WAEC SSCE - Biology - 2005

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In the marine food web, the source of energy for producers comes from the sun. This is because plants and algae, which are the primary producers in the marine ecosystem, use sunlight to carry out photosynthesis and produce organic matter. This organic matter serves as a source of food and energy for other organisms in the food web, such as herbivores and carnivores. Therefore, the sun plays a crucial role in providing energy for life in the ocean.

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If the pink color of a petal is dominant over white, then when a pure pink flowered plant is crossed with a white flowered plant, all of the F1 generation plants will have pink flowers. This is because the dominant trait (pink) will mask the recessive trait (white). However, when the F1 generation plants are crossed with each other, their offspring in the F2 generation will have a 3:1 ratio of pink to white flowers. This is because each parent plant in the F1 generation carries one pink allele and one white allele, but only expresses the pink trait. When they produce gametes (reproductive cells), there is a 50% chance that the gamete will carry the pink allele and a 50% chance that it will carry the white allele. So, when the F1 plants are crossed with each other, there is a 25% chance that both parents will contribute a white allele to their offspring, resulting in a white flowered plant. The other 75% of the offspring will have at least one pink allele, resulting in pink flowers. Therefore, the color of the flower of the F2 generation would be a mixture of pink and white flowers, with a ratio of 3 pink flowers to 1 white flower. Purple and yellow are not relevant to this scenario, as the question only mentions pink and white flowers.

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The appendix is the organ that can be considered vestigial in humans but functional in other mammals. The appendix is a small, thin, finger-shaped pouch attached to the large intestine. In humans, the appendix does not appear to have any significant function, but in other mammals, it is used to digest cellulose, a tough carbohydrate found in plants. Therefore, in humans, the appendix is considered a vestigial organ, which means it no longer serves a useful function. However, in some cases, the appendix can become infected, leading to a condition called appendicitis, which requires medical attention.

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The organism that is well adapted for fluid feeding is the mosquito. Mosquitoes are adapted to feed on fluids because their mouthparts are specially designed to pierce the skin of animals, including humans, and suck blood. Mosquitoes have a long, thin, and flexible proboscis that can be easily inserted into the skin of animals. Additionally, their saliva contains anticoagulants that prevent the blood from clotting, which allows them to feed for longer periods. Mosquitoes are also able to detect their prey through the carbon dioxide and other chemicals that animals release, which helps them to find their targets.

Maelezo ya Majibu

Maelezo ya Majibu

The organism that changes light energy into stored chemical energy in an ecosystem is the producer. Producers, also known as autotrophs, are organisms that can synthesize their own organic molecules, such as glucose, from inorganic sources like water and carbon dioxide. They do this through the process of photosynthesis, which involves using light energy from the sun to convert inorganic molecules into organic molecules. Plants, algae, and some bacteria are examples of producers. They form the base of the food chain in an ecosystem, as they are the only organisms capable of producing their own energy-rich organic molecules. All other organisms in the ecosystem rely on these producers, either directly or indirectly, for their energy needs. Consumers, on the other hand, are organisms that cannot produce their own organic molecules and must obtain them from other organisms. Decomposers are organisms that break down dead organic matter and recycle nutrients back into the ecosystem. Carnivores are a type of consumer that primarily eat meat. Therefore, the organism that changes light energy into stored chemical energy in an ecosystem is the producer.

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Maelezo ya Majibu

The main similarity between unicellular and multicellular organisms is that both perform all life activities. This means that both types of organisms carry out the essential functions necessary for life, such as obtaining nutrients, producing energy, reproducing, and responding to their environment. However, the way in which these activities are carried out differs between unicellular and multicellular organisms. Unicellular organisms perform all of these activities within a single cell, while multicellular organisms have specialized cells and tissues that perform specific functions, such as the heart for pumping blood or the lungs for breathing.

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The basis of growth involves the following processes: cell division, cell differentiation, and cell enlargement. These processes work together to increase the number, diversity, and size of cells in an organism. However, cell reduction is not a process involved in growth. In fact, cell reduction is a process that can occur in certain situations, such as during programmed cell death or in response to injury or disease. Therefore, cell reduction is not a part of the normal growth process.

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When you bend your arm, the biceps contract and the triceps relax. The biceps muscle is located in the front of the upper arm and is responsible for flexing the elbow joint, while the triceps muscle is located at the back of the upper arm and is responsible for extending the elbow joint. When you want to bend your arm, your brain sends a signal to your biceps muscle to contract, causing the biceps to shorten and pull the forearm upward. At the same time, your brain sends a signal to your triceps muscle to relax, allowing the arm to bend. When you want to straighten your arm, your triceps muscle contracts, causing the triceps to shorten and pull the forearm downward. At the same time, your biceps muscle relaxes, allowing the arm to straighten. Therefore, is the correct statement about the movement of the forearm.

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The stable self-sustaining environment produced by an interaction between the biotic (living) and abiotic (non-living) components is best described as an ecosystem. An ecosystem consists of all the living organisms (biotic) in a particular area, as well as the physical and non-living (abiotic) factors in the environment such as water, air, soil, sunlight, temperature, and climate. These components interact with each other to form a stable and sustainable environment where organisms can thrive and survive. A habitat is a specific place where an organism lives, while a niche is the role or function that an organism has within its habitat. A community refers to all the different species of organisms living in a particular area or ecosystem.

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The means of conservation that is not effective is the burning of vegetation before cropping. This is because burning vegetation releases carbon dioxide into the atmosphere which contributes to climate change. It can also lead to soil erosion and loss of soil fertility, making it difficult for new crops to grow in the future. On the other hand, controlling excessive deforestation, prevention of poaching and replacing harvested mature trees with seedlings are all effective means of conservation. Controlling excessive deforestation helps to maintain a healthy balance between the amount of carbon dioxide in the atmosphere and the number of trees available to absorb it. Prevention of poaching helps to protect endangered animal species and maintain a balance in the ecosystem. Replacing harvested mature trees with seedlings ensures that new trees are planted to replace the ones that were cut down, helping to maintain the forest cover and prevent soil erosion.

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In active transport, molecules move from a region of low concentration to a region of high concentration. This is against the natural tendency of molecules to move from a region of high concentration to a region of low concentration, which is known as the concentration gradient. Active transport requires the use of energy to transport molecules across a cell membrane, such as through the use of specialized proteins or pumps. Therefore, active transport is essential for maintaining the proper balance of molecules inside and outside of cells.

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Maelezo ya Majibu

Maelezo ya Majibu

Edaphic is the factor that is not associated with aquatic habitats. This term refers to the study of soil characteristics and their relationship with plants, but it has no relevance to aquatic environments. Aquatic habitats are characterized by specific physical and chemical factors that are different from those of terrestrial habitats. Salinity is the concentration of dissolved salts in water, which affects the types of organisms that can survive in it. Turbidity is a measure of the clarity of water and is affected by the presence of suspended particles. Temperature is a critical factor that influences the metabolic rates and distribution of aquatic organisms. In summary, edaphic is not associated with aquatic habitats because it is a term that relates to soil characteristics and not water.

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Fats have the highest amount of energy in joules per unit weight compared to carbohydrates, proteins, and vitamins. This is because fats have more carbon-hydrogen bonds in their molecular structure, which store more energy than the oxygen-hydrogen bonds found in carbohydrates and proteins. When fats are broken down through a process called metabolism, they release more energy per unit weight than carbohydrates and proteins. Therefore, foods that are high in fat tend to have a higher caloric value than foods that are high in carbohydrates or proteins. Vitamins, on the other hand, are essential micronutrients that do not provide energy when metabolized and therefore are not a significant source of calories.

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A population is best described as a group of the same species of organisms living together in a specific area or habitat. This means that all members of the population are of the same type and can potentially interbreed with each other to produce fertile offspring. For example, a population of deer may live in a forested area and consist of only one species of deer. The size of a population can vary depending on factors such as availability of resources and environmental conditions. Understanding population dynamics is important for conservation efforts and managing natural resources.

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Measles is unlikely to respond to antibiotic treatment. Measles is a highly contagious viral infection that is spread through respiratory droplets. Antibiotics are used to treat bacterial infections, not viral infections like measles. In some cases, antibiotics may be prescribed to prevent secondary bacterial infections that can occur as a result of measles, but they do not treat the measles virus itself. Therefore, the primary treatment for measles involves supportive care, such as rest, hydration, and fever reduction.

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The variation that exhibits a wide range from one extreme to the other with very little difference between the intermediates is called continuous variation. This type of variation can be seen in traits that are controlled by multiple genes and are influenced by both genetic and environmental factors. For example, human height is a trait that shows continuous variation, where individuals can vary in height from very short to very tall, with a wide range of intermediate heights in between. This type of variation can be represented by a bell-shaped curve, where most individuals fall in the middle of the range and fewer individuals are found at the extremes. In contrast, discontinuous variation refers to traits that have distinct, non-overlapping categories, such as blood type or eye color, and phenotypic and genotypic variations are related to the expression of traits, but they do not describe the range of variation exhibited.

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The correct statement is: "The genotype is affected". Mutation refers to a change in the DNA sequence of an organism. DNA is the genetic material that carries the instructions for the development and functioning of living things. A mutation can occur spontaneously or can be induced by external factors such as radiation or chemicals. When a mutation occurs, it affects the genotype of an organism by altering the sequence of nucleotides in its DNA. This, in turn, can lead to changes in the phenotype (observable traits) of an organism. These changes can be either beneficial, harmful, or neutral depending on the specific mutation and the environment in which the organism lives. Therefore, it is accurate to say that the genotype is affected by a mutation.

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Mollusca is a phylum of animals that are mostly characterized by having soft, non-segmented bodies. This means that their bodies are not divided into distinct segments, as is the case with other animals like insects and worms. Mollusks also have a hard external shell that protects their bodies, although some species have lost their shells or have internal shells. Examples of mollusks include snails, clams, squid, and octopuses.

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The pair of organisms that are photosynthetic are Chlamydomonas and Euglena. Photosynthesis is the process by which plants and certain other organisms convert light energy into chemical energy in the form of organic compounds, such as carbohydrates. Chlamydomonas and Euglena are both unicellular organisms that are capable of photosynthesis, meaning they can produce their own food using energy from the sun. On the other hand, Amoeba and Paramecium are heterotrophic organisms, which means they obtain their energy by consuming other organisms. Volvox is a colonial organism made up of many cells, some of which are capable of photosynthesis, but it is not a unicellular organism. Rhizopus is a type of fungus that obtains its energy by absorbing nutrients from decaying organic matter. Nostoc is a type of cyanobacteria that is capable of photosynthesis, but Plasmodium is a parasitic protozoan that relies on a host organism for its energy needs.

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Maelezo ya Majibu

The organism that causes syphilis is Treponema pallidum. Syphilis is a sexually transmitted disease that is caused by this bacterium. It spreads from person to person through direct contact with a syphilis sore during sexual activity. The bacteria can enter the body through tiny cuts or breaks in the skin or mucous membranes. If left untreated, it can cause serious health problems, including damage to the heart and brain. It is important to seek medical attention if you think you may have syphilis.

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A person with blood group B can donate blood to individuals with blood group B and AB. This is because people with blood group B have antigens on the surface of their red blood cells that are recognized by the immune system of individuals with blood group B and AB. These antigens are not present on the red blood cells of people with blood group A or O. However, people with blood group B should not donate blood to individuals with blood group A or O because the immune system of individuals with blood group A or O will recognize the antigens on the surface of the red blood cells as foreign and attack them. This can cause serious complications and even be life-threatening. So, in summary, people with blood group B can donate blood to individuals with blood group B and AB, but not to individuals with blood group A or O.

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The juice that contains the enzyme ptyalin is saliva. Ptyalin, also known as salivary amylase, is an enzyme that breaks down carbohydrates in the mouth. When you chew your food, your saliva glands produce saliva that contains ptyalin, which begins the process of breaking down carbohydrates into simpler sugars that can be absorbed by the body. This is why it's important to chew your food thoroughly, to allow the ptyalin in saliva to work effectively. The other juices listed, such as gastric juice, pancreatic juice, and succus, do not contain ptyalin and have different functions in the digestive process.

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Polymorphism is not an evidence of evolution. Polymorphism refers to the presence of different forms or types of a trait within a population. While it can be influenced by evolutionary processes such as natural selection or genetic drift, polymorphism alone is not enough to prove that evolution has occurred. On the other hand, fossil records, comparative embryology, and comparative anatomy are all strong evidence for evolution. Fossil records show the progression of life forms over time, while comparative embryology reveals similarities in early development across species that suggest a common ancestry. Comparative anatomy also reveals similarities in the structures and functions of organisms that suggest evolutionary relationships.

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The biological classification system groups living organisms into different categories based on their characteristics and evolutionary relationships. Among the given options, the group that includes all the others is the "Kingdom." A kingdom is a taxonomic rank that consists of a group of similar phyla. In other words, a kingdom is a larger and more inclusive group than phylum, class, or species. All organisms are classified into one of the five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. Each kingdom is then further divided into smaller and more specific groups such as phylum, class, order, family, genus, and species. Therefore, all living organisms belong to a kingdom, and each kingdom includes several phyla, classes, and species. So, the Kingdom embraces all the other given options.

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Phosphorus is required in large amounts by plants. It is an essential nutrient for plant growth and development, playing a vital role in many biological processes such as photosynthesis, energy transfer, and cell division. Phosphorus is also important for the development of strong roots and seeds. Without enough phosphorus, plants will have stunted growth and poor yields. Therefore, it is crucial to ensure that plants receive an adequate supply of phosphorus through the soil or fertilizers to promote healthy growth and high yields.

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The density-dependent factors that operate to regulate a population size may include the shortage of food supply, spread of diseases, and increased competition. These factors are influenced by the size of the population, as they become more significant when the population density is high. For example, when there are too many individuals in a population and not enough food, competition for resources increases and the population size may decrease as a result. Similarly, diseases can spread more easily when there are more individuals living in close proximity to each other. However, fire outbreak is not considered a density-dependent factor because it is not influenced by the size of the population. It can occur regardless of the population size and is more likely to be influenced by factors such as weather conditions or human activity.

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Fertilization is the process by which a sperm cell fuses with an egg cell to form a zygote, which is the first cell of a new individual. Among the options listed, the one that describes an example of fertilization in higher organisms is the fusion of sperm and egg nuclei. This occurs when a sperm cell, which is produced by the male, penetrates the egg cell, which is produced by the female, and their nuclei merge to form a single cell with a complete set of chromosomes. This process typically occurs in the fallopian tube of the female reproductive system. The other options listed describe other aspects of sexual reproduction, but they do not involve the actual fusion of sperm and egg nuclei that defines fertilization.

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The social insect is the honey bee. Social insects are insects that live in large groups or colonies, and they have specific roles within their communities. Honey bees live in hives, where each bee has a specific job to do such as foraging, caring for the young, or defending the hive. They work together to build and maintain the hive, collect food, and care for their queen. In contrast, grasshoppers, butterflies, and houseflies are not social insects and live relatively solitary lives.

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The incorrect base pairing on the DNA strand is Uracil and Thymine. This is because Uracil is found in RNA, not DNA, and it pairs with Adenine instead of Thymine. In DNA, Adenine always pairs with Thymine, and Cytosine always pairs with Guanine. These base pairs are important for maintaining the structure and stability of the DNA molecule, which is essential for proper functioning of our cells.

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Phosphorus is the element required in large amounts by plants. It is an essential macronutrient that plays a critical role in many biological processes, such as photosynthesis, respiration, and energy storage and transfer. Phosphorus is a component of DNA, RNA, and ATP, which are crucial molecules for plant growth and reproduction. Without adequate phosphorus, plants can develop stunted growth, weak roots, and have difficulty producing flowers and fruits. Therefore, phosphorus is an essential nutrient for plants to survive and thrive.

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Maelezo ya Majibu

A honey bee worker communicates with other bees to share the location of a food source by dancing. The bee will perform a special dance called the "waggle dance" which involves moving in a figure-eight pattern and waggling its body. The direction and duration of the waggle dance provide information about the distance and direction to the food source. Other bees can read this information and use it to fly directly to the food source. This is a remarkable way in which honey bees communicate and work together as a community.

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When a person's body temperature rises above 37°C, sweating and vasodilation take place. The body has a natural mechanism to regulate its temperature called thermoregulation. When the body temperature rises above its normal range, sweat glands located in the skin become active, and the sweat they produce evaporates from the skin, cooling the body down. This is known as sweating. In addition, the blood vessels in the skin widen or dilate, known as vasodilation. This increases the blood flow to the skin, which allows the heat to escape from the body more efficiently. Therefore, sweating and vasodilation work together to cool down the body when its temperature rises above the normal range. This helps to prevent overheating and maintain the body's internal temperature within a safe range.

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Maelezo ya Majibu

The serious disadvantage of complexity in higher organisms is a high demand for food and energy. As organisms become more complex, their bodies require more energy to function properly. This energy is obtained from the food they eat, which means that more complex organisms need to consume larger amounts of food to meet their energy requirements. This demand for food and energy can be a disadvantage because it can limit an organism's ability to survive in environments where food is scarce or competition for resources is high. Additionally, the need for more energy can also make complex organisms more vulnerable to environmental stresses or changes, such as climate change or habitat loss.

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The statement that is not true of the light stage of photosynthesis is that "Water is formed." During the light stage of photosynthesis, chlorophyll absorbs sunlight energy, which is then used to split water molecules into hydrogen ions, electrons, and oxygen gas. The oxygen gas is released into the atmosphere as a by-product, and the hydrogen ions and electrons are used to produce energy-rich molecules such as ATP and NADPH2, which are used in the next stage of photosynthesis. Therefore, water is not formed during the light stage of photosynthesis; instead, it is split into oxygen gas, hydrogen ions, and electrons.

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The pair of organisms that exist as colonies are Pandorina and Volvox. Pandorina and Volvox are both types of green algae that live in aquatic environments. They are unique in that they are composed of individual cells that form a colony. The individual cells are connected to each other by thin strands of cytoplasm, which allow them to communicate and coordinate their movements. In the case of Pandorina, a colony is formed by a group of 16 to 32 cells that are arranged in a spherical shape. In contrast, Volvox is a much larger colony that can consist of up to 50,000 individual cells. The cells in a Volvox colony are arranged in a hollow sphere, with some cells specialized for reproduction and others for movement. Both Pandorina and Volvox have a coordinated movement, with the cells working together to propel the colony through the water. This type of colonial organization allows for greater efficiency in movement and feeding, and also provides a level of protection for the individual cells within the colony.

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Reading the verdict of a case by a judge or magistrate is an example of a voluntary action. This means that the judge or magistrate consciously and intentionally chooses to read the verdict, as opposed to it being a reflex or instinctive response, or a conditioned reflex. The judge or magistrate has to use their judgment and decision-making abilities to arrive at a conclusion, and then take the voluntary action of reading the verdict out loud.

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The faster color change of a dry cobalt chloride paper affixed to the lower surface of a leaf than the upper one indicates that the lower surface of the leaf has more stomata. Cobalt chloride paper is used to detect the presence of water vapor. When exposed to water vapor, the paper changes color from blue to pink. The stomata are tiny openings on the surface of leaves through which water vapor is released. Since the lower surface of the leaf has more stomata than the upper surface, more water vapor is released from the lower surface. This results in faster color change of the cobalt chloride paper attached to the lower surface than the one attached to the upper surface. Therefore, the faster color change of the cobalt chloride paper affixed to the lower surface of the leaf than the upper one indicates that the lower surface of the leaf has more stomata.

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The instrument used to measure the speed of a stream is a simple float. This involves placing a floating object, such as a cork or a ping pong ball, in the stream and measuring how quickly it moves downstream. By timing how long it takes the float to travel a certain distance, you can calculate the speed of the stream. This method is useful for monitoring the flow of water in a stream or river, which can be important for predicting floods or understanding the health of aquatic ecosystems. The other options listed are not used for measuring the speed of a stream: - A Secchi disc is used to measure water transparency or clarity. - A quadrat frame is used to measure the distribution of plants or other organisms in a particular area. - A rain gauge is used to measure the amount of precipitation that falls in a particular area.

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Maelezo ya Majibu

The gland that secretes a substance into the bloodstream of a frightened person is the adrenal gland. The adrenal gland produces adrenaline, a hormone that prepares the body for a "fight or flight" response in stressful situations. When a person is frightened, the adrenal gland releases adrenaline into the bloodstream, causing an increase in heart rate, blood pressure, and breathing rate. This response is designed to help the person respond quickly to a potential threat.

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The heavy thick bark on trees in savannah habitats serves primarily to protect them from harm. It helps to reduce water loss through transpiration, which is important in dry environments. It also protects the trees from the scorching sun and heavy winds, both of which can damage the tree's leaves and branches. Finally, thick bark can help trees resist bush fires, which are common in savannah habitats.

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The factors responsible for inheritance, also known as genes, are located on the chromosomes in the nucleus of a living cell. The nucleoplasm is the gel-like substance that fills the nucleus, but the genes are specifically located on the chromosomes within the nucleoplasm. The nuclear membrane surrounds the nucleus, separating it from the cytoplasm, but it does not play a direct role in inheritance. The nucleolus is a structure within the nucleus that is responsible for producing ribosomes, but it also does not contain genes involved in inheritance.

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Conservation of wildlife is important mainly because it helps to prevent the extinction of species. When we protect the habitats and natural environments where wild animals live, we help to ensure that these animals have the resources they need to survive and thrive. This is important because many species are facing threats from habitat loss, pollution, hunting, and climate change. By protecting these animals, we are also helping to maintain the biodiversity of our planet. This is important because every species plays a role in the ecosystem, and losing one species can have a ripple effect on the entire ecosystem. Additionally, many people enjoy observing wild animals, and many predator wild animals help in controlling pests. So, conserving wildlife is not just important for the animals themselves, but for the health of our planet and for the enjoyment of future generations.

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Maelezo ya Majibu

Green plants are autotrophic, which means they can make their own food using energy from the sun through a process called photosynthesis. This is a crucial characteristic of green plants that sets them apart from other living things, as they don't need to rely on consuming other organisms for nutrients. Instead, they use chlorophyll to convert carbon dioxide and water into glucose and oxygen, which can be used as a source of energy for the plant's growth and survival.

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Maelezo ya Majibu

Green plants require inorganic substances to manufacture their food through the process of photosynthesis. These substances include water, carbon dioxide, and minerals like nitrogen, phosphorus, and potassium. Plants take in water from the soil through their roots and carbon dioxide from the air through tiny pores in their leaves. They use energy from sunlight to convert these raw materials into glucose (sugar), which they use as a source of energy and to build more complex organic molecules like proteins and fats. Therefore, green plants need inorganic substances, not mainly fluids, living materials or mainly gases, to produce their food.

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Water is the substance that passes through the root cell membrane by osmosis. Osmosis is the process where water molecules move from an area of high water concentration to an area of low water concentration across a selectively permeable membrane. In the case of a plant's root cell, water molecules move into the cell where the concentration of solutes (dissolved substances) is higher, resulting in a net movement of water from the soil into the root cell. This is an important process for plants as it allows them to absorb water and nutrients from the soil to support their growth and survival. The other substances listed, such as cell sap, carbon dioxide, and oxygen, can also move across the root cell membrane, but they do so through different mechanisms, such as active transport or diffusion.

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In dim light, it is difficult to see clearly because too little light reaches the retina, where images are formed. The cones in the retina are responsible for detecting fine details and colors in bright light, but they may not be stimulated at all in dim light. This is because the pupil, which controls how much light enters the eye, closes up in dim light, allowing less light to reach the retina. As a result, we struggle to see objects clearly in the dark.

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Maelezo ya Majibu

Possession of strong adhesives is a feature of animals living on rocky shores. Rocky shores are intertidal zones that are exposed to air during low tide and submerged in water during high tide. The constant exposure to the elements can make it difficult for animals to maintain their position, and they may be dislodged by waves or currents. Therefore, animals that live on rocky shores have developed strong adhesives to help them adhere to the rocky surfaces and withstand the force of the waves. These adhesives can be found in a variety of marine animals, such as mussels, barnacles, and limpets.

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The disease that is sex-linked and mainly affects male offspring is called haemophilia. This is because the gene that causes haemophilia is located on the X chromosome. Since females have two X chromosomes, if they inherit one copy of the haemophilia gene, they usually have a healthy copy on their other X chromosome to compensate. However, males only have one X chromosome, so if they inherit the haemophilia gene from their mother, they will develop the disease. Females can also be carriers of the haemophilia gene and pass it on to their male offspring. Haemophilia is a bleeding disorder that affects the blood's ability to clot properly, leading to excessive bleeding and bruising.

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Denitrification is the process that does not contribute to the maintenance of nitrogen content in the soil. Denitrification is the conversion of nitrates into nitrogen gas, which is released into the atmosphere. This process occurs under anaerobic conditions and is usually carried out by bacteria. Since nitrogen gas is not usable by plants, denitrification reduces the amount of available nitrogen in the soil. On the other hand, the other processes listed contribute to the maintenance of nitrogen content in the soil. Nitrogen fixation is the process of converting nitrogen gas from the atmosphere into a form that plants can use, and nitrification is the conversion of ammonium into nitrate, which is also a form of nitrogen that plants can use. Decomposition is the breakdown of organic matter, which releases nitrogen and other nutrients back into the soil. All of these processes help to maintain a healthy and fertile soil for plant growth.

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Maelezo ya Majibu

(a) Short notes

(i) Habitat: the particular natural place or type of environment where an organism lives, providing it with the conditions and resources it needs, e.g. a pond, a forest floor or the soil. It answers the question 'where does the organism live?'

(ii) Ecological niche: the role or function of an organism within its habitat, including how it obtains food, its relationships with other organisms and the conditions it requires. It answers 'what does the organism do and how does it fit into the community?' No two species can occupy exactly the same niche indefinitely.

(b)(i) and (ii) Instruments for measuring ecological factors and their uses

(Other acceptable instruments: wind vane - wind direction; anemometer - wind speed; photometer/light meter - light intensity; pH meter - acidity/alkalinity of soil or water.)

(c) Organisms found in savannah vegetation

(i) Three plants: shea butter tree (Vitellaria), locust bean tree (Parkia), baobab, acacia, elephant grass or spear grass (any three).

(ii) Two animals: grasscutter (cane rat), antelope, grasshopper, lion, hare or guinea fowl (any two).

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(a) Definition of enzymes

Enzymes are organic catalysts, made of protein, produced by living cells, which speed up the rate of biochemical reactions without themselves being used up or altered in the process.

(b) Six characteristics of enzymes

1. They are proteins in nature.
2. They are specific in action (each enzyme acts on one substrate or type of reaction).
3. They are required in very small quantities.
4. They are not used up in the reaction, so they can be used again (catalysts).
5. Their activity is affected by temperature and is destroyed (denatured) by high temperature.
6. Their activity is affected by pH; each works best at an optimum pH.

(Also acceptable: their action can be reversible; their activity is affected by substrate concentration.)

(c) Role of pancreatic juice in digestion of carbohydrates and proteins

Pancreatic juice is poured into the duodenum and contains several enzymes:

• Pancreatic amylase digests starch (carbohydrate) into maltose.
• Trypsin (secreted as inactive trypsinogen and activated by enterokinase) digests proteins and peptones into smaller peptides and amino acids.

The juice is also alkaline, providing the correct pH for these enzymes to work.

(d) Form in which carbohydrate is stored

(i) In animals: glycogen (in the liver and muscles).
(ii) In plants: starch.

(e) Saprophytic nutrition of Rhizopus

Rhizopus (bread mould) feeds saprophytically on dead organic matter such as bread. It grows fine thread-like hyphae; the root-like rhizoids penetrate the food and secrete digestive enzymes onto it. These enzymes digest the food externally (extracellular digestion), breaking down starch and proteins into soluble substances. The soluble products are then absorbed through the hyphae into the fungus and used for energy and growth, while excess food is stored.

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(a) Four functions of the mammalian skeleton and the part that performs each

(b) How muscles and bones bring about movement at the elbow

The elbow is a hinge joint between the humerus (upper arm) and the radius and ulna (forearm). Two muscles act as an antagonistic pair: the biceps (a flexor) on the front and the triceps (an extensor) at the back. To bend (flex) the arm, the biceps contracts and shortens while the triceps relaxes, pulling the forearm up. To straighten (extend) the arm, the triceps contracts and the biceps relaxes, pulling the forearm down. Because each muscle can only pull (not push), the two work in opposition to move the bones about the joint.

(c) Support in plants

(i) Herbaceous plants: support comes mainly from the turgidity of their cells; water in the vacuoles keeps the cells firm, and the collenchyma and turgid parenchyma keep the soft stem upright.

(ii) Woody plants: support comes from the lignified (woody) xylem tissue and sclerenchyma, and from secondary thickening of the stem, which provide rigid mechanical strength.

(d) One vitamin and one mineral for healthy bones

Vitamin: vitamin D. Mineral element: calcium (phosphorus is also acceptable).

Maelezo ya Majibu

(a) Explanation of terms

• (i) Trait: a distinct inherited characteristic or feature of an organism, e.g. eye colour, height or blood group.
• (ii) Recessive gene: an allele whose effect is masked in the presence of a dominant allele; it is only expressed when it is present in the homozygous condition (two recessive alleles together).
• (iii) Test cross: a cross between an individual of unknown genotype (showing the dominant trait) and a homozygous recessive individual, done to find out whether the unknown is homozygous or heterozygous.
• (iv) Heterozygous: having two different alleles of a gene for a particular trait, e.g. Bb.

(b) Determining fatherhood using blood groups

A person with blood group O has the genotype ii; he can only pass on an i allele. A person with blood group AB has the genotype I^AI^B. A child of blood group AB must have received I^A from one parent and I^B from the other. Since the group-O man can only give i, he cannot supply either I^A or I^B. Therefore a group-O man cannot be the biological father of an AB child; the AB child cannot be his.

(c)(i) Determining that a brown male rabbit is homozygous

Carry out a test cross: mate the brown male with several white (homozygous recessive, ww) females. If the male is homozygous WW, all the offspring will be brown. If any white offspring appear, the male is heterozygous Ww. So if all offspring are brown, the male is homozygous.

(c)(ii) Difference in chromosome number

A gamete has the haploid number of chromosomes (n), which is half the number in a body cell. A body (somatic) cell has the diploid number (2n), which is twice that of the gamete.

Maelezo ya Majibu

(a) Importance of an effective transport system in mammals

Mammals are large, active, warm-blooded animals with a high metabolic rate and a small surface-area-to-volume ratio, so diffusion alone cannot supply their deep-lying cells fast enough. An effective transport system (the blood circulatory system) is therefore essential to carry oxygen and digested food to all the cells, to remove carbon dioxide and other waste products to the excretory organs, to distribute heat and hormones round the body, and to defend the body against disease. Without it the cells would be starved of nutrients and poisoned by accumulated wastes.

(b) Eight functions of blood in mammals

1. Transport of oxygen from the lungs to the tissues.
2. Transport of carbon dioxide from the tissues to the lungs.
3. Transport of digested food (glucose, amino acids) to the cells.
4. Transport of nitrogenous waste (urea) to the kidneys for excretion.
5. Transport of hormones from endocrine glands to their target organs.
6. Distribution of heat to regulate body temperature.
7. Defence against disease by white blood cells and antibodies.
8. Clotting of blood to seal wounds and prevent loss of blood.

(c) Four materials transported in the bodies of flowering plants

1. Water (through the xylem).
2. Dissolved mineral salts (through the xylem).
3. Manufactured food, especially sucrose (through the phloem).
4. Amino acids and other organic solutes (through the phloem).

Maelezo ya Majibu

(a)(i) Definition of asexual reproduction

Asexual reproduction is the production of a new individual (offspring) from a single parent without the fusion of gametes (no fertilization) and without any change in the chromosome number. The offspring produced are genetically identical to the parent.

(a)(ii) Two types of asexual reproduction in animals (with one example each)

• Binary fission - the parent divides into two equal daughter cells. Example: Amoeba (or Paramecium).
• Budding - a small outgrowth (bud) develops on the parent and later detaches to form a new individual. Example: Hydra (or Obelia).

(Sporulation in Plasmodium, or parthenogenesis in aphids and honey bees, are also acceptable.)

(b) Four differences between sexual and asexual reproduction

(c) Large, labelled diagram of the human spermatozoon (8 - 10 cm long)

The spermatozoon is divided into three main regions: the head (bearing the acrosome and the haploid nucleus), the middle piece (packed with mitochondria arranged in a spiral around the axial filament), and the long whip-like tail (flagellum) used for swimming.

(d) One function each of three organelles found in the spermatozoon

• Acrosome (cap of the head): contains digestive (lytic) enzymes that dissolve the membranes surrounding the ovum, allowing the sperm to penetrate and fertilize the egg.
• Nucleus (in the head): carries the haploid number of chromosomes (the male genetic material / DNA) that combine with those of the ovum at fertilization.
• Mitochondria (in the middle piece): contain respiratory enzymes and release energy (ATP) that powers the beating of the tail for the sperm's movement.