Biology Paper 2 Marking Scheme
KCSE CLUSTER TEST 14
Biology Paper 2
SECTION A (40 Marks)
(b) (i) Saliva
― softens food;
―dissolves food;
―digest food;
―lubricates food ; ( 1mk) (Any one)
(ii) Pushing food along the canal;
―Act as valves to open and close different parts of the canal; Acc one (1mk)
(c) Absorption of digested food; Digestion; ( 2mks)
Letters should be in the lower case
Rej IF separation lines are missing.
8 marks
(c) Has a lower susceptibility to malaria than the people with normal red blood cells because the
plasmodium survive poorly in sickled red blood cells ; (1mk)
(d) (i)It is a phenomenon where an organism has more than two sets(2n) of chromosomes;
(ii)It is the genetic manipulation of genes to produce desired characteristics;
It is the practice that involves the identification of a desired gene, altering,
isolating and transferring it from one living organism to another ; (1mk)
8 marks
(a) Alveolus ; (1mk)
(b) X- Epithelium of the alveolus; (2mks)
Y-Moist surface/water film; (2mks)
(c) (i) Diffusion; (1mk)
(ii) Pulmonary Vein ; (1mk)
(d) ―(Cork)cells are loosely arranged for efficient circulation of gases;
―(Cork)cells have moist surfaces to dissolve respiratory gases; (2mks)
(e) Maintains a steep diffusion gradient for gaseous exchange; (1mk)
8 marks
a)
B – Antipodal cells;
C – Egg cell /ovum; (2mks)
b) ―Allows passage of the male nuclei to the embryo sac;
―Secretes enzymes that digests tissues of the style ;( any one) (1mk)
HbA HbS HbA HbS
Genotype
Gametes
F1 generation
Phenotypes
c)
―Allows water into the seed;
―Point at which pollen tube enters an ovule ;( any one) (1mk)
d)
(i) Double fertilisation; (1mk)
(ii)
―One male nucleus fuses with the egg cell nucleus, to form a diploid zygote that develops into an embryo;
―The second male nucleus fuses with two polar nuclei to form a triploid nucleus that forms the
primary endosperm nucleus; (2mks)
e) It develops into a seed; (1mk)
8 marks
(a) Maximum number of members of a species that an area can support without them
causing degradation of the environment depletion of the resources; (1mk)
(b) (i) Producer ; (1mk)
(ii) Snake; (1mk)
(c) (i) Nitrates; (1mk)
Rej NO-3
(ii) I―Nitrosomonas/Nitrococcus bacteria; (1mk)
II―Nitrobacter; (1mk)
(d) Corrosion of metallic structure; accept correct examples,
Damages leaves;
Kills aquatic animals;
Leaches minerals salts reducing soil fertility; (1mk)
8 marks
SECTION B (40 Marks)
20 marks
(a) (i) Natural selection; (1mk)
(ii) Phenotypically acquired characteristics cannot be inherited; Acc.Environmentally
acquired for phenotypically acquired characteristics. (1mk)
(b) •Fossil Records/Palaentology; Remains of organisms preserved in rocks for many years
reveals gradual changes of structures from simple to more complex ones;
•Comparative anatomy; Comparison of forms and structures reveals resemblances of
structures performing the same function; i.e homologous structures. Analogous structures
which are morphologically different perform same functions;
e.g. wings of insects and birds that suggest common ancestry;
•Comparative embryology;. Embryos of vertebrates at their early stages of development
shows great structural similarity suggesting common ancestry; they have long tails
gill slits and similar circulatory systems;
•Geographical distribution; Organisms are believed to have originated from a common
dispersal centre when the present continents were joined together; continental drift occurred;
isolating the organisms which brought different species/speciation; due to adaptation to new environment;
•Comparative serology; Different organisms have antigens and antibodies that show similar
reactions suggesting common ancestry;
•Cell Biology; Different organisms have similar cell organelles performing similar functions
suggesting common ancestry; (18mks)
20 marks
(a) ―Broad lamina which offers a large surface area for diffusion of gases/absorption of light;
―Thin lamina which provides a short distance for diffusion of carbon (IV) oxide to the photosynthetic cells;
―Presence of veins which transports manufactured food/water and mineral salts/support the
lamina in a favourable position to receive light;
―Presence of stomata for efficient diffusion of respiratory gases/carbon (IV) oxide or oxygen;
―Transparent cuticle/epidermis to allow penetration of light to the photosynthetic cells;
―Numerous chloroplasts in the palisade cells to receive maximum light for photosynthesis;
―Palisade cells are closely packed/vertically elongated to allow many to be packed beneath
the epidermis to receive maximum light;
―Chloroplasts have chlorophyll fort absorbing/trapping light;
―Interconnected intercellular air spaces for rapid diffusion of carbon
(IV) oxide into palisade cells and oxygen out into the atmosphere;
―Mosaic leaf arrangement to ensure all leaves receive light by reducing over lapping/over shadowing; (10mks)
Rej correct function without correct adaptation.
(b) ―Some fruits have hooks/sharp hairs; to stick on animal fur/human clothes (as they pass);
―Fruits are brightly coloured; to attract animals; ―Fruits are scented; to attract animals;
―Fruits are juicy/succulent; to attract animals that eat them and carry the seeds away from the parent plant;
―The seed coats of some seeds are resistant to digestive enzymes; hence pass out undigested;
and deposited far away from the parent plant;
Total 11 mks
Max. 10mks
20 marks