JAMB UTME - Biology - 1991

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The exchange of genes between homologous chromosomes is called crossing-over. During meiosis, homologous chromosomes pair up and form structures called bivalents. Within these bivalents, sections of DNA can break and then rejoin with the corresponding section on the homologous chromosome. This process can result in the exchange of genetic information between the two chromosomes, leading to the creation of new combinations of genes. Crossing-over is an important mechanism of genetic recombination, which increases the genetic diversity of offspring. It is not to be confused with other genetic terms such as test cross, back cross, or mutation, which refer to different genetic phenomena.

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The crown of the mammalian tooth is covered with enamel. Enamel is a hard, mineralized substance that is the hardest tissue in the human body. It covers the outer layer of the tooth, known as the crown, and protects it from wear and tear. Enamel is made up of a crystalline structure composed of calcium and phosphate minerals. It is formed by specialized cells called ameloblasts during tooth development and cannot be regenerated once it is lost. Enamel is the first line of defense against tooth decay and cavities. It is not cement, dentine, or caries that cover the crown of the mammalian tooth.

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The greatest contribution to genetic studies was made by Gregor Mendel. He was an Austrian monk who discovered the basic principles of inheritance through his experiments with pea plants in the mid-19th century. Mendel's experiments involved cross-breeding different pea plants and observing how certain traits, such as flower color or seed shape, were passed down from generation to generation. He noticed that certain traits would always appear in the offspring in predictable ratios, suggesting that there were underlying "units of inheritance" that were being passed down from the parents. Mendel's work laid the foundation for the field of genetics and provided the first clear understanding of how traits are inherited from one generation to the next. He proposed the idea of dominant and recessive traits, and also introduced the concept of genetic segregation, which explains how traits can be passed down from parents to offspring independently of each other. Overall, Mendel's discoveries helped scientists to understand the basic rules of heredity and set the stage for future breakthroughs in genetics.

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Fibrinogen and prothrombin both play important roles in the clotting of blood. When there is an injury to a blood vessel, these proteins work together with other clotting factors to form a blood clot, which helps to stop bleeding and promote healing. Fibrinogen is converted to fibrin, which forms a mesh-like network that traps platelets and other blood cells to form the clot. Prothrombin is converted to thrombin, which then helps to convert fibrinogen to fibrin. Without these proteins, the clotting process would be impaired, and bleeding could become uncontrolled. Therefore, fibrinogen and prothrombin are crucial for maintaining the integrity of the circulatory system and promoting healing after injury.

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The element common to protein, carbohydrate, and lipid is hydrogen. Hydrogen is a chemical element that is present in all organic compounds, including the biomolecules that make up living organisms such as proteins, carbohydrates, and lipids. Proteins, carbohydrates, and lipids are all made up of different combinations of carbon, hydrogen, and oxygen atoms. However, nitrogen and sometimes sulfur and phosphorus can also be present in proteins, while nitrogen can also be present in some carbohydrates. In summary, while all of these biomolecules have unique properties and functions, they all contain hydrogen as a common element.

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The vertebra that lacks a centrum is the Atlas. The Atlas is the first cervical vertebra located just below the skull. Unlike other vertebrae, it lacks a vertebral body or centrum, which is the thick, disc-shaped part of the vertebra that supports the weight of the head and body. Instead, the Atlas has a ring-like structure that supports the skull and allows for its movement. The Atlas also has a pair of lateral masses that articulate with the occipital condyles of the skull, forming the atlanto-occipital joint which allows the head to nod up and down. In summary, the Atlas is the vertebra that lacks a centrum and is specially adapted to support the weight and movement of the skull.

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The function of the epididymis in mammals is the storage of sperms. The epididymis is a long, coiled tube that sits on the surface of the testis. It is where the sperm produced in the testis is stored and matured until it is ready to be ejaculated during sexual intercourse. The epididymis provides a suitable environment for the sperms to mature, gain motility and fertilizing ability. It also helps to transport the sperm from the testis to the vas deferens, which is the tube that carries the sperm out of the body. In summary, the epididymis plays a crucial role in the reproduction of mammals by storing and maturing sperm until they are ready for ejaculation.

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Deoxygenated blood flows into the right and left lungs through the pulmonary artery. The heart is a vital organ that pumps blood throughout the body. Deoxygenated blood enters the right atrium of the heart through the superior and inferior vena cava. From there, it passes through the tricuspid valve and into the right ventricle, which then pumps the blood through the pulmonary artery and into the lungs. In the lungs, carbon dioxide is removed from the blood, and oxygen is taken up by the red blood cells. The now oxygenated blood then returns to the heart through the pulmonary veins and enters the left atrium. From there, it passes through the mitral valve and into the left ventricle, which pumps the oxygenated blood out to the rest of the body. So, the pulmonary artery is the blood vessel that carries deoxygenated blood from the heart to the lungs for oxygenation, whereas the pulmonary vein carries oxygenated blood from the lungs to the heart.

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The application of gibberellin can stimulate a dwarf plant to grow to normal height. Gibberellins are a type of plant hormone that play a critical role in regulating plant growth and development. In particular, they stimulate stem elongation and cell division, which can lead to an increase in overall plant height. By applying gibberellin to a dwarf plant, we can mimic the natural processes that occur in normal-sized plants and promote growth to a more typical height.

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In living cells, glucose can be broken down through two processes, aerobic respiration (with oxygen) and anaerobic respiration (without oxygen). If there is insufficient oxygen available for aerobic respiration, the cells will switch to anaerobic respiration. During anaerobic respiration, glucose is broken down into lactic acid. Lactic acid is then transported to the liver, where it can be converted back into glucose when oxygen is available again. This process is commonly known as the "lactic acid fermentation" and occurs in cells like muscle cells during strenuous exercise when there is not enough oxygen available to produce energy through aerobic respiration.

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Breathing roots are specialized roots in certain plants that grow in waterlogged soils or submerged in water. They have special adaptations to facilitate gaseous exchange, which is the process of taking in oxygen and releasing carbon dioxide. The adaptations include the presence of small openings called lenticels, which are pores on the surface of the roots that allow for the exchange of gases. The lenticels are surrounded by spongy tissue that is rich in air spaces. This allows the roots to absorb oxygen from the air and release carbon dioxide produced during respiration. Stomata, cuticle, and mitochondria are not adaptations found in breathing roots.

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A food web is more stable than a food chain because it contains more organisms and every organism has an alternative source of food. In a food chain, if one organism is affected, it can have a ripple effect on the entire chain and cause it to collapse. However, in a food web, there are many interconnected food chains, and if one chain is disrupted, there are other sources of food for the organisms involved. This makes the food web more resilient and less likely to be destroyed by external factors such as changes in the environment or human activities. Additionally, since a food web has a greater energy source, there is a constant supply of food to support the organisms, which further contributes to its stability.

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In the earthworm, the cocoon is secreted by the citellum. The citellum is a thickened glandular and non-segmented section of the earthworm's body that is located near the anterior end. During mating, the earthworm's body secretes a mucus that forms a ring around the worm's body, and as the worm moves forward, the ring slides towards the anterior end, picking up eggs from the ovaries and sperm from the seminal vesicles. As the mucus ring passes over the citellum, the gland secretes a thick and albuminous secretion that covers the worm's body, forming a cocoon that encloses the eggs and sperm. The cocoon then slips off the worm's body and is deposited in the soil, where the eggs develop and eventually hatch into small earthworms. Therefore, the citellum plays an important role in the reproduction of earthworms by secreting the mucus and albuminous secretion that forms the cocoon.

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The feature that is NOT an adaptive feature for arboreal life is possession of teeth. Arboreal animals are those that live in trees, and they need to be adapted to this lifestyle to survive. Possession of a long tail helps animals maintain balance while moving through the branches. Possession of claws is also important for gripping onto branches and climbing trees. Counter shading in coat colour helps to camouflage animals from predators while they move through the trees. However, possession of teeth is not a unique adaptation to arboreal life. Most animals, regardless of their habitat, have teeth for feeding and survival. Therefore, possession of teeth is not an adaptive feature that specifically helps animals survive in arboreal environments.

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The non-green plant among the options given is fungi. Plants have chlorophyll, a pigment that gives them their green color, and allows them to make their own food through photosynthesis. However, fungi are not plants and they do not have chlorophyll. Instead, they obtain their food by absorbing nutrients from other organisms or from dead organic matter in their environment. Euglena and Spirogyra are both types of algae and they are green because they contain chlorophyll, like other plants. Angiosperms, on the other hand, are flowering plants, and they also contain chlorophyll, allowing them to photosynthesize and produce their own food. In summary, fungi are the non-green plants among the given options because they do not contain chlorophyll and do not photosynthesize to obtain their food.

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The process by which water moves from X to Y through the semi-permeable membrane is called osmosis. Osmosis is the movement of water molecules across a semi-permeable membrane from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration). The semi-permeable membrane allows only water molecules to pass through, while the solute particles are retained on one side of the membrane. This results in the movement of water molecules from a region of high water potential to a region of lower water potential. Osmosis is an important process in the uptake of water by plant roots and in the maintenance of water balance in animal cells. Therefore, the process by which water moves from X to Y through the semi-permeable membrane is called osmosis.

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Organisms in an ecosystem are usually grouped into two main categories based on how they obtain their food or energy. The first group is called producers, which are usually plants or algae that make their food through a process called photosynthesis, using energy from the sun, carbon dioxide, and water. The second group is called consumers, which include animals that eat other organisms to obtain their energy. Consumers can be further divided into three subcategories based on what they eat: - Herbivores: animals that eat plants - Carnivores: animals that eat other animals - Omnivores: animals that eat both plants and animals Parasites are organisms that live on or inside other organisms, known as hosts, and obtain their food from them. Epiphytes are plants that grow on the surface of other plants and obtain their nutrients and moisture from the air and rainwater. Saprophytes are organisms, usually fungi and bacteria, that obtain their food by decomposing dead organic matter, such as dead plants and animals. Therefore, the correct answer to the question is "producers and consumers".

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The disease that can be prevented by inoculation is Tuberculosis. Tuberculosis (TB) is a bacterial infection caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs but can also affect other parts of the body. One of the most effective ways to prevent TB is by vaccination. The TB vaccine, called Bacille Calmette-Guérin (BCG), is a live attenuated vaccine that can provide immunity against the disease in children. BCG vaccination is recommended in many countries with a high prevalence of TB, especially for children who are at the highest risk of developing the disease. While the vaccine is not 100% effective, it can greatly reduce the risk of developing severe forms of TB, such as TB meningitis and disseminated TB. In summary, tuberculosis is the disease that can be prevented by inoculation with the BCG vaccine.

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Nitrogen-fixing microorganisms live in a special structure called root nodules that form on the roots of leguminous plants. These microorganisms, called rhizobia, have the ability to convert atmospheric nitrogen into a form that plants can use to grow. This process, called nitrogen fixation, is essential for plant growth because nitrogen is a crucial component of many important molecules, such as DNA and proteins. In exchange for fixing nitrogen, the rhizobia receive carbohydrates and other nutrients from the plant. This symbiotic relationship between leguminous plants and nitrogen-fixing microorganisms is important for the health of the plant and the surrounding ecosystem.

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The annulus of the fern sporangium helps in spore dispersal. The annulus is a specialized ring of cells that contracts and expands as it dries and absorbs moisture. This motion causes the sporangium to rupture and release the spores, which are then carried away by wind or other means to grow into new ferns. In summary, the annulus is an essential structure for the dissemination of spores, which is necessary for ferns' reproduction and survival.

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Epigeal germination is a type of seed germination that occurs when the cotyledons of the seedling are brought above the ground level. This process is also known as hypogeal germination. Among the options provided, groundnut is an example of a plant that exhibits epigeal germination. During the germination process, the hypocotyl of the groundnut seed elongates and pushes the cotyledons above the ground, while the epicotyl remains below. This brings the cotyledons above the soil level, where they can photosynthesize and provide energy for the seedling to grow. Sorghum, maize, and millet, on the other hand, exhibit hypogeal germination, in which the cotyledons remain below the soil surface.

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When two heterozygotes mate, the dominant trait will appear in both the F1 and F2 generations. The dominant trait masks the recessive trait in the heterozygous individuals of the F1 generation. However, in the F2 generation, there is a 3:1 phenotypic ratio of dominant to recessive traits, as some of the F1 individuals may carry the recessive trait and pass it on to their offspring. Thus, the dominant trait will continue to appear in subsequent generations as long as it is present in the gene pool.

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The movement of the whole organism in response to an external stimulus is called taxis. This means that the organism is able to sense the stimulus and move towards or away from it. For example, if a plant is exposed to sunlight, it may exhibit a phototropic movement by growing towards the light source. Similarly, if an insect is exposed to a certain odor, it may exhibit a chemotactic movement by moving towards or away from the source of the odor. Taxis is different from tropism, which refers to the growth or movement of a part of an organism in response to a stimulus, and from nastic movement, which is a non-directional response to a stimulus.

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Sting cells, also known as cnidocytes, are specialized cells that contain nematocysts in their cytoplasm. These cells are typically found in the body of Hydra, which is a small, freshwater, tentacled, tubular animal belonging to the phylum Cnidaria. The sting cells are used by the Hydra for defense and prey capture. When the tentacles come into contact with an organism, the nematocysts inside the sting cells are triggered to release a toxin, which can paralyze or kill the prey. Thus, sting cells are an important adaptation of the Hydra for survival.

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Maxillipeds are specialized appendages found in crayfish that are used for feeding. These appendages are located near the mouth and are made up of two parts, the maxilla and the foot. The maxilla is the upper part of the appendage and is covered in small hairs called setae. The foot is the lower part of the appendage and is used to manipulate food. When crayfish feed, they use their maxillipeds to grab and manipulate their food. The setae on the maxilla help to sense the presence of food particles in the water, while the foot is used to grasp and crush the food. The maxillipeds also help to move food towards the mouth, where it can be further processed by other mouthparts. Therefore, the primary function of maxillipeds in crayfish is to aid in feeding. They play a critical role in helping crayfish capture and process their food, which is essential for their survival.

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The accessory organ of the digestive system is the liver. The liver produces bile, a substance that helps break down fats in the small intestine. Bile is then released into the small intestine through a duct called the bile duct. The liver also plays a role in processing nutrients from the food we eat and filtering out toxins from the blood. Overall, the liver is a vital organ in the digestive process and helps maintain overall health.

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Angiosperms and gymnosperms belong to the plant group known as spermatophyta, also called seed plants. Spermatophyta is a large and diverse group of plants that produce seeds. Unlike non-seed plants such as mosses and ferns, seed plants have a more advanced reproductive system that enables them to produce seeds, which are the main means of reproduction and dispersal. Gymnosperms are a type of seed plant that produce seeds without enclosing them in a fruit. They are often called "naked seed" plants, and examples include conifers such as pine trees. Angiosperms, on the other hand, are a more advanced type of seed plant that produce seeds within a protective structure called a fruit. They are also known as flowering plants, and examples include apple trees, roses, and sunflowers. In summary, spermatophyta is a group of plants that produce seeds, and within this group, gymnosperms and angiosperms are two distinct types of seed plants that differ in their seed production and structure.

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One of the features that adapts Paramecium to its environment is the possession of cilia. Cilia are tiny hair-like structures that cover the surface of the Paramecium and allow it to move and interact with its environment. The cilia work together to create a wave-like motion that propels the Paramecium forward through the water. This movement helps the Paramecium to find food, avoid predators, and navigate its environment. The cilia also help the Paramecium to exchange gases and remove waste products from its body. In summary, the possession of cilia is an important adaptation for Paramecium as it helps it to survive and thrive in its aquatic environment.

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The gill rakers of fishes take part in feeding. Gill rakers are bony or cartilaginous structures that project from the gill arches into the pharyngeal cavity of fish. They act as a filter to prevent food particles from escaping through the gills while allowing water to pass over them for respiration. The gill rakers trap food particles such as plankton, detritus, and other small organisms that are suspended in the water as the fish ingests it. The trapped food particles are then transported to the digestive tract where they are broken down and absorbed. In summary, gill rakers are important structures that enable fish to feed by filtering food particles from the water as it passes over their gills.

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Reduced humidity can bring about the greatest increase in the rate of transpiration. Transpiration is the process by which water evaporates from the leaves of plants, primarily through small pores called stomata. When the air surrounding the plant is humid, it already contains a high amount of water vapor, which makes it more difficult for water to evaporate from the leaves. On the other hand, when the air is dry, there is less water vapor in the air, creating a larger concentration gradient that drives water to evaporate from the leaves. This results in a higher rate of transpiration. Therefore, reduced humidity can lead to an increase in the rate of transpiration in plants. The other options - increased humidity, reduced temperature, and reduced wind speed - all work in the opposite direction and can decrease the rate of transpiration.

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During the dry season in a deciduous forest, the ground becomes dry and water is scarce. As a result, the trees and plants in the forest adapt to conserve water. One common adaptation is the shedding of leaves, which helps to reduce water loss through transpiration. Therefore, new leaves are unlikely to be formed during the dry season. Instead, the trees enter a period of dormancy, conserving energy and resources until the rains return. This period of dormancy can give the appearance that the trees are dead, but they are actually alive and waiting for better conditions to resume growth. The undergrowth may also decrease during the dry season, as plants and animals struggle to survive in the dry conditions. The ground may become covered in dry leaves and other plant debris, but it is unlikely to become completely bare.

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Among the given options, Pteridophyta are differentiated into true roots, stems and leaves. Pteridophyta are a group of vascular plants that include ferns, horsetails, and clubmosses. Unlike bryophytes (such as mosses) and algae, pteridophytes have true roots, stems, and leaves. These structures allow pteridophytes to grow tall and be more complex in their form and function.

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Fertilizers are lost from the soil through leaching, underground seepages, and run-off. Leaching occurs when excess water passes through the soil and carries soluble nutrients like nitrogen and potassium with it, thus removing them from the root zone. Underground seepages happen when water-soluble nutrients dissolve in water and are transported with it to groundwater reservoirs. Run-off occurs when water moves over the surface of the soil, carrying away the fertilizers. This can occur during heavy rainfall or irrigation. Sheet, gully, and wind erosion can also cause soil degradation, leading to the loss of nutrients, but they are not the main mechanisms of fertilizer loss from the soil. Therefore, fertilizers are lost from the soil mainly through leaching, underground seepages, and run-off.

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