WAEC SSCE - Biology - 2010 (Objective)

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A typical plant cell is mainly distinguished from an animal cell by the possession of a cell wall and chloroplasts. While both plant and animal cells share many common features such as a nucleus, cytoplasm, and mitochondria, there are a few key differences. One of the most notable differences is the presence of a cell wall in plant cells. The cell wall is a rigid outer layer made of cellulose that provides support and protection to the cell. This is not found in animal cells. Another important difference is the presence of chloroplasts in plant cells. Chloroplasts are organelles that contain chlorophyll and are involved in photosynthesis. This allows plants to produce their own food using energy from sunlight, while animals must consume food to obtain energy. Animal cells do not have chloroplasts. Therefore, the presence of a cell wall and chloroplasts are the main features that distinguish a typical plant cell from an animal cell.

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The mechanism of opening and closing of stomata in plants is based on "turgidity and flaccidity." Stomata are small openings on the leaves of plants that allow for gas exchange, such as the intake of carbon dioxide and the release of oxygen and water vapor. The opening and closing of stomata is regulated by the guard cells that surround the pore. When the guard cells are filled with water, they become turgid and the stomata open. This allows for gas exchange and also allows for water to escape through transpiration. On the other hand, when the guard cells lose water, they become flaccid and the stomata close. This prevents excessive water loss from the plant during periods of drought or when the plant is under stress. Therefore, the correct answer is "turgidity and flaccidity" because the opening and closing of stomata in plants is based on the water content and pressure of the guard cells, which causes them to become turgid or flaccid and regulate the size of the stomatal pore.

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The ear pinna, also known as the outer ear or auricle, is strengthened by "cartilage." Cartilage is a type of flexible connective tissue that is found in various parts of the body, including the ears, nose, and joints. It is composed of cells called chondrocytes and an extracellular matrix made up of collagen and proteoglycans. The ear pinna is made up of a thin layer of skin that covers a framework of cartilage. This cartilage provides the pinna with its distinctive shape and structure, and allows it to maintain its position and orientation relative to the head. It also helps to protect the ear canal and the delicate structures within the ear from injury. While blood pressure, bone, and turgor pressure are all important for various physiological functions in the body, they are not directly involved in strengthening the ear pinna. Therefore, the correct answer is "cartilage."

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In a particular habitat, the role of an organism is referred to as its niche. A niche is the way in which an organism fits into and interacts with its environment, including the physical and biological factors. It describes the organism's way of life, including its feeding habits, reproductive strategies, and interactions with other species. The niche of an organism is important because it determines its place in the ecosystem and how it contributes to the functioning of the ecosystem. Different organisms can have different niches, even if they occupy the same habitat, because they may have different adaptations, behaviors, or requirements. Understanding the niche of an organism is important for understanding its ecological relationships and for making conservation and management decisions.

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The reason that correctly explains why all the children in a family of eight (8) are girls is that the sperm of the father carried only the X chromosome. In humans, the sex of an individual is determined by the sex chromosomes contributed by the parents during fertilization. Females have two X chromosomes (XX) while males have one X and one Y chromosome (XY). The father in this case must have produced sperm carrying only the X chromosome, which when fertilized with the mother's X chromosome, produced only female offspring. This is a rare occurrence, but it can happen due to random chance. The other options presented in the question are possible causes of having fewer male offspring, but they do not explain the specific scenario described in the question where all the children are girls.

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The axial skeleton is composed of the skull and vertebral column. The axial skeleton is the part of the skeleton that runs along the central axis of the body, including the skull, vertebral column, and rib cage. It forms the core of the body and provides support and protection for vital organs such as the brain, spinal cord, and heart. The skull is composed of several bones that make up the cranium and the face. The cranium is the part of the skull that surrounds and protects the brain, while the face bones protect the sensory organs such as the eyes, ears, and nose. The vertebral column is a series of bones called vertebrae that run down the back of the body. The vertebrae protect the spinal cord and provide support for the body. The vertebral column is divided into five regions, including the cervical, thoracic, lumbar, sacral, and coccygeal regions. The axial skeleton is distinct from the appendicular skeleton, which includes the bones of the limbs and girdles that attach the limbs to the axial skeleton. In summary, the axial skeleton is composed of the skull and vertebral column, which provide support and protection for vital organs and form the core of the body.

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A saprophytic relationship is one where an organism feeds on dead or decaying organic matter. Therefore, an example of a saprophytic relationship is the mushroom growing on decaying vegetation because mushrooms obtain nutrients by breaking down the organic matter of dead and decaying plants. The vulture feeding on decaying meat is an example of scavenging, the boy eating stale bread is an example of a human eating stale food, and the earthworm feeding on decaying vegetation is an example of detritivores.

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Rural-urban migration refers to the movement of people from rural areas to urban areas in search of better opportunities and improved quality of life. To prevent rural-urban migration in developing countries, it is important to address the root causes of migration. One effective approach is to improve the living conditions in rural areas by providing basic amenities such as good roads, electricity, water supply, healthcare facilities, and schools. This will help to create job opportunities and improve the standard of living in rural areas, making it less attractive for people to migrate to urban areas. Additionally, encouraging the establishment of small-scale industries in rural areas can also create employment opportunities and help to reduce rural-urban migration. Overall, the key is to ensure that there is an even distribution of facilities and opportunities in both rural and urban areas to discourage migration.

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The organ that receives reduced flow of blood during vigorous exercise is the brain. During exercise, the body needs more oxygen and nutrients to produce energy, which requires an increase in blood flow to the muscles. To meet this demand, blood vessels in the muscles dilate, and blood is redirected away from other organs, including the brain. This is known as the "fight or flight" response, and it allows the body to prioritize the delivery of oxygen and nutrients to the muscles that need it most. While the brain does require a lot of oxygen and nutrients, it is able to maintain function with a reduced flow of blood for short periods of time during vigorous exercise.

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The relationship between the retina and the brain is similar to that between the cochlea and the brain. The retina is the layer of tissue at the back of the eye that contains photoreceptor cells that detect light and send visual signals to the brain via the optic nerve. The cochlea is the part of the ear that contains hair cells that detect sound and send auditory signals to the brain via the auditory nerve. In both cases, sensory information is detected by specialized cells and transmitted to the brain for interpretation and processing. Therefore, the relationship between the retina and the brain is analogous to that between the cochlea and the brain.

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Excretion in Paramecium sp. is by diffusion because it has a large surface area to volume ratio. Paramecium is a single-celled organism that lives in aquatic environments, where it constantly takes in water and nutrients and expels waste products. Because Paramecium is small and simple, with only a few internal organs, it relies on diffusion to excrete waste products such as carbon dioxide and ammonia. Diffusion is the process by which molecules move from an area of high concentration to an area of low concentration, and it is very efficient in small organisms like Paramecium that have a high surface area to volume ratio. This means that the organism's outer surface area is relatively large compared to its overall volume, allowing for efficient exchange of gases and other small molecules through the cell membrane.

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A chromosome consists of two chromatids joined at the centromere. Chromosomes are structures within the nucleus of a cell that carry genetic information in the form of DNA. Each chromosome is made up of two identical sister chromatids, which are joined at the centromere. The chromatids contain the genetic information in the form of genes, which are the units of inheritance. During cell division, the chromatids separate and each daughter cell receives one chromatid, which becomes a new chromosome.

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The parameters of size, height, weight and color in a population of living things are examples of continuous variations. Continuous variations are traits that show a wide range of differences, and they can be measured and expressed as a range of values. These variations are influenced by both genetic and environmental factors, and they are not limited to specific categories or groups. In contrast, discontinuous variations are traits that can only be expressed in specific categories, such as blood group or presence of certain diseases, and they are generally controlled by specific genes.

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Deforestation is the act of cutting down trees and destroying forests. It has several effects on the environment. Gully erosion, extinction of plant species, and migration of wildlife are some of the negative effects of deforestation. However, an increase in rainfall is not associated with deforestation. In fact, deforestation leads to a decrease in rainfall as trees play a crucial role in the water cycle by absorbing water from the soil and releasing it into the atmosphere through a process called transpiration. Without trees, the soil becomes drier, and there is less moisture in the air, leading to less rainfall.

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The statement "always transmitted by one parent" is not true about heredity. In heredity, the traits are carried by genes, which are contained in the ovum and sperm of both parents. Traits are transmitted from both parents to their offspring. While certain traits may be more dominant or expressed more strongly in one parent, both parents contribute to the genetic makeup of their offspring. Therefore, the statement that heredity is always transmitted by one parent is incorrect.

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Sucrose - pepsin is incorrectly linked to its enzyme. Pepsin is a digestive enzyme that breaks down proteins into smaller peptides. It is produced in the stomach and works best in acidic conditions. Sucrose, on the other hand, is a disaccharide composed of glucose and fructose. It is broken down into its component monosaccharides by the enzyme sucrase, which is produced in the small intestine. Therefore, the correct enzyme linked to sucrose is sucrase, not pepsin.

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The excretory system in mammals is responsible for removing waste and excess fluids from the body. It consists of several parts, including the kidneys, ureters, bladder, and urethra. The kidneys are two bean-shaped organs located on either side of the spine. They filter waste and excess fluids from the blood and produce urine, which is then transported to the bladder through two tubes called ureters. The bladder is a muscular sac that stores urine until it is ready to be expelled from the body. When the bladder is full, the urine is expelled through a single tube called the urethra. So, the correct answer to the question is "two bladders." Mammals have only one bladder, which is a part of their excretory system.

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Fingerprints are useful in crime detection because no two people have the same fingerprint. This means that if a suspect leaves their fingerprints at the scene of a crime, investigators can compare them to a database of known fingerprints and identify the individual responsible. Fingerprint analysis is a widely used forensic tool and has been used successfully in many criminal investigations. The uniqueness of fingerprints makes them a reliable means of identifying suspects and linking them to crime scenes.

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The animal that exhibits territoriality is the lizard. Territoriality is a behavior exhibited by many animals in which an individual or group of individuals defends a specific area, or territory, from others of the same species. In lizards, this behavior is often related to the need to establish a breeding territory or to protect limited resources such as food, water, or shelter. Lizards may display a variety of behaviors to defend their territory, including aggressive displays, vocalizations, and physical combat. The other animals listed (rabbit, earthworm, toad) may also have territories or defend resources, but they are not typically known for exhibiting territorial behavior to the same extent as lizards.

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Greenhouse gases are gases in the Earth's atmosphere that trap heat and contribute to the greenhouse effect. Carbon dioxide, chlorofluorocarbons (CFCs), and methane are all examples of greenhouse gases because they absorb and re-emit infrared radiation, causing the Earth's temperature to rise. Oxygen is not a greenhouse gas because it does not contribute significantly to the greenhouse effect. Instead, it is essential for the respiration of living organisms.

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Out of the given options, fungi is the biotic component of an ecosystem. Biotic components refer to the living organisms, such as plants, animals, and microorganisms that interact with each other in an ecosystem. Fungi are a diverse group of organisms that play an essential role in many ecosystems, from decomposing dead organic matter to forming mutualistic relationships with plants. They can be found in soil, on plants, and even in the air. Therefore, fungi is a biotic component of an ecosystem.

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The percentage probability that a normal male married to a carrier woman would have a haemophilic male child is 50%. Hemophilia is a genetic disorder that is carried on the X chromosome. Since females have two X chromosomes, they can be either carriers or affected by the disorder. Males, on the other hand, have only one X chromosome and one Y chromosome, which means that if they inherit the hemophilia gene, they will have the disorder. When a carrier woman (who has one normal X chromosome and one X chromosome with the hemophilia gene) marries a normal male (who has one X and one Y chromosome), there is a 50% chance that any male offspring will inherit the hemophilia gene and develop the disorder. There is also a 50% chance that any female offspring will inherit the carrier status like their mother. Therefore, the percentage probability that a normal male married to a carrier woman would have a haemophilic male child is 50%.

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Since Mr. Andrew's blood group is A, he could have the genotype IA IA or IA IO. Similarly, since his wife's blood group is B, her genotype could be IB IB or IB IO. Their child's blood group is O, which means the child must have the genotype IO IO. Therefore, the possible genotypes of both parents are IA IO and IB IO, as they are the only combinations that can produce a child with the genotype IO IO.

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Muscles are attached to bones by tendons. Tendons are strong, fibrous cords of connective tissue that connect muscles to bones. They are made up of collagen fibers that are able to withstand the tensile forces created when muscles contract and pull on bones. When a muscle contracts, it pulls on the tendon, which in turn pulls on the bone, causing it to move. This is how muscles are able to control movement of the body. Without tendons, muscles would not be able to effectively transmit their forces to the bones, making movement difficult or impossible.

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The speed of wind is measured using an anemometer. An anemometer is a device that is used to measure the speed of the wind. It works by catching the wind in its cups and then measuring the speed at which the cups are rotating. The faster the cups rotate, the stronger the wind is blowing. Anemometers can measure wind speed in various units such as kilometers per hour, miles per hour, or meters per second.

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Transportation of water in the xylem tissue involves translocation except. Translocation refers to the movement of sugars and other organic compounds through the phloem tissue, which is responsible for the transport of nutrients and other materials in plants. The transportation of water in the xylem tissue occurs through a combination of root pressure, capillary action, and transpiration pull. Root pressure occurs when water enters the roots of plants due to osmosis and builds up, pushing water up through the xylem. Capillary action occurs when water is pulled up through narrow tubes in the xylem due to the cohesive forces between water molecules. Transpiration pull occurs when water is pulled up from the roots to the leaves due to the evaporation of water from the leaves, creating a negative pressure gradient that draws water up through the xylem.

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The organism that is not classified as an animal is "Euglena." Animals are a diverse group of multicellular organisms that belong to the kingdom Animalia. They are characterized by their ability to move, consume organic matter as a source of nutrition, and lack of cell walls. Amoeba, Paramecium, and Obelia are all classified as animals. Amoebas and Parameciums are single-celled organisms that are classified as protozoans, which are a type of animal-like protist. Obelia is a colonial animal that belongs to the phylum Cnidaria, which also includes jellyfish and coral. Euglena, on the other hand, is a unicellular organism that is classified as a protist. Although it possesses some animal-like characteristics, such as the ability to move and consume organic matter, it also possesses features that are more typical of plant-like organisms, such as the presence of chloroplasts for photosynthesis. Therefore, the correct answer is "Euglena" because it is not classified as an animal, but rather as a protist.

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Cellular respiration is a process that converts glucose and oxygen into ATP (adenosine triphosphate), which is the primary energy currency of cells. During cellular respiration, the energy is made available to organisms by breaking off a phosphate group from ATP. When ATP loses one of its phosphate groups, it becomes ADP (adenosine diphosphate), and energy is released. This energy is used by the cell for various functions like muscle contraction, active transport, and synthesis of molecules.

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The cornified layer is the outermost layer of the skin, composed of dead skin cells that lack nuclei and organelles, including mitochondria. Therefore, the correct answer is "Cells of the cornified layer." Mitochondria are tiny organelles that are often referred to as the "powerhouses" of the cell because they generate most of the cell's energy. However, as the cells of the cornified layer are dead, they do not require energy and have no use for mitochondria. Therefore, they do not have any mitochondria.

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An herbivore cannot feed on a piece of meat because it has no canines to tear up the meat. Canines are long, pointed teeth located between the incisors and premolars in mammals, which are used for grasping and tearing flesh. Herbivores, such as cows, horses, and rabbits, have teeth that are adapted for grinding and chewing plant material. Their teeth are flat and broad, with ridges for grinding and crushing tough plant fibers. They have no sharp canines for tearing flesh. Thus, an herbivore would have difficulty consuming a piece of meat because it lacks the appropriate teeth to tear it up. Conversely, carnivores, such as lions and wolves, have prominent canines and sharp teeth that are adapted for tearing and cutting flesh, making them efficient meat-eaters.

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In testing for starch in a leaf, the leaf is first boiled in water for about a minute so that the cells are killed. When a leaf is boiled in water, the high temperature causes the cells in the leaf to burst and break open. This releases the contents of the cells, including any starch that may be present. Boiling also deactivates the enzymes that break down starch, preventing them from interfering with the starch test. Once the cells are killed, iodine solution can be applied to the leaf to test for the presence of starch. The iodine will penetrate the cells and react with any starch that is present, causing it to turn blue-black in color.

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A pulse is best described as the pumping action of the heart to move blood around the body. The heart is a muscular organ that pumps blood throughout the body. As the heart beats, it creates pressure in the blood vessels, which causes the blood to flow through them. This pressure wave can be felt as a pulse in certain areas of the body, such as the wrist, neck, or groin. The pulse rate is the number of times the heart beats per minute and can be used to assess a person's heart rate and overall health. A normal resting heart rate for an adult is usually between 60 and 100 beats per minute. Therefore, a pulse is a measure of the heart's pumping action and can be felt as a pressure wave in certain areas of the body.

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Food shortage in a population can lead to intra-specific competition. When there is not enough food to go around, individuals within the same population will have to compete with each other for limited resources. This can lead to a decrease in overall fitness, as weaker individuals may not be able to obtain enough food to survive and reproduce. It may also result in changes in behavior, such as increased aggression or territoriality. Ultimately, a population that experiences prolonged food shortage may suffer from reduced growth rates, increased mortality, and decreased reproductive success.

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The correct answer is the contractile vacuole. Protozoans are unicellular organisms that live in aquatic environments. The contractile vacuole is a specialized organelle found in protozoans that helps to maintain osmotic balance by collecting and expelling excess water from the cell. The contractile vacuole works by pumping water out of the cell and into the surrounding environment, preventing the protozoan from bursting due to excessive water intake. Therefore, the contractile vacuole plays an important role in maintaining the survival of protozoans in their aquatic habitats.

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The main reason for the conservation of wildlife is to save some species from extinction. Wildlife refers to all the living organisms that exist in the natural world, including animals, plants, and microorganisms. Unfortunately, many species of wildlife are at risk of becoming extinct due to human activities such as habitat destruction, pollution, and climate change. Conservation efforts aim to protect these species and their habitats, ensuring that they can continue to survive and thrive in their natural environment. This includes efforts to create protected areas, such as national parks and wildlife reserves, where wildlife can live undisturbed by human activity. Conservation also plays an important role in maintaining ecological balance in communities. All living organisms are interconnected, and changes to one species or habitat can have far-reaching effects on others. Conserving wildlife helps to ensure that the delicate balance of ecosystems is not upset, which can have significant consequences for humans as well. While conservation does provide opportunities for recreation in national parks and other protected areas, this is not the main reason for its importance. Similarly, preventing hunters from being cruel to animals is a worthy goal, but it is not the primary reason for wildlife conservation. In summary, the main reason for the conservation of wildlife is to save some species from extinction and maintain ecological balance in communities.

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The organic compound in which the hydrogen-oxygen ratio is equal to 2:1 is carbohydrates. Carbohydrates are organic molecules that are composed of carbon, hydrogen, and oxygen atoms, with a hydrogen-oxygen ratio of 2:1, which is the same as that found in water (H2O). This means that for every carbon atom in a carbohydrate, there are two hydrogen atoms and one oxygen atom. Carbohydrates are an important source of energy for the body and are found in foods such as bread, pasta, rice, and fruits.

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The correct statement about transpiration is that it is the loss of water in the form of vapor from the surface of the leaf. Transpiration is the process by which plants lose water through small pores on the surface of their leaves called stomata. These stomata open to allow the exchange of gases such as carbon dioxide and oxygen, which are necessary for photosynthesis. However, water vapor also escapes through these pores during this process. This loss of water helps plants maintain their internal water balance and is important for nutrient uptake and growth.

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The inorganic components of bone are the mineralized components, which make up about 65-70% of the bone's weight. These components are mainly composed of calcium, phosphorus, and magnesium, with smaller amounts of other minerals such as sodium, potassium, and carbonate ions. Therefore, is correct: magnesium, phosphorus, and calcium are the inorganic components of bone. These minerals provide the bone with its hardness and strength.

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Xerophytic plants are plants that have adapted to survive in environments with little water, such as deserts. The main problem facing these plants is the lack of adequate water. Xerophytes have developed a number of adaptations to conserve water, such as having thick cuticles, reduced leaves, and extensive root systems to absorb water. However, even with these adaptations, xerophytic plants still face the challenge of obtaining enough water to survive, which is often limited in arid environments. Without adequate water, these plants cannot carry out essential processes such as photosynthesis, and will eventually die. Therefore, the lack of adequate water is the main problem facing xerophytic plants.

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The process that involves diffusion is "absorption of digested food into the villi." Diffusion is the movement of molecules or particles from an area of high concentration to an area of low concentration. This process occurs naturally and does not require energy input. In the case of absorption of digested food into the villi, nutrients such as glucose and amino acids are transported from the small intestine into the bloodstream. This process occurs through the walls of the villi, which are lined with a thin layer of epithelial cells. These cells are specialized for absorption and have microvilli on their surface that increase the surface area for nutrient absorption. As the digested food particles move from an area of high concentration (the small intestine) to an area of low concentration (the bloodstream), they diffuse across the cell membranes of the epithelial cells and into the bloodstream. This process allows the body to obtain the necessary nutrients from the food that has been consumed. While opening and closing of stomatal pores, turgidity of herbaceous plants, and absorption of water through the root hairs are all important biological processes, they do not involve diffusion. Therefore, the correct answer is "absorption of digested food into the villi."

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The probability that a man heterozygous for albino gene marries a woman who is also heterozygous for the gene and they will have an albino child is "1/4."

The man is heterozygous for the albino gene, which means he has one dominant allele for normal skin color and one recessive allele for albino skin color. The woman is also heterozygous for the same gene. Therefore, both have a 50% chance of passing on the dominant allele and a 50% chance of passing on the recessive allele to their offspring.

To determine the probability of having an albino child, we need to use a Punnett square.

      A     a
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A | AA  |  Aa |
  |-------|------|
a | Aa  |  aa |
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In the Punnett square above, we have listed all possible allele combinations that can be passed on from the parents to their offspring. The uppercase A represents the dominant allele for normal skin color, and the lowercase a represents the recessive allele for albino skin color.

From the Punnett square, we can see that there is a 25% chance (1/4) of the couple having an albino child (represented by the aa genotype), and a 75% chance (3/4) of having a child with normal skin color.

Therefore, the probability that the man and woman will have an albino child is "1/4."

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The statement that is not correct about the development of the fetus is: "The circulatory system of the fetus is directly connected to the maternal blood vessels". Explanation: The circulatory system of the fetus is not directly connected to the maternal blood vessels. Instead, the placenta, which is attached to the uterine wall, acts as an interface between the fetal and maternal blood systems. The placenta enables the exchange of nutrients, oxygen, and waste products between the fetus and the mother's blood without their blood mixing. The umbilical cord connects the fetus to the placenta and serves as a conduit for the exchange of these substances.

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In artificial selection, the goal is to breed individuals with desirable traits. In order to achieve this, individuals without the desired traits may be prevented from mating. Sterilization is one method of preventing individuals from mating. By sterilizing an individual, they are unable to produce offspring, and therefore their genes will not be passed on to the next generation. This allows only individuals with desirable traits to reproduce and pass on their genes, increasing the frequency of those traits in the population over time.

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A person with blood group O can be given blood from persons who have blood belonging to group O only. This is because individuals with blood group O do not have any antigens on the surface of their red blood cells, which means that they do not have anything that the immune system of the recipient can react against. Blood group A has A antigens, blood group B has B antigens, and blood group AB has both A and B antigens on the surface of their red blood cells. Therefore, if a person with blood group O receives blood from a person with a different blood group, the recipient's immune system may recognize the antigens on the surface of the red blood cells as foreign and mount an immune response, which can result in serious complications.

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The option that is NOT a determining factor in the distribution of organisms in a fresh water habitat is the "pH of the soil". This is because freshwater habitats like streams and ponds are not associated with soil, but rather with water. The distribution of organisms in these habitats is determined by factors such as light penetration, rainfall, and temperature, which affect the availability of resources, such as nutrients and oxygen, that are necessary for the survival and growth of different species of plants and animals.

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Fungi share the characteristic of storing carbohydrates as glycogen with animals. Glycogen is a complex carbohydrate that is stored in the liver and muscles of animals as a source of energy. Similarly, fungi store their carbohydrates in the form of glycogen in their cells. This is in contrast to plants that store their carbohydrates as starch. Although fungi and animals are different in many ways, they share some similarities in their biochemistry and cellular processes.

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An organism that operates at the cellular level of organization carries out its physiological activities by using its organelles. Cells are the basic unit of life, and each cell has organelles that perform specific functions to keep the cell alive and functioning properly. These organelles include the nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes, among others. For example, the nucleus contains the cell's genetic material and controls the cell's activities by regulating the expression of genes. Mitochondria are responsible for producing energy in the form of ATP through cellular respiration. Ribosomes are responsible for synthesizing proteins. Endoplasmic reticulum and Golgi apparatus work together to synthesize and transport proteins and lipids. Lysosomes and peroxisomes are involved in the breakdown of cellular waste and toxins. Therefore, an organism that operates at the cellular level of organization relies on its organelles to carry out its physiological activities. These organelles work together in a coordinated manner to ensure the survival and functioning of the cell.

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The enzymes renin and pepsin are produced and work in the stomach to help break down food. The best pH for the action of these enzymes is pH2. This is because the stomach secretes hydrochloric acid (HCl) which lowers the pH of the stomach to around pH2. This acidic environment helps activate both renin and pepsin, allowing them to function properly. Renin works to coagulate milk proteins in infants, while pepsin is responsible for breaking down proteins into smaller molecules that can be absorbed by the body. At a pH of 7 or higher, the stomach would become too alkaline, and the enzymes would not work as efficiently. This is because alkaline environments are not conducive to the action of acidic enzymes like renin and pepsin. So, in summary, a pH of 2 is the best for the action of renin and pepsin in the stomach because it provides the optimal acidic environment for these enzymes to function properly.

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An example of variation is "tongue rolling." Variation refers to the differences or variations that exist within a species or population. These variations can be genetic or environmental, and can affect a wide range of traits and characteristics. In the case of tongue rolling, some individuals are able to roll their tongue into a tube shape, while others are not. This is a genetic trait that is inherited from one or both parents. Some people may have the gene for tongue rolling, while others do not. This variation in the ability to roll the tongue is an example of genetic variation within a population. On the other hand, blood type, reproduction, and growth are not examples of variation. While there may be some differences in blood type, reproduction, and growth between individuals, they are not traits that exhibit significant variation within a population. Blood types, for example, are determined by a set of well-defined genetic markers and do not vary significantly within a population. Reproduction and growth are essential biological processes that occur in all individuals of a species, and while there may be some variation in the timing or manner in which these processes occur, they are not traits that exhibit significant variation within a population.