JAMB UTME - Biology - 1990

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The distal part of the nephron and collecting duct fine-tune water reabsorption and regulate electrolyte balance under hormonal control, crucial for maintaining the body's water, electrolyte, and pH balance. These segments respond to hormonal signals such as antidiuretic hormone and aldosterone to adjust water permeability and ion transport, ensuring proper fluid and electrolyte levels in the body.

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Physiological adaptation to very dry condition in animals is called aestivation. Aestivation is a survival strategy used by animals in extremely hot and dry environments where water and food may be scarce. It involves the slowing down of metabolism, reduction of water loss, and the ability to remain inactive for long periods of time until environmental conditions improve. Aestivation is often seen in amphibians, reptiles, and some invertebrates such as snails and insects.

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The villi in the small intestine are finger-like projections that line the inner surface of the intestine. Their significant function is to increase the surface area for absorption of nutrients from digested food into the bloodstream. This absorption is made possible by the presence of microvilli on the surface of the villi. The microvilli create a brush border, which greatly increases the surface area available for the absorption of nutrients such as glucose and amino acids. The villi also contain blood vessels and lacteals that help in the transport of absorbed nutrients to the liver and the rest of the body.

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A feature that adapts birds to flight is the possession of light bones. Birds have several adaptations that allow them to fly, and one of the most crucial is their lightweight skeleton. Unlike mammals, birds have a skeleton that is thin and filled with air pockets, which makes it much lighter. This allows them to generate lift and stay in the air for extended periods without using too much energy. In addition to their light bones, birds also have other adaptations that aid their flight, such as wings with feathers, powerful chest muscles, and a unique respiratory system that allows them to extract oxygen more efficiently. Overall, the possession of a lightweight skeleton is a critical adaptation that enables birds to achieve the remarkable feat of flight.

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The set of diseases that is spread mainly by insect vectors is "Malaria, cholera and river blindness". Insect vectors are organisms like mosquitoes, ticks, and flies that can carry and transmit disease-causing pathogens like bacteria and viruses. Malaria is spread by the Anopheles mosquito, cholera by the Vibrio cholerae bacteria which can contaminate water sources, and river blindness by the black fly which carries the parasite Onchocerca volvulus. The other options do not have diseases that are primarily spread by insect vectors.

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Transpiration can be measured with a potometer. A potometer is a device used to measure the rate of water uptake or loss by a plant. It consists of a glass tube attached to a plant stem, which is then placed in a water-filled container. As the plant loses water through transpiration, the water in the tube is drawn up, and the rate of water loss can be measured by tracking the movement of the water in the tube. Therefore, a potometer is an effective instrument for measuring the rate of transpiration in plants.

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Etiolation is caused by the influence of the absence of light. Etiolation is a phenomenon that occurs in plants when they are grown in the absence of light or insufficient light. When a plant is deprived of light, it will begin to elongate rapidly and become pale in color. This is because light is essential for the process of photosynthesis, which produces energy for the plant to grow and develop. In the absence of light, the plant cannot produce chlorophyll, the green pigment that absorbs light and is necessary for photosynthesis to occur. As a result, the plant will grow tall and spindly in search of light, and its leaves will become thin and pale. This process of elongation and pale coloration is known as etiolation. So, in summary, etiolation is caused by the influence of the absence of light, which prevents the plant from producing chlorophyll and carrying out photosynthesis.

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In a savanna ecosystem, the abiotic factors include water, temperature, and soil. A savanna is a type of grassland ecosystem that is characterized by a distinct wet and dry season. Because of the variability in rainfall, water is a critical abiotic factor that shapes the savanna ecosystem. Temperature is also an important factor, as savannas are typically found in tropical or subtropical regions where the climate is warm. Soil is also an important abiotic factor, as it provides the necessary nutrients for plant growth and plays a role in water retention. While legumes, minerals, oxygen, sandy soil, and reptiles are all components of a savanna ecosystem, they are not considered abiotic factors. Legumes are a type of plant that is commonly found in savannas, while minerals and oxygen are essential components of soil. Sandy soil may also be present in some areas of a savanna, but it is not a defining abiotic factor. Reptiles, while a common biotic factor in savannas, are not abiotic.

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A brackish environment is a place where freshwater and saltwater mix, such as an estuary or a mangrove swamp. The salinity of this environment varies depending on the amount of freshwater and saltwater present. During the rainy season, there is usually an influx of freshwater, which dilutes the saltwater and reduces the salinity. Therefore, the salinity of a brackish environment tends to decrease during the rainy season. On the other hand, during the dry season, there is less freshwater and more evaporation, which leads to an increase in salt concentration and an increase in salinity. Therefore, the salinity of a brackish environment tends to increase during the dry season.

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The correct answer is collenchyma. Collenchyma cells are elongated cells with unevenly thickened cell walls, which provide support to growing plant organs. They are living at maturity and have thin walls compared to other types of cells such as sclerenchyma cells. Sieve tubes and xylem vessels are specialized transport cells in plants, while sclerenchyma cells are specialized for support and protection.

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The glomerulus is structure number 3 in the given options. The glomerulus is a tiny network of blood vessels located in the Bowman's capsule of the kidney. It is a part of the renal corpuscle, which is responsible for filtering blood and removing waste products from it. The glomerulus receives blood from an afferent arteriole and blood is drained from it by an efferent arteriole. As blood passes through the glomerulus, wastes, excess water, and other substances are filtered out and passed into the Bowman's capsule, while important substances are retained in the blood. This filtered fluid is then processed further in the kidney to form urine.

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In a mono-hybrid cross, two pure breeding parents that differ in only one characteristic are crossed to produce the first filial generation (F1). When the gene for normal wings is dominant over the gene for short wings, the F1 generation resulting from the cross between pure line normal-winged Drosophila flies and pure line short-winged flies will all have normal wings because they will inherit the dominant gene from the normal-winged parent. In the second filial generation (F2), the offspring resulting from the cross of F1 individuals, the dominant and recessive traits will segregate in a 3:1 ratio. This means that approximately three-quarters of the F2 flies will have normal wings, and one-quarter will have short wings. Therefore, the correct answer is "F1 flies all normal-winged and three-quarters of F2 flies are normal-winged".

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The organism that will have the lowest population in an ecosystem depends on various factors such as availability of resources, predators, competition for resources, etc. However, in general, the top predators such as the hawk tend to have lower populations than other organisms in the ecosystem. This is because they are at the top of the food chain and rely on the energy and biomass of all the organisms below them in the chain. In contrast, organisms lower in the food chain, such as the cowpea, praying mantis, and mouse, tend to have larger populations. The cowpea is a type of legume that is often grown as a crop, so its population may be artificially controlled by humans. Praying mantises are carnivorous insects that feed on other insects and are often found in gardens and other natural areas. Mice are small rodents that are widely distributed and can thrive in a variety of habitats. Therefore, while there is no clear-cut answer to which organism will have the lowest population in an ecosystem, in general, the top predators such as the hawk are likely to have smaller populations than other organisms.

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The part of the ear that is concerned with balance is the semi-circular canals. These canals are located in the inner ear and are filled with fluid. They are responsible for detecting rotational movements of the head, such as when we turn our head or spin around. The fluid in the semi-circular canals moves in response to these movements, and tiny hair cells within the canals detect this movement and send signals to the brain, which allows us to maintain our balance and orientation in space. The incus and malleus are small bones in the middle ear that help to transmit sound vibrations from the eardrum to the inner ear. The Eustachian tube connects the middle ear to the back of the throat and helps to equalize pressure on either side of the eardrum, which can help to prevent discomfort and hearing problems.

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Lizard has homodont dentition. Homodont dentition refers to having teeth of the same shape and size in the jaws. Lizards have teeth of the same shape and size in their jaws, whereas the other options have heterodont dentition (teeth of different shape and size in their jaws).

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Large amounts of oestrogen and progesterone are produced in the placenta during mammalian embryo development. The placenta is a specialized organ that develops in the uterus during pregnancy and is responsible for exchanging nutrients, gases, and waste products between the mother and the developing fetus. The placenta is formed from both maternal and fetal tissues and contains a network of blood vessels that allow for the exchange of substances. The placenta is also responsible for producing hormones, including oestrogen and progesterone, which help to maintain the pregnancy and support the growth and development of the fetus.

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Muscles are indirectly attached to bones by means of tendons. Tendons are tough, fibrous connective tissues that connect muscles to bones. They transmit the forces generated by the contraction of muscles to the bones, resulting in movement. Tendons are important in providing stability to joints and allowing for smooth and coordinated movement.

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Haemophilia results from the mutation of the genes which control the mechanism for blood-clotting. Haemophilia is a genetic disorder that affects the blood's ability to clot. It is caused by a mutation in one of the genes that are responsible for making clotting factors in the blood. These genes are located on the X chromosome, which means that haemophilia is more common in males since they only have one X chromosome. Females have two X chromosomes, and if one is affected, the other can compensate for the mutation. When a person with haemophilia is injured, their blood does not clot correctly, leading to prolonged bleeding and bruising. There are different types of haemophilia, depending on which clotting factor is affected, and the severity of the disorder can also vary. Overall, haemophilia is a genetic disorder that is caused by a mutation in the genes that control the mechanism for blood-clotting.

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Glucose will produce a brick-red colour when warmed with Benedict's solution. Benedict's solution is a test reagent used to detect the presence of reducing sugars in a sample. When Benedict's solution is heated in the presence of a reducing sugar such as glucose, the copper (II) ions in the reagent are reduced to copper (I) ions, which form a brick-red precipitate. Starch, egg white, and maltose are not reducing sugars, and therefore, will not react with Benedict's solution to produce a brick-red colour.

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The group of invertebrates that reproduces by budding is Coelenterata. Coelenterates are a group of animals that includes jellyfish, sea anemones, and corals. They reproduce both sexually and asexually, with budding being a common method of asexual reproduction. Budding is a form of asexual reproduction in which a new individual grows from a small outgrowth or bud on the parent organism. The bud develops into a miniature replica of the parent and eventually separates from the parent to become a fully independent individual. While arthropods, annelids, and mollusks are all important groups of invertebrates, they do not reproduce by budding. Arthropods, for example, reproduce sexually, with the female laying eggs that are fertilized by the male. Annelids reproduce sexually by exchanging gametes, and mollusks reproduce either sexually or by laying eggs.

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The first step in the process of photosynthesis is the activation of the chlorophyll. Chlorophyll is a green pigment found in the chloroplasts of plant cells. It is responsible for absorbing light energy from the sun, which is then used to power the process of photosynthesis. When light energy is absorbed by chlorophyll, it causes electrons to become excited and move to a higher energy state. This process is known as photoexcitation and is the first step in the process of photosynthesis. The excited electrons are then used to power the other steps in the process of photosynthesis, including the photolysis of water, the reduction of carbon dioxide, and the formation of sugar. So, in summary, the first step in the process of photosynthesis is the activation of the chlorophyll, which absorbs light energy from the sun and initiates the process of photosynthesis.

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Viruses are not considered to be living organisms because they do not possess all the characteristics of life. They cannot carry out any metabolic processes, cannot reproduce on their own, and do not respond to stimuli. Therefore, they are not considered to be alive. However, viruses can possess transmittable characters, such as genetic material or proteins, which allow them to infect and replicate within host cells.

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Free nitrogen is released to the atmosphere by denitrifying bacteria. Denitrifying bacteria convert nitrates in soil back into gaseous nitrogen and release it into the atmosphere, thereby completing the nitrogen cycle. Nitrogen fixation is the process by which atmospheric nitrogen is converted into organic compounds, such as ammonia and amino acids, by nitrogen-fixing bacteria. Nitrifying bacteria convert ammonium into nitrates. Saprophytic bacteria break down dead organic matter and recycle nutrients, but they do not release free nitrogen to the atmosphere.

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The algae, bryophytes and pteridophytes are similar in that they **require moisture for fertilization**. This means that these organisms need a moist environment in order for their gametes (reproductive cells) to come together and fertilize, leading to the formation of a new individual. They all lack specialized structures for transporting water and nutrients throughout their bodies, which is called vascular tissue. However, not all of them are microscopic. While some species of algae can be very small, bryophytes and pteridophytes can be much larger and visible to the naked eye.

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Hydra removes undigested food by passing it through the mouth. After digesting its food, the remaining waste is expelled through the same opening it used to take in the food, the mouth. Hydra does not have a specialized anus for waste removal, so all waste materials are ejected through the same opening used for intake.

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Excretory products responsible for the red, purple and blue colours of flowers are called anthocyanins. Anthocyanins are water-soluble pigments that belong to the flavonoid group. They are synthesized by plants in response to various environmental stimuli, such as light, temperature, and pH. Anthocyanins are responsible for the red, purple, and blue colors in many flowers, fruits, and vegetables. They play important roles in attracting pollinators, protecting plants from UV radiation, and regulating plant growth and development.

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In the tapeworm, the suckers on the scolex are used for holding fast to the host. The scolex is the head of the tapeworm and contains the hooks and suckers that the parasite uses to attach itself to the lining of the host's intestine. Once attached, the tapeworm begins to grow and feed on the host's digested food. The suckers on the scolex are like small suction cups that can create a vacuum-like seal against the host's intestinal wall. This allows the tapeworm to anchor itself securely in place and avoid being expelled from the host's body through peristalsis (the wave-like contractions of the intestines that move food through the digestive system). So, in summary, the suckers on the scolex of a tapeworm are used for holding fast to the host's intestinal wall and avoiding expulsion from the body.

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The organ that secretes digestive enzymes as well as hormones is the pancreas. The pancreas is a glandular organ located in the abdomen, behind the stomach. It plays an important role in digestion by producing enzymes that help break down carbohydrates, proteins, and fats in the small intestine. These enzymes are released into the small intestine through the pancreatic duct. In addition to producing digestive enzymes, the pancreas also secretes hormones such as insulin and glucagon into the bloodstream. These hormones help regulate blood sugar levels and play a critical role in the metabolism of carbohydrates and fats. Overall, the pancreas is a vital organ that plays a key role in both digestion and metabolism.

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The characteristic that is common to Amoeba and Paramecium is the presence of a contractile vacuole. A contractile vacuole is a specialized organelle found in many single-celled organisms, including Amoeba and Paramecium. Its primary function is to pump excess water out of the cell, helping to maintain the proper balance of water and solutes within the cell. Both Amoeba and Paramecium live in aquatic environments where they are constantly taking in water by osmosis. If they were to accumulate too much water, they could burst, so the contractile vacuole is important for preventing this from happening. While both Amoeba and Paramecium also have other organelles, such as the oral groove and cilia (respectively), the presence of a contractile vacuole is the characteristic that they share in common.

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An individual in the AB blood group is a universal recipient for blood donation because there are no anti-A and anti-B antibodies in the serum. In the AB blood group, both A and B antigens are present on the surface of red blood cells, and the individual's immune system does not produce antibodies against these antigens. As a result, they can receive blood from individuals with any blood type without the risk of rejection.

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The nephridia in an earthworm are part of the excretory system. Nephridia are small, tubular structures that function like kidneys to filter and remove metabolic waste products from the body. In earthworms, they are located in pairs in each segment of the body and are responsible for removing nitrogenous waste from the blood and excreting it out of the body as urine.

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An omnivore is an animal that eats both plants and animals. Among the options given, the only animal that fits this description is the mouse. Praying mantises are carnivorous, hawks are carnivorous or predatory, and grasshoppers are herbivorous.

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If a ring of bark and phloem is removed from a stem, the movement of food (sugar) is affected, while the movement of minerals is not hardly affected. The ring of bark and phloem, known as the vascular cambium, is responsible for transporting food (sugar) from the leaves to the rest of the plant. By removing this ring, the plant is no longer able to transport food (sugar) to the rest of the plant, leading to its death after some time. However, the movement of minerals, which is transported through the xylem, is not affected because it is located on the inner side of the vascular cambium, which was not removed.

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Fruits which develop without fertilization are described as "pathenocarpic." Pathenocarpic fruits are formed without the need for pollination or fertilization of the ovules. Instead, they are produced through the stimulation of hormones, such as auxins, in the plant. This process can occur naturally or be induced through the use of chemicals or other means. Pathenocarpic fruits are often seedless, and examples include bananas, grapes, and some citrus fruits.

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External fertilization is a reproductive process in which the fusion of gametes (sperm and egg) occurs outside the body of the female. Among the given options, the organism that undergoes external fertilization is the toad. Toads are amphibians that lay eggs in water. During mating, the male toad releases sperm over the eggs as they are being laid by the female. The sperm fertilizes the eggs, and the resulting embryos develop externally in the water until they hatch into tadpoles. This process is known as external fertilization. In contrast, birds, lizards, and cockroaches are examples of organisms that undergo internal fertilization, where fertilization occurs inside the female's body. The sperm is deposited inside the female, and then fertilizes the eggs.