WAEC SSCE - Agricultural Science - 1997

Maelezo ya Majibu

The main component of egg shell is calcium. Egg shell is a hard, protective covering that surrounds the egg and serves as a source of calcium for the developing embryo. Calcium is an essential nutrient for bone growth and strength, and it is also required for muscle function, nerve transmission, and other physiological processes in the body. Therefore, calcium is an important nutrient for both the developing embryo and for the health of the adult bird.

Maelezo ya Majibu

For effective dissemination of new ideas and techniques to farmers, the agricultural extension officer must work with existing community organizations and local leaders. This is because the agricultural extension officer needs to understand the cultural, social, and economic factors that affect the farmers' practices and behavior. By working with local leaders and organizations, the extension officer can gain the trust and support of the community, which is necessary for the successful adoption of new practices. The extension officer can also use these local networks to disseminate information and provide support to the farmers. Giving financial support, equipment or inputs alone is not sufficient without working with the community and local leaders.

Maelezo ya Majibu

Quartz is a mineral that has a glass-like appearance, is granular in nature, semi-translucent, and has a shiny surface. However, one characteristic that does not apply to quartz is having cleavage. Cleavage is the tendency of a mineral to break along specific planes of weakness, producing smooth surfaces. Quartz lacks cleavage, and instead has a conchoidal fracture, which is a type of fracture that produces curved, shell-like surfaces when the mineral is broken.

Maelezo ya Majibu

High fibre and low energy feeds are classified as roughages. Roughages are feed materials that are high in fibre and low in energy, such as hay, straw, and silage. These feeds are often bulky and take longer to digest, providing sustained energy over a longer period of time. Roughages are an important component of the diet for ruminants like cows and sheep, as their digestive systems are adapted to break down fibrous plant material. In contrast, concentrates are feed materials that are high in energy and low in fibre, such as grains and oilseed meals. They provide a quick source of energy and are often used to supplement roughages in an animal's diet.

Maelezo ya Majibu

In cattle, high fever and sudden death are symptoms of anthrax. Anthrax is a highly infectious bacterial disease that affects mainly animals, especially cattle, sheep, and goats. The disease is caused by the bacterium Bacillus anthracis, which forms spores that can survive in the soil for many years. In cattle, the disease can cause high fever, depression, and sudden death, with little or no warning. Other symptoms may include bloody discharge from the body orifices and difficulty breathing. Anthrax is a zoonotic disease, meaning it can be transmitted from animals to humans, and therefore, it is important to take necessary precautions to prevent its spread.

Maelezo ya Majibu

Maelezo ya Majibu

Commodity boards were responsible for the marketing of various crops, especially cash crops. However, yams are not typically considered cash crops, but rather subsistence crops. Therefore, it can be concluded that commodity boards were not responsible for the marketing of yams.

Maelezo ya Majibu

The difference between the total assets and total liabilities of a farm enterprise within a specified period before taxation is known as "net worth". This is because it represents the residual interest of the owner(s) in the assets of the farm after all liabilities have been settled. In other words, net worth is the value of the farm to its owners. It is calculated by subtracting the total liabilities from the total assets.

Maelezo ya Majibu

Maelezo ya Majibu

When granting loans to farmers, the credit officer should consider mostly the production and essential needs of the farmers. This means that the loan should be granted based on the farmer's intended use of the funds to produce crops or raise livestock. The credit officer should assess the viability of the project, the potential yield, and the marketability of the product to ensure that the loan will be used for a profitable venture that will enable the farmer to repay the loan. Factors such as the age, consumption needs, family size, and experience of the farmer may also be considered, but they are secondary to the production and essential needs of the farmers in assessing the viability of the loan.

Maelezo ya Majibu

Smut diseases are a group of fungal diseases that affect various crops. The symptoms include the formation of black soot-like masses of spores on the affected parts of the plant. Based on the options given, the group of crops that can be attacked by smut diseases include rice, maize, and guinea corn.

Maelezo ya Majibu

Overgrazing can have negative effects on the soil. The options given in the question are possible effects of overgrazing except for one. One of the effects mentioned is the "improvement of soil structure", which is not a negative effect of overgrazing. Overgrazing can lead to the exposure of soil to erosion, which is the removal of the topsoil layer by wind or water. This can result in soil infertility, as the topsoil is rich in nutrients necessary for plant growth. Overgrazing can also lead to the depletion of soil nutrients, as the plants are not given enough time to replenish the soil with their root system. In addition, overgrazing can lead to soil compaction, as the constant pressure of animal hooves on the soil can cause it to become tightly packed. Finally, overgrazing can lead to the exposure of soil to direct rays of the sun, which can cause the soil to dry out and become less fertile.

Maelezo ya Majibu

When crops are grown in nitrogen deficient soil, they suffer from a lack of nitrogen which is an essential nutrient for plant growth. As a result, they exhibit several characteristics including poor growth, stunted growth, chlorosis in growing crops, and yellowing of lower leaves. The nitrogen deficiency slows down the plant's metabolic processes, which can delay the ripening of the fruit. Therefore, the correct option is (E) timely ripening of fruits, as it is not a characteristic of crops grown in nitrogen deficient soil.

Maelezo ya Majibu

Maelezo ya Majibu

Progeny selection involves selecting breeding stock based on the performance of their offspring. This means that the offspring of a particular breeding pair are evaluated for specific traits or characteristics, such as growth rate, meat quality, milk production, or disease resistance. The animals that perform well in these traits are then selected as breeding stock for future generations. By selecting based on offspring performance, the breeder can improve the overall genetic quality of the herd or flock over time. This is in contrast to other forms of selection, such as selection based solely on the merits of the parents or on pedigree, which may not necessarily result in the desired traits being passed on to the offspring.

Maelezo ya Majibu

Maelezo ya Majibu

Iron is a soil micro-nutrient. Micro-nutrients are essential elements required by plants in small amounts for their growth and development. Iron is required for the formation of chlorophyll in plants, which is necessary for photosynthesis, and it also plays a vital role in the respiration process of plants. Although iron is required in small quantities, its deficiency can lead to chlorosis or yellowing of leaves, which can reduce the plant's growth and yield.

Maelezo ya Majibu

Night blindness in animals is caused by a deficiency of vitamin A. Vitamin A is an essential nutrient that is necessary for maintaining normal vision. Animals that do not have enough vitamin A in their diet may experience a range of vision problems, including night blindness. Night blindness is the inability to see clearly in low light or at night, which can be dangerous for animals that are active during these times. Therefore, ensuring that animals have a diet that is rich in vitamin A is important for maintaining their vision and overall health.

Maelezo ya Majibu

Maelezo ya Majibu

Maelezo ya Majibu

The answer is "ammonification". Ammonification is a biological process that converts organic nitrogen to ammonia and ammonium ions, which can contribute to soil fertility. However, it is not directly involved in rock weathering. The other options - water, carbonation, roots, and temperature - all play significant roles in the weathering of rocks. Water can cause physical weathering through erosion and can chemically weather rocks through dissolution and oxidation. Carbonation is the reaction of carbon dioxide with minerals in rocks, which can dissolve and break down the rock. Roots can grow into cracks in rocks and exert pressure, causing physical weathering. Temperature can also cause physical weathering through thermal expansion and contraction.

Maelezo ya Majibu

The answer is "slow growth". A good pasture is one that can support the grazing needs of animals by providing high quality grasses and legumes with a high leaf to stem ratio. It should also have the ability to withstand trampling from the animals and be drought-resistant. Slow growth, on the other hand, would be a disadvantage as it means that the animals would have to wait longer for the grass to grow back after grazing. This would result in overgrazing and eventually lead to the depletion of the pasture.

Maelezo ya Majibu

The crop that cannot be grown as a cover crop is Nicotiana tabacum. Cover crops are crops that are grown primarily to provide ground cover to protect the soil against erosion, suppress weed growth, and improve soil health. They are usually grown between periods of regular crop production. The other options listed - pueraria phaseoloides, stylozanthes gracillis, centrosema pubescens, and calopogonium mucunoides - are all examples of crops that can be grown as cover crops.

Maelezo ya Majibu

Maelezo ya Majibu

Maelezo ya Majibu

Maelezo ya Majibu

The question is asking which option is not an aim of crop improvement. Crop improvement involves the application of scientific techniques to produce crops with desired characteristics. The options listed are aims of crop improvement, except for "improving the infrastructural facilities in a farm". While infrastructure may facilitate crop production, it is not considered an aim of crop improvement. Therefore, the answer is "improving the infracstructural facilities in a farm".

Maelezo ya Majibu

Maelezo ya Majibu

Maelezo ya Majibu

Reforestation is the organised planting of trees in areas from which forest trees have been removed. It is a deliberate effort to restore the ecological function and structure of deforested or degraded land. The objective of reforestation is to establish a forest with a structure and composition that is as similar as possible to the original forest. It is a crucial process for mitigating the negative impacts of deforestation on the environment, including soil erosion, loss of biodiversity, and climate change.

Maelezo ya Majibu

New-born animals should be fed with colostrum because it contains antibodies protecting them against diseases. Colostrum is the first milk produced by the mammary glands of female mammals after giving birth. It is rich in antibodies, growth factors, and other essential nutrients that are important for the development and survival of the newborn. The antibodies present in colostrum provide passive immunity to the newborn, protecting them against diseases and infections. Colostrum is essential for the health and survival of the newborn animal.

Maelezo ya Majibu

Maelezo ya Majibu

The proportion of the different types of feed given to an animal daily is known as a ration. It is the total amount of feed provided to an animal in a day, including roughages, concentrates, supplements, and additives. The correct balance of each component in a ration is critical for the animal's health, productivity, and overall well-being. The proper ration will vary depending on the animal's species, breed, age, weight, and level of activity. The goal of formulating a balanced ration is to provide the animal with all the essential nutrients it needs to maintain health, growth, and production.

Maelezo ya Majibu

The causal organism of mastitis in cattle is a bacterium. Mastitis is an inflammation of the mammary gland in cows which can be caused by various bacteria, but the most common ones are Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli. Bacteria can enter the udder through the teat canal and cause an infection which results in swelling, pain, and the production of abnormal milk.

Maelezo ya Majibu

The farm manager has several roles to play on the farm, but planting crops and vegetables is not one of them. The farm manager is responsible for planning the farm programme of work, co-ordinating the farm activities, organizing sales of farm products, controlling farm workers and managing the resources of the farm to ensure maximum productivity. The farm manager is also responsible for managing the finances of the farm, including budgeting, accounting, and financial reporting. In addition, the farm manager is responsible for managing risk and making strategic decisions to ensure the long-term sustainability of the farm.

Maelezo ya Majibu

Maelezo ya Majibu

The primary function of the gizzard is to grind ingested food into smaller particles. This is necessary for the mechanical breakdown of food in the digestive system of birds and some other animals, since these animals lack teeth to chew and grind their food. The gizzard is a muscular, thick-walled organ that contracts rhythmically to break down food particles by grinding them against each other and against small stones or grit that the animal has ingested. The ground-up food then passes on to the rest of the digestive system for further processing and absorption of nutrients.

Maelezo ya Majibu

The effect of North-East trade winds on agriculture are well-known. However, one of the options listed is not a direct effect of these winds, which is "causing heavy rainfall." While North-East trade winds bring moisture and precipitation to some regions, they do not typically cause heavy rainfall. Therefore, the correct answer is "causing heavy rainfall."

Maelezo ya Majibu

Maelezo ya Majibu

Energy for photosynthesis in crops is provided by the sun. Photosynthesis is the process by which plants use energy from sunlight, carbon dioxide, and water to produce glucose and oxygen. The process of photosynthesis occurs in specialized structures in plant cells called chloroplasts, which contain chlorophyll pigments that absorb light energy from the sun. This light energy is then used to convert carbon dioxide and water into glucose and oxygen, which the plant uses as a source of energy for growth and development. Therefore, the energy for photosynthesis in crops is provided by the sun.

Maelezo ya Majibu

The statement that is not true about rearing livestock under the free-range system is "adequate veterinary care." In a free-range system, livestock are allowed to move freely and fend for themselves, which makes it difficult to provide adequate veterinary care. This is because the animals are not confined in a specific location, and it is challenging to monitor their health and provide them with necessary treatments. As a result, livestock under the free-range system are at higher risk of infestation by parasites, and the young animals may have a high mortality rate due to lack of care. Also, since the animals are free to move around, there is a higher chance of loss due to predators or accidents.

Maelezo ya Majibu

Maelezo ya Majibu

The amount of air and water in the soil is mostly affected by the structure of the soil. Soil structure refers to the arrangement of soil particles into aggregates or clumps. The spaces between these aggregates determine the amount of air and water in the soil. If the soil has a good structure with well-formed aggregates, there will be more spaces for air and water to move through the soil. On the other hand, if the soil has poor structure, with few or no aggregates, the soil will have poor aeration and drainage. The other options, such as location, rainfall, chemical composition, and living organisms, can also have an impact on soil air and water content, but they are not the primary factors.

Maelezo ya Majibu

The pasture grass among the options given is Cynodon dactylon. This is because Cynodon dactylon, also known as Bermuda grass or African couch grass, is a well-known and widely used pasture grass that is native to Africa but is now found in many parts of the world. It is a highly valued grass because it is drought-tolerant, grows well in warm climates, and can withstand heavy grazing pressure. The other options listed are legumes that are often grown alongside grasses in pastures to improve soil fertility and provide additional nutrition for grazing animals.

Maelezo ya Majibu

Maelezo ya Majibu

The question asks for an option that is NOT a role of government in the development of agriculture. Therefore, we need to look for an option that is not a responsibility of the government in the development of agriculture. The correct option is "training of farmers' children" because it is not a direct role of the government in agriculture development. While the government may provide education and training opportunities for farmers, it is not specifically responsible for the education of their children. The other options listed are all roles that the government can play in promoting and supporting agricultural development.

Maelezo ya Majibu

Maelezo ya Majibu

The most important pests of vegetable crops are insects. Insects are the most common and harmful pests that attack vegetable crops, causing damage to leaves, stems, roots, and fruits. They feed on the plant tissues, sucking the sap or chewing the leaves, and can also transmit diseases. Some of the most common insects that attack vegetable crops include aphids, caterpillars, whiteflies, thrips, mites, and beetles. Insects can cause significant damage to crops, resulting in reduced yields and economic losses for farmers. Therefore, effective pest control measures are necessary to protect vegetable crops from insect damage.

Maelezo ya Majibu

The hormone generally called pregnancy hormone in farm animals is progesterone. Progesterone is a hormone that is essential for the maintenance of pregnancy in mammals. It is produced by the corpus luteum in the ovary and later by the placenta after implantation of the fertilized egg. It helps to prepare the uterus for implantation and maintain the pregnancy by inhibiting contractions of the uterus. In farm animals, progesterone is used to synchronize estrus cycles and to support pregnancy in breeding programs.

Maelezo ya Majibu

Maelezo ya Majibu

The agent of controlled pollination in crops is man. Controlled pollination is the process of transferring pollen from one plant to another with a specific goal in mind, such as developing a new variety or increasing yield. In this process, humans intervene to manipulate the transfer of pollen, rather than relying on natural pollination by wind or insects. This is done by using tools such as brushes or by physically transferring the pollen by hand. Hence, the answer is "man".

Maelezo ya Majibu

The answer is "bone meal". Bone meal is a feed ingredient made of ground animal bones and is used as a source of minerals such as calcium and phosphorus. It does not contain carbohydrates, which are a major source of energy for animals. The other options listed are all feedstuffs that supply carbohydrates to animals, such as maize, guinea corn, rice bran, and palm kernel cake.

Maelezo ya Majibu

The branch of crop production that is normally concerned with crop improvement is plant breeding. Plant breeding involves selecting and crossing plants with desirable traits, such as increased yield, disease resistance, or improved quality, in order to develop new and improved varieties. This is done through careful selection of parent plants, controlled pollination, and evaluation of offspring. Plant breeding is an important aspect of agriculture as it helps to develop crops that can better meet the needs of farmers and consumers.

Maelezo ya Majibu

Maelezo ya Majibu

Cassava is a popular crop that is cultivated in many ecological zones due to its tolerance to low rainfall and poor soil fertility. Unlike other crops, cassava can grow in areas with low rainfall and in soils that are not very fertile. Additionally, cassava has a relatively short growth period, making it possible to harvest the crop after about 8 to 18 months of planting. Cassava can be used for both industrial and domestic purposes, and it is also resistant to some diseases and pests. Its low production costs make it a suitable crop for smallholder farmers, contributing to food security in many regions.

Maelezo ya Majibu

Maelezo ya Majibu

The function of organic matter in soil is very important for soil health and productivity. The options (a), (b), (c) and (e) are all functions of organic matter in the soil. Organic matter helps to retain moisture in the soil, reduces soil erosion, prevents nutrient leaching and improves soil structure. However,, "inhibiting seed germination", is not a function of organic matter in the soil. In fact, organic matter helps to provide nutrients and a favorable environment for seed germination and plant growth.

Maelezo ya Majibu

Short notes on four of the listed terms:

(a) Deforestation: This is the clearing, felling or removal of trees and forest vegetation from an area of land without replacing them. It is done to obtain timber, fuel wood and farmland or to build settlements. It exposes the soil to erosion, reduces rainfall, destroys wildlife habitats and lowers soil fertility, and it is therefore a harmful practice when uncontrolled.

(b) Regeneration: This is the natural or artificial renewal or re-establishment of a forest. Natural regeneration occurs when trees reseed themselves from fallen seeds or coppice from stumps, while artificial regeneration is achieved by deliberately planting seedlings. It restores the tree cover on land that has been logged or degraded.

(c) Afforestation: This is the deliberate planting of trees to establish a forest on land that was previously bare, grassland or farmland that had no forest before. It is practised to check erosion and desertification, provide timber and fuel, serve as windbreaks and improve the environment.

(d) Selective exploitation: This is a system of forest harvesting in which only mature trees of desired species and size are felled, while young and immature trees are left standing to continue growing. It conserves the forest, allows continuous yield and maintains forest cover, unlike clear felling.

(e) Taungya system: This is a form of agro-forestry in which farmers are allowed to raise arable food crops in between newly planted forest tree seedlings on the same land. The farmer tends both the crops and the young trees; he harvests the food crops while the trees grow, and moves on when the canopy closes. It combines food production with forest establishment and reduces the cost of raising the forest.

Maelezo ya Majibu

(a) Types of credit in agricultural production:

• (i) Short term credit: This is a loan granted for a short period, usually up to one year, used to meet running or recurrent expenses such as buying seeds, fertilizer, agro-chemicals and paying labour. It is repaid after harvest and sale of produce.
• (ii) Medium term credit: This is a loan given for a moderate period, usually between one and five years, used to buy items of medium durability such as work animals, small implements, dairy stock and to fence or improve the farm.
• (iii) Long term credit: This is a loan granted for a long period, usually above five years, used for heavy capital investment such as buying land, tractors and machinery, erecting farm buildings and establishing plantations or orchards.

(b)(i) Four sources of agricultural credit:

1. Commercial and agricultural (development) banks
2. Government agencies and schemes (for example the Agricultural Credit Guarantee Scheme)
3. Co-operative societies and thrift societies
4. Money lenders, friends and relatives

(b)(ii) Four reasons why farmers find it difficult to get loans from banks:

1. Lack of collateral security: Many small farmers have no land title, buildings or other acceptable assets to pledge against the loan.
2. High risk of farming: Because farming is exposed to drought, flood, pests and diseases, banks fear the farmer may not be able to repay.
3. Illiteracy and poor record keeping: Many farmers cannot prepare the loan applications, feasibility reports and accounts that banks demand.
4. High interest rates and short repayment periods: The cost of borrowing is high and repayment terms often do not match the farmer's harvest season, discouraging both the farmer and the lender.

(Other reasons include remoteness of banks from rural areas and cumbersome loan procedures.)

Maelezo ya Majibu

Brief explanation of four terms in animal production:

(a) Oestrus cycle: This is the regular reproductive cycle in a mature non-pregnant female animal, being the interval from the beginning of one heat period to the beginning of the next. It is controlled by hormones and includes the phases of pro-oestrus, oestrus, met-oestrus and di-oestrus. In the cow it is about 21 days.

(b) Heat period (oestrus): This is the period within the oestrus cycle when the female is sexually receptive and will readily accept the male for mating. It is the time when ripe eggs are released (ovulation) and is the correct time for natural service or artificial insemination. The animal shows signs such as restlessness, mounting others and a swollen vulva.

(c) Gestation period: This is the length of time an animal carries its young in the womb, from the day of successful fertilization (conception) to the day of birth. It varies with the species, for example about 280 days in the cow, 150 days in the sheep and goat, and 114 days in the pig.

(d) Parturition: This is the act of giving birth, that is, the expulsion of the fully developed young one from the womb of the mother at the end of the gestation period. It is called calving in cattle, lambing in sheep, kidding in goats and farrowing in pigs.

(e) Colostrum: This is the first thick, yellowish milk produced by the mother immediately after parturition. It is rich in proteins, vitamins and antibodies which give the newborn immunity against diseases, and it also acts as a mild laxative to clear the young animal's gut.

Maelezo ya Majibu

(a)(i) Definition of weathering: Weathering is the gradual breaking down, disintegration and decomposition of rocks into smaller particles and eventually into soil, in their place of origin (in situ), through the action of physical, chemical and biological agents.

(a)(ii) Two types of weathering:

• Physical (mechanical) weathering
• Chemical weathering

(Biological weathering is a recognised third type.)

(b) Four factors that influence weathering:

1. Temperature: Alternate heating and cooling causes rock minerals to expand and contract at different rates. This sets up stresses that crack and flake the rock, so areas with wide temperature ranges weather faster.
2. Water (rainfall): Water carries out chemical reactions such as hydrolysis, hydration and solution that decompose rock minerals. Rain water also seeps into cracks and, on freezing or through flow, widens them and washes away loosened particles.
3. Living organisms: Plant roots grow into cracks and prise rocks apart, while burrowing animals, lichens, bacteria and decaying organic matter release acids that dissolve and break down the rock.
4. Nature (composition and structure) of the rock: Soft, porous and jointed rocks with easily soluble minerals weather quickly, whereas hard, compact rocks with resistant minerals weather slowly.

Other influencing factors include wind (abrasion and removal of particles) and topography/relief (steep slopes expose fresh rock to rapid weathering).

Maelezo ya Majibu

Explanation of the terms:

(a) Salvage value: This is the estimated amount of money that an asset, such as a machine or building, is expected to be worth at the end of its useful life, that is, its scrap or disposal value after it has been fully used or depreciated.

(b) Farm inventory: This is a complete list or record of all the property, goods and resources on the farm, together with their money values, taken at a particular date (usually the beginning or end of the year). It includes land, buildings, livestock, machinery, stored produce and cash.

(c) Farm assets: These are all the valuable properties and resources owned by the farm business that have money value and can be used to generate income. They include fixed assets such as land, buildings and machinery, and current assets such as growing crops, livestock, stored produce and cash.

(d) Point of diminishing return: This is the point in production at which the addition of one more unit of a variable input to fixed inputs begins to yield a smaller (less than proportionate) increase in total output. Beyond this point, each extra unit of input adds less to total product than the unit before it.

(e) Depreciation: This is the gradual loss or reduction in the value of a durable farm asset (such as a tractor, implement or building) over time due to wear and tear, age and obsolescence. It is treated as a cost of production and spread over the useful life of the asset.

Maelezo ya Majibu

(a) Communal land tenure

Essential features:

• Land is owned collectively by the whole community, village or extended family.
• It is controlled and administered by the community head, chief or family head.
• Individual members are allocated portions to use but cannot sell or permanently own the land.
• Rights of use are passed down through generations, and every member has access to land.

Effects on agriculture:

• Insecurity of tenure discourages farmers from planting permanent/tree crops or improving the land.
• Land cannot easily be used as collateral to obtain loans.
• Fragmentation of holdings discourages mechanization, though it does guarantee land access for all members.

(b) Individual land tenure

Essential features:

• Land is owned by an individual who has full rights over it.
• The owner can use, sell, lease, mortgage or bequeath the land.
• Ownership is usually backed by a title deed or certificate of ownership.

Effects on agriculture:

• Security of ownership encourages long-term investment, permanent crops and land improvement.
• The land can be used as collateral to secure agricultural loans.
• Consolidated holdings encourage mechanization, though the system may lead to landlessness for the poor and to land speculation.

Maelezo ya Majibu

(a) Hybridization

Hybridization is the crossing of two genetically different plants, usually different varieties of the same species, in order to obtain hybrid offspring which combine desirable inherited characters of both parents.

(b) Aims of crop improvement

1. To produce crop varieties with higher yield.
2. To improve the quality of produce, such as size, taste, nutritive value and keeping quality.
3. To produce varieties resistant to pests and diseases.
4. To produce varieties adapted to adverse or varying climatic and soil conditions, for example drought or poor soils.
5. To produce early-maturing, uniform varieties with good harvesting and processing qualities.

(c) Monohybrid cross and Mendel's Law of Segregation

A monohybrid cross is a genetic cross involving only one pair of contrasting characters. Mendel's Law of Segregation states that the two alleles controlling a character separate during gamete formation, so that each gamete receives only one allele. The alleles unite randomly again at fertilization.

For example, let T represent the allele for tallness and t the allele for shortness. Tallness is dominant over shortness.

In the parental generation, a pure tall plant, TT, is crossed with a pure short plant, tt. Every first filial generation plant receives T from the tall parent and t from the short parent; hence all the F₁ plants are Tt and tall.

When two F₁ plants are selfed, Tt × Tt, the alleles segregate during gamete formation. Each parent produces two types of gamete, T and t. Random fertilization gives:

• F₂ genotypic ratio: 1 TT : 2 Tt : 1 tt.
• F₂ phenotypic ratio: 3 tall : 1 short.

The reappearance of short plants (tt) in the F₂ generation shows that the alleles did not blend in the F₁ generation; they segregated into separate gametes.

Maelezo ya Majibu

The sheep is a ruminant herbivore, whereas poultry is a non-ruminant bird. The sheep is adapted for microbial digestion of fibrous feeds and chewing of cud; poultry is adapted mainly for rapid digestion of grains and other concentrated feeds.

Labelled diagrams of the alimentary canals

Differences between the digestive systems

Feature	Sheep	Poultry
Type of feeder	Ruminant, adapted to grazing and roughage.	Non-ruminant bird, adapted mainly to grains and other concentrated feeds.
Mouth and teeth	Has teeth for biting and grinding food. It later regurgitates and rechews cud.	Has a beak and no teeth. Food is swallowed without chewing.
Crop	No crop.	Crop present for temporary storage and softening of food.
Stomach	Has a four-compartment stomach: rumen, reticulum, omasum and abomasum.	Has a glandular stomach, the proventriculus, followed by a muscular gizzard.
Grinding of food	Food is ground by molar teeth during mastication and rumination.	Food is ground in the thick muscular gizzard, often with swallowed grit or small stones.
Cellulose digestion	Micro-organisms in the rumen digest cellulose and other fibrous materials.	Cellulose digestion is very limited; only slight fermentation occurs in the paired caeca.
Caeca	Has one caecum.	Has two caeca.
Terminal opening	The alimentary canal ends at the anus.	The digestive, urinary and reproductive tracts open into the cloaca, which opens at the vent.

Food pathway in sheep: mouth → oesophagus → rumen/reticulum → omasum → abomasum → small intestine → large intestine → anus.

Food pathway in poultry: beak → oesophagus → crop → proventriculus → gizzard → small intestine → paired caeca → large intestine → cloaca → vent.

Maelezo ya Majibu

Farm power refers to the energy or force applied to perform agricultural operations such as ploughing, harvesting, pumping and processing. Four sources are discussed below.

1. Human (muscular) power: This is the energy supplied by the farmer and farm labourers using their muscles. It is used for light operations such as hoeing, weeding, planting, harvesting and carrying loads. It is readily available and cheap but is slow, tedious and low in output, making it suitable only for small holdings.
2. Animal (draught) power: This is power provided by work animals such as bulls, oxen, donkeys, horses and camels. The animals are harnessed to implements to plough, ridge, harrow and haul carts. It is cheaper than machines, uses locally available feed and its dung manures the soil, but it is slow and the animals may be attacked by tsetse fly in the humid zones.
3. Mechanical power: This is power supplied by engines and machines such as tractors, combine harvesters, water pumps and processing mills, driven by petrol or diesel. It is fast, does heavy work and can cover large areas within a short time, but it is expensive to buy, needs fuel and skilled maintenance.
4. Electrical power: This is energy supplied through electricity used to drive pumps, mills, incubators, lighting in poultry houses, milking machines and cold rooms. It is clean, convenient and easily controlled, but it depends on a reliable supply and is not always available in rural areas.

Other sources include wind power (windmills for pumping water) and solar power (for drying, lighting and pumping).

Maelezo ya Majibu

(a)(i) Six uses of lime in agriculture:

1. It reduces soil acidity by raising the soil pH.
2. It supplies the plant nutrients calcium and (in dolomite) magnesium.
3. It improves soil structure by causing clay particles to floculate, giving better aeration and drainage.
4. It promotes the activity of soil micro-organisms and hastens decomposition of organic matter.
5. It increases the availability of other nutrients such as phosphorus and molybdenum in acid soils.
6. It reduces the toxicity of iron, aluminium and manganese in strongly acid soils, and helps to control some soil-borne pests and diseases.

(a)(ii) Four common liming materials:

• Quicklime (calcium oxide, CaO)
• Slaked or hydrated lime (calcium hydroxide, Ca(OH)₂)
• Ground limestone (calcium carbonate, CaCO₃)
• Dolomitic limestone (CaMg(CO₃)₂); wood ash and marl are also used.

(b)(i) Three examples of nitrogenous fertilizer:

• Urea
• Ammonium sulphate
• Ammonium nitrate (calcium ammonium nitrate and sodium nitrate are also acceptable)

(b)(ii) Three examples of a phosphorus fertilizer:

• Single superphosphate
• Triple superphosphate
• Rock phosphate (bone meal and basic slag are also acceptable)