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IB Biology Mock Paper (first assessment 2025): Paper 1 Data Questions and Paper 2 Extended Response with Answers
TUTORZONE ORIGINAL MOCK PAPER · IB BIOLOGY (first assessment 2025)
Written to the IBO subject brief for first assessment 2025: Paper 1 (multiple-choice plus data-based questions) is 36%% (SL 1.5 h / HL 2 h), Paper 2 (short-answer and extended-response) is 44%% (SL 1.5 / HL 2.5 h) and the scientific investigation is 20%%. This paper has 10 MC items, 2 data-based and 2 extended-response questions with answers and mark allocation.
How are Paper 1 and Paper 2 weighted in IB IB Biology?
Direct answer: per the IBO subject brief for first assessment 2025, Paper 1 (1A multiple-choice + 1B data-based) is 36% of the final grade (SL 1.5 h / HL 2 h), Paper 2 (short-answer and extended-response) is 44% (SL 1.5 / HL 2.5 h) and the scientific investigation is 20%.
Assessment at a glance (2027)
| Component | Content | Weighting | Duration |
|---|---|---|---|
| Paper 1 (1A multiple-choice + 1B data-based) | All syllabus themes; 36% of the final grade | 36% | SL 1.5 h / HL 2 h |
| Paper 2 (short-answer + extended-response) | Short-answer and extended-response; 44% of the final grade | 44% | SL 1.5 h / HL 2.5 h |
| Scientific investigation (IA) | Open-ended investigation, 20% of the final grade (10 recommended hours) | 20% | done in school |
Paper 1B marks come from reading, calculation and unit – miss one and you lose the mark. Paper 2 extended-response answers should be point, mechanism, example, with evidence behind every claim. Finish 1A in about 25 minutes and spend the rest on 1B and the essays.
How this paper was built
This is a TutorZone original mock paper: the questions follow the Paper 1/Paper 2 formats of the 2025 first assessment and the answers are our own, not IB past papers or official marking references; only the 36/44/20 weightings come from the IBO subject brief.
The IB publishes no fixed question count, so this paper sets its own: 10 MC items, 2 data-based questions and 2 extended-response questions. Every numeric answer was recomputed programmatically.
Pacing
| Section | Marks | Suggested time | What to do first |
|---|---|---|---|
| Paper 1 (1A multiple-choice + 1B data-based) | 36% | about 25 min for 1A, 45 for 1B (SL) | On 1B show reading, calculation and unit |
| Paper 2 (short-answer + extended-response) | 44% | roughly 70% short-answer, 30% extended-response | Structure essays as point, mechanism, example |
| Scientific investigation (IA) | 20% | not covered here | Handled by your school; this page trains Papers 1 and 2 |
How do I score fully on Paper 1B data questions?
Direct answer: write all three: the value read from the graph with its unit, the formula and substitution, and the answer with significant figures. Marks are allocated to those three steps, so a bare final answer earns only the answer mark.
Paper 1A: multiple-choice (10 questions)
Aim for about 25 minutes at SL.
Question 1
What is the main function of mitochondria?
A. 進行有氧呼吸產生 ATPB. 合成蛋白質C. 貯存遺傳物質D. 進行光合作用
Question 2
An enzyme irreversibly loses activity after 80 °C because?
A. 受質被耗盡B. pH 改變C. 活性部位的結構被破壞（變性）D. 酶被稀釋
Question 3
The reactants of photosynthesis are?
A. 氧氣與葡萄糖B. 氧氣與水C. 二氧化碳與水D. 葡萄糖與水
Question 4
Two Aa individuals are crossed. The chance of a recessive phenotype is?
A. 3/4B. 1/2C. 0D. 1/4
Question 5
If producers fix 20 000 kJ, roughly how much reaches primary consumers at 10% efficiency?
A. 2 000 kJB. 20 kJC. 200 kJD. 200 000 kJ
Question 6
A body cell has 2n = 8 chromosomes. How many does one of its gametes carry?
A. 8B. 2C. 4D. 16
Question 7
Water enters root cells mainly by?
A. 滲透B. 主動運輸C. 幫助擴散D. 胞吞作用
Question 8
The rise of antibiotic-resistant bacteria illustrates which process?
A. 基因改造B. 人工選擇C. 自然選擇D. 遺傳漂變（在小族群）
Question 9
The main function of xylem is to?
A. 進行光合作用B. 運送蔗糖C. 運送水分與礦物質D. 貯存澱粉
Question 10
Vaccination produces immunity because?
A. 令病原體變異B. 產生抗體與記憶細胞C. 直接注入大量抗體D. 殺死所有病原體
Paper 1B: data-based questions (2 questions)
Aim for about 45 minutes. Read the values off the graph, calculate, then give the unit.
Question 1 (8 marks)
Experimental data: identical pondweed is placed at different distances from a lamp and bubbles per minute are counted.
Distance / cm: 10, 20, 30, 40; bubbles per minute: 48, 25, 12, 6.
(a) Describe the relationship; (b) explain why the rate falls as distance increases; (c) name two variables to keep constant.
Question 2 (7 marks)
Genetic data: both parents show the dominant phenotype but one of their children shows the recessive trait. (a) Deduce the parents’ genotypes and explain; (b) use a Punnett square to give the offspring genotype ratio; (c) find the probability that the next child shows the recessive trait.
Paper 2: short-answer and extended-response (2 questions)
Use point, mechanism, example for each extended answer.
Question 1 (12 marks)
Discuss how the properties of enzymes affect metabolism in organisms, giving one measurable example each for temperature and pH.
Question 2 (10 marks)
Discuss how human activity affects energy flow and nutrient cycling in ecosystems, and propose one measurable mitigation.
Where are the answers, and is there a mark allocation?
Direct answer: each question is followed by an answer-and-marks block: data questions give the reading, the working and the unit, and extended answers give each point with its mechanism, example and marks, ready to use as a self-marking sheet.
Paper 1A answers and explanations
Question 1
Answer: A (進行有氧呼吸產生 ATP) Mitochondria host aerobic respiration, converting chemical energy into usable ATP.
Question 2
Answer: C (活性部位的結構被破壞（變性）) Heat destroys the tertiary structure and active site: denaturation is irreversible.
Question 3
Answer: C (二氧化碳與水) 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, driven by light.
Question 4
Answer: D (1/4) AA : Aa : aa = 1 : 2 : 1, and only aa is recessive.
Question 5
Answer: A (2 000 kJ) Each trophic level retains roughly 10%.
Question 6
Answer: C (4) Gametes are produced by meiosis, so the number halves to 4.
Question 7
Answer: A (滲透) Water moves down a water potential gradient through the membrane: osmosis, a passive process.
Question 8
Answer: C (自然選擇) Antibiotics kill sensitive cells and resistant ones survive and reproduce, so the resistant proportion rises: natural selection.
Question 9
Answer: C (運送水分與礦物質) Xylem carries water and minerals upward; phloem transports sugars.
Question 10
Answer: B (產生抗體與記憶細胞) The vaccine provides the antigen so the immune system builds antibodies and memory cells for a faster, stronger response.
Paper 1B answers and mark allocation
Question 1
(a) As distance increases the bubble count falls, roughly to a quarter each time the distance doubles, matching the inverse-square fall in light intensity (3 marks); (b) light intensity at the plant drops with distance, so the light reaction supplies less energy and reducing power and the rate of photosynthesis falls, releasing less oxygen (3 marks); (c) water temperature, sodium hydrogencarbonate concentration (or size/number of shoots) (2 marks).
Question 2
(a) A recessive child must inherit one recessive allele from each parent, so both parents are heterozygous Aa (3 marks); (b) AA : Aa : aa = 1 : 2 : 1 (2 marks); (c) the probability is 1/4 (2 marks).
Paper 2 answers and mark allocation
Question 1
Specificity: the active site is complementary to one substrate, which orders the steps of a metabolic pathway (3 marks). Temperature: rate rises to an optimum then collapses as the enzyme denatures (3 marks); measurable example: incubate amylase and starch in water baths and time the disappearance of starch with iodine (2 marks). pH: each enzyme has an optimum, and deviation alters the charge and shape of the active site (2 marks); measurable example: pepsin is most active near pH 2 and almost inactive at pH 8 (2 marks).
Question 2
Deforestation, urbanisation and pollution cut producer biomass, reducing the total energy entering food chains (3 marks) and disrupting nutrient cycling, for example fertiliser runoff causing eutrophication and an imbalance in the nitrogen and phosphorus cycles (3 marks). A measurable mitigation: a constructed wetland for farm runoff – measure nitrate concentrations in and out and compare algal biomass before and after to verify nutrient removal (4 marks).
Where are marks most easily lost on this paper?
Direct answer: data questions without a recorded reading; essays that list points with no mechanism; ignored significant figures and uncertainty; and answering HL questions at SL depth or the reverse. All four are cases of knowing the science but writing too little.
Where these marks are usually lost
| Mistake | What it looks like | What it costs | Instead |
|---|---|---|---|
| No reading recorded on data questions | Straight to the calculation | 1B marks are reading, calculation and unit – each is separate | Write the value read off the graph, then the working, then the unit |
| Listing points in an essay | Three lines of bullet points | Extended-response answers need mechanism and example | Add a mechanism and a syllabus example to every point |
| Ignoring uncertainty | A single bare number | IB science marks uncertainty and significant figures | State the accuracy and identify a source of error |
| Confusing SL and HL depth | One depth for both | HL expects deeper mechanisms and quantitative treatment | Decide whether you sit SL or HL first |
How to use this paper
First sit: no references, timing Paper 1 (25 minutes for 1A, 45 for 1B) and Paper 2 as separate blocks.
Mark it: check reading, calculation and unit on every data part, and that each essay point carries a mechanism and an example.
Second sit: redo it three to seven days later aiming to hit every mark-allocation point on the essays.
What should I do after this paper?
Direct answer: turn reading-calculation-unit into a fixed template for data questions; template the extended answers as point, mechanism, example; drill by topic and keep an uncertainty-analysis note; then redo this paper three to seven days later.
FAQ
Is this an IB paper?
No. The questions, answers and mark allocation are TutorZone originals; only the weightings (Paper 1 36%, Paper 2 44%, investigation 20%) come from the IBO subject brief for first assessment 2025.
What is the difference between SL and HL?
Paper 1 runs 1.5 h at SL and 2 h at HL; Paper 2 runs 1.5 h at SL and 2.5 h at HL, with greater depth and breadth at HL. These questions cover the SL core, with extension work left for HL students.
How do I prepare for the IA?
It is done in school and worth 20%: research question, variable control, data processing and uncertainty analysis. This page trains Papers 1 and 2.
Official references
| Resource | What to check |
|---|---|
| https://www.ibo.org/programmes/diploma-programme/curriculum/sciences/ | IBO DP sciences curriculum and subject briefs (first assessment 2025) |
| https://www.tutorzone.com.hk/en-ib-biology-past-paper-drill-guide/ | IB Biology drilling guide: pacing and answering frames for Papers 1 and 2 |
Related: practice area · IB Maths AA SL mock
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