WAEC SSCE - Biology - 1990

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The process by which plants and animals are modified in structure, physiology and behavior in order to survive is known as adaptation. Adaptation is a natural process that occurs over time through the mechanism of natural selection. It allows organisms to better survive and reproduce in their environment by developing characteristics that enhance their chances of survival. These adaptations can be physical, such as the development of camouflage, or behavioral, such as the migration of birds to warmer climates in the winter. Through adaptation, organisms are able to better compete for resources, evade predators, and withstand environmental pressures.

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Artificial pollination is a process of manually transferring pollen from the male reproductive organ of one plant to the female reproductive organ of another plant in order to produce a hybrid plant with desirable traits. The effect of using artificial pollination in plant breeding is the improvement of the variety of crops. This is because it allows plant breeders to selectively breed plants with desirable traits such as disease resistance, higher yield, improved quality, and other beneficial characteristics. By controlling the pollination process, plant breeders can ensure that the resulting offspring have the desired characteristics, which may not be possible through natural pollination. Overall, artificial pollination can result in the production of healthier crops and increased crop yield, as well as greater resistance to pests and diseases. It does not make crops susceptible to diseases or encourage competition amongst crops, nor does it typically lengthen the maturity time of crops.

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Water rises most rapidly in sandy soil. This is because sandy soil has large spaces or pores between the sand particles, which allows water to flow through quickly, increasing the rate of water movement. In contrast, clayey soil has very small spaces or pores, which causes water to move more slowly through the soil. Loamy soil is a mixture of sand, silt, and clay, which can have varying rates of water movement depending on the proportions of each component. Humus soil refers to soil that has a high content of organic matter, which can help improve soil structure and water-holding capacity, but may not necessarily affect the rate of water movement.

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The statement that is not true about auxins is: "They are used in the site of production". Auxins are plant hormones that are produced by plants themselves, and they play a crucial role in regulating the growth rate and direction of plants. They are typically present in small quantities in the cells of plants, and they can be transported to other parts of the plant where they are needed. However, they are not used in the site of their production, but rather they are transported to other parts of the plant where they can stimulate cell elongation, cell division, and other growth processes.

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The part of the mammalian brain that is involved in taking the decision to run rather than walk is the "Cerebrum." The cerebrum is the largest part of the brain and is responsible for conscious thought and voluntary movements. It is divided into two hemispheres, each of which is responsible for controlling the opposite side of the body. When a mammal is faced with a situation that requires quick action, such as the need to run away from a predator, the cerebrum receives sensory input from the eyes, ears, and other sensory organs, and processes this information to make a decision. The cerebrum then sends signals to the muscles of the legs and other parts of the body to initiate the appropriate movement, which in this case would be running. Therefore, the correct option is: "Cerebrum" is the part of the mammalian brain involved in taking the decision to run rather than walk.

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The structure that controls the activities of the living cell is the nucleus. The nucleus is a membrane-bound organelle found in eukaryotic cells that contains the cell's genetic material in the form of DNA. It acts as the control center of the cell, directing cellular activities such as growth, metabolism, and reproduction. The nucleus regulates gene expression, DNA replication, and cell division, and it also plays a role in the synthesis of RNA and proteins. The other organelles mentioned, such as the centrosome, chloroplast, Golgi body, and mitochondrion, have different functions in the cell and do not control the activities of the living cell.

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The condition known as cretinism is caused by the deficiency of thyroxin. Thyroxin is a hormone produced by the thyroid gland that regulates many of the body's metabolic processes. In infants and children, a deficiency of thyroxin can lead to a condition called cretinism, which is characterized by stunted growth, mental retardation, and other developmental abnormalities. Thyroxin is important for the development of the brain and nervous system, and a deficiency during early childhood can cause irreversible damage. Cretinism is most commonly caused by a lack of dietary iodine, which is needed by the thyroid gland to produce thyroxin. Without enough iodine, the thyroid gland cannot produce enough thyroxin, leading to the symptoms of cretinism. The other options listed are not associated with the development of cretinism. Adrenalin is a hormone produced by the adrenal glands that helps the body respond to stress. Vitamin A is important for vision and immune function. Insulin is a hormone produced by the pancreas that regulates blood sugar levels. Vitamin C is important for collagen synthesis and immune function. While these nutrients are important for overall health and development, they do not play a role in the development of cretinism.

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The process that is not involved in the carbon cycle is transpiration. Transpiration is the process by which plants lose water through the pores of their leaves. While transpiration is an important process in plants, it does not directly involve the transfer of carbon. The carbon cycle involves the movement of carbon between the atmosphere, living organisms, and the Earth's surface. The processes involved in the carbon cycle include photosynthesis, respiration, burning, and decay. During photosynthesis, plants absorb carbon dioxide from the atmosphere and use it to produce organic compounds. Respiration, on the other hand, releases carbon dioxide back into the atmosphere. Burning of fossil fuels also releases carbon dioxide into the atmosphere while decay of dead organic matter returns carbon to the soil.

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The stimulus that is not perceived through the skin of mammals is "Light." Light is not perceived through the skin of mammals because it requires specialized cells in the eye, called photoreceptors, to detect it. These cells are not present in the skin of mammals and are only found in the eyes. On the other hand, the skin of mammals can perceive other stimuli such as pressure, pain, heat, and cold. Mechanoreceptors in the skin detect pressure, nociceptors detect pain, and thermoreceptors detect heat and cold. These receptors are specialized cells that respond to specific types of stimuli and send signals to the brain to be interpreted as touch, pain, or temperature.

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The difference between viviparous and oviparous animals is how they give birth to their offspring. Viviparous animals give birth to live young that have developed inside the mother's body. In this case, the embryos receive nutrients from the mother through a placenta or similar structure. Examples of viviparous animals include most mammals, including humans, as well as some reptiles, such as certain species of snakes and lizards. Oviparous animals, on the other hand, lay eggs that hatch outside the mother's body. The eggs are typically fertilized before being laid, and the embryos develop inside the eggs. The eggs are either laid in a protected environment or are actively guarded by the parents until they hatch. Examples of oviparous animals include birds, reptiles, amphibians, and some insects. Therefore, the correct option is: "Laying and brooding of eggs" is the difference between viviparous and oviparous animals.

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The increase in width of blood vessels in the mammalian skin at high temperatures is known as "vasodilation". This means that the blood vessels in the skin widen, allowing more blood to flow through them. This helps to increase blood flow to the skin, which can help to cool the body down in hot temperatures. As the blood flows closer to the surface of the skin, more heat can be lost through radiation and convection, which can help to regulate body temperature.

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The stage of mitosis at which the two daughter chromosomes separate completely is "Anaphase". Anaphase is the stage of mitosis where the spindle fibers begin to contract, pulling the sister chromatids apart towards opposite poles of the cell. As a result of this separation, each chromatid is now considered an individual chromosome. The separated chromosomes move towards the poles of the cell and become more condensed. Therefore, the correct option is: "Anaphase" is the stage of mitosis where the two daughter chromosomes separate completely.

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The process of detoxification in the liver involves the conversion of poisonous substances in the body into harmless substances. The liver is responsible for breaking down toxic substances, including drugs, alcohol, and metabolic waste products, and transforming them into less harmful substances that can be excreted from the body. The liver uses a series of chemical reactions, including oxidation, reduction, and hydrolysis, to convert these toxic substances into more soluble and easily excreted compounds. This process is called biotransformation, and it involves two phases. In phase one, the liver enzymes modify the toxic substances, making them more reactive and easier to eliminate. In phase two, the modified substances are combined with other molecules, such as glutathione or glucuronic acid, to form water-soluble compounds that can be easily eliminated from the body through urine or bile. Therefore, the correct option is "Poisonous substances in the body are converted into harmless substances" when it comes to the process of detoxication in the liver.

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The statement that "Flippers are modified for grasping in sharks" is not correct. Flippers are actually modified for swimming in sharks, not for grasping. Sharks use their flippers to provide lift and maneuverability while swimming through the water. Their flattened shape also helps to reduce drag and increase speed. Grasping is not a primary function of shark flippers, as sharks primarily use their jaws for grasping prey.

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The glomerular filtrate is formed in the kidneys when blood is filtered through tiny structures called glomeruli. This filtrate contains useful substances such as glucose, ions, and water, as well as waste products that need to be removed from the body. Reabsorption is the mechanism by which useful materials in the glomerular filtrate are taken back into the blood. As the filtrate flows through the tubules of the kidney, certain substances that the body needs are transported back into the bloodstream. For example, glucose and amino acids are actively transported back into the blood. Water, ions, and other substances are also reabsorbed through passive transport mechanisms. Therefore, the correct answer is "reabsorption."

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The bee dance is a way that honeybees communicate with each other by using body movements. It conveys information about the location of a food source to other bees. The dance consists of the dancing bee moving in a figure-eight pattern and changing the angle of her body in relation to the sun. The direction and duration of the dance indicate the distance and quality of the food source. Other bees in the hive can detect the scent of the food brought back by the dancing bee and use the information to find the food source. Therefore, the significance of the bee dance to other bees is to inform them about the presence of food.

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The structure that differentiates an animal cell from a plant cell is the chloroplast. Chloroplasts are specialized organelles found in plant cells that are responsible for photosynthesis, the process by which plants convert sunlight into energy. Chloroplasts contain chlorophyll, a pigment that gives plants their green color and is essential for capturing light energy. Animal cells do not have chloroplasts, which means they cannot undergo photosynthesis. Instead, animal cells rely on other organelles, such as mitochondria, to produce energy through cellular respiration. Mitochondria are present in both animal and plant cells and are responsible for producing the energy currency of the cell, called ATP. Therefore, the correct option is "Chloroplast" when it comes to the structure that differentiates an animal cell from a plant cell.

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The brain and spinal cord make up the central nervous system. This system is responsible for receiving and processing sensory information from the body and sending out motor commands to muscles and organs. It is also responsible for higher functions such as thinking, memory, and emotion.

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At the end of mitosis, the number of cells produced from a parent cell is two. During mitosis, a parent cell divides into two identical daughter cells, each containing the same number of chromosomes as the parent cell. Therefore, the number of cells produced at the end of mitosis is two.

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The organ located in the mammalian abdominal cavity just below the diaphragm and lying on top of the stomach is the liver. The liver is a vital organ responsible for various metabolic functions, including the production of bile, storage of glycogen, detoxification of harmful substances, and synthesis of important proteins. It plays a crucial role in maintaining homeostasis in the body and is connected to the digestive system via the bile ducts.

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The cup-shaped part of the Bowman’s capsule contains the "glomerulus". The Bowman’s capsule is a cup-shaped structure that forms the beginning of the nephron, the functional unit of the kidney. It surrounds the glomerulus, which is a network of tiny blood vessels called capillaries. The Bowman's capsule is responsible for filtering blood to remove waste products and excess fluids from the body. When blood enters the Bowman's capsule, it passes through the capillaries of the glomerulus, which filters out waste products and excess fluids. The filtered fluid then passes through the tubules of the nephron, where valuable substances are reabsorbed into the bloodstream and the remaining waste products are excreted as urine. Therefore, the correct option is "glomerulus".

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Thrombocytes, also known as platelets, are blood cells responsible for initiating the clotting of blood. When there is an injury to a blood vessel, thrombocytes are activated and begin to stick to the damaged area. This triggers a series of chemical reactions that lead to the formation of a blood clot, which helps to stop the bleeding. The process of blood clotting is important to prevent excessive blood loss from injuries. Thrombocytes play a crucial role in this process by initiating the formation of a clot at the site of the injury. The clot is formed by a network of fibrin, a protein that is produced in response to the activation of thrombocytes. The fibrin forms a mesh that traps blood cells and platelets, forming a plug that stops the bleeding. The other options listed are not functions of thrombocytes. Phagocytosis of bacteria is performed by white blood cells such as neutrophils and macrophages. The synthesis of ribosomes is a cellular process that occurs in the cytoplasm of cells. Immunity to certain infectious diseases is mediated by antibodies produced by white blood cells such as B cells. Removal of carbon dioxide from tissues is mainly performed by red blood cells.

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Changes in energy flow between organisms in a habitat can be represented by a pyramid of energy. A pyramid of energy is a graphical representation of the flow of energy between different levels of a food chain or food web. It shows the amount of energy available at each level of the ecosystem and how much of that energy is transferred to the next level. The pyramid of energy represents the fact that energy is lost as it flows through each level of the food chain or food web. Only a small fraction of the energy consumed by an organism is converted into biomass or stored as potential energy, while the rest is lost as heat or used in metabolic processes. This means that there is less energy available at higher trophic levels than at lower trophic levels. Therefore, the correct option is "pyramid of energy" when it comes to representing changes in energy flow between organisms in a habitat.

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Water in the human body is derived from various sources such as drinking water, food substances, cytoplasm of worn-out cells, and respiratory activity. However, water is not typically absorbed by the skin. Drinking water is one of the main sources of water for the human body. Water from the food we eat and metabolic water produced during the breakdown of nutrients in our body also contribute to our body's water content. When cells in our body break down, water is released into the body, contributing to our overall water content. Respiratory activity also contributes to our body's water content. When we exhale, we lose water in the form of water vapor. While the skin does play a role in regulating water balance in the body, it is not a significant source of water absorption. The skin helps to prevent excessive water loss through evaporation and sweating, but it does not typically absorb water from the external environment. Therefore, the correct answer to the question is "absorption by the skin."

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The precondition for transfusion of blood to an accident victim is cross-matching the blood group of the donor with that of the accident victim. This is important because if the blood types are not compatible, it can cause a life-threatening reaction in the recipient's body. Seeking the consent of the victim's parents, ascertaining the victim's religious belief, and rewarding the donor with food and money are not preconditions for blood transfusion. It is important to ensure that the blood donor is free of any diseases that could be transmitted through the transfusion, but curing the donor of any disease traced in his blood is not a precondition for blood transfusion.

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The conservation of natural resources refers to the sustainable use and management of natural resources such as land, water, minerals, and forests to ensure their long-term availability for future generations. All the options listed except "deregulated harvesting" can help achieve conservation of natural resources. Creation of national parks and establishment of game reserves are ways of preserving and protecting natural areas from human activities such as hunting, logging, and mining. Conservation societies and agencies work towards the protection of natural resources and habitats. Making laws on conservation is a vital aspect of ensuring that natural resources are utilized sustainably and that biodiversity is protected. On the other hand, deregulated harvesting means unrestricted removal of resources without considering sustainability, which can lead to overexploitation and depletion of natural resources. Therefore, the option that does not contribute to the conservation of natural resources is "deregulated harvesting."

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The method of reproduction common to both Paramecium and Amoeba is binary fission. Binary fission is a type of asexual reproduction in which a single parent cell divides into two identical daughter cells. During binary fission in Paramecium, the organism replicates its genetic material and divides into two identical daughter cells. In Amoeba, the organism first elongates, then splits into two equal parts, and each part becomes a new individual. This method of reproduction allows these single-celled organisms to rapidly increase their population in favorable conditions.

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Water vapor is lost in plants during transpiration through stomata and lenticels. Stomata are tiny pores on the surface of leaves that allow for the exchange of gases, including water vapor. When the stomata are open, water vapor is released into the air through a process called transpiration. Lenticels are small openings on the stems and roots of plants that also allow for gas exchange. Transpiration is an important process in plants as it helps to pull water and nutrients up from the roots to the leaves. As water evaporates from the leaves through transpiration, it creates a negative pressure or tension in the xylem, the tissue responsible for transporting water and nutrients from the roots to the rest of the plant. This negative pressure pulls water and nutrients up from the roots to the leaves, a process known as the transpiration-cohesion-tension mechanism. The other options listed do not play a direct role in the process of transpiration. Xylem is the tissue responsible for transporting water and nutrients, but it is not involved in the release of water vapor during transpiration. Sclerenchyma and parenchyma are types of plant cells that provide structural support and perform various functions, but they are not directly involved in transpiration. Guard cells are specialized cells that control the opening and closing of stomata, but they are not involved in the loss of water vapor during transpiration.

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The statement that is not correct of respiration is: "Carbondioxide produced in the tissues is removed by the process of osmosis." Carbon dioxide produced in the tissues is not removed by the process of osmosis, but rather by diffusion. During respiration, cells produce carbon dioxide as a waste product, which diffuses out of the cells and into the bloodstream. From there, it is transported to the lungs where it diffuses across the respiratory membrane and is exhaled. Osmosis is the diffusion of water molecules across a selectively permeable membrane, while diffusion is the movement of particles from an area of high concentration to an area of low concentration. Therefore, it is incorrect to say that carbon dioxide is removed by osmosis in the process of respiration.

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The breathing movement in mammals is accompanied by regular movements of the diaphragm and the intercostal muscles. The diaphragm is a dome-shaped muscle located at the bottom of the chest cavity, separating the thoracic and abdominal cavities. When we inhale, the diaphragm contracts and moves downwards, creating a vacuum that pulls air into the lungs. When we exhale, the diaphragm relaxes and moves upwards, pushing air out of the lungs. The intercostal muscles are the muscles located between the ribs. There are two sets of intercostal muscles, the external and internal intercostal muscles. These muscles work together to move the ribcage up and out during inhalation and down and in during exhalation. The external intercostal muscles contract during inhalation, pulling the ribs up and out, while the internal intercostal muscles contract during exhalation, pulling the ribs down and in. So, the regular movements of the diaphragm and intercostal muscles work together to enable breathing in mammals.

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When gametes from pure breeding parents with contrasting features such as tallness and shortness are involved in monohybrid cross, the offspring in the first filial generation are usually heterozygous dominant. This means that the offspring inherit one allele for tallness (T) and one allele for shortness (t) from their parents, and the allele for tallness is dominant over the allele for shortness. As a result, the offspring exhibit the dominant trait of tallness, but they carry the recessive allele for shortness as well. This type of inheritance is known as Mendelian inheritance and follows the law of segregation, which states that each individual has two alleles for a particular trait, but only one is passed on to each offspring. The other allele is hidden or masked by the dominant allele.

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The stems of young herbaceous plants are kept upright mainly by turgor pressure. Turgor pressure is the pressure exerted by water inside the plant cells against the cell walls. When the plant cells are filled with water, the cell walls become rigid, and this rigidity supports the stem, keeping it upright. The plant takes in water through the roots, and this water moves up to the stem through the xylem. The water then enters the plant cells, creating a pressure that helps to keep the stem upright. When there is not enough water in the plant cells, the turgor pressure decreases, and the stem may wilt or bend. The other options listed are not primarily responsible for keeping the stems of young herbaceous plants upright. Osmotic pressure refers to the movement of water across a semi-permeable membrane to equalize the concentration of solutes on either side of the membrane. Transpiration pull is the movement of water from the roots to the leaves due to evaporation at the leaf surface, and suction pressure is the pressure created by transpiration pull. Root pressure is the pressure created by water moving into the roots from the soil. While these processes may contribute to the overall health and growth of the plant, they are not the main mechanisms responsible for keeping the stem upright.

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The reagent used for the test for starch is iodine solution. Iodine solution reacts with the starch molecules to produce a blue-black color. This is due to the formation of an iodine-starch complex. Million’s reagent is used to test for tannins, Fehling’s solution is used to test for reducing sugars, Sudan III is used to test for lipids, and Benedict’s solution is used to test for the presence of reducing sugars, but not specifically for starch.

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An autotrophic mode of nutrition refers to the ability of an organism to produce its food using simple inorganic substances such as carbon dioxide, water, and sunlight. Among the options listed, only chemosynthesis is an example of an autotrophic mode of nutrition. Chemosynthesis involves the synthesis of organic compounds by bacteria or other organisms using energy derived from the oxidation of simple inorganic compounds, such as hydrogen sulfide, instead of sunlight. This process is commonly found in deep-sea ecosystems, where there is no access to sunlight, and organisms rely on chemosynthesis to produce food. Therefore, the correct answer is chemosynthesis.

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The majority of the energy in a cell is produced in the mitochondrion. Mitochondria are small, bean-shaped organelles that are found in almost all eukaryotic cells. They are often referred to as the "powerhouses" of the cell because they are responsible for producing the majority of the cell's energy currency, known as ATP (adenosine triphosphate). Mitochondria generate ATP through a process called cellular respiration, which involves the breakdown of glucose and other molecules to release energy. This process occurs in several stages, including glycolysis, the Krebs cycle, and the electron transport chain. These processes take place in different parts of the mitochondrion and involve a series of chemical reactions that ultimately result in the production of ATP. In summary, the mitochondrion is responsible for producing the majority of the energy in a cell through a process called cellular respiration.

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The genetic make-up of an organism is described as its genotype. This refers to the complete set of genes and genetic material present in an organism, including both the dominant and recessive alleles for each trait. Genotype plays a critical role in determining an organism's physical characteristics, known as its phenotype. While the genotype represents the genetic potential of an organism, the phenotype reflects how that potential is expressed in the organism's physical traits. Therefore, by studying an organism's genotype, scientists can make predictions about the traits that the organism will display in its phenotype.

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Gaseous exchange takes place in the adult toad through the skin, buccal cavity, and lungs. The skin of the toad is thin and moist, allowing oxygen to diffuse in and carbon dioxide to diffuse out. The buccal cavity, which includes the mouth and nostrils, also plays a role in respiration by allowing air to enter and exit the body. Air is then drawn into the lungs, where oxygen is exchanged with carbon dioxide in the alveoli. This process of gaseous exchange is essential for the toad to obtain the oxygen it needs for respiration and to release the waste product of carbon dioxide.

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Among the given options, clay soil has the highest water-retaining capacity. This is because clay soil has very small soil particles with spaces in between them, which can hold onto water molecules tightly due to the electrostatic forces between the particles and water molecules. As a result, water is absorbed and retained in the soil for a longer period, making clay soil ideal for farming and gardening. On the other hand, sandy soils have large particles with gaps between them, which allow water to pass through easily, causing less retention of water in the soil.

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When we talk about a pair of genes controlling a trait, we are referring to the basic unit of inheritance called "alleles." Each gene has two alleles, one inherited from each parent, that together determine the characteristics or traits of an organism. In this context, a dominant allele will always be expressed in an organism's traits when present, even if only one copy is inherited. On the other hand, a recessive allele will only be expressed when two copies are inherited, one from each parent. A variant refers to any alternative form of a gene that may differ from the most common or "wild-type" allele. Finally, a hybrid refers to an offspring resulting from the mating of two organisms from different species or varieties. So, when we say a pair of genes controls a trait, we are essentially describing how different combinations of dominant and recessive alleles, as well as different variants, can determine an organism's physical or behavioral traits.

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The option that is not a way of reducing air pollution is "Recycling tins, cans, and bottles." Although recycling is an essential practice to reduce waste and conserve resources, it does not directly contribute to reducing air pollution. Recycling helps in reducing waste accumulation in landfills, which can lead to water and soil pollution, but it doesn't address air pollution. The other options mentioned are ways of reducing air pollution. Siting factories and power stations away from residential areas helps in minimizing the exposure of people to harmful air pollutants. Building tall factory chimneys allows pollutants to disperse over a larger area and not accumulate close to the ground level where people breathe. Passing waste gases through filters and absorbers removes harmful substances from industrial emissions before they are released into the air. Using lead-free petrol in cars helps in reducing emissions of harmful substances, such as carbon monoxide, nitrogen oxide, and particulate matter, which contribute to air pollution.

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The statement that is not correct about the functions of each group of mammalian vertebrae is: "Sacral vertebrae support the skull and allow nodding and rotating movements." This statement is incorrect because sacral vertebrae are actually located in the pelvic region of the spine and support the weight of the upper body when sitting. They also help to transfer weight from the upper body to the lower limbs during movement. To clarify the functions of the other groups of mammalian vertebrae: - Cervical vertebrae are located in the neck region and support the weight of the head while allowing for a wide range of movement and flexibility. - Thoracic vertebrae are located in the chest region and articulate with the ribs to provide protection for the vital organs in the chest cavity and support respiratory functions. - Lumbar vertebrae are located in the lower back and provide attachment for the large muscles of the back and abdomen, which are important for movement and stability. - Caudal vertebrae are located in the tail region and support the tail, which is used for balance, communication, and movement in some animals.

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The structure in the cell that controls the movement of substances in and out of the cell is the cytoplasmic membrane. It is also known as the cell membrane and is a thin, semi-permeable membrane that surrounds and encloses the cell. It consists of a lipid bilayer with proteins embedded in it, and acts as a barrier to the free flow of substances in and out of the cell. The cytoplasmic membrane is responsible for maintaining the cell's internal environment by controlling the movement of substances such as ions, nutrients, and waste products. It allows some substances to pass through while preventing others from entering or leaving the cell.

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The factor that is not associated with an aquatic habitat is humidity. Humidity is a measure of the amount of water vapor in the air, and while it is an important factor for terrestrial habitats, it does not play a significant role in aquatic habitats. In contrast, temperature, light intensity, turbidity, and wave action are all important factors that can affect the health and survival of aquatic organisms. Temperature affects the metabolism and growth of aquatic organisms, light intensity affects the photosynthesis of aquatic plants, turbidity affects the amount of light and nutrients that can penetrate the water, and wave action affects the physical structure of the habitat and the ability of organisms to obtain food and oxygen.

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The statement that is not associated with the theory of natural selection is "Food and other needs are abundant". The theory of natural selection is a process by which organisms better adapted to their environment tend to survive and produce more offspring. The struggle for existence and competition among the offspring are a crucial part of natural selection. Weaker offspring who cannot compete for resources are eliminated, and nature selects those who survive to reproduce their kind. However, the abundance of food and other resources does not necessarily play a role in natural selection as it does not create a competitive advantage for organisms.

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The water cycle is a natural process that involves the continuous movement of water from the earth's surface to the atmosphere and back to the surface. The following are the processes involved in the water cycle: - Evaporation: This is the process by which water from oceans, lakes, rivers, and other water bodies turns into water vapor due to heat from the sun. - Condensation: This is the process by which the water vapor in the atmosphere turns into liquid droplets that form clouds. - Precipitation: This is the process by which the liquid droplets in clouds become heavy and fall to the earth's surface as rain, snow, sleet, or hail. Therefore, the correct answer is "Evaporation, condensation and precipitation."

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(a) How meiotic division contributes to variation in a population

Meiosis introduces variation in two main ways:

• Crossing over: during the first meiotic division, homologous chromosomes pair and exchange segments (genes) at the chiasmata. This produces new combinations of alleles in the resulting gametes.
• Independent (random) assortment: the homologous chromosome pairs line up and separate independently of one another, so the chromosomes are shuffled and each gamete receives a different mixture of maternal and paternal chromosomes.

Because of these events, meiosis produces gametes that are genetically different from one another and from the parent cell. When these varied gametes fuse at random during fertilization, offspring with new gene combinations are formed, giving rise to variation within the population.

(b) Mendel's first and second laws

First law (Law of Segregation): the two members of a pair of alleles controlling a character separate (segregate) during the formation of gametes, so that each gamete carries only one allele of the pair.

Second law (Law of Independent Assortment): when two or more pairs of contrasting characters are considered together, each pair of alleles segregates and is distributed into the gametes independently of the other pairs.

(c) Cross of brown rat (BB) x white rat (bb) to the second filial generation

Let B = brown (dominant), b = white (recessive).

Parents: \(BB\) (brown) \(\times\) \(bb\) (white). Gametes: \(B\) and \(b\).

F1: all \(Bb\) - brown rats.

F1 selfed: \(Bb \times Bb\). Gametes: \(B\) and \(b\) from each.

F2 genotypes: \(1\ BB : 2\ Bb : 1\ bb\).

F2 phenotypes: 3 brown : 1 white, i.e. \(3:1\).

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(a)(i) Two reasons why termites are described as social insects

1. They live together in large organised colonies in which members depend on one another.
2. There is division of labour, with different castes performing different specialised duties for the good of the whole colony.

(a)(ii) Four castes in a termite nest, with the function of each

(b) Five behavioural adaptations of termites for survival

1. Division of labour among castes: each caste performs a special task (reproduction, feeding, defence), which makes the colony efficient and better able to survive.
2. Building of termitaria (mounds): they construct strong, ventilated mounds that protect the colony from enemies, heat and desiccation and keep conditions inside cool and moist.
3. Cooperative feeding and care of young: workers feed the queen, king, soldiers and larvae, so members that cannot feed themselves survive.
4. Cultivation of fungus gardens: workers grow fungus on chewed plant material as a reliable food supply.
5. Communication by chemicals (pheromones) and grooming: termites signal danger and coordinate activities, and constant grooming keeps the colony free from disease.

Also acceptable: swarming/nuptial flight for dispersal and starting new colonies, and remaining hidden inside tunnels away from light and predators.

Détails de la réponse

(a) Process of succession on an abandoned farm land

Succession is the gradual and orderly replacement of one community of organisms by another over a period of time until a stable community is reached. On an abandoned farm land it proceeds as follows:

1. Colonisation by pioneer plants: the bare, exposed soil is first invaded by fast-growing weeds and grasses whose light seeds are easily dispersed. These are the pioneer species.
2. Improvement of the soil: as these plants grow, die and decay, they add humus to the soil, improving its fertility, water-holding capacity and structure.
3. Replacement by larger plants: the enriched soil now supports taller herbs and shrubs, which grow up and shade out and replace the grasses (they compete for light, water and nutrients).
4. Development of woody plants: shrubs are in turn replaced by small trees and then larger trees as conditions continue to improve.
5. Climax community: eventually a stable, self-maintaining community of tall trees (a forest, in a rainforest zone) develops. This final stage, which remains in balance with the environment, is the climax community. Each stage is called a sere.

Alongside the plants, the animal community also changes, so that the animals present at each stage match the vegetation.

(b) Seven ways by which micro-organisms can be controlled to maintain good health

1. Sterilization of instruments and materials by heat (e.g. autoclaving, boiling).
2. Use of antiseptics on the skin and wounds (e.g. iodine, Dettol).
3. Use of disinfectants on floors, surfaces and toilets (e.g. bleach, phenol).
4. Pasteurization of milk and other drinks to kill harmful microbes.
5. Proper cooking and refrigeration of food to kill or slow the growth of microbes.
6. Personal and environmental hygiene such as regular washing of hands, bathing and proper disposal of refuse and sewage.
7. Immunization (vaccination) and the use of drugs such as antibiotics to fight micro-organisms in the body.

Détails de la réponse

(a) Breakdown of glucose in the cell to produce energy (ATP)

The release of energy from glucose is called cellular respiration. It takes place in two main stages:

• Glycolysis (in the cytoplasm): a molecule of glucose is broken down through a series of enzyme-controlled steps into two molecules of pyruvic acid, producing a small amount of ATP. This stage does not require oxygen.
• Aerobic breakdown (in the mitochondria): in the presence of oxygen, pyruvic acid is completely broken down through the Krebs cycle and the electron transport chain into carbon dioxide and water, releasing a large amount of ATP.

The overall aerobic reaction is:

\[ C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)} \]

In the absence of oxygen (anaerobic respiration), the pyruvic acid is only partly broken down, giving lactic acid (in animals) or ethanol and carbon dioxide (in plants and yeast), with the release of only a little energy.

(b) Two conditions under which glycogen can be converted to glucose

1. When the blood glucose level falls (e.g. during hunger/fasting or strenuous exercise), the hormone glucagon (or adrenaline) stimulates the liver to convert glycogen to glucose.
2. When the body needs extra energy quickly, such as during vigorous muscular activity.

(c) Experiment to demonstrate that oxygen is released by green plants during photosynthesis

• Place some water plants (e.g. Elodea or Hydrilla) in a beaker of pond water and cover them with a short-stemmed glass funnel, mouth downwards.
• Fill a test tube completely with water and invert it over the funnel stem so that no air enters.
• Set up a second identical apparatus in the dark as a control, and place the first in bright sunlight.

Observation: in the apparatus kept in sunlight, bubbles of gas rise from the plant and collect in the test tube, gradually displacing the water. When enough gas has collected, a glowing splint inserted into it is rekindled (relights), showing that the gas is oxygen. No gas collects in the apparatus kept in the dark.

Conclusion: green plants release oxygen during photosynthesis, and only in the presence of light.