How to answer the IBO Hong Kong paper
Sunday 1 November 2026, 11:30 a.m. to 1:30 p.m. Fifty multiple-choice questions. Arrive at 11:00. University MTR Station, Exit A, CUHK. If morning school is cancelled for bad weather, the contest moves to Sunday 8 November.
Bring your Hong Kong identity card, student card, the QR code from your teacher, HB pencils, an eraser, a ruler, and a calculator printed with HKEAA APPROVED. No formula sheet is given. The rules do not take a mark off for a wrong answer, so fill every row. Notes and phones found on you cost marks. Leave this page outside.
1. Why a question looks impossible
The stem looks like a research paper: a Latin name, a citation, a protein you have never met. You are not expected to know that protein. The mark is in the table or the graph.
Students lose the mark by guessing from the scary word, by ticking the first true statement and stopping, or by missing the word INCORRECT, NOT, or CANNOT.
2. Do this on every question
- Circle the job. The last sentence is the job: supported by the data, which is correct, or which is INCORRECT / CANNOT. If one sentence is clumsy, glance at the other language, then go back. Do not read both versions of all 50.
- Translate the axis. Write what a high value means. Food remaining high means the animal ate less. Percent normal high means the mutation did little harm. On a gel, an equal loading-control band (GAPDH or actin) means the lanes were loaded equally. Only then is a darker test band a real increase.
- Mark (I) (II) (III) (IV) before you look at A to D. Write T or F. A statement is T only when the table shows it. It is F when the numbers go the other way, when it says only / always / completely / all / never and the table has one exception, or when it names a mechanism this experiment never measured.
- Match the pattern. One false Roman numeral usually deletes two options. A true statement sitting inside the wrong option is still wrong.
- Three minutes, then move. If two options remain, underline the words that differ and check them against one number. Then fill a circle. A blank is a lost mark.
3. Traps that keep coming back
- Partial effect kills “only when completely blocked”. If a low dose already changes the result, the process was not fully stopped. Also read the control: it may already show a little of the “abnormal” result.
- A pathway order is not free. “A acts downstream of B” needs an experiment that moves B and watches A. “Both copies together are worse than either alone” does not show the order.
- Old cells in a young body. If they still fail, the fault travelled with the cells. If young cells fail in an old body, the environment is the problem.
- A plus B looks like B alone. Then A’s effect has disappeared. The two treatments are not independent, because an independent A would still pull the combined bar.
- A stiff artery. Systolic pressure rises. Diastolic pressure can fall, because the vessel stays wide while the heart rests. Pulse pressure = systolic − diastolic, so it widens. Mean arterial pressure ≈ diastolic + ⅓(systolic − diastolic). An equal rise and fall does not leave the mean unchanged.
- Capillaries. One capillary is the narrowest tube. All the capillaries together have the biggest total area, so blood is slowest there. Diameter and total area move in opposite directions.
- Relaxing arterial muscle lowers pressure. The vessel gets wider.
- Donor egg. You get mitochondrial DNA. Blood groups and almost everything else are in the nucleus. Sperm mitochondria sit in the neck and are not what joins the egg.
- Mitotic index up can mean cells are stuck in mitosis, not that more cells are being born. A later fall can mean those cells have died.
- Ribosomes start at the 5′ end. If initiation is blocked, density falls at the 5′ end first. Profiling measures translation, not the amount of mRNA.
- Giving-up density. Food left behind. Higher bar, less eaten.
4. Blood, in one table
The recipient’s antibodies attack antigens on the donor red cells.
| Group | Antigens on red cells | Antibodies in plasma |
|---|---|---|
| A | A | anti-B |
| B | B | anti-A |
| AB | A and B | neither |
| O | neither | anti-A and anti-B |
O negative red cells carry no A, no B and no Rh(D). They are the safest red cells when the patient’s group is unknown. Read whether the option is about cells or about plasma.
5. Trees, in one picture
A node is a common ancestor. Two species are closer when you meet their shared node sooner. Species that split at the same node are equally related to a species outside that node.
Lizard and bird are the closest pair. Human is closer to the bird than the frog is. The frog is equally related to the lizard and the bird. “Human + lizard” with the bird left out is not a clade: a clade keeps every branch.
Homoplasy: the same look evolved twice (pangolin scales and snake scales). Living in the same place does not make one species. Members of one species can mate and produce offspring that can also reproduce.
6. Formulae to memorise
| Quantity | Relationship |
|---|---|
| Pulse pressure | systolic − diastolic |
| Mean arterial pressure | diastolic + ⅓ (systolic − diastolic) |
| Cardiac output | heart rate × stroke volume |
| Energy transfer | (energy kept by the next level ÷ energy eaten) × 100% |
| Percentage change | (new − old) ÷ old × 100% |
| Hardy–Weinberg | p + q = 1 and p² + 2pq + q² = 1 |
| Dilution | C₁V₁ = C₂V₂ |
For a rare autosomal recessive child of two carriers, the chance the next child is affected is 1/4. The chance that child is also a girl is 1/4 × 1/2 = 1/8. If the question has already said the child is a girl, do not multiply by 1/2 again.
7. Words worth translating once
| On the paper | It means |
|---|---|
| wild type | the normal, unmutated one |
| maternal / zygotic | already in the egg / made by the embryo after fertilisation |
| apoptosis, caspase | planned cell death, and the enzyme that carries it out |
| clade | an ancestor plus every descendant |
| loading control | a protein that should be equal in every lane |
| antisense | a strand that sticks to mRNA and blocks translation |
| GEF / GAP | switches a GTPase on (GTP) / switches it off |
| C4 and CAM | two ways of storing CO₂ so Rubisco meets less oxygen |
| photorespiration | Rubisco grabbing oxygen instead of CO₂ |
| quorum sensing | bacteria detecting that the crowd is dense enough |
| supported by the data | if the figure did not measure it, do not tick it |
8. How to use the two papers
- Tonight, read sections 1 to 3 above.
- Do 2025 questions 1–25 in 60 minutes, one language, then open the 2025 page for the ones you missed. Write one line on why: axis backwards, negative word, mechanism not in the data, or clade.
- Do 2025 questions 26–50 the same way, then the 2024 paper.
- Friday, redo only the questions you got wrong, with the answer page closed.
- Saturday afternoon, stop. Sleep.