Daily Pass, KSh 20 M-Pesa or card. Nothing renews.
Updated November 2026. Looking for KCSE biology paper 3 practical questions and answers? Below are original practical questions in the KCSE style, each with a worked answer that shows exactly what an examiner wants to see in a drawing, a table or an explanation. KCSE Biology Paper 3 (231/3) is the practical paper. It is out of 40 marks, and the KNEC 2026 KCSE timetable places it on Friday 13 November 2026 from 8.00 to 9.45 am, so you have only 1 hour 45 minutes.
Everything on this page is original CBC Guide practice in the KCSE format. It is not an official KNEC paper, a marking scheme or a leaked confidential.
What the Biology Practical Tests
A typical 231/3 paper has three questions. One is usually an experiment, such as food tests, enzyme action or osmosis in potato or pawpaw cylinders. One uses fresh specimens, such as fruits, seeds, flowers or leaves, for observation, drawing and classification. The third often uses photographs of specimens, for example bones, arthropods or a dicot stem section. Because the paper is short, speed in drawing and recording matters as much as knowledge.
About the “Biology Paper 3 Confidential”
The confidential that schools receive is a list of specimens and reagents to prepare, such as “a mature bean seed, Benedict’s solution, a ripe orange”. It gives clues about the type of practical, but it never contains questions or answers. Buying or sharing exam material before a paper is an irregularity under the KNEC rules for the KCSE examination. The safest preparation is to master the skills below.
KCSE Biology Paper 3 Practical Questions and Answers
Question 1: Food tests
You are given solution K, an extract of a seed. (a) Test K for starch, reducing sugar and protein. Record the procedure, observation and conclusion in a table. (b) Name a seed likely to give these results if starch and protein are present but reducing sugar is absent.
Worked answer: (a) Starch: add two drops of iodine solution to 2 cm3 of K. A blue-black colour means starch is present; if it stays brown, starch is absent. Reducing sugar: add an equal volume of Benedict’s solution and boil. Green, yellow, orange or brick-red precipitate means reducing sugar is present; if the solution stays blue, it is absent. Protein: add 1 cm3 of sodium hydroxide then three drops of copper(II) sulphate. A purple or violet colour means protein is present. (b) A bean seed is a good answer. Examiners award the observation only if you state the actual colour change seen, such as “blue colour of Benedict’s solution persists”, and not just “negative”.
Question 2: Osmosis in potato cylinders
Three potato cylinders, each 50 mm long, are placed in distilled water, 0.5 M sucrose and 1.0 M sucrose for 30 minutes. Their final lengths are 54 mm, 50 mm and 46 mm. (a) Calculate the percentage change for each. (b) Explain the result in distilled water. (c) What does the 0.5 M result suggest?
Worked answer: (a) Distilled water: (54 − 50) ÷ 50 × 100 = +8%. 0.5 M: 0%. 1.0 M: (46 − 50) ÷ 50 × 100 = −8%. (b) The cell sap was hypertonic to distilled water, so water entered the cells by osmosis. The cells became turgid and the cylinder lengthened. (c) Cell sap is roughly isotonic to 0.5 M sucrose, so there was no net movement of water. Always show the formula and keep the sign: a loss is a negative change.
Question 3: Fruits and seeds
Specimen M is a mango fruit and specimen N is a black jack (Bidens) fruit. (a) State the agent of dispersal for each and give two features that adapt each to it. (b) Name the type of placentation you would expect in a cut bean pod.
Worked answer: (a) M is dispersed by animals: it has a fleshy, juicy, edible mesocarp and a bright colour when ripe. N is also dispersed by animals, but externally: it has hooks or barbed bristles that catch on fur or clothing, and it is light. (b) Marginal placentation, with the seeds attached along one edge of the ovary wall.
Question 4: Drawing skills
Draw and label specimen M cut longitudinally. What magnification rule must you state?
Worked answer: Use a sharp pencil, continuous single lines, no shading, label lines ruled to the edge without arrowheads, and a drawing larger than the specimen. Label the epicarp, mesocarp, endocarp and seed. Calculate magnification as drawing length ÷ actual length, for example 12 cm ÷ 8 cm = ×1.5, and write it under the drawing.
Timing a 1 Hour 45 Minute Practical
- Spend roughly 35 minutes per question and start the experiment that needs waiting time (osmosis, enzyme action) first.
- Write observations as you see them; do not leave the table to fill in “from memory”.
- Use the exact wording “brick-red precipitate”, “blue-black colour” and “turgid”.
- For photographs, name the feature and its function together, since many marks need both.
Want complete practicals with worked answers? Try the first questions on every CBC Guide paper free, then unlock full Biology papers with a Day Pass (KSh 20) or Weekly Pass. Pay once, with no auto-renewal. See all passes.
Frequently Asked Questions
When is KCSE Biology Paper 3 (231/3) in 2026?
The KNEC 2026 timetable lists it on Friday 13 November 2026 from 8.00 to 9.45 am, a duration of 1 hour 45 minutes.
How many marks is the KCSE Biology practical?
Biology Paper 3 is out of 40 marks and usually has three questions based on an experiment, fresh specimens and photographs.
What is in the KCSE Biology Paper 3 confidential?
It is a list of specimens, reagents and apparatus that the school prepares. It does not contain the questions or answers, and leaked “confidentials” with answers sold online are scams.
Is this the KNEC marking scheme for Biology Paper 3?
No. These are original practice questions with worked answers by CBC Guide, matched to the KCSE practical format.