Agriculture 0600 | Paper 1 Mock 01 | Theory

Labelled answer diagram:

(a)(i) The structures labelled in the diagram of the chicken respiratory system:

• P = Trachea (windpipe) - the main airway connecting the larynx to the bronchi [1].
• Q = Bronchus (primary bronchus) - the branch that carries air from the trachea into the lung [1].
• R = Air sac - the thin-walled extension of the respiratory system unique to birds, which stores air and facilitates unidirectional airflow through the lungs [1].

(a)(ii) How Newcastle disease affects the respiratory system (3 marks):

1. The Newcastle disease virus (a paramyxovirus) attacks and inflames the epithelial lining of the trachea and bronchi, causing swelling and excess mucus production [1].
2. Affected birds show gasping, coughing, sneezing and nasal discharge as they struggle to move air through the inflamed, mucus-clogged airways [1].
3. The air sacs may become clouded or thickened, reducing gas exchange efficiency. In severe cases the respiratory damage allows secondary bacterial infections to establish, worsening the condition [1].

(b) How Newcastle disease spreads between birds (3 marks):

1. Direct contact - healthy birds become infected through close contact with sick birds or their respiratory secretions [1].
2. Airborne droplets - coughing and sneezing release virus-laden aerosol droplets that nearby birds inhale [1].
3. Fomites and environment - contaminated feed, water, equipment, litter and droppings carry the virus. Wild birds, rodents and human visitors can also transport the virus between farms on their bodies or clothing [1].

(c)(i) A suitable vaccination programme for Newcastle disease (3 marks):

1. Vaccinate chicks at day-old with a live attenuated vaccine (e.g. Hitchner B1 strain) administered by eye drop or in the drinking water [1].
2. Give a booster vaccination at 3-4 weeks of age to strengthen immunity as maternal antibodies wane [1].
3. Revaccinate layers every 8-12 weeks (or as recommended by the vaccine manufacturer) to maintain protective antibody levels throughout the laying period. Keep written records of vaccination dates and batch numbers [1].

(c)(ii) Three biosecurity measures apart from vaccination (any three for [3]):

1. Restrict access - limit entry to the poultry house to essential workers only and provide disinfectant footbaths at every entrance, so that pathogens are not carried in on shoes or clothing [1].
2. All-in, all-out management - do not mix birds from different sources or age groups. Bringing in birds of uniform age and origin, then cleaning thoroughly between batches, prevents disease cycling between cohorts [1].
3. Prompt carcass disposal - remove and bury or burn dead birds immediately rather than leaving them on the farm, eliminating a major source of virus amplification and environmental contamination [1].

Also acceptable: netting open sides to exclude wild birds; cleaning and disinfecting feeders, drinkers and equipment regularly.

(a)(i) From the table, tomatoes have the highest water requirement at 620 mm per season. [1]

(a)(ii) The cost of irrigating 5 hectares of tomatoes:

\[ \text{Total cost} = \text{cost per hectare} \times \text{number of hectares} = \$185 \times 5 = \$925 \] [2]

(b)(i) In furrow irrigation, water is released at the top of a gently sloping field and flows by gravity along shallow furrows (trenches) dug between the crop rows. [1] As the water moves along each furrow it soaks laterally (sideways) through the soil into the raised ridges or beds where the crop roots are growing. [1]

(b)(ii) Two advantages of drip irrigation over furrow irrigation for vegetable production:

1. Higher water-use efficiency - drip delivers water directly to the root zone of each plant through small emitters, so very little is lost to evaporation or surface run-off. In a semi-arid setting or where water is costly, this can substantially reduce total water consumption. [1]
2. Reduced foliar disease risk - because drip irrigation does not wet the leaves, the moist microclimate that favours fungal diseases (such as downy mildew or blight on tomatoes) is avoided. Furrow irrigation can splash soil onto lower leaves, and sprinkler systems wet the entire canopy. [1]

(c) Over-irrigation in semi-arid regions causes soil salination through a two-step process:

1. All irrigation water contains some dissolved salts. When water is applied generously, it carries these salts into the soil. [1]
2. In a semi-arid climate, high temperatures and low humidity drive intense evaporation. Water is drawn upward through the soil by capillary action and evaporates at or near the surface, but the salts it carried cannot evaporate. They accumulate in the upper soil layers. Repeated irrigation cycles without adequate drainage concentrate these salts to toxic levels, forming a visible white crust and poisoning plant roots. [1]

Labelled answer diagram:

(a)(i) The structures labelled on the longitudinal section of the flower: [3]

• X = Anther (the part of the stamen that produces and releases pollen grains) [1]
• Y = Ovary (the swollen base of the carpel/pistil that contains the ovules) [1]
• Z = Stigma (the sticky receptive surface at the top of the carpel where pollen lands) [1]

(a)(ii) The function of structure Y (the ovary) is to contain the ovules, which, after fertilisation, develop into seeds. [1] The ovary wall itself develops into the fruit wall (pericarp), protecting the developing seeds.

(b) Pollination is the transfer of pollen grains from the anther to the stigma of a flower. [1] It is a physical transport event that can be carried out by wind, insects or other agents. Fertilisation is the fusion of the male gamete (from the pollen grain) with the female gamete (egg cell) inside the ovule. [1] Pollination must occur first to deliver the pollen to the stigma; only then can the pollen tube grow down the style to the ovule and fertilisation can take place. Pollination delivers the pollen; fertilisation is the actual union of the sex cells to form a zygote. [1]

(c) Two features that distinguish wind-pollinated flowers from insect-pollinated flowers (any two paired comparisons): [2]

1. Wind-pollinated flowers have small, inconspicuous petals (or no petals at all), since they do not need to attract insects; insect-pollinated flowers have large, brightly coloured petals to attract pollinators. [1]
2. Wind-pollinated flowers produce large quantities of light, smooth pollen that is easily carried by air currents; insect-pollinated flowers produce smaller amounts of sticky or spiny pollen that adheres to the body of visiting insects. [1]

Another acceptable comparison: wind-pollinated flowers have large, feathery stigmas that hang outside the flower to catch airborne pollen, while insect-pollinated flowers have stigmas positioned inside the flower where visiting insects will brush against them.

(a) Green manuring is the practice of growing a crop (usually a legume) specifically for the purpose of ploughing it back into the soil while the plants are still green and actively growing, [1] in order to add organic matter and nutrients to the soil and improve its fertility. [1]

(b)(i) Two benefits the cowpea crop provides to the soil before it is ploughed in (any two): [2]

1. The cowpea roots bear nodules containing Rhizobium bacteria that fix atmospheric nitrogen, adding nitrogen to the soil even before the crop is ploughed in. [1]
2. The plant canopy covers the soil surface, reducing erosion from rain splash and wind, and suppressing weeds by shading them out and competing for light and space. [1]

(b)(ii) Why ploughing in at the flowering stage is more beneficial than waiting until seed maturity: [2]

1. At the flowering stage, the plant tissue has its highest nitrogen content and is soft and succulent, so it decomposes rapidly once ploughed in. [1]
2. After seed maturity, the stems become woody and lignified, with a high carbon-to-nitrogen (C:N) ratio. Material with a high C:N ratio decomposes slowly, and decomposing bacteria actually draw nitrogen from the surrounding soil to break down the carbon, temporarily reducing the nitrogen available to the next crop (nitrogen immobilisation). [1]

(c) Two other methods of adding organic matter to the soil, apart from green manuring (any two): [2]

1. Applying animal manure (farmyard manure / cattle or poultry manure). [1]
2. Adding compost made from decomposed crop residues and organic waste. [1]

Other acceptable answers: mulching with crop residues; applying biosolids / sewage sludge.

(a) Four signs that indicate an animal may be suffering from ill health (any four): [4]

1. Loss of appetite or reduced feed intake. [1]
2. Loss of body condition, visible weight loss, or emaciation. [1]
3. A dull, rough, or staring coat (the hair stands on end rather than lying flat and glossy). [1]
4. Isolation from the rest of the herd, standing apart, or reluctance to move. [1]

Other acceptable signs: discharge from eyes or nose; diarrhoea or abnormal droppings; reduced milk yield; pale mucous membranes (indicating anaemia); coughing; swollen joints or lameness; elevated body temperature.

(b) Three effects of internal parasites on beef cattle productivity (any three): [3]

1. Reduced weight gain: Internal parasites (e.g. roundworms, liver fluke) compete with the host for nutrients absorbed from digested feed, diverting energy and protein away from muscle growth. [1]
2. Anaemia: Blood-feeding parasites such as Haemonchus (barber's pole worm) remove blood from the gut lining, causing anaemia that reduces the animal's energy and capacity for growth. [1]
3. Damaged gut lining: Worms attach to and damage the intestinal wall, reducing the surface area available for nutrient absorption, so even adequate feed is poorly utilised. [1]

Other valid effects: reduced feed conversion efficiency; liver damage from liver fluke reducing protein metabolism.

(c) Administering an oral anthelmintic dose: [2]

1. Restrain the animal securely, for example in a crush or race, to prevent it from moving. [1]
2. Insert the nozzle of the drenching gun into the side of the mouth, over the back of the tongue, and administer the correct measured dose slowly. Delivering slowly prevents choking or aspiration of the liquid into the lungs. [1]

(a) Two differences between extensive and intensive pasture management:

(b)(i) Stocking rate calculation:

\[ \text{Stocking rate} = \frac{\text{Total area}}{\text{Number of animals}} = \frac{200 \text{ ha}}{80 \text{ cattle}} = 2.5 \text{ ha per animal} \quad [1] \]

(b)(ii) The stocking rate on natural veld is lower (more hectares per animal) than on improved pasture because natural veld has lower grass productivity and slower regrowth rates [1]. The unimproved grasses also have lower nutritive value (less protein, less digestible energy), so each animal needs a larger grazing area to meet its daily feed requirements [1].

(c) Two ways controlled burning manages natural veld (any two for [2]):

1. Removes moribund material - fire burns old, dead, unpalatable thatch, stimulating fresh, palatable regrowth from the grass crowns [1].
2. Controls bush encroachment - fire kills or suppresses woody seedlings and shrubs that compete with grasses for light and water, maintaining the area as open grazing land [1].

Other acceptable points: stimulates germination of fire-adapted grass species; reduces tick and parasite habitat in dead thatch.

(a)(i) Crop rotation is the practice of growing different crops in a planned sequence on the same piece of land over a period of years or seasons. [2] Each crop in the sequence is chosen to complement the others in terms of nutrient use, pest susceptibility, and soil structure effects.

(a)(ii) Including a legume in the rotation is important because legumes (such as beans and groundnuts) have root nodules containing nitrogen-fixing bacteria (Rhizobium). [1] These bacteria convert atmospheric nitrogen gas into ammonium/nitrates that remain in the soil after the legume crop is harvested or ploughed in, enriching the soil with nitrogen for the benefit of the next crop in the sequence. [1]

(a)(iii) Two other ways crop rotation helps maintain soil fertility (any two): [2]

1. Different crops have different nutrient requirements and root depths, so alternating them prevents the progressive depletion of any single nutrient and allows nutrients from different soil layers to be utilised. [1]
2. Rotation breaks pest and disease cycles that build up when the same crop is grown repeatedly on the same land. Pathogens and soil-borne pests specific to one crop cannot survive as easily when a different, non-host crop follows. [1]

(b)(i) Mass of nitrogen applied to the field:

\[ \text{Nitrogen} = \frac{20}{100} \times 200 \text{ kg} = 40 \text{ kg} \]

[1] for the correct method and [1] for the answer of 40 kg.

(b)(ii) Rate of nitrogen application per hectare:

\[ \text{Rate} = \frac{40 \text{ kg}}{0.5 \text{ ha}} = 80 \text{ kg per hectare} \]

[1]

(c) Two problems from excessive nitrogen fertiliser (any two): [2]

1. Excess nitrogen promotes excessive vegetative (leaf and stem) growth at the expense of grain or cob formation. The tall, lush plants may also be prone to lodging (falling over). [1]
2. Surplus nitrates that are not taken up by the crop leach through the soil into groundwater, contaminating drinking water sources and contributing to eutrophication of rivers and lakes. [1]

Other valid problems: delayed crop maturity; increased susceptibility to fungal diseases and pest attack due to soft, sappy growth.

(d) The role of phosphorus in plant growth: [2]

1. Phosphorus promotes strong root development and establishment, enabling the plant to access water and nutrients from a larger soil volume. [1]
2. It is essential for energy transfer within the plant (as a component of ATP) and is critically needed for flowering, fruiting, and seed formation. [1]

(a)(i) Two methods to clear bush vegetation (any two for [2]):

1. Slashing with cutlasses or machetes [1].
2. Mechanical clearing using a bulldozer or tractor with a front-mounted blade to push down trees [1].

Also acceptable: uprooting stumps with chains/winch; ring-barking large trees; applying herbicide before clearing.

(a)(ii) Three reasons why burning cleared vegetation may not be the best option:

1. Destroys organic matter - the vegetation, if incorporated into the soil instead, would decompose to form humus that improves soil structure, water-holding capacity and nutrient cycling [1].
2. Kills soil organisms - intense heat from burning destroys beneficial organisms such as earthworms, mycorrhizal fungi and decomposer bacteria that maintain soil health [1].
3. Nutrient loss - the mineral ash released by burning is highly soluble; if rain falls before planting, much of the potassium, calcium and other nutrients can be leached or washed away before the crop can use them [1].

(b)(i) How a mouldboard plough turns the soil:

1. The ploughshare (the pointed, horizontal blade) cuts a slice of soil horizontally along the base of the furrow [1].
2. The mouldboard (the curved plate behind the share) lifts the cut furrow slice and turns it over [1].
3. The inverted furrow slice is laid upside-down beside the open furrow, burying surface vegetation, weeds and crop residues beneath the soil [1].

(b)(ii) Two effects of primary tillage on soil physical condition (any two for [2]):

1. Breaks up compacted layers, increasing the volume of air spaces between soil particles (improved aeration) [1].
2. Improves water infiltration and drainage by loosening the soil structure [1].

Also acceptable: buries surface weeds and residues; loosens soil for easier root penetration.

(c) Secondary tillage is needed because primary ploughing leaves the field rough, with large clods of soil. Secondary tillage (harrowing) breaks these clods into a fine tilth [1], creating a level, crumbly seedbed that provides good seed-to-soil contact for even germination and allows uniform planting depth [1].

(a)(i) The genotypes of both parent birds are Ff (heterozygous). [1] Both parents have feathered shanks (dominant phenotype), yet some chicks have clean shanks (recessive phenotype ff). For a clean-shanked chick to appear, it must inherit a recessive allele (f) from each parent, so both parents must carry at least one f allele.

(a)(ii) The type of allele not expressed in the phenotype of a heterozygous individual is the recessive allele. [1] In a heterozygous organism (Ff), the dominant allele (F) determines the phenotype, and the recessive allele (f) is present but its effect is masked.

(b)(i) The genotype of a clean-shanked bird is ff (homozygous recessive). [1] Clean shanks only appear when no dominant allele is present.

(b)(ii) To produce a flock that breeds true for clean shanks within two generations:

1. Select clean-shanked birds (ff) from the current flock. These birds are guaranteed to be homozygous recessive. [1]
2. Mate these clean-shanked birds together (ff x ff). [1]
3. Since both parents can only contribute the recessive allele (f), all offspring will be ff and will have clean shanks. The flock breeds true because no dominant allele exists in the breeding stock. [1]

This is achievable within two generations because the farmer already has ff birds available in the flock.

(c) The difference between genotype and phenotype:

• Genotype is the genetic makeup of an organism - the specific combination of alleles it possesses for a given gene (e.g. Ff, FF, or ff). [1]
• Phenotype is the observable, physical characteristics of the organism that result from the interaction between its genotype and the environment (e.g. feathered shanks or clean shanks). [1]

(a) Progeny testing is the practice of judging the breeding value of an animal [1] by examining the quality and performance of its offspring (progeny). [1] Rather than assessing the animal itself, the breeder measures traits in the next generation to determine what genes the parent actually transmits.

(b) Progeny testing is more reliable than judging the bull by its own appearance because:

1. A bull's external conformation does not reliably predict the quality of calves it will produce. A bull may look impressive but carry hidden recessive alleles that only manifest in offspring. [1]
2. Some economically important traits, such as milk yield and maternal ability, can only be measured in female offspring. A bull cannot express milk production itself, so its genetic potential for dairy traits can only be assessed through daughters. [1]
3. Progeny testing reveals whether the bull actually passes on desirable genes rather than merely possessing them. A heterozygous bull may not transmit a trait consistently, and only offspring data reveals this. [1]

(c) Procedure for a progeny test comparing Bull A and Bull B:

1. Mate Bull A with one group of cows and Bull B with a separate, similar group of cows. The cow groups should be of the same breed, similar age, and similar body condition to eliminate maternal effects as a confounding variable. [1]
2. Rear all offspring under the same conditions of feeding, housing, and management, so that any differences in performance are attributable to the sire's genetics rather than environmental factors. [1]
3. Record the performance of each group of offspring over a defined period, measuring traits such as daily weight gain, feed conversion efficiency, carcass quality at slaughter, and disease resistance. [1]
4. Compare the average performance of Bull A's offspring with Bull B's offspring. The bull whose progeny have the superior average for the target traits (e.g. higher growth rate, better carcass grade) is selected for future breeding use. [1]

(a) The causative agent of East Coast fever is Theileria parva, a protozoan parasite [1].

(b) Transmission of East Coast fever (3 marks):

1. The disease is transmitted by the brown ear tick (Rhipicephalus appendiculatus), which acts as the biological vector [1].
2. When the tick feeds on an infected animal, it ingests blood cells containing Theileria parasites. The parasite undergoes development stages inside the tick [1].
3. When the infected tick subsequently feeds on a healthy animal, it injects the parasite into the animal's bloodstream through its saliva during feeding [1].

(c)(i) Two other signs of East Coast fever besides swollen lymph nodes and fever (any two for [2]):

1. Discharge from the eyes and nose (lacrimation and nasal discharge) [1].
2. Difficulty breathing (dyspnoea) due to fluid accumulation in the lungs [1].

Also acceptable: diarrhoea; loss of appetite; rough coat; anaemia (pale mucous membranes).

(c)(ii) Two preventive measures explained (each for [2], total [4]):

1. Regular acaricide treatment - dip or spray all cattle with an acaricide on a strict schedule (e.g. every 7-14 days during the tick season). This kills ticks on the animals before they can transmit the parasite, breaking the disease cycle. The dip concentration must be maintained correctly to remain effective [2].
2. Quarantine of new stock - isolate newly purchased animals in a separate holding area for at least 21 days before introducing them to the main herd. This observation period allows any incubating disease to become apparent, preventing an infected newcomer from introducing Theileria into a clean herd [2].

Also acceptable: rotational grazing to reduce tick burdens on pasture; vaccination where available (infection-and-treatment immunisation method).

(a)(i) The male flower cluster at the top of a maize plant is called the tassel. [1]

(a)(ii) Pollen is released from the anthers on the tassel at the top of the maize plant. [1] Wind carries the light, dry pollen grains downward and sideways, where they land on the exposed silks (stigmas) that protrude from the ear (the female flower structure) on the same or neighbouring plants. [1]

(a)(iii) Maize is described as a cross-pollinated crop because the male flowers (tassel) and female flowers (ear/silks) on the same plant typically mature at slightly different times, a phenomenon called protandry (the tassel sheds pollen before the silks on the same plant are fully receptive). [1] This timing difference means that pollen from one plant is more likely to land on the receptive silks of a neighbouring plant rather than its own, promoting cross-pollination and genetic mixing within the population. [1]

(b)(i) Steps to produce F1 hybrid maize seed from two inbred parent lines: [5]

1. Two inbred (homozygous) parent lines, Line A and Line B, are planted in adjacent rows in an isolation plot, far enough from other maize fields to prevent contamination by stray pollen. [1]
2. Before the tassels of Line A (the designated female parent) begin to shed pollen, all tassels are physically removed from every Line A plant. This process is called detasselling. [1]
3. Because Line A plants have no tassels, they cannot self-pollinate. They can only be pollinated by wind-blown pollen from the intact tassels of neighbouring Line B plants. [1]
4. The seed that develops on the ears of Line A plants is the F1 hybrid seed, carrying one set of genes from each inbred parent. [1]
5. The F1 hybrid plants grown from this seed display hybrid vigour (heterosis), producing significantly higher yields, stronger growth and greater uniformity than either inbred parent line alone. [1]

(b)(ii) Farmers are advised to buy fresh hybrid seed each season because F1 hybrid plants are heterozygous (carrying different alleles from the two parent lines). [1] If the farmer saves grain from an F1 crop and plants it, the resulting F2 generation will segregate genetically, showing wide variation in plant height, maturity, disease resistance and yield. This genetic recombination leads to reduced vigour and uneven, lower yields compared with the uniform F1 generation. [1]

(c) Three characteristics a breeder would select for in a drought-prone region (any three): [3]

1. Early maturity / short growing season: the crop completes its life cycle before soil moisture is exhausted. [1]
2. Deep root system: roots can access water stored deeper in the soil profile during dry spells. [1]
3. Tolerance to high temperatures or water stress: the plant can maintain physiological function (photosynthesis, grain filling) even under limited water supply, avoiding severe yield loss. [1]

Other acceptable characteristics include resistance to storage pests (weevils) and resistance to common diseases in the region such as maize streak virus.

(a) Soil temperature differences between the two farms during the growing season:

1. Farm P (hot, dry savanna) has higher soil temperatures because it receives intense solar radiation with less cloud cover, and the higher ambient air temperature heats the soil surface directly. Dry soils also warm up faster because there is less water to absorb heat energy (water has a high specific heat capacity). [1]
2. Farm Q (cool, wet highland) has lower soil temperatures because of higher altitude (temperature drops approximately 6.5 degrees Celsius per 1000 m elevation gain), greater cloud cover that blocks incoming solar radiation, and wetter soil that absorbs more energy before its temperature rises. [1]

(b) Two effects of high soil temperature on soil organisms:

1. Death or dormancy of microorganisms - at very high temperatures (above 40-45 degrees Celsius), many beneficial soil bacteria and fungi are killed or become inactive because their cellular enzymes denature. This reduces the microbial population responsible for decomposing organic matter and releasing nutrients. [1]
2. Reduced earthworm activity - earthworms are sensitive to heat and will burrow deeper into the soil or become dormant when surface temperatures are too high. Since earthworms are major contributors to soil aeration, mixing, and organic matter incorporation, their retreat reduces soil health. [1]

(c) One method to reduce soil temperature at Farm P, with an explanation of how it works:

Apply mulch to the soil surface (using dried grass, straw, crop residues, or other organic material).

1. Shading effect - the mulch layer physically blocks direct sunlight from reaching the soil surface, reducing the amount of solar radiation absorbed by the soil. [1]
2. Insulation - the air trapped within the mulch layer acts as an insulator, buffering the soil from rapid temperature fluctuations and keeping it cooler during the hottest part of the day. Mulch also reduces evaporation, maintaining soil moisture, which in turn moderates temperature because wet soil warms more slowly than dry soil. [1]

[3]

(d) The farmer at Farm Q (cool, wet highland) might need raised beds for vegetable production because:

1. Excess moisture and poor drainage - in a cool, wet climate the soil is frequently saturated or waterlogged. Raised beds lift the root zone above the surrounding water table, allowing excess water to drain off the sides and preventing roots from sitting in saturated soil. [1]
2. Improved root health - with better drainage, the root zone has adequate air-filled pore space for aerobic respiration. This prevents root rot and oxygen starvation that would otherwise kill or stunt vegetable crops, which are generally intolerant of waterlogging. [1]

(a) Line breeding is a form of selective breeding in which animals that are related, but not as closely as parent-offspring or full siblings, are mated together (e.g. half-siblings, cousins, uncle-niece). [1] The aim is to concentrate the genes of a particular outstanding ancestor in the offspring, increasing the likelihood that the ancestor's desirable traits are inherited homozygously. [1]

(b)(i) How the breeder would carry out line breeding over three generations to increase litter size:

1. Generation 1: Select the sows in the herd that produce the largest litters and mate them with a boar that is a relative of a high-performing sow (e.g. a half-brother or maternal grandson of an outstanding dam), but not a direct parent or full sibling. [1]
2. Generation 2: From the offspring, select the gilts (young females) that produce the largest litters in their first farrowing. Mate them with a boar from the same family line (e.g. a cousin or half-brother from the same outstanding ancestor). [1]
3. Generation 3: Again select the females with the largest litters from this generation and mate them with a male from the same bloodline, continuing to concentrate the genes associated with prolificacy. [1]
4. Throughout all three generations, always select strictly for large litter size and keep the breeding stock within the family line of the original outstanding ancestor, while avoiding the closest matings (parent x offspring or full sibling x sibling). [1]

(b)(ii) One risk of continuing line breeding for too many generations is inbreeding depression. As relatedness accumulates, harmful recessive alleles become homozygous, leading to reduced fertility, smaller litters, lower disease resistance, and poorer overall performance. [1]

(c) Boar D has the best feed conversion ratio at 2.8. [1] A lower feed conversion ratio means the animal converts feed into body mass more efficiently - it needs fewer kilograms of feed to gain one kilogram of body weight. Therefore Boar D is the most feed-efficient, reducing feed costs per kilogram of pork produced. [1]

(d) A farmer might choose to buy hybrid breeding stock from a commercial breeder rather than running an on-farm programme because:

1. Hybrid stock may display hybrid vigour (heterosis), giving faster growth, better feed conversion, and improved reproductive performance compared to purebred animals. [1]
2. Purchasing ready-made hybrids saves the farmer years of time and the specialist expertise required to maintain pedigree records, conduct progeny tests, and manage a multi-generation selection programme. [1]

(e) Two other characteristics a pig farmer might select for:

1. Backfat thickness / lean meat percentage - consumers and processors prefer leaner carcasses, so selecting for low backfat increases the market value of each pig. [1]
2. Growth rate / daily weight gain - faster-growing pigs reach slaughter weight sooner, reducing the total feed cost per animal and increasing throughput. [1]

(f) One way selective breeding differs from natural selection:

In selective breeding, humans deliberately choose which animals are allowed to reproduce, based on traits the farmer considers economically desirable (such as litter size or growth rate). [1] In natural selection, the environment determines which animals survive and reproduce. Traits that aid survival and reproduction in that environment are favoured, regardless of whether they are useful to humans. Selective breeding is therefore directed towards human goals, while natural selection is driven by environmental fitness. [1]