END OF TERM 3 2024

BIOLOGY MARKING SCHEME

FORM TWO

1. Give the function of the following parts of a light microscope. (2 marks)

i. Diaphragm.
Regulates the amount of light passing through the condenser onto the stage;
ii. Condenser.
Concentrates light onto the stage to illuminate the specimen;
2. Plasmodium vivax and Plasmodium ovale are transmitted by a mosquito. State with a reason whether two
organisms can interbreed. (2 marks)
They cannot interbreed; because they belong to the same genus but different species; therefore, their
offspring is infertile
3. Name the organelles that perform each of the following functions: (2marks)
a) Digestion and destruction of worn out organelles.
Lysosomes
b) Osmoregulation
Contractile vacuole;
4. An experiment was set up as shown in the diagram below.

The set-up was left for 30 minutes.

a. Name the process that is being investigated. (1mark)
Osmosis;
b. State the expected results. (2marks)
Visking tubing will become swollen/ increase in size/increase in volume;while level of distilled water in the
beaker drops;
c. Explain your answer in (a) above. (2marks)

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Sucrose solution is hypertonic to distilled water in the beaker;/distilled water is hypotonic compared to
sucrose solution. Water molecules moves from the beaker into visking tubing by osmosis through
semipermeable visking tubing;( making the visking tubing swell or increase in size/volume)
5. The action of ptyalin stops at the stomach. Explain. (2marks)
In the stomach there is acidic medium; (due to presence of hydrochloric acid) and ptyalin woks on slightly
alkaline medium hence its denatured; by a low pH.

6. In an experiment to investigate a factor affecting photosynthesis, a leaf of a potted plant which had been kept in
the dark overnight was covered with aluminum foil as shown in the diagram below,

The set up was kept in the sunlight for three hours after which a food test was carried out.
a. Which factor was being investigated in the experiment. (1 mark)
Light intensity;
b. Why was it necessary to keep the plants in the darkness before the experiment? (1 mark)
To de-starch the leaf;/ use up all starch in the leaf
c. What food test was carried out.(1 mark)
Starch test;
d. State the results of the food test. (1 mark)
The covered part of the leaf remains brown/ retains the color of iodine solution; and the uncovered part
turned blue-black.;
e. Account for the results in (d)above. (2 marks)
Photosynthesize occurred and starch was formed in the uncovered part of the leaf because of the presence
of light;while starch was not formed in the covered part of the leaf because of lack of light hence
photosynthesize did not occur;
7. Explain how age as a factor determine the daily energy requirement in human. (1 mark)
Young children/people have many actively dividing cells and are physically more active than adults;As they
grow older they become less active physically and their energy requirements decrease;
8. The diagram below represent skull obtained from an animal

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 i. State the special name given to the structures labelled L and M. (1 mark)
Carnassial teeth;rej wrong spelling
ii. state the likely diet of the animal from which the skull was obtained. (1 mark)
Flesh; accept meat
iii. Name the substance that is responsible for hardening of teeth. (1 mark)
Calcium phosphate;
9. The diagram below shows how food boles move along the human oesophogus and the Intestine

(a) Identify the process illustrated in the diagram. (1 mark)

Peristalsis;
(b) Name one component of a person’s diet that assists in the movement of food bolus from position 1 to positon
2. (1 mark)
Roughage;
10. Distinguish between transpiration and guttation. (2 marks)
It’s the process by which plants lose water in the form of water vapour in the atmosphere through stomata,
lenticels and cuticle while guttation it’s the process by which plants lose water in the form of water droplets
in the atmosphere through hydathodes;
11. Name a disease that causes thickening and hardening of arteries. (1 mark)
Arteriosclerosis;
12. The diagram shows a section through a plant organ.

a. From which plant organ was the section obtained. (1 mark)

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Dicotyledonous root; root accept root
b. Give two reasons form your answer in (a) above. (2 marks)
Presence of root hairs;
Star shaped xylem/phloem between the arms of the xylem;

c. How is the part labelled C adapted to its functions? (3marks)

-Tubular with hollow Long narrow lumen to facilitate capillarity;

-Lignified walls to provide mechanical support and prevent it from collapsing;
-Made of dead cells to allow flow of water and mineral salts without interruption;
–Has pits on the side walls for lateral movement of water and mineral salts to adjacent cells;
13. The diagram below represents an experiment that was used to investigate a certain process.

a) Name the process that was being investigated, (1mark)

Translocation;
b) Account for the swelling in diagram 2. (2marks)
Accumulation of food materials that were being transported from the leaves; but could not get across the
ringed part since phloem tissue was removed;
14. State the functions of each of the following parts of the nervous system in control of the heart beat

I. The vagus nerve. (1mark)

Slows down the rate of heart beat;

II. Sympathetic nerve. (1mark)

Speeds up the rate of heart beat;
15. The diagram below shows single circulation in a fish

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Write down the names of the parts labelled V and T. (2 marks)
V- ventricle;
T- Gills accept capillaries of gills;
a. How is this type of circulation different from that found in man? (2 marks)
Blood in the fish passes through the heart once in a complete circulation; whereas in a man, blood passes
through theheart twice in every complete circulation;
b. Explain the main disadvantage of this type of circulation. (1 mark)

Blood flows at a low pressure. Since it is only pumped once hence low rate of distribution of oxygen and
nutrients to tissues;
16. Explain how red blood cells of mammals are adapted to their functions. (3 marks)
-Biconcave in shape to increase surface area for more haemoglobinpackaging, thereby increasing oxygen
absorption;
-Absence of nucleus and other organelles to create more room for haemoglobin hence more oxygen
absorption;
-Flexible/pliable to squeeze through narrow lumen of capillaries;
-Contain carbonic anhydraseenzyme that catalyzes rate of reaction to transport carbon (IV) oxide;
-Numerous to increase surface area for transport of gases;
-Have haemoglobin, a blood transport pigment with a very high affinity for oxygen hence faster oxygen
transport;
17. The diagram below shows a vertical section through a mammalian heart

i. Name the parts labelled A, B, C and D. (4 marks)

A-aorta; B-pulmonary vein;
C-Bicuspid valve; D-Right atrium /auricle;
ii. Use arrows to show the direction in which blood flows out of the heart. (2 marks)
iii. Explain why left ventricle has thicker walls than right ventricle. (2 marks)

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The left ventricle pumps blood for a longer distance to all parts of the body while right ventricle pumps
blood to a shorter distance/ to the lungs; therefore, the left ventricle has thicker walls to generate and exert
more pressure to push blood for longer distances;
iv. Give three structural differences between A and B. (3 marks)
A B
Have thick muscular walls Have thin and less muscular walls

Have narrow lumen Have wider lumen

Haveno valves except at junction with Valve present at intervals throughout their
heart. length

18. The diagram below illustrates the role played by red blood cells in the transportation of carbon (IV) oxide.

a.Name substance T. (1 mark)

Water;
b. Name enzyme S and state its role in the reaction. (2 marks)
Carbonic anhydrase;rej wrong spelling
c.Other than carbon (IV) oxide transportation in the red blood cells, name the other form of carbon (IV)
oxide transportation in humans. (1 mark)
Carbaminohaemoglobin; solution form in plasma / hydrogen carbonate;
19.State two ways in which the heart muscles are special. (2 marks)
Muscles are myogenic; –able to initiate their own contractions without nervous stimulation.
Can contract continuously without fatigue;
20. (i) Name the type of circulatory system in insects. (1mark)
Open circulatory system;
(ii) State the openings in the chamber of the heart of an insect. (1mark)
Ostia;rej ostium
21. Name the blood vessel that
i. Provides the liver with oxygenated blood. (1mark)
Hepatic artery;
ii. Nourishes the cardiac muscles of the heart. (1mark)
Coronary artery;
22.State two functions of pericardium membrane. (2 marks)
Secretes pericardial fluid that lubricates / reduces friction of the heart as it is working;
Keeps the heart in position and prevents over dilation of the heart;

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