JAMB UTME - Biology - 2001

Which of the following organisms does not exist as a single free living cell?

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All of the given options are unicellular organisms and exist as single free-living cells, except for Volvox. Volvox is a colonial organism, which means it consists of many individual cells that live and work together as a unit. Each cell in the colony performs a specific function, such as reproduction, movement, or photosynthesis. The cells are connected by thin strands of cytoplasm, which allow them to communicate and share nutrients. Although Volvox appears to be a single organism to the naked eye, it is actually a collection of many individual cells that work together for the survival of the colony.

The greatest influence on a stable ecosystem in nature is exerted by

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The part labelled II is the

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The center for learning and memory in the human brain is the

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The center for learning and memory in the human brain is the cerebrum. The cerebrum is the largest and most complex part of the brain, and it is responsible for many higher brain functions, including learning and memory. It is divided into two hemispheres, the left and right cerebral hemispheres, which are connected by a bundle of nerve fibers called the corpus callosum. The cerebrum is involved in conscious thought, perception, emotion, and many other complex mental activities, making it the primary site for learning and memory formation in the brain.

A green snake in green grass is able to escape notice from predators because of its

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The ability of a green snake in green grass to escape notice from predators is due to its cryptic colouration. Cryptic colouration, also known as camouflage, is a form of coloration that allows an organism to blend in with its environment, making it difficult to be noticed by predators or prey. In this case, the green snake's body coloration closely matches the color of the surrounding green grass, making it harder for predators to spot the snake.

The hygrometer is used for measuring

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The hygrometer is used for measuring relative humidity. Relative humidity is a measure of how much water vapor is in the air, compared to the maximum amount of water vapor that the air could hold at a given temperature. The hygrometer works by measuring the amount of water vapor in the air, typically using a hair or synthetic sensor that changes in length or electrical resistance as the humidity changes. This change is then translated into a reading that can be displayed on a gauge or digital display. By measuring relative humidity, the hygrometer is useful in a variety of applications, such as weather forecasting, monitoring of indoor air quality, and control of industrial processes.

The epiphytic habitat can best be described as

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The epiphytic habitat refers to a type of environment where certain plants or organisms live attached to the surface of other plants or objects, usually in trees or other tall structures. This means that epiphytes grow without the need for soil, but rely on moisture and nutrients obtained from the air, rain, or debris that accumulates around them. Therefore, the best term to describe the epiphytic habitat is "arboreal", which means living in or relating to trees. Examples of epiphytes include bromeliads, orchids, ferns, mosses, and lichens.

The physical space occupied by an organism together with its functional role in community can be described as

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The most important adaptation of xerophytes is the ability of the protoplasm to

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Xerophytes are plants that are adapted to grow in environments with very little water, such as deserts. One of the most important adaptations of xerophytes is their ability to resist being damaged by the loss of water. This adaptation is achieved by the ability of the protoplasm to shrink from the cell wall. When xerophytes are exposed to high temperatures and low humidity, they lose water through transpiration at a very high rate. If the protoplasm were to remain in contact with the cell wall, it would dry out and become damaged. However, xerophytes have developed a mechanism to avoid this by shrinking their protoplasm away from the cell wall. This creates a space between the protoplasm and the cell wall, which is filled with air. The air layer provides insulation and reduces the rate of water loss from the plant. This process of shrinking away from the cell wall is known as cytorrhysis, and it is a reversible process. When water becomes available again, the protoplasm swells and returns to its original position against the cell wall. Therefore, the correct answer to the question is: The most important adaptation of xerophytes is the ability of the protoplasm to resist being damaged by the loss of water by shrinking from the cell wall.

The transportation of oxygen and carbon (IV) oxide in mammals is carried out by

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The transportation of oxygen and carbon dioxide in mammals is carried out by erythrocytes, which are also known as red blood cells. Erythrocytes are specialized cells that contain a protein called hemoglobin, which binds to oxygen and carbon dioxide molecules. Oxygen is transported from the lungs to the tissues of the body, while carbon dioxide is transported from the tissues back to the lungs for exhalation. When erythrocytes pick up oxygen in the lungs, the oxygen molecules bind to the hemoglobin in the red blood cells and form a complex called oxyhemoglobin. This complex is then transported by the erythrocytes to the tissues of the body where the oxygen is released and diffuses into the cells. At the same time, erythrocytes pick up carbon dioxide molecules that are produced by the cells during cellular respiration. The carbon dioxide binds to the hemoglobin in the erythrocytes and is transported back to the lungs where it is released and exhaled. Leucocytes, thrombocytes, and phagocytes are other types of blood cells that play different roles in the immune system and blood clotting, but they do not play a significant role in the transportation of oxygen and carbon dioxide in mammals.

The mode of feeding in Amoeba and Hydra is

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Amoeba and Hydra are two different organisms with different modes of feeding. Amoeba is a unicellular organism that belongs to the group of protozoans. It is a heterotroph, which means that it obtains its food by ingesting other organisms or organic matter. Amoeba feeds by extending its pseudopodia (false feet) around its prey and engulfing it, forming a food vacuole inside the cell. The food is then broken down by enzymes in the vacuole and the nutrients are absorbed by the cell. Hydra, on the other hand, is a multicellular organism that belongs to the group of cnidarians. It is a holophytic organism, which means that it obtains its food by photosynthesis. Hydra contains chloroplasts, which are responsible for capturing light energy and producing food in the form of glucose. However, Hydra can also be a heterotroph and feed on small aquatic organisms, such as plankton. Therefore, the correct answer to the question is: Amoeba is a heterotrophic organism, while Hydra is a holophytic and heterotrophic organism.

Amphibian are normally found

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Amphibians are a group of cold-blooded animals that are characterized by their ability to live both in water and on land. However, the specific habitat of amphibians can vary depending on the species. Most amphibians start their life cycle in water, where they lay their eggs. The eggs hatch into aquatic larvae, such as tadpoles, which breathe through gills and live exclusively in water. As they mature, they develop lungs and limbs, and gradually transition to a terrestrial lifestyle. However, even as adults, many amphibians still require access to water for reproduction, hydration, and thermoregulation. Therefore, the correct answer to the question is: Amphibians are generally found in both water and on moist land. However, some species spend more time in the water, while others are more adapted to living on land.

An association between the root nodule of a leguminous plant and rhizobium sp, is known as

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The association between the root nodule of a leguminous plant and Rhizobium sp. is an example of symbiosis. Symbiosis is a relationship between two organisms of different species that benefits at least one of the organisms involved. In the case of the leguminous plant and Rhizobium sp., the plant provides a home for the bacteria within its root nodules. The bacteria, in turn, help the plant to fix atmospheric nitrogen, which is essential for plant growth. This is done through a process called nitrogen fixation, which converts nitrogen gas from the air into a form that can be used by the plant. Therefore, the correct answer to the question is: The association between the root nodule of a leguminous plant and Rhizobium sp. is an example of symbiosis.

The parts which function together to bring about hearing are labelled

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The parts which function together to bring about hearing are labelled as I, II, III and IV. These labels refer to the different structures in the ear that work together to allow us to hear sound. Label I refers to the outer ear, which collects sound waves and directs them towards the middle ear (II). Label III represents the inner ear, which contains the cochlea and the vestibular system responsible for balance, as well as the auditory nerve. Finally, label IV is the auditory cortex in the brain, which processes and interprets the sounds we hear. Therefore, all the parts of the ear involved in hearing, from the outer ear to the brain, are necessary for the sense of hearing to function properly.

The structure that holds the yolk in position is labelled

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When yeast respire anaerobically, it converts simple sugar to carbon (IV) oxide and

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When yeast respires anaerobically, it converts simple sugar into carbon dioxide and alcohol. Anaerobic respiration occurs in the absence of oxygen, so instead of using oxygen as an electron acceptor, yeast uses another molecule such as pyruvate. The process is called alcoholic fermentation, and it converts glucose, a simple sugar, into two molecules of pyruvate, which is then converted into alcohol and carbon dioxide. The alcohol produced is usually ethanol, which is commonly used in the production of beer, wine, and bread. The carbon dioxide produced is responsible for the bubbles in beer and the rise in bread dough.

The ability of an organism to live successfully in an environment is known as

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The ability of an organism to live successfully in an environment is known as adaptation. Adaptation refers to the ability of an organism to adjust to its environment by changing its physical, behavioral, or physiological characteristics. These changes allow the organism to survive and reproduce in the environment, and to compete successfully for resources. Adaptation is a key concept in evolutionary biology, as it is through adaptation that species can evolve over time to better fit their environment. Resistance refers to the ability of an organism to withstand or fight off a particular stressor, such as a disease or toxin. Competition refers to the interaction between two or more organisms competing for the same resources, such as food or habitat. Succession refers to the process by which an ecosystem changes over time, as different species come and go in response to changes in the environment.

A tall plant crossed with a dwarf one produces offspring of which half are tall and half are dwarf. What are the genotypes of the parents?

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This pattern of inheritance can be explained by the laws of segregation and independent assortment proposed by Gregor Mendel. According to these laws, every individual has two copies of each gene, one inherited from each parent, and these copies can be either dominant or recessive. In this case, we are told that a tall plant (let's call it T) was crossed with a dwarf one (let's call it t) and produced offspring that were half tall and half dwarf. This means that the tall parent must have had two dominant alleles (TT), while the dwarf parent must have had two recessive alleles (tt). When the two parents were crossed, their offspring inherited one allele from each parent. Since the tall parent had two dominant alleles, it could only contribute a T allele to its offspring, while the dwarf parent could only contribute a t allele. This means that all the offspring were heterozygous (Tt), meaning they had one dominant allele and one recessive allele. Half of the offspring were tall, meaning they inherited a dominant T allele from the tall parent. The other half were dwarf, meaning they inherited a recessive t allele from the dwarf parent. Therefore, the genotypes of the parents are Tt and tt.

In ferns, the structure above is equivalent to the

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Blood vessel usually pass through the structure labelled

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Most monocots are easily recognized by their

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Most monocots are easily recognized by their long and sword-like leaves. Monocots are a class of flowering plants that are characterized by a number of features, including the presence of a single cotyledon (or seed leaf) in their embryo, parallel-veined leaves, and scattered vascular bundles in their stem. One of the most distinctive features of monocots is their leaves, which are typically long and narrow, with parallel veins running the length of the leaf. This is in contrast to dicots, which have broad leaves with branching veins. The long and sword-like leaves of monocots are an adaptation to their environment, as they help the plant to efficiently capture sunlight for photosynthesis, while also minimizing water loss through transpiration. The narrow leaves also allow monocots to grow closely together, which is advantageous in crowded environments where space is limited.

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Salts and water are absorbed in the roots and transported to the leaves by osmosis through the xylem tissues. The xylem is a specialized tissue in plants that transports water and minerals from the roots to the leaves. Water and mineral ions, such as salts, are absorbed by the roots through osmosis, which is the movement of water from an area of high concentration to an area of low concentration. As the concentration of water and minerals in the roots increases, it creates a pressure gradient that forces the water and minerals up through the xylem vessels. Diffusion, on the other hand, is the movement of particles from an area of high concentration to an area of low concentration. While diffusion can occur in plant tissues, it is not the primary mechanism for the transport of water and minerals from the roots to the leaves. The phloem, another specialized tissue in plants, transports sugars and other organic molecules from the leaves to other parts of the plant. While osmosis and diffusion are involved in the transport of these molecules through the phloem, they are not involved in the transport of water and minerals from the roots to the leaves. In summary, salts and water are absorbed in the roots and transported to the leaves by osmosis through the xylem tissues.

A seedling grown in the dark is likely to be

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A seedling grown in the dark is likely to be etiolated. Etiolation is a term used to describe the abnormal growth of a plant in darkness or low light conditions. When a plant is grown in the dark, it elongates its stem and produces small leaves to try and reach for light. This results in a tall, spindly plant that appears weak and fragile. This is because the plant is using all its energy to grow upwards to get more light, rather than developing a sturdy stem and strong leaves. Therefore, a seedling grown in the dark is likely to be etiolated.

The role of the male adult honey bee is to

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The role of the male adult honey bee, also known as a drone, is to mate with the queen bee. The drone's primary purpose is to fertilize the queen during mating flights, after which the drone dies. Drones do not have stingers and do not gather nectar or pollen, nor do they contribute to the day-to-day activities of the hive, such as cleaning, ventilation, or caring for the young. Their sole purpose is to mate with the queen and ensure the survival of the colony by producing new worker bees.

The highest percentage of energy in an ecosystem occurs at the level of the

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The highest percentage of energy in an ecosystem occurs at the level of the producers. Producers, also known as autotrophs, are organisms that make their own food using sunlight, water, and carbon dioxide through a process called photosynthesis. They are usually plants, algae, and some bacteria. Producers are the foundation of the food chain, and all other organisms in the ecosystem depend on them for energy. When producers are eaten by primary consumers, such as herbivores, only about 10% of the energy stored in the food is transferred to the next level, which is the secondary consumers. This is known as the 10% rule. As a result, the highest percentage of energy is always found at the lowest level of the food chain, which is the producers.

The probability of a baby being a boy or a girl depends on the contribution of the

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The probability of a baby being a boy or a girl depends on the contribution of the father's sex cell. The father's sex cell, also known as the sperm cell, contains either an X or a Y chromosome. If a sperm cell carrying an X chromosome fertilizes the mother's egg, the resulting baby will be female (XX). If a sperm cell carrying a Y chromosome fertilizes the egg, the resulting baby will be male (XY). Therefore, the sex of the baby is determined by the contribution of the father's sex cell.

In man, the ability to roll the tongue is a variation classified as

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Both recessive and dominant characters are found

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Both recessive and dominant characters are found at the same locus of a homologous chromosome. Each chromosome in a pair is inherited from one parent, and the genes located on these chromosomes determine the traits that an individual exhibits. A gene is a section of DNA that contains the instructions for producing a specific protein or RNA molecule. The locus is the specific location of a gene on a chromosome. In diploid organisms like humans, each locus is present in two copies, one inherited from each parent. Dominant traits are those that are expressed when at least one copy of the gene is present, while recessive traits are only expressed when two copies of the same gene are present. Therefore, both dominant and recessive characters can be found at the same locus of a homologous chromosome. For example, in humans, the gene for brown eyes (dominant) and blue eyes (recessive) are found at the same locus on chromosome 15. This means that an individual can inherit one copy of the brown eyes gene from one parent and one copy of the blue eyes gene from the other parent. In this case, the dominant brown eyes gene will be expressed, and the recessive blue eyes gene will be masked. In summary, both dominant and recessive characters can be found at the same locus of a homologous chromosome, and their expression is determined by the number of copies of the gene an individual inherits.

The structure above represents a

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Water fleas, wood lice and barnacles belong to the group

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Water fleas, wood lice, and barnacles belong to the group Crustacea. Crustaceans are a large group of arthropods that live in aquatic environments, and they include familiar creatures such as crabs, lobsters, and shrimp. They have two pairs of antennae and two or three pairs of mouthparts, and their bodies are covered by a hard exoskeleton. Water fleas are small crustaceans that live in freshwater, wood lice are crustaceans that live on land, and barnacles are crustaceans that live attached to rocks, boats, and other surfaces in the ocean. Crustaceans play an important role in aquatic ecosystems as both predators and prey, and they are also used as a food source for humans.

For heterotrophic organisms, competition is least caused by the inadequacy of

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For heterotrophic organisms, competition is least caused by the inadequacy of light. Heterotrophic organisms are living beings that obtain their food by consuming other organisms, either directly or indirectly. Examples include animals, fungi, and some bacteria. Since heterotrophs require organic compounds for their survival, the availability of nutrients and space are usually the main limiting factors for their growth and reproduction. Competition arises when multiple individuals or populations compete for limited resources. In the case of heterotrophic organisms, competition can be intense for resources such as nutrients and space, as these are necessary for their survival and reproduction. However, light is not a major resource for heterotrophs since they do not produce their own food through photosynthesis. Therefore, the inadequacy of light is least likely to cause competition among heterotrophic organisms.

The number of plants species obtained from a population study of a garden is as follows: Guinea grass (15), Ipomea spp (5), sida spp (7) and Imperata spp (23). What is the percentage of occurrence of Imperata spp?

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To calculate the percentage of occurrence of Imperata spp, we need to divide the number of individuals of Imperata spp by the total number of individuals in the population, then multiply by 100. So, the total number of individuals in the population is: 15 (Guinea grass) + 5 (Ipomea spp) + 7 (sida spp) + 23 (Imperata spp) = 50 The number of individuals of Imperata spp is 23, so the percentage of occurrence of Imperata spp is: (23 / 50) x 100 = 46% Therefore, the answer is 46%.

Which of following groups is the most advanced?

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To determine which group is the most advanced, we need to define what is meant by "advanced." In general, we could say that a group is more advanced if it has more complex structures and functions, is better adapted to its environment, and has a greater diversity of species. Based on these criteria, we can eliminate Bryophytes and Thallophytes from consideration as the most advanced group. While both groups have important ecological roles, they are generally less complex and less diverse than the other two groups. Between Pteridophytes and Gymnosperms, it is generally accepted that Gymnosperms are more advanced. This is because Gymnosperms have evolved some key adaptations that have allowed them to be successful in diverse environments. For example, they have evolved a woody stem that allows them to grow tall and compete for sunlight, and they have developed seeds that are protected by cones, which allow them to disperse to new areas and survive harsh conditions. Additionally, Gymnosperms are generally more diverse than Pteridophytes, with over 1,000 species compared to around 12,000 species of ferns and other Pteridophytes. In summary, Gymnosperms are generally considered to be the most advanced group out of the four options listed, due to their complex structures, adaptations, and diversity of species.

The factor that least affects food shortages in sub-saharan Africa is

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The factor that least affects food shortages in sub-Saharan Africa is mixed-cropping. Food shortages in sub-Saharan Africa can be caused by a variety of factors, including drought, flooding, pests, and poor agricultural practices. However, mixed-cropping is not a major factor contributing to food shortages in the region. Mixed-cropping is a traditional agricultural practice where multiple crops are grown in the same field. This method is often used to maximize yields and reduce the risk of crop failure. While mixed-cropping may not be the most efficient method of farming, it is generally not a major factor contributing to food shortages. In contrast, drought, flooding, and pests can have a significant impact on crop yields and contribute to food shortages in the region. For example, prolonged droughts can cause crops to wither and die, while flooding can damage crops and make it difficult to plant and harvest. Pests, such as locusts and armyworms, can also destroy crops and cause significant damage to agricultural production. In summary, mixed-cropping is the factor that least affects food shortages in sub-Saharan Africa, with drought, flooding, and pests being more significant contributors to the problem.

A freshwater pond may contain

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The distribution of plants in a rain forest is governed mainly by

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The distribution of plants in a rainforest is mainly governed by the rainfall pattern. Rainforests are characterized by high levels of rainfall and humidity, and these conditions play a crucial role in determining the distribution of plant species within the ecosystem. The amount and distribution of rainfall is a key factor in determining the availability of water for plants, and this in turn affects their growth and survival. In a rainforest, plant species are distributed according to their tolerance for varying levels of moisture and light. Some species require large amounts of water and can only grow in areas that receive high levels of rainfall, while others can tolerate drier conditions and can be found in areas with lower levels of rainfall. Overall, rainfall patterns are the main factor governing the distribution of plants in a rainforest, as they determine the availability of water and the conditions under which different plant species can survive and thrive.

The veins of the leaf are formed by the

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The veins of the leaf are formed by the vascular bundles. These bundles contain specialized cells, such as xylem and phloem, which transport water, nutrients, and sugars throughout the plant. The xylem cells carry water and minerals from the roots to the leaves, while the phloem cells transport sugars produced during photosynthesis from the leaves to other parts of the plant. The arrangement and pattern of the veins can vary among different plant species and can also help to support the leaf structure.

The jointed structure in insects that bears organs which are sensitive to touch, smell and vibration is the

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The jointed structure in insects that bears organs which are sensitive to touch, smell, and vibration is the antenna. Antennae are located on the head of an insect and consist of small segments called flagellum. Antennae are extremely sensitive and serve as sensory organs for insects, allowing them to navigate their environment, find food, and communicate with other insects. They are responsible for detecting touch, taste, and smell, as well as sensing changes in temperature, humidity, and air currents. Therefore, the antenna is an essential structure for insects as it plays a crucial role in their survival and adaptation to their surroundings.

Which of the following is likely to encourage inbreeding in plants?

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Monoecious plants are more likely to encourage inbreeding. Monoecious plants have separate male and female flowers on the same plant, which can increase the likelihood of self-fertilization and inbreeding. Inbreeding can result in a loss of genetic diversity, which can lead to reduced fitness and adaptability of the plant population. In contrast, dioecious plants have separate male and female plants, which reduces the likelihood of self-fertilization and promotes outcrossing, or fertilization between different plants. Protandrous plants have male and female flowers that mature at different times, which can also reduce the likelihood of self-fertilization. Hermaphrodite plants have both male and female reproductive structures in the same flower, but they still have mechanisms to reduce self-fertilization, such as physical separation of the male and female parts or temporal separation of pollen release and stigma receptivity.

Darwin is considered the first scientist who correctly explained the theory of

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Darwin is considered the first scientist who correctly explained the theory of organic evolution. This theory explains how species of organisms change over time through the process of natural selection. Darwin observed that organisms that are better adapted to their environment are more likely to survive and pass on their advantageous traits to their offspring, eventually leading to the development of new species. Darwin's work was based on extensive observations and research, and his theory of organic evolution is now widely accepted in the scientific community.

Urea formation occurs in the

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Urea formation occurs in the liver. The liver is responsible for many functions in the body, one of which is removing harmful toxins such as ammonia from the bloodstream. Ammonia is produced when the body breaks down protein from the foods we eat. To prevent ammonia from building up in the body, the liver converts it into a less harmful substance called urea. Urea can then be safely transported through the bloodstream to the kidneys and eventually eliminated from the body through urine. So, the liver plays a crucial role in the process of urea formation, which helps to maintain a healthy balance of nitrogenous waste products in the body.

The enzyme invertase will hydrolyze sucrose to give

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The enzyme invertase will hydrolyze sucrose to give glucose and fructose. Sucrose is a disaccharide composed of glucose and fructose molecules linked together. Invertase is an enzyme that catalyzes the hydrolysis of sucrose, breaking it down into its component parts. Specifically, invertase cleaves the glycosidic bond between glucose and fructose, releasing them as separate molecules. This process is known as inversion, which is where invertase gets its name. Therefore, when sucrose is hydrolyzed by invertase, it yields glucose and fructose.

The gas produced during tissue respiration can be identified by using

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The gas produced during tissue respiration is carbon dioxide. It can be identified by using calcium hydroxide, also known as lime water. When carbon dioxide is passed through lime water, it forms a milky precipitate of calcium carbonate. Therefore, calcium hydroxide can be used to test for the presence of carbon dioxide, which is the gas produced during tissue respiration.

The stem of a typical aqautic plant usually has many

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Carbon (IV) oxide content of the atmosphere is least affected by

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Which of the following statements is true of blood groups and blood transfusion?

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The statement that is true of blood groups and blood transfusion is that group AB is the universal recipient. Blood groups are determined by the presence or absence of certain antigens on the surface of red blood cells. There are four main blood groups: A, B, AB, and O. When a person needs a blood transfusion, it is important to match their blood group with the blood group of the donor. Group O blood does not have any A or B antigens, so it can be given to people with any blood group. Therefore, Group O is often called the universal donor. However, Group O individuals can only receive Group O blood. Group A blood has A antigens on the surface of its red blood cells, and Group B blood has B antigens. Group AB blood has both A and B antigens, while Group O has none. Because Group AB blood has both A and B antigens, it can receive blood from any blood group without the risk of an adverse reaction. Therefore, Group AB is the universal recipient. Group A individuals can donate blood to people with Group A or AB blood, while Group B individuals can donate to people with Group B or AB blood. This is because a person's immune system can react to a blood transfusion with an incompatible blood type, which can cause serious complications.

When specimen X is mixed with few drops of iodine solution, the appearance of a blue-black colour confirms that X is

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When specimen X is mixed with a few drops of iodine solution and a blue-black color appears, it confirms that X is starch. Iodine solution is commonly used to test for the presence of starch in a sample. Iodine reacts with the starch molecule to form a dark blue or black color, indicating the presence of starch. Starch is a complex carbohydrate that is found in many plant-based foods, such as potatoes, rice, and wheat. It is made up of many glucose molecules linked together in a chain-like structure. When iodine solution is added to a sample that contains starch, the iodine molecules are able to fit in between the glucose molecules in the starch chain, forming a complex that reflects light differently and giving the blue-black color. In summary, the appearance of a blue-black color when specimen X is mixed with iodine solution confirms that X is starch.

The structures labelled II and III respectively are

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Archegonium = Female Reproductive Organ

Source

The part labelled IV is the

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Viviparity occurs mainly in the

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Viviparity is the ability of an animal to give birth to live young instead of laying eggs. Among the four given options, viviparity mainly occurs in mammals. This is because mammals have developed a unique reproductive system in which the embryos develop within the mother's body through a specialized organ called the placenta. The placenta allows the developing fetus to obtain nutrients and oxygen from the mother's bloodstream, while also removing waste products. This process of internal gestation and nourishment is what allows mammals to give birth to live young, rather than laying eggs like other animals such as reptiles, aves (birds), and amphibians. So, the correct option is mammals.