WAEC SSCE - Biology - 1997

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Denitrification is the process of reducing nitrates to gaseous nitrogen, which is then released into the atmosphere. This occurs in anaerobic conditions, such as in waterlogged soils, where there is a lack of oxygen to support the aerobic nitrifying bacteria. During denitrification, specialized bacteria convert nitrates (NO3-) into gaseous nitrogen (N2), nitrous oxide (N2O), and sometimes nitrogen dioxide (NO2), which are all released into the atmosphere. This process is an important part of the nitrogen cycle and helps to maintain the balance of nitrogen in the environment.

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The early removal of the pituitary gland in animals may cause cessation of growth. The pituitary gland is a small gland located at the base of the brain that produces and releases hormones that regulate growth, reproduction, and various other physiological processes in animals. Removal of this gland, especially at an early age, can lead to a deficiency of growth hormone, which is important for bone growth and body development. This deficiency can result in a condition called pituitary dwarfism, which is characterized by a reduced growth rate, short stature, and delayed sexual development. In contrast, gigantism occurs when there is an excess of growth hormone, often caused by a pituitary tumor. Poor mental development, goiter, and inability to digest food are not directly related to the function of the pituitary gland.

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The factor that does not affect the distribution of organisms in an aquatic habitat is "humidity." Humidity is a measure of the amount of water vapor in the air, which is not a relevant factor in aquatic environments. The other factors listed can affect the distribution of aquatic organisms. - Turbidity: the measure of how clear or cloudy the water is, which affects the penetration of light and the photosynthetic activity of aquatic plants. - Depth of water: affects the amount of light and temperature, and the types of organisms that can survive in a particular depth range. - Temperature: affects the metabolic rate of aquatic organisms, and the rate of chemical reactions in the water. - Availability of nutrients: affects the growth and reproduction of aquatic plants and algae, which form the base of the aquatic food chain.

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Among the options given, Euglena is an organism that possesses both plant and animal characteristics. Euglena is a single-celled organism that can perform photosynthesis using chloroplasts, just like a plant, to produce its own food. It also has a unique structure called an eyespot that allows it to detect light and move towards it, much like how an animal would do. In addition to that, Euglena can also obtain its nutrition by ingesting other small organisms, making it a mixotroph, which means it can obtain nutrients from both autotrophic (producing own food) and heterotrophic (consuming other organisms) methods. Hence, Euglena is an excellent example of an organism that has characteristics of both plant and animal.

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The organelle that helps to remove excess water from cells is the contractile vacuole. This organelle is found in many single-celled organisms, such as amoebas and paramecia, as well as in some specialized cells in multicellular organisms. The contractile vacuole works by pumping excess water out of the cell and into the environment. This is important for maintaining the proper balance of water and other substances within the cell, and for preventing the cell from bursting due to osmotic pressure. The other organelles listed, such as mitochondria, ribosomes, Golgi bodies, and nuclei, do not have a direct role in removing excess water from cells.

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Intensive cropping can cause loss of soil fertility. This is because when crops are grown continuously without rotation, the soil is depleted of essential nutrients that the crops need to grow. As a result, the soil becomes less fertile over time, which can lead to reduced crop yields. On the other hand, mulching, compost application, use of fertilizers, and terracing are farm practices that help to maintain or improve soil fertility. Mulching and compost application add organic matter to the soil, which helps to retain moisture and nutrients. Use of fertilizers adds essential nutrients to the soil, while terracing helps to prevent soil erosion and runoff, which can lead to loss of soil fertility.

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Sheep is the organism that is viviparous. Viviparity is a mode of reproduction where the embryo develops inside the mother's body and is nourished through a placenta or a similar structure, and the offspring are born alive. Sheep are mammals and, like other mammals, give birth to live young ones that have been nourished inside the mother's body through a placenta. The other organisms listed are not viviparous, as tapeworms, snails, and grasshoppers are oviparous, meaning they lay eggs, and lizards are oviparous or ovoviviparous, meaning they lay eggs or retain the eggs inside their body until they are ready to hatch.

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A high concentration of auxin in the root will stimulate growth. Auxin is a plant hormone that is responsible for promoting and regulating plant growth and development. When the concentration of auxin is high in the root, it causes the cells in the root to elongate, leading to the stimulation of growth. This process is important for the development and establishment of the root system, which is essential for water and nutrient uptake by the plant. Therefore, a high concentration of auxin in the root will lead to the stimulation of growth, rather than inhibition or reduction of water absorption.

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Insects breathe through a series of tiny tubes called tracheae, which are connected to the atmosphere by openings called spiracles. Therefore, the structure associated with respiration in insects is the spiracle. Spiracles are tiny openings located along the sides of the insect's body, which allow air to enter and exit the tracheal system.

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The part labelled I in the diagram is called a lenticel. A lenticel is a small, spongy pore or opening in the bark of woody plants that allows for gas exchange between the internal tissues of the plant and the surrounding environment. Plants need to exchange gases such as oxygen and carbon dioxide with their surroundings, just like animals do. However, unlike animals, plants do not have lungs or other specialized respiratory organs. Instead, they rely on small openings in their leaves, stems, and bark to allow for gas exchange. Lenticels are found on the stems and branches of woody plants, and are particularly important for gas exchange in older or thicker bark where gas exchange through the bark surface itself is limited. They are often visible as small, raised areas on the bark, and can vary in size, shape, and color depending on the plant species. Therefore, the part labelled I in the diagram is a lenticel, a small pore in the bark of a woody plant that allows for gas exchange.

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Crops grown mainly to feed animals are called "forage crops". Forage crops are plants that are grown to provide forage for livestock. They are rich in nutrients and are used to feed animals like cows, sheep, goats, horses, and others. Some examples of forage crops include alfalfa, clover, grasses, and other legumes. These crops are usually harvested when they are young and tender, before they have a chance to produce seeds, and are fed to animals either fresh or dried.

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The structure that transports water from the roots to the leaves is called the xylem. The xylem is a specialized tissue found in vascular plants, which forms a series of continuous tubes that run throughout the plant's stem and roots. It is responsible for the transport of water, minerals, and other nutrients from the roots to the rest of the plant. The water travels from the roots to the leaves in a process called transpiration, which is driven by the evaporation of water from the leaves. In summary, the xylem is responsible for the upward movement of water and nutrients in the plant.

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The characteristic that is NOT associated with wind dispersed fruits and seeds is "Sticky juice". Wind-dispersed fruits and seeds rely on wind to carry them away from the parent plant to a new location for germination and growth. They usually have adaptations such as being lightweight, having wings, floss, or parachutes to aid in their dispersal by wind. These adaptations help the fruits and seeds to catch the wind and get carried away to new places. However, having sticky juice would make it difficult for the fruits and seeds to be dispersed by wind as they would get stuck to the parent plant or the ground, which would hinder their dispersal.

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Carbohydrates in yam are primarily stored in the form of starch. Starch is a complex carbohydrate that is made up of long chains of glucose molecules. When yams photosynthesize, they convert the energy from sunlight into glucose, which they then store as starch in their underground tubers. Starch is an excellent storage molecule because it can be broken down into glucose when energy is needed. This allows yams to survive periods of low sunlight and water by using their stored starch for energy. The other carbohydrate options listed - glucose, maltose, glycogen, and cellulose - are not typically stored in yams. Glucose is a simple sugar that is used for energy production in cells. Maltose is a disaccharide made up of two glucose molecules and is found in grains and some vegetables, but not typically in yams. Glycogen is a complex carbohydrate that is similar to starch, but it is primarily stored in animals rather than plants. Finally, cellulose is a structural carbohydrate found in plant cell walls, and it is not typically used for energy storage.

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The part labelled I in the diagram is the chloroplast. Chloroplasts are specialized organelles found in plant cells that contain chlorophyll, a green pigment that absorbs light energy from the sun during the process of photosynthesis. They are responsible for the conversion of light energy into chemical energy, which is used by the plant to produce food (glucose) and release oxygen. Chloroplasts are usually located in the mesophyll layer of the leaf and are green in color due to the presence of chlorophyll.

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"Tongue rolling" is not a morphological variation. Morphology refers to the study of the form and structure of organisms, and morphological variations refer to differences in the physical characteristics of individuals within a species. The shape of the nose, color of the skin, color of the eyes, and ear lobe are all examples of morphological variations that can be observed in humans. However, the ability to roll one's tongue is not a morphological variation because it is a function of the muscles in the tongue and not a physical characteristic of the tongue itself. Some people are able to roll their tongues, while others are not, but this difference is not related to the structure or form of the tongue. Instead, it is a genetic trait that is inherited independently of other physical traits. Therefore, tongue rolling is not a morphological variation.

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Feeding the organisms is not necessary in population sampling. Population sampling is a technique used by ecologists to estimate the abundance and distribution of different species within a given habitat. It involves selecting a representative sample of the habitat and then counting the number of organisms present within that sample. The other activities listed - selecting the habitat, dividing the selected habitat into portions, throwing the quadrat randomly, and counting the number of organisms - are all necessary components of population sampling. Selecting the habitat involves choosing an area that is representative of the larger habitat being studied. Dividing the selected habitat into portions is necessary to ensure that the sample is representative of the larger habitat. Throwing the quadrat randomly helps to ensure that the sample is not biased in any particular direction, and counting the number of organisms is necessary to estimate the abundance of each species present within the sample. Feeding the organisms, however, is not necessary for population sampling, as it does not contribute to the estimation of population abundance or distribution.

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Only reduced birth rate may not cause over-crowding. Over-crowding occurs when there are too many individuals in a given space, leading to competition for resources such as food, water, and shelter. Limited space, scarcity of food, increased birth rate, and loose immigration conditions are all factors that can lead to over-crowding by increasing the number of individuals in a given area. However, reduced birth rate decreases the number of individuals in the area and can help to alleviate over-crowding.

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The association between protozoa and termites is an example of "symbiosis". Symbiosis is a type of relationship between two different species where both organisms benefit from each other. In the case of protozoa and termites, protozoa live inside the gut of termites and help to break down the tough plant fibers that termites eat, making it easier for termites to digest their food. In return, protozoa get a safe and stable habitat to live in, and a constant supply of food from the termite's gut. This mutualistic relationship benefits both the protozoa and termites, and is an example of symbiosis.

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Northern Guinea savanna is associated with abundant grasses. The Northern Guinea savanna is a vegetation zone that stretches across West Africa, including countries such as Nigeria, Ghana, and Cameroon. The zone is characterized by tall grasses and a few scattered trees, shrubs, and small plants. It is also known for its relatively dry climate with a rainy season that lasts for about six months. The abundance of grasses in the Northern Guinea savanna makes it ideal for grazing animals such as cattle, sheep, and goats.

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In an inter-species competition, the less successful species usually become eliminated. Inter-species competition refers to a type of competition where two or more species are competing for the same resources such as food, water, and shelter. In this type of competition, the species that is better adapted to the environment and can utilize the resources more efficiently has a competitive edge over the other species. As a result, the less successful species usually cannot acquire enough resources to survive and reproduce, leading to their elimination. Therefore, becoming eliminated is the most likely outcome for the less successful species in inter-species competition.

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Clotting of blood is a complex process that involves the formation of a blood clot to stop bleeding after injury. One of the important factors in this process is vitamin K, which is essential for the production of certain proteins that are needed for blood clotting. When there is an injury or damage to a blood vessel, platelets in the blood begin to clump together and form a plug at the site of injury. This plug is then reinforced by a network of proteins called fibrin, which are produced by a series of chemical reactions known as the coagulation cascade. Vitamin K is necessary for the production of several of the proteins involved in the coagulation cascade, including prothrombin and factors VII, IX, and X. These proteins require vitamin K for a process called carboxylation, which is necessary for their activation and function in the coagulation cascade. Without sufficient vitamin K, the coagulation cascade cannot function properly, leading to an increased risk of bleeding and bruising. So, vitamin K is essential for the proper clotting of blood.

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Filtered blood from the kidney is carried back to the circulatory system through the renal vein. The renal vein is the blood vessel that carries blood away from the kidney and back into the circulatory system. It is responsible for transporting blood that has been filtered by the kidneys, where waste products and excess water are removed from the blood and sent to the bladder for excretion. The other options listed - hepatic portal vein, renal artery, pulmonary vein, and vena cava - refer to different blood vessels that have different functions in the circulatory system, and are not directly involved in the transport of filtered blood from the kidney. The hepatic portal vein carries blood from the digestive system to the liver, while the renal artery carries blood to the kidney for filtration. The pulmonary vein carries oxygenated blood from the lungs to the heart, while the vena cava carries deoxygenated blood from the body back to the heart.

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Yeast is commonly used as a fermenting agent in brewing. During the process of fermentation, yeast converts sugars (such as sucrose and glucose) into alcohol (ethanol) and carbon dioxide gas. Therefore, the product of brewing when yeast is used as a fermenting agent is ethanol.

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Flatworms are classified as Platyhelminthes. Platyhelminthes is a phylum of soft-bodied, flattened worms that includes flatworms. They are characterized by their flattened body shape and lack of a true coelom (body cavity). Flatworms can be found in a variety of environments, including freshwater, marine, and terrestrial habitats. They are also known for their ability to regenerate lost body parts, which is a unique characteristic among animals.

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Phytoplankton will have the highest biomass among the listed organisms. Biomass is the total mass of living matter within a given area or ecosystem. It is an important measure of the productivity and ecological health of an ecosystem. Phytoplankton are microscopic plant-like organisms that live in aquatic environments such as oceans, lakes, and rivers. They are the primary producers in aquatic ecosystems, meaning they are the organisms that convert sunlight into organic matter through the process of photosynthesis. Phytoplankton serve as the base of the aquatic food chain, providing food for small fish and other aquatic organisms. Because of their small size and rapid reproduction rates, phytoplankton can rapidly increase in numbers and achieve a high biomass. In contrast, larger organisms such as fish and hawks have lower biomass due to their higher trophic levels in the food chain. This is because as energy is transferred from one trophic level to another, much of it is lost as heat or used for metabolic processes, resulting in a decrease in biomass. Therefore, among the listed organisms, phytoplankton will have the highest biomass due to their role as primary producers and their ability to rapidly reproduce.

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The farming practice by which an exhausted farm land is left for a number of years before cultivation is known as "bush fallowing". In this practice, the farmer allows the land to rest and regenerate by allowing natural vegetation to grow back over a period of time. This allows the soil to regain its nutrients and become fertile again. Bush fallowing is a traditional method of agriculture that has been used in many parts of the world for centuries. It is particularly useful in areas where the soil is poor and prone to erosion, as it helps to improve soil quality and prevent soil degradation. After the fallow period, the land can be used for cultivation again, and the cycle can be repeated. This practice is sustainable and helps to maintain soil fertility, biodiversity, and ecosystem health.

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Among the given options, the fruit that is a schizocarp is Desmodium. A schizocarp is a type of dry fruit that splits into separate one-seeded segments called mericarps upon maturity. In other words, the fruit breaks apart into smaller, individual units, each containing a single seed. Out of the given options, Desmodium has a fruit that is a schizocarp. Its fruit splits into several segments (mericarps), each containing a single seed, when it's matured. The other options have different types of fruits such as legume (Groundnut), nut (Cashew), capsule (Pride of Barbados) or a legume-like fruit called a loment (Crotalaria), which don't split into mericarps.

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An abiotic factor refers to the non-living components of an ecosystem that affect living organisms, such as temperature, water, sunlight, soil, etc. Based on this definition, the abiotic factor among the options given is "Rainfall." It is a non-living component of the environment and an important abiotic factor that affects various aspects of an ecosystem, including the growth and survival of plants and animals. Rainfall provides the necessary water for plants to grow and for animals to drink, and it affects the distribution of species and the productivity of ecosystems.

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The Malpighian tubule is a tubular structure found in insects that plays a major role in excretion. The tubule helps to filter waste products such as uric acid, which are then transported to the hindgut for elimination. The Malpighian tubule also helps to maintain the water and ion balance in the insect's body.

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The maximum and minimum thermometer is used to measure the highest and lowest temperature of the day. This thermometer consists of a U-shaped glass tube filled with alcohol or mercury. The liquid in the thermometer expands when heated and contracts when cooled, causing it to move up or down the tube. At one end of the thermometer, there is a small bulb containing alcohol or mercury, and at the other end, there is a constriction in the tube. The constriction prevents the liquid from flowing back to the bulb when it contracts due to cooling. The thermometer is designed in a way that the liquid moves to indicate the highest temperature reached during the day, and the lowest temperature reached during the night. The thermometer is reset every day to record new maximum and minimum temperatures. This information can be used to determine the temperature range for a given day, which is useful in understanding the local weather patterns. Therefore, the correct option is "highest and lowest temperature of the day". It is important to note that this type of thermometer is not used to measure light intensity, atmospheric pressure, rainfall, or soil temperature.

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The correct sequence for energy transfer and nutrient cycling among living things in an ecosystem is: Producers → consumers → decomposers Producers are organisms that produce their own food through photosynthesis or chemosynthesis. They are the base of the food chain and transfer energy to the consumers (herbivores, carnivores, and omnivores) when they are consumed. The consumers, in turn, pass on the energy to the decomposers, which break down the dead organic matter and return nutrients to the soil, completing the nutrient cycle. Therefore, the correct sequence is producers → consumers → decomposers.

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The enamel is the hardest and the outermost part of the tooth. It is the first part of the tooth that gets damaged during dental decay. Dental decay occurs when the bacteria in the mouth produce acids that dissolve the enamel and create holes in it, known as cavities. If the decay is not treated promptly, it can progress to the dentin and ultimately to the pulp, which can lead to infection and pain. Therefore, regular dental check-ups are essential to prevent dental decay and to detect and treat it at an early stage.

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Bees communicate with one another to obtain information about the direction of food sources through a complicated set of dances. When a honey bee finds a food source, it returns to the hive and performs a series of dances on the honeycomb to communicate the location of the food to other bees in the hive. The dance involves the bee moving in a figure-eight pattern while waggling its abdomen and making a buzzing sound. The direction of the food source is indicated by the angle of the dance in relation to the sun, and the distance is communicated by the duration of the dance. This communication method is known as the "waggle dance" and is a sophisticated way for bees to share information about the location of food sources with other members of their hive. The other options listed - smell, contact notes, observation, and sounds - may also play a role in how bees communicate with one another, but the primary method for communicating the direction of food sources is through the waggle dance.

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An example of a reflex action is sneezing. When an irritant enters the nasal passage, the receptors in the nose send a signal to the brain which then sends a message to the muscles in the chest, throat, and face to quickly expel air, removing the irritant. This action is automatic and involuntary, occurring without conscious thought or effort. Biting, dancing, singing, and talking are not reflex actions as they involve more complex movements and cognitive processing.

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The femur is the hind limb bone that is equivalent to the humerus of the forelimb. The humerus is the long bone in the upper arm of mammals that connects the shoulder to the elbow. In the hind limb of mammals, the femur is the long bone that connects the hip to the knee. The femur and the humerus have a similar structure and function, as they are both weight-bearing bones that support the body and allow for movement. They also have similar shapes, with rounded heads that fit into sockets to form joints. In contrast, the other hind limb bones listed - patella, tarsal, tibia, and fibula - have different shapes and functions compared to the humerus. The patella is the kneecap, a small, triangular bone that sits in front of the knee joint and helps to protect the joint and increase the leverage of the thigh muscles. The tarsal bones are a group of seven bones in the ankle that help to support the foot and enable movement. The tibia and fibula are the two long bones in the lower leg that connect the knee to the ankle. The tibia is the larger and stronger of the two, and is the main weight-bearing bone in the lower leg. The fibula is a thinner bone that runs alongside the tibia and helps to provide support and stability to the ankle joint. Therefore, the femur is the hind limb bone that is equivalent to the humerus of the forelimb, as they have a similar structure, function, and shape.

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A habitat with low rainfall, very low humidity, exposed soil with little plant cover, few trees, and shrubs is likely to be a desert. Deserts are characterized by arid conditions, sparse vegetation, and harsh climatic conditions. The lack of rainfall limits the growth of plants, resulting in bare soil and exposed rocks. The high temperature and low humidity make the desert habitat unsuitable for most living organisms.

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The essential parts of a flower are the androecium and gynoecium. The androecium is the male reproductive part of the flower, which includes the anther and filament. The anther is the part of the flower that produces pollen, and the filament supports the anther. The gynoecium is the female reproductive part of the flower, which includes the stigma and style. The stigma is the part of the flower where pollen lands, and the style connects the stigma to the ovary. The ovary contains the ovules, which develop into seeds after fertilization. While petals and sepals may play important roles in attracting pollinators and protecting the flower, they are not considered essential for the reproduction of the plant.

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