Download nakuru district sec

NAKURU DISTRICT SEC. SCHOOLS K.C.S.E TRIAL
EXAMINATIONS-2014
Kenya Certificate of Secondary Education (K.C.S.E)
MARKING SCHEME
231/2 BIOLOGY
PAPER 2
1.
X chromosome;
(1 mark)
(ii) Genotype XB Y x XbXb;
gamets
correct genotypes
♀
Xb;
Xb
correct offsprings Acc. in order of alphabet XY not YX
♂;
Rej.
XB
XBXb;
XBXb
Y
XbY
XbY
♀
♂
(4 marks)
(1 mark)
b) Haemophilia;
c) Inform would be couples on facts and possibilities of inherited disorders to enable them decide on
whether to marry or not/prepare them to handle the disorders in their children.
( 1mark)
d) Expose to radioactive rays e.g. gamma rays
- Heavy metals
- Chemical substances e.g. mustard gas, colchicine
(Any one)
2
( 1mark)
a) Response of shoot to unidirectional light;
(1 mark)
- Role of tip in response;
(1 mark)
b)
;
B
(2 marks)
A
Nakuru District Sec. Schools Trial Examination @ 2014 Biology Paper 2 Marking Scheme
Page 1
c) Seedlings A – No growth, no response metal prevented auxins at tip from diffusing to the region
of growth/auxins did not pass thro ugh metal block;
(1 marks)
Seedlings B – Auxins from tip diffused through agar; light from one direction caused more auxins
to be distributed to side away from light; caused more cell elongation than on the
lighted side, hence curative towards light.
(2 marks)
(d) Act as control experiment
3
(1 mark)
a) Diffusion:
( 1mark)
b) Starch solution in the beaker turned blue-black; Iodine diffused from visking tubing to beaker.
Iodine solution in the visking tubing remained brown; starch molecules too big to pass across
visking tubing;
(4 marks)
4
5
c) Reabsorption of sugars and some salts by the kidney.
- Absorption of digested food from alimentary canal to the bloodstream
- Excretion of waste products from body cells
(3 marks)
a) Capillary;
(1 mark)
b) Thin walled/ one cell thick to reduce distance for exchange of substances;
- Narrow lumen to offer resistance to blood flow enhancing ultrafiltration;
- Numerous to reach everybody cell;
(Any 2)
(2 marks)
c) X – Red blood cell;
U – Endothelial cell; (rej. Endothelium)
Y – White blood cell.
(3 marks)
d) Important in blood clotting process;
(1 mark)
e) Plasma;
(1 mark)
a)(i) Healing and repair of uterine wall;
(ii) Proliferation/thickening of uterine wall;
( 2 mark)
b) Stimulates secretion of Oestrogen; and development of grafian follicle;
(2 marks)
c) Corpus Luteum;
(1 mark)
d) Both prevent ovulation;
(1mark)
e) Placenta;
During pregnancy;
(2 marks)
Nakuru District Sec. Schools Trial Examination @ 2014 Biology Paper 2 Marking Scheme
Page 2
6
a)
Population of species N and P
Time in months
Nb: Labeling both axis;
Scale for both axis
Smooth curve and identity of each
Accurately plotted points for each curve
(2 marks)
(2 marks)
(2 marks)
(2 marks)
b) (i) as rainfall increases, the population of N also increase;
- as rainfall decreases, the population of N also decreases;
(ii) N feed on vegetation/ is a herbivore, rainfall increase lead to more vegetation; due to bundant
food the number/population of N increases and viceversa;
c) (i) P is a predator to N/N is prey to P
(ii) reduced rainfall in July and August resulted in reduced food vegetation for N whose numbers
therefore decreases. The reduced population of N could not sustain the high population of P
hence some members starved/migrated and population reduced;
d) (i) N
(1 mark)
- Population would decrease drastically as a result of starvation due to increased competition
for food
(ii) P
(1mark)
- Population would increase in number due to plenty of food;
Nakuru District Sec. Schools Trial Examination @ 2014 Biology Paper 2 Marking Scheme
Page 3
7 a)(i) A group of undifferentiated cell in plants which are capable of continuous initotic cell
division;
(1 mark).
(ii) Thin cell walls;
- Dense cytoplasm;
- No vacuoles;
(3 marks)
b) Secondary Thickening in flowering plants.
Secondary thickening results into an increase in girths/width; due to the activity of the cambium.
In secondary growth new tissues are formed by vascular cambium; and cork cambium; the
vascular cambium divides radially to produce new cambium cells between the vascular bundles.
This forms a continuous cambium ring; The new cells of the cambium differentiate to become
secondary phloem on the outsides; those to the inner side differentiate to form secondary xylem,
more secondary xylem; is formed than secondary phloem; the interfascular cambium divides to
form parenchyma thereby increasing the growth of medullary rays;
As a result of the increase in volume of the secondary tissue; pressure is exerted on the outer cells
of the stem resulting in rupturing of epidermal cells; In order to replace the protective outer cover
a new band of cambium cells are formed in the cortex. The cork cambium/phellogen
differentiate into secondary cortex on the inner side; and cork cells on the outside; cork cells are
dead with thickened walls which became coated with a water proof substance called suberin;
The cork cells increase in a number and become the bark of the stem which prevents loss of
water; prevents infection from fungi and is also insulators. Bark is normally impermeable to
water and respiratory gases; periodically the cork cells form a loose mass of cells known as
lenticels which makes gaseous exchange possible; The rate of secondary growth is stem varies
with seasonal changes; eg. during rainy season xylem vessels and tracheids are formed in large
numbers; the cells are large thin walled and with wood with light texture; in dry season xylem
and tracheids formed are few in number, are small and their wood have a dark colour. This leads
to development of two distinct layers within the secondary xylem formed in a year called annual
rings; (allow marks on correctly annoted diagrams)
( 14 marks
8
Cervical Vertebrae;
 Have vertebrarterial canals for passage of neck blood vessels and nerves;
 Atlas has v\broad surfaces for articulation with condyles of skull to permit nodding movement of
skull;
 Axis has odontoid process of Centrum which acts as a pivot for atlas/skull forming a pivotal joint
to permit rotational movement of skull;
 Have short brunched transverse processes for attachment of neck muscles;
 Short neural spine for attachment of muscles;
 Wide neural canal for passage of spinal cord;
 Broad neural arch for protection of spinal cord;
(Max. 7 marks)
Thoracic Vertebrae;
 Long neural spine provide a L.S.A for attachment of back muscles;
 Tubercular and capitular facets for articulation with tuberculum and capitulum of the rib;
 Reduced T.P for attachment of muscles;
 Neural arch for protection of spinal cord;
 Pre and postzygapophyses for articulation with those of adjacent vertebrae;
 Centrum for attachment of the T.P;
(Max 5 marks)
Nakuru District Sec. Schools Trial Examination @ 2014 Biology Paper 2 Marking Scheme
Page 4
Lumbar Vertebrae
Long T.P for attachment of muscles that maintain posture and flexes the spine;
 Broad neural spine for attachment of powerful back and abdominal muscles;
 Metapophyses and Hypapophyses provide additional muscle attachement
 Thick centrum for support;
 Pre and post zygapophyses for articulation between vertebrae and muscle attachement
(Max 5 marks)
Sacral Vertebrae
 Vertebrae fused to provide strength/firmness to bear body weight;
 The first anterior sacral vertebra has large wing-like T.P fused to pelvic girdle to provide strength;
 Large and broad centrum to offer support;
(Max 3 marks)
Nakuru District Sec. Schools Trial Examination @ 2014 Biology Paper 2 Marking Scheme
Page 5