrated urine C. Drinks sea water and excretes excess salt through the gills, passing little urine D. Absorbs water continuously through the skin | Answer: C | Its body fluids are more dilute than sea water so it loses water; it drinks sea water, excretes salt actively via the gills and passes small volumes of urine. |
Section C – Health and Diseases (12 marks)
1 mark each. Choose the best answer.
| # | Question | Answer and marking notes |
|---|---|---|
| 25 | Why should a doctor not prescribe antibiotics for a cold caused by a virus? A. Antibiotics make viruses multiply faster B. Antibiotics act only on bacteria, not on viruses C. Viruses break down antibiotics D. Antibiotics work only on fungi | Answer: B | Antibiotics target bacterial structures such as the cell wall or ribosomes, which viruses do not have. |
| 26 | After vaccination the body makes antibody very quickly on later exposure to the same pathogen. What makes this possible? A. Memory cells B. Red blood cells C. Platelets D. The keratinised skin layer | Answer: A | Vaccination leaves memory B and T cells, so a second exposure triggers a fast, large antibody response. |
| 27 | HIV mainly attacks which cells, lowering the patient’s immunity? A. Red blood cells B. Nerve cells C. Platelets D. Helper T cells | Answer: D | HIV infects helper T cells and destroys them, so the coordination of the immune response fails and opportunistic infections follow. |
| 28 | Which is NOT a known risk factor for coronary heart disease? A. Smoking B. A diet high in saturated fat C. Regular moderate exercise D. High blood pressure | Answer: C | Regular exercise lowers the risk; smoking, saturated fat and hypertension all raise it. |
| 29 | A person weighs 68 kg and is 1.60 m tall. What is the BMI and which category does it fall in? A. 23.6, normal B. 25.0, normal C. 26.6, overweight D. 42.5, obese | Answer: C | BMI = mass / height squared = 68 / 1.60^2 = 26.6, which is in the overweight range for adults. |
| 30 | What is the main difference between a cancer cell and a normal cell? A. It has lost control of cell division and can invade other tissues B. It no longer respires C. It has no nucleus D. It cannot make protein | Answer: A | Mutations remove the controls on division, so cancer cells divide repeatedly and may spread to other tissues. |
| 31 | A person has persistently high fasting blood glucose and is diagnosed with type 2 diabetes. Which explanation fits best? A. Too much insulin is secreted B. The body responds too strongly to insulin C. Too few red blood cells D. Cells respond poorly to insulin, so glucose enters them slowly | Answer: D | Type 2 diabetes is mainly insulin resistance: target cells respond weakly, so glucose stays in the blood. |
| 32 | Students press unwashed and washed (20 s) fingers onto agar plates and count 84 and 21 colonies. By what percentage does hand washing reduce the colonies? A. 25% B. 75% C. 63% D. 400% | Answer: B | (84 – 21) / 84 x 100% = 75%, a fall of three quarters. |
| 33 | Overuse of antibiotics leads to more resistant bacteria. How does Darwinian theory explain this? A. Resistant individuals survive and reproduce, passing on resistance genes B. Bacteria learn to resist antibiotics C. Antibiotics make bacteria mutate to become stronger D. Resistance comes from vaccines | Answer: A | Antibiotics kill susceptible cells, so resistant individuals survive and reproduce: natural selection. Resistance genes also spread between bacteria on plasmids. |
| 34 | When a flu patient coughs or sneezes, droplets carrying the pathogen reach people nearby. Which route of transmission is this? A. Food-borne B. Vector-borne C. Droplet D. Blood-borne | Answer: C | Coughing and sneezing release droplets that are inhaled at close range: droplet transmission, reduced by wearing a mask. |
| 35 | An adult has a blood pressure reading of 150/95 mmHg. Which statement is correct? A. Systolic normal, diastolic high B. Both normal C. Systolic too low D. Both systolic and diastolic are high: hypertension | Answer: D | Around 120/80 mmHg is usual for adults; 140/90 or above sustained is hypertension, and both values here exceed it. |
| 36 | An allergic reaction such as hay fever is mainly caused by which mechanism? A. Too few platelets B. The immune system making antibody against a harmless substance and releasing histamine C. Bacteria destroying red blood cells D. Too much insulin | Answer: B | Allergy is the immune system mistaking a harmless substance such as pollen for an antigen; antibody triggers histamine release, causing itching and a runny nose. |
A TutorZone practice paper; original questions and passages, not publisher material.
