JAMB UTME - Biology - 1999
Pregunta 1 Informe
Insects visit flowers in order to
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Insects visit flowers in order to feed on the nectar, and in the process, they help to pollinate the flowers. Nectar is a sugary liquid produced by flowers to attract pollinators, such as bees, butterflies, and moths. When insects feed on the nectar, they inadvertently brush against the flower's reproductive structures, such as the anthers (the male reproductive organs) and the stigma (the female reproductive organ). This can result in the transfer of pollen from one flower to another, which is essential for fertilization and seed production. Pollination is the process by which pollen is transferred from the male reproductive organs to the female reproductive organs of a plant, leading to the formation of seeds. Insects play an important role in pollination by carrying pollen from one flower to another as they feed on nectar. This process helps to ensure that plants can reproduce and produce the fruits and seeds that are essential for the survival of many animals, including humans.
Pregunta 2 Informe
The group of Arthropods that has no antennae is the
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The group of Arthropods that has no antennae is the Arachnida. Arachnids are a group of invertebrates that include spiders, scorpions, ticks, and mites, among others. Unlike most other arthropods, arachnids lack antennae. Instead, they have two main body parts (the cephalothorax and the abdomen) and four pairs of legs, which are attached to the cephalothorax. Arachnids have various adaptations to help them sense their environment and locate prey without antennae. For example, many arachnids have specialized sensory structures on their legs, such as setae (hairs) or sensilla (sensory receptors), that can detect vibrations, chemicals, and other stimuli. Some arachnids also have additional sensory organs, such as eyes or chemoreceptors, that can help them navigate their surroundings.
Pregunta 3 Informe
Options
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The older a fossil-bearing rock is, the more likely it is to contain simpler and primitive organisms, and less likely to contain complex and advanced organisms. This is because simple and primitive organisms existed before complex and advanced organisms evolved. Therefore, the correct option in this case is "invertebrates as opposed to vertebrates". Invertebrates are simpler and more primitive than vertebrates and thus were the dominant form of life for a long time before vertebrates evolved.
Pregunta 6 Informe
The lymphatic system of mammals rejoins the blood circulatory system at the
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The lymphatic system is a network of vessels and tissues that help to remove excess fluids and waste products from the body's tissues. Lymphatic vessels transport a fluid called lymph, which contains immune cells and waste products, away from the tissues and towards the heart. At a certain point, lymphatic vessels converge and join to form larger vessels called lymphatic ducts. These ducts eventually empty into a large vein called the subclavian vein, which is located near the collarbone. Therefore, the answer is the subclavian vein, where the lymphatic system of mammals rejoins the blood circulatory system.
Pregunta 7 Informe
Fertilization in humans usually takes place in the
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Fertilization in humans usually takes place in the upper part of the oviduct. The oviduct, also known as the fallopian tube, is a tube that connects the ovaries to the uterus. During ovulation, an egg is released from the ovary and travels down the oviduct towards the uterus. If sperm are present in the oviduct, they can fertilize the egg in the upper part of the oviduct. The upper part of the oviduct is the site of fertilization because this is where the egg and sperm usually meet. The oviduct has finger-like projections called fimbriae that help to capture the egg as it is released from the ovary. The lining of the oviduct also contains cilia, which help to move the egg and sperm towards each other. Once the sperm and egg meet, they fuse together to form a zygote, which will continue to divide and develop into an embryo. is the correct answer because the upper part of the oviduct is the most likely site of fertilization in humans. The lower part of the oviduct and the lower and upper parts of the uterus are not typically involved in the process of fertilization.
Pregunta 8 Informe
They key event in the transition of the amphibians from water to land is the
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The key event in the transition of the amphibians from water to land is the replacement of the gills with lungs. This allowed them to extract oxygen from the air instead of extracting it from water through gills. As a result, amphibians could now survive in areas with little to no water, making it possible for them to venture onto land.
Pregunta 9 Informe
Floating microscopic heterotrophs are mostly grouped as
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Floating microscopic heterotrophs are mostly grouped as zooplankton. Zooplankton are small, drifting animals that live in the open water of oceans and freshwater bodies. They are an important part of the aquatic food chain, serving as a primary food source for many larger aquatic animals. Unlike phytoplankton, which are photosynthetic and produce their own food, zooplankton are heterotrophic and must consume other organisms to obtain their energy. They feed on a variety of food sources, including algae, bacteria, and other small planktonic animals. Zooplankton are incredibly diverse, with thousands of species that come in a wide variety of shapes and sizes. They range from tiny single-celled organisms to larger animals such as jellyfish and krill. Despite their small size, zooplankton play a crucial role in the ecology of aquatic systems, serving as a key link between primary producers and higher trophic levels in the food chain. Therefore, floating microscopic heterotrophs are mostly grouped as zooplankton.
Pregunta 10 Informe
The structure that is most commonly identified in all living cells under the light microscope is the
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Pregunta 11 Informe
After a meal of yam has been digested, the highest concentration of glucose is to be found in the
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After a meal of yam has been digested, the highest concentration of glucose is to be found in the hepatic portal vein. The hepatic portal vein is a blood vessel that carries blood from the digestive system to the liver. After a meal, carbohydrates such as yam are broken down into glucose in the digestive system. The glucose is absorbed into the bloodstream and transported to the liver through the hepatic portal vein. The liver is responsible for regulating the concentration of glucose in the blood. It stores excess glucose as glycogen and releases it into the bloodstream when the body needs it. So, in summary, after a meal of yam has been digested, the highest concentration of glucose is to be found in the hepatic portal vein because it carries blood from the digestive system to the liver, where glucose is regulated and stored.
Pregunta 12 Informe
In the woody stems, gaseous exchange takes place through the
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In woody stems, gaseous exchange takes place through the lenticels. Lenticels are small pores or openings on the bark of woody stems that allow for gas exchange between the inner tissues of the stem and the surrounding environment. Unlike stomata, which are found on leaves and are used for gas exchange in herbaceous plants, lenticels are specifically adapted for gas exchange in woody stems. They allow for the exchange of gases like oxygen, carbon dioxide, and water vapor, which are important for the survival of the plant. Lenticels are particularly important during periods of active growth and development, as well as in response to environmental stresses such as flooding, drought, and extreme temperatures.
Pregunta 13 Informe
The construction of dams may lead to an increase in the prevalence of
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The construction of dams may lead to an increase in the prevalence of malaria, bilharziasis, and onchocerciasis. When a dam is built, it creates an artificial body of water which provides a breeding ground for mosquitoes that transmit malaria. The stagnant water created by the dam may also increase the prevalence of bilharziasis and onchocerciasis, which are caused by parasitic worms that live in freshwater snails and black flies respectively. The increased prevalence of these diseases can be attributed to the increased exposure of people to the parasites, as well as the creation of suitable habitats for their respective vectors.
Pregunta 14 Informe
The richest source of vitamin A are
Detalles de la respuesta
The richest source of vitamin A are palm oil and carrot. Vitamin A is a fat-soluble vitamin that is important for vision, immune function, and skin health. Palm oil is a rich source of beta-carotene, which is converted to vitamin A in the body. Carrots are also rich in beta-carotene, which makes them an excellent source of vitamin A. Rice and oranges are not particularly high in vitamin A, and while groundnut oil contains some vitamin A, it is not as rich a source as palm oil or carrot.
Pregunta 16 Informe
The loud cry made by a brooding hen when a predator is around is meant to
Detalles de la respuesta
The loud cry made by a brooding hen when a predator is around is meant to warn its chicks and other chickens of impending danger. The brooding hen is protective of her young and will sound the alarm when she senses danger, such as a predator nearby. The loud cry is a warning signal to her chicks and other chickens to hide or flee to safety. This behavior is an instinctual way of protecting and ensuring the survival of her offspring and flock.
Pregunta 18 Informe
The division of a body into two equal halves along a longitudinal plane is called
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Pregunta 19 Informe
Th chitin in the exoskeleton of many arthropods is strengthened by
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Pregunta 20 Informe
The most important environment factor which epiphytes in the rain forest compete for is
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The most important environmental factor that epiphytes in the rainforest compete for is light. Epiphytes are plants that grow on the surface of other plants, such as tree trunks and branches. They do not grow in soil and obtain their nutrients and water from the air and rain. Because they grow on other plants, they are often shaded from direct sunlight. This creates competition for the available light among the epiphytes. The ones that are able to capture more light will have an advantage over those that do not. This is why many epiphytes have adapted to have specialized structures, such as large leaves or aerial roots, that help them capture and absorb as much light as possible. Therefore, light is the most important environmental factor that epiphytes compete for in the rainforest.
Pregunta 23 Informe
The biological factor that is unique to each individual is the
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The biological factor that is unique to each individual is their DNA. DNA (Deoxyribonucleic Acid) is a molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms. It is found in the cells of every living thing and contains the genetic information that determines the traits and characteristics of an individual, such as eye colour, blood group, and other physical and biological attributes. Each individual has a unique sequence of DNA, which is determined by the combination of genetic information inherited from their parents. DNA is responsible for passing on hereditary traits from one generation to the next and is the main factor that makes each individual unique.
Pregunta 24 Informe
If the offspring of a cross between a brown mouse (bb) and a black mouse (BB) are allowed to interbreed, how many different genotypes would result?
Detalles de la respuesta
If the offspring of a cross between a brown mouse (bb) and a black mouse (BB) are allowed to interbreed, four different genotypes would result.
When the brown mouse (bb) and black mouse (BB) are crossed, their offspring are all heterozygous (Bb) and have a black coat due to the dominant black allele. If these offspring are allowed to interbreed, their offspring can have any of the four possible combinations of alleles from their parents: BB, Bb, bB, or bb. The BB and bb genotypes will produce black and brown coat colors respectively, while the Bb and bB genotypes will produce a black coat, as the black allele is dominant. Therefore, the four possible genotypes that can result from the interbreeding of the offspring are BB, Bb, bB, and bb.
Pregunta 25 Informe
Bacteria multiply rapidly by means of
Detalles de la respuesta
Bacteria multiply rapidly by means of binary fission. Binary fission is a type of asexual reproduction in which a single bacterium divides into two identical daughter cells. This process involves DNA replication, followed by the elongation of the cell and the separation of the two identical DNA copies into each of the two daughter cells. This means that bacteria can multiply rapidly and produce a large number of offspring in a short period of time, allowing them to quickly colonize new environments and grow in number. The other options, such as budding, fragmentation, and spore formation, are types of reproduction or growth that occur in some other organisms but not in bacteria.
Pregunta 26 Informe
Vaccination is carried out in order to
Detalles de la respuesta
Vaccination is carried out to stimulate the production of antibodies. Vaccines contain a weakened or dead version of a disease-causing pathogen or its parts, which triggers an immune response in the body. This immune response leads to the production of antibodies, which are specific proteins that can recognize and neutralize the pathogen if the person is exposed to it in the future. Thus, vaccination helps to prevent or reduce the severity of the disease caused by the pathogen.
Pregunta 27 Informe
The habitat of the cysticercus of taenia solium is
Detalles de la respuesta
The habitat of the cysticercus of Taenia solium is the muscles of pig. Taenia solium is a parasitic tapeworm that infects pigs and humans. The adult tapeworm lives in the small intestine of humans, while the larval stage, known as cysticercus, can form cysts in various tissues of the pig, including the muscles, heart, and brain. When humans eat undercooked or raw pork infected with cysticercus, the larvae can develop into adult tapeworms in their small intestine. Therefore, it is important to cook pork thoroughly to kill any cysticerci that may be present and to prevent infection.
Pregunta 28 Informe
In plant cells, the chloroplast are located
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In plant cells, the chloroplasts are located within the cytoplasm. Chloroplasts are organelles found in plant cells that are responsible for photosynthesis. They contain chlorophyll, a pigment that absorbs light energy and converts it into chemical energy that can be used by the plant. Chloroplasts are unique to plant cells and are not found in animal cells. The cytoplasm is the gel-like substance that fills the cell and surrounds the organelles. It is where many of the cell's metabolic reactions occur. Chloroplasts are one of the organelles that are located within the cytoplasm of plant cells. Chloroplasts are typically found in the mesophyll cells of the plant's leaves, where they are most exposed to sunlight. They are also found in other green parts of the plant, such as the stem and immature fruit.
Pregunta 30 Informe
The force that holds water together in the form of a stream within the xylem tube is the
Detalles de la respuesta
The force that holds water together in the form of a stream within the xylem tube is cohesion of water molecules to one another by hydrogen bond. Water molecules are attracted to each other through hydrogen bonds, which create a strong cohesive force. This cohesive force is what allows water molecules to stick together and form a continuous column within the xylem tube, even in the face of gravity. It's this force that helps water move from the roots of plants, up through the xylem, and all the way to the leaves, where it's used in photosynthesis.
Pregunta 31 Informe
Which of the following characterizes the white mangrove?
Detalles de la respuesta
The white mangrove is characterized by breathing roots. Mangroves are a group of trees and shrubs that grow in coastal areas and are adapted to survive in saltwater environments. The white mangrove (Laguncularia racemosa) is one of the three most common species of mangrove found in the Americas. It grows in muddy coastal areas and has a unique adaptation called "pneumatophores" or breathing roots, which extend from the soil surface to above the waterline. These roots help the tree to breathe in the oxygen it needs to survive in the anaerobic soil of the intertidal zone. The other options, such as prop roots, buttress roots, and stilt roots, are characteristic of other species of mangroves.
Pregunta 32 Informe
A soil consisting of alumina and iron (II)oxide is known as
Detalles de la respuesta
A soil consisting of alumina and iron (II) oxide is known as laterite. Laterite is a soil type that is common in tropical regions with high temperatures and heavy rainfall. It is a weathered, reddish-brown soil that is formed by the leaching of silica and other minerals, leaving behind a concentration of alumina and iron oxide. Laterite soil is characterized by its high content of clay and its ability to retain moisture, making it suitable for growing crops such as rice, tea, and coffee. It is also commonly used as a building material in tropical regions, due to its strength and durability. In contrast, loamy soil is a mixture of sand, silt, and clay, and is considered ideal for gardening and farming. Clayey soil is dominated by clay particles, and is often poorly drained and difficult to work with. Podzol is a soil type that is characterized by its acidic, nutrient-poor properties, and is found in colder, more temperate regions.
Pregunta 33 Informe
The possession of scales, laying of eggs with shells and bony structure of the head are characteristics shared by
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Pregunta 34 Informe
In which of the following organisms does each cell combine the function of nutrition, reproduction and growth?
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The organism in which each cell combines the function of nutrition, reproduction, and growth is Spirogyra. Spirogyra is a type of filamentous green algae that consists of a long chain of cells. Each cell of Spirogyra has a nucleus, chloroplasts, and a large central vacuole. The chloroplasts are responsible for photosynthesis and the production of food for the cell. The nucleus controls the cell's activities, including growth and reproduction. Spirogyra reproduces asexually by the process of fragmentation, where a part of the filament breaks off and forms a new filament. It also reproduces sexually by the process of conjugation, where two filaments come together and exchange genetic material. So, in summary, Spirogyra is the organism in which each cell combines the function of nutrition, reproduction, and growth.
Pregunta 35 Informe
Which of the following is an organ?
Detalles de la respuesta
The liver is an organ. An organ is a group of tissues that work together to perform a specific function in the body. The liver is an essential organ located in the upper right-hand side of the abdomen, just below the diaphragm. It plays a vital role in metabolism, detoxification, digestion, and the production of various hormones and proteins. The liver produces bile, which helps to digest fats and absorb fat-soluble vitamins. It also helps to regulate the levels of glucose, cholesterol, and other substances in the blood. The liver is a vital organ for maintaining good health, and any dysfunction or damage to it can have serious consequences for the body.
Pregunta 36 Informe
The organism that has a hydrostatic skeleton is
Detalles de la respuesta
The organism that has a hydrostatic skeleton is an earthworm. A hydrostatic skeleton is a structure found in soft-bodied invertebrates, which uses the pressure of fluid-filled body cavities to provide support and movement. In earthworms, the hydrostatic skeleton is made up of a fluid-filled body cavity called the coelom, which is surrounded by muscle tissue. When the circular muscles in one segment contract, the fluid is pushed towards the longitudinal muscles in the next segment, causing them to extend and push the worm forward. The hydrostatic skeleton also allows the earthworm to change its shape and move through narrow spaces. In contrast, Tilapia, Hydra, and mosquito larva do not have a hydrostatic skeleton. Tilapia is a fish that has a bony skeleton, while Hydra is a freshwater animal that has a simple body structure without a well-defined skeleton. Mosquito larvae also have a soft body and use their muscles to move, but they do not have a hydrostatic skeleton. Therefore, the correct answer is "earthworm", as it is the organism that has a hydrostatic skeleton, which is a structure found in soft-bodied invertebrates, that uses the pressure of fluid-filled body cavities to provide support and movement.
Pregunta 37 Informe
Yellowing of leaves is a symptom associated with deficiency of
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Pregunta 38 Informe
The structure labelled II is known as
Detalles de la respuesta
The structure labeled II is a lymph vessel. Lymph vessels are part of the lymphatic system, which is responsible for removing excess fluids and waste products from the body's tissues. Lymph vessels are similar in structure to blood vessels but they carry lymph, a clear fluid that contains immune cells and waste products, instead of blood. Lymph vessels have thin walls and valves that help to move the lymph through the body. In the image or diagram being referred to, the structure labeled II has a characteristic appearance of a lymph vessel, with a thin wall and a round or oval shape. Therefore, the correct answer is "lymph vessel".
Pregunta 39 Informe
The structure labelled II articulates with III to form
Detalles de la respuesta
The structure labelled II articulates with III to form a hinge joint. A joint is where two bones come together, and the type of joint depends on the way the bones are able to move in relation to each other. A hinge joint allows for movement in one direction, like a door hinge. It is composed of two bones that fit together and move along a single axis. Structure II is likely referring to a bone that has a convex, rounded end, while structure III is a bone that has a concave, curved surface. When these two bones come together, they form a hinge joint that allows for movement in one direction only, such as the elbow or knee joint. In contrast, a sliding joint allows bones to glide past each other, a pivot joint allows for rotation around a single axis, and a ball-and-socket joint allows for movement in multiple directions.
Pregunta 40 Informe
The least adaptive feature of aboreal life is the
Detalles de la respuesta
The least adaptive feature of arboreal life is shading of coat colour. Arboreal animals are animals that live primarily in trees, and they have evolved many adaptations that allow them to live and move effectively in this environment. For example, possession of four limbs and claws are adaptations that help arboreal animals to grip onto branches and climb trees. Development of a long tail is another adaptation that helps with balance and maneuvering in trees. However, shading of coat colour is not an adaptive feature for arboreal life. While some arboreal animals may have developed specific coat colours to help them blend in with their surroundings and avoid predators, this is not a universal adaptation for all arboreal animals. In fact, some arboreal animals have bright or distinctive colours to help them attract mates or communicate with other members of their species. Therefore, the correct answer is "shading of coat colour" as it is the least adaptive feature of arboreal life compared to the other options given.
Pregunta 41 Informe
Mammals acclimatize to reduced oxygen content at high altitudes by
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Pregunta 42 Informe
The correct sequence for the perception of smell in mammals is
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When mammals inhale air, the airborne molecules carrying various scents dissolve in the mucus membrane lining the nasal cavity. The dissolved chemicals bind to the olfactory receptor neurons present in the sensory cells, generating electrical impulses that travel along the olfactory nerve fibers to the olfactory bulb, which is part of the brain. From the olfactory bulb, the impulses are transmitted to various parts of the brain responsible for processing the smell. Therefore, the correct sequence for the perception of smell in mammals is "dissolved chemicals → sensory cells → olfactory nerve → brain".
Pregunta 43 Informe
Substance manufactured by the leaves are transported to other parts of the plant through the
Detalles de la respuesta
The substance manufactured by the leaves, such as sugars and other nutrients, are transported to other parts of the plant through a specialized tissue called phloem. The phloem is a vascular tissue that is responsible for carrying the products of photosynthesis, as well as other nutrients, from the leaves to other parts of the plant, such as the roots, stems, and flowers. The phloem is made up of two types of cells: sieve tubes and companion cells. The sieve tubes are long, cylindrical cells that are responsible for transporting the sugars and nutrients. The companion cells are located next to the sieve tubes and are responsible for controlling the movement of materials into and out of the sieve tubes. Together, the sieve tubes and companion cells form a complex network that transports the products of photosynthesis and other nutrients throughout the plant. So, in summary, the substances manufactured by the leaves are transported to other parts of the plant through a specialized tissue called phloem, which is made up of sieve tubes and companion cells.
Pregunta 44 Informe
The structure labelled III represents the
Detalles de la respuesta
The structure labelled III represents the proboscis. A proboscis is a tubular feeding organ found in some animals, which is used to suck up liquids or to pierce and suck blood or nectar from flowers. In insects, the proboscis is a specialized mouthpart that is used to extract nectar from flowers or to pierce the skin of other animals to feed on their blood. The proboscis is made up of several parts, including the labium, which is the lower lip of the insect, and the hypopharynx, which is a tube that runs through the center of the proboscis. In the image or diagram being referred to, the structure labelled III has a characteristic appearance of a proboscis, with a long, thin, and tubular shape. Therefore, the correct answer is "proboscis".
Pregunta 45 Informe
The modes of nutrition in Nitrobacter, Ascaris and Homo sapiens respectively are
Detalles de la respuesta
Nitrobacter is a type of bacteria that obtains energy by oxidizing nitrogen compounds. Ascaris is a parasitic roundworm that feeds on nutrients from its host's intestine. Homo sapiens, like most animals, are holozoic and obtain nutrients by consuming other organisms. Therefore, the modes of nutrition for Nitrobacter, Ascaris and Homo sapiens respectively are chemosynthetic, parasitic and holozoic.
Pregunta 46 Informe
In mammals, the organ which performs digestive and endocrine functions is the
Detalles de la respuesta
The organ which performs digestive and endocrine functions in mammals is the pancreas. The pancreas is a glandular organ located near the stomach and small intestine, and it plays a key role in digestion and maintaining blood sugar levels in the body. The digestive function of the pancreas involves producing and secreting digestive enzymes into the small intestine to break down food. These enzymes include proteases that break down proteins, lipases that break down fats, and amylases that break down carbohydrates. In addition to its digestive function, the pancreas also has an endocrine function. It produces hormones such as insulin and glucagon, which are important for regulating blood sugar levels in the body. Insulin helps to lower blood sugar levels, while glucagon helps to raise them. Therefore, the pancreas is the organ in mammals that performs both digestive and endocrine functions.
Pregunta 47 Informe
In epigeal germination, the cotyledons are
Detalles de la respuesta
In epigeal germination, the cotyledons are carried above the ground by the elongating hypocotyl. Epigeal germination is a type of seed germination in which the cotyledons emerge above the soil surface, and the hypocotyl elongates to lift them up. The hypocotyl is the part of the stem that is located between the cotyledons and the radicle. As the hypocotyl elongates, it raises the cotyledons, which become the first leaves of the young seedling. This is in contrast to hypogeal germination, where the cotyledons remain below the soil surface and the epicotyl elongates to raise the plumule (shoot) above the ground.
Pregunta 48 Informe
In dissection, the rib cage of mammal has to be opened in order to expose the
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Pregunta 49 Informe
The sign + is used to indicate an association where an organism gains, while 0 is used where an organism is unaffected. An association indicated as +0 is known as
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An association indicated as +0 is known as commensalism. Commensalism is a type of symbiotic relationship between two organisms where one organism benefits while the other is neither helped nor harmed. In the given context, the plus sign (+) indicates that one organism benefits from the association, while the zero (0) indicates that the other organism is unaffected. Therefore, in a +0 association, one organism benefits, while the other is neither helped nor harmed. Examples of commensalism in nature include certain species of fish that follow larger animals such as whales or sharks, feeding on the leftovers from their meals without harming them. Similarly, some species of birds build their nests in the trees of other birds, using the existing structure without affecting the host bird's ability to use the nest. Therefore, an association indicated as +0 is known as commensalism, which is a type of symbiotic relationship where one organism benefits while the other is unaffected.
Pregunta 50 Informe
Which of the following is one of Lamarck's theories?
Detalles de la respuesta
One of Lamarck's theories is that new species originate through the inheritance of acquired traits. Lamarck was a French naturalist who developed a theory of evolution before Darwin. He believed that organisms could acquire new traits during their lifetime through the use or disuse of certain parts of their bodies, and that these acquired traits could be passed down to their offspring. For example, Lamarck believed that if a giraffe stretched its neck to reach higher leaves on a tree, it would develop a longer neck over time. He also believed that if a blacksmith developed large muscles from using his arms and hands, his children would inherit those large muscles. This theory of the inheritance of acquired traits has since been disproven, as it is now known that traits are determined by genetics and are not acquired during an individual's lifetime. However, Lamarck's ideas were influential in the development of the theory of evolution, and his emphasis on the importance of adaptation and change over time was an important contribution to the field. The other options given in the question are not theories of Lamarck, but rather concepts in the field of biology. "Some variations are more favourable to existence in a given environment than others" is a concept related to natural selection, which was proposed by Darwin. "All living organisms are constantly involved in a struggle to existence" is a concept related to the idea of survival of the fittest, which was also proposed by Darwin. "The size of a given population remains fairly constant" is a concept related to the principle of population ecology, which is the study of how populations of organisms interact with their environment.
