Name …………………………………..…..........................................

… ADM …………………………

Class ………………...… Admission Number…………………

231
BIOLOGY
PAPER
(THEORY)
1
TIME: 2 HOURS
2
FORM THREE 2025 OPENER EXAM TERM 3
Kenya Certificate of Secondary Education
INSTRUCTIONS TO CANDIDATES

MARKING SCHEME

 Write your name and admission number in the spaces provided.

 Answer all questions in the spaces provided
 Candidates should check the question paper to ascertain all the pages are printed as indicated and no
questions are missing.
For Examiners Use Only

GRAND TOTAL

This paper consists of printed pages. Candidates should check the question paper to ascertain that
all pages are printed as indicated and that no pages are missing

1. State the name given to the study of each of the following. (2marks)

(a) Micro-organisms.
Microbiology;
(b) Birds
 Ornithology;
2. Name two instruments used in the laboratory for magnification. (2marks)

Microscope;
Hand lens/magnifying lens;
3. Give reasons why microscopic sections require to be:. (2marks)

(a) Very thin.

To allow light to pass through;
(b) Kept wet during processing.
To keep the cells turgid/ Prevent them from drying;
4. An animal cell was viewed under a light microscope using objective lens of X100 and
eye piece lens of X10. Determine the total magnification of the image. (2marks)

Total magnification =Eye piece lens magnification X Objective lens magnification;

=10X100
= X1000;
5. In an investigation form 3 students extracted two pairs of potato cylinders using a
cork borer, the cylinders were cut 5 cm each in length and placed in a beaker
containing a solution.
The results result after 30 minutes were a shown in the table below.
Feature Results
Average length of cylinder (mm) 55 mm
Stiffness of the cylinder Stiff

(a) What was the process being investigated? (1mark)

Osmosis;
(b) Account for the results in the above table. (3marks)

The cylinders increased in length and became stiff because they were placed in a
hypotonic solution compared to the cytoplasm of the potato cells; the cells gained
water by osmosis hence became turgid; and they increased in length and became firm;
(c) What would be a suitable control set-up for the above investigation. (2marks)
 Using boiled potato; because the cells are dead therefore cannot gain water by osmosis;
6. a). Give the roles of the following in the alimentary canal:
i)Hydrochloric acid in the stomach (2marks)

Unfolds proteins
provide acidic condition for action of stomach enzymes;
kills harmful micro-organisms that may be present in the food substance;

ii)Mucus (1mark)

Forms a barrier protecting the stomach walls from being corroded by hydrochloric
acid
and being digested by enzymes;
b) Name the cells that secrete enzyme pepsin and renin in the stomach (1mark)

Chief peptic cells/chief cells

c) Enzyme enterokinase activates trypsinogen to trypsin. Give the origin of the
enzyme (1 mark)
Duodenal wall
7. Explain what happens during the light stage of photosynthesis. (4marks)

Light energy is absorbed by chlorophyll molecules; used to split water molecules;

into oxygen and hydrogen atoms/ions; light energy is converted into chemical
energy (ATP) and stored;
8. The diagram below illustrates a section of circulatory system. Study it.
 a) Name the process that leads to formation of the fluid labeled R. (1mark)

Ultrafiltration;
b) Describe how the process named in (a) above occurs. (3marks)

The pumping action of the heart; the narrow lumen of arterioles and highly
branching of the arterioles into capillaries; generate high blood pressure; which
forces liquid part of blood and substances of low molecular size out of capillaries
into intercellular spaces of capillaries to form tissue fluid;

c) Name one blood cell that is present in fluid R. (1mark)

Some white blood cells/phagocyte /monocyte;

d) Give two adaptations of capillaries to the process named in (a) above. (2marks)

Have narrow lumen to create resistance to blood flow and hence generate high
blood pressure;
Has selectively permeable wall to allow substances of low molecular size to pass
through;
e) Identify fluid labeled Q. (1mark)

Lymph;
9. (a) Name the causative agent of the following respiratory diseases. (3marks)
 (i) Whooping cough
Bordetella pertussis;
(ii) Pneumonia.
Streptococcus pneumoniae;
(ii) Tuberculosis.
Mycobacterium tuberculosis;
(b) Apart from lungs, name two other respiratory surfaces in a frog. (2marks)

Skin; Buccal cavity;

10. The diagram below shows an experiment set up by a group of students to investigate
respiration in yeast.

a) Identify the type of respiration above. (1mark)

Anaerobic respiration;

b) Account for the observation above, after 20hrs. (2marks)

There was production of Carbon (IV) oxide gas; that caused the inflation of the
balloon;

c) State the economic importance of the by-products of the above process. (2marks)

Carbon (IV) oxide causes rising of bread during baking.

Ethanol is used in making of alcoholic beverages
 11. (a) State two major roles of the kidney. (2marks)

Homeostasis; Excretion;
(c) State one economic importance of each of the following plant excretory products.

(3marks)
(i) Quinine Treatment of Malaria;
(ii) Papain Used as meat tenderizer;
(iii) Cocaine Used as local Anaesthesia;
12. A person was found to pass large amounts of dilute urine frequently. Name the:
a) i) Disease the person was suffering from. (1mark)

Diabetes insipidus;
ii) Hormone that was deficient (1mark)

Antidiuretic (hormone); reject ADH;

13. A student mixed a sample of human urine/ with Benedict’s solution and heated, the
colour changed to orange.
a) What was present in the urine sample? (1mark)
Glucose
b) What did the student conclude on the health status of the person? (1mark)
The patient was suffering from diabetes mellitus;
c) How can the health status of the above patient be improved. (1mark)

Inject with insulin hormone;

14. The scientific name of a bean is Phaseolus vulgaris. What do the names represent?
a) Phaseolus. (1 mark)
Genus;
b) Vulgaris. (1 mark)
Species;
15. a) Identify the class of phylum Arthropoda with organisms that have three body parts and three
pairs of legs. (1mark)
Insecta;
(b) Members of the class stated in (a) above are the most successful among the invertebrates.
Explain THREE characteristics that make them most successful. (3marks)
- Hardened exoskeleton made of chitin which protect them from desiccation and predation;
- Have jointed appendages adapted for different functions;
- Excrete uric acid that needs less water to eliminate;
- Ability to fly to escape predators/ dangers/seek food/look for mate;
- Small size consumes less food/fit in many habitats;
- Diverse mouth parts suited for feeding on variety of food;
Any three correct
16. Name three economic importance of organisms in kingdom Fungi. (3marks)
- Penicillium manufacture penicillin drugs;
- Yeast used in baking and brewing;
- Mushroom used as source of food ;
- causes diseases e.g. athlete foot, blights, rusts;
- causes food spoilage e.g. bread mould
any other correct (max 3 marks)
17. Why are green plants referred to as primary producers in an ecosystem. (2marks)
Green plants utilise energy from the sun to manufacture food by photosynthesis; for the
subsequent trophic levels to utilise them;
18. During mitosis, an animal’s chromatid failed to separate and move to opposite poles.
a) Name the organelle that the cell was lacking. (1mark)

Centrioles;
b) Name THREE regions in plants where cells actively undergo mitosis. (3marks)

Root tips; shoot tips; cambium;

19. State two features of pollen grains of insect pollinated flowers. (2marks)
Rough and sticky; Heavy;
20. Study the photographs below and use them to answer the questions that follow;
a) Name the class of the plant from which each of the flowers was obtained. Give a reason
for your answer in each case (4marks)

Flower Class Reason

A1 Dicotyledonae; Has four petals;

B1 Monocotyledonae; Has three stamens;

b) Name the parts labelled S and T (2marks)

S - Petal;
T - Sepal; Accept Calyx;
c) What type of ovary is shown in flower B1? Give a reason for your answer. (2marks)

Type - Superior;
Reason – above receptacle;
d) i) Name the agent responsible for the process represented by the arrow labelled R in B2.

(1mark)
 Wind;
ii) Give a reason for your answer in e (i) above (1mark)
Feathery stigma; (to increase surface area for trapping pollen grains from the air)
e) (i) Name an agent that brings about a similar process as the one shown by the arrow in B2
for
A1. (1mark)

Insects;
ii) Give a reason for your answer in f(i) above. (1mark)

Tubular/ bell shaped corolla;

Accept large petals;
21. Giving relevant examples describe five biotic inter-relationship in an ecosystem. (20marks)
a) Predation/ predator -prey;
A predator is an organism that kill another organism for food and either feed on it wholly
or in parts; A prey is an organism being feed on by the predator;
The predators have adaptations which make them efficient in capturing the prey. They
include:
- Sharp eyesight, fast flight, modified beaks and talons in birds eg in eagles, hawks,
kingfisher (acc any other bird of prey)
- Strong jaws to hold on the prey, carnassial teeth to crush bones and strip through
flesh e.g. in lions, leopard, cheater, dog; ( acc any other carnivore)
- Enlarged fore limbs with spikes for capturing the prey eg praying mantis;
- Moving against the wind to avoid prey detecting their smell eg loin;
- Group hunting to take down large animals eg a pack of wolves, a pride of lion;
Preys also have defence mechanisms like
- Defence weapons e.g. porcupine have spikes to confront a predator, Shunk uses
an odour by spraying musk if another animal comes too close;
 - Swift movement like in gazelles and antelopes;
- Camouflage to resemble its background and blend well to confuse, hide, distract
other animals. E.g. rabbits, gazelles, stripes of zebra;
- Well-developed sense of sight, hearing, and smell e.g. antelopes, gazelles;
b) Competition;
Is an association where two or more organisms depends on the same limited resources
e.g. food, light, water, mates and shelter;
E.g. zebra and gazelles competing for grass;
Poorly adapted organism dies or migrates while organisms which are well adapted
survive hence the species increases;
Intraspecific competition; - is competition among members of the same species;
Interspecific competition; - Competition among members of different species;
Competition helps to regulate population size of organisms;
c) Symbiosis;
It’s an association between organisms of different species where both organisms
benefit from each other; e.g.
- Rhizobium bacteria live in the root nodules of leguminous plants where they
convert free atmospheric Nitrogen into Nitrates; The plants benefit from the
Nitrates fixed by the Rhizobium bacteria while bacteria benefits by absorbing
carbohydrates provided by the plants; The relationship enables the plant to thrive
in Nitrogen deficient soil;
- In the caecum of herbivores there is bacteria that secretes cellulase enzymes that
digest cellulose; while the bacteria benefits by absorbing products of digestion in
the gut;
- Bacteria in human digestive system, bacteria are sheltered and uses digested food
materials; Human’s benefits since bacteria synthesises Vitamin K and B12;
- Mycorrhizal association between roots of the plants and fungus; The fungus
colonises the roots and is provided with the carbohydrates, sucrose and glucose;
In exchange the plants benefit from fungi higher water and mineral absorption
capabilities;
-
d) Parasitism;
It’s a relationship between two species where organism (parasites) lives in or on
another organism(host) and obtain nutrients causing harm to the host; A parasite
benefits in terms of food and shelter from the host; while causing harm by
weakening the host or can cause or transmit diseases to the host eventually killing
them;
Endoparasites are parasites that live inside the host’s body; eg Plasmodium causes
Malaria, Amoeba causes amoebic dysentery, Trypanosoma causes sleeping sickness.
 Some endoparasites reduces the host fitness and weakens them eg hookworm,
tapeworm, roundworm;
Ectoparasites are parasites that lives on the body surface of the host but do not
commonly cause diseases e.g. ticks, fleas, leeches, and lice live on animal hosts;
Parasitic plants eg mistletoe, dodder plant derives nutrients from another living
plant;

e) Saprophytism;
It’s a relationship where organisms obtain nutrients from dead organic matter
causing decomposition. E.g. bacteria and fungi;
Decomposition releases nutrients into the ecosystem which are then made available
toother living organisms;
(maximum 20marks)