NAME........................................................................................CLASS...............ADM………….
DATE……………………….SIGN………………………………SCHOOL……………………
231/1
BIOLOGY
PAPER 1
MARCH- APRIL 2025
TIME: 2 HOURS
MARKING SCHEME
MOKASA 1 EXAMINATIONS
(Kenya Certificate of Secondary Education)
BIOLOGY THEORY
Instructions
Write your name, class and admission number in the space provided above.
Write the date of the examination and sign in the space provided above.
Answer all the questions in the spaces provided.
You may be penalized for wrong spelling especially technical terms.
For Examiner’s Use Only
QUESTION MAXIMUM SCORE CANDIDATES SCORE
1-34 80
This paper consists of 10 printed pages. Candidates should check the question paper to
ascertain that all the pages are printed as indicated and no questions are missing.
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1. Give reasons for the following precautions during collection and after study of
specimens. (2 marks)
a) Returning specimens to their natural habitat.
To maintain ecological balance
b) Not destroying the specimen
To avoid distortion of specimen’s features
2. List down reasons for the following importance of carrying out classification of living
things. (2 marks)
a) Putting living organisms in the correct group
Reference
b) Arranging information about living things in an orderly manner
To avoid chaos and confusion
3. State two differences between modern and artificial classification (2 marks)
Modern Artificial
Universal/world wide Local
A name consisting of 2 parts, generic A name that not split
and specific
Base phylogenetic Based superficial features
4. State three distinguishing characteristics of bacteria (3 marks)
Cell wall made of murrain
Few organelles
Prokaryotic
5. Enumerate three ways of controlling spread of epidemic diseases (3 marks)
Quarantine
Isolation
Vaccination
6. Explain how the following factors influence distribution of organisms in an ecosystem.
(i) Change in pH in soil habitat (2 marks)
Low pH leaching acid
N2 fixing organisms – denature enzymes in the organisms
Saprophytes
(ii) Strong wind in the Maasai Mara National park (2 marks)
Destroy trees/stunted growth plants
High rate of transpiration
Bring about rain bearing clouds
7. State two behavioral adaptations of a lion which makes it efficient for predation
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(2 marks)
Moving against wind direction to get scent from the prey
Camouflage to hide it from preys
Producing a sound similar to the prey to attract the prey
8. Name the parasite that causes amoebic dysentery (1 mark)
Entamoeba histolytica
9. State any three effects of oil spillage in aquatic environment (3 marks)
Cuts of O2 and CO2 supply to aquatic plants and animals
Reduces light penetration that inters with photosynthesis
Clogs birds feathers making flight difficult
Block respiratory surfaces of organisms
10. The concentration of carbon (IV) oxide in a tropical forest was measured for 24 hour
period. The graph below shows the results obtained.
Account for the results obtained at
a) Mid night (2 marks)
Very low light intensity and no use of CO2 in photosynthesis
b) At noon (2 marks)
High light intensity and the maximum use of CO2 for photosynthesis
11. Name the respiratory surfaces of the following; (2 marks)
a) Mosquito larvae
Tracheales
b) Tadpoles
Gill filaments
12. a) What name is given to the reaction of the body after coming into contact with
pollen grains (1 mark)
Allergy
b) Explain how anaphylaxis occurs (2 marks)
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Antigen leads over production of antibodies resulting into antigen – antibody
reaction which release histamine causes over dilation of blood vessels
13. The diagram below shows the tracheal system of an insect. Study it and use it to answer
the questions that follow.
a) Name the structure labelled X (1 mark)
Spiracle
b) State how the structure X is adapted to its function (1 mark)
Hairy to trap solids and prevent from entering the system
Has muscular valve to control it’s opening
c) How is ventilation maintained in the tracheal system (1 mark)
Has chitin to keep it open/prevent collapsing.
14. List down two processes that transport manufactured food in plants (2 marks)
Active transport – diffusion
Mass flow
15. Describe the function of insulin in the human body (2 marks)
Stimulates the liver cells to convert excess glucose
16. Define homeostasis (1 mark)
Maintenance of constant internal environment despite changes in the internal
environment
17. Distinguish between positive and negative feedback as used in homeostasis (1 mark)
Negative feed is a mechanism that restores correct a worsening situation
Whereas positive feed back worsens the situation
18. a) Premature baldness is due to a recessive gene located on one of the sex
chromosomes. Construct a genetic cross of marriage where the husband has premature
baldness. Use letter h to represent the gene for premature baldness.
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b) Explain why most of the colour blind people are male (2 marks)
Since male has to inherit one colourblind gene for him to suffer but for female has
to inherit two of the genes.
19. Explain how surface area to volume ratio affects the rate of diffusion (2 marks)
An organism with large SIA/VR the rate of diffusion is high since molecules pass
through short distance.
20. Distinguish between osmosis and active transport (1 mark)
Osmosis is the movement of water from their region of water concentration to a
region of low water concentration across a semi-permeable membrane.
Active transport movement of particles from a region of low to high concentration
across a semi-permeable membrane.
21. The diagram below illustrates an experiment on respiration in a small insect.
Explain the observation made after 10 minutes in the above experiment (3 marks)
Rise in the level of coloured water in the delivery tube;
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Insect respired using O2 in the flask and produced CO2 which was absorbed by
NaOH creating a partial vacuum (reduction in pressure). Atmospheric pressure
pressed against the coloured water.
22. The diagram below shows the internal structure of a leaf obtained from a plant in a
certain habitat.
(i) State two observable adaptations of the leaf to its habitat in relation to gaseous
exchange. (2 marks)
Acrenchyma/air spaces for storage of air for buoyancy/for respiration and
photosynthesis.
Thin/lack cubicle to reduce the distance for diffusion of respiratory gases;
large/many stomata to increase area for g/E
(ii) Apart from the stoma, name other two sites for gaseous exchange in plants.
(2 marks)
Lenticels
Cuticle/young epidermis
(iii) State two adaptations of the spongy mesophyll cells to gaseous exchange.
(2 marks)
Thin wall to reduce the gaseous exchange distance
Moist membrane to dissolve respiratory gases
23. Distinguish between guttation and transpiration (1 mark)
Lose water in form of droplets (through hyathodes)
Transpiration – Plants lose water in form of water vapour (through
stoma/lenticel/young epidermis)
24. Name the tissues in plants responsible for transport of; (2 marks)
a) Carbohydrates
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Phloem
b) Mineral ions
Xylem
25. State the functions of the following plant tissues (3 marks)
(i) Endodermis
……………………………………………………………………………………………..
……………………………………………………………………………………………..
(ii) Sclerenchyma
……………………………………………………………………………………………..
……………………………………………………………………………………………..
(iii) Piliferons layer
……………………………………………………………………………………………..
……………………………………………………………………………………………..
26. The experimental set up shown below investigates a certain physiological process in
plants. Use it to answer the questions below it.
a) What was being investigated (1 mark)
Transpiration
b) Give the role of the oil layer in the experiment (1 mark)
Prevent evaporation of water from the beaker
27. Define mutation (1 mark)
Sudden/sprutaneous change in the genetic make-up of an organism
28. The diagrams below illustrate some of beaks in birds.
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a) Identify the evolutionary phenomenon displayed by the beaks above (1 mark)
Adaptive radiation/Divergent evolution
b) Explain how the phenomenon above might have risen (2 marks)
Birds exposed to different habitat/environment, their beaks become modified to
enable them to feed to the food available on the environment
29. List any two limitations of fossil record as an evidence of organic evolution (2 marks)
Mixing inks
Lack fossilization
Distortion by geolical process
Scavenging of the animal material
30. Explain why Lamark’s theory of evolution is disputed by modern scientists (1 mark)
Phenotypically acquired characteristics cannot affect the genotype of an organisms
31. List two hormones that stimulate germination (2 marks)
Gibberlins
Ethylene, Cytokimis
32. Name two parts in a cell where respiration occurs (2 marks)
Matrix of the mitochondria
Cytoplasm
33. State two structural adaptations of anemophilous flowers (2 marks)
Many pollen grains to increase chances of pollination, Anthers looing and loosely
hanging exposed to environment so as the pollen grains to be easily boumgrass
34. State the functions of the following in human digestion (2 marks)
a) Cholecystokinin
Stimulates the pancrease to secrete pancreatic enzymes; stimulate the gall bladder
to secrete bile.
b) Smooth muscles in the stomach wall (1 mark)
Relax and contract to bring about churming
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