WAEC SSCE - Agricultural Science - 2007

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The relative proportion of each fraction of soil in a soil sample determines its texture. Soil texture refers to the composition of different sizes of mineral particles in the soil, which include sand, silt, and clay. The proportion of these particles affects soil properties such as water holding capacity, nutrient retention, and aeration. Soil texture is determined by the relative proportions of these soil particles in the sample, with sand particles being the largest, followed by silt, and then clay. Therefore, the soil sample with a higher proportion of sand particles will have a coarser texture than the soil sample with a higher proportion of clay particles, which will have a finer texture. Texture is one of the most important soil properties, and it influences several soil processes and properties, including fertility, drainage, and erosion.

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The correct answer is elephant grass. Elephant grass is a tall tropical perennial grass with broad hairy leaves that can grow up to 3-6 meters tall. It is commonly used for pasture and silage production for livestock feeding due to its high yield potential and nutrient content. It is also used as a source of bioenergy, and for erosion control and soil improvement.

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The group of macro-nutrients that is a constituent of protein is nitrogen, phosphorus, and sulfur. Proteins are made up of building blocks called amino acids, which consist of nitrogen, carbon, hydrogen, and oxygen. Nitrogen is a key component of amino acids, and it is obtained by plants through the soil in the form of nitrate or ammonium. Phosphorus and sulfur are also important components of amino acids and are necessary for the synthesis of proteins in plants. Therefore, the correct option is nitrogen, phosphorus, and sulfur.

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Detalles de la respuesta

Layering is advantageous because it avoids the possible failure of fertilization. In layering, a stem or branch of a plant is bent down and buried in the soil while still attached to the parent plant. The buried section of the stem or branch will eventually develop roots and grow into a new, independent plant. This method ensures that the new plant will be genetically identical to the parent plant, unlike sexual reproduction where the offspring may vary genetically. Since layering does not require fertilization or pollination, the chance of failure due to poor pollination or genetic variability is minimized.

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The structure that is not connected to the urethra of a bull is the rectum. The urethra is a tube that connects the urinary bladder to the external environment, allowing for the passage of urine. In bulls, the urethra passes through the penis and is responsible for the transportation of both urine and semen during ejaculation. However, the rectum is not connected to the urethra and is part of the digestive system, responsible for the storage and elimination of fecal matter.

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Detalles de la respuesta

Detalles de la respuesta

The livestock disease that affects the reproductive system is brucellosis. Brucellosis is a bacterial disease that commonly affects cattle, sheep, and goats, and it can also infect other animals and humans. The bacteria can cause abortions, stillbirths, and infertility in infected animals. It can be transmitted from animals to humans through direct contact with infected animals or consumption of contaminated animal products such as unpasteurized milk. Therefore, it is important to regularly test and vaccinate livestock to prevent the spread of the disease.

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A glue-processing industry would require cassava as an agricultural raw material. Cassava contains a high amount of starch which can be extracted and processed into glue. Cotton is a fiber crop, coconut is used for oil production and kola is a nut used for medicinal and cultural purposes.

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Assuming that in sheep, the allele for black coat colour is dominant over that for brown coat colour, crossing a heterozygote black with a homozygote brown will result in 50% of the offspring having a black coat colour and 50% having a brown coat colour. This is because the heterozygote parent carries one dominant black allele and one recessive brown allele, and the homozygote brown parent carries two recessive brown alleles. Therefore, the possible combinations of alleles for the offspring are BB (black), Bb (black), and bb (brown). The probability of each outcome is 50% black and 50% brown.

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Delayed harvesting of maize may result in a high incidence of pest infestation. This is because when maize is left in the field for too long, it becomes more susceptible to attack by pests such as weevils, borers, and rodents. These pests can cause significant damage to the crop, leading to losses in yield and quality. Additionally, delayed harvesting may also lead to grain shattering, which can result in low seed viability and reduced yields. Furthermore, the longer maize is left in the field, the more likely it is to be exposed to adverse weather conditions, which can lead to yellow colouration of the grains and further reduce their quality.

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Drying of harvested crops is necessary because it reduces the moisture content and allows for better storage. When crops are harvested, they contain a lot of moisture which can cause spoilage, mold growth, and insect infestation during storage. Drying the crops reduces the moisture content, which slows down these processes and allows the crops to be stored for longer periods without spoiling. Drying also helps to prevent the growth of microorganisms, which can cause diseases and spoilage of the crops. In addition, dried crops are easier to transport and can be sold to consumers when they are dry, making them more appealing and easier to handle. Therefore, drying harvested crops is an important step in ensuring food security and reducing post-harvest losses.

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Water-logged soils impede good crop growth and development because crop roots are deprived of sufficient oxygen. When the soil is water-logged, the spaces between soil particles become filled with water, which displaces the air in the soil. Roots need oxygen to respire and to convert sugars into energy for growth, so without it, the roots cannot function properly. As a result, the crop may experience stunted growth or even die.

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The standard length of a Gunter's chain is approximately 20 meters. A Gunter's chain is a measuring tool that was used in the past to measure land, and it consists of 100 links, with each link measuring 0.2 meters or 20 centimeters. Therefore, the total length of a Gunter's chain is 100 links x 0.2 meters per link = 20 meters.

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Detalles de la respuesta

Fertilizing a fish pond with compost manure would most likely increase phytoplankton population and increase fish yield. This is because the compost manure serves as a source of nutrients for the phytoplankton, which are the primary food for fish in the pond. The increased availability of food for the fish leads to increased growth and productivity, resulting in a higher yield. However, excessive use of compost manure may lead to overgrowth of phytoplankton, leading to reduced oxygen levels in the water and ultimately, reduced fish yield.

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A farmstead is best described as the farmer's abode, which includes the main farmhouse, outbuildings, and other structures related to the living and management of the farm. It is the central hub of activity on a farm, where the farmer and their family live and work, and where most of the daily farm activities are carried out. The farmstead can also include areas for animal pens, crop production, and equipment and storage facilities, but its primary function is to serve as the farmer's home and base of operations for the farm.

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Detalles de la respuesta

The deficiency symptom described in the question is the yellowing or whitening of the areas between the veins of leaves, known as chlorosis. This chlorosis has a distinctive pattern of parallel white or yellow streaks along the veins. This is a symptom of magnesium deficiency in plants. Therefore, the correct answer to the question is option B: magnesium.

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The correct answer is option D: uprooting the weeds. Biological methods of weed control involve the use of living organisms to control or suppress weed growth. Options A, B, and C are all examples of biological weed control methods. In contrast, uprooting the weeds is a physical method of weed control that involves physically removing the weeds from the soil.

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Detalles de la respuesta

Ruminants do not normally show deficiency symptoms of vitamin B complex because the bacteria present in their rumen synthesize the vitamins. These bacteria are able to produce the vitamin B complex in adequate amounts, which is then absorbed by the ruminant's body. This process is made possible due to the unique four-chambered stomach of the ruminants, which allows for the fermentation of plant materials by the bacteria in the rumen. As a result, ruminants are able to derive their vitamin B complex requirements from the microbial synthesis in their rumen, and do not rely on dietary sources for these vitamins.

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Agricultural credits are funds made available to farmers or agribusinesses to finance their activities. The purpose of agricultural credits is to enhance agricultural productivity and help farmers overcome financial constraints. Agricultural credits should be used to finance activities that will increase agricultural productivity, and not for personal or non-agricultural purposes. Therefore, agricultural credits should not be put towards meeting family needs, such as paying for household expenses, or towards improving structures that are not directly related to agricultural productivity, such as building a new house. Instead, agricultural credits should be used to purchase inputs, such as seeds, fertilizers, or pesticides, and to adopt innovations, such as new farming techniques or technologies that can increase yields and efficiency.

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The statement that is true about soil water is: "crops utilize capillary water in the soil." Capillary water is the water held in the soil pores and is available to plants for use. The roots of plants absorb water from the soil through the process of osmosis. Capillary water is held in the soil by the surface tension of the water and the adhesion forces between water molecules and the soil particles. It is the most important source of water for plants, and its availability in the soil affects plant growth and crop yield. Therefore, farmers need to manage soil moisture levels to ensure that the plants have access to the required amount of capillary water.

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The statement that is not an advantage of drainage is "supplies moisture for plant growth". This is because drainage is meant to remove excess water from the soil, which can be harmful to plant growth by reducing the amount of oxygen available to the roots. While drainage can indirectly improve soil moisture levels by preventing waterlogging, its main purpose is to prevent excess water accumulation, not to supply moisture. Drainage can improve soil structure by reducing compaction and allowing better root penetration. It can also reclaim waterlogged land and swamps by making the soil more suitable for plant growth.

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The most versatile source of farm power in West Africa is animal power. This is because animals can be used to perform a wide range of tasks on the farm, such as plowing, harrowing, weeding, and transporting goods. They are also relatively easy to maintain and can be fed with locally available feedstuffs. In contrast, biogas, wind, and water power may not be as widely available or may require more specialized equipment and maintenance, making them less versatile.

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Detalles de la respuesta

Micronutrients are essential nutrients required in small quantities by plants for their proper growth and development. They include elements such as zinc, boron, iron, manganese, copper, and molybdenum. These nutrients are likely to be deficient in soils with low pH levels because acidic conditions in the soil limit the availability of micronutrients to the plants. This means that even though these nutrients may be present in the soil, the plant cannot access them in sufficient quantities for their growth and development. Additionally, the use of high-phosphate fertilizers and excessive irrigation can also cause micronutrient deficiencies in plants. Soils with high organic matter content or fine texture are not necessarily deficient in micronutrients. In fact, organic matter can contribute to the availability of micronutrients in the soil, while fine texture soils generally have a higher nutrient holding capacity. Cleared virgin forest soils can also have varying levels of micronutrients depending on the soil type and the amount of weathering that has occurred.

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Tomato plants are primarily staked to raise the fruits from the ground. When tomato plants are not staked, the fruits may come in contact with the soil and become susceptible to diseases, pests, and rotting. Staking allows the fruits to hang freely in the air, reducing the likelihood of damage and disease. Staking also facilitates air circulation and exposes the plants to more sunlight, which can increase crop growth and yield.

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Urea cannot be used for liming. Liming is the process of adding materials to soil to increase its pH level, which makes the soil less acidic and more alkaline. Urea is a nitrogen-based fertilizer that is commonly used to provide plants with nitrogen. It does not have any liming properties and will not increase the pH level of the soil. Therefore, urea is not a suitable material for liming. The other options (gypsum, basic slag, and chalk) can be used for liming because they contain calcium or magnesium carbonate, which can react with the soil to increase its pH level.

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To improve soil fertility status, the combination of practices should aim at increasing soil nutrients and organic matter, reducing soil erosion, and promoting soil microorganisms. Out of the given options, applying organic fertilizer (II), growing legumes (IV), and allowing land to fallow (I) are practices that can improve soil fertility. Organic fertilizers increase soil organic matter content and nutrient availability, legumes improve soil nitrogen levels through nitrogen fixation, and allowing land to fallow promotes soil conservation by reducing soil erosion and increasing organic matter content. Practicing monoculture (III) can lead to soil depletion and reduction of soil nutrients over time. Therefore, the correct combination of practices that can help to improve soil fertility status is I, II, and IV only.

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The option that is excluded from the list of side effects of various preventive and control measures of pests and diseases of crops is "improved quality of farm produce." Explanation: The other options listed - environmental pollution, poisoning of wildlife, and disruption of the ecosystem - are potential negative effects of using certain pest and disease control measures such as synthetic pesticides and herbicides. While these measures can effectively control pests and diseases, they can also harm the environment and non-target organisms. Improved quality of farm produce is not a negative side effect, but rather a desired outcome of using these measures. For example, using disease-resistant crop varieties can lead to improved quality and yield of the crop.

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Detalles de la respuesta

The practice of burning of trash can lead to loss of soil water because it exposes the soil to direct sunlight, which can cause rapid evaporation of water from the soil. Slashing of undergrowth and seed bed preparation can help to conserve soil moisture by providing mulch cover and reducing soil erosion. Soil tillage can either help to conserve or enhance loss of soil water depending on the timing, depth and frequency of tillage operations. Therefore, the correct answer is option A - I and II.

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The factor that will not influence the yield of crops is wind direction and speed. While the other factors listed can affect crop growth and development, wind direction and speed typically do not have a direct impact on crop yield. However, it is worth noting that extreme wind conditions, such as strong winds or tornadoes, can physically damage crops and lead to yield losses.

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Detalles de la respuesta

Silos ensure good storage because of the air-tight environment created. Silos are designed to be airtight, which helps to prevent moisture and air from entering, which can lead to spoilage or insect infestation. By keeping the stored grains or other agricultural produce in an air-tight environment, the quality and shelf life of the produce can be preserved for longer periods of time. This is particularly important for long-term storage of produce to prevent spoilage, which can result in losses for farmers.

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Detalles de la respuesta

The correct answer is liver flukes. Snails are intermediate hosts of liver flukes, which are a type of parasitic flatworm that infects livestock such as cattle, sheep, and goats. These liver flukes can cause serious damage to the liver and other organs, and can even be fatal in severe cases. By eradicating snails from pastures, farmers can help control the spread of liver flukes and protect their livestock. Therefore, the farmer is attempting to control liver flukes by controlling the snail population.

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In this scenario, we are crossing two heterozygotes (Bb x Bb) where B represents the dominant allele for black coat color and b represents the recessive allele for brown coat color. Each parent has one dominant allele and one recessive allele. When we cross these two heterozygotes, their offspring will inherit one allele from each parent. The possible combinations are BB, Bb, Bb, and bb. BB represents homozygous dominant, which means the offspring will have black coat color. Bb represents heterozygous, which means the offspring will also have black coat color because the dominant allele masks the recessive allele. bb represents homozygous recessive, which means the offspring will have brown coat color. Therefore, out of the four possible combinations, 3 have at least one dominant allele, which will produce black coat color. So, the percentage of the F1 generation that will have black color is 75% (3 out of 4 possible combinations). Hence, the answer is 75%.

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When poultry flock pass out green, foul-smelling faeces with nervous symptoms, it means that the farmer has neglected to treat them against gumboro disease. Gumboro disease, also known as infectious bursal disease, is a viral infection that primarily affects young chickens. It can cause diarrhea, depression, and nervous symptoms in affected birds. The disease is highly contagious and can spread rapidly through a flock, leading to significant economic losses for poultry farmers. Therefore, it is important for farmers to take preventative measures, such as vaccination, to protect their flocks from gumboro disease.

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The gestation period of ewe is 149 days. This means the time between when a female sheep gets pregnant and when she gives birth to a lamb is approximately 149 days.

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To calculate the production cost of maize per kg, we need to first calculate the total revenue and then subtract the profit from it. Total revenue = 260 kg * N5.50/kg = N1,430.00 Profit = N430.00 Therefore, the production cost of maize per kg is: Production cost = (Total revenue - Profit) / Total quantity = (N1,430.00 - N430.00) / 260 kg = N1000.00 / 260 kg = N3.85/kg So, the answer is N3.85.

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Detalles de la respuesta

The correct sequence of land preparation for planting yam is option II, I, IV, and III, which is "slashing of undergrowth, burning of trash, soil tillage, and seed bed preparation" respectively. Slashing of undergrowth is done to clear the farm of any unwanted plant debris or weeds that could interfere with the growth of yam. Burning of trash is done to further clear the farm and also to provide the soil with some nutrients from the ashes. Soil tillage is done to loosen the soil and make it easier for the yam to penetrate and spread its roots. Seed bed preparation is done to create mounds or ridges where the yam can be planted, as well as to create spaces for applying fertilizers or mulch.

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The system of poultry management in which the spread of diseases can be kept to a minimum is the battery cage system. In this system, birds are kept in individual cages, which reduces the chances of them coming into contact with each other's feces or bodily fluids, and thus limits the spread of diseases. The other systems, such as deep litter, fold, and free range, involve birds having more contact with each other and their environment, which increases the risk of disease transmission.

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Detalles de la respuesta

Detalles de la respuesta

Detalles de la respuesta

Detalles de la respuesta

The correct option is: "improves soil structure". This statement is not true because farm mechanization does not directly improve soil structure. Instead, it can cause soil compaction if heavy machinery is used excessively or when soil moisture content is high. However, farm mechanization has many advantages, including saving labour, reducing drudgery, and increasing output. Mechanization can also lead to improved efficiency, timeliness, and precision in farming operations.

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The false statement about farm settlement schemes is that they are set up for research and publicity. Farm settlement schemes are typically established to encourage young people to take up farming, provide employment for young school leavers, and develop rural infrastructure. While research may be conducted on these schemes, and they may receive some publicity, these are not the primary purposes for their establishment.

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Deforestation is the clearing of forests, which results in the removal of trees from the land. This can have negative impacts on the environment and ecosystems, and can eventually lead to the loss of soil organic matter. Trees play an important role in maintaining soil organic matter, as they help to store and cycle nutrients, prevent soil erosion, and provide habitat for soil organisms. When trees are removed, the soil can become exposed to the elements, which can cause it to dry out and become more prone to erosion. This can lead to a decline in soil quality, which can reduce the fertility and texture of the soil, and eventually lead to desertification in some cases. Additionally, deforestation can contribute to climate change, as trees absorb carbon dioxide from the atmosphere and release oxygen. When trees are removed, the amount of carbon dioxide in the atmosphere can increase, leading to global warming and other negative impacts on the environment.

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Golden brown lesions on peeled yam tuber indicate infection by fungi. Fungal infections in yam tubers can lead to various postharvest losses. The fungi penetrate the yam skin, and lesions or spots appear on the surface of the yam tuber. These lesions can develop into a sunken, dark, and dry rot that can spread throughout the yam. Golden brown lesions can be caused by several types of fungi, including Fusarium and Aspergillus species.

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The hormone that influences the movement of the pelvic ligaments during parturition in farm animals is known as relaxin. Relaxin is a hormone produced in the ovaries and placenta of pregnant animals, including cows, pigs, and dogs. It causes the ligaments that support the pelvic bones to soften and stretch, allowing the pelvic opening to widen during birth. This allows the offspring to pass through the birth canal more easily. Relaxin is also involved in other aspects of pregnancy, such as regulating the growth and development of the fetus and preparing the mammary glands for lactation.

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Temperature is an important climatic (environmental) factor that strongly affects livestock performance. Its effects on the following are discussed.

(a) Brooding of chicks: Young chicks cannot regulate their own body temperature, so warmth must be supplied artificially during brooding. The correct temperature (about 35 degrees Celsius in the first week, reduced gradually) keeps the chicks comfortable, active and evenly spread under the brooder, and promotes good growth. If it is too cold the chicks huddle together and may be smothered or die of chilling; if it is too hot they pant, move away from the heat source, eat less and grow poorly.

(b) Reproduction in livestock: Moderate temperatures favour normal reproduction, but very high temperature (heat stress) reduces fertility. In males it lowers the quantity and quality of sperm produced, and in females it interferes with the oestrus cycle, weakens the signs of heat and can cause early embryo death and abortion. Very low temperatures also depress reproductive activity.

(c) Milk production: Dairy animals give the most milk within a comfortable (thermo-neutral) temperature range. Under high temperature the animals feel heat stress, eat less feed and use energy to keep cool, so milk yield and the butterfat content fall. Very cold weather also lowers yield because more feed energy is diverted to keeping the body warm.

(d) Egg production: Laying birds produce best at moderate temperatures. When temperature is very high the birds pant, drink more water, eat less and lay fewer eggs with thinner shells and smaller size. Very low temperature increases the feed needed for body warmth and can also reduce the rate of lay.

Detalles de la respuesta

(a) Explanation of four management practices:

• (i) Steaming up: This is the extra (increased) feeding of a pregnant animal with concentrates and good rations during the last few weeks before parturition. It builds up the animal's body reserves, ensures the birth of a healthy young one and prepares the mother for heavy milk production.
• (ii) Culling: This is the removal from the herd or flock of animals that are old, unproductive, sickly, deformed or of poor quality, so that only healthy and productive animals are kept. It improves the overall quality and productivity of the stock.
• (iii) Candling: This is the passing of a bright light through an egg in a dark room to examine its internal quality. It is used to detect cracks, blood spots and rotten eggs, and during incubation to check whether the egg is fertile and developing.
• (v) Creep feeding: This is the provision of supplementary feed to young animals (such as piglets or calves) in a special enclosure (creep) that only the young can enter, keeping out the adults. It helps the young to grow fast and prepares them for weaning.

(Tattooing is the marking of an animal for identification by pricking a number or symbol into the skin or ear with ink.)

(b) Five signs of heat in animals:

1. Restlessness and frequent bellowing or bleating.
2. Swelling and reddening of the vulva.
3. Discharge of clear mucus from the vulva.
4. Mounting other animals and standing to be mounted.
5. Loss of appetite and reduced milk yield; frequent urination.

(c) Three reasons for castrating farm animals:

1. To make the animals docile and easy to handle and manage.
2. To improve the quality and tenderness of the meat and remove its offensive smell.
3. To prevent indiscriminate (uncontrolled) mating and allow only selected males to breed.

Detalles de la respuesta

(a) Eight characteristics of agricultural systems in West Africa:

1. Farming is dominated by small-scale, subsistence holdings producing mainly for the family.
2. Simple, crude hand tools such as the hoe and cutlass are widely used, with little mechanisation.
3. Land is largely held under communal or family (traditional) land tenure, causing fragmentation of holdings.
4. Shifting cultivation and bush fallowing are commonly practised to restore soil fertility.
5. Production depends heavily on rainfall (rain-fed agriculture), so it is seasonal.
6. Mixed cropping and mixed farming are common on the same piece of land.
7. There is low use of improved inputs such as fertilizers, improved seeds and agro-chemicals, giving low yields.
8. Farm labour is supplied mainly by the family and unskilled hired hands, and productivity per worker is low.

(Other features: use of local/unimproved crop varieties and livestock breeds, and poor storage, processing and marketing facilities.)

(b) Four ways land tenure systems affect agricultural production:

1. Insecurity of tenure discourages investment: Where a farmer does not own the land permanently, he is unwilling to invest in permanent improvements such as tree crops, irrigation or buildings for fear of losing them.
2. Fragmentation of holdings: Communal and inheritance systems split land into small scattered plots that are uneconomic to work and cannot be mechanised.
3. Difficulty in obtaining credit: A farmer without a registered land title has no acceptable collateral, so he cannot easily secure loans to expand production.
4. Restriction on land use and expansion: Communal ownership and customary rules may prevent an individual from acquiring enough land or from choosing freely how to use it, limiting large-scale production.

Detalles de la respuesta

(a) Pasture: A pasture is an area of land covered with grasses and legumes (herbage) which is used for grazing or feeding livestock.

(b) Three features of natural pastures:

• They grow on their own without being deliberately planted or managed by man.
• They contain a mixture of many different, often unimproved, species of grasses and legumes.
• They are usually of low quality and low carrying capacity, and their growth depends on rainfall.

(c) Calculations:

(i) Population of the legume at one seed per stand:

Area of the circular land, \( A = \pi r^{2} \), with \( r = 200\,\text{m} \) and \( \pi = 3.142 \):

\[ A = 3.142 \times (200)^{2} = 3.142 \times 40000 = 125680\ \text{m}^{2} \]

Spacing \( = 1\,\text{m} \times 50\,\text{cm} = 1\,\text{m} \times 0.5\,\text{m} = 0.5\ \text{m}^{2} \) per stand.

\[ \text{Population} = \dfrac{\text{Area}}{\text{Spacing}} = \dfrac{125680}{0.5} = 251360\ \text{stands} \]

At one seed per stand, the population of the legume \( = 251{,}360 \) plants.

(ii) Expected plant population at 75% germination:

\[ \text{Expected population} = \dfrac{75}{100} \times 251360 = 188520\ \text{plants} \]

(iii) Two ways Stylosanthes gracilis is important in agricultural production:

• Being a legume, it fixes atmospheric nitrogen and improves soil fertility (it is also used as green manure and cover crop to check erosion).
• It provides nutritious, protein-rich forage (fodder) for feeding livestock.

Detalles de la respuesta

(a) Three main extension teaching methods:

1. Individual (personal) method
2. Group method
3. Mass (mass-media) method

(b) Three types under each method:

Individual method:

• Farm and home visits
• Office (personal) calls by the farmer
• Personal letters and telephone calls

Group method:

• Method demonstration
• Result demonstration
• Group meetings, discussions and field days (farm tours)

Mass method:

• Radio and television broadcasts
• Printed matter such as newspapers, bulletins, leaflets and posters
• Exhibitions, agricultural shows and campaigns

(c) Four qualities of a good extension agent:

1. He should be knowledgeable and well trained in agriculture and able to teach and demonstrate practically.
2. He should be patient, friendly and able to relate well with farmers, respecting their customs.
3. He should be hard-working, honest and dedicated, with a genuine interest in helping farmers.
4. He should be a good communicator who can speak the local language and pass on information clearly and simply.

Detalles de la respuesta

(a) Three ways by which nitrogen is added to the soil:

1. Biological nitrogen fixation by leguminous plants (Rhizobium bacteria in root nodules) and free-living soil bacteria.
2. Application of nitrogenous fertilizers and organic manures, and decay of dead plant and animal remains.
3. Fixation of atmospheric nitrogen by lightning, which brings it down in rain as nitrates.

(b) Five ways by which nitrogen is lost from the soil:

1. Leaching of soluble nitrates down beyond the root zone.
2. Denitrification, in which bacteria convert nitrates back to free nitrogen gas.
3. Removal (uptake) of nitrogen by crops that are harvested and taken off the land.
4. Volatilisation of ammonia into the air, especially from surface manures and fertilizers.
5. Loss through soil erosion and by burning of vegetation and crop residues.

(c) Importance of the nitrogen cycle: It ensures a continuous natural supply and recycling of nitrogen, keeping the soil fertile so that plants can obtain the nitrates needed to make proteins for growth. It maintains a balance between the nitrogen used up by plants and micro-organisms and the nitrogen returned to the soil and atmosphere.

(d) Three processes leading to formation of nitrate from organic matter:

1. Ammonification: Decomposing bacteria and fungi break down proteins in dead plant and animal matter and release ammonia (ammonium compounds).
2. Nitritation: Nitrifying bacteria (Nitrosomonas) oxidise the ammonium compounds to nitrites.
3. Nitratation: Nitrifying bacteria (Nitrobacter) further oxidise the nitrites to nitrates, the form absorbed by plants. (Nitritation and nitratation together make up nitrification.)

Detalles de la respuesta

(a)(i) Law of diminishing returns: The law states that as successive (equal) units of a variable input are added to a fixed quantity of other inputs, the extra (marginal) output obtained from each additional unit of the variable input first rises, but after a certain point begins to fall, provided technology is held constant.

(a)(ii) How it affects agricultural production: It guides the farmer on how much of an input (such as fertilizer, labour or seed) to apply. Adding more of an input raises total yield only up to the point of diminishing returns; beyond that point each extra unit adds less to output, and eventually total output may fall, so the farmer wastes money. The most profitable level of production is therefore where the value of the extra output just equals the cost of the extra input, and the farmer should not go on adding inputs beyond this optimum.

(b) How each factor affects the supply of agricultural produce:

• (i) Price: When the price of a produce rises, farmers are encouraged to produce and offer more for sale, so supply increases; when the price falls, supply is reduced (direct relationship).
• (ii) Technology: Improved technology such as better seeds, machines and agro-chemicals raises yield per hectare and lowers the cost of production, so more is produced and supply increases.
• (iii) Weather: Favourable weather (adequate rainfall and sunshine) gives good harvests and increases supply, while drought, flood or storms reduce yields and lower supply.
• (iv) Subsidy: A subsidy reduces the cost of inputs such as fertilizer and seed to the farmer, encouraging him to produce more, so supply increases.
• (v) Government policy: Favourable policies such as guaranteed prices, provision of credit, good roads and storage encourage production and raise supply, whereas heavy taxes, bans or unfavourable policies discourage production and reduce supply.

Detalles de la respuesta

(a) Economic importance of rocks:

(i) To man:

• They are quarried for building and construction materials (stones, gravel, sand, cement).
• They are sources of valuable minerals and metals (gold, iron, tin, coal).
• They are used to make roads, dams and other engineering works.
• Some rocks yield mineral fuels and salts used in industry.

(ii) In agriculture:

• They weather to form the soil in which crops grow.
• They release and supply plant nutrients (such as phosphorus, potassium and calcium) to the soil.
• Rock materials such as limestone provide liming materials to reduce soil acidity.
• Rock phosphate and other rocks serve as raw materials for making fertilizers.

(b) Two characteristics of each rock type:

• (i) Igneous rock: It is formed from cooled and solidified molten magma; it is usually hard, crystalline and contains no fossils. Examples are granite and basalt.
• (ii) Metamorphic rock: It is formed when existing rocks are changed by great heat and pressure; it is hard, often has a banded or layered (foliated) appearance and is more compact than the parent rock. Examples are marble and slate.

(c) Mode of formation of sedimentary rocks: Sedimentary rocks are formed from the products of weathering and erosion of existing rocks. Rock fragments, sand, mud and the remains of plants and animals are carried by wind, water and ice and deposited in layers in low areas such as river beds, lakes and the sea. Over a long period these deposits (sediments) accumulate, the upper layers press down on the lower ones (compaction), and dissolved minerals cement the particles together (cementation). The compacted and cemented layers gradually harden into sedimentary rock. They are typically layered (stratified) and often contain fossils. Examples are sandstone, limestone and shale.

Detalles de la respuesta

(a) Explanation of terms:

• (i) Floriculture: This is the branch of horticulture concerned with the cultivation, management and marketing of flowers and flowering (ornamental) plants for beauty and decoration.
• (ii) Taungya farming: This is a system of agro-forestry in which arable food crops are grown in between young forest tree seedlings on the same land, the farmer tending both until the trees form a canopy.
• (iii) Ley farming: This is a system in which land is put under grasses and legumes (pasture, called a ley) for a few years to graze livestock and restore fertility, then ploughed and used for arable crops in rotation.

(b) Eight uses of ornamental plants to man:

1. For beautification and decoration of homes, offices and surroundings.
2. For landscaping of gardens, parks and recreation grounds.
3. As live fences, hedges and screens for privacy.
4. To provide shade around buildings and along roads.
5. As a source of income when sold as cut flowers and potted plants.
6. To check soil erosion and serve as ground cover.
7. For religious, ceremonial and social occasions (bouquets, wreaths, gifts).
8. To purify and improve the environment and provide a pleasant micro-climate.

(c) Four fibre crops grown in the country:

• Cotton
• Jute
• Kenaf
• Sisal (hemp is also acceptable)

Detalles de la respuesta

(a) Explanation of terms:

• (i) Primary tillage implement: This is a heavy implement used for the first, deep opening and breaking of the soil to loosen and turn it before planting, for example the disc plough or mouldboard plough.
• (ii) Secondary tillage implement: This is a lighter implement used after primary tillage to break the large clods into a fine, level seedbed and to control weeds, for example the harrow, ridger and cultivator.

(b)(i) Three reasons why disc ploughs are better suited to West African soils than mouldboard ploughs:

1. The disc plough rolls over stumps, roots and stones without being damaged, whereas the mouldboard plough would be broken by them.
2. It works well in hard, dry and sticky soils common in the tropics because the rolling disc scours and does not clog easily.
3. It is not easily worn out by the abrasive tropical soils, so it lasts longer and needs less repair.

(b)(ii) Six major parts of a disc plough:

• Disc (concave steel plate)
• Disc bearing / hub
• Standard (frame arm carrying the disc)
• Scraper
• Beam or main frame
• Furrow wheel and hitch (linkage to the tractor)

(c) Three reasons why secondary tillage is necessary before sowing:

1. To break the large clods left by ploughing into a fine tilth suitable for good seed germination.
2. To level the field and make ridges or beds for easy planting and drainage.
3. To destroy weeds and incorporate manure and crop residues into the soil.

(d) Three precautions when spraying chemicals:

1. Wear protective clothing such as overalls, hand gloves, nose mask and goggles.
2. Spray along the direction of the wind (down-wind), not against it, to avoid drift onto the operator.
3. Do not eat, drink or smoke while spraying, and wash the body and equipment thoroughly after use.