TRIAL 3 2023

231/1
BIOLOGY PAPER 1
MARKING SCHEME
1.

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a) Classification ;
b) Microbiology ;
2. What is the role of Seechi disk in experimental biology? (1
To measure the depth of penetration of light in the water bodies/aquatic ecosystems
3. What role does the blood play in the following in human body:
a. Nutrition (1 mark)
It transports nutrients to the cells/tissues. Accept glucose/ammo acids
b. Thermoregulation (1 mark)
It distributes heat from the liver and muscles to other body parts (enhancing thermoregulation);
c. Development and coordination (1 mark)
Blood transports hormones from glands to sites of action (where they stimulate growth processes);
4. You have set up your light microscope for use to observe epidermal cells. However, upon looking through
the eyepiece lens, you are not able to see the field of view. Suggest three possible adjustments you can
make to the microscope to rectify the case (3 marks)
 Adjusting the mirror to reflect light towards the stage;
 Adjust the diaphragm to allow more light to pass through;
 To adjust the revolving nosepieee so that the objective lens
clicks into position;
5. Below is a red blood cell appearance after treatment in a given solution.
a) Account for the appearance of the red blood cell (3 mrks
The red blood cell was placed in a hypotonic solution; the cell contents being more concentrated than the
solution, it drew water/gained water by osmosis; making it to swell (and lose its biconcave shape);
b) Even with a damage to the sympathetic and vagus nerves, the heartbeat continues. Explain this
observation (1 mark)
The heart muscles are myogenic hence do not require nervous stimulation to contract.
6. a). Define apical dominance (1 mark)
This is the inhibition to growth of the lateral buds by the auxins produced bv the apical bud. OWTTE
b). Abscisic acid is known to promote leaf fall through formation of the abscission layer. Give two beneficial
advantages of leaf fall to plants (2 marks)
 Enables plants to minimize water loss during droughts,
 Enables plants to dispose of the metabolic wastes deposited on the leaves.
7. Despite the best efforts to make and use the most effective pesticides, bedbugs have not been eradicated from
most homes. Give an explanation for this observation (2 marks)
This is because the bedbugs undergo mutations; that gives them resistance against the pesticides;
8. Explain how the structure of the blood vessels entering and leaving the glomerulus contribute to presence of
glucose in the Bowman's capsule (2 marks)
The blood vessel entering the glomerulus/afferent arteriole has a wider lumen thai the bloodvessel leaving
glomerulus/ efferent arteriole; this generates high pressure that forces glucose molecules out of the
capillary walls into the Bowman "s capsule;
9. Some entemophilous flowers do not have brightly coloured petals but they still attract
insects. Give two reasons (2 marks)
 Some of the flowers are scented to attract insects:
 Some of the flowers have nectarines/nectaries/nectar glands
to produce nectar to attract insects;
 Some are large and conspicuous enabling insects to easily
spot them,
 Some flowers have body shapes mimicking the female insect
shapes to attract the male insects;
10. Give two differences between a human male gamete and a
male gamete from an angiospenn (2 marks)
 The human male gamete Is mononedeated while the
angiosperm male gamete is binucieated;
 The human male gamete has a tail giving it mobility while
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 the angiosperm male gamete lacks a tail making it
immobile;
11. During hyperglycemia, what is the effect of insulin on:
 it stimulates the muscle cells to increase uptake of glucose
for respiration and cellular metabolism/stimulates increased respiration in muscle tissues;
12. a). For what purpose in experimental biology do we use
Biuret's reagent? (1 mark)
To test for proteins; Acc: Peptide bonds ' -
b). Give the interpretation of the test/procedure you have identified
above (2 marks)
If the colour turns purple or violet then proteins/peptides are present; while if there is no colour
change/blue colour persists then proteins/peptides are absent;Reject: If there is no change…..
13. Poor support systems in plants affect vital processes in plants. Highlight two ways in which a leaf achieves
support (2 marks)
 Presence of leaf petiole;
 Presence of xylem tissues and fibers;
 Turgidity of the mesophyll cells;
 Rigidity of the cellulose cell walls;
 Reject osmosis
Any 2 correct X I mark= 2 marks
14. Below is a set up that was used to investigate a certain process
in plants
a. What was the aim of the experiment (1mark)
To estimate/measure the rate of transpiration;
b. What is the limitation of this apparatus in investigating
the aim you have stated above (1 mark)
It does not determine the rate of water loss through transpiration; it measures the rate of water
absorption instead;
c. What is the role of the water reservoir? (1 mark)
To recharge/reset the air bubble;
d. Suggest a control experiment for the set up above? (1 mark)
 Use a shoot with all the leaves detached;
 Use the set up with the leaves covered with an airtight/
polythene bag;
15.
a) overall (trend) is an increase in deaths / AW ;decrease in 2011 ;
big(gest) increase, between 2011 and 2012 / in 2012 ;
small(est ) increase, between 2012 and 2013 / in 2013 OR
similar numbers of deaths in 2012 and 2013 ;
(b )any two from:
depressant ;
increases reaction time / AW ;
reduces self-control ;
AVP ;; e.g. reduced pain or temperature perception / loss of
consciousness / lack of coordination
(c) liver

16. Study the diagram below representing a neurone and answer

the questions that follow

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a) Give function of A (1 mark)
Speeds up transmission of nerve impulses. Reject transfusion
b) Place an arrow on the diagram to show the direction of the
impulse (1 mark)
On the diagram from cell body towards terminal dendrites;
c) On the diagram indicate with X a point at which there will be
secretion of a neurotransmitter (1 mrk)
As on the diagram;
d) What is the role of the neurone above (1 mark)
It transmits impulses from the central nervous system to the effector; Accept gland/muscle for effector
17. The diagram below represents a female reproductive system
a) Identify the part affected by both pituitary hormones
regulating the menstrual cycle (1 mark)
A. Accept ovary;
Reject small a
b) Label with letter M. the part of the diagram most sensitive to oxytocin (1 mark)
Any part on the myometrium;
Reject labeling on endometrium (innermost uterus lining)
c. Suggest why implantation on part B must be terminated (1 mk
It would put the life of the mother at risk/can cause maternal death;
d) Highlight two functions of the female reproductive system (2
 Production of female gametes;
 Protection of the developing foetus;
 Production of hormones such as oestrogen and
progesterone;
 Reception of the male gametes;
Any 2 correct x 1= 2 marks.
18. a. A – Hydrogen ions; (1 mk)
B - Carbon (IV) Oxide/CO2; → Rej Carbon (iv) Oxide Carbon IV oxide

chlorophyll
b) 6CO2 + 6H2O → C6H12O6 + 6O2
Sunlight

Or

Chlorophyll
Carbon (IV) Oxide + Water Carbohydrates + Oxygen
Sunlight

NB/ Equations must be balanced

19. Give two differences between respiration and gaseous
exchange (2 marks)
 Gaseous exchange is the interchange of oxygen and carbon
(IV) oxide at the respiratory surfaces while respiration is the process of breakdown of food substances
in living cells to release energy;
 Gaseous exchange is a physical process while respiration is
a chemical process.
 Gaseous exchange occurs at the respiratory surfaces while
respiration occurs in all living cells;
20. Your class is to embark on a practical lesson to study the
digestive system of a rabbit.
a) Name any three instruments you are likely to use during the

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 dissection (3 marks)
- Dissecting board; - Scalpel (blade);
- Dissecting pins; - Dissecting probe;
- Kemostat; - Dissecting forceps;
- Dissecting scissors; - Dissecting needle;
Any first 3 correct x 1= 3 marks
b) Give two factors determining energy requirements in man (2m
- Sex; - Occupation;
- Body size; - Age;
- Basal metabolic rate; Any 2 correct x 1 mark= 2 mrks
21. Below is a leaf cross section
a) Name one tissue type found at both points V and Y (1 mark)
Epidermis/Epidermal tissue; Reject cuticle
b) Give two adaptations of cells at point Z (2 marks)
 The guard cells have chioroplasts to synthesize sugars
raising the osmotic pressure of the guard cells to facilitate water uptake;
 The guard cells have wails that are differentially thick to
bulge when expanding facilitating opening of stomata;
22. The table below contains information about various
components of the mammalian circulatory system.
blood blood in
tissue Lymp
in vena
fluid h
aorta cava
Red blood cells Many None; None Many
White blood cells Many Some Some Many
Glucose High High Low; High
concentration'
Pressure High Low Low Low
a) Complete the unfilled boxes in the table with the most appropriate word (2 marks)
b) Explain the difference in glucose concentration in the tissue fluid and lymph (2 marks)
There is low glucose concentration in lymph than in tissue fluid; because most of the glucose shall have
been taken up by the cells for cellular metabolism (from tissue fluid);
23. Mr. Kamau sues Neema Hospital for exchanging his son 15
years ago. Mr. Kamau's son is colour blind while both the parents have normal colour vision. According to
Mr. Kamau, this means the son must have been exchanged at birth. Explain why Mr. Kamau may lose the
case (2 marks)
Mr. Kamau may lose the case because there is a probability they may have a colour blind son; if the
mother is a carrier for colour blindness trait;
24. State two ways in which bryophites are of ecological
significance in an ecosystem (2 marks)
 Some bryophytes form a carpet over the ground surface
conserving moisture/retaining soil moisture;
 Act as a source of food;
 Provide shelter for small organisms; f Initiate soil
formation;
 Provide oxygen to other organisms
 Regulate amount of respiratory gases in the atmosphere;
 They prevent soil erosion;
Any 2 correct x 1 = 2 marks
Mark first 2 only
25. The diagram below is a scanning electron micrograph of some xylem vessels.
Give two adaptations visible in the picture that adapts the tissue to its function (4 marks)
 They xylem vessels have a hollow lumen; to permit
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 passage of water up the plant;
 The xylem walls are lignified; to provide support/prevent
them from collapsing (ensuring water is conducted up the plant);
 The xylem vessels have bordered pits; for lateral
movement of water;
26. Distinguish between chemical evolution and organic evolution theories (2 marks)
Chemical evolution theory proposes that life originated from chemical reactions in the past while
organic evolution theory proposes that the complex life forms seen presently originated from simpler
preexisting life forms over a very long period of time;
27. Below is a representation of one of the organs of the mammalian body
a) Name the part labelled B (1 mark)
Hair erector pili muscle;
b) The opening through which structure A emanates provides a possible pathway for bacteria to get into a
mammalian body. How is this possible risk minimized in the organ above? (1 mark)
Presence of sebum (from sebaceous glands) that has antibacterial properties (protecting against
infection);
c. John, a class five pupil wondered why on a hot day his puppy is smaller than on a cold day. What could be the
reason for this? (2 marks)
On a cold day (to conserve heat loss)., hair erector pili muscles contract making the hair strands to be
erect; this makes the puppy to appear bigger;
Accept Reverse Argument
On a hot day (to facilitate heat loss), hair erector pili muscles relax making the hair strands to lie flat;
this makes the puppy to appear smaller;