NAME:…………………………………..……….…………………………….. SIGN:….
…………
SCHOOL: ……………………………………...ADM NO………CLASS:…….DATE:…………
Marking Scheme
231/1
BIOLOGY
Paper 1
(Theory)
March/April 2025
TIME: 2Hours
(Kenya Certificate of Secondary Education)
231/1
BIOLOGY (Theory)
Paper 1
Time: 2Hours
INSTRUCTIONS TO CANDIDATES
Write your name and admission number in the spaces provided at
the top of this page.
Sign and write the date of examination in the spaces provided above.
This paper consist of a single section.
Answer all questions in the spaces provided.
For Examiners Use Only
QUESTION MAXIMUM SCORE CANDIDATE’S SCORE
1 -30 80
TOTAL SCORE
Qsn.1 (i) Ornithology;
Page | 1
(ii) Entomology;
Qsn.2 a) Presence of cornified layer;
Secretion of sebum;
b) White blood cell/Leucocyte; acc. correctly named
example.
c) Thrombin;
Qsn.3 a) Tube nucleus;
b) One male nucleus fuses with egg cell nucleus to form a
(diploid) zygote; the other (male nucleus) fuses with the
polar nuclei to form (triploid primary) endosperm
(nucleus);
Qsn.4 Monoecious plant is a plant with staminate/male and
pistilate/female flowers borne separately on same plant;
Dioecious plant has staminate/male and pistilate/female
flowers on two different plants (of same kind);
Qsn.5 A change above/below normal leading to further undesirable
change/deviation from the normal; [OWTTE.]
Qsn.6 a) Process by which Red Blood Cells gain water by osmosis,
swell and burst (when placed in hypotonic solution);
b) Process by which plant cell/cells has lost water and is
(fully) plasmolysed;
Qsn.7 a) Fungi/Mycophyta;
b) Saprophytism;
c) (i) Hypha;
(ii) Secretes digestive enzymes;
Anchorage;
Absorption of nutrients;
[Any Correct]
Qsn.8 The areas have low oxygen concentration; encourage
increased production of Red Blood Cells; which
improves transport of oxygen to body tissues/muscles for
respiration; hence more energy generated;
[4 Max ×3]
Page | 2
Volume of CO2 produced
Qsn.9 a) RQ = Volume of O2 consumed
;
3
199.75 cm
= 3
200 cm
= 0.9988 ; rej with units
b) Carbohydrate(s); acc. Glucose
c) - Converted into fats and stored/deposited (in adipose
tissues);
- Converted into glycogen and stored (in the liver);
Acc increased oxidation
[Any 1 correct]
Qsn.10 Enzymes; acc. correct example
Water;
Qsn.11 a) Absorbs Carbon (IV) oxide exhaled by the mouse; denying
plant CO2 for photosynthesis; hence mouse suffocates/dies
due to absence of oxygen; [OWTTE]
b) Bell jar is transparent/allows light entry/penetration for
photosynthesis/Tin box is opaque and could
easily lead to increased temperature above optimum;
Qsn.12 a) Zone of cell elongation;
b) Actively dividing;
Very small in size;
Thin walled;
Oval/rounded/rectangular in shape;
Single/Large/Prominent nucleus;
No intercellular air spaces/closely packed;
High rate of metabolism;
No food store/vacuole/present very small;
Dense cytoplasm;
[1st 2]
c) Zone of permanent tissue/differentiation;
Qsn.13 a) Attract/Trap small organisms/animals;
Page | 3
b) Collecting /Keeping collected specimen;
Diameter of image
Qsn.14 Magnification = Diameter of object
;
2× 1000
= A
;
A = 2.5 µ m;
Qsn.15 a) Diffusion is movement of molecules from a region of high
to a region of low concentration; Active transport is
movement of molecules from a region of low to high
concentration(using energy);
b) Boiling destroys/denatures cell wall/cell membrane;
rendering it impermeable;
Qsn.16 (i) Scurvy;
(ii) Goitre;
Qsn.17 - Oxidized to Carbon (IV) oxide, water and energy in the
presence of oxygen;
- Some taken into the liver and converted into glycogen;
Qsn.18 Urea is less toxic;
Urea requires less water to excrete;
Qsn.19 Has mammary glands;
Has sweat glands;
Body covered with fur/hair;
Heterodont;
Gives birth/viviparous;
External ears/pinna;
[ANY -2]
Qsn.20 (i) Rapid increase in rate since increased temperature
activates enzymes;
(ii) Maximum rate because temperature is optimum;
Qsn.21 Growth;
Development;
Reproduction;
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[1st – 2]
Qsn.22 Scientific double naming system; in which an organism is
assigned
Genus/generic and species specific name;
Qsn.23 (a) Gene for haemophilia is linked to X chromosome which is
only one in males; [OWTTE]
(b) Presence of more than two sets of chromosomes in a cell;
Qsn.24 (a) Palisade mesophyll;
(b) (Immediately) beneath upper epidermis;
Qsn.25 a) – Biotic factors; acc community of living organisms
- A biotic factors; acc physical/non-living environment
b) Its components interact; to maintain a stable self-
perpetuating system;
Qsn.26 a) Sertoli cell;
b) Interstitial cells;
c) (i) Meosis;
(ii) 23;
Qsn.27 a) A process where environment allows organisms that are
well adopted to live and reproduce while those that are
not well adopted are eliminated before they
reach reproductive stage;
b) Eliminates traits that are disadvantageous in a
population/perpetuates traits that are advantageous;
- Enables better adopted organisms to survive in
environments with adverse conditions;
Qsn.28 a) Positive phototaxis; acc positive aerotaxis
b) Negative chemotaxis;
Qsn.29 Ammonium (Compound);
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b) B: Absorption;
X: Nitrification;
Y: (Nitrogen) fixation;
Qsn.30 5 Carbon Sugar-Nitrogenous base phosphate;
Page | 6
