WAEC SSCE - Biology - 2014

Maelezo ya Majibu

Maelezo ya Majibu

In dihybrid inheritance, Mendel considered two pairs of contrasting characters. This means that he studied how two different traits, each with two different variations, are inherited together. For example, he studied pea plants that had different colors for their seeds (yellow or green) and different shapes for their pods (inflated or constricted). By studying how these traits were passed down from generation to generation, Mendel was able to develop his laws of inheritance, which are still used today to understand how traits are passed down from parents to their offspring.

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Rhizopus is the most specialized organism among the given options. Rhizopus is a fungus that belongs to the class Zygomycetes, and it is characterized by the formation of a specific structure called a zygospore during sexual reproduction. Rhizopus is also known for its ability to grow and spread rapidly on organic materials, and it is commonly found on bread, fruits, and other decaying plant matter. In contrast, paramecium, amoeba, and spirogyra are all unicellular organisms that lack specialized tissues and organs, making them less specialized than Rhizopus.

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Among the adaptations listed, the one that is not associated with the flight of birds is "clawed digits." Birds have evolved many adaptations to enable them to fly, including reduced body weight, streamlined shape, and powerful muscles. Reducing body weight makes it easier for birds to take off and stay in the air, while their streamlined shape reduces air resistance and allows for more efficient flight. Birds also have powerful muscles that enable them to flap their wings and generate lift. However, clawed digits are not necessary for flight and are not typically associated with this adaptation. Instead, birds have evolved specialized feet and toes that are adapted for perching, walking, and capturing prey.

Maelezo ya Majibu

Maelezo ya Majibu

Gaseous exchange is not a function of mammalian skin. Mammalian skin is made up of multiple layers, with the outermost layer being the epidermis, which is impermeable to gases. Therefore, it cannot facilitate gaseous exchange. Instead, gaseous exchange in mammals occurs through the respiratory system, which includes the lungs and associated structures. In contrast, the other options mentioned are all functions of the mammalian skin. The skin helps regulate body temperature through processes such as sweating and blood vessel dilation/contraction. The skin also contains sensory receptors that allow for the reception of external stimuli such as touch, pressure, and temperature. Additionally, the skin can excrete waste products such as salts, water, and small amounts of urea through sweat glands.

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Characteristics that exhibit continuous variation are generally controlled by multiple genes. Continuous variation refers to traits that can vary along a continuous range, such as height or weight. These traits are not controlled by a single gene, but rather by the combined effects of multiple genes, often with additive effects. This is why the distribution of traits in a population tends to follow a bell-shaped curve, with most individuals clustering around the average and fewer individuals at the extremes.

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Coal is a non-renewable natural resource. This means that once it is extracted from the earth and used, it cannot be replenished or replaced within a human lifespan. Coal takes millions of years to form, and therefore it is not considered a sustainable resource. In contrast, resources such as water and air are renewable, as they can be replenished naturally over time. Forests can be renewable if they are managed sustainably, but if they are over-harvested or destroyed, it can take many years for them to regrow and function as they did before.

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Out of the options given, sickle cell anemia is the disease that can be inherited. Sickle cell anemia is an inherited genetic disorder that affects the red blood cells. It is caused by a mutation in the HBB gene that provides instructions for making a protein called hemoglobin, which carries oxygen in the blood. In sickle cell anemia, the mutation leads to the production of abnormal hemoglobin, which causes the red blood cells to become rigid, sticky and sickle-shaped. These cells can block small blood vessels, leading to pain, organ damage, and other complications. Sickle cell anemia is an example of an inherited disease, meaning it is passed down from parent to child through their genes.

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The placenta is an organ that connects the mother's blood supply to the developing foetus, allowing for the exchange of nutrients, oxygen, and waste products. Carbon dioxide and glucose are two examples of substances that pass from the mother's blood into the foetus's blood through the placenta. However, viruses do not pass from the mother's blood to the foetus's blood through the placenta. Similarly, antibodies, which are produced by the mother's immune system, can cross the placenta and provide passive immunity to the foetus against certain infections, so they also pass from the mother's blood to the foetus's blood through the placenta.

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The part labelled II in the diagram is the contractile vacuole. A contractile vacuole is an organelle found in certain unicellular organisms that helps to regulate water content within the cell. It works by actively pumping excess water out of the cell, which helps to prevent the cell from bursting due to osmotic pressure. The contractile vacuole is easily identified in the diagram due to its spherical shape and proximity to the cell membrane.

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Older parts of plant roots do not normally absorb water because they lack root hairs. Root hairs are tiny protrusions from the epidermal cells of the root that increase the surface area for water and mineral absorption. As roots get older, the root hairs wear out and do not regenerate, leading to reduced surface area and a decrease in the plant's ability to absorb water and minerals. However, the xylem, which transports water and minerals, is present in the entire length of the root, including the older parts.

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The new plant reproduced asexually with the same genotype as the parent plant. This process is called vegetative propagation, where a new plant is produced from a vegetative part of the parent plant (in this case, a stem) without the involvement of gametes or fertilization. The new plant is essentially a clone of the parent plant and has the same genetic makeup.

Maelezo ya Majibu

Maelezo ya Majibu

Bacteria like Azotobacter are found in the root nodules of leguminous plants. Leguminous plants, such as beans, peas, and peanuts, have a symbiotic relationship with certain bacteria, including Azotobacter. The bacteria are able to take nitrogen gas from the air and convert it into a form of nitrogen that the plant can use for growth, in exchange for carbohydrates that the plant produces. The root nodules of the leguminous plant provide a suitable environment for the bacteria to live and carry out this process, which is important for the growth and development of the plant. Therefore, the correct option is "in the root nodules".

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The statement that is not correct about the circulation of water in nature is "removed from ocean is permanently lost". This is incorrect because water removed from the ocean through evaporation is not permanently lost, but rather it goes through the water cycle, which is the continuous movement of water on, above, and below the surface of the Earth. The water cycle involves the evaporation of water from oceans, lakes, and rivers, which then forms clouds in the atmosphere. These clouds then release water in the form of precipitation (rain, snow, sleet, or hail) which falls on the land surface and replenishes rivers, lakes, and groundwater. Therefore, the water that evaporates from the ocean is not permanently lost but rather becomes part of the Earth's water cycle.

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Differences in characteristics that exist among individuals of the same species is referred to as variation. This means that individuals of the same species can have different traits or features, such as height, weight, color, or behavior. Variation can be influenced by genetic factors, environmental factors, or a combination of both. The presence of variation is important for the process of natural selection, which allows individuals with advantageous traits to survive and reproduce, while individuals with less advantageous traits are less likely to survive and pass on their genes to the next generation.

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A characteristic feature of plant parasites is the development of haustoria. Haustoria are specialized organs that penetrate the host plant's tissue and allow the parasite to absorb nutrients and water from the host plant. This is a common adaptation seen in parasitic plants, such as mistletoe and dodder. Possession of holdfast, rhizoids or development of hanging roots are not necessarily associated with parasitism but may be adaptations for anchoring or absorbing nutrients in non-parasitic plants.

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A meal consisting of yam and a lot of vegetables is not balanced because it does not contain enough proteins. While yam and vegetables are good sources of carbohydrates, vitamins, and minerals, they lack significant amounts of protein. Proteins are essential nutrients that play a crucial role in building and repairing body tissues, enzymes, and hormones. A balanced meal should contain a variety of foods from different food groups, including carbohydrates, proteins, vitamins, and minerals, in the right proportions.

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Grasshoppers are not social insects. Social insects are those that live in highly organized colonies or communities where there are divisions of labor, communication, and cooperation among individuals. Examples of social insects include termites, ants, and bees. Grasshoppers, on the other hand, are solitary insects that do not live in colonies or exhibit social behavior.

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The correct statement about chromosomes is that the chromosome number present in a species is constant. Chromosomes are thread-like structures found in the nucleus of a cell and carry genetic information in the form of DNA. Each species has a specific number of chromosomes, and this number is constant within the species. For example, humans have 46 chromosomes, dogs have 78 chromosomes, and cats have 38 chromosomes. Chromosomes vary in size, shape, and arrangement, and they are not neatly arranged in the cytoplasm. The outer membrane of the nucleus bears nuclear pores, which allow molecules such as RNA to move in and out of the nucleus, but not ribosomes. The ability to bear ribosomes is a characteristic of the rough endoplasmic reticulum, which is an organelle involved in protein synthesis.

Maelezo ya Majibu

Maelezo ya Majibu

Maelezo ya Majibu

Maelezo ya Majibu

The correct answer is "allows for quick regrowth of grasses". This statement does not provide a reason for banning bush burning. In fact, it suggests that bush burning could be beneficial for the regrowth of grasses. However, the other options provide reasons for banning bush burning, such as killing soil microorganisms, leaving the soil bare of vegetation, and burning off organic soil nutrients.

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Osmosis is the movement of water molecules from an area of higher concentration to an area of lower concentration through a semi-permeable membrane. In the context of yam tissues, osmosis will occur in those tissues that are separated from their environment by a semi-permeable membrane. Out of the given options, the tissues that are most likely to undergo osmosis are the raw and peeled yam tissues. This is because the raw yam tissues have intact cell membranes which act as semi-permeable membranes, allowing the movement of water molecules in and out of the cells through osmosis. Additionally, peeling the yam removes the waxy cuticle layer which further enhances the permeability of the cell membrane to water molecules. On the other hand, boiling and roasting alter the cell structure of the yam tissues, making them less likely to undergo osmosis. Boiling and roasting cause the cell walls to rupture and lose their semi-permeable nature, which makes it difficult for water molecules to move in and out of the cells through osmosis. In summary, osmosis is most likely to occur in the raw and peeled yam tissues, as they have intact cell membranes that act as semi-permeable membranes. The boiled and unpeeled yam tissues may also undergo osmosis, but to a lesser extent due to the alteration of the cell walls caused by boiling. The roasted and peeled yam tissues are the least likely to undergo osmosis due to the complete alteration of the cell structure caused by roasting.

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The trait that is not a morphological variation in humans is the ability to taste PTC. PTC is a chemical substance that is either bitter or tasteless to people depending on their genetic makeup. While colour, fingerprints, and size are physical traits that can vary among individuals, the ability to taste PTC is not a visible or physical characteristic. Instead, it is determined by a person's genetic makeup, specifically a gene called TAS2R38. Therefore, the ability to taste PTC is not considered a morphological variation, but rather a genetic variation.

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Lamarck's theory of evolution is based on the idea that organisms can acquire new traits during their lifetime through use or disuse of certain body parts, and that these acquired traits can be passed down to their offspring. In other words, Lamarck believed that an organism can change its characteristics over time, and those changes can be inherited by its offspring. This is known as the theory of inheritance of acquired characteristics. However, this theory has been largely discredited by modern science, as it is now understood that genetic information is only passed down through DNA, and not through changes that occur during an organism's lifetime.

Maelezo ya Majibu

During germination, the embryo in a seed grows into a new plant. In order for the embryo to grow, it needs energy and building materials. The energy is obtained through respiration, which breaks down stored food molecules such as starch into smaller molecules that can be used by the plant. Therefore, the starch in the seed is used up as a source of energy for respiration and for building new cells as the plant grows. This is why the amount of starch in a germinating seed decreases. The other options, building cellulose cell wall, developing meristematic tissues, and producing enzymes, may require energy and building materials, but do not directly lead to the breakdown of starch.

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Among the options provided, the condition that enhances self-pollination in flowering plants is cleistogamy. Cleistogamous flowers are self-fertile and never open, meaning the anthers and stigma are in close proximity to facilitate self-pollination. This adaptation is useful in ensuring successful reproduction even when pollinators are scarce or absent. Heterostyly, protandry, and protogyny are mechanisms that promote cross-pollination. Heterostyly involves the presence of flowers with different style and stamen lengths, which promotes cross-pollination between different plants. Protandry is the condition where the anthers mature before the stigma, while protogyny is the opposite condition where the stigma matures before the anthers. Both conditions promote cross-pollination as they encourage the plant to receive pollen from a different plant or source.

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The correct sequence of events during mitosis is: II. Chromosomes become visible; III. Chromosomes align at the equator; I. Chromatids separate; IV. Cytoplasm divides (Cytokinesis). This means that first, the chromosomes become visible, then they align at the equator, then the chromatids separate, and finally, the cytoplasm divides to form two daughter cells.

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To conduct a Biuret test, after adding sodium hydroxide to the protein solution, copper sulphate should be added to the mixture for a positive result. This is because the Biuret test is a colorimetric test used to detect peptide bonds in proteins. When copper (II) ions react with peptide bonds in an alkaline solution, a complex is formed that results in a violet or purple color. Therefore, the presence of copper sulphate in the protein-sodium hydroxide mixture is necessary for the test to detect the presence of protein.

Maelezo ya Majibu

The correct answer is: a community is made up of populations of living organisms while a population is made up of organisms of the same species. A population refers to a group of individuals of the same species living in a particular area at a particular time, while a community refers to all the populations of different species living in a particular area at a particular time. For example, a population can refer to all the lions in a particular game reserve, while the community would include all the different species of organisms living in the same game reserve, such as lions, zebras, giraffes, and many others. Therefore, the main difference between a community and a population is that a community includes different populations of different species, while a population includes individuals of the same species.

Maelezo ya Majibu

Maelezo ya Majibu

The inability to maintain proper balance of the body in humans may be due to a defect in the Semi-circular canals. The Semi-circular canals are three fluid-filled tubes located in the inner ear that are responsible for maintaining balance and detecting head movements. When the head moves, the fluid in the canals moves, which sends signals to the brain to help the body maintain its balance. If there is a defect in the semi-circular canals, it can affect the normal functioning of the balance system and cause balance problems such as vertigo, dizziness, and unsteadiness.

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In genetics, the physical appearance or trait expressed by an organism is determined by the alleles it inherits from its parents. Alleles are different versions of the same gene, and they can be either dominant or recessive. In this case, the F1 generation (first filial generation) of a cross between a red cock and white hen were all red, which means that they inherited the red allele from the red cock parent. The gene for the red color is dominant over the gene for white color, which is recessive. Therefore, in the F1 generation, all the offspring expressed the dominant allele for red color and not the recessive allele for white color, which did not segregate. Thus, the correct option is "red color was dominant".

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An inferior ovary of a flower is situated below the floral parts. In a flower, the ovary is the structure that contains the ovules and later develops into a fruit. If the ovary is inferior, it means that it is located beneath the attachment point of the other floral parts such as the petals, sepals, and stamens. The inferior ovary is often surrounded by a floral tube formed by the fusion of the sepals, petals, and stamens. This is in contrast to a superior ovary, which is located above the attachment point of the other floral parts.

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Yeast is a living organism. Yeast is a type of fungus that belongs to the Kingdom Fungi. It is a unicellular organism, meaning it is made up of a single cell, and it can reproduce asexually by budding. Yeast is commonly used in baking and brewing because it can convert sugar into alcohol and carbon dioxide through a process called fermentation. In addition to being used in food production, yeast is also used in scientific research as a model organism to study genetics and cell biology.

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Protozoans are single-celled organisms that carry out various life processes. Like other living things, they produce waste products, which must be excreted from their bodies to maintain the proper internal environment. The excretory product in protozoans is usually ammonia, a compound that is produced when proteins are broken down during cellular metabolism. Ammonia is highly toxic to cells and needs to be excreted quickly to avoid damaging the organism. Therefore, protozoans have specialized structures that help them get rid of excess ammonia, such as contractile vacuoles or diffusion through the cell membrane. Other excretory products such as urea, uric acid or amino acids are commonly found in more complex organisms with more advanced excretory systems.

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Lysosome is the cell inclusion that can destroy other cell organelles. Lysosomes are membrane-bound organelles that contain enzymes capable of breaking down biomolecules. They function as the cell's digestive system, breaking down worn-out organelles, cell debris, and foreign substances that have been ingested by the cell. In the process of autophagy, lysosomes also degrade and recycle old or damaged cell components. Therefore, lysosomes have the ability to destroy other cell organelles.

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Nuptial flight in termites is a behavior that involves the winged reproductive individuals leaving their parent colony to mate and start new colonies. The main reason for nuptial flight in termites is to form new colonies. During nuptial flight, male and female reproductive termites leave the parent colony and fly together in search of a suitable site for starting a new colony. Once they find a suitable site, they shed their wings and mate, after which the female starts to lay eggs and establish a new termite colony. Therefore, the main reason for nuptial flight in termites is to ensure the survival and propagation of the species through the formation of new colonies.

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The correct option is "temperate grassland". West Africa is known for its diverse ecological zones, which include mangrove swamps, Sahel savanna, and savanna grassland. However, temperate grasslands are not found in West Africa. Temperate grasslands are typically located in regions with a continental climate and moderate rainfall, such as the Great Plains in North America, the Pampas in South America, and the steppes of Eurasia. They are characterized by vast expanses of grasses and few trees, with hot summers and cold winters. In contrast, West Africa is located near the equator and has a tropical climate, with high temperatures and distinct wet and dry seasons.

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The correct statement about asexual reproduction is that it always involves one parent and the offspring is genetically identical to the parent. In asexual reproduction, a single parent organism produces offspring that are genetically identical to itself, without the involvement of gametes or the fusion of nuclei. This type of reproduction is common in simple organisms like bacteria, protists, and some plants. The offspring produced through asexual reproduction have the same DNA as the parent organism, which means they are genetically identical. This process helps to maintain the characteristics of a particular species over time.

Maelezo ya Majibu

Maelezo ya Majibu

(a) Ecological terms

• (i) Biosphere: the part of the earth (land, water and air) and its atmosphere in which living organisms exist and can survive.
• (ii) Habitat: the specific place or natural environment where an organism (or community) lives, feeds and reproduces.

(b) Mode of nutrition in a named carnivorous plant (Sundew, Drosera): the sundew is a green plant that photosynthesises but grows in nitrogen-poor soil, so it supplements its nitrogen by trapping insects. Its leaves bear tentacles tipped with a sticky, glistening fluid that attracts and traps insects. When an insect lands, the tentacles bend inwards and hold it fast. The leaf then secretes digestive enzymes that break down the insect's proteins into soluble nitrogenous compounds, which are absorbed by the leaf. (Pitcher plant or Venus fly-trap are equally acceptable.)

(c) Three reasons why dispersal of fruits and seeds is important

• To reduce overcrowding and competition for light, water, space and nutrients between parent and offspring.
• To spread the species to new areas and colonise fresh habitats.
• To reduce the spread of diseases and pests among plants of the same kind.

(d) Six methods of conserving soil

• Crop rotation.
• Terracing on slopes.
• Contour ploughing/ridging.
• Afforestation and planting cover crops (mulching).
• Strip cropping.
• Building of windbreaks/shelter belts and avoiding overgrazing/bush burning.

Maelezo ya Majibu

(a) Definitions

• (i) Elimination (egestion): the removal of undigested food materials (faeces) from the alimentary canal through the anus.
• (ii) Excretion: the removal from the body of waste products of metabolism, such as carbon dioxide, urea and excess water and salts.
• (iii) Secretion: the production and release of useful substances (such as enzymes, hormones and mucus) by cells or glands for use in the body.

(b) Digestion of boiled fish (protein) in the human gut

1. Mouth: the fish is chewed and mixed with saliva to form a bolus; no chemical digestion of protein occurs here.
2. Stomach: gastric juice containing hydrochloric acid and the enzyme pepsin acts on the protein. Pepsin digests proteins into peptones and polypeptides. \(\text{Proteins} \rightarrow \text{peptones/polypeptides}\)
3. Duodenum: pancreatic juice adds trypsin, which continues breaking proteins and peptones into smaller peptides.
4. Ileum: intestinal juice contains peptidase (erepsin) which completes digestion, converting peptides into amino acids. \(\text{Peptides} \rightarrow \text{amino acids}\)
5. The soluble amino acids are then absorbed into the bloodstream through the villi.

(c) A labelled longitudinal-section diagram of a villus, 8-10 cm long, is required (showing epithelium, lacteal, blood capillary network, arteriole, venule and goblet cells).

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(a)(i) Three characteristics of living organisms: nutrition, respiration, and movement (growth, reproduction, excretion, irritability/sensitivity are also valid).

(ii) Brief explanation

• Nutrition: the taking in and use of food materials for energy, growth and repair of the body.
• Respiration: the breakdown of food in cells to release energy needed for life activities.
• Movement: the ability of an organism, or parts of it, to change position or place.

(b) Four differences between plants and animals

(c)(i) Organism exhibiting both plant and animal features: Euglena.

(ii) Four animal features: moves using a flagellum; has a contractile vacuole; has an eyespot (stigma) sensitive to light; lacks a cellulose cell wall (has a flexible pellicle) and can feed heterotrophically.

Two plant features: possesses chloroplasts and carries out photosynthesis; contains pyrenoids associated with food (starch) storage.

Maelezo ya Majibu

(a) Five reasons why animals move from place to place

• To search for food.
• To find water.
• To escape from predators and danger.
• To search for a mate for reproduction.
• To seek shelter or favourable conditions (suitable temperature, breeding sites).

(b) One function each of plant structures

• (i) Epidermis: protects the inner tissues and (in leaves) reduces water loss.
• (ii) Phloem: transports (translocates) manufactured food from the leaves to other parts of the plant.
• (iii) Sclerenchyma: provides mechanical support and strength to the plant.

(c) Two examples each

• (i) Parasitic plants: mistletoe and dodder (Cassytha).
• (ii) Saprophytes: Mucor and Rhizopus (mushrooms/toadstools also acceptable).

(d) Two adaptive features of salt-water-swamp (mangrove) plants: possession of breathing roots (pneumatophores) for gaseous exchange in waterlogged mud; and viviparous germination (seeds germinate while still attached to the parent) with prop/stilt roots for support.

(e) Population density

• (i) Increase: high birth rate (natality) and immigration (or abundant food).
• (ii) Decrease: high death rate (mortality) and emigration (or disease/predation).

(f) Four ways modern agriculture threatens species survival

• Clearing of forests (deforestation) destroys natural habitats.
• Use of pesticides and herbicides kills non-target organisms.
• Bush burning destroys organisms and their habitats.
• Monoculture and drainage of wetlands reduce biodiversity; overgrazing degrades land.

(g) Three reasons why mitosis is important

• It brings about growth by increasing the number of cells.
• It enables repair and replacement of worn-out or damaged cells.
• It maintains a constant chromosome number and enables asexual reproduction.

(h) Three causes of food spoilage: activity of microorganisms (bacteria and fungi); action of enzymes in the food (autolysis); and attack by pests/insects (also moisture, heat and improper storage).

Maelezo ya Majibu

(a)(i) Co-dominance

Co-dominance is a condition in which both alleles of a gene are fully and equally expressed in a heterozygous individual. Neither allele masks the other. For example, \(I^A\) and \(I^B\) are co-dominant alleles; hence \(I^AI^B\) produces blood group AB.

Survey calculations

Blood group	Percentage	Number out of 250
A	8.0%	20
B	14.0%	35
AB	32.8%	82
O	45.2%	113

(a)(ii) The co-dominant blood group is AB.

\[\frac{32.8}{100}\times250=82\]

Therefore, 82 individuals have the co-dominant blood group.

(a)(iii) A person with blood group B can receive blood from persons with blood groups B and O.

\[\text{Number with group B}=\frac{14.0}{100}\times250=35\]

\[\text{Number with group O}=\frac{45.2}{100}\times250=113\]

\[35+113=148\]

Therefore, 148 individuals can donate blood to the accident victim with blood group B.

(b) Genetic diagram

Heterozygous blood group A man: \(I^Ai\)
Blood group AB woman: \(I^AI^B\)

Gametes from the man are \(I^A\) and \(i\), while gametes from the woman are \(I^A\) and \(I^B\).

The possible genotypes and phenotypes of the children are:

• \(I^AI^A\): blood group A
• \(I^Ai\): blood group A
• \(I^AI^B\): blood group AB
• \(I^Bi\): blood group B

Thus, the possible blood groups are A, AB and B, in the ratio:

\[2\text{ A}:1\text{ AB}:1\text{ B}\]

That is, 50% blood group A, 25% blood group AB and 25% blood group B. No child will have blood group O.