WAEC SSCE - Biology - 2003

Maelezo ya Majibu

Placentation of plants refers to the arrangement of ovules within the ovary of a flower. The ovules are attached to the placenta, which is a structure within the ovary. The arrangement of the ovules on the placenta is important in determining the type of fruit that will form after fertilization. The different types of placentation include axile, free central, parietal, basal, and laminar, which are based on the position and attachment of the ovules on the placenta. Therefore, the correct answer is: "arrangement of ovules in the ovary".

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The gas produced during decomposition of matter is not chlorine or oxygen, as they are not usually produced during the process. Carbon monoxide may be produced in some cases, but it is not the main gas. The correct answer is hydrogen sulphide. When organic matter decomposes, bacteria break down the compounds and release various gases, including hydrogen sulphide. This gas has a characteristic rotten egg smell and can be toxic in high concentrations.

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The value showing the total biomass of organisms in a food chain that represents the secondary consumer is 20. This is because in a food chain, the secondary consumer is the organism that feeds on the primary consumer. The biomass of the secondary consumer is usually less than that of the primary consumer, and even less than that of the producers. Therefore, the value of 20, which is the smallest value among the options, is the most likely to represent the biomass of the secondary consumer in the food chain.

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Viruses are pathogens of all the diseases listed except tuberculosis. Tuberculosis is caused by a bacterium called Mycobacterium tuberculosis. Measles, smallpox, and poliomyelitis are all caused by viruses. Measles and smallpox have been largely eradicated due to effective vaccination programs, while poliomyelitis still remains endemic in some parts of the world.

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Out of the given options, mineral salts are the essential substances contained in vegetables. Mineral salts, also known as micronutrients, are inorganic elements that are required by living organisms in small quantities to maintain good health. They play a critical role in various physiological and metabolic functions, including maintaining healthy bones, regulating the heartbeat, and producing energy. Vegetables are a good source of mineral salts as they are absorbed by the plants from the soil. Common mineral salts found in vegetables include calcium, iron, potassium, magnesium, and zinc.

Maelezo ya Majibu

Maelezo ya Majibu

Legumes incorporate nitrogen gas into their proteins because they possess root nodules containing Rhizobium bacteria. Rhizobium bacteria, which form a symbiotic relationship with legumes, can convert nitrogen gas (N2) in the atmosphere into a form of nitrogen that can be utilized by the plant. This form of nitrogen is converted into ammonia, which is then utilized by the plant to produce proteins. Therefore, the presence of Rhizobium in legume root nodules is responsible for their ability to fix nitrogen and produce high protein yields.

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The correct answer is "kill and make the leaf permeable". Placing the leaf in boiling water helps to kill the cells of the leaf and make the cell membrane more permeable, allowing the iodine solution used in the test to enter the cells and react with any starch present. The heat also denatures the enzymes that might break down the starch, which could otherwise interfere with the test. The boiling water doesn't have any effect on the chlorophyll or the waxy cuticle of the leaf, and it doesn't directly cause the leaf to turn blue-black; rather, it provides the necessary conditions for the iodine solution to do so.

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Maelezo ya Majibu

Moulds exhibit extracellular digestion. Extracellular digestion is a type of digestion in which the breakdown of complex molecules into smaller ones occurs outside the cell, in the extracellular space. Moulds secrete enzymes into their surroundings to break down organic matter, and then absorb the nutrients. In contrast, green plants, algae, and bryophytes utilize intracellular digestion, where digestion of complex molecules occurs within the cell.

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The function of the iris of the mammalian eye is to regulate the amount of light entering the eye. The iris is the colored part of the eye surrounding the pupil, and it contains muscles that control the size of the pupil. These muscles can contract or expand, depending on the amount of light present. In bright light, the iris contracts and the pupil becomes smaller, which reduces the amount of light entering the eye. In dim light, the iris expands and the pupil becomes larger, which allows more light to enter the eye. This mechanism helps to protect the sensitive retina at the back of the eye from being overwhelmed by too much light, while still allowing sufficient light to pass through for clear vision.

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Darwin did not propose that evolution occurred because "food and other needs are abundant". Rather, he proposed that evolution occurred through a process of natural selection, which involves several factors, including competition among offspring and the elimination of weaker individuals. The key idea behind natural selection is that individuals with traits that are better suited to their environment are more likely to survive and reproduce, passing on those traits to their offspring. Over time, this can lead to the evolution of new species with unique characteristics.

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Among the given options, mutation will have the least effect on the rate of change of the numbers in a population. This is because mutation is a random and rare event that occurs at a very low rate, which means that it is unlikely to have a significant impact on the overall population size or growth rate. On the other hand, factors such as food supply, predation, and disease can have a major impact on the rate of change of the numbers in a population. For example, if the food supply decreases, the population size may decrease due to starvation or migration, while predation and disease can also cause a reduction in the population size by killing off individuals.

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Forest conservation is the practice of protecting forests and their natural resources for the benefit of the present and future generations. It involves a range of activities aimed at ensuring the sustainable use of forest resources while maintaining their ecological integrity. The options presented are examples of activities that can be carried out in forest conservation. Prevention of bushfires, replacing harvested trees by planting seedlings, and selective exploitation of forest trees are all activities that contribute to forest conservation. However, extensive felling of forest trees is not considered a practice that promotes forest conservation, as it involves the removal of a large number of trees from an area. This can have negative impacts on the environment, such as soil erosion, habitat loss, and reduced biodiversity. Therefore, the answer is "extensive felling of forest trees."

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The option that is not correct is "providing resistance against malaria." This is because good quality food cannot provide resistance against malaria, which is a disease caused by a parasite that is transmitted through the bite of infected mosquitoes. While good nutrition can support a healthy immune system and overall health, it cannot directly protect against specific diseases like malaria. Good quality food performs functions such as supplying energy, sustaining growth, and maintaining health by providing essential nutrients such as carbohydrates, proteins, fats, vitamins, and minerals.

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Pneumatophores are essential for breathing in certain species of trees such as mangroves. These structures are specialized roots that grow upwards from the waterlogged soil or water surface, allowing oxygen to reach the submerged roots. The pneumatophores contain pores called lenticels which facilitate the exchange of gases between the roots and the atmosphere. This adaptation is necessary for survival in waterlogged soils where oxygen is limited, and it helps the trees to grow and thrive in these environments. Therefore, the correct answer is "breathing."

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The option that is not a behavioural adaptation used by social animals is "Season". This is because season is not a behavioural adaptation but rather a natural phenomenon that affects the behavior of animals. Cryptic, Mimicry, and Flash are behavioural adaptations used by social animals to protect themselves from predators or attract mates. Cryptic adaptation involves blending with the environment to avoid detection, while mimicry involves resembling a harmful or dangerous organism to deter predators. Flash adaptation involves sudden displays of bright colors or movements to startle or distract predators.

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Renewable resources are formed by organisms that are constantly regenerating themselves. These resources can be replenished or regenerated naturally in a relatively short period of time, making them sustainable for human use. Examples of renewable resources include solar energy, wind energy, hydropower, biomass, and geothermal energy. These resources are essential for the survival of human and animal life on earth, and their sustainable use is crucial for the future of our planet. Unlike non-renewable resources such as fossil fuels, renewable resources can be used indefinitely without depleting them, as long as they are managed properly.

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The statement that is not correct about a human cell is "All the cells in organism are the same." This is because human beings have different types of cells that perform specific functions. For example, muscle cells are different from nerve cells, and skin cells are different from blood cells. Each cell type has a unique shape, size, and function that is essential to the survival of the organism. Therefore, not all the cells in the organism are the same.

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The endocrine gland secreting hormone that induces the thyroid gland to produce more thyroxine is the pituitary gland. The pituitary gland produces thyroid-stimulating hormone (TSH) which stimulates the thyroid gland to produce more thyroxine, a hormone that is important for regulating metabolism in the body. When there is a decrease in the level of thyroxine in the blood, the pituitary gland releases TSH which acts on the thyroid gland to increase the production of thyroxine. This process helps to maintain the level of thyroxine in the blood within a normal range.

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Maelezo ya Majibu

The glomerular filtrate is a fluid that is formed in the kidneys during the process of filtration. It is composed of water and various solutes that are present in the blood. The solutes that are found in the glomerular filtrate include glucose, urea, and other waste products. However, blood corpuscles (i.e. red and white blood cells) are not normally found in the glomerular filtrate, as they are too large to pass through the filtration membrane. Therefore, the correct answer is blood corpuscles.

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The organ that removes the largest quantity of water from the blood is the kidney. The kidney is a bean-shaped organ that helps to filter waste products from the blood and excrete them from the body in the form of urine. It also plays a crucial role in regulating the body's fluid balance by removing excess water from the blood and excreting it as urine. This process is essential for maintaining proper blood pressure and preventing fluid buildup in the body, which can lead to swelling and other complications. Therefore, the kidney plays a critical role in maintaining the overall health of the body.

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Maelezo ya Majibu

Turbidity is not considered in a terrestrial habitat. Turbidity refers to the degree to which water loses its transparency due to the presence of suspended particles. As a result, it is a factor that only applies to aquatic habitats and not to terrestrial ones. Terrestrial habitats are land-based and include forests, deserts, grasslands, and tundra. The environmental factors that are typically considered in a terrestrial habitat include temperature, sunlight, humidity, soil type, and precipitation. These factors can affect the growth and survival of plants and animals in the habitat.

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The type of nutrition shown by Spirogyra is holophytic. Holophytic nutrition is a type of nutrition in which an organism produces its food by photosynthesis. Spirogyra is a green algae that contains chloroplasts, which carry out photosynthesis. It absorbs carbon dioxide from the atmosphere and uses sunlight to convert it into glucose, which is stored as starch. Therefore, Spirogyra uses holophytic nutrition.

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The function of the amniotic fluid in humans is to protect the foetus against shocks. The amniotic fluid is a clear liquid that surrounds the developing foetus in the uterus. It provides a cushion for the foetus, protecting it from physical shock and injury. The fluid also helps to maintain a constant temperature for the foetus, and provides a sterile environment that helps to prevent infection. In addition, the amniotic fluid allows the foetus to move and develop without being compressed by the walls of the uterus.

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Ecology is the study of the inter-relationship between living organisms and their environment. This includes studying how organisms interact with each other and their physical surroundings, as well as how the environment impacts the behavior, growth, and survival of these organisms. In essence, ecology is about understanding how living things and their environment are interconnected, and how changes in one can affect the other.

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The example of discontinuous variation is "Offspring, including the two male cats and three female cats". Discontinuous variation refers to traits that have distinct categories, and individuals can be clearly classified into these categories. In the case of the offspring of cats, they can be categorized into either male or female, which are distinct categories. Other examples of traits that exhibit discontinuous variation include blood groups, presence or absence of wings in insects, and flower color in some plants.

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The correct answer is Landsteiner and Levine. In 1937, Karl Landsteiner and Alexander S. Wiener discovered the Rhesus factor in human blood, which is a protein present on the surface of red blood cells. They named the protein after the Rhesus monkey, as it was first identified in the blood of this species. Later, in 1940, Philip Levine identified the Rh factor as the cause of hemolytic disease of the newborn.

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The statement "plays a role in the formation of vitamin" is not correct. Water does not play a role in the formation of vitamins in the human body. Vitamins are organic compounds that the body needs in small amounts for various metabolic processes, but they are not produced by water. Water mainly serves as a solvent, which means it helps to dissolve and transport essential nutrients, like vitamins, minerals, and glucose, throughout the body. It also helps regulate body temperature by releasing heat through sweating and respiration. Additionally, water is involved in many biochemical reactions in the body, making it essential for various life processes.

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In cold conditions, the mammalian body reacts by trying to maintain its core temperature to ensure that all the metabolic processes continue to work properly. The body does this through a process called thermoregulation. One of the ways it does this is by shivering, which generates heat through muscle contraction. Additionally, the body can constrict blood capillaries in the skin to reduce heat loss to the environment. However, dilation of the capillaries supplying blood to the skin would increase heat loss to the environment, so it is not a reaction that occurs in cold conditions. Finally, while the body may increase its metabolic rate in response to cold to generate more heat, it is not a universal response and may vary depending on the individual and the severity of the cold conditions.

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Maelezo ya Majibu

Fish cannot survive on land because they do not have lungs and rely on their gills to extract oxygen from water. Their bodies are also not adapted for movement on land as they do not have any walking appendages like legs. Additionally, their skin is not designed to retain moisture, which is necessary for survival on land. Finally, fish have a streamlined body that is designed for swimming in water, but would not be efficient for movement on land.

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The layer of light-sensitive cells in the human eye is called the retina. The retina is located at the back of the eye and contains photoreceptor cells that convert light energy into electrical signals that are sent to the brain via the optic nerve. These signals are then interpreted by the brain as visual images. The other options listed, cornea, sclerotic layer, and conjunctiva, are all parts of the eye as well, but they do not contain light-sensitive cells and do not play a direct role in vision.

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Maelezo ya Majibu

Competition among individuals of a population increases the survival of the fittest. This is because competition creates a struggle for resources, such as food, water, and shelter. The individuals that are best adapted to their environment and are able to acquire these resources have a higher chance of surviving and reproducing. Over time, this can lead to the evolution of traits that increase an individual's ability to compete for resources, resulting in a population of individuals that are well-suited to their environment. Therefore, competition increases the selection pressure on the population, leading to the survival of the fittest.

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The pituitary gland is known as the "master gland" because it regulates and controls the functions of other endocrine glands in the body. It produces and releases various hormones that control growth, metabolism, reproduction, and other vital functions in the body. Therefore, the correct answer is the pituitary gland.

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The products of the light stage of photosynthesis are NADPH2, Oxygen and ATP. Ribulose bi-phosphate (RuBP) is a substrate molecule in the Calvin cycle of photosynthesis, which takes place in the dark stage. Therefore, is the correct answer.

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