WAEC SSCE - Biology - 2006

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The central nervous system (CNS) in humans is made up of the brain and spinal cord. The brain is located in the skull and is responsible for processing sensory information, controlling behavior and movement, and regulating bodily functions. The spinal cord is a long, thin, tubular bundle of nerves that extends from the brain down through the vertebral column. It carries signals between the brain and the rest of the body, and is responsible for reflex actions. Together, the brain and spinal cord make up the CNS, which is the control center of the body's nervous system.

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Gaseous exchange refers to the process of exchanging gases, such as oxygen and carbon dioxide, between an organism and its environment. Spiracles and tracheae are respiratory structures found in insects and some other arthropods that allow for gaseous exchange. Alveoli and lungs are respiratory structures found in mammals that allow for the exchange of gases between the body and the environment. Stomata and lenticels are structures found in plants that allow for gaseous exchange. However, chloroplasts and plastids are not involved in gaseous exchange. They are organelles found in plant cells that are involved in photosynthesis and storage of nutrients. Therefore, the correct answer is "chloroplast and plastids".

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The epidermis of the mammalian skin is an example of a tissue because the cells have a similar structure and function. A tissue is a group of cells with similar structures and functions that work together to perform a specific task. In the epidermis of the mammalian skin, the cells are tightly packed together to form a protective layer that prevents excessive loss of water, helps regulate body temperature, and protects against physical and chemical damage. The cells in the epidermis also contain keratin, which makes the skin tough and waterproof. Therefore, the epidermis is a good example of a tissue because its cells have similar structures and functions that work together to provide protection and other important functions for the body.

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Measles cannot be spread by an insect. Measles is a viral disease that spreads from person to person through respiratory droplets when an infected person talks, coughs, or sneezes. Insects do not play a role in the transmission of measles. Cholera, malaria, and trypanosomiasis can be spread by insects such as flies, mosquitoes, and tsetse flies, respectively.

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The appendicular skeleton includes the bones of the limbs and their girdles. The atlas is the first cervical vertebra of the axial skeleton and is not part of the appendicular skeleton. Therefore, the answer is "Atlas."

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The blood group in humans referred to as a universal recipient is AB. This is because people with blood group AB have both A and B antigens on their red blood cells and do not have antibodies against either A or B blood groups in their plasma. As a result, they can receive blood from all blood groups (A, B, AB and O) without the risk of an adverse transfusion reaction.

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The deficiency caused by the lack of vitamin A is night blindness (VI). Vitamin A is essential for the production of rhodopsin, which is a pigment in the retina of the eye that is responsible for vision in low light conditions. Deficiency of vitamin A leads to a decreased production of rhodopsin, which results in night blindness. The other deficiencies listed are caused by other nutrient deficiencies: I - protein deficiency, II - vitamin C deficiency, III - vitamin D and calcium deficiency, IV - iodine deficiency, and V - vitamin K deficiency.

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The vitamin that would correct the deficiency numbered V (failure of blood to clot) is Vitamin K. This is because Vitamin K plays a crucial role in blood clotting. It activates certain proteins in the blood that are necessary for the formation of blood clots to stop bleeding. Without sufficient Vitamin K, blood clotting may be impaired, leading to prolonged bleeding and an increased risk of hemorrhage. Therefore, adequate intake of Vitamin K is important for normal blood clotting and prevention of bleeding disorders.

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The first step in carrying out ecological studies in a terrestrial habitat is mapping the area. This involves obtaining an overview of the area by identifying and marking its boundaries, noting its topography and geography, and creating a base map. This information is important in helping researchers to identify sampling points, understand the distribution of the organisms and the environmental factors that may influence them. Mapping the area also provides a foundation for other ecological studies such as population dynamics, succession, and nutrient cycling.

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Support in young herbaceous plants is provided by turgidity. Turgidity refers to the state of being swollen and distended due to the absorption of water by the vacuoles in the plant cells. In young herbaceous plants, the cells are packed with water, which causes them to become turgid and stiff, providing support for the plant. This is why young plants that lack turgor pressure wilt and become limp. Therefore, turgidity plays a vital role in supporting young herbaceous plants.

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Cell plasmolysis does not contribute towards growth. Plasmolysis is the shrinking of the protoplasm of a plant cell due to the loss of water by osmosis. It occurs when a plant cell is placed in a hypertonic solution, causing the water to move out of the cell. This can lead to a reduction in the size of the cell and affect the plant's overall growth. However, cell division, cell enlargement, and cell differentiation are all processes that contribute towards growth. Cell division involves the splitting of one cell into two or more, which increases the number of cells in an organism. Cell enlargement involves an increase in the size of individual cells, which also contributes to overall growth. Finally, cell differentiation is the process by which cells become specialized for specific functions, such as muscle cells or nerve cells, which is important for the growth and development of complex organisms.

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The vertebrae are the bones that make up the spinal column or backbone. They are divided into regions, and each region has a different number and shape of vertebrae. The thoracic vertebrae are the ones that provide articulating surfaces for the ribs. There are 12 thoracic vertebrae, and each one has a pair of ribs attached to it. The ribs articulate with the thoracic vertebrae at two points, the facet joints and the costovertebral joints. The thoracic vertebrae also have long spinous processes that project downward and overlap with the vertebrae below them, providing protection for the spinal cord.

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During the process of osmosis, a semi-permeable membrane allows only solvent molecules to pass through it. In osmosis, solvent molecules move from an area of higher concentration to an area of lower concentration across a semi-permeable membrane until the concentration of the solvent is equal on both sides of the membrane. This process occurs in order to equalize the concentration of solutes on both sides of the membrane, and it plays a crucial role in many biological processes, such as the absorption of water by plant roots and the regulation of water balance in animal cells.

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The contrasting pair of genes affecting a trait and located at the same position on homologous chromosomes is referred to as "alleles." Alleles are different versions of the same gene that code for different traits, and they are located on the same locus on each of the two homologous chromosomes. One allele is inherited from each parent and determines the expression of the trait. The two alleles can be either homozygous (identical) or heterozygous (different), and the expression of the trait will depend on whether one or both of the alleles are dominant or recessive.

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The ventricles of the mammalian heart have thicker muscular walls than the auricles because the ventricles have to pump blood to longer distances than the auricles. The ventricles receive blood from the atria and then pump it out to the entire body, so they need to generate more force to overcome the resistance of the blood vessels. Therefore, their muscular walls are thicker and more powerful to provide the necessary force to pump blood to the different parts of the body.

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Euglena feeds both autotrophically and heterotrophically. Euglena is a unicellular organism with chloroplasts that allow it to carry out photosynthesis and produce its own food from sunlight, carbon dioxide, and water. However, it also has a primitive mouth-like structure that enables it to consume other small organisms as a supplementary source of nutrition. This feeding strategy makes Euglena unique compared to other organisms on the list, which rely exclusively on either autotrophic or heterotrophic nutrition.

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Building tall factory chimneys is not an effective method to reduce air pollution. Although it can help to disperse pollutants over a wider area, it does not actually reduce the amount of pollution being produced. The other methods listed, such as passing waste gases through filters and absorbers, using lead-free petrol, and recycling, can all help to reduce the amount of pollutants being released into the air.

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The long necks and legs of present-day giraffes were some of the basis of Lamarck's theory of evolution. Lamarck believed that acquired traits could be passed down to offspring, so he proposed that giraffes stretched their necks to reach leaves high up in trees and that this stretching caused their necks to lengthen over generations. However, this theory has been largely disproven by the modern understanding of genetics and evolution.

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In this scenario, the white cat is homozygous dominant, meaning it has two copies of the dominant white gene. The black cat is homozygous recessive, meaning it has two copies of the recessive black gene. When the two cats mate, their offspring (F1 generation) will all inherit one copy of the white gene from the white cat and one copy of the black gene from the black cat, making them all heterozygous. However, since the white gene is dominant over the black gene, the F1 generation will all have white fur. Therefore, the answer is "Heterozygous white."

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Pollination is the transfer of pollen grains from the male reproductive organ (anther) of a flower to the female reproductive organ (stigma) of the same or a different flower of the same or different species. Therefore, the best statement that describes pollination is "the transfer of pollen grain from anther to stigmas".

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A group of several populations that interact and share a habitat form a community. A community refers to all the living organisms that coexist and interact with each other in a particular habitat. These living organisms can be plants, animals, fungi, and microorganisms. They depend on each other for survival through various interactions such as predation, competition, and symbiosis. The relationships between the organisms in a community contribute to the overall functioning of the ecosystem.

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The physical and chemical factors which affect the life of organisms in an environment are described as abiotic factors. Abiotic factors are non-living components of an ecosystem that can influence the survival and growth of living organisms. Examples of abiotic factors include temperature, water availability, light intensity, soil pH, and nutrient availability. These factors are important because they can limit the distribution and abundance of species in an ecosystem. Understanding abiotic factors is crucial for the management and conservation of natural resources.

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Habitat is not a component that contributes to the biomass of an ecosystem. Producers (plants), consumers (herbivores, carnivores, and omnivores), and micro-organisms (bacteria, fungi, etc.) are all living organisms that contribute to the biomass of an ecosystem, which refers to the total mass of living matter in a given area. Habitat, on the other hand, refers to the physical and biological environment in which these living organisms reside, and does not have a direct contribution to the biomass of the system.

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Organisms that feed essentially on plants within any ecosystem may be referred to as herbivores. Herbivores are animals that consume plant material such as leaves, stems, roots, and fruits. They play an important role in the food chain by converting the energy stored in plant tissues into forms that can be used by other animals. Examples of herbivores include cows, deer, rabbits, and caterpillars.

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Ability to roll the tongue is not a morphological variation in humans. Morphological variations refer to differences in the physical structure or appearance of individuals within a species. Height, shape of head, and colour of skin are all examples of morphological variations. The ability to roll the tongue, on the other hand, is a genetic trait that is not related to physical structure or appearance. It is caused by the interaction of multiple genes and is not considered a morphological variation.

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The heart is a muscular organ that pumps blood throughout the body. The circulatory system in mammals can be single or double. The double circulatory system involves blood being pumped twice: once to the lungs to pick up oxygen, and then to the rest of the body. In this type of circulatory system, there are two circuits: the pulmonary circuit and the systemic circuit. The pulmonary circuit carries blood from the heart to the lungs where it is oxygenated, and then back to the heart. The systemic circuit carries oxygenated blood from the heart to the rest of the body, and then returns deoxygenated blood back to the heart. To cope with this double circulation, the heart needs to have two separate pumps, each with its own set of valves. The best adapted heart structure for this is the one with two auricles and two ventricles. This is because the two ventricles can contract at different times, allowing for better separation of oxygenated and deoxygenated blood. Additionally, the two sets of valves help prevent the mixing of oxygenated and deoxygenated blood. Therefore, the answer is: Two auricles and two ventricles.

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Afforestation, contour ploughing and establishment of game reserves can contribute towards the conservation of natural resources while deforestation does not. Afforestation involves planting new forests or woodlands on land that was not previously forested, which helps to increase the overall forest cover and reduce soil erosion. Contour ploughing involves ploughing across the slope of a hill instead of up and down the slope, which helps to slow down water runoff and reduce soil erosion. Establishment of game reserves helps to protect natural habitats and biodiversity. On the other hand, deforestation involves the clearing of forests or woodlands for agricultural or commercial purposes, which can lead to soil erosion, loss of biodiversity, and climate change. Therefore, deforestation is not a practice that contributes towards the conservation of natural resources.

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The vertebrae that provide articulating surfaces for the ribs are called the thoracic vertebrae. These are the twelve vertebrae in the middle of the back, between the cervical (neck) and lumbar (lower back) vertebrae. The thoracic vertebrae have small joints on their sides called costovertebral joints, where the head of the rib attaches to the vertebra, and larger joints called costotransverse joints, where the tubercle of the rib attaches to the transverse process of the vertebra. These joints allow the ribs to move during breathing and provide stability to the thoracic spine.

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The ventricles of the mammalian heart have thicker muscular walls than the auricles because the ventricles pump blood to longer distances. The heart has four chambers, two atria (auricles) and two ventricles. The atria receive blood and then pass it to the ventricles. The ventricles pump blood to the entire body and the lungs. Since the ventricles pump blood to longer distances, they need more forceful contractions, which require more muscular tissue. This explains why the ventricles have thicker muscular walls than the atria.

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A one-seeded fruit in which the pericarp has fused with the seed coat is classified as a caryopsis. In caryopsis, the fruit wall and the seed coat are fused, and the seed cannot be separated from the fruit wall. Caryopsis is commonly found in the grass family (Poaceae) and is the type of fruit produced by cereal crops such as wheat, rice, maize, and barley.

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The part of the ear in mammals responsible for the detection of sound is the cochlea. The cochlea is a spiral-shaped structure located in the inner ear that contains sensory cells called hair cells. These hair cells are responsible for converting sound vibrations into electrical signals that are transmitted to the brain via the auditory nerve, where they are interpreted as sound. The cochlea is a vital part of the ear that allows us to hear and distinguish different sounds.

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The organelle that is common to both plant and animal cells is mitochondrion. Mitochondria are known as the powerhouse of the cell and are responsible for generating energy in the form of ATP. They are found in both plant and animal cells and are responsible for cellular respiration, a process that breaks down glucose to produce energy. Chloroplasts are specific to plant cells and are responsible for photosynthesis, while centrioles are only found in animal cells and are involved in cell division. Pyrenoid is a specialized organelle found only in certain types of algae.

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An organism which maintains a constant temperature irrespective of environmental temperature fluctuation is a mammal. Mammals are endothermic, meaning they have the ability to regulate their body temperature internally, which allows them to survive in various environments regardless of external temperature changes. In contrast, insects, amphibians, and fish are ectothermic, meaning they cannot regulate their body temperature internally and their body temperature is dependent on the environment they are in.

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The correct order that represents the trend in eutrophication is excess nitrates and phosphates → massive algal growth → lack of oxygen → death of aquatic organisms. Excess nitrates and phosphates are nutrients that promote the growth of aquatic plants and algae. When these nutrients are present in excess, they can cause a rapid increase in the growth of algae, leading to a phenomenon called "algal bloom." As the algae die and decompose, bacteria consume large amounts of oxygen, leading to a reduction in the oxygen levels in the water. This can result in the death of aquatic organisms, such as fish and invertebrates, that require oxygen to survive. Therefore, the correct order of events in eutrophication is excess nitrates and phosphates → massive algal growth → lack of oxygen → death of aquatic organisms.

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The correct answer is "photosynthesis." Plants carry out photosynthesis to produce food (glucose) using light energy, carbon dioxide, and water. This process does not occur in animals, so it is not a life process common to both plants and animals. Respiration, growth, and reproduction are all life processes that occur in both plants and animals. Respiration involves the breakdown of food molecules to release energy, growth refers to an increase in size or number of cells, and reproduction involves the production of offspring.

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The structure used for movement in Amoeba is pseudopodia. Pseudopodia is a temporary extension of the cell membrane and cytoplasm of some cells, including Amoeba. It is used for movement by extending the pseudopodia in a particular direction and then pulling the rest of the cell forward. The pseudopodia can also be used for engulfing food particles. Cilia and flagella are also used for movement in some organisms, but Amoeba moves using pseudopodia. Endoplasm is the inner part of the cytoplasm of the cell.

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The physical and chemical factors that affect the life of organisms in an environment are described as abiotic factors. Abiotic factors are non-living components of an ecosystem that include things like temperature, light, water, soil, air, and nutrients. These factors play a crucial role in determining the distribution and abundance of living organisms in an ecosystem, as they influence the survival, growth, and reproduction of these organisms. Abiotic factors can vary greatly from one environment to another, and can have both direct and indirect effects on the living organisms that inhabit these environments.

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Rhizopus is not considered as a parasitic plant. Rhizopus is a type of fungi that grows on decaying organic matter and is commonly found in soil. While it may be harmful to some plants, it is not a parasitic plant in the same way that Cassytha, Dodder, and Mistletoe are. Cassytha, Dodder, and Mistletoe are all plants that obtain their nutrition by attaching themselves to a host plant and extracting nutrients from it, making them parasitic plants.

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The correct answer is "Low production of insulin". Insulin is a hormone produced by the pancreas that regulates the amount of sugar (glucose) in the blood. In diabetic patients, the pancreas either produces very little insulin or no insulin at all, which results in high levels of glucose in the blood. This happens because insulin is responsible for helping glucose enter the body's cells to be used as energy. When there is not enough insulin, glucose remains in the bloodstream, leading to high blood sugar levels. Therefore, low production of insulin is responsible for the presence of sugar in the blood of diabetic patients.

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The answer is "reversible increase in size". Growth in living organisms is a process that involves an increase in size, weight, and number of cells. However, the increase in size is usually irreversible, which means that once an organism has reached its maximum size, it cannot shrink back to its previous size. The increase in dry weight is a measure of the total amount of organic matter in an organism, while the increase in length is a measure of the size of the organism. The increase in the number of cells is another aspect of growth, which is the result of cell division.

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Siphons and gills are structures in aquatic organisms used for gaseous exchange. Siphons are tube-like structures found in bivalve mollusks, while gills are feathery structures found in fish and some mollusks. Both structures are used to extract oxygen from water and release carbon dioxide, which is necessary for respiration. Siphons and gills are highly adapted for aquatic life, as the concentration of oxygen in water is lower than in air, and they enable organisms to extract enough oxygen to sustain life.

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Disposal of raw sewage into the sea is not an effective management of natural resources to ensure their continued yield from generation to generation. It can cause pollution, harm marine life and disrupt the food chain. Effective management of natural resources involves protecting and conserving them for future generations. Therefore, options A, B, and C are correct as they involve protecting wildlife, preventing habitat destruction, and controlling pests in a sustainable manner to ensure the continued yield of natural resources.

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The ideal environmental condition for plant cells to remain turgid is cool, humid weather. Turgidity is the state of a plant cell being swollen or rigid due to the water content of the cell vacuole. Cool, humid weather provides the necessary moisture to prevent excess transpiration, which can lead to water stress and loss of turgor in plant cells. Hot, dry weather and windy weather tend to increase the rate of transpiration and reduce the amount of moisture available to plants, resulting in wilting and loss of turgor. Cold, dry weather also reduces the availability of moisture to plants, which can lead to water stress and loss of turgor.

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The folded portion of the mitochondrion is called cristae. Mitochondria are organelles that are present in most eukaryotic cells, and they play a crucial role in producing energy for the cell. Cristae are the inner membrane folds of the mitochondria that increase the surface area of the membrane. This increased surface area allows for more electron transport chains and ATP synthase enzymes to be present, which increases the efficiency of ATP production.

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Hydra is the autotrophic organism that is not included among the given options. Explanation: Autotrophic organisms are those that are capable of synthesizing their own food by using inorganic materials such as water, carbon dioxide, and minerals. The examples of autotrophic organisms include Euglena, Chlamydomonas, and Spirogyra, which are capable of carrying out photosynthesis. However, Hydra is a heterotrophic organism that feeds on small aquatic animals and thus is not an autotroph.

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The correct order that represents the trend in eutrophication is: Excess nitrates and phosphates → Massive algal growth → Lack of oxygen → Death of aquatic organisms. Eutrophication is a process in which excessive nutrients, primarily nitrogen and phosphorus, enter water bodies and promote the growth of algae and other aquatic plants. This overgrowth of aquatic plants is called an algal bloom, which can block sunlight and reduce the oxygen levels in water. As a result, aquatic organisms may die due to oxygen depletion. Therefore, the correct order of the trend in eutrophication is excess nitrates and phosphates → massive algal growth → lack of oxygen → death of aquatic organisms.

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The correct statement about feeding relationships is: "In a food chain on land, green plant is the producer." This means that green plants are the first organism in the food chain, as they are able to produce their own food through photosynthesis. They convert sunlight, water, and carbon dioxide into energy that they use to grow and reproduce. All other organisms in the food chain depend on the green plants for their survival. For example, a herbivorous animal like a rabbit eats the green plant, and a carnivorous animal like a fox eats the rabbit. In this way, energy and nutrients are transferred from one organism to another in a linear fashion, with each organism being eaten by another. In contrast, the other statements contain incorrect information. In the first statement, the grasshopper is portrayed as both a predator and prey, which is not accurate. In the second statement, the term "food web" is used instead of "food chain," which changes the meaning of the statement. In the third statement, mollusc larvae are incorrectly identified as producers, when in fact they are consumers. And in the fourth statement, copepods are portrayed as feeding on both mollusk larvae and sand eel, which is not accurate.

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The haploid number of chromosomes in humans is 23. This means that each human cell contains two sets of 23 chromosomes, one inherited from the mother and one from the father. When the egg and sperm combine during fertilization, the resulting zygote has a full complement of 46 chromosomes, which are later halved during the formation of gametes (sperm or egg cells) so that each gamete carries only 23 chromosomes. This number is important for genetic diversity and helps to ensure that offspring have a unique combination of genes from both parents.

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The factor that does not contribute towards the ascent of water in plants is turgor pressure. Explanation: The ascent of water in plants occurs due to a combination of factors including root pressure, capillarity, and transpiration pull. Root pressure is the pressure exerted by the root system on the water in the roots. Capillarity is the ability of water to move up small tubes due to surface tension. Transpiration pull is the force generated by the evaporation of water from the leaves, which creates a negative pressure that draws water up from the roots. Turgor pressure, on the other hand, is the pressure exerted by the cell contents against the cell wall in a plant cell. It helps to maintain the rigidity of the cell, but it does not contribute to the ascent of water in plants.

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The physical process which occurs when a red blood cell is placed in distilled water causing it to burst and break down is known as haemolysis. Haemolysis occurs when red blood cells are placed in a hypotonic solution such as distilled water, which has a lower concentration of solutes than the cytoplasm of the cell. As a result, water moves into the cell causing it to swell and burst, leading to the breakdown of the cell and release of its contents into the surrounding fluid.

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The vertebrae that provide articulating surfaces for the ribs are called the thoracic vertebrae. The thoracic vertebrae are the 12 vertebrae that make up the middle region of the vertebral column and are located between the cervical vertebrae (neck) and the lumbar vertebrae (lower back). The ribs articulate with the thoracic vertebrae at points called facet joints, which allow for movement of the rib cage during breathing. The lumbar vertebrae do not have facets for the articulation of ribs, and the cervical vertebrae only have transverse processes that serve as attachment points for muscles and ligaments. The sacral vertebrae are fused together to form the sacrum and do not have any articulation with the ribs.

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Variation is a factor that enables organisms to adapt to the environment. Variation refers to the differences that exist between individuals of the same species, such as differences in physical characteristics, behavior, or genetics. These differences can provide certain individuals with advantages in their environment, allowing them to survive and reproduce more effectively. Over time, these advantageous traits can become more prevalent in a population, leading to adaptation to the environment. Therefore, variation is an important factor that contributes to the survival and evolution of a species.

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If the mucus in the air track of mammals dry up and the hairs in the nostrils are removed, impure air would be breathed into their lungs. The mucus and hairs in the nostrils serve as filters that trap dust, dirt and other harmful particles that could enter the respiratory system. Without these protective mechanisms, impure air would pass through the nostrils and enter the lungs, potentially causing harm to the respiratory system. The drying up of mucus would also make it difficult for the cilia in the airways to move mucus up and out of the respiratory system, which could lead to the accumulation of mucus and further respiratory problems.

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The question is asking about the pH level in the human gut that is best for enzyme activities if an enzyme works best in an acid medium. The pH level indicates the level of acidity or alkalinity in a solution. Enzymes are proteins that catalyze chemical reactions, and their activity is influenced by the pH level of their environment. Since the enzyme works best in an acid medium, the pH level in the human gut that is best for enzyme activities is a low pH level. The stomach has a low pH level of about 2.0 due to the presence of hydrochloric acid, which helps in the digestion of food and also kills bacteria in the food. Therefore, the stomach is the correct answer to the question.

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If a heterozygous red flowered plant (Rr) was self-fertilized, the offspring would be expected to be a mix of red and white flowered plants in a 3:1 ratio. This is because the R allele is dominant over the r allele, so the heterozygous plant will express the red flowered phenotype. However, during meiosis, the alleles segregate, and each gamete (pollen or egg) only carries one allele. So, half of the gametes will carry the R allele and the other half will carry the r allele. When these gametes combine, the resulting offspring will have different combinations of the R and r alleles, resulting in a 3:1 ratio of red to white flowered plants.

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Honey-bee workers are the sterile females of the hive and carry out a number of important functions to maintain the hive and support the queen. They are responsible for building and repairing the comb, collecting food and water, caring for the young, and defending the hive. However, they do not lay eggs as that is the sole responsibility of the queen bee. Therefore, the correct answer is "laying eggs".

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(a)(i) Respiration

Respiration is the biochemical process by which food substances (chiefly glucose) are broken down within living cells to release energy, which is stored as ATP for the various activities of the organism. It usually involves the intake of oxygen and the release of carbon dioxide and water.

(a)(ii) Two types of respiration with balanced equations

Aerobic respiration (in the presence of oxygen):

Anaerobic respiration (in the absence of oxygen):

In plants/yeast (alcoholic fermentation):

In animal muscle (lactic acid formation):

(b) Mechanisms of breathing in human beings

(i) Inhalation (breathing in)

• The muscles of the diaphragm contract so that the diaphragm flattens and moves downward.
• The external intercostal muscles contract, pulling the ribs upward and outward.
• These increase the volume of the thoracic cavity and lower the pressure inside the lungs below atmospheric pressure.
• Air therefore rushes in through the nose and trachea into the lungs, which inflate.

(ii) Exhalation (breathing out)

• The muscles of the diaphragm relax so that the diaphragm curves upward (dome-shaped) again.
• The external intercostal muscles relax, allowing the ribs to move downward and inward.
• These decrease the volume of the thoracic cavity and raise the pressure inside the lungs above atmospheric pressure.
• Air is therefore forced out of the lungs through the trachea and nose.

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(a) Conservation of natural resources

Conservation of natural resources is the wise and careful use, protection and management of natural resources (soil, water, forests, wildlife, minerals) so that they are not wasted, degraded or destroyed, but are preserved and can be used continuously by both the present and future generations.

(b)(i) Seven methods of soil conservation

1. Crop rotation.
2. Cover cropping / mulching.
3. Contour ploughing (ploughing across the slope).
4. Terracing of hillsides.
5. Afforestation and planting of wind breaks/shelter belts.
6. Addition of manure and fertilizers (maintaining fertility).
7. Avoiding overgrazing and bush burning; strip cropping.

(b)(ii) Four other natural resources that may be conserved

1. Water.
2. Forests (timber/vegetation).
3. Wildlife (animals).
4. Minerals (for example petroleum, coal).

(c) Three factors that negatively affect conservation of forest in West Africa

1. Indiscriminate felling of trees (logging) for timber and fuel wood.
2. Bush burning and clearing of forest for farming (shifting cultivation) and settlement.
3. Overgrazing by animals and rapid population growth increasing demand for land.

(d) The denitrification stage of the nitrogen cycle

Denitrification is carried out by denitrifying bacteria (for example Pseudomonas, Thiobacillus) living in poorly aerated (anaerobic/waterlogged) soils. During this stage the bacteria break down nitrates in the soil into free gaseous nitrogen and oxides of nitrogen, which are released back into the atmosphere. This reduces the amount of nitrates available to plants and returns nitrogen to the air.

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None

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(a) What is a hormone?

A hormone is a chemical substance (chemical messenger) secreted in small quantities directly into the blood by an endocrine (ductless) gland, and carried by the blood to a target organ where it regulates or coordinates a particular body activity.

(b) Role of adrenaline in an emergency situation

Adrenaline is secreted by the adrenal (suprarenal) glands during fright, anger or excitement to prepare the body for 'fight or flight'. It:

• Increases the heart rate and force of heartbeat, and raises blood pressure, so more blood reaches the muscles.
• Raises the blood glucose level by converting stored glycogen in the liver to glucose, supplying energy.
• Increases the rate and depth of breathing, supplying more oxygen.
• Dilates the pupils and diverts blood from the gut and skin to the skeletal muscles, making the body alert and ready for vigorous action.

(c) Five differences between hormonal and nervous coordination

(d) Three animal hormones and two plant hormones

• Animal hormones: adrenaline, insulin, thyroxine (also acceptable: oestrogen, testosterone).
• Plant hormones: auxin, gibberellin (also acceptable: cytokinin, abscisic acid, ethylene).

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(a)(i) Functions of a typical foliage leaf

• Manufacture of food by photosynthesis.
• Gaseous exchange (intake of carbon dioxide and oxygen) through the stomata.
• Loss of water vapour by transpiration, which helps in the upward pull of water.
• Storage of food and water in some leaves.

(a)(ii) Three types of leaf modification with one example each

(Also acceptable: insect-trapping leaf - pitcher plant; bract - Bougainvillea.)

(b) Diagram of the female reproductive part of a flowering plant

The female part is the pistil (carpel/gynoecium). A clear drawing (8-10 cm) should show and label, from top to bottom: the stigma (sticky, receives pollen); the style (stalk connecting stigma to ovary); and the swollen ovary cut to show the ovules attached to the placenta by the funicle, with the micropyle and ovule wall (integuments) indicated.

(c) Three plants pollinated by insects

1. Hibiscus (flamboyant/showy flower).
2. Flamboyant (Delonix regia).
3. Crotalaria (or sunflower, Bougainvillea, Ixora).

Detalles de la respuesta

(a) Short notes

• (i) Ecosystem: An ecosystem is a natural unit made up of all the living organisms (the biotic community) in a given area together with the non-living (abiotic) components of their environment, interacting as a functional whole through the flow of energy and the cycling of nutrients. Examples are a pond, a forest or a grassland.
• (ii) Population: A population is a group of organisms of the same species living together in the same habitat at a particular time and able to interbreed, for example all the tilapia fish in a pond.
• (iii) Ecological succession in plants: This is the gradual and orderly replacement of one plant community by another over a period of time until a stable, self-perpetuating community (the climax community) is reached. It begins with pioneer species (for example lichens and mosses) that colonise bare land, which change the conditions and are succeeded by grasses, then shrubs, and finally trees.

(b) Five ways nitrogen can be made available to the soil for plant growth

1. By nitrogen-fixing bacteria in the root nodules of legumes and free-living soil bacteria (for example Rhizobium, Azotobacter) fixing atmospheric nitrogen into nitrates.
2. By nitrifying bacteria converting ammonium compounds to nitrites and then to nitrates (nitrification).
3. By lightning (thunderstorms) causing nitrogen and oxygen to combine, forming oxides that dissolve in rain as nitrates.
4. By decay of dead plants and animals and their waste, releasing ammonia which is nitrified (action of decomposers/ammonifying bacteria).
5. By addition of nitrogenous fertilizers and organic manure by farmers.