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BIOLOGY PAPER 1
FORM 3
END-OF-YEAR EXAM - 2024
MARKING SCHEME:
1. The diagram below shows the structure of the embryo sac.
a) Name the structures labeled A and B. (2mks)
A – Two polar nuclei.
B – Antipodal cells.
b) What does structure labeled C transform into after fertilization? (1mk)
Diploid zygote.
2. State two reasons why lipids are not the main respiratory substrates although they give more energy per
molecule than carbohydrates. (2mks)
- They require a lot of oxygen for oxidation.
- They are not soluble hence cannot be transported easily to the respiratory surface.
3. (a) What is meant by the term seed dormancy? (1mk)
It is a period of rest after ripening where seed perform all its life physiological processes slowly using very
little food.
(b) State three causes of seed dormancy. (3mks)
- Presence of chemical inhibitors.
- Low concentration of hormones and enzymes that promote germination.
- Immature embryo / not fully developed embryo.
- Hard impermeable seed coat or testa.
- Absence of certain favourable environmental conditions.
4. Explain why the following conditions are necessary during seed germination.
a) Oxygen. (2mks)
Oxygen is required in aerobic respiration/ oxidation to release energy from food reserve for
germination.
b) Water. (2mks)
- Softens the seed coat to facilitate emergence of radical.
- Breaks down stored food for soluble form/ dissolves.
- Activates enzymes – provides a medium for enzymatic activities.
- Provides a medium for transportation of dissolved food substances.
5. When are two organisms considered to belong in the same species? (2mks)
When they are capable of interbreeding to produce a viable/ fertile offsprings.
6. A group of students in Huduma boys, set up an experiment to investigate a certain physiological process.
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a) After sometime, the students noted that the visking tubing shrunk and become flabby. What conclusion
would you make about the concentration of solutions A and B.?
(2mks)
A – Hypotonic solution.
B – Hypertonic solution.
b) What does a visking tubing correspond to in a living organism? (1mk)
Cell membrane.
7. Name the cell organelles responsible for the following; (2mks)
a) Respiration –mitochondria
b) Photosynthesis – chloroplasts.
8. The diagram below represents a moss plant. Use it to answer the questions that follow.
i) Name the parts labeled A – C. (3mks)
A – capsule
B – seta
C – rhizoid
ii) To which division does the plant belong? (1mk)
Bryophyta.
9. The diagram below represents regions of a root tip.
a) Name the two regions above X in ascending order. (2mks)
Zone of cell division
Zone of cell elongation
b) State the function f the part labeled x. (1mk)
To protect the apical meristem.
10. Distinguish between protandry and protogyny. (2mks)
Protandry – condition where male parts i.e stamens mature before carpels of the same flower are ready to
receive pollen grains.
Protogyny - condition where carpels; pistil; female parts mature before stamens of the same flower shed
the pollen grains.
11. A process that occurs in plants is represented by the equation below.
C6H12O6 → 2C2H5OH + 2CO2 + Energy
(Glucose) (Ethanol)
a) Name the process. (1mk)
Anaerobic respiration in plants.
b) State two economic importance of process named in (a) above.. (2mks)
i) In brewing or baking industries
ii) In sewage treatment
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12. State the role of the following hormones in the life cycle of insects. (2mks)
a) Ecdysone hormone –
Stimulates moulting or shedding of adult cuticles/ exoskeleton
b) Juvenile hormone –
Stimulates maintenance of larval characteristics.
13. (a) What is meant by the term eutrophication? (1mk)
Rapid growth of water plants as a result of presence of a lot of nitrogen in water derived from inorganic
fertilizers and untreated sewage.
(b) State one possible cause of eutrophication. (1mk)
- Discharge of untreated sewage into water bodies.
- Inorganic fertilizers used in the farms being carried by underground streams and surface
runoffs into water bodies.
(c) What problem does eutrophication create in aquatic ecosystem? (1mk)
- As a result of eutrophication, some aquatic plants die due to competition for the available
resources.
- Leads to suffocation of aquatic organisms due to lack of oxygen.
14. Using the axes provided below, sketch a curve to illustrate the growth pattern observed in phylum arthropoda.
(2mks)
Length (mm)
15. State one function of Deoxyribonucleic acid (DNA) molecule. (1mk)
- Stores genetic information
Time (Days) in a coded form as nucleotide bases.
- Enables transfer of genetic information unchanged to daughter cells through replication.
- Translates the genetic information into the characteristics of an organism through protein
synthesis.
16. Explain why plants do not require specialized excretory organs. (2mks)
- Some products are formed slowly thus little accumulation of waste.
- Some waste products such as oxygen are reused.
- Some waste products are stored in non-toxic forms in leaves, flowers, fruits and old bark, and
then drop off.
- Some waste products are mainly made from carbohydrate and hence are not as harmful as
proteinases materials.
17. How is the human sperm cell structurally specialized? (3mks)
- It has acrosome with lytic enzyme to dissolve ovum membrane for easier penetration.
- It has a long tail to propel the sperm side to side movement.
- Large number of mitochondria which provide energy necessary for movement of the sperm.
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- Has a large nucleus which carries haploid number of genetic material to restore diploid state
of an organism.
18. State any two applications of plant hormones in agriculture. (2mks)
- Induce pathonocarpy.
- Promotes flowering
- Breaks seed dormancy
- Accelerates ripening of fruits.
- Encourages sprouting of side branches.
- Induce fast growth in stem cut to curl around support.
19. Differentiate between continuous and discontinuous variation giving an example in each case.
(3mks)
Continuous variation is a characteristic for which there is a range with many intermediates; example; body
weight, height.
Discontinuous variation is a characteristic for which there are discrete/ distinct/ definite categories or units
or clear out differences; example; sex where an individual is either male or female, ABO blood group
system.
20. In fish, blood in the gill filaments and water flowing over their surfaces, flow in the opposite direction.
a) What name is given to the system or type of flow? (1mk)
Counter – current flow mechanism.
b) What is the biological importance of this type of flow? (2mks)
It maintains high diffusion/ concentration gradient between blood and water for maximum gaseous
exchange.
c) With the aid of a well labeled diagram, illustrate this type of flow. (2mks)
Blood
21. Name a disease caused by lack of each of the following in human diet. (2mks)Water
a) Vitamin D –Rickets
b) Iodine – Goitre
22. Why are green plants referred to as primary producers in an ecosystem? (2mks)
Green plants utilize energy from the sun to manufacture food by photosynthesis for subsequent trophic
level or consumers or other organisms to utilize.
23. State two main causes of variations in living things. (2mks)
- Mixing up of genetic materials from two different parents during fertilization.
- mutations
24. The diagram below represents a stage during germination of a seed.
i) Name the type of germination illustrated in the diagram above. (1mk)
Epigeal germination.
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ii) Name and state the role of part labeled x during germination of the seed (2mks)
Name: hypocotyl
- Protection of the delicate plumule.
- It elongates and pulls the cotyledons above the ground.
25. The chemical equation shown below represents the oxidation of a certain substrate in the living tissues of a
grasshopper.
C5H104O8 + 80O2 → 57CO2 + 5H2O + ATP
a) Calculate the RQ value of the food substrate. (3mks)
Volume of carbon ( IV ) oxide produced
Respiratory Quotient (RQ) =
Volume of oxygen consumed
57
80
= 0.7125
b) Identify the food substrate whose RQ value has been worked in (a) above. (1mk)
Fat
26 a)
i) Coronary artery
ii) P - Aorta
Q – Fat layer/adipose tissue
b) Spread the wave of excitation //contraction wave/muscle contraction from the atrio- ventriculave node to the
ventricular muscles//ventricular myo cardium.
c. -Blood clot
-Fat deposits
-Bone fragments.
d. -Arteriosclerosis
-Varicose vein
26. Name the forces which are responsible for the upward movement of water from the roots towards the stem.
(3mks)
- Root pressure
- Transpiration pull
- Capillarity force.
- Adhesion and cohesion forces.
27. (a) State the features and mechanisms which hinder self pollination and self fertilization from taking place in
plants. (3mks)
- Protogyny and protandry
- Self-sterility or incompatibility.
- Dichogamy
- Dioecious plants where pistillate and staminate flowers are borne on different plants.
(b) Give a reason why secondary thickening does not occur in bamboo and maize plant.
(2mks)
Being monocots, they lack cambium whose activities lead to increase in girth.
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