WAEC SSCE - Biology - 2021

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The eye defect illustrated in the diagram is Myopia, also known as nearsightedness. Myopia is a common eye condition that causes distant objects to appear blurry while nearby objects remain clear. In the diagram, the light rays coming from the distant object do not focus directly on the retina, which is the light-sensitive layer at the back of the eye. Instead, they focus in front of the retina, causing a blurred image. This happens because the eyeball is too long or the cornea is too curved, which causes light to focus incorrectly in the eye. People with myopia often have trouble seeing things like road signs or blackboards in a classroom, but can see things like books or computer screens clearly. Myopia can be corrected with eyeglasses, contact lenses, or refractive surgery, which can help to redirect the light rays onto the retina so that distant objects appear clear.

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Eating uncooked meat / dysentery, cholera, food poisoning. Eating raw or undercooked meat can expose a person to harmful bacteria, such as Salmonella, Escherichia coli, and others, that can cause food poisoning. Food poisoning is a common illness that results from eating contaminated food. Dysentery and cholera are both diseases that are caused by bacteria and are spread through contaminated food and water. They can cause severe diarrhea and dehydration, and can be life-threatening if left untreated. It is important to always properly cook meat to kill any harmful bacteria and to practice good hygiene to reduce the risk of foodborne illnesses.

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An enzyme reaction may begin to decline when the pH of the medium is altered. Enzymes are biological catalysts that speed up chemical reactions in living organisms. Each enzyme has an optimum range of pH and temperature at which it functions best. Any deviation from this optimal range can cause the enzyme to become denatured, which means that the shape of the enzyme is changed and it can no longer catalyze the reaction. Changes in pH can alter the charges on the amino acids that make up the enzyme, which can affect the shape of the enzyme and its ability to bind to the substrate. Therefore, if the pH of the medium is altered, the enzyme reaction may begin to decline as the enzyme becomes denatured and is no longer able to catalyze the reaction. Based on the given options, the correct answer is the pH of the medium is altered.

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The organism that is not an example of a carnivorous plant is the gloriosa. The other three options (venus flytrap, pitcher plant, and Utricularia) are all examples of carnivorous plants. Carnivorous plants are unique types of plants that have evolved to obtain nutrients, particularly nitrogen, from the digestion of small animals such as insects, spiders, and even small vertebrates. These plants are typically found in nutrient-poor environments, such as bogs and swamps, where they have adapted to supplement their diet with the nutrients they cannot obtain from the soil. The Venus flytrap is a carnivorous plant that captures insects by using modified leaves that snap shut when triggered by the movement of the prey. The pitcher plant, on the other hand, uses a modified leaf that forms a deep, slippery cavity filled with digestive enzymes to trap and digest insects. Finally, Utricularia is a type of aquatic carnivorous plant that uses small bladders on its leaves to capture tiny aquatic organisms. In contrast, the gloriosa is not a carnivorous plant. It is a type of flowering plant that belongs to the family Colchicaceae. It does not have any special adaptations for capturing and digesting prey and obtains its nutrients through photosynthesis like most other plants.

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When a large number of organisms share limited resources, the result is competition. Competition is a type of interaction that occurs when two or more organisms compete for the same limited resource, such as food, water, or shelter. The competition can be between members of the same species or between different species. Competition can have both positive and negative effects on the organisms involved. On the one hand, competition can lead to the evolution of traits that help individuals compete for resources more effectively, such as faster running or better camouflage. On the other hand, competition can also lead to negative effects, such as reduced growth rates, lower reproductive success, and increased mortality. Overall, competition is a common and important ecological process that helps to regulate the abundance and distribution of organisms in an ecosystem. It plays a key role in shaping the evolution of species and can have significant impacts on the structure and function of ecosystems over time.

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Mixing blood containing antigen A and blood containing antibody a will lead to agglutination. Agglutination occurs when the antibodies in the blood bind to the antigens on the surface of the red blood cells, causing them to clump together. In this case, the antibody a will bind to the antigen A on the red blood cells, leading to agglutination. This can cause serious health problems, such as blocking blood vessels and cutting off the blood supply to vital organs. Therefore, it is important to match blood types properly before transfusions to avoid agglutination and ensure a successful blood transfusion.

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The fruit that has the illustrated sections is a "hesperidium." Hesperidium is a type of fruit that is derived from a compound ovary with a leathery rind and is typically found in citrus fruits such as oranges, lemons, and limes. The fruit is divided into segments, each containing juice-filled sacs, called vesicles, that are surrounded by a tough, membranous tissue. The sections or vesicles are derived from the carpels of the ovary and are separated by thin walls. The term "hesperidium" comes from the Greek word for "golden apple," which was a reference to the fruit's yellowish color and round shape. The other options listed (capsule, drupe, and cypsela) do not have the same structural characteristics as a hesperidium.

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The factor most likely responsible for the various types of comb in domestic fowl is genetics. Comb type is determined by the genes that control the development of the head and face in birds. Different combinations of genes can result in different comb types, including single, pea, rose, and others. These genetic differences can be passed down from generation to generation, leading to the variation in comb types seen in domestic fowl. Environmental factors, such as temperature and nutrition, can also play a role in the development of combs, but the underlying genetic differences are what primarily determine the type of comb a bird will have.

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The practice that is a wildlife conservation method among the options listed is "discouraging poaching." Poaching refers to the illegal hunting or killing of wild animals for their body parts or meat. This practice can severely impact wildlife populations and disrupt ecosystems. Therefore, discouraging poaching is an important conservation method to protect endangered or threatened species from extinction. This can be achieved through public awareness campaigns, stricter law enforcement, and the creation of protected areas where hunting is prohibited. By reducing poaching, wildlife populations can recover and ecosystems can remain healthy and balanced.

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The organelle that is common to both plant and animal cells is the cell membrane. The cell membrane is a thin, semi-permeable layer that surrounds the cell and separates its internal environment from the external environment. It is made up of lipids and proteins, and its main function is to control the movement of substances in and out of the cell. In both plant and animal cells, the cell membrane is essential for maintaining cell integrity and regulating the exchange of nutrients, gases, and waste products with the surrounding environment. While plant cells also have a cellulose cell wall and a large central vacuole, animal cells do not have these structures. Chlorophyll, on the other hand, is a pigment found in plant cells that is responsible for absorbing light energy during photosynthesis. It is not present in animal cells. Therefore, the correct answer is the cell membrane.

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The detoxification of urea takes place in the liver. Urea is a waste product produced by the breakdown of proteins in the liver. It is a toxic substance and needs to be removed from the body to maintain a healthy balance of nitrogenous waste products. The liver plays a key role in the detoxification of urea by converting it into less toxic compounds, such as ammonia and then urea cycle which converts ammonia to urea. This process of urea detoxification in the liver is called the urea cycle or the ornithine cycle. The urea is then transported to the kidneys for excretion in the urine. In summary, the liver is responsible for the detoxification of urea, a toxic waste product of protein metabolism, by converting it into less toxic compounds through the urea cycle. This process helps to maintain the proper balance of nitrogenous waste products in the body and supports overall health and wellbeing.

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The statement that is not correct about mitosis is "four daughter cells are produced." Mitosis is a process of cell division that occurs in somatic cells (non-reproductive cells) of eukaryotic organisms. It is a type of asexual reproduction that results in the formation of two genetically identical daughter cells, each containing the same number of chromosomes as the parent cell. During mitosis, the DNA in the parent cell is replicated and separated into two identical sets of chromosomes. These chromosomes then line up in the middle of the cell and are pulled apart by spindle fibers, which leads to the formation of two daughter cells. Each daughter cell contains a complete set of chromosomes and is genetically identical to the parent cell. In contrast, the formation of four daughter cells is a characteristic of meiosis, which is a type of cell division that occurs in the cells of reproductive organs. Meiosis involves the formation of bi-valents, which are pairs of homologous chromosomes that exchange genetic material through a process called crossing over, resulting in genetic variation in the daughter cells. Additionally, chiasmata, which are points of crossing over, are formed during meiosis but not during mitosis. Therefore, the statement "four daughter cells are produced" is not correct about mitosis, since mitosis only produces two daughter cells that are genetically identical to the parent cell.

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The structure labeled II is the sporangium. A sporangium is a structure found in plants, fungi, and some bacteria that produces and contains spores. In plants, the sporangium is commonly found in the reproductive organs of the plant, such as the flowers, and is responsible for producing spores that will eventually become the seeds of the plant. In fungi, the sporangium is found at the end of specialized hyphae and is responsible for producing spores that will give rise to new fungal organisms. Sporangia can take on many different shapes and sizes depending on the organism, but they all serve the same basic purpose of producing and containing spores. Therefore, based on the given options, the correct answer is sporangium.

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When a person is frightened, the hormone adrenaline is suddenly secreted into the bloodstream. This hormone, also known as the "fight or flight hormone," prepares the body for a sudden burst of energy and increased physical activity. It increases heart rate, breathing rate, and blood pressure, and redirects blood flow to the muscles and away from less essential organs. This prepares the body to respond quickly and effectively to a perceived threat.

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Offspring formed by sexual reproduction exhibit more variation than those formed by asexual reproduction because gametes of parents have different genetic composition. In sexual reproduction, two parents contribute different sets of genes, which combine to produce unique offspring with a diverse genetic makeup. This genetic diversity results in a wide range of phenotypic traits, such as eye color, height, and susceptibility to diseases. In contrast, asexual reproduction involves only one parent, and the offspring produced are genetically identical to the parent. Therefore, sexual reproduction increases genetic diversity and promotes adaptation to changing environments, while asexual reproduction maintains genetic uniformity.

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The blood vessel which carries blood from the alimentary canal (digestive system) to the liver is called the "hepatic portal vein." Unlike most veins, which carry blood back to the heart, the hepatic portal vein carries nutrient-rich blood from the digestive organs, such as the stomach, small intestine, and large intestine, to the liver. The liver plays a crucial role in metabolizing and detoxifying nutrients and toxins absorbed from the digestive system before the blood enters the systemic circulation. The hepatic portal vein allows the liver to regulate and process the nutrients and toxins before they enter the bloodstream, which helps maintain homeostasis in the body. The other options listed (hepatic artery, hepatic vein, and mesenteric artery) are not involved in carrying blood from the digestive system to the liver.

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Maelezo ya Majibu

The terms longitudinal and transverse refer to different orientations or directions of a section or cut through an object. A longitudinal section is a cut that runs along the long axis of an object, dividing it into two parts, left and right. For example, if you were to cut an apple in half from stem to bottom, the resulting sections would be longitudinal sections. In contrast, a transverse section is a cut that runs perpendicular to the long axis of an object, dividing it into two parts, top and bottom. For example, if you were to cut an apple in half around its equator, the resulting sections would be transverse sections. Therefore, if we know that section X is a transverse section and section Y is a longitudinal section, we can conclude that the answer is "transverse and longitudinal". If the question had been reversed, with X being longitudinal and Y being transverse, the answer would be "longitudinal and transverse".

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Endangered species are organisms that are likely to disappear from the surface of the earth. This means that they are at risk of becoming extinct in the wild due to a variety of factors, including habitat loss, climate change, poaching, and pollution. Endangered species are not likely to migrate to other favourable lands because their habitats are typically already fragmented or destroyed. In addition, endangered species do not necessarily reproduce profusely in an area, as their populations are often small and declining. Finally, endangered species are not typically dangerous to humans or other animals, and in fact, many of them are vulnerable because they have been overhunted or because their habitats have been destroyed by human activities.

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The level of organization of an organism refers to how the different parts of the organism are arranged and function together. There are several levels of organization, ranging from the smallest unit of life, the cell, to the largest, the entire organism. At the level of a cell, the organism is made up of individual units of life that carry out specific functions necessary for the survival of the organism. Cells can exist independently, or they can come together to form tissues. At the level of tissues, groups of similar cells work together to perform a particular function, such as muscle tissue for movement or nervous tissue for communication. At the level of organs, two or more tissues come together to form a structure that performs a specific function, such as the heart for pumping blood or the lungs for breathing. Finally, at the level of systems, groups of organs work together to perform more complex functions necessary for the survival of the organism, such as the digestive system for processing food or the circulatory system for transporting nutrients and oxygen throughout the body. In summary, the level of organization of an organism refers to how its different parts, ranging from cells to tissues to organs to systems, work together to carry out necessary functions for the survival of the organism.

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If the population of domestic fowl decreases, the grasshopper population would increase. This is because domestic fowl are predators of grasshoppers, so if their population decreases, there will be fewer predators to control the grasshopper population. As a result, the grasshopper population will increase, which could lead to overgrazing and depletion of the grasses available to grasshoppers. This could, in turn, affect the entire food chain, as there may not be enough grasses available to support the grasshoppers, which are the primary food source for the domestic fowl and the hawk. The hawk population may also decline if there are not enough grasshoppers available to support their diet. Therefore, a decrease in the population of one species in a food chain can have a cascading effect on the entire ecosystem.

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The temperature control center in mammals is located in the hypothalamus, which is a region in the brain. The hypothalamus helps regulate various body functions including temperature, hunger, thirst, and fatigue. It acts as a thermostat for the body, monitoring and adjusting the body temperature to maintain homeostasis. The pituitary gland and adrenal gland also play a role in regulating the body's temperature, but the hypothalamus is the primary temperature control center.

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The statement that is not Lamarck's postulate on evolution is "survivors in a competitive community must have inherited useful traits." Lamarck's theory of evolution, also known as Lamarckism, proposed that organisms can change during their lifetime by adapting to their environment and that these changes can be passed down to their offspring. This idea is often summarized in the phrase "use it or lose it," which means that organs that are used frequently become stronger and better developed, while those that are not used may become vestigial or disappear altogether. Lamarck also believed that the changes an organism acquired during its lifetime could be passed down to its offspring, which is known as the inheritance of acquired characteristics. For example, if a giraffe stretched its neck to reach high branches and kept doing so throughout its life, it would develop a longer neck and pass this trait down to its offspring. Lamarck did not, however, explicitly state that survivors in a competitive community must have inherited useful traits. This idea is more closely associated with Darwin's theory of natural selection, which suggests that organisms with advantageous traits are more likely to survive and reproduce, passing these traits on to their offspring.

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Termites exhibit division of labor. Division of labor refers to the division of tasks and responsibilities among different individuals within a group. In termites, different members of the colony have specific roles, such as workers, soldiers, or reproductive individuals. The workers are responsible for gathering food, caring for the young, and maintaining the nest, while the soldiers protect the colony from predators. The reproductive individuals are responsible for producing new offspring. This division of labor allows termites to efficiently carry out the tasks necessary for the survival and success of the colony.

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A community is made up of different populations of plants and animals that live in the same area and interact with each other. It is a group of organisms that live in the same place and interact with each other and with their physical environment. These interactions can be both positive and negative, and they determine the balance of life in the ecosystem. For example, plants provide food and shelter for animals, while animals help pollinate plants and spread their seeds.

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Butterfly does not undergo incomplete metamorphosis. Incomplete metamorphosis is a type of metamorphosis in which an insect hatches from an egg into a nymph, which then goes through a series of molts until it reaches adulthood. The nymphs look similar to adults, but lack wings and reproductive structures. Butterflies, on the other hand, undergo complete metamorphosis, which involves four distinct stages: egg, larva (caterpillar), pupa (chrysalis), and adult. In the larval stage, the caterpillar looks very different from the adult butterfly, and during the pupal stage, it undergoes a dramatic transformation before emerging as an adult butterfly with wings and reproductive structures. Therefore, the correct answer is butterfly as it undergoes complete metamorphosis, unlike locust, grasshopper, and cockroach which undergo incomplete metamorphosis.

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The radius and ulna are bones of the lower arm. The lower arm is the part of the upper limb between the elbow and wrist joints. The ulna is located on the side of the arm opposite to the thumb and is slightly longer than the radius. The radius is located on the thumb side of the arm and is shorter than the ulna. The radius and ulna are parallel to each other, and they work together to allow movement of the forearm and hand. The other options listed (pectoral girdle, upper arm, and pelvic girdle) are not related to the bones of the lower arm.

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The diagram shows an illustration of a person with myopia, also known as nearsightedness, where distant objects appear blurry. This eye defect can be corrected by using a concave lens. A concave lens is thinner at the center and thicker at the edges, causing light rays entering the lens to spread out, which counteracts the focusing power of the myopic eye. When the concave lens is placed in front of the myopic eye, it corrects the angle at which light enters the eye, and the image is focused correctly on the retina, resulting in clearer vision. In contrast, a convex lens is thicker at the center and thinner at the edges, and it can be used to correct hyperopia or farsightedness. A cylindrical lens is used to correct astigmatism, which is a condition where the cornea has an irregular shape, causing blurry vision at all distances. Bifocal lenses are used to correct presbyopia, an age-related condition where the eye loses its ability to focus on nearby objects.

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The diagrams above illustrate the different types of comb found in domestic fowl, showing variation in the physical characteristics of the comb. A comb is a fleshy growth on top of the head of domestic fowl, and the different types of combs have different shapes and sizes. This variation in comb types is an example of genetic inheritance, which means that offspring inherit certain traits from their parents. The inheritance of comb type in domestic fowl is controlled by multiple genes, and the different types of combs can be used in courtship behavior by males to attract females. Therefore, the diagrams above show variation in comb types that are inherited genetically and used in courtship behavior.

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Rabbits cannot survive in an aquatic habitat because they have no gills. Gills are specialized structures found in aquatic animals that allow them to extract oxygen from water. Rabbits, like most mammals, have lungs instead of gills and therefore need air to breathe. They are adapted to live on land and do not have the adaptations necessary to survive in an aquatic environment. Without gills, rabbits would not be able to extract enough oxygen from the water to survive, and they would quickly suffocate. They are best suited to a terrestrial environment where they can breathe air and find food and shelter.

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The association between living organisms in which one organism lives on and feeds at the expense of the other organism is called parasitism. In this relationship, the parasite benefits by taking resources from the host, which may harm or even kill the host. The parasite gets all the benefits, while the host is harmed. Examples of parasites include ticks, fleas, and tapeworms.

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Autotrophic nutrition is a process whereby an organism obtains food by synthesizing simple substances using energy. In autotrophic nutrition, an organism is able to produce its own food using simple inorganic substances, such as carbon dioxide and water, and an external energy source, such as sunlight or chemical reactions. This process is called photosynthesis in plants and some bacteria, and chemosynthesis in other bacteria. Through this process, autotrophs are able to create complex organic molecules, such as carbohydrates, lipids, and proteins, that they use as a source of energy and building blocks for their cells. Autotrophic nutrition is different from heterotrophic nutrition, where an organism obtains food by consuming other living or dead organisms. Therefore, based on the given options, the correct answer is by synthesizing simple substances using energy.

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Wind is not necessary for photosynthesis. Photosynthesis is a process that occurs in plants where they use energy from sunlight to convert carbon dioxide and water into food (glucose). Sunlight provides the energy, water and carbon dioxide are the raw materials, while chlorophyll in the plant absorbs the light and performs the chemical reactions. Wind can help distribute the gases and cool the plant, but it is not necessary for the actual process of photosynthesis to occur.

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Garbage cannot be conserved as it is the waste material that has already been used and cannot be reused again for its original purpose. Garbage is generated from households, industries, and commercial establishments, and consists of waste materials such as food scraps, plastics, paper, and other materials that cannot be used again in their original form. While some garbage can be recycled, reused or repurposed, the bulk of it is sent to landfills or incinerators for disposal, and cannot be conserved as a resource. On the other hand, forests, water, and soil can be conserved by using them sustainably, managing them wisely, and protecting them from degradation or destruction.

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Two gametes are produced in the pollen grain of a flowering plant before fertilization. The pollen grain contains the male reproductive cells of the plant, which are called gametes. These gametes are produced through a process called meiosis, in which a single cell divides into two cells, each with half the number of chromosomes as the original cell. In flowering plants, each pollen grain produces two gametes, which are then released into the air and carried to the female reproductive structures, where fertilization can occur. This process is essential for the reproduction and continuation of the species.

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The diagram shows the growth of a plant in a water culture, and it is noted that after a few days, the solution turned green and the plant died. This suggests that the cause of death of the plant is related to the green color of the solution. The most likely explanation for the green color of the solution is that there was an overgrowth of algae in the water culture. Algae are simple, plant-like organisms that can grow rapidly in water with a high nutrient content, such as the solution used in the water culture. Algae can compete with plants for nutrients and sunlight, and their overgrowth can cause a reduction in the oxygen content of the water, which can be harmful to plants. Therefore, the death of the plant was likely caused by the excess supply of nutrients to the plant, which led to the overgrowth of algae in the solution. The algae then competed with the plant for nutrients and sunlight, which led to the plant's death.

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(a)

Fungi

(b) (i) Products of decomposition:

1. Carbon dioxide
2. Water
3. Organic matter
4. Nutrients

(ii) Roles of decomposers on a refuse dump:

1. Breaking down organic matter into smaller components that can be reabsorbed by the ecosystem
2. Returning nutrients to the soil, thereby supporting plant growth
3. Reducing the volume of waste in the refuse dump.

(c) Three materials found in a refuse dump which would not be affected by the action of decomposers:

1. Glass
2. Metals (such as aluminum, iron, or steel)
3. Plastic

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(a) Nutrient cycle for each process

(b)(i) What is irritability?

Irritability (sensitivity) is the ability of a living organism to detect and respond to changes (stimuli) in its internal or external environment.

(b)(ii) Type of response elicited by each action

(c) Three animals that exhibit each behaviour

(i) Territoriality: male Agama lizard; male Tilapia (fish); dog.

(ii) Seasonal migration: swallow; wildebeest; salmon.

(iii) Display: peacock; domestic fowl (cock); pigeon.

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(a) Dentition in animals

Dentition is the type, number, arrangement and pattern of the teeth in the jaws of an animal. The kind of dentition an animal has (for example the presence and development of incisors, canines, premolars and molars) is related to its mode of feeding.

(b) Generalised structure of a tooth

A tooth has two main regions: the crown, which projects above the gum, and the root, which is embedded in the socket of the jaw bone; the slightly narrowed part where they meet, at gum level, is the neck.

• Enamel - the hard, white, non-living outer covering of the crown; it is the hardest substance in the body and resists wear.
• Dentine - a bone-like living layer beneath the enamel that makes up the bulk of the tooth.
• Pulp cavity - the central space containing the pulp, which is made of blood vessels (supplying food and oxygen) and nerve fibres (sensitive to pain and temperature).
• Cement - a layer that covers the dentine of the root and, together with the periodontal fibres, fixes the tooth firmly in its socket.

(c) Three food substances plants manufacture from glucose

• Starch (for storage).
• Cellulose (for building cell walls).
• Sucrose (for transport); also fats/oils and, with nitrogen, proteins.

(d) Diagram of an experimental set-up to show that oxygen is produced during photosynthesis

Make a labelled drawing 6 - 8 cm long of the classic aquatic-plant set-up: a beaker of water containing sprigs of a water plant such as Elodea (or Hydrilla), the plant covered by an inverted glass funnel, and an inverted test tube full of water placed over the funnel stem to collect the gas. Label the water plant, the funnel, the test tube and the gas bubbles (oxygen) collecting at the top of the test tube. When placed in sunlight, bubbles of gas rise and collect in the tube; the collected gas relights a glowing splint, showing it is oxygen.

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(a) Five West African wildlife animals and the body part that makes them endangered by human activity

(b) Effects of the following factors on conservation of natural resources

(i) Poor economy of a nation

• There is insufficient funding to establish and maintain game reserves and national parks.
• Poverty pushes citizens into illegal hunting, logging and over-exploitation of resources for survival.
• Enforcement of conservation laws is weak because there is little money to pay and equip game wardens.

(ii) Poaching

• It reduces the population of wildlife and can drive some species to extinction.
• It disrupts the food chain and upsets the balance of the ecosystem.
• It reduces the genetic diversity (loss of some genes) of the affected species.

(c) Four roles played by the Government in conservation of natural resources

1. Establishing and maintaining game reserves, national parks and forest reserves.
2. Making and enforcing laws that prohibit poaching, indiscriminate felling of trees and bush burning.
3. Educating the public and creating awareness on the need to conserve natural resources.
4. Providing funds and trained personnel (game wardens) for the protection of wildlife and forests.

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(a) Four main components of blood

• Plasma
• Red blood cells (erythrocytes)
• White blood cells (leucocytes)
• Platelets (thrombocytes)

(b) Naming the component described

• (i) Forms the top layer in the test tube - plasma (it is the lightest and stays on top after spinning).
• (ii) Destroys pathogens - white blood cells.
• (iii) Is biconcave in shape - red blood cells.
• (iv) Would be relatively low in a haemophilic condition - platelets.
• (v) Is produced in the bone marrow - red blood cells.
• (vi) Is a thrombocyte - platelets.
• (vii) Is nucleated - white blood cells.

(c) Three chemical substances transported by plasma (the component in b(i))

• Digested food substances such as glucose and amino acids.
• Excretory waste such as urea (and carbon dioxide as hydrogencarbonate).
• Hormones (also dissolved mineral salts and antibodies).

(d) Four diseases associated with blood

• Anaemia
• Leukaemia
• Sickle-cell anaemia
• Haemophilia (also thrombosis)

(e) Why a disease of the blood could be dangerous

Blood circulates throughout the whole body and performs vital functions such as transporting oxygen, food, hormones and waste, defending the body against disease, and clotting to prevent excessive bleeding. A disease of the blood therefore affects the entire body at once: it can reduce the supply of oxygen and nutrients to the tissues, weaken the body's defence against infection, prevent proper clotting so that a person may bleed to death, and, because the affected blood reaches every organ, the disorder spreads quickly and can be fatal.