KAHURO/KIHARU DISTRICT JOINT EXAMINATION – 2015
231/2 – BIOLOGY PAPER 2 MARKING SCHEME
1. (a) Genes located on sex chromosomes and are transmitted along with those that determine sex;
(b) Colour blindness;
Haemophillia;
Hairy ears / pinna;
Baldness;
(c)
♀
; 1mk
♂
XRXR
Gametes
XR
X
XRY
XR
XRXr
Xr
XRY
XRXr
(1mk)
(2mks)
; 1mk
Y
XRY
; 1mk
(5mks)
; 1mk
Phenotypic ratio =>
Red eyed males :
Red eyed females;
1
:
1
2. (a) To show that oxygen is necessary for germination;
(b) To absorb oxygen present in jar;
(c) A – No germination occurred in A;
B – Germination occurred;
(d) - Scarification;
- Soaking in Gibberalic acid;
- Providing adequate water, oxygen moisture and appropriate temperature;
- Boiling seeds in water;
(e) - Gibberellins;
- Auxins;
3. (a) To show that Carbon (IV) oxide is produced when glucose is heated;
(b) A white precipitate was formed;
(c) Carbon (IV) oxide combines with calcium hydroxide to form calcium carbonate that is insoluble.
(d) Glucose => Ethanol + Carbon (IV) oxide + Energy.
(1mk)
(e) - Biogas production;
- Treatment of sewage;
- Manufacture of alcoholic drinks
- Manufacture of milk products
- Manufacture of organic acid
- Leavening of bread
(any 4 x 1 = 4mks)
4. (a) (i) Preserved remains of dead organism that lived in ancient times and were accidentally
preserved under sedimentary rocks;
(ii) Structure that are greatly reduced in size and have ceased to be functional;
(b) - Nictitating membrane;
- Appendix;
- Body hair;
- Caecum;
(c) - Comparative embryology;
- Comparative serology;
- Comparative anatomy;
- Geographical distribution of organisms;
- Fossil records;
(1mk)
(any 2x1 = 2mks)
5. (a) dipeptide;
(b) X – Condensation;
Y – Hydrolysis;
(c) Pepsin breakdown proteins into peptides; salivary amylase breakdown starch
into maltose; enterokinase activates trypsinogen into trypsin;
(1mk)
(1mk)
(1mk)
(3mks)
6. (a)
(b)
(c)
(d)
(e)
(f)
Marks distribution
 Drawing of correct x and y axis with units.
(2mks)
 x and y axis scales.
(2mks)
 plotting of smooth curves for x and y.
(2mks)
 naming of the two graphs.
(1mk)
Insect Population decrease; due to drying of grass hence less food and little habitat and
camouflage from predators; migration, stiff competition for food;
As the insect population increases the number of predators increases; due to adequate food;
and as the insect population decreases the number of predators decrease due to less food;
Decreases due to fewer insects hence less food; more competition (for food) hence migration
or death which causes the population to decrease;
(i)
Secondary consumers;
(ii)
Primary consumers;
(iii)
Producers
(i)
Capture recapture;
(ii)
Capture recapture;
(iii)
Qudrat / Belt transect
Biology P2MS
2
(2mks)
(3mks)
(2mks)
Kahuro/Kiharu
7. (a) (i) It serves to cool the leaves especially during hot environment;
(ii) It provides a mechanism through which mineral salts are transported in the plants;
(iii) Allows loss of excess water from the plants;
(b) Root pressure: This is the force which push water from the root to the stem.
Cohesion and adhesion force
Cohesion force – force which attracts water molecules together maintaining a continuous column
of water preventing the break of water column.
Adhesion force – water molecules cling to the sides of the xylem vessels wall.
Capillary force – The forces of adhesion and cohesion are the basis of capillarity the rise of liquids in
capillary tubes.
Transpiration pull – as water evaporates from the cells on the exposed parts of plants, water molecules
are drawn from the adjacent cells. Eventually those cells that are adjacent to the xylem vessels draw
water from them by osmosis.
(c) The guard cells have chloroplasts; in presence of light; photosynthesis occur in the guard cells of stomata;
producing sugar in guard cells; This increases the osmotic pressure of guard cells; water is drawn from the
neighbouring cells by osmosis; causing turgidity of guard cells; the inner walls of the guard cells which are
thicker than outer wall stretch more causing the guard cells to bulge outwards; stomata open.
In absence of light, no photosynthesis in guard cells; sugar in guard cells is converted into starch; osmotic
pressure lowers; guard cell lose water to adjacent epidermal cells by osmosis; become flaccid; the inner
walls of guard cells shrink; the thicker wall reduces; this closes this stomata.
8. Adaptation of mammalian eye
 Have conjunctiva: colourless epithelium which protects the eyeball from mechanical damage, also enables
the eyeball to move / rotate easily by secreting mucus;
 Cornea is transparent; to allow light into the eye and curved to refract light entering the eye;
 Have aqueous and vitreous humours; which are thin, aqueous and jelly like fluids; to allow light to pass
through and refract light. The fluids also act as hydrostatic pressure maintaining the shape of eye ball.
They also contain sugars, salts and proteins that provide nourishment to the eye;
 The Iris; is opaque and contractile to control light intensity / amount of light entering the eye (by controlling
the size of the pupil).
 Cilliary body; contains ciliary muscles; which are contractile for controlling the curvature and hence focal
length of the lens; the ciliary body is also glandular to secret aqueous and vitreous humour;
 Presence of suspensory ligaments; are fibrous to hold the lens in position;
 Has transparent biconvex lens; to allow light to pass through and to refract light and focus it onto the retina.
 Retina; contains light sensitive / photosensitive cells which receive light and send impulses to the brain
through optic nerves where image is focused.
 Has cones; which have iodopsin pigment; for colour vision / bright light, rods have rhodopsin for dim light
vision.
 Fovea centralis; have high concentration of cones for accurate vision.
 Choroids layer; for nourishment of the eye, the layer is dark pigmented to stop / reduce light reflection
and absorb stray light;
 Have tough fibrous sclera / scleroid / scleoric layer to protect the eye.
 Optic nerves; contain sensory neurone for transmission of impulses from retina to the brain.
 Pupil; aperture through which light passes through.
(max. 20mks)
Biology P2MS
3
Kahuro/Kiharu