WAEC SSCE - Agricultural Science - 1995

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The water-snail is important in the life-cycle of a liver fluke. The liver fluke is a parasitic flatworm that infects the liver of various animals, including humans. The adult fluke releases its eggs in the bile ducts of the host, which are then excreted through feces. The eggs hatch in water, and the larvae infect snails. Inside the snail, the larvae multiply and undergo a series of developmental stages, eventually emerging as infectious forms that can infect other animals, including humans, through the consumption of contaminated water or vegetation. Therefore, the water-snail plays a crucial role in the life-cycle of the liver fluke by serving as an intermediate host for the parasite.

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Molasses is a major by-product that is obtained after the processing of sugarcane. When sugarcane is processed to extract sugar, the juice is boiled to remove the water content and concentrate the sugar. Molasses is the thick, syrupy residue that is left behind after the sugar crystals have been removed. It is often used in animal feed as a source of energy and as a binding agent in feed pellets. It can also be used in the production of alcohol, rum, and other distilled spirits.

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The type of breeding described in the question is called "selection". Selection involves choosing individual plants with desired traits from a population of plants and using them to produce the next generation. This can be done over many generations to develop a population of plants with consistently desirable traits. In this type of breeding, plants that already have desirable traits that are well-adapted to their environment are chosen for breeding to develop a new population of plants with those desirable traits. This method is commonly used in agriculture to develop new crop varieties that have improved yield, disease resistance, or other desirable traits.

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Forestry is the study and management of forests and forest resources. It involves the science and practice of creating, maintaining, and managing forests for various purposes such as conservation, recreation, timber production, and wildlife habitat. Forestry aims to strike a balance between economic, social, and ecological benefits of forest resources, and it includes activities such as planting and caring for trees, managing forest ecosystems, protecting forests from pests and diseases, and harvesting timber in a sustainable manner.

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The edaphic factors are soil factors that affect agricultural production. Predators, on the other hand, are not related to soil but are biotic factors that may affect agricultural production. Therefore, predators is the answer as it is not an edaphic factor affecting agricultural production.

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Yam is a tuber crop that requires a well-drained soil that is rich in organic matter. The most suitable soil for cultivating yam is a well-drained loamy soil with a good amount of organic matter. This type of soil is called clay loam, which is a mixture of sand, silt, and clay. Clay loam has good water retention capacity and provides a favorable environment for the growth of yam. Additionally, it is important to note that the soil pH should be between 5.5 and 6.5 for optimum growth of yam.

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The correct answer is "increase in soil acidity." Grazing can have various effects on soil, such as exposing it to erosion, destroying soil structure, and reducing the rate of water percolation. However, grazing does not directly cause an increase in soil acidity. Grazing animals can produce acidic urine, but this is generally balanced by the alkaline effect of their dung. Therefore, grazing does not directly lead to an increase in soil acidity.

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The amount of feed that is needed to maintain the live weight of an animal, without causing an increase or a decrease in weight, is called the maintenance ration. This means that the animal is neither gaining nor losing weight, but is simply maintaining its current weight. The maintenance ration is important because it ensures that the animal is getting the necessary nutrients to maintain its body functions and perform its daily activities, without being overfed or underfed. The other options listed are specific types of rations for different categories of animals, such as weaners, breeders, and animals in production, which require different levels and types of nutrients to support their growth and reproductive processes.

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Air sacs are present in poultry. Poultry, such as chickens, have a unique respiratory system that includes not only lungs but also air sacs. These air sacs are connected to the lungs and extend throughout the body cavity, allowing for efficient gas exchange and respiratory function. Air moves through the lungs and air sacs in a continuous, one-way flow, which helps birds to obtain oxygen and remove carbon dioxide more effectively than other animals with a less complex respiratory system. Therefore, air sacs are a key feature of the respiratory system of poultry, enabling them to have efficient gas exchange and support their high metabolic rate.

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A metamorphic limestone is marble. Marble is a type of rock that forms when limestone, a sedimentary rock made of calcite or aragonite minerals, undergoes high pressure and heat over a long period of time. This process, called metamorphism, causes the limestone to recrystallize and change into a harder, more dense rock with a characteristic smooth and shiny surface. Marble is commonly used in architecture and sculpture due to its beauty, durability, and workability.

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Agricultural finance is not a method or agent of disseminating agricultural information. Agricultural finance refers to the financial services provided to farmers or agribusinesses for agricultural purposes, such as loans, insurance, and investments. In contrast, the other options mentioned are all methods or agents of disseminating agricultural information, including individual contact (such as farmer field schools), agricultural programmes (such as extension services), marketing channels (such as market information systems), and co-operative societies (such as farmer organizations).

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A soil with a pH of 2 is highly acidic. The pH scale ranges from 0 to 14, where 7 is neutral, values below 7 are acidic, and values above 7 are alkaline. A pH of 2 is very low on the scale, indicating that the soil is highly acidic. Highly acidic soils can be harmful to plant growth as they can limit the availability of nutrients essential for plant growth. It is important to adjust soil pH to the appropriate range for the type of plants being grown.

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Farm-gate price is usually obtained through the producer. The term "farm-gate price" refers to the price that a farmer receives for their produce at the farm gate, before any additional costs such as transportation, storage, and marketing are added. This price is negotiated directly between the farmer and the buyer, which could be a middleman, commodity board, co-operative, or wholesaler. However, in general, the producer is the one who sets the initial farm-gate price.

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Ground maize, also known as cornmeal, is a common ingredient in livestock feed. Its main function is to provide energy to the animals. Maize contains high levels of carbohydrates, which are easily digestible and can be converted into energy by the animal's body. This energy is necessary for the animal to carry out its normal activities, including growth, reproduction, and movement. While maize does contain some protein, it is not a significant source of building blocks for the animal's body. Other feed ingredients, such as soybean meal or alfalfa, are typically added to provide the necessary proteins for body building. Ground maize also helps to add bulk to the feed, making it more filling and providing the animal with a sense of satiety.

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In underground drainage, water seeps into the tiles to reach an outlet where water is disposed. Underground drainage is a method of removing excess water from the soil through a system of buried tiles, which are porous and allow water to seep through. These tiles are laid out in a network of drains or channels, leading to an outlet or a collection point where water can be disposed of. The water is directed away from the crop roots and towards a designated disposal area, preventing waterlogging and soil saturation that can damage crops.

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N'dama cattle are well adapted to West Africa mainly because the breed is resistant to trypanosomiasis. Trypanosomiasis is a deadly disease that affects both humans and animals, and is caused by a parasite transmitted by the tsetse fly. It is prevalent in West Africa, making it challenging to rear livestock in the region. However, N'dama cattle have developed resistance to the disease over time, making them better adapted to the environment. This has made N'dama cattle a valuable breed in the region, as they provide a source of food and income for the local communities.

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Blackarm is a bacterial disease that affects cotton. It is caused by the bacterium Xanthomonas campestris pv. malvacearum. The disease affects the leaves, stems, and bolls of the cotton plant, causing dark, water-soaked lesions that can eventually lead to defoliation and yield loss. The bacteria can survive in soil and plant debris, and can be spread by wind, rain, and agricultural practices such as pruning and harvesting.

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The female sex hormone that is responsible for oestrus in farm animals is called "oestrogen". Oestrogen is produced by the ovaries and plays a key role in regulating the female reproductive system. It stimulates the development of the reproductive tract and secondary sexual characteristics, and triggers the onset of oestrus, which is the period of sexual receptivity in female animals. During oestrus, the female is ready to mate with a male and conceive offspring.

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The gestation period in days of a sow is 114. The gestation period refers to the length of time between fertilization and birth. In the case of a sow, this is the period of time that the piglets develop inside the mother's womb. The gestation period of a sow is approximately 3 months, 3 weeks, and 3 days or 114 days. This is an important factor to consider for pig farmers as it determines the timing of farrowing and other management practices related to reproduction.

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In a high rainfall area, the poor yield of fertile soil may be due to leaching of soil nutrients. This occurs when there is excessive rainfall, which causes the nutrients in the soil to be washed away, leaving the soil nutrient-deficient. When this happens, the plants growing on the soil will not have the necessary nutrients for growth and development, which can lead to poor yield. The other options, such as low pH, lack of soil microbes, high alkalinity, and erosion, can also affect agricultural productivity, but they may not be specifically related to high rainfall areas.

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Flood irrigation is mainly used in arid areas. In this type of irrigation, water is allowed to flow over the surface of the soil to wet the plants. This is a very old and simple method of irrigation that is still used today in areas where there is not enough water for other types of irrigation systems. Flood irrigation is effective in arid areas because it allows water to be distributed over a large area, and the water can seep down into the soil to reach the roots of the plants.

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The characteristic that is not normally considered in the selection of animal for breeding is horn size. This is because the size of the horn does not have a significant impact on the animal's productivity or ability to produce quality offspring. The other characteristics listed, such as fertility, growth rate, resistance to disease, and milk quality and quantity, are all important factors that are typically considered in the selection of animals for breeding to ensure that the next generation of animals will be healthy, productive, and profitable.

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The best option for controlling water level in a fish pond with minimal loss of fish is a "monk with panel, screens and outlet channel". A monk is a structure that controls the flow of water in a pond. With a monk, water can be drained from the pond while the fish are kept safe in a compartment created by screens and panels. This method is effective in preventing fish from being carried away with the water during drainage. Wooden panels alone or wooden panels with screens may not be as effective in controlling the flow of water as the monk method. Similarly, using only screens or a monk without an outlet channel may not provide the necessary drainage required for the pond.

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The major difference between loan and subsidy is that a loan is money borrowed from a lender which must be paid back with interest, while a subsidy is financial assistance given by the government to reduce the cost of a particular product or service. A subsidy does not have to be repaid, and it can be given to both individuals and businesses to encourage specific activities or behaviors. On the other hand, a loan must be repaid within a specified period, and the borrower is usually required to pay interest on the amount borrowed.

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Depreciation is the loss in value of an asset over time due to wear and tear or obsolescence resulting from its use in the normal course of business. It reflects the decrease in an asset's value over time, which is recorded as an expense on a company's income statement. This decrease in value is due to factors such as age, wear and tear, and obsolescence, and it affects the asset's book value or carrying value. Depreciation is important in financial accounting because it helps to accurately reflect the true value of assets on a company's balance sheet.

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A fertile soil is important for the selection of a site for a fish pond because it stimulates the growth of lower plants, which are sources of food to fish. When the soil is fertile, the plants growing in and around the pond will have access to necessary nutrients that they need to thrive. The plants will, in turn, produce more organic matter, which will support the growth of plankton and other microorganisms in the water. This increase in food will provide a suitable habitat for fish to grow, feed, and reproduce. Therefore, a fertile soil is crucial in promoting a healthy and productive ecosystem in a fish pond.

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The castrated male cattle is referred to as a "steer." When a male cow is castrated before reaching sexual maturity, it is called a steer. Steers are often raised for meat production, as they tend to gain weight quickly and have a calm disposition, making them easier to handle. They do not develop the physical characteristics of an adult bull and are typically smaller in size.

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Clay will retain the greatest amount of water compared to the other options. This is because clay has smaller particles than sand or silt, which allows it to hold more water due to the greater surface area available for water molecules to bond to. Clay soils can retain water for longer periods of time, which can be beneficial for plant growth during dry periods. In contrast, sandy soils have larger particles with fewer surfaces available for water bonding, causing water to drain away more quickly. Loam soils are a mixture of sand, silt, and clay, and can have varying water retention capacities depending on the ratio of the soil components.

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The mesocarp of an oil palm fruit refers to the fleshy, fibrous layer between the outer skin and the hard inner shell. It is commonly referred to as the "pulp" and contains the majority of the oil produced by the fruit. The other parts of the fruit include the nut (which contains the kernel), the shell (the hard outer layer), and the seed (which is the whole fruit, including the shell and kernel).

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The option that is not a characteristic of a good pasture is "low leaf to stem ratio". A good pasture should have a high leaf to stem ratio because the leaves are the most palatable and nutritious part of the plant. High palatability, high nutritive value, high digestibility, and high resistance to trampling are all desirable characteristics of a good pasture. High palatability ensures that animals will consume enough forage, high nutritive value ensures that the forage meets the animal's nutritional requirements, high digestibility ensures that the animal can utilize the nutrients in the forage efficiently, and high resistance to trampling ensures that the pasture can withstand the grazing pressure from animals without being damaged.

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Crop rotation has numerous benefits on the soil, including maintenance of soil fertility, reducing concentration of soil pests, improving soil structure, and reducing soil erosion. However, crop rotation does not predispose the soil to leaching. In fact, crop rotation can help to reduce leaching by improving soil structure, increasing soil organic matter, and reducing soil compaction. So, the correct option is "predisposing soil to leaching".

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The readiness of farmers to adopt viable agricultural research results is the most important factor that determines the rate of agriculture development in a country. Agricultural research is a key driver of innovation and technology adoption in agriculture. The success of agriculture largely depends on the ability of farmers to use modern technologies and techniques to improve yields, reduce losses, and increase profits. The readiness of farmers to adopt viable agricultural research results is crucial because it determines how fast new technologies and techniques can be introduced and spread across the farming community. The more willing farmers are to adopt new methods and technologies, the faster agriculture development will occur in the country.

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The anti-sterility vitamin in livestock nutrition is vitamin E. Vitamin E is an important antioxidant nutrient that protects body tissues from damage caused by free radicals. In livestock, it plays a crucial role in maintaining reproductive health and preventing infertility, hence its name "anti-sterility vitamin." It also helps in improving the immune system, preventing muscle disorders, and promoting healthy skin and hair.

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The reason for not preferring rotational grazing to continuous grazing is "avoiding excessive amount of organic manuring." Rotational grazing involves the movement of livestock from one paddock to another in a planned sequence. This helps to avoid overgrazing in a particular area and allows time for pasture regrowth, which can result in more uniform quality of herbage, persistence of desired species, breaking the life-cycle of some pests, and avoiding build-up of livestock pests. However, rotational grazing can also lead to excessive accumulation of animal waste in a particular area, which can result in soil compaction, nutrient imbalance, and potential environmental issues. Therefore, it is important to manage rotational grazing properly to avoid excessive accumulation of organic matter in one area.

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Jute, cotton and sisal are classified as fiber crops. Fiber crops are plants cultivated for their fibers, which are used to make various products such as textiles, paper, and rope. Jute is a long, soft, and shiny fiber that is commonly used in the production of burlap sacks and twine. Cotton is a soft, fluffy fiber that grows in a boll, and is widely used in the textile industry. Sisal is a tough, hard fiber that is commonly used for making rope and twine.

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The most common soil mineral found in all crystalline rocks and a main constituent of granite and sandstone is quartz. This mineral is very abundant on the earth's crust and it is formed by the combination of silicon and oxygen. Quartz is known for its durability and resistance to weathering, which makes it a common component of soils and sediments. It is also used in a variety of industrial applications, such as construction, electronics, and glassmaking.

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Subsistence agriculture is a type of agriculture where the main aim is to produce enough food to sustain the farmer and their family. Therefore, a characteristic feature of subsistence agriculture is that the labour needed for farming is usually provided by the farm family themselves. This means that family members are often involved in various aspects of farming, such as planting, weeding, and harvesting. The focus is not on making a profit but on producing enough food to meet the needs of the family.

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(a) Two examples of crops in each group:

(b) Production of tomato.

(i) Sowing method: tomato seeds are first sown in a nursery (seed bed or seed box). Shallow rows (drills) are made and the seeds are drilled thinly, then lightly covered with fine soil and watered regularly. Sowing in the nursery gives strong, uniform seedlings before transplanting.

(ii) Transplanting: when the seedlings are about 4 to 6 weeks old and 10 to 15 cm tall with a few true leaves, they are watered, lifted carefully with soil around the roots, and transplanted to the prepared field in the cool of the evening at a spacing of about 60 cm by 45 cm. They are watered immediately after transplanting.

(iii) Varieties: examples of tomato varieties include Roma, Ronita, Ibadan Local, Beske and other improved and local varieties.

(iv) Harvesting: the fruits are ready for harvest about 3 to 4 months after transplanting. Mature fruits are picked by hand at the mature-green, pink or fully ripe (red) stage depending on the market; harvesting is done at intervals as the fruits ripen.

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(a) Ten tools or equipment used on a dairy cattle farm:

1. Milking machine
2. Milking pails/buckets
3. Milk churns / milk cans
4. Milk strainer or sieve (filter)
5. Milk cooler / refrigerator
6. Lactometer (for testing milk quality/density)
7. Cream separator
8. Weighing scale (or milk-measuring cans)
9. Wheelbarrow (for feed and dung) and feeding troughs
10. Water troughs and hose/hoses; disinfectant and udder-washing cloths/towels

(b) Three harmful contaminants of milk:

1. Disease-causing micro-organisms (bacteria) such as those causing tuberculosis and brucellosis.
2. Dirt and dust (soil, dung, hair) falling into the milk.
3. Chemical residues such as antibiotic and drug residues (or traces of detergents and disinfectants).

(c) Three precautions to obtain clean milk:

1. Clean the animal and the udder: wash and dry the cow's udder and teats with a clean cloth and mild antiseptic before milking, and keep the animal and its surroundings clean, so that dirt and germs do not fall into the milk.
2. Use clean, sterilised utensils and clean hands: all pails, churns and the milking machine must be thoroughly washed, sterilised and dried, and the milker's hands must be clean and healthy, to prevent contamination.
3. Handle and store milk hygienically: strain the milk immediately after milking and cool it quickly to a low temperature in a covered container, keeping it away from dust and flies, to check the growth of bacteria.

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(a)(i) Surface drainage. It is the removal of excess water from the surface of the land by directing it into open channels, ditches, drains or furrows that carry the water away, usually by shaping and sloping the land so that water flows off freely. It prevents water-logging of the topsoil.

(ii) Three disadvantages of surface drainage:

1. The open channels and ditches occupy land that could otherwise be cropped.
2. The channels can cause soil erosion and gullying as the flowing water carries away topsoil.
3. They require regular cleaning and maintenance, since they easily become blocked by weeds and silt.

(b)(i) Irrigation. Irrigation is the artificial application of water to the soil (crops) through pipes, channels or sprinklers to supplement rainfall and provide the moisture needed for plant growth, especially during the dry season.

(ii) Two aims of irrigation:

1. To supply crops with adequate water for growth where rainfall is insufficient or unreliable.
2. To make dry-season (all-year-round) crop production possible and to increase yields.

(iii) Five problems associated with irrigation:

1. High cost of installing and maintaining irrigation equipment and structures.
2. Build-up of salts in the soil (salinity), which reduces soil fertility.
3. Water-logging of the soil when drainage is poor.
4. It can encourage water-borne diseases (such as bilharzia) and breeding of disease vectors.
5. Scarcity or unreliable supply of water at the source, and silting of dams and canals.

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(a) Agricultural Extension. Agricultural extension is an informal, out-of-school educational service that takes useful, research-based agricultural knowledge, improved skills and new technologies to farmers and their families on their farms and in their homes. It teaches farmers to adopt improved practices so that they can increase their production, raise their income and improve their standard of living, and it also carries the farmers' problems back to research stations.

(b) Seven roles of an Agricultural Extension Worker:

1. Teaching farmers improved farming practices and new technologies (for example through demonstrations).
2. Passing on the results of agricultural research from research institutes to the farmers.
3. Conveying the farmers' problems and needs back to research stations and government for solutions.
4. Advising and guiding farmers on the selection and use of improved inputs such as seeds, fertilisers and agro-chemicals.
5. Helping farmers to form and run cooperative societies and other farmer organisations.
6. Assisting farmers to obtain credit, inputs and marketing facilities.
7. Motivating and encouraging farmers to adopt innovations, and helping to improve rural home and community life (nutrition, health and sanitation).

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(a) Tractors: Tractors are versatile farm machines that are used for various operations such as plowing, tilling, planting, and harvesting. They are powerful machines that are designed to provide high torque and pulling capacity, making them ideal for use on farms. Tractors are usually equipped with a three-point hitch that enables the attachment of different implements such as plows, cultivators, and harrows, making them very versatile. Tractors can be powered by gasoline, diesel, or electric motors, and they come in various sizes and configurations to meet different farm needs.

(b) Incubators: Incubators are machines that are used to hatch eggs artificially. They are designed to provide the ideal conditions for the development of embryos in eggs, such as temperature, humidity, and ventilation. Incubators come in various sizes, from small ones for home use to large ones for commercial hatcheries. They are usually equipped with a thermostat, a timer, and an egg turner to ensure that the eggs are incubated under optimal conditions.

(c) Sprayers: Sprayers are farm machines that are used to apply chemicals such as pesticides, herbicides, and fertilizers to crops. They are designed to ensure that the chemicals are applied evenly and at the right rate to achieve maximum efficacy. Sprayers can be either hand-operated or motorized, and they come in various sizes and configurations to meet different farm needs. They are usually equipped with a tank for holding the chemicals, a pump for pressurizing the tank, and nozzles for spraying the chemicals.

(d) Shelters: Shelters are structures that are used to provide protection to livestock or crops from adverse weather conditions such as rain, wind, and extreme temperatures. They can be made of various materials such as wood, metal, or plastic, and they come in different sizes and configurations. Shelters can be either permanent or temporary, depending on the farm needs. They are designed to provide a comfortable and safe environment for livestock or crops, thus promoting their growth and productivity.

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(a) Six problems of agricultural development in Nigeria:

1. Inadequate finance and poor access to credit facilities by farmers.
2. Poor storage and processing facilities, leading to heavy post-harvest losses.
3. Poor transportation network and bad rural roads.
4. Use of crude and outdated farm implements with low mechanisation.
5. Land tenure system that fragments land and discourages large-scale farming.
6. Inadequate and inefficient agricultural extension services.

(b) Five possible solutions:

1. Provide soft loans and agricultural credit to farmers through banks and cooperatives.
2. Establish modern storage and processing facilities such as silos and cold rooms.
3. Construct and maintain good rural roads and provide affordable transport.
4. Encourage mechanisation by subsidising tractors and modern implements.
5. Reform the land tenure system and strengthen extension services to reach more farmers.

(c) Five ways inadequate storage and processing facilities have affected agricultural development:

1. High post-harvest losses: much produce spoils and rots before it can be sold or used, wasting farmers' effort.
2. Reduced farmers' income: farmers are forced to sell perishable produce cheaply and quickly at harvest, lowering their earnings.
3. Seasonal gluts and scarcity: produce is abundant and cheap at harvest but scarce and expensive off-season, causing price instability.
4. Discouragement of large-scale production: farmers avoid producing more than they can store or sell, keeping output low.
5. Loss of quality and value: unprocessed and poorly stored produce loses quality, reducing its value and limiting export and industrial use.

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(a) Rosette disease of groundnut.

(i) Causal organism: a virus, the groundnut rosette virus.

(ii) Symptoms: stunted growth of the plant; yellowing (chlorosis) and mottling of the leaves; the leaves become small, curled and crowded together, giving a bushy, rosette-like appearance; there is general dwarfing and few or no pods are formed.

(iii) Method of transmission: it is transmitted from infected to healthy plants by an insect vector, the groundnut aphid (Aphis craccivora), which sucks the sap.

(iv) Damage done: it stunts the plants and reduces leaf area and photosynthesis, causing poor pod and seed formation; this leads to a heavy reduction in yield, and severe early infection can cause almost total crop loss.

(v) Preventive and control measures: plant resistant/tolerant varieties; plant early and at the recommended close spacing to reduce aphid spread; control the aphid vector with appropriate insecticides; rogue out and destroy infected plants; and practise good field hygiene and crop rotation.

(b) Plant population calculation.

Spacing per stand = 30 cm by 30 cm = 0.3 m by 0.3 m.

Area occupied by one stand = \(0.3 \times 0.3 = 0.09 \text{ m}^2\).

Total area of land = \(60 \times 30 = 1800 \text{ m}^2\).

Plant population = \(\dfrac{\text{total area}}{\text{area per stand}} = \dfrac{1800}{0.09} = 20{,}000\) plants.

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The four major food nutrients required in livestock production, with two sources and two functions of each, are shown below.

(Vitamins and water are also essential dietary constituents; the four nutrients above are the standard answer required.)

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The nitrogen cycle is a natural process that involves the transformation of nitrogen from one form to another. Nitrogen is a crucial element required for the growth and development of plants and other living organisms. However, nitrogen in its gaseous form (N₂) cannot be used by plants directly. Therefore, it has to be converted into other forms such as ammonia, nitrate, and nitrite, which plants can absorb and use.

The nitrogen cycle can be divided into several steps:

1. Nitrogen Fixation: The first step in the nitrogen cycle is nitrogen fixation. Nitrogen gas (N₂) is converted into ammonia (NH₃) by nitrogen-fixing bacteria such as Rhizobium found in the root nodules of legumes like beans and peas. Some free-living bacteria like Azotobacter and Clostridium also fix atmospheric nitrogen.
2. Nitrification: The next step is nitrification, where ammonia (NH₃) is converted into nitrite (NO₂^-) and then into nitrate (NO₃^-) by nitrifying bacteria. Nitrate is the form of nitrogen that is most commonly taken up by plants.
3. Assimilation: Assimilation is the process by which plants and animals absorb nitrogen in the form of ammonia, nitrate, and other nitrogen compounds to synthesize amino acids, proteins, and other nitrogen-containing organic molecules.
4. Ammonification: Ammonification is the process by which decomposers like bacteria and fungi break down nitrogen-containing organic matter such as dead plants and animals and release ammonia into the soil.
5. Denitrification: Denitrification is the final step in the nitrogen cycle, where nitrate (NO₃^-) is converted back into gaseous nitrogen (N₂) by denitrifying bacteria under anaerobic conditions in soil and water.

Here is a labelled diagram of the nitrogen cycle:

            Nitrogen Fixation
                N2 + 3H2 -> 2NH3
                        NH3
                         |
                     Nitrification
                    NH3 -> NO2- -> NO3-
                    Assimilation
                         |
                    NH3, NO3-
                         |
                    Amino acids, proteins, etc.
                 Ammonification
                      Organic nitrogen
                          |
                          NH3
                 Denitrification
                        NO3-
                         |
                NO2-, NO, N2O, N2
                         |
                         N2

Overall, the nitrogen cycle is an essential process that enables the conversion of atmospheric nitrogen into forms that

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(a)(i) Marketing in agriculture. Marketing is the sum total of all the activities and business processes involved in moving agricultural produce from the producer (farmer) to the final consumer. It covers assembling, buying, selling, processing, grading, storage, transportation, financing and distribution, together with the exchange of ownership, so that the produce reaches the consumer at the right place, time and form.

(ii) Five stages involved in marketing agricultural produce:

1. Assembling (collecting the produce from scattered farmers).
2. Processing (converting the produce into usable/storable form).
3. Grading and standardisation (sorting produce into uniform quality grades).
4. Storage (holding the produce until it is needed).
5. Transportation and distribution (moving and selling the produce to consumers).

(b) Four agents of marketing:

• Wholesalers: middlemen who buy agricultural produce in large quantities from producers (or assemblers) and sell in smaller lots to retailers. They provide storage and bulk-breaking services.
• Retailers: middlemen who buy produce in fairly small quantities from wholesalers and sell directly to the final consumers in small units at convenient places such as markets and shops.
• Commission agents (brokers): agents who buy and sell produce on behalf of others and are paid a commission; they bring buyers and sellers together but do not usually own the goods.
• Cooperative marketing societies: associations formed by farmers to jointly assemble, grade, store and sell their members' produce, thereby securing better prices and reducing exploitation by middlemen.