WAEC SSCE - Biology - 2018 (Objective)

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The exchange of genes between homologous chromosomes is called crossing over. During meiosis, which is the process by which cells divide to form gametes, homologous chromosomes pair up and exchange segments of their genetic material. This exchange occurs at specific points called chiasmata, which are where the chromosomes break and rejoin with each other. Crossing over can result in the exchange of alleles, which are alternative versions of a gene, between the homologous chromosomes. This can lead to the production of new combinations of alleles that were not present in either parent, which contributes to genetic diversity. Back cross and test cross are different types of breeding experiments, while mutation refers to a change in the DNA sequence that can arise spontaneously or be induced by environmental factors.

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Active transport differs from diffusion in that active transport allows the movement of substances against the concentration gradient. Diffusion is the process by which molecules move from an area of high concentration to an area of low concentration. This is driven by the natural tendency of molecules to distribute evenly in a system. Active transport, on the other hand, requires energy to move substances against the concentration gradient, from an area of low concentration to an area of high concentration. This process is important in cells because it allows the cell to take in nutrients, eliminate waste, and maintain a balance of ions and other substances inside and outside the cell. Therefore, active transport differs from diffusion in that active transport allows the movement of substances against the concentration gradient.

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The association between living organisms in which one lives on and feeds at the expense of the other is called parasitism. In this relationship, one organism (the parasite) benefits while the other organism (the host) is harmed. The parasite lives on or within the host and uses its resources for food and shelter. Examples of parasites include tapeworms, lice, and mosquitoes.

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The odontoid process is found on the axis vertebra. The axis is the second cervical (neck) vertebra, which is located just below the atlas vertebra. The odontoid process is a projection of bone that extends from the upper surface of the axis vertebra and serves as a pivot point for the rotation of the head.

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The thyroid gland is a part of the endocrine system, and it is located in the neck, specifically at the base of the neck. The gland is butterfly-shaped, with two lobes on either side of the trachea (windpipe) and connected by a thin strip of tissue called the isthmus. It produces hormones that regulate metabolism and other bodily functions.

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The greatest contribution to genetic studies was made by Gregor Mendel. Mendel was an Austrian monk who conducted a series of experiments in the mid-19th century with pea plants, which allowed him to discover the basic principles of inheritance and the patterns of transmission of genetic traits from parents to offspring. He established the laws of segregation and independent assortment, which provided a framework for understanding the mechanisms of genetic inheritance. His work laid the foundation for the modern science of genetics, and he is widely regarded as the father of genetics.

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A plant cell has 14 chromosomes prior to mitosis, but the number of chromosomes in the daughter cells depends on the type of cell division. During mitosis, the cell duplicates its chromosomes and then separates them equally into two identical daughter cells. This means that each daughter cell will receive the same number of chromosomes as the parent cell. So, after mitosis, each daughter cell will also have 14 chromosomes, the same as the parent cell. However, in other forms of cell division such as meiosis, the number of chromosomes in the daughter cells can be different from the parent cell. But for mitosis, the number of chromosomes in the daughter cells is the same as the parent cell.

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The chemical bond that holds the base pairs of the two strands of DNA together is a hydrogen bond. DNA is composed of two strands of nucleotides, which are composed of a sugar molecule, a phosphate group, and a nitrogen-containing base. The nitrogen-containing bases in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). The two strands of DNA are held together by hydrogen bonds between the nitrogen-containing bases. Adenine always bonds with thymine, and cytosine always bonds with guanine. These hydrogen bonds are relatively weak, but they are strong enough to hold the two strands of DNA together. Therefore, the chemical bond that holds the base pairs of the two strands of DNA together is a hydrogen bond.

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The scientist who introduced the system of naming organisms using two Latin names, known as binomial nomenclature, was Carolus Linnaeus. Linnaeus was a Swedish botanist and zoologist who lived in the 18th century. He created a system for classifying and naming all living things, which is still used today. In this system, each species is given a unique two-part name, consisting of the genus name and the species name, both written in Latin. For example, the scientific name for humans is Homo sapiens, where Homo is the genus name and sapiens is the species name. This system allows scientists to clearly and precisely communicate about specific species, and to understand their relationships to other species. Linnaeus' system of classification and naming has been incredibly important for the study of biology and the understanding of the diversity of life on Earth.

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The theory depicted in the illustration is known as Lamarckism or Lamarckian evolution, and it was proposed by Jean Lamarck. Lamarck proposed that organisms can acquire traits during their lifetime based on their environment and behavior, and these acquired traits can be passed on to their offspring. He believed that the environment could drive evolution by selecting for advantageous traits and gradually eliminating disadvantageous ones. However, this theory was later largely discredited by scientific evidence, and it was replaced by the theory of natural selection proposed by Charles Darwin.

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Starch is a complex carbohydrate made up of many glucose units linked together. The process by which starch is converted into maltose is called hydrolysis. In hydrolysis, a water molecule is added to the bond between two glucose units, breaking the bond and forming two separate molecules of glucose. This process is catalyzed by an enzyme called amylase. Therefore, the correct answer is (a) Hydrolysis.

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Fossils are naturally preserved in rocks. When a plant or animal dies, its body may become buried in sediment, such as sand or mud. Over time, more layers of sediment can accumulate on top, which can compress and harden the lower layers into rock. As the body decays, minerals from the surrounding sediment can seep into the bones or other hard parts, replacing the organic material with rock-like minerals. This process is called fossilization, and it can preserve the remains of the organism for millions of years. Later on, erosion and weathering can expose these fossils, allowing us to study and learn about the organisms that lived long ago.

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The larva in the diagram is commonly referred to as a caterpillar. Caterpillars are the juvenile form of butterflies and moths. They have a worm-like appearance and are characterized by their multiple legs, which they use to move around and search for food. As they grow, they molt their skin several times, eventually transforming into a pupa or chrysalis, where they undergo metamorphosis and emerge as an adult butterfly or moth.

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The streaming movement of cytoplasm within the Paramecium is known as Cyclosis. Cytoplasm is the gel-like substance that makes up most of a cell's interior and contains all the organelles and other cellular structures. In the Paramecium, the cytoplasm moves in a continuous, circular flow, which is called Cyclosis. This flow helps distribute nutrients, waste, and other materials throughout the cell, and it also helps mix and distribute chemicals that are involved in various cellular processes. Overall, Cyclosis plays a critical role in maintaining the health and function of the Paramecium cell.

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The correct statement is: "Intensity of stimulus must reach a threshold value before the neurons can be excited." Neurons, which are the basic building blocks of the nervous system, respond to various stimuli by transmitting electrical signals. However, not all stimuli are strong enough to trigger this response. The stimulus must reach a certain level of intensity or strength, known as the threshold, before the neuron will be excited and transmit an electrical signal. If the stimulus is below the threshold, the neuron will not respond. This is why neurons must receive a stimulus of sufficient intensity before they can be excited.

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Ultrafiltration in the kidney takes place in Bowman's capsule. Bowman's capsule is a cup-shaped structure located in the outer part of the kidney, called the cortex. It surrounds a cluster of blood vessels called the glomerulus. The glomerulus and Bowman's capsule together form a structure called the renal corpuscle. During ultrafiltration, blood from the glomerulus flows into Bowman's capsule. The glomerulus is made up of a network of capillaries with very small pores. These pores allow small molecules such as water, salts, and waste products to be filtered out of the blood and into the Bowman's capsule. The larger molecules such as proteins and blood cells cannot pass through the pores and remain in the bloodstream. The filtered fluid in Bowman's capsule is called the glomerular filtrate. It contains water, salts, glucose, and other small molecules. This filtrate then passes through the rest of the nephron, where it is further processed and modified before being excreted as urine. So, in summary, ultrafiltration in the kidney takes place in Bowman's capsule, where small molecules are filtered out of the blood and into the nephron to form the glomerular filtrate.

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The instrument used to determine the turbidity of water is a Secchi disc. Turbidity refers to the cloudiness or haziness of a liquid, caused by the presence of suspended particles in the water. The Secchi disc is a simple, circular device that is used to measure water turbidity by determining the depth at which the disc is no longer visible when it is lowered into the water. The Secchi disc is typically painted in alternating black and white quadrants, and is used by lowering it into the water until it is no longer visible. The depth at which the disc disappears is recorded, and this measurement is used to estimate the turbidity of the water. Therefore, the instrument used to determine the turbidity of water is a Secchi disc.

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One major difference between plant and animal nutrition is the ability of plants to synthesize food. Plants are able to produce their own food through the process of photosynthesis, in which they use energy from sunlight to convert carbon dioxide and water into sugars and oxygen. Animals, on the other hand, cannot produce their own food and must obtain energy by consuming other organisms, either directly (as predators) or indirectly (as herbivores). This means that plants are autotrophic, while animals are heterotrophic. The ability to synthesize food is a key difference between plant and animal nutrition, and it is one of the reasons why plants are considered the primary producers in most ecosystems.

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The hospital should have carried out an agglutination test on both patients X and Y before transfusing the blood from the donor. The agglutination test is a standard blood test that determines the compatibility between the donor's blood and the recipient's blood. The test checks for the presence of antigens and antibodies in the blood, which could trigger an adverse reaction in the recipient. In this case, patient X has blood group AO, which means they have A antigens on their red blood cells and anti-B antibodies in their plasma. Patient Y, on the other hand, has blood group AB, which means they have both A and B antigens on their red blood cells and no antibodies in their plasma. The blood transfusion from the donor may have contained B antigens, which would have triggered an immune response in patient X, causing difficulty in breathing. Therefore, the agglutination test would have prevented the transfusion of incompatible blood and avoided any adverse reactions.

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The disease caused by a bacterium is syphilis. Syphilis is a sexually transmitted disease caused by the bacterium Treponema pallidum. It is transmitted through sexual contact and can also be transmitted from an infected mother to her unborn child. Syphilis can cause a variety of symptoms, including genital sores, skin rashes, and fever. If left untreated, syphilis can cause serious complications such as blindness, dementia, and even death. Syphilis can be treated effectively with antibiotics.

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The organelle that is found only in plant cells is plastids. Plastids are organelles that are involved in the synthesis and storage of food, pigments, and other materials in plant cells. They are responsible for storing and converting energy, and they can also play a role in the coloration of plant tissues. Plastids come in several forms, including chloroplasts, which contain chlorophyll and are involved in photosynthesis, and chromoplasts, which contain pigments that give fruits and flowers their color. Mitochondria, ribosomes, and lysosomes are all found in both plant and animal cells.

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The ascent of water in tall trees is mainly due to transpiration pull. Transpiration is the process by which water evaporates from the leaves of plants and creates a negative pressure or tension in the water column of the xylem, which is the tissue responsible for transporting water in plants. This negative pressure or tension, combined with the cohesive forces between water molecules, creates a continuous column of water that extends from the roots to the leaves of the tree. The cohesive forces between water molecules allow the water column to remain unbroken, while the transpiration pull provides the force that moves the water up the tree. Adhesive forces between the water and the cell walls of the xylem also help to keep the water column intact and prevent it from breaking under tension. Root pressure, which is the pressure created by the roots of a plant, can also play a role in moving water up a tree, but it is not the main mechanism responsible for water ascent in tall trees.

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The digestion of starch, protein, and lipids would be affected if the duodenum of a person was surgically removed. The duodenum is the first part of the small intestine, where digestive enzymes from the pancreas and bile from the liver are mixed with partially digested food from the stomach. The enzymes in the duodenum help break down starch into smaller sugar molecules, protein into amino acids, and lipids into fatty acids and glycerol. If the duodenum is removed, the digestive enzymes and bile will not mix with the food, and the digestion of these substances will be impaired. Therefore, the person may have difficulty digesting starch, protein, and lipids, leading to malabsorption and other digestive problems.

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Oxygen is not an excretory product of animals. Oxygen is essential for respiration, which is the process that releases energy from food. During respiration, animals take in oxygen and release carbon dioxide as a waste product. Urea is a waste product formed in the liver as a result of protein metabolism, and it is excreted by the kidneys. Sweat is also an excretory product that is produced by sweat glands to regulate body temperature and remove excess water and salts. Therefore, the correct answer is option D, which is oxygen.

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The social insect that is not included in the given list is the housefly. Houseflies are not social insects because they do not live in colonies or work together to maintain a nest or hive. Houseflies are solitary insects that do not exhibit any social behavior. In contrast, termites, honeybees, and ants are all social insects that live in colonies or hives and exhibit a division of labor where different individuals perform different tasks to maintain the colony. For example, in an ant colony, there are workers that gather food, soldiers that defend the colony, and a queen that lays eggs. The individuals in a social insect colony work together to ensure the survival and success of the colony.

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The process being investigated in this experiment is the ascent of water through the xylem. By placing the seedling in a solution of red ink, the red dye is able to travel up the xylem vessels along with the water. When a transverse section of the stem is examined under a microscope, the red dye can be seen in the xylem vessels, showing the path taken by water through the plant. This process is also known as transpiration, where water evaporates from the leaves and creates a negative pressure, which draws water up through the roots and into the xylem. The study of this process is important for understanding how plants transport water and nutrients from the roots to the rest of the plant.

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Genes that remain linked are those that are close to each other on the chromosomes. Chromosomes are structures in the cell that carry genetic information in the form of genes. Genes are segments of DNA that contain the instructions for making proteins, which are the building blocks of the body. In sexually reproducing organisms, such as humans, each parent contributes one chromosome to each pair of chromosomes in the offspring. As a result, offspring have two copies of each gene, one from each parent. Genes that are located close to each other on the same chromosome are more likely to be inherited together because they are physically close and cannot easily separate during the process of meiosis, which is the process by which cells divide to form gametes, such as sperm and eggs. Therefore, genes that remain linked are those that are close to each other on the chromosomes.

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Conservation of wildlife is necessary for several reasons, one of the main reasons being to prevent extinction of species. Extinction means that a species is no longer found on the Earth and has disappeared forever. This is a serious problem because once a species is gone, it cannot be brought back. Additionally, loss of species can also have a cascading effect on the ecosystem and other species that rely on it. Another important reason for conservation is that many wild animals play important roles in the ecosystem. For example, predators help control populations of other species and maintain balance in the ecosystem. Wild species also provide valuable resources and ecosystem services, such as pollination and seed dispersal, that are essential for human well-being. Finally, conservation of wildlife is also important for cultural, educational, and aesthetic reasons. Many people derive pleasure from observing wild animals and appreciate their beauty and diversity. Wildlife also provides important opportunities for scientific study and research that can help us better understand the natural world and improve our ability to protect it. In conclusion, conservation of wildlife is necessary to protect species from extinction, maintain the balance of ecosystems, and provide cultural, educational, and aesthetic benefits.

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When large numbers of organisms share limited space and resources, the immediate result is competition. Competition occurs when organisms within a population compete with each other for resources such as food, water, shelter, and mates. As the population grows, resources become more scarce, and the competition intensifies. This can lead to natural selection, where individuals with advantageous traits for obtaining resources, such as better camouflage or faster running speed, are more likely to survive and reproduce. Those with less advantageous traits may struggle to compete and may not survive long enough to reproduce, which can lead to a decrease in their numbers over time. While some individuals may choose to emigrate or immigrate to find new resources, if the competition remains intense, it can lead to extinction for some species.

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Spirogyra is an organism composed of cells, so it belongs to the level of organization known as a "cell." Spirogyra is a type of filamentous green algae that consists of many individual cells arranged in a long chain, held together by a gel-like substance. Although Spirogyra cells can perform some specialized functions, such as photosynthesis, they are not organized into tissues or organs. Therefore, Spirogyra is not classified as a "tissue" or "organ" level of organization. Finally, since Spirogyra is an individual organism and not part of a larger system, it is also not classified as a "system" level of organization.

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Using contact lenses may lead to an eye infection. Contact lenses sit directly on the eye, and if they are not cleaned and stored properly, bacteria can accumulate on the lenses and cause an infection. Symptoms of an eye infection include redness, pain, sensitivity to light, and discharge. To prevent eye infections when wearing contact lenses, it is important to wash your hands thoroughly before handling them, clean and disinfect them regularly, and avoid wearing them for too long or while sleeping. It is also important to follow your eye doctor's instructions for proper use and care of your contact lenses. Convex lenses, biconcave lenses, and concave lenses are not likely to lead to an eye infection, as they are not worn directly on the eye and do not come into contact with it. These types of lenses are used to correct vision problems and do not pose a risk of infection unless they are contaminated and come into contact with the eye.

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Xerophytes have the following characteristics aimed at conserving water except broad leaf surfaces. Xerophytes are plants that have adaptations to survive in arid or desert environments where water is scarce. To conserve water, xerophytes have several adaptations, including: - Thick cuticle: A thick cuticle is a waxy layer on the surface of leaves that reduces water loss through transpiration. - Sunken stomata: Stomata are tiny pores on the surface of leaves that allow for gas exchange. In xerophytes, stomata are often sunken into the leaf surface, which reduces the surface area exposed to the air and reduces water loss. - Waxy cuticle: Like a thick cuticle, a waxy cuticle helps reduce water loss through transpiration. Broad leaf surfaces, on the other hand, increase the surface area of the leaf and can increase water loss through transpiration. Therefore, the characteristic of xerophytes aimed at conserving water that is not present is broad leaf surfaces.

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The most important factor(s) that influence(s) the ecological niche of an organism is/are the competition for food and space. Ecological niche refers to the role and position of a species within its habitat. It encompasses all the interactions between the species and its biotic and abiotic environment. Competition for resources such as food, water, and space is a major factor that shapes the ecological niche of an organism. The availability of these resources determines the survival and growth of a population, as well as the interactions between different species in the ecosystem. Therefore, the competition for food and space is a crucial factor that shapes the ecological niche of an organism.