In an ecological study, a locust population and that of crows was estimated in a grassland area over a period of one year. The results were tabulated as shown below:-

Months	J	F	M	A	M	J	J	A	S	O	N	D
Number of locusts	90	20	11	25	200	450	652	15	10	35	192	456
Number of crows(birds)	4	2	0	1	8	16	22	2	1	1	5	15
Amount of rainfall	20	0	55	350	520	400	350	10	25	190	256	350

Draw a graph of population of locusts and crows (birds) against time. (8mks)

(i) State the relationship between rainfall and locust population. (1mk)

(ii) Account for the relationship you have stated in (b) (i) above (1mk)

What happens on the populations of locusts and crows in the months of January to

March ? Give a reason. 2mks)

State one method used to estimate the population of locust. (1mk)

(i) State the trophic level of the; (2mks)

Locusts –

Crows –

(ii) Construct a simple complete food chain involving these organisms (2mks).

If the locusts were removed from the food chain, what would be its effect ? (1mk)

Define the following terms (2mks)

(i)Biomass

(ii)Ecosystem

Describe how hydrophytes and xerophytes are adapted to deal with environmental problems in the regions where they grow. (20mks)

Describe how the mammalian skin regulates body temperature.(20mks)

FORM 3 BIOLOGY PP 2 MARKING SCHEME

END OF TERM 2

1(a)(i) A – Nucleus

C – Cell wall

(ii) – Maintain the shape of the cell;

Providing support to herbaceous plants; (any 1)
Stores sugar and salts;

(b) Hypotonic solution / dilute solution / dilute sugar / salt solution.

water molecules by osmosis (through semi-permeable membrane) to become plasmolysed.

(d) – Opening and closing of stomata.

– Absorption of water by root hairs.

– Absorption of water in intestines.

– Reabsorption of water in kidney nephron. (any 2)

– Feeding in insectivorous plants.

– Movement of water from cell to cell.

– Osmoregulation.

2(a) Cartepillars

Aphids

Mice each (1/2 mk)

Slugs

Primary consumers

(b)(i) Plants Cartepillars Insectivorous hawks ;

Birds

(ii) Plants Slugs Frogs Snakes Hawks (any 1)

Plants Aphids Beetles Insectivorous Hawks

Plants

(c)(i) Largest Biomass – plants

Directly obtain energy from the sun.

(ii) Least biomass – Hawks

Loss of energy in form of heat, respiration, defaceation, excretion.

Sun / solar energy.

3(a) A – Villus

B – Lacteal

(b) A – Increases surface area for maximum digestion and absorption.

B – Absorption of fatty acids and glycerol.

– Absorption of soluble products of digestion.

(d) Produces bile juice which contain bile salts that emulsify fats; and neutralizes the acidic chyme from the stomach;

4(a) Deamination

(b) Liver

– Availing of energy in the body. (any 1)

– Formation of glycogen / fats for storage.

(award any one)

(d) Urea

(e) It is transported to the kidney where it is excreted.

(f) (i) Diabetes inspidus

(ii) Antidiuretic Hormone / Vasopressin

(iii) Pituitary gland.

5(a) To remove / expel dissolved air from the glucose solution.

(b) To prevent entry of oxygen into the yeast – glucose solution.

(d) Becomes white precipitate.

(e) High temperature kills the yeast cells; hence the reaction stops;

(f) – Making of beer / Brewing / Ethanol / Alcohol.

– Baking industry / Raising of the dough. (any 2)

6(a)

Axes labelling (2mks)

Scale (x and y – axis) (2mks)

Curve plotting – each (1mk) total 2mks

Curve labeling – each (1mk) total 2mks

(b)(i)The population of locusts increase with increase in the amount of rainfall.

(ii)Increased amount of food;

Improved breeding conditions;

The population of both decreases;

Less food availability to locusts and crows.

Capture – Recapture method.

(i) Locust – Primary consumers

Crows – Secondary consumers

(ii) Grass Locusts Crows

Grass would increase

crows would reduce

(i) Biomass – The total dry weight of organisms at a particular trophic level.

Ecosystem – A natural unit composed of abiotic and biotic factors whose

interactions lead to a self-sustaining system.

Xerophytes

Have thick cuticle to prevent cuticular transpiration.
Have reduced stomata on lower leaf surface to lower transpiration.
Fold or curl leaves in dry weather to protect stomata from direct sunlight.
Have reversed stomatal opening rhythm where they open at night to reduce water loss.
Have succulent stems and leaves to store water for use in dry season.
Some have superficial roots to absorb light showers of rain.
Some are deep rooted to absorb water from water table.
Shedding of leaves during dry season.
Some have short life cycles and survive as underground perennating structures or seeds during drought.
Hairy leaves.
Sunken stomata 1 x 10 = 10mks.

Hydrophytes

Submerged plants have dissected leaves to increase surface area for maximum light absorption.
Emerged plants have broad leaves with stomata on upper surface to increase transpiration.
Have aerenchyma tissue to increase buoyancy and for gaseous exchange.
Floating water plants have raised flower for pollination.
Poorly developed roots that lack root hairs to reduce absorption of water.
Some submerged plants have sensitive chloroplasts that photosynthesise in low light intensities. 5 x 2 = 10mks

High body temperature above normal:

Sweat glands; Produce sweat; water in the sweat evaporates / sweat evaporates; absorbing latent heat of vaporization producing a cooling effect;
Hairs lie flat; due to relaxation of erector pilli muscles; no / little air is trapped; hence increased heat loss from the body;
Blood vessels / arterioles; vasodilate / dilate; more blood flow to the skin hence loss of heat from the body, by radiation and convection;

When body temperature is low below normal:

Sweat glands produce less / no sweat; no latent heat is absorbed; more heat retained in the body;
The hairs stand upright / erect; to trap air between them; that insulate the body against heat loss; more heat retained in the body.
Blood vessels / arterioles vasoconstrict / constrict;

Less blood flow to the skin; reduces heat loss / more heat is retained in the body;

(20mks)

(;) means a marking point.

By Editorial Team

The Education News Hub Editorial Team is made up of vibrant and experienced editors. Brian Yano is an accomplished longtime Digital Media Journalist at Educationnewshub.co.ke with a great passion for research and fact-checking. He delivers engaging content across diverse topics, with a special interest in Education matters. On her part, Yvonne Kemunto is a journalist, dedicated to unraveling stories that matter. With a keen eye for detail and a passion for storytelling, she brings a fresh perspective to the world of media. Her commitment to detail and excellence shines through in every piece she crafts. Our newest member of the Editorial Team is Jennifer Mumbo. She is a Seasoned Multimedia Journalist with several years' experience; dating back to 2018. Jennifer has a passion for education, sports, tech, politics and entertainment. You can reach the editors at educationnewshub3@gmail.com.