Last reviewed: 1 November 2026
Updated November 2026. If you searched for KCSE 2025 Biology Paper 1 questions and answers, this page gives you twelve original short-answer questions in the 231/1 style, each with a worked answer and a note on where candidates drop marks. Biology Paper 1 is a 2-hour theory paper of 80 marks, made up of short compulsory questions from across the four-year syllabus. The 2026 sitting is on Tuesday 10 November, 2.00 to 4.00 pm, so these work as a final check on definitions, diagrams and calculations.
Original practice questions written for revision. They are not the KNEC 2025 Biology paper and not a KNEC marking scheme.
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How the 2025 Biology Paper 1 (231/1) Was Set Out
The KNEC 2025 KCSE timetable placed 231/1 Biology on Tuesday 11 November 2025, 2.00 to 4.00 pm, and the KNEC 2026 KCSE timetable, instructions and guidelines keeps the same 2 hours. Paper 1 is a long set of short questions worth a few marks each, all compulsory, answered in the spaces on the paper. Paper 2 (231/2) has the longer structured questions and an essay, and Paper 3 (231/3) is the practical.
With 80 marks in 120 minutes you have about 1½ minutes per mark. Short answers are marked point by point, so precise biological terms matter more than long sentences.
KCSE 2025 Biology Paper 1 Answers: 12 Practice Questions
1. State two differences between plant and animal cells. (2 marks)
Worked answer: plant cells have a cellulose cell wall while animal cells do not; plant cells have chloroplasts while animal cells lack them; plant cells have a large permanent vacuole while animal cells have small temporary vacuoles. Each difference must state both sides.
2. A specimen measures 6 mm on a drawing that is 3 cm long. Calculate the magnification. (2 marks)
Worked answer: convert to the same units: 3 cm = 30 mm. Magnification = drawing ÷ actual = 30 ÷ 6 = ×5. Leaving the units unconverted is the usual mark lost here.
3. Name the kingdom to which mushrooms belong and give one reason. (2 marks)
Worked answer: Fungi; they lack chlorophyll and feed saprophytically, or their cell walls contain chitin, or they reproduce by spores.
4. Explain why the rate of photosynthesis levels off at high light intensity. (2 marks)
Worked answer: another factor, such as carbon dioxide concentration or temperature, becomes limiting, so extra light cannot increase the rate further.
5. State the role of bile in digestion. (2 marks)
Worked answer: bile salts emulsify fats into small droplets, increasing the surface area for lipase; bile is alkaline and neutralises acidic chyme, giving a suitable pH for pancreatic enzymes.
6. Give two adaptations of alveoli for gaseous exchange. (2 marks)
Worked answer: thin epithelium, one cell thick, for a short diffusion distance; large surface area; moist lining to dissolve gases; dense capillary network to maintain a concentration gradient.
7. Write a word equation for anaerobic respiration in yeast. (1 mark)
Worked answer: glucose → ethanol + carbon dioxide + energy. Writing “lactic acid” (the animal pathway) earns zero.
8. Name the hormone that regulates water reabsorption in the kidney and where it is produced. (2 marks)
Worked answer: antidiuretic hormone (ADH); produced by the hypothalamus and released from the posterior pituitary gland. Either site accepted in most marking guides, but naming the pituitary is safest.
9. State two functions of the placenta. (2 marks)
Worked answer: allows exchange of oxygen, nutrients and wastes between mother and foetus; produces hormones such as progesterone; acts as a barrier to many pathogens; prevents mixing of maternal and foetal blood.
10. In a cross between two heterozygous tall pea plants (Tt × Tt), what proportion of offspring will be short? (2 marks)
Worked answer: gametes T, t from each parent give TT, Tt, Tt, tt. Short plants (tt) are ¼ (25%). Show the Punnett square or gametes: the working carries a mark.
11. Define the term “ecological niche”. (1 mark)
Worked answer: the role and position of an organism in its habitat, including what it feeds on and how it interacts with other organisms and the environment.
12. Explain why a person’s breathing rate rises during exercise. (3 marks)
Worked answer: muscles respire faster and produce more carbon dioxide; rising CO₂ in the blood is detected by chemoreceptors and the medulla oblongata; impulses increase the rate and depth of breathing to remove CO₂ and supply more oxygen.
Where Candidates Lose Marks in Biology Paper 1
- Spelling a technical term so badly that it becomes another word (for example “ureter” and “urethra”)
- Giving three answers when two are asked: examiners mark the first two only
- Missing units in magnification and rate calculations
- Describing when the question says “explain”, so no reason is given
Likely Topics to Revise for Biology Paper 1
Nobody knows the real questions, but short items come from every form. Cover cell biology, classification, nutrition in plants and animals, transport, gaseous exchange, respiration, excretion and homeostasis, reproduction, growth, genetics, evolution, ecology, support and movement, and coordination. The full checklist is in the KCSE Biology Paper 1 revision guide.
Then test yourself: the KCSE Biology Paper 1 challenge is timed and marked instantly, the KCSE Biology quiz drills short items, and the KCSE quiz index and KCSE challenges page cover the other subjects. More original papers sit on the KCSE Biology practice papers page, and the KCSE 2026 hub has the timetable and plans.
For perspective on the stakes: as reported by the Kenya News Agency on the KCSE 2025 results release, 993,226 candidates sat KCSE 2025 and 27.18% scored C+ and above.
Frequently Asked Questions
How long is KCSE Biology Paper 1?
2 hours for 80 marks. In 2026 it runs on Tuesday 10 November from 2.00 to 4.00 pm.
Where can I find the KCSE 2025 Biology Paper 1 marking scheme?
KNEC does not publish marking schemes for sale. Practise with worked answers like these and compare your wording with the key terms given.
Are all questions in Biology Paper 1 compulsory?
Yes. Paper 1 is short-answer questions, all compulsory, answered in the spaces provided.
Is there a reliable KCSE Biology Paper 1 prediction for 2025?
No. Prediction papers are practice papers written by teachers. Use them for timing, but revise every topic.
Want a full paper with worked answers? The first challenge questions are free. A Day Pass (KSh 20) or Monthly Pass (KSh 500) unlocks full KCSE practice papers, paid once by M-Pesa, no auto-renewal. See all passes.