WAEC SSCE - Biology - 2015

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Oil applied to the surface of water kills the larvae of mosquitoes through suffocation. Mosquito larvae breathe air through a tube called a siphon, which they use to reach the surface of the water to breathe. When a layer of oil is applied to the surface of the water, it creates a film that covers the siphon and prevents the larvae from accessing air. As a result, the larvae suffocate and die. This method is often used as a non-toxic and environmentally friendly way to control mosquito populations.

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The farmer can prevent the seeds from sprouting by using abscisic acid (ABA). ABA is a plant hormone that is involved in the regulation of seed dormancy and the prevention of premature germination. When seeds are exposed to ABA, it inhibits the action of gibberellins, which are responsible for seed germination. By applying ABA to the seeds, the farmer can prevent them from sprouting for up to three years while keeping them in storage. Therefore, the correct answer is abscisin.

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Ascaris is not a protozoan. Ascaris is a roundworm, which belongs to the phylum Nematoda. The other three options, Amoeba, Plasmodium, and Paramecium are all protozoans, which are unicellular eukaryotic organisms.

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A non-renewable resource is a natural resource that cannot be replaced once it is used up. Among the given options, the mineral deposit is a non-renewable resource because once it is extracted from the earth and used up, it cannot be replenished. Forest reserves and wildlife can be conserved and replenished with proper management and conservation efforts, while water is a renewable resource that can be replenished through the water cycle.

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The variety that is most likely to outlive the others is the one whose markings are similar to those of the environment (option C). This is because such a variety is better able to blend in with its surroundings and is less likely to be seen by predators. As a result, it has a better chance of survival and passing on its genes to the next generation. This is an example of natural selection, where individuals with advantageous traits are more likely to survive and reproduce.

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The statement that is not correct is "consists the nucleus only". This is because the protoplasm of a cell is the living substance that makes up the entire cell, including the nucleus, cytoplasm, and cell organelles. The nucleus is just one component of the protoplasm, which also includes the cytoplasm and cell organelles such as mitochondria, ribosomes, and the endoplasmic reticulum. Therefore, the correct statement would be "comprises of the nucleus, cytoplasm, and cell organelles".

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The diagram above shows a Punnett square used to predict the possible genotypes of the offspring of a cross between a spotted leopard (Hh) and a black panther (hh) with the gene for skin colour represented by the letter H. The possible genotypes of the offspring are shown in the boxes formed by the Punnett square. Looking at the Punnett square, it can be observed that the genotypes of the parents are Spotted Leopard Hh and Black Panther hh, since each parent contributes one allele to each offspring. Therefore, the correct answer is "Spotted Leopard Hh Black Panther hh".

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A community reaches a climax when the composition and size of the community remains relatively constant over a long period of time. At this stage, the community has reached a stable state and is in balance with the surrounding environment. The climax community is characterized by a complex and diverse mix of plant and animal species that have evolved to live in harmony with each other and their environment. The community has reached a state of equilibrium, where the growth of each species is balanced by the growth of other species and the availability of resources in the ecosystem. This means that there are no longer new habitats being formed, and there is little to no introduction of new plant and animal species within the community. The pioneer organisms that were present during the early stages of the community's development have been replaced by more complex and specialized organisms. In summary, a climax community is a stable and diverse community that has reached a state of balance with its environment, and it is characterized by a constant composition and size over a long period of time.

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The given diagram shows a cross between a Spotted Leopard and a Black Panther. The gene for skin color is represented by the letter H. From the diagram, we can see that all the offspring have the genotype Hh for the skin color gene. This means that one parent must have the genotype Hh and the other parent must have the genotype hh. Since the Black Panther parent has the homozygous recessive genotype (hh), it must have inherited one h allele from each of its parents. Therefore, the Spotted Leopard parent must have the genotype Hh, with one H allele inherited from one parent and one h allele from the other parent. So, the answer is: Spotted Leopard Hh Black Panther hh.

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The part of the mammalian skeleton illustrated in the diagram is the cervical vertebrae. This is because the cervical vertebrae are the seven vertebrae that make up the neck of the mammal, and the diagram shows seven vertebrae with the characteristic features of cervical vertebrae, such as a small body, a large vertebral foramen, and transverse foramina for the passage of blood vessels.

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The correct answer is: "bile emulsifies fat and oil." Bile is a digestive fluid produced by the liver and stored in the gallbladder. It helps in the digestion and absorption of fats and oils in the small intestine. Bile contains bile salts which act as emulsifying agents. Emulsification is the process by which large fat globules are broken down into smaller droplets, making it easier for enzymes to break down the fats and for them to be absorbed into the bloodstream. When the bile duct is obstructed, bile cannot flow into the small intestine, leading to a decrease in the amount of bile available for digestion. As a result, the digestion and absorption of fats and oils become compromised, leading to symptoms such as abdominal pain, bloating, and diarrhea. Therefore, people with bile duct obstruction are advised to avoid consuming fats and oils to prevent worsening of their symptoms.

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The student added dilute hydrochloric acid to the sugar solution in step ll to hydrolyze the non-reducing sugar into its reducing sugar components. This step breaks down the non-reducing sugar into smaller reducing sugar units that can then react with Benedict's solution in the subsequent steps. Without hydrolyzing the non-reducing sugar, it would not be able to react with Benedict's solution and give a positive result. Therefore, the addition of hydrochloric acid is an important step in testing for non-reducing sugars.

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The feature that could be used to determine the growth of a seedling is the length of the radicle. The radicle is the first part of the seedling to emerge during germination, and it is the embryonic root of the plant. As the radicle grows, it anchors the seedling in the soil and begins to absorb water and nutrients from the surrounding environment. Therefore, the length of the radicle is a good indicator of how well the seedling is growing and developing. The other options - number of flowers, number of leaves, and length of flowers - are not as good indicators of seedling growth. These features are more relevant to the reproductive phase of the plant's life cycle, and they may not be present or fully developed in a young seedling. Therefore, the length of the radicle is the best feature to use when determining the growth of a seedling.

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The plant that commonly undergoes vegetative propagation by means of leaves is Bryophyllum. Bryophyllum is a succulent plant that produces plantlets at the edges of its leaves. These plantlets fall off the leaf, take root in the soil, and grow into new plants. This method of asexual reproduction through leaves is known as leaf-budding. The new plants produced through this method are genetically identical to the parent plant.

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The labelled parts of the crocodile that enable it to stay underwater most of the time are the following: 1. The eyes (part I): Crocodile's eyes are equipped with a special membrane called the nictitating membrane that allows them to see underwater. This helps the crocodile to locate its prey, predators, and also avoid obstacles while underwater. 2. The lungs (part II): Crocodile's lungs are specially adapted to hold more oxygen than most reptiles. This enables them to stay underwater for long periods without the need to come to the surface to breathe. 3. The tail (part IV): The tail of the crocodile is a powerful swimming tool that propels it through the water. The crocodile uses its tail to move quickly and efficiently underwater, allowing it to stay submerged for extended periods. Therefore, the correct answer is option (II) I, II and V.

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Among the given options, Spirogyra is the organism that does not have structures for movement. Spirogyra is a type of algae that has a filamentous structure and does not possess any specialized structures such as cilia or flagella for movement. Amoeba moves by the extension and contraction of its pseudopodia, Paramecium moves by the coordinated action of cilia, and Volvox moves by the synchronized beating of flagella on its surface. Hence, the correct answer is Spirogyra.

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A specialized cell is a cell that has a specific structure and function to perform a particular task within an organism. Of the options given, the cell that is a specialized cell is the guard cell. The guard cell is a specialized cell found in the epidermis of leaves, which regulates the opening and closing of stomata, tiny pores on the surface of leaves that allow for gas exchange. The guard cell has a kidney-shaped structure with a thickened inner wall and a thinner outer wall. When water enters the guard cell, it swells, and the thin outer wall expands, causing the guard cell to bend and create an opening between the two cells. This opening allows for gas exchange between the plant and its environment. The amoeba and Plasmodium are unicellular organisms that do not have specialized cells as they perform all the necessary functions within a single cell. The meristematic cell is a type of plant cell that has the ability to divide and differentiate into various types of plant cells, but it is not considered a specialized cell as it does not have a specific structure and function to perform a particular task. In summary, the guard cell is a specialized cell because of its specific structure and function to regulate the opening and closing of stomata in plant leaves.

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Blood pressure is higher in the arteries as a result of contraction and relaxation. Arteries are the blood vessels that carry oxygenated blood away from the heart to other parts of the body. The heart pumps blood into the arteries, and the contraction of the heart muscles forces blood into the arteries, creating pressure in them. This pressure is known as systolic blood pressure. When the heart relaxes, the pressure in the arteries decreases, which is known as diastolic blood pressure. The alternating contraction and relaxation of the heart muscles along with the elasticity of the arterial walls maintain the blood pressure in the arteries. This pressure is necessary for proper circulation of blood and delivery of oxygen and nutrients to the body tissues.

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When a Spirogyra filament is placed in a concentrated salt solution for 30 minutes, the cell would become plasmolysed. This is because the salt solution has a higher concentration of solutes than the cell, causing water to move out of the cell and into the surrounding solution through osmosis. As a result, the protoplasm and cell membrane shrink and detach from the cell wall, causing the cell to shrink and the cytoplasm to become concentrated. This process is called plasmolysis, and it is reversible if the cell is placed in a hypotonic solution (one with a lower concentration of solutes) to allow water to move back into the cell through osmosis.

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The process that removes carbon (IV) oxide from the atmosphere is photosynthesis. During photosynthesis, plants absorb carbon (IV) oxide from the atmosphere and use it, along with water and sunlight, to produce glucose and oxygen. The oxygen is released into the atmosphere as a byproduct, while the glucose is used as an energy source by the plant. This process helps to reduce the amount of carbon (IV) oxide in the atmosphere, which is important for maintaining the balance of gases and preventing global warming.

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Soil erosion can be prevented by cover-cropping. Cover-cropping involves planting a crop on the land during the fallow period to cover the soil and protect it from erosion caused by wind or rain. The roots of the cover crop hold the soil in place and help to build soil health by adding organic matter. Cover crops also improve soil fertility, reduce soil compaction, and suppress weeds. This method is a sustainable and effective way to protect the soil from erosion and maintain the health of the land for long-term productivity. Flooding a farmland can cause more harm than good as it can wash away topsoil and nutrients. Deforestation and leaving the soil bare also contribute to soil erosion as they leave the soil exposed to wind and rain.

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The component that make up an ecosystem are living and non-living factors. An ecosystem is a community of living organisms (biotic factors) interacting with the non-living (abiotic) components of their environment. Biotic factors are the living organisms such as plants, animals, and decomposers that interact with one another within an ecosystem. Abiotic factors, on the other hand, are the non-living components of the ecosystem such as air, water, sunlight, soil, and temperature. Plants and animals depend on abiotic factors for survival. For example, plants use sunlight to produce energy through photosynthesis, and they also need water and nutrients from the soil to grow. Similarly, animals require water, air, and food to survive. Decomposers such as bacteria and fungi are also an important part of an ecosystem, as they break down dead plant and animal matter into nutrients that can be reused by other living organisms. In summary, an ecosystem is made up of living (biotic) and non-living (abiotic) components that interact with one another to form a complex web of relationships.

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The correct statement about the cross in the diagram is "The gene for the spotted coat is dominant over the gene for the black coat." This can be deduced from the fact that all the offspring in the F1 generation have the spotted coat, despite having one parent with a black coat (which is a recessive trait). If the gene for the black coat were dominant over the gene for the spotted coat, then all the offspring in the F1 generation would have black coats. Similarly, if the two genes were co-dominant, then the offspring in the F1 generation would have coats that show both black and spotted patterns, which is not the case in the diagram. Therefore, the correct answer is that the gene for the spotted coat is dominant over the gene for the black coat.

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If a normal cell has four chromosomes, it means that it has two pairs of chromosomes. During gamete formation, meiosis occurs and the chromosome pairs separate, producing haploid gametes that have only one chromosome from each pair. This means that each gamete will have only two chromosomes, one from each pair. Therefore, the answer is 2.

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The organ that is not correctly matched with its function in the given options is the Appendix - releases enzymes. The Appendix is actually a small, finger-shaped pouch that is located near the junction of the small and large intestines. While the function of the appendix is not entirely clear, it is believed to play a role in immune function and may also have a role in maintaining a healthy balance of bacteria in the gut. The other options are correctly matched with their functions. The gallbladder stores bile, which is produced by the liver and helps to digest fats in the small intestine. The liver also plays a role in storing glycogen, which is a form of glucose that can be used by the body for energy when needed. Teeth are responsible for mechanically breaking down food by grinding and crushing it, which makes it easier to swallow and digest.

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The ability of the human eye to focus images accurately on the retina is called accommodation. This is the process by which the lens of the eye changes shape to adjust the focal length of the eye and ensure that objects at different distances are focused correctly on the retina. When we look at a distant object, the ciliary muscles in the eye relax, making the lens thinner and flatter. When we look at a nearby object, the ciliary muscles contract, making the lens thicker and more curved. This change in the shape of the lens is what allows us to see objects at different distances clearly.

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The sense of smell is facilitated by olfactory receptors located in the nose. When odors are detected, these receptors send signals to the olfactory lobes of the brain, which interprets and processes the information as the sense of smell. Therefore, if a person loses their sense of smell after a head injury that affected the skull but not the nose, it is likely that the accident caused damage to the olfactory lobes of the brain. So, the correct option is (b) olfactory lobes of the brain.

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The structure of the cell membrane is a middle bi-layer of lipid with a protein layer on either surface. The cell membrane is composed of two layers of phospholipid molecules arranged tail-to-tail, which forms a barrier that separates the inside of the cell from the outside environment. The proteins are embedded within the lipid bilayer, with some extending through the entire membrane and others located only on one surface or the other. This structure allows the cell membrane to control what enters and leaves the cell, as well as to communicate with other cells and the environment.

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