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;ü (1 mark)

(ii) Genotype XB Y x XbXb;

gamets correct genotypes

Xb; / Xb
XB / XBXb; / XBXb
Y / XbY / XbY

correct offsprings Acc. in order of alphabet XY not YX

Rej.
(4 marks)

b) Haemophilia; (1 mark)

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 ( 1mark)

(Any one)

2  a) Response of shoot to unidirectional light; (1 mark)

- Role of tip in response; (1 mark)

b)

;

B (2 marks)

A

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 (1 mark)

3  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)

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)

4  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)

5  a)(i) Healing and repair of uterine wall; ( 2 mark)

(ii) Proliferation/thickening of uterine wall;

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)

6  a)

Nb: Labeling both axis; (2 marks)

Scale for both axis (2 marks)

Smooth curve and identity of each (2 marks)

Accurately plotted points for each curve (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;

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)

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 1