WAEC SSCE - Biology - 2001

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The vector of malaria fever is the female Anopheles mosquito. Malaria is a disease caused by a parasite that is transmitted to humans through the bites of infected female Anopheles mosquitoes. When a mosquito feeds on the blood of an infected person, it ingests the malaria parasite which then reproduces within the mosquito. Later, when the same mosquito bites another person, it transmits the parasite to the new person through its saliva. Therefore, the correct answer to the question is "Female Anopheles mosquito" as it is the only mosquito species listed that is known to transmit malaria to humans. Male mosquitoes, on the other hand, feed on plant nectar and do not transmit the disease. The Culex mosquito is known to transmit other diseases such as West Nile virus, but not malaria.

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Wind is the agent of pollination of grasses. Grasses are flowering plants, and like many other flowering plants, they require pollination in order to reproduce. Pollination is the transfer of pollen from the male reproductive structure (the stamen) to the female reproductive structure (the pistil) of a flower. In the case of grasses, the flowers are typically small and inconspicuous, and they lack the showy petals and bright colors that attract insect or mammal pollinators. Instead, the male flowers produce large quantities of lightweight, dry, and dusty pollen, which is easily carried by the wind to nearby female flowers. This is called wind pollination, and it is a common method of pollination in grasses and other plants that live in open, exposed environments. Therefore, the correct option to the question is "Wind" as it is the main agent of pollination of grasses. While insects, water, and mammals can also be agents of pollination for certain types of plants, they are not typically involved in the pollination of grasses.

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The option that indicates that Euglena is a plant is "Presence of starch grain". Euglena is a unicellular organism that possesses both plant-like and animal-like characteristics. It contains chloroplasts, which are responsible for photosynthesis, and stores food in the form of paramylon, a type of starch grain. The conspicuous "eye" spot is actually a light-sensitive organelle that helps Euglena detect light for photosynthesis. The presence of a gullet in Euglena allows it to feed like an animal by ingesting food particles, and the flagellum enables it to move in a manner similar to that of animals.

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The correct answer is: - Homologous chromosomes, nuclear membrane and spindle fibers. During mitosis in a plant cell, the homologous chromosomes condense and become visible. The nuclear membrane breaks down, and spindle fibers, which are made up of microtubules, attach to the chromosomes and pull them apart into two new nuclei. The cell wall remains intact throughout mitosis, so cell wall and centrioles are not visible during the process. Nucleolus is also not visible as it disappears during the process of mitosis.

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Birds incubate their eggs. Birds have a special pouch called the brood pouch, which is located on their underbelly. The brood pouch is where the eggs are incubated until they hatch. The parent bird sits on the eggs to provide warmth and ensure that the eggs develop properly. During this process, the parent bird may leave the eggs briefly to feed or drink, but returns to continue the incubation process. Once the eggs hatch, the parent bird continues to provide care for the hatchlings until they are able to fend for themselves.

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In mammals, fertilization usually occurs in the oviduct, also known as the fallopian tube. After the egg is released from the ovary, it travels through the oviduct, which is where it may encounter sperm. If there is a viable sperm present, fertilization can occur within the oviduct. The fertilized egg then travels down the oviduct towards the uterus, where it will implant and develop into a fetus. The cervix is the opening between the uterus and the vagina, and the vagina is the muscular canal that connects the cervix to the external environment. While the sperm may travel through the vagina to reach the oviduct, fertilization itself does not occur in either the vagina or the cervix.

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Poor drainage affects plant growth in an alkaline soil. Alkaline soil is characterized by a high pH level, typically above 7.0, which can lead to a variety of problems for plants. One of the major issues is poor nutrient availability, as many essential plant nutrients become less soluble and therefore less available to plants at high pH levels. Poor drainage exacerbates this problem by further reducing the availability of nutrients. When water is unable to drain effectively from the soil, it can become stagnant and oxygen-deprived, leading to anaerobic conditions that are detrimental to plant growth. This can also cause root damage or death, which further limits the plant's ability to take up nutrients and water from the soil. As a result, poor drainage is a major factor that affects plant growth in alkaline soils.

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The major function of the cell membrane is to delimit the cytoplasm, which is the fluid-filled interior of the cell, and to act as a selective barrier that controls the movement of substances into and out of the cell. The cell membrane is made up of a phospholipid bilayer, which consists of two layers of lipid molecules. This lipid bilayer forms a barrier that separates the inside of the cell from the outside environment. The phospholipid bilayer is also studded with various proteins, which are involved in a variety of functions such as transport, cell signaling, and cell adhesion. The cell membrane is selectively permeable, which means that it allows some substances to pass through while preventing others from crossing. This selective permeability is important for maintaining the internal environment of the cell and for regulating various cellular processes. Therefore, the correct option to the question is "delimits the cytoplasm" as it describes the primary function of the cell membrane. The other options listed (synthesizes protein, breaks down worn-out organelles, and is the site for photosynthesis) are functions of other organelles within the cell, such as ribosomes, lysosomes, and chloroplasts, respectively.

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The palisade cells are the structures labelled as number III. The palisade cells are a type of leaf cells found in the mesophyll layer of a leaf. They are located just below the upper epidermis and are arranged vertically, standing upright like a palisade fence. The palisade cells are responsible for carrying out most of the photosynthesis in the leaf. They contain a large number of chloroplasts, which are the organelles responsible for capturing light energy and converting it into chemical energy through the process of photosynthesis. The palisade cells are specifically adapted to capture sunlight efficiently, as they are located close to the top of the leaf where they can receive the most light. Therefore, the correct option to the question is "III" as the palisade cells are located in the structure labelled as number III.

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The excretory product of Amoeba is ammonia. Amoeba is a unicellular organism that belongs to the kingdom Protista. As an organism, it carries out metabolic processes like all living organisms do, and waste products are produced as a result. Ammonia is one of the waste products produced during the metabolism of Amoeba. Ammonia is a highly toxic substance that needs to be eliminated from the body of the Amoeba. Amoeba does not have specialized excretory organs like animals do, but it has a cell membrane that helps it to excrete waste products, including ammonia, through a process known as diffusion. Therefore, the correct option to the question is "Ammonia" as it is the excretory product of Amoeba.

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Methylated spirit is suitable for removing chlorophyll in a green leaf. This is because methylated spirit contains ethanol, which is a good solvent for chlorophyll. When the green leaf is dipped into the methylated spirit, the chlorophyll will dissolve in the alcohol, making the leaf lose its green color.

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Bacteria have proved very useful in medicine due to the production of antibiotics. Antibiotics are drugs that are used to treat bacterial infections by killing or inhibiting the growth of bacteria. They have been instrumental in the treatment of many diseases caused by bacteria, including pneumonia, tuberculosis, and meningitis. The discovery of antibiotics has revolutionized medicine and has saved countless lives.

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The substances recycled in the soil by the activities of micro-organisms during the decay of dead organisms are first utilized by the autotrophs. Autotrophs are organisms that can produce their own food through the process of photosynthesis. They use the nutrients and other substances released during the decay of dead organisms to synthesize organic molecules like carbohydrates, proteins, and fats. These organic molecules are used as food by other organisms such as herbivores, carnivores, and scavengers in the food chain. Therefore, autotrophs play a crucial role in the cycling of nutrients in the ecosystem.

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Agama lizards compete for space, food, and mates. Competition is a natural phenomenon that occurs when resources are limited and must be shared between individuals of the same or different species. In the case of Agama lizards, they compete for resources such as food, which is necessary for their survival, and space, which provides them with shelter, basking sites, and escape routes. Additionally, Agama lizards also compete for mates, particularly during the breeding season when males fight for the opportunity to mate with females. Therefore, the correct answer to the question is "Space, food, and mates" as Agama lizards compete for all three factors listed in the options.

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The character that expresses itself in the presence of the contrasting characters is called the dominant trait. This means that if an organism inherits one copy of the dominant allele, it will show that trait, even if it also inherits a different, contrasting allele from the other parent. The recessive trait, on the other hand, only expresses itself when an organism inherits two copies of the recessive allele. The term "hybrid" refers to an organism that has two different alleles for a particular trait. So, in summary, the dominant trait is the one that dominates over the recessive trait in terms of expression, and a hybrid organism has two different alleles for the same trait.

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The question asks to identify the option which is NOT an advantage of sexual reproduction. Sexual reproduction is a process of reproduction that involves the fusion of gametes from two different parents. The advantages of sexual reproduction include: 1. It allows the formation of new species: Sexual reproduction promotes genetic diversity by allowing the shuffling of genes from two different individuals, which may lead to the formation of new species. 2. It allows production of desirable traits: Sexual reproduction permits the exchange of genetic material between two parents, allowing desirable traits to be passed on to offspring. 3. It permits variation of individuals: Sexual reproduction leads to the creation of offspring with genetic diversity, allowing for variations in characteristics such as color, size, and behavior. 4. It provides means for the variation of chromosome number from generation to generation: Sexual reproduction ensures that the number of chromosomes in the offspring is a combination of the parent's chromosomes, which can lead to variations in chromosome number from generation to generation. Therefore, the answer to the question is option D, "it provides means for the variation of chromosome number from generation to generation," as it is an advantage of sexual reproduction.

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The major reason why the red blood cells can survive in the blood is that the blood plasma and the red blood cells are isotonic. This means that the concentration of solutes, such as salts and proteins, is the same in both the blood plasma and the red blood cells. As a result, there is no net movement of water across the cell membrane of the red blood cells, and they do not shrink or swell. This isotonicity helps to maintain the shape and integrity of the red blood cells, allowing them to carry oxygen and carbon dioxide throughout the body.

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Micronutrients are essential nutrients that are required in small amounts by the body for proper growth, development, and maintenance of physiological functions. They include vitamins and minerals such as iron, iodine, zinc, and copper, among others. Potassium is not considered a micronutrient because it is required in relatively large amounts by the body and is classified as a macronutrient along with other nutrients such as carbohydrates, proteins, and fats. Potassium is important for many physiological functions such as maintaining fluid balance and regulating heartbeat, and it is commonly found in many foods such as bananas, potatoes, and spinach.

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The statement that is true about blood groupings is that Group O has no antigen. Antigens are proteins that are found on the surface of red blood cells, and they are what determine a person's blood type. Blood types are classified into different groups, including A, B, AB, and O, based on the presence or absence of certain antigens. In Group A, the A antigen is present on the surface of red blood cells, and in Group B, the B antigen is present. In Group AB, both A and B antigens are present, while in Group O, neither A nor B antigens are present. Because Group O does not have any antigens on the surface of its red blood cells, it is considered a universal donor, not a universal recipient as stated in one of the options. Group AB, on the other hand, can receive blood from any group because it has both A and B antigens on its red blood cells. Therefore, the correct statement is that Group O has no antigen.

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The process in which light energy is converted to ATP is photosynthesis. During photosynthesis, plants use the energy from sunlight to convert carbon dioxide and water into glucose, a type of sugar. This process occurs in the chloroplasts of plant cells and involves two main stages: the light-dependent reactions and the light-independent reactions. In the light-dependent reactions, light energy is absorbed by pigments called chlorophyll and converted into ATP and NADPH. These energy-rich molecules are then used in the light-independent reactions to fuel the production of glucose. So, Photosynthesis is the correct answer.

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The correct answer is translocation. Translocation is the process by which plants transport food materials such as sucrose and amino acids from the leaves (where they are produced during photosynthesis) to the other parts of the plant such as stems, roots and fruits where they are utilized for growth and other metabolic processes. This transportation occurs through specialized tissues called phloem, which are made up of sieve tubes and companion cells. The movement of food in the phloem is usually from a source to a sink, and this process is facilitated by pressure gradient, which can be created by the active transport of sugars from source cells into the phloem.

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The tissue is the Epidermis. Epidermis is a tissue, which is a group of cells that work together to perform a specific function. In this case, the epidermis is a tissue that covers the surface of the body and protects it from damage and dehydration. It is found in animals, including humans, and is made up of several layers of cells. The other options, Volvox, Chlamydomonas, and Paramecium, are organisms, but they do not qualify as tissues because they are made up of only one or a few cells that perform all necessary functions.

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The effect of the contraction of the muscles of the diaphragm is that the volume of the thoracic cavity increases. The diaphragm is a sheet of muscle that separates the chest cavity from the abdominal cavity. When the diaphragm contracts, it flattens out and moves downward, which increases the volume of the thoracic cavity. This, in turn, causes a decrease in pressure within the thoracic cavity, allowing air to flow into the lungs. As the volume of the thoracic cavity increases, the lungs are able to expand, drawing air in through the nose and mouth. The increased air intake brings in more oxygen, which is necessary for the body's metabolic processes. Therefore, the effect of the contraction of the muscles of the diaphragm is that the volume of the thoracic cavity increases, allowing air to flow into the lungs and providing the body with the necessary oxygen.

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The statement "They have intermediate hosts" is not correct for both tsetse flies and mosquitoes. Tsetse flies and mosquitoes both harbour protozoa as disease agents, possess piercing and sucking mouthparts, and inject disease-causing organisms into the bloodstream. However, only some species of mosquitoes have intermediate hosts, which are typically other insects such as snails or mosquito larvae, in the life cycle of the parasites they transmit. Tsetse flies, on the other hand, do not have intermediate hosts in their transmission of diseases. Instead, they directly transmit the parasites to their mammalian hosts through their bite.

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Magnesium is needed by plants for the formation of chlorophyll, which is the pigment responsible for the green color in leaves and is essential for photosynthesis. Photosynthesis is the process by which plants produce their own food using sunlight, carbon dioxide, and water. Chlorophyll is a critical component of this process as it captures the energy from sunlight and converts it into chemical energy that the plant can use to fuel its growth and metabolism. Magnesium is a key component of the chlorophyll molecule, and without it, plants are unable to produce chlorophyll. This can lead to a condition called chlorosis, where the leaves of the plant turn yellow or white due to a lack of chlorophyll. Therefore, the correct option to the question is "formation of chlorophyll" as magnesium is required for the synthesis of this essential pigment. The other options listed (protein synthesis, formation of cell membrane, and activation of enzymes) are also important functions of magnesium in plants, but they are not directly related to the formation of chlorophyll.

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The part of the gill of a fish that is involved in gaseous exchange is the gill filament. Gill filaments are thin and thread-like structures that project from the gill arches. They are covered with tiny finger-like projections called lamellae, which are rich in blood vessels. As water flows over the lamellae, oxygen diffuses from the water into the blood vessels, and carbon dioxide diffuses from the blood vessels into the water. This exchange of gases is facilitated by the thin walls of the gill filaments, which provide a large surface area for gas exchange to occur.

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The association that can upset the balance of nature is parasitism. Parasitism is a relationship between two organisms, where one benefits (the parasite) and the other is harmed (the host). The parasite obtains its food and shelter at the expense of the host, often causing damage or even death. This relationship can upset the balance of nature by reducing the population of the host species, disrupting food chains and ecosystems, and even leading to the extinction of certain species. Epiphytism, symbiosis, and saprophytism are all natural associations between different organisms that play important roles in the ecosystem, but do not necessarily upset the balance of nature. Epiphytism is a type of commensalism where one plant grows on the surface of another plant for support, without harming it. Symbiosis is a relationship where two different species live together in a mutually beneficial relationship, such as the partnership between pollinators and plants. Saprophytism is a type of heterotrophic nutrition in which an organism obtains its food by decomposing dead organic matter. Therefore, the association that can upset the balance of nature is parasitism.

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The structure in a housefly that aids in the transmission of diseases to humans is its hairs. Houseflies are known to carry various disease-causing microorganisms such as bacteria, viruses, and parasites on their body parts, including their hairs. These microorganisms can be picked up by the housefly when it feeds on contaminated materials such as feces, garbage, or decaying matter, and can then be transferred to humans when the housefly lands on food or surfaces that humans come into contact with. Housefly hairs are particularly effective in transmitting diseases because they can trap and hold onto small particles, including microorganisms. The hairs on their legs and body can easily pick up and transfer these microorganisms to new surfaces or onto human skin when they land on them. Therefore, it is important to keep houseflies away from food and living areas to reduce the risk of disease transmission. This can be done by practicing good sanitation, keeping food covered, and using fly traps or insecticides.

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Platelets are not a constituent of blood plasma. Blood plasma is the yellowish liquid component of blood in which blood cells are suspended. It is composed of water, proteins, mineral salts, hormones, and other components. Platelets, on the other hand, are a type of blood cell that is responsible for blood clotting. They are formed in the bone marrow and are not found in blood plasma.

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Bacteria is a chemo-autotroph. Chemo-autotrophs are organisms that obtain energy from chemical reactions and use this energy to synthesize organic compounds from inorganic substances, such as carbon dioxide. They do not require sunlight or organic nutrients to survive. Bacteria are a diverse group of microorganisms that can be found in various environments, including soil, water, and the human body. Some bacteria are chemo-autotrophs, which means they obtain energy by breaking down inorganic compounds such as ammonia, sulfur, and iron. They use this energy to synthesize their own organic compounds, including amino acids, nucleotides, and carbohydrates. Chemo-autotrophic bacteria play important roles in the ecosystem by serving as primary producers and recycling nutrients. Some chemo-autotrophic bacteria are also involved in processes such as bioremediation, which is the use of microorganisms to clean up environmental pollutants. In contrast, viruses are not considered living organisms because they cannot carry out metabolic processes on their own and require a host cell to reproduce. Paramecium and Euglena are eukaryotic organisms that are capable of carrying out photosynthesis and are therefore considered photoautotrophs.

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Iron is the mineral needed for the formation of haemoglobin. Haemoglobin is the protein molecule in red blood cells responsible for transporting oxygen from the lungs to the body's tissues. Iron is a crucial component of haemoglobin, as it binds to oxygen and helps to transport it throughout the body. Without enough iron, the body cannot produce enough haemoglobin, leading to a condition called iron deficiency anaemia. Therefore, consuming iron-rich foods or supplements is essential for the formation of haemoglobin and the overall health of the body.

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The chloroplast is the organelle in plant cells that is responsible for photosynthesis, which is the process by which plants make food. To identify which group of structures contains chloroplasts, we need to look for structures involved in photosynthesis. Structures I and II are not involved in photosynthesis. Structure VII is the mitochondria which are responsible for cellular respiration, which is the process by which cells convert nutrients into energy. Therefore, option B is also incorrect. Structures III, VIII, and IX are involved in photosynthesis and structure XI is the vacuole which is responsible for storing water and other substances. Therefore, the correct answer is option C: III, VIII, and IX.

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The phenomenon of display in animals refers to a specific behavior that an animal exhibits to communicate with others of its own species. It is often a visual display, such as a series of postures or movements, that conveys information about the animal's readiness to mate, social status, or intention to defend its territory. Display can also involve vocalizations or the release of pheromones. Therefore, out of the options given, the correct one would be "ready for mating" as display is a behavior that animals engage in to attract potential mates and signal their readiness to mate. This behavior is often seen in birds during their mating season where they perform elaborate displays of feathers and calls to attract a mate.

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Short-sightedness or myopia is a condition where distant objects appear blurred while close objects appear clear. This occurs when the light entering the eye is not properly focused on the retina but in front of it. To correct this, a concave lens is used. A concave lens is thinner at the center and thicker at the edges, and it diverges light rays. By placing a concave lens in front of the eye, it helps to focus the light rays properly on the retina, thereby correcting the myopia.

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Micro-organisms that break down dead organisms and absorb their nutrients are called decomposers. They play an important role in the ecosystem by breaking down organic matter and returning nutrients back to the soil. Examples of decomposers include bacteria and fungi, which secrete enzymes to break down the complex organic molecules in dead plants and animals into simpler molecules that can be absorbed by other organisms.

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The human characteristics that are discontinuous variations are III and IV only, which is option IV. Discontinuous variations are traits that can be classified into distinct categories with no intermediate values. In other words, individuals can be placed into specific groups based on the presence or absence of a particular characteristic. Blood Rh factor is a discontinuous variation because individuals can be classified as either Rh-positive or Rh-negative, with no intermediate values. Similarly, color blindness is also a discontinuous variation because individuals can be classified as either color-blind or not color-blind. Complexion and height, on the other hand, are continuous variations because they show a range of intermediate values between two extremes. For example, complexion can range from very light to very dark, with many intermediate shades in between. Height can also vary along a continuum, with individuals ranging from very short to very tall. Therefore, the human characteristics that are discontinuous variations are III and IV only, which is option IV.

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The evidence of photosynthesis is the formation of starch. Starch is a complex carbohydrate that is synthesized by plants during the process of photosynthesis. The energy for this process is obtained from the absorption of light by pigments such as chlorophyll. Carbon dioxide from the air and water from the soil are also necessary for photosynthesis to occur. During photosynthesis, water molecules are split into hydrogen and oxygen, but this process is not considered as direct evidence of photosynthesis. Therefore, the correct answer is the formation of starch.

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Lizards exhibit territoriality. Territoriality is a behavior in which an animal defends a specific area or territory from intruders of the same species. This behavior is commonly observed in animals that need space and resources to survive and reproduce. Lizards are known to exhibit territorial behavior, particularly during the breeding season when males establish and defend their territories from other males. They use various behaviors such as head-bobbing, push-ups, and displaying bright colors to signal their ownership of the territory and to deter other males from entering. Territoriality in lizards is important for their survival and reproductive success because it helps ensure that they have access to resources such as food, water, and mates.

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The spinneret found in the caterpillar of butterfly is used for the production of silk thread. Caterpillars are the larval stage of butterflies, and they use the spinneret to produce silk for various purposes such as creating a cocoon for metamorphosis, making a protective covering, or spinning a silk thread to help them climb or move around on leaves. The spinneret is located on the lower part of the caterpillar's head and is made up of a series of small tubes through which the silk is extruded. The silk is produced from special glands in the caterpillar's body and is forced through the spinneret, where it is spun into a thread. The caterpillar can produce different types of silk for different purposes, such as strong silk for cocoon-making or sticky silk for trapping prey.

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(a) Eight human activities that may pollute water bodies

1. Discharge of untreated sewage and human excreta into rivers and streams.
2. Dumping of industrial effluents and chemical wastes into water bodies.
3. Washing of clothes and bathing with detergents and soaps in streams.
4. Application of fertilizers on farms which are washed by run-off into water (causing eutrophication).
5. Spraying of pesticides and herbicides that drain into water bodies.
6. Oil spillage from tankers, refineries and pipelines.
7. Dumping of refuse and solid domestic waste into rivers and lakes.
8. Discharge of hot water (thermal pollution) from factories and power stations.

Others include mining activities that release heavy metals, and dumping of dead animals into water.

(b) Measures to prevent pollution of water bodies

• Treatment of sewage and effluents before they are discharged, so that harmful materials are removed.
• Enactment and enforcement of laws that prohibit the dumping of waste into water bodies, with penalties for offenders.
• Public enlightenment and education on the dangers of water pollution and the need for clean water.
• Proper disposal of refuse in designated dumps or by controlled incineration rather than in rivers.
• Controlled and moderate use of fertilizers and pesticides, and the use of biodegradable chemicals.
• Provision of pit latrines and toilets sited away from streams to prevent faecal contamination.
• Prompt control of oil spillage and proper maintenance of pipelines and tankers.

(c) Four methods of purifying water

1. Boiling - heating water to kill micro-organisms.
2. Filtration - passing water through sand and gravel beds to remove suspended particles.
3. Chlorination - adding chlorine or chlorine compounds to kill germs.
4. Distillation - boiling water and condensing the steam to give pure water.

Sedimentation with alum (coagulation) is also acceptable.

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(a)(i) Definitions

Tropic movement (tropism): a growth movement of a plant or part of a plant in response to an external stimulus that comes from a definite direction, the direction of the movement being determined by the direction of the stimulus.

Nastic movement (nasty): a non-directional movement of a plant part in response to a diffuse (non-directional) stimulus, where the direction of the response is independent of the direction of the stimulus.

(a)(ii) Four differences between tropic and nastic movements

(b) Experiment to show that auxins are produced in the apical cells (tip) of a shoot

• Take several similar germinating oat (or maize) seedlings (coleoptiles).
• Leave one seedling intact as a control.
• From a second seedling, cut off the tip of the coleoptile.
• On a third seedling, cut off the tip and then replace it on the stump.
• On a fourth, cut off the tip and place it back with a thin block of agar jelly between the tip and the stump.
• Keep all seedlings under the same conditions and illuminate them from one side.

Observation: the intact seedling and the ones with the tip replaced (directly or through agar) continue to grow and bend towards the light. The seedling whose tip was removed stops growing and does not bend.

Conclusion: because growth and curvature occur only when the tip is present, and the influence passes through the agar block, the growth substance (auxin) is produced in the apical cells of the shoot.

(c)(i) Two plant hormones other than auxins

1. Gibberellin (gibberellic acid).
2. Cytokinin (kinin).

Abscisic acid and ethylene are also acceptable.

(c)(ii) Two examples of tropism

1. Phototropism - shoot bending towards light.
2. Geotropism - root growing downwards towards gravity.

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(a) What is an ecosystem?

An ecosystem is a natural unit made up of a community of living organisms (the biotic component) interacting with one another and with the non-living (abiotic) part of their environment, together with the exchange of materials and flow of energy between them. Examples include a pond, a forest and a grassland.

(b) Two abiotic factors each affecting plants and animals in a terrestrial habitat

Factors affecting plants: (i) light intensity; (ii) rainfall (water/humidity). Others: temperature, wind, soil nutrients.

Factors affecting animals: (i) temperature; (ii) humidity. Others: light, wind.

(c) Effect of three abiotic factors on a named plant and a named animal

Named plant: maize plant. Named animal: grasshopper (in a grassland habitat).

• Light: Light provides the energy for photosynthesis in the maize plant; without adequate light the maize becomes pale (etiolated) and grows poorly. In the grasshopper, light controls its daily activity, feeding and breeding rhythm.
• Temperature: A suitable temperature speeds up the enzyme reactions of photosynthesis and growth in the maize; very high or very low temperatures reduce growth and may cause wilting or death. Being cold-blooded (poikilothermic), the grasshopper's body temperature and rate of activity rise and fall with the surrounding temperature; extreme cold makes it sluggish and extreme heat can be fatal.
• Water (rainfall/humidity): Water is needed by the maize for photosynthesis, transport of materials and turgidity; shortage of water causes wilting and stunted growth. For the grasshopper, humidity affects water loss from its body; low humidity increases the risk of desiccation, so it seeks moist shelter.

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(a)(i) Labelled diagram of a human sperm cell

(ii) Sperm cells are produced in the seminiferous tubules of the testes and are stored temporarily in the epididymis.

(b) How the structure of the sperm cell enables it to function in fertilisation

1. The acrosome, situated at the tip of the head, contains enzymes which digest the egg membrane and enable the sperm to penetrate the egg.
2. The nucleus in the head contains a haploid set of chromosomes. It carries the male genetic material which fuses with the female nucleus during fertilisation.
3. The middle piece contains numerous mitochondria which release energy for movement of the sperm.
4. The long, whip-like tail or flagellum beats to propel the sperm through the female reproductive tract towards the egg.
5. Its small, streamlined shape reduces resistance as it swims towards the ovum.

(c) Four advantages of sexual reproduction

1. It produces variation among offspring.
2. The variation enables some individuals to survive changes in the environment and resist diseases.
3. It permits the combination of desirable characteristics from two parents, producing improved varieties or hybrids.
4. It maintains the chromosome number of a species from one generation to the next.

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(a)(i) Longitudinal section of a mammalian heart

Labels: aorta, pulmonary artery, pulmonary veins, superior vena cava, inferior vena cava, right atrium, left atrium, right ventricle, left ventricle, tricuspid valve, bicuspid (mitral) valve, semilunar valves and septum.

(a)(ii) Pulmonary circulation

Deoxygenated blood is pumped from the right ventricle through the pulmonary semilunar valve into the pulmonary artery. The pulmonary artery carries it to the capillaries of the lungs, where carbon dioxide diffuses out of the blood and oxygen diffuses into it. The oxygenated blood then returns to the left atrium through the pulmonary veins.

(b) Processes by which the mammalian body reduces its temperature

1. Increased sweating: Sweat is secreted onto the skin. Its evaporation absorbs heat from the body and cools it.
2. Vasodilation: Skin arterioles widen, allowing more warm blood to flow through surface capillaries, where heat is lost to the surroundings.
3. Relaxation of hair erector muscles: Body hairs lie flat, reducing the layer of trapped insulating air and increasing heat loss.
4. Reduced muscular activity: Less heat is produced by muscle contraction.
5. Reduced metabolic activity: The rate of heat-producing chemical reactions in the body is lowered.