OPENER TERM TWO 2023

BIOLOGY FORM 3 – MARKING SCHEME

1. Distinguish between a cell and an organelle (2mk).

A cell is the basic unit in an organism that performs a given function; while organelles are
structures that constitute a cell;
2. State the name given to the study of;
i) The cell (1mk)
Cytology;
ii) Microorganisms (1mk)
Microbiology;
3. (a) State two characteristics of living organisms that are specific to plants. (2mks)
- Autotrophic nutrition;
- Limited movement;
- Growth occurs at specific regions;
4. The diagram shows two types of cells placed in a certain solution. Study them and answer questions that
follow

a. Name the physiological process responsible for the observed results. (1mk)

Osmosis

b. Give the correct biological term used to describe cells A & B. (2mks)
A – Flaccid; /plasmolysed

B – Crenated
5. Give a reason for each of the following biological phenomena
a) when placed in fresh water Entamoeba histolytica does not burst (2mks)
Has contractile vacuole; that collect and discharge excess water out of the cell;

b) A mature plant cell does not lose its shape after losing water (1mk)
 Has a cell wall which gives a plant a regular shape

6. Name the polysaccharide that constitute the

i. Cell wall of plant cells (1mk)
Cellulose
 ii. Cell wall of fungi cells. (1mk)
Cellulose /chitin;
iii. Xylem vessels and tracheal (1mk)
Lignin

7. The figure below is a diagram of a vertical section of a mammalian tooth.

(i) Name the part labelled A and B. (2mks)

A Enamel
B Gum
(ii) State two ways in which structure D is adapted to its functions. (2mks)

- Contains blood vessels which supplies food nutrients and oxygen and remove carbon IV oxide and
nitrogenous waste products;
- Contains nerve endings for sensitivity;
(iii) List two ways of preventing gingivitis. (2mks)
- Regular brushing of teeth;
-Proper exercise of the teeth by eating tough fibrous food;
- Eating foods that are rich in vitamin C

8. Below is a set up that was used to investigate a certain process in plants

 a) State what the above apparatus can be used to measure. (1mk)
To measure the rate of transpiration;

i) Give two precautions that should be taken when setting up the experiment[2marks]
- Set up should be air tight;
- Leafy shoot shoot should be cut under water;
(ii) State a reason for each precautions stated in b (i) above [2marks]
Prevent introduction of an air bubble in the xylem which would block the xylem/flow of water;
(c) List two structural factors that affect the process under investigation [2marks]

Leaf size and shape;

Thickness of he cuticle;
Hairy leaf;
Sunken stomata; (AVP)
9. Shown below are diagrams of the same mammalian blood cell

a) State two morphological features of cell represented in the diagram above (2mks)
- Biconcave;
- Lacks nucleus and other organelles;
b) How is the feature stated above advantageous to the cell.. (2mks)
- Biconcave - Increase surface area for diffusion of respiratory gases;
- Lack of nucleus - Create more room for packing of more haemoglobin;
10. Study the diagram below and answer the questions that follow
 a. i) Identify the type of circulatory system shown above (1mk)
 Single circulatory systems
ii) Give a reason for your answer in (a) (i) (1mk)
 Blood flows through the heart once in a complete circulation
ii) Give a disadvantage of this type of circulation (2mk)
 Blood flows under low pressure ; making circulation slow hence the animals are less active;

11. An individual is blood group A positive (2mks)

a) Name the antigens in the individual’s blood
A and rhesus factor or antigen ‘D’
b) Give the reason why the individual cannot receive blood from blood group A donor (2mks)
 Recipient plasma has antibody ‘b’ which corresponds to antigen B; which causes antigen
antibody reaction causing agglutinations of red blood cells;

12. The equation below shows an oxidation reaction of food substances.

C51H98O6 + 145O2 ------- 102 CO2 + 98 H2O + energy

a) What do you understand by the term respiratory quotient? (1mk)

Volumetric relationship between Carbon (IV) oxide produced and oxygen consumed
b) Determine respiratory quotient of the oxidation of food substance. (2mks)
R.Q = CO2 produced
 O2 used up
R.Q = 102/145
R.Q = 0.7

c) Identify the food substances. (1mk)

Fat/ Lipid
d) In a cell where does aerobic respiration occur? (2mks).
Cytoplasm;
Mitochondria;

13. Explain the following

a) The stomach lining is made of protein but is not digested by protein-digesting enzymes (2mks)
Proteases/pepsinogen are released in their inactive form/pepsinogen;
Stomach lining is coated by mucus;
b) Digestion of starch does not continue in the stomach. ( 2mks)
No starch-digesting enzyme/amylase/ptyalin is secreted in the stomach;
Hydrochloric acid/Acidic pH in the stomach denatures/destroys amylase/ptyalin;
c) One easily suffers nose bleeding when climbing mountain. (2mks)
Blood pressure is higher than the atmospheric pressure leading to rupturing/bursting of blood
capillaries in the nasal region;
d) A camel can stay for 60 days without drinking water. (1mk)

Breaks down stored fats into metabolic water used in body metabolism;
14. Name three sites where gaseous exchange takes place in plants. 3mks)

Stomata
Lenticels
Aerenchyma-Fresh water;
Pneumatophores- Salty water/salty soils/swamps;
15. Describe the changes that occur to the rib cage and the diaphragm during inspiration. (4mks)
 External intercostal muscles contract; and internal intercostal musclces relax;
 Ribs move upwards and outwards;
 Causing increase in volume and decrease in pressure;
 Air is sucked in;

16. Explain the hormonal differences between these two homeostatic disorders, diabetes Mellitus and
diabetes insipidus (4mks)

Diabetes Mellitus. Diabetes insipidus.

 Failure of Pancreas ; to release/ secrete/ Failure of pituitary gland; to release/
insulin / secrete inadequate insulin; secrete antidiuretic hormone or secrete
inadequate ADH;

17. Below is a diagram of Euglena gacilis. use it to answer questions that follow.

(a) Classify the organism into the following taxa. (2mks)

(i) Kingdom Protoctista;
(ii) Genus Euglena;
(b) Name the structure labeled X. (1mark)
Contractile vacuole;
(c) How is the structure Y adapted to its function? (1mark)
Contain chlorophyll pigment that trap light energy for photosynthesis;

18.
19. Form three students wanted to estimate the population in 5km2 grass field near a school compound. They
captured 36 grass hoppers and marked them before returning them to the field. After a few days they
made another catch of grasshoppers. They collected 45 grasshoppers out of which only 4 had marks.
a) Name the method of population estimation the students used. (1mk)
Capture-recapture;
 b) State two assumptions that were made by the students during the study. (2mks)
Enough time allowed for grasshoppers to randomly mix;
The marking does not affect the animals behavior;
No emigration or immigration;

c) From the data, calculate the population size of grasshopper. (2mks)

Population=First capture x second capture

Marked recapture
= 36 X 45;
4
= 405 grasshopppers;

20. Give three ways in which atmospheric nitrogen is fixed into nitrates.
(3 marks)
 Nitrogen fixation by nitrogen fixing bacteria; some algae; (accept examples e.g. Rhizobium,
Azotobacter, clostridium, specific algae e.g. anaboena, chlorella, nostoc);
By lightning; Rj wrong spelling e.g. lighting, lightening;

21. Name the polysaccharide that constitute the

i. Cell wall of plant cells (1mk)
Cellulose
ii. Cell wall of fungi cells. (1mk)
Cellulose /chitin;
iii. Xylem vessels and tracheal (1mk)
Lignin

22. A wild beast in maasai mara national park was found to be infested with a lot of ticks. State the trophic
level occupied by the following organisms.
(a)(i) Wild beast. (1mark)
Primary consumer;
(ii) Ticks. (1mark)
Secondary consumer;
(b) Sketch a pyramid of numbers to represent the above feeding retionship. (1mk)
 23.
24. A student observed feeding relationship while on a tour in a coastal Island.
Eagles feed on small fish, Small fish feed on sea grass, Insect larvae and molluscs feed on sea grass,
Insect larvae fed on by small fish, while crabs feed on insect larvae and molluscs.

a) From the above information, construct a food web. (3mks)

b) In which trophic level is small fish found. (1mk)

Second / Third
c) Extract a food chain where the Eagle is a tertiary consumer. (1mk)

d) Suppose all the crabs were poisoned, what would be the immediate effect in the ecosystem? Give
a reason. (1mk)
The population of molluscs / insect larvae would increase; due to decreased predation;

(e) Give a reason why pyramid of biomass is a better representation of energy flow in an ecosystem
than pyramid of numbers. (1mk)

Shows the actual amount of energy flow of a food chain;

25. (a) Define the term poikilotherm. (1mk)
An animal whose body temperature varies with that of the environment.

(b) Describe the role of mammalian skin in thermoregulation. (19mks)

Low temperature
- Animals in cold habitats have a thick layer of subcutaneous fat; for insulation/reduce heat loss;
- Erector pili muscle contract raise the hair upright; hair traps a thick layer of air for insulation;
- Superficial vessels in the skin vasoconstrict; so that less blood flows near the skin surface; thus
reduces heat loss:
- Metabolic rate rise to produce extra heat;
- Shivering ( involuntary, rhythm contraction of skeletal muscles) to generate heat;
High temperature
- Animals in hot climate have a localized fat deposit; so as to reduce insulation thickness;
- Erector pili muscle relax; hair lies flat on skin; trap no or little air; thus promotes heat loss;
- Blood vessels in skin vasodilate; so that more blood flows near the surface; this promotes heat
loss;
- Sweating and panting; sweat evaporates from skin surface of cooling the body as it
absorbs/latent heat of vapourization;
- Metabolic rate falls less heat is generated; (Animals less active) ( max 19mks)