WAEC SSCE - Agricultural Science - 2005 (Essay)

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(a) Weed. A weed is any plant that grows where it is not wanted, that is, a plant growing out of place and competing with cultivated crops for space, light, water and nutrients.

(b) Four methods of weed control:

1. Cultural (mechanical/manual) method: weeds are removed by hand-pulling, hoeing, slashing, mulching, crop rotation, close spacing and good tillage practices.
2. Chemical method: weed-killers (herbicides) such as pre-emergence and post-emergence herbicides are sprayed to kill the weeds.
3. Biological method: living organisms (insects, animals or pathogens) are used to feed on or destroy specific weeds; for example grazing animals or introduced insect predators.
4. Physical method: weeds are destroyed by burning, flooding or by covering (smothering) with materials to deprive them of light.

(c) Six reasons for controlling weeds on the farm:

1. Weeds compete with crops for nutrients, water, light and space, reducing crop yield.
2. Weeds harbour pests and diseases that attack crops.
3. Some weeds are parasitic on crops (for example Striga) and reduce their vigour.
4. Weeds lower the quality and market value of harvested produce when mixed with it.
5. Weeds obstruct farm operations such as harvesting and increase the cost of production.
6. Some weeds are poisonous to livestock, and weeds can cause water loss from the soil through transpiration.

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(a) Soil porosity experiment.

Given: volume of dry soil = 50 cm\(^3\); volume of water added = 50 cm\(^3\); total volume of soil and water together = 75 cm\(^3\).

When the water is poured onto the dry soil, it fills the air spaces (pores) between the soil particles. If there were no air spaces, the combined volume would have been \(50 + 50 = 100\) cm\(^3\). Because the actual combined volume is only 75 cm\(^3\), the water has occupied the pore (air) spaces.

(i) Volume of air space = (volume of soil + volume of water) \(-\) total volume

\[ = (50 + 50) - 75 = 100 - 75 = 25 \text{ cm}^3 \]

(ii) Porosity = \(\dfrac{\text{volume of air space (pore space)}}{\text{volume of soil}} \times 100\)

\[ = \frac{25}{50} \times 100 = 50\% \]

(b) Three reasons why soil porosity is important:

1. It allows aeration, supplying oxygen to plant roots and soil organisms.
2. It controls the movement, drainage and retention of water in the soil.
3. It promotes root penetration and the free movement of soil air, water and micro-organisms, aiding plant growth.

(c) Four characteristics of each rock type:

Igneous rocks:

1. Formed by the cooling and solidification of molten magma or lava.
2. They are hard, crystalline and non-porous.
3. They contain no fossils.
4. They occur in massive form and are not arranged in layers (non-stratified); examples are granite and basalt.

Sedimentary rocks:

1. Formed by the deposition, compaction and cementation of sediments (weathered rock particles).
2. They are usually soft and often porous.
3. They frequently contain fossils.
4. They are arranged in layers (stratified); examples are limestone and sandstone.

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(a) Five aims of crop improvement:

1. To increase crop yield per unit area.
2. To produce varieties that are resistant to pests and diseases.
3. To produce varieties that are tolerant of adverse conditions such as drought and poor soils.
4. To improve the quality of produce (for example higher nutrient, oil or protein content).
5. To produce early-maturing varieties and improve other desirable characters such as ease of harvesting and better market qualities.

(b) Selection. Selection in crop improvement is the process of choosing and keeping plants (or seeds) that have desirable characters, such as high yield or disease resistance, for propagation, while rejecting and discarding the undesirable ones.

(c) Three methods of selection:

1. Mass selection.
2. Pure-line selection.
3. Pedigree selection (progeny selection).

(d) Genetic terms:

• (i) Homozygotes: individuals that carry two identical alleles of a gene for a particular character (for example TT or tt); they breed true for that character.
• (ii) Back cross: a cross between an F₁ offspring (a hybrid) and one of its parents (or an individual genetically identical to a parent); a cross with the homozygous recessive parent is a test cross used to find the genotype of the offspring.
• (iii) Dominance: the condition in which one allele (the dominant allele) masks or suppresses the expression of its partner (the recessive allele) in a heterozygote, so that only the dominant character is shown in the individual.

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Three advantages and one disadvantage of each marketing agent are given below.

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(a) Seven objectives of agricultural extension:

1. To teach farmers improved farming practices and modern technologies.
2. To increase agricultural production and productivity.
3. To raise the income and improve the standard of living of farmers and their families.
4. To disseminate the results of agricultural research to farmers.
5. To convey farmers' problems and needs back to research institutes for solution.
6. To encourage farmers to form cooperatives and other self-help organisations.
7. To improve rural home and community life, including nutrition, health, sanitation and youth development.

(b) Three main types of extension teaching methods:

1. Individual (person-to-person) methods.
2. Group methods.
3. Mass (mass-media) methods.

Explanation of any two:

Individual methods: the extension worker deals with one farmer at a time, giving direct, personal advice suited to that farmer's particular situation. Examples include farm and home visits, office calls and personal letters. The method allows a close relationship and detailed attention, but it is slow and reaches only a few farmers.

Group methods: the extension worker teaches a number of farmers together at the same time. Examples include result and method demonstrations, group discussions, lectures, field days and farm tours. It reaches more farmers than individual methods, encourages the sharing of ideas and is fairly convincing through practical demonstration.

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(a) Manual labour.

Three advantages:

1. It has a low initial (capital) cost and requires no fuel or expensive machinery.
2. It is suitable for small farms, rough or hilly land and for delicate operations such as transplanting and harvesting where machines cannot work well.
3. It provides employment for many people and causes less damage to the soil structure.

Two disadvantages:

1. It is slow and has low output, so large areas cannot be covered quickly.
2. It is tedious and tiring, and labour is often scarce and costly at peak periods.

(b) Four qualities of good draught animals:

1. They should be strong, healthy and muscular with good stamina.
2. They should be docile, gentle and easy to train and control.
3. They should be well adapted to the local climate and resistant to diseases and pests.
4. They should be of good body size and weight, with sound legs and hooves.

(c) Two precautions when using draught animals:

1. Do not overwork the animals; give them rest, adequate feed and water.
2. Use well-fitting, comfortable harnesses/yokes to avoid injury and sores.

(d) Harnessing power:

(i) Sun (solar energy): sunlight is trapped by solar panels (photovoltaic cells) which convert it into electricity that can be stored in batteries and used to pump water, power electric fences, dry crops and light farm buildings; solar dryers also use the sun's heat directly to dry produce.

(ii) Biogas: animal dung and other farm wastes are put into an airtight digester where bacteria decompose them (anaerobic digestion) to produce biogas (mainly methane). The gas is collected and piped out to be burned for cooking, heating, lighting and running gas engines/generators on the farm, while the slurry left behind is used as manure.

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(a) Seven characteristic features of a good layer:

1. It has a bright, red and well-developed comb and wattles.
2. It has bright, prominent and alert eyes.
3. It has a large, moist, soft and expanded vent (cloaca).
4. It has a wide span between the pubic (pelvic) bones, able to admit two to three fingers.
5. It has a soft, pliable and large abdomen (well-developed egg-laying capacity).
6. It is active, alert and has a good appetite (feeds well).
7. It has smooth, well-bleached shanks/beak (in yellow-skinned birds) and a good, healthy body condition free from disease.

(b) Preparations for receiving day-old chicks:

1. Clean, wash and disinfect the brooder house and all equipment thoroughly and allow it to rest before the chicks arrive.
2. Spread clean, dry litter (such as wood shavings) on the floor and set up the brooder guard (chick guard) in a circle.
3. Provide and test the source of heat (brooder/lamp) and warm the house to the correct brooding temperature (about 35 degrees Celsius) before the chicks arrive.
4. Arrange clean feeders and drinkers, and provide feed (chick mash) and clean water (with glucose/vitamins) ready for the chicks.
5. Ensure the house is well ventilated, rodent-proof and predator-proof, and count and inspect the chicks on arrival, placing them gently under the brooder.

(c) How poor storage facilities affect agricultural marketing: Without adequate storage, farmers cannot hold their produce, so they are forced to sell perishable produce quickly and cheaply immediately after harvest; much produce spoils, rots or is attacked by pests, causing heavy losses. This leads to gluts and low prices at harvest and scarcity and high prices off-season, unstable prices, poor produce quality, reduced farmers' income and difficulty in storing goods to await better market prices.

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(a) Four reasons for rearing goats in West Africa:

1. They provide meat (chevon) which is a valuable source of animal protein.
2. They provide milk, skin (hides for leather) and manure.
3. They are a source of income and a form of savings/wealth to farmers.
4. They are small, cheap to acquire and easy to manage, and they can feed on a wide range of vegetation and thrive under harsh conditions.

(b) Extensive system of rearing goats.

Three advantages:

1. It is cheap, requiring little capital, housing or equipment.
2. The animals feed themselves on natural range/browse, so feeding costs are low.
3. It requires little labour and management, and the animals exercise freely and are generally healthy.

Three disadvantages:

1. The animals are exposed to predators, theft, accidents and bad weather.
2. Diseases and parasites spread easily and are difficult to control.
3. Feeding, breeding and record-keeping cannot be controlled, so growth and productivity are low.

(c) Six general characteristics of West African cattle breeds:

1. They are generally small to medium in body size (dwarf types are small).
2. Many are trypanotolerant (resistant to trypanosomiasis) and adapted to the humid zone.
3. They are hardy and well adapted to the local climate and poor feeding.
4. They are mostly of the humpless (taurine) type such as the N'Dama and Muturu, though zebu (humped) types occur in the north.
5. They are dual-purpose (kept for meat and, in some, milk and work) but are generally low in milk yield.
6. They mature slowly and have relatively low meat and milk productivity, but resist local diseases well.

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(a) Climate. Climate is the average weather condition of a place taken over a long period of time (usually 30 years or more). It is the composite of elements such as rainfall, temperature, humidity, sunshine and wind for a given area.

Three importances of climate in agriculture:

1. It determines the type of crops and livestock that can be produced in an area.
2. It determines the farming season and the timing of operations such as planting and harvesting.
3. It affects the growth, yield, spread of pests and diseases, and the distribution of vegetation.

(b) Five ways in which high rainfall affects agricultural production:

1. It causes leaching, washing away soluble plant nutrients from the topsoil and reducing soil fertility.
2. It promotes soil erosion, removing the fertile topsoil.
3. It causes water-logging and flooding of farmland, which damages crops and roots.
4. It encourages the spread of pests, diseases and rapid weed growth.
5. It leaches out nutrients and can make land tillage and harvesting difficult, and causes spoilage of harvested produce; however, adequate rainfall also supplies the water crops need for growth.

(c) Forms in which water exists in the soil: gravitational water (drains away freely under gravity), capillary water (held in the soil pores and available to plants) and hygroscopic water (held tightly as a thin film around soil particles and unavailable to plants).

(d) Three ways soil water may be lost:

1. Evaporation from the soil surface.
2. Transpiration through plants.
3. Drainage/percolation (deep drainage) and run-off.

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(a) Ten poultry equipment and the main use of each:

(b) Two parts of a tractor involved in coupling and operation of implements:

1. The drawbar / three-point hitch (linkage) for coupling (attaching) implements.
2. The power take-off (PTO) shaft for transmitting power to drive the implements.

(c) Four maintenance practices of a tractor:

1. Check and top up the engine oil, hydraulic oil, coolant (water) and fuel regularly, and change the oil at the recommended intervals.
2. Grease and lubricate all moving parts and check the tyre pressure regularly.
3. Clean the air, oil and fuel filters and the radiator; wash the tractor after work.
4. Service the battery and check nuts, bolts and belts; carry out repairs promptly and keep the tractor under shelter when not in use.