WAEC SSCE - Agricultural Science - 2000 (Practical)

(a) Disease condition and causative agent

• Specimen J (maize plant): the leaves show a mottled mosaic pattern, the disease is maize mosaic disease, and its causative agent is a virus.
• Specimen K (cassava leaf): the leaf shows brown circular spots, the disease is cassava leaf spot, and its causative agent is a fungus.

(b) Mode of transmission

• Specimen J: the virus is transmitted from plant to plant by an insect vector, the aphid.
• Specimen K: the fungus is airborne and is also spread by water and rain splash.

(c) Two effects and two control measures of each disease

Specimen J (maize mosaic) effects: it reduces the photosynthetic area of the leaf and causes stunted growth with a reduction in yield. Control: use resistant varieties and practise early planting; also eradicate the insect vectors and remove and burn infected plants.

Specimen K (cassava leaf spot) effects: it reduces the photosynthetic area of the leaf and lowers the rate of growth and yield of the crop. Control: apply fungicides and use resistant varieties; also remove and burn infected plants and practise crop rotation.

(d) Two other diseases of specimen K (cassava)

• Cassava mosaic disease.
• Cassava bacterial blight.

(a) Identification of specimens

• Specimen L: NPK fertiliser
• Specimen M: Tilapia fish
• Specimen N: Litmus paper

(b) Identification of specimens O and P using litmus paper

Litmus paper is used to test whether water is acidic or alkaline:

• Specimen O: acidic pond water, if it turns blue litmus paper red.
• Specimen P: alkaline pond water, if it turns red litmus paper blue.

(c) Pond in which tilapia will survive better

Tilapia will survive better in specimen P, the alkaline pond water. Tilapia generally grows best in water that is near neutral to slightly alkaline. Acidic water can stress fish and reduce their growth and survival.

(d) Relevance of NPK fertiliser in tilapia production

NPK fertiliser supplies nutrients, especially nitrogen and phosphorus, to the pond. These nutrients encourage the growth of phytoplankton and other aquatic organisms, which form natural food for tilapia. This can improve fish growth and yield.

(e) Pond management practices to improve acidic pond water for tilapia production

• Apply agricultural lime to the pond to reduce acidity and raise the pH.
• Drain or flush out excessively acidic water and replace it with clean water of a suitable pH.

(f) Ways of controlling loss of tilapia on a farm

• Fence or secure the farm and pond area to prevent theft.
• Use nets, screens, or barriers to prevent predators such as birds, snakes, and frogs from entering the pond.
• Maintain good water quality and control diseases through proper feeding, correct stocking density, and prompt removal of sick or dead fish.

(g) Harvesting methods for tilapia

• Partial harvesting: use a seine net or cast net to catch only market-sized fish, leaving smaller fish in the pond to continue growing.
• Complete harvesting: drain the pond and collect all the fish.

Examination reminder: When litmus paper is used, remember that blue litmus turns red in an acid, while red litmus turns blue in an alkali. For fish ponds, acidic water is commonly corrected by liming.

(a) Type of rock to which each specimen belongs

• Specimen D is an igneous rock.
• Specimen E is a sedimentary rock.
• Specimen F is an igneous rock.

(b) Type of weathering caused by each specimen

• Specimen G (earthworm) causes biological weathering (through its mechanical burrowing action).
• Specimen H (water) causes chemical weathering and physical (mechanical) weathering.
• Specimen I (ice block) causes physical (mechanical) weathering.

(c) Two ways by which each specimen causes weathering

• Specimen G (earthworm): it burrows into and widens cracks in the rock, breaking it into smaller particles; the burrows also admit water and air which further speed up rock disintegration.
• Specimen H (water): it dissolves soluble rock minerals and forms weak acids that chemically attack the rock; running water also drags rock particles which collide and wear against one another and the channel walls, breaking them down.
• Specimen I (ice block): when water in rock cracks freezes to ice it increases in volume, and the pressure exerted widens the cracks until the rock splits; the movement of ice along a path also dislodges and drags away rock particles.

(d) Three ways in which specimen D (igneous rock) is important to agriculture

• On weathering it breaks down to form soil, serving as the parent material of the soil.
• It releases and supplies mineral nutrients such as calcium and potassium to the soil.
• It is piled up to check erosion and is used to construct farm structures and access roads.

(a) Identification of specimens

• Specimen A: Nut and bolt.
• Specimen B: Knapsack sprayer.
• Specimen C: Identification tag.

(b) One function of each specimen

• A (nut and bolt): Used for tightening, fastening, fixing or holding joints of implements and machines together.
• B (knapsack sprayer): Used for spraying and applying agrochemicals such as fungicides, insecticides, herbicides and liquid fertilizers on crops.
• C (identification tag): Used for the identification of animals.

(c) Two ways of maintaining each of specimens A and B

Specimen A (nut and bolt):

1. Grease or oil it to prevent rusting.
2. Re-thread worn-out threads and store in a cool, dry place. (Straightening a bent bolt or nut is also acceptable.)

Specimen B (knapsack sprayer):

1. Wash and clean the tank, filters and nozzles with water after every use, and drain the tank by turning it upside down.
2. Check for leakages and block them, replace damaged or worn parts such as filters and nozzles, and store the sprayer under cover.

(d) Three other farm implements that perform the same function as specimen B

1. Motorized sprayer
2. Boom sprayer
3. Hand sprayer (electrodyne/knapsack-type sprayers are also acceptable)

(e) Two precautions to be observed when using specimen B

1. Wear protective clothing and a nose mask, and do not eat, drink or smoke while spraying.
2. Ensure that spraying is done along the direction of the wind, not against it, and never blow a blocked nozzle with the mouth.