JAMB UTME - Biology - 1992

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Mammals are classified as placental or non-placental mammals. Non-placental mammals have eggs with a large yolk sac which provides nutrients to the developing embryo. However, placental mammals, including humans, do not have a yolk sac in their embryos. Instead, the placenta serves as a connection between the mother's blood supply and the developing embryo, providing nutrients, oxygen and removing waste. Therefore, in mammalian development, the yolk sac does not have a function in placental mammals.

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The level of the pyramid with the least total stored energy is level H. This is because as you move up the pyramid from level A to level H, there is a decrease in the amount of energy available. This is due to the loss of energy as it is transferred from one trophic level to the next through various ecological processes, such as respiration, heat loss, and incomplete digestion. At each level, only a small fraction of the energy available at the previous level is passed on. Therefore, the higher up the pyramid you go, the less energy is stored. Level H is at the top of the pyramid, which means it has the least total stored energy.

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An onion is a bulb because it has a reduced stem and thick fleshy leaves. The leaves of the onion plant store food in the form of carbohydrates in a bulb, which is a specialized underground stem. This bulb is covered by thin, papery layers that protect the bulb and keep it from drying out. When the bulb sprouts, the stored food provides energy for the plant to grow and produce leaves, flowers, and seeds.

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A climax community is the stable, final stage of ecological succession, and it persists until the environment or climate changes. It is the end result of a series of ecological changes, and it is characterized by a diverse and relatively stable community of organisms that are in equilibrium with each other and their environment. The other options provided are not true of climax community: it does not change drastically from one year to the next, it is not the first stage in succession, and it is not necessarily made up of the tallest trees and smallest organisms.

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A major difference between platyhelminthes and coelenterates is that platyhelminthes have developed a mesoderm. The mesoderm is a middle layer of cells that lies between the endoderm (innermost layer) and the ectoderm (outermost layer) in most triploblastic animals. Platyhelminthes are triploblastic animals, which means they have three germ layers (ectoderm, mesoderm, and endoderm). In contrast, coelenterates are diploblastic animals, which means they have only two germ layers (ectoderm and endoderm) and do not have a mesoderm. The development of a mesoderm is an important evolutionary advancement because it allows for the development of more complex organs and systems in animals, such as muscles, circulatory systems, and kidneys. Therefore, the development of a mesoderm is a significant difference between platyhelminthes and coelenterates.

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Soil with the finest particles is called clay. Clay particles are smaller than sand and silt particles, with a diameter less than 0.002 mm. These tiny particles allow for greater surface area, which provides better water and nutrient holding capacity in the soil. Clay soils can be dense, and can have slow drainage, but can also be very fertile and productive.

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The reason why pawpaw seeds collected from a tree with many desirable agronomic qualities did not give rise to plants of desirable character as the parent is that uncontrolled out-crossing can introduce unwanted variability. This means that the pollen from other pawpaw trees with undesirable traits may have fertilized the flowers of the parent tree, leading to offspring with a mixture of desirable and undesirable traits. Therefore, to maintain the desirable agronomic qualities of a pawpaw tree, controlled pollination or vegetative propagation may be a better option.

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The blood vessel which carries blood from the alimentary canal (the digestive tract) to the liver is the hepatic portal vein. This vein collects nutrient-rich blood from the intestines and transports it to the liver, where the nutrients are processed and stored. The hepatic portal vein is important in regulating glucose metabolism, detoxifying harmful substances, and maintaining overall body homeostasis.

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An example of plant adaptation to a xerophytic (dry) environment is represented by the development of fleshy tissue and reduced leaves. This adaptation helps plants conserve water in an environment where water is scarce. Fleshy tissue allows the plant to store water, while reduced leaves reduce water loss through transpiration. This adaptation is commonly seen in succulent plants, such as cacti, which are able to survive in hot and dry environments. By reducing the amount of water lost through transpiration and storing water in fleshy tissues, these plants are able to thrive in environments where other plants would struggle to survive.

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Neurons that receive stimuli from the body or internal organs are called sensory neurons. They are specialized cells that convert external and internal stimuli into electrical impulses, which are then transmitted to the central nervous system (CNS) for processing and interpretation. Sensory neurons are responsible for sensing different types of stimuli, such as touch, pressure, temperature, pain, sound, and light, and play a critical role in allowing organisms to respond to changes in their environment.

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The purple colour observed after adding 5 cm3 dilute sodium hydroxide solution and 5 cm3 one percent copper sulphate solution to a solution of food specimen shows the presence of protein. This is because the Biuret test is used to detect proteins in a sample. In this test, the copper ions in the copper sulphate solution react with the peptide bonds in the protein molecule to form a purple complex. The intensity of the purple colour is directly proportional to the concentration of the protein present in the sample.

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Fruits which develop without fertilization of the ovule are called parthenocarpic fruits. This means that the fruit is formed without the need for pollination or fertilization. This can occur naturally or can be induced through various methods such as hormone treatments. Examples of parthenocarpic fruits include bananas, seedless grapes, and seedless watermelons. These fruits are often preferred by consumers as they have no seeds or reduced seed content, making them easier to eat and use in various food preparations.

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If a man has hemophilia, it means that he has a genetic mutation that affects his blood's ability to clot properly. Hemophilia is a sex-linked disorder, which means that the gene for the disorder is located on the X chromosome. Women have two X chromosomes, while men have one X chromosome and one Y chromosome. If a man with hemophilia marries a woman who is not a carrier of the disorder and does not have any affected family members, then all of their daughters will be carriers of the hemophilia gene, but none of their sons will have hemophilia or be carriers. This is because the daughters will inherit one X chromosome from their father (which has the hemophilia gene) and one X chromosome from their mother (which does not have the hemophilia gene). Since the mother does not have the hemophilia gene, she cannot pass it on to her sons. The sons will inherit their father's Y chromosome (which does not carry the hemophilia gene) and their mother's X chromosome (which also does not carry the hemophilia gene). Therefore, the correct answer is: all their daughters will be carriers.

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The excretory organ in insects is the malpighian tubule. Malpighian tubules are long, slender tubes in insects that are involved in the excretion of metabolic waste products, primarily uric acid. They are connected to the gut and actively transport waste products from the hemolymph into the gut, where they can be eliminated from the body. Insects do not have kidneys like vertebrates do, so malpighian tubules serve as their primary excretory organs.

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Fossil records found in sedimentary rocks offer some explanation for the theory of evolution because the deposits have remains of organisms characteristic of when they were formed. Sedimentary rocks are formed over time from sedimentation, and when plants or animals die, they may become buried in sediment, which over time becomes rock. The remains of these organisms can be preserved in the rock as fossils. By studying these fossils, scientists can determine what kind of organisms lived in the past, how they evolved, and what their characteristics were. Fossils found in different layers of sedimentary rock also show how organisms changed over time, supporting the theory of evolution. Therefore, fossil records are an important source of evidence for the theory of evolution.

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In a typical predator food chain involving secondary and tertiary consumers, the organisms become progressively larger and fewer along the food chain. This is because the energy from the primary producers (plants) is transferred to the primary consumers (herbivores) and then to the secondary consumers (carnivores) and finally to the tertiary consumers (top carnivores). As this energy is transferred, a lot of it is lost as heat or used for metabolism, so there is less and less energy available for the higher levels of the food chain. Therefore, the organisms at the top of the food chain (tertiary consumers) tend to be larger in size and fewer in number compared to those at the bottom (primary producers and herbivores).

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The organelle involved in tissue respiration is the mitochondrion. Mitochondria are known as the "powerhouses" of the cell because they produce energy-rich ATP molecules through cellular respiration. Tissue respiration is the process by which cells in the body consume oxygen to produce energy in the form of ATP. This process occurs within the mitochondria, which are found in virtually all types of eukaryotic cells and are particularly abundant in tissues with high energy demands, such as muscle tissue. The other organelles listed (endoplasmic reticulum, ribosome, and golgi body) are not directly involved in cellular respiration.

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A tertiary consumer is an organism that eats secondary consumers. In the given pyramid, the shark is the only organism that feeds on other consumers, specifically small fish that are secondary consumers. Therefore, the shark functions as a tertiary consumer.

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If a child has a blood group genotype that is different from both parents and the mother has a genotype of OO, it means that the child must have inherited an allele from the father that is different from O. Since the mother's genotype is OO, she can only contribute an O allele to the child. This means that the father must have contributed either an A, B or AB allele to the child, since these are the only other possible blood group alleles. Therefore, the father of the child can only have a genotype of either A, B, or AB.

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The part labelled 3 is the auxillary bud. This is a structure that is found on the stem of a plant, typically at the base of a leaf or at the node. The auxillary bud has the potential to develop into a new branch or flower cluster. It contains a dormant shoot that can grow when activated by environmental factors or pruning. The auxillary bud is important for the growth and development of the plant and plays a key role in branching and flower production.

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Salinity is the least likely factor to affect animals living in a freshwater habitat. Salinity refers to the concentration of dissolved salts in water, and since freshwater habitats have low salt concentration, the animals that live there have adapted to these conditions. On the other hand, turbidity, temperature, and pH are all important factors that can affect the health and survival of animals in freshwater habitats. Turbidity, for instance, can reduce the amount of light that penetrates the water, affecting the growth of aquatic plants and the ability of animals to find food. Temperature and pH, on the other hand, can affect the metabolic processes of aquatic organisms, and extreme variations in these factors can be harmful or even lethal to some species.

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The insect that undergoes incomplete metamorphosis is the termite. In incomplete metamorphosis, the insect hatches from an egg into a nymph that resembles an adult, but is smaller and has no wings. The nymph molts several times, each time becoming more similar in appearance to the adult, until it reaches full size and develops wings (if it is a flying species). In contrast, insects that undergo complete metamorphosis, such as the moth, have a distinct larval stage, which looks completely different from the adult, and goes through a pupal stage before emerging as an adult.

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Fungi are heterotrophic because they lack chlorophyll. Chlorophyll is the green pigment found in plants that allows them to produce their own food through photosynthesis. Since fungi do not have chlorophyll, they cannot produce their own food like plants do. Instead, they obtain their nutrients from other organisms, either living or dead. This means that they have to feed on organic matter to survive, making them heterotrophic. Therefore, we can say that fungi are heterotrophic because they lack chlorophyll and cannot produce their own food through photosynthesis, so they must obtain nutrients from other sources.

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The bone of the neck on which the skull rests is known as the "atlas". The atlas is the first cervical vertebra, located at the top of the spine, just beneath the skull. It is responsible for supporting the weight of the head and allowing the head to nod up and down. The name "atlas" comes from the mythological figure Atlas who was believed to carry the weight of the world on his shoulders.

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The part of the curve that represents the fastest rate of growth is labeled as M. This is because the slope of the curve is steepest at this point, indicating a rapid increase in the growth rate. As we move from left to right along the curve, the rate of growth gradually increases, reaches its maximum at point M, and then begins to decrease until it reaches zero at point N. Therefore, point M represents the peak growth rate of the organism or population.

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Double fertilization in higher plants is significant because it ensures the formation of a fertile embryo and the endosperm. Double fertilization is a process that occurs during the fertilization of angiosperms (flowering plants), where two sperm cells are involved in the fertilization of the ovule. One sperm fertilizes the egg cell, leading to the formation of the zygote, which develops into the embryo. The other sperm fuses with the two polar nuclei in the central cell of the female gametophyte, leading to the formation of the endosperm. The endosperm provides nutrients to the developing embryo and is an important part of the seed. Double fertilization ensures that both the embryo and the endosperm are fertile, which is important for the successful reproduction and survival of the plant species.

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The hereditary materials of the cell is the DNA (Deoxyribonucleic acid). DNA is a complex molecule that carries genetic information that determines the characteristics of living organisms. It is found in the nucleus of cells and also in some organelles such as mitochondria and chloroplasts. DNA is made up of four basic building blocks called nucleotides, and the sequence of these nucleotides carries the genetic code. DNA is responsible for transmitting genetic information from one generation to the next through the process of replication, which occurs before cell division.

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Mangrove swamps can be found where a river meets the sea. They are coastal wetlands that are typically found in tropical and subtropical regions. The mangrove trees that make up these swamps are adapted to living in brackish water, where freshwater from the river mixes with saltwater from the sea. This unique ecosystem is important for protecting coastlines from erosion, providing habitats for a variety of plant and animal species, and serving as a nursery for many fish and shellfish species.

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Pancreatic juice contains amylase, lipase, and trypsin. Amylase is an enzyme that breaks down carbohydrates into simple sugars, lipase breaks down fats into fatty acids and glycerol, while trypsin breaks down proteins into peptides. These enzymes are important for digestion and are produced in the pancreas before being released into the small intestine to aid in the breakdown of food.

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In genetics, the capital letter 'R' represents a dominant allele for a particular gene, while the lowercase letter 'r' represents a recessive allele. When an individual has two copies of the same allele, it is called homozygous (RR or rr). When an individual has one dominant and one recessive allele, it is called heterozygous (Rr). So, if RR (homozygous dominant) is crossed with Rr (heterozygous), the possible gametes for RR are R, and the possible gametes for Rr are R and r. Thus, the possible offspring are 50% RR (homozygous dominant) and 50% Rr (heterozygous). This means that the correct answer is: 2RR, 2Rr.

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In the absence of oxygen, the pyruvic acid produced during glycolysis undergoes fermentation. This process converts the pyruvic acid to either lactic acid or ethanol and CO2, depending on the type of fermentation. Therefore, the correct answer to the question is ethanol.

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Gaseous exchange in Aves (birds) occurs in the air sacs. These air sacs are connected to the lungs and extend throughout the bird's body, including into the hollow bones. As the bird breathes, air moves through the trachea and into the posterior air sacs, then into the lungs, and finally into the anterior air sacs before being expelled out of the body. During this process, the air sacs act as bellows, keeping air constantly flowing over the respiratory surfaces of the lungs, ensuring efficient gas exchange. Therefore, the correct answer is option C - air sacs.

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The theory of natural selection was developed by Charles Darwin and Alfred Russel Wallace. Darwin is often credited with the theory of evolution by natural selection, which proposes that species change over time as a result of natural selection acting on inherited variation. Wallace independently came up with a similar theory of natural selection, which he described in a letter to Darwin. Darwin then published his own ideas and credited Wallace, leading to their joint recognition as the developers of the theory of natural selection.