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TRANS NZOIA WEST DISTRICT MOCK EXAMINATION – 2008
Kenya Certificate of Secondary Education (K.C.S.E)
231/2
BIOLOGY
PAPAR 2
MARKING SCHEME
CONFIDENTIAL
1.
2.
a)
b)
c)
c)
e)
a)
b)
c)
d)
3.
a)
b)
c.i)
ii)
d)
4.
a)
b)
Endotherm/ Homeoiotherm
(1mk)
It ensures that metabolism occurs without being affected by external factor;
Sweating; excretion; breathing; defecation;
(any 2mks)
- Erector filli muscles relax; thus body hair lies flat decreasing insulation and increasing heat loss;
- Vasodilation occurs; - it increases blood flow in superficial blood vessels, hence increasing heat loss by
convection and radiation;
- Sweat glands secrete more sweat; which evaporates increasing loss of heat through latent heat of
vaporization.
(3mks)
To prevent overheating in the body / to prevent heat stroke
(1mk)
A – Gill filament
B – Gill bar
(2mks)
Filter solid particles/ food particles from inflowing water
(1mk)
Water in the gill filament flow in opposite direction to the flow of the blood in the
filaments; creating a steep diffusion gradient for faster/ maximum
gaseous exchange;
Concentration of O2 in water is higher than its concentration in the protozoa;
O2 diffusises a cross the cell membrane into the protozoa ; concentration of CO 2 in the protozoa is higher
than in the water surrounding due to respiration ; CO2 diffuses out into the water across the cell membrane;
(Any 3 mks for any 3 points)
Curve Y; - it starts with a higher population than X, the predator;
(2mk)
The number of predators dropped due to increase competition for food; as a result of a decrease in the
number of prey;
(2mks)
Prey – predator relationship or predation
(1mk)
It maintains the numbers of prey and predators at the carrying capacity of the habitat;
It removes weak organism from the population by natural selection;
There would be an increase in the herbivorous population due to reduced predation;
Herbivores would feed on a lot of vegetation which would reduce primary productivity – hence causing soil
erosion;
( 2mks)
Aa; Aa;
(2mks)
Parental phenotype
P. genotype
Normal
Aa
Normal
Aa1 ½
Gametes
Fusion
Genotype of normal pigmented children :AA;
Aa;
Genotype of albino child – aa;
Trans-Nzoia West Examination Panel
(2mks)
(1mk)
1
Biology 231/2
5.
c)
a)
1/5
(1mk)
Oestrogen
- Heals and repairs uterine wall
- together with progesterone causes prolifenation of the uterine lining in preparation for implantation;
- Makes uterine muscle more sensitive to oxytocine;
(any 1 pint, 1mk)
Progesterone:
- Causes prolifenation of the uterine wall;
- Maintains thickening of the uterine wall;
- Prevents miscarriage / maintains pregnancy;
( any 1 pt 1mk)
b)i
ii)
Umbilical artery;
Umbilical vein;
c)
-Umbilical artery – Co2; Nitrogenous wastes
- Umbilical vein – Oxygen; food nutrients;
- Antibodies;
(any 1 pt, 1mk)
Oestrogen inhibits the production of FSH, no follide grows;
- Progesterone inhibits the production of FSH and LH. No ovulation can occur; (2mks)
Nitric acid; carbonic acid;
(2mk)
on the graph;
Title - ½ mk
Scale - ½ mk
Correct curves ( 2mks)
Y axis – mean length in mm
(2mks)
X axis – acid concentration
(mol dm x 10)
(2mks)
Growth of shoot – as the acid conc. increases, growth of the shoot decreases; due to the low pH which is
toxic to the cells;
(2mks)
The length of the root increases slightly at the beginning; but as the acid concentration increase, the growth
of the root decreases; low pH is not suitable for the growth of root;
(2mks)
At 5 x 10-3
- Mean shoot length 2.0mm ± 0.1;
- Mean root length 2.0 mm ± o.1;
(2mks)
- Kills organisms in water and soil;
- Corrodes walls and roofs of buildings;
- Causes leaching of aluminum from soil;
(any 2 points 2mks)
- Use of substances that extract sulphur from sulphur containing substances;
- Fitting chimneys with scrubbers that dissolve gases like sulphur dioxide and nitrogendioxide;
- More use of electricity instead of fossil fuels;
- Fitting automobiles with filters and catalytic converters in their exhaust pipes to reduce emission of
sulpur oxides;
( any 3 points, 3mks)
d)
6.
a)
b)
c)i
ii)
d)
e)
f)
Trans-Nzoia West Examination Panel
(1mk)
(1mk)
2
Biology 231/2
SECTION B
7.
In the mouth;
There is mechanical breakdown of food using teeth; to increase the surface arae for enzyme action; food is moistened;
and lubricated by saliva; for easy swallowing;
The enzyme ptyalin; converts starch; to maltose; food is then rolled into bolluses; and pushed down the gullet by the
tongue;
There is no chemical digestion of protein in the mouth; since no protein digesting enzymes are there;
Trans-Nzoia West Examination Panel
3
Biology 231/2
In the stomach
HCL acid provides a suitable PH; to activate pepsinogen; to pepsin; protein in the egg is converted by pepsin; to
peptides; and peptones; No digestion of starch; because the pH is not suitable for ptyalin to continue acting on starch;
Food is churned; by rhythmical contraction of the muscular wall of the stomach; to form chyme;
In the duodenum;
Bile; provides a suitable PH and neutralizes the acid chime;
Pancreatic amylase; converts starch to maltose;
Trypsin; converts proteins into peptides and peptones;
Bile salts; emulsify the fats in the egg; pancreatic lipase; digests fat to fatty acids and glycerol’s;
In the ileum;
Maltase; converts maltose into glucose;
Peptidase; convert peptides into amino acids;
Lipase converts fats to fatty acids and glycerol;
8.
( Any 20 points 20mks)
Evidences of evolution
Comparative anatomy/ Taxonomy;
Members of a phylum/ group show similarities; organisms have similar structures/ similar organs performing the
same functions; eg digestive system, urinary system, nervous system/ any correct example; vestigial organs e.g
appendix, coccyx tail; vertebrate heart;
The pendactyl limb/ any correct example;
Analogous structures/ different structures performing the same function; e.g wings of insects bats and birds – show
convergent evolution;
Homologous structures/ structures with same origin but performing different functions; show divergent evolution;
Fossilrecord / palaentology;
These are remains of organisms preserved in naturally occurring materials for many years; show morphological
changes of organisms over a long period of time; e.g skull of man, leg of horse;
(4 mks)
Comparative embryology;
Vertebrate embryos are morphologically similar; suggesting the organisms have a common origin / ancestry;
( 3mks)
Geographical distribution;
Present continents are thought to have been a large land mass joined together; and as a result of continental drift
isolation occurred; bringing about different patterns of evolution; eg kangaroos in Australia, Jaquar in South America,
Liama in Amazon;
(any correct example)
Coparative serology/ physiology;
Antigen – antibody reactions/ Rh. Factors blood group/ haemoglobin structure; reveal some relationship among
organisms/ common ancestry;
(2mks)
(Total 23 max, 20mks)
Trans-Nzoia West Examination Panel
4
Biology 231/2