WAEC SSCE - Biology - 2007

Détails de la réponse

The effect of chlorofluorocarbon is the depletion of the ozone layer. Chlorofluorocarbons (CFCs) are chemicals that were once commonly used in refrigeration, air conditioning, and aerosol sprays. When they are released into the atmosphere, they rise up to the ozone layer and break down the ozone molecules, leading to a reduction in the thickness of the ozone layer. This can have serious consequences, as the ozone layer helps protect the Earth from harmful ultraviolet radiation from the sun. Without the ozone layer, more UV rays can reach the Earth's surface, leading to increased risks of skin cancer, cataracts, and other health problems, as well as negative effects on plant and animal life.

Détails de la réponse

The feature of the tadpole that indicates it is herbivorous is the possession of a long coiled intestine. Herbivorous animals are those that mainly feed on plants, and therefore, their digestive system is adapted to break down and extract nutrients from plant matter, which can be quite difficult to digest. The long coiled intestine in tadpoles provides a greater surface area for digestion, which enables the tadpole to extract more nutrients from plant matter. On the other hand, carnivorous tadpoles have shorter and straighter intestines because they require less digestion to extract nutrients from animal matter. Therefore, the presence of a long coiled intestine in a tadpole indicates that it is adapted to feed on plant matter and is likely herbivorous. Thus, the answer to this question is the possession of a long coiled intestine.

Détails de la réponse

Boiling the leaf in alcohol is done to decolourise it. This process is necessary because chlorophyll, the green pigment in the leaf, can interfere with the test for starch. By boiling the leaf in alcohol, the chlorophyll is extracted, leaving behind a white or pale-yellow leaf. This makes it easier to detect the presence of starch in the leaf using a test solution, such as iodine.

Détails de la réponse

Détails de la réponse

If two tall plants were crossed and some of their offspring were tall and others were short, then the possible genotypes of the parent plants are Tt and Tt. This is because tallness is a dominant trait and shortness is a recessive trait. Each parent plant would have had one allele for tallness (T) and one allele for shortness (t), making them both heterozygous for the trait. When the two parent plants are crossed, their offspring inherit one allele from each parent, giving them a 50% chance of inheriting the dominant T allele and being tall, and a 50% chance of inheriting the recessive t allele and being short. Therefore, some offspring will be homozygous dominant (TT), some will be heterozygous (Tt), and some will be homozygous recessive (tt), resulting in a 3:1 phenotypic ratio of tall to short plants.

Détails de la réponse

Détails de la réponse

The persistent presence of glucose in a person's urine is an indication of malfunctioning of the pancreas. The pancreas is responsible for producing insulin, a hormone that regulates glucose levels in the blood. When the pancreas fails to produce enough insulin or produces ineffective insulin, glucose accumulates in the bloodstream and spills over into the urine. This condition is known as diabetes mellitus and can have serious health consequences if left untreated.

Détails de la réponse

Détails de la réponse

Biuret's test is carried out on a food substance to indicate the presence of proteins. Proteins are a type of macromolecule that is essential for many biological processes, including growth, repair, and energy production. Biuret's test is a simple chemical test that is used to detect the presence of proteins in a sample. The test involves adding a small amount of the food substance to a solution of sodium hydroxide (NaOH) and copper sulfate (CuSO4). If proteins are present in the sample, they will react with the copper ions in the solution to form a violet-colored complex. The intensity of the violet color indicates the amount of protein present in the sample. Biuret's test is commonly used in food analysis to determine the protein content of various foods, such as milk, meat, and beans. It is also used in clinical chemistry to measure protein levels in blood and urine. Therefore, Biuret's test is carried out on a food substance to indicate the presence of proteins.

Détails de la réponse

A change in the environment of an organism is termed a stimulus. A stimulus is any change or signal in the environment that can be detected by an organism and can lead to a response or reaction. Stimuli can come in many forms, such as light, sound, touch, temperature, and chemicals. When a stimulus is detected, it triggers a response in the organism, which is a specific reaction or behavior to the stimulus. For example, a plant may respond to a stimulus of light by bending towards the light source, or an animal may respond to a stimulus of food by moving towards it.

Détails de la réponse

If a cross between a red-flowered plant and a white-flowered plant produced red-flowered plants, the result can be described as an example of dominance. Dominance is a concept in genetics that refers to the relationship between two versions of a gene. In this case, the gene for red flowers is dominant over the gene for white flowers. When a red-flowered plant and a white-flowered plant are crossed, their offspring inherit one copy of the red flower gene and one copy of the white flower gene. Since the red flower gene is dominant, it masks the expression of the white flower gene, resulting in the offspring having red flowers. This is an example of Mendelian inheritance, which describes how traits are passed down from parents to offspring through genes. Therefore, the result of a cross between a red-flowered plant and a white-flowered plant producing red-flowered plants is an example of dominance.

Détails de la réponse

Protozoans are single-celled organisms that belong to the kingdom Protista. Some protozoans are free-living, while others are parasitic and feed on other organisms. Out of the options given, the protozoan that feeds parasitically is Plasmodium. Plasmodium is the protozoan that causes malaria, a life-threatening disease that affects millions of people worldwide. Plasmodium feeds parasitically on red blood cells, causing them to rupture and leading to the symptoms of malaria, including fever, chills, and anemia. Paramecium is a free-living protozoan that feeds on bacteria and other small organisms through a process called phagocytosis. Chlamydomonas and Euglena are also free-living protozoans that are capable of photosynthesis and can produce their food. Therefore, the answer to this question is Plasmodium, as it is the only protozoan in the list that feeds parasitically.

Détails de la réponse

Wind speed is measured with an anemometer. An anemometer is a device that is used to measure the speed and direction of wind. It consists of several cups that are attached to a central axis. As the wind blows, it causes the cups to rotate, and the speed of rotation is proportional to the wind speed. The anemometer is connected to a display unit that measures and displays the wind speed in units such as miles per hour (mph), kilometers per hour (km/h), or meters per second (m/s). Anemometers are commonly used in weather stations to measure wind speed, which is an important parameter in weather forecasting and climate modeling. Wind speed can also have significant impacts on many aspects of human life, including aviation, transportation, agriculture, and energy production. Therefore, an anemometer is the device used to measure wind speed.

Détails de la réponse

White blood cells, also known as leukocytes, are a type of blood cell that plays a crucial role in the immune system. They help to fight off infections and foreign substances in the body. Among the given options, the only statement that is true about white blood cells is that they are large nucleated cells. They are typically larger in size than red blood cells and contain a nucleus, unlike red blood cells which lack a nucleus. White blood cells are also less numerous than red blood cells.

Détails de la réponse

The colour that is associated with a positive iodine test is blue-black. Iodine is often used as a reagent to test for the presence of starch in a substance. When iodine comes into contact with starch, it forms a complex that has a blue-black colour. Therefore, if the substance being tested contains starch, a positive iodine test will result in the blue-black colour. If there is no starch present, then the colour will remain unchanged.

Détails de la réponse

The micronutrients essential for the synthesis of chlorophyll are iron and magnesium. Chlorophyll is the green pigment found in plants that is responsible for photosynthesis, the process by which plants convert light energy into chemical energy. Iron is needed for the synthesis of the heme group, which is an essential component of the chlorophyll molecule. Magnesium, on the other hand, is a central atom in the chlorophyll molecule and is required for the formation of the chlorophyll molecule itself. Without sufficient amounts of iron and magnesium, plants cannot synthesize chlorophyll, and thus cannot carry out photosynthesis, which can lead to stunted growth and poor plant health.

Détails de la réponse

The hereditary material in a living organism is located inside the nucleus. The nucleus is a membrane-bound organelle found in eukaryotic cells that contains the genetic material of the cell in the form of DNA (deoxyribonucleic acid). DNA contains the instructions for the development, growth, and reproduction of all living organisms. The information in DNA is used to make proteins, which are the building blocks of cells and perform many important functions in the body. The nucleus also contains the nucleolus, which is responsible for the production of ribosomes, the organelles that synthesize proteins. While other organelles, such as lysosomes and cytoplasm, are important for various cellular functions, they do not contain the hereditary material of the cell.

Détails de la réponse

Insulin is produced by the pancreas. The pancreas is a glandular organ located in the abdomen, behind the stomach. It has both exocrine and endocrine functions. The exocrine function of the pancreas is to secrete digestive enzymes into the small intestine to aid in the digestion of food. The endocrine function of the pancreas is to secrete hormones into the bloodstream that regulate blood sugar levels. Insulin is one of the hormones produced by the endocrine cells in the pancreas called beta cells. It plays a crucial role in regulating blood sugar levels by promoting the uptake of glucose from the bloodstream into the body's cells. Insulin helps to lower the amount of glucose in the bloodstream by signaling the liver, muscles, and fat cells to take up glucose from the blood and store it for later use as energy. If the body does not produce enough insulin or cannot use it effectively, this can result in high blood sugar levels, a condition known as diabetes.

Détails de la réponse

When a plant cell is put in a hypotonic solution, it means that the solution outside the cell has a lower concentration of solutes than inside the cell. This creates a concentration gradient, causing water to move from the solution into the cell to equalize the concentration. As a result, the cell becomes swollen and firm due to the excess water it has gained. This process is called osmosis and the condition of the cell when it becomes swollen and firm is called turgid. Therefore, the correct answer is: "Water moves into the cell and the cell becomes turgid".

Détails de la réponse

The malpighian body of the mammalian kidney is made up of the glomerulus and Bowman's capsule. The glomerulus is a tiny network of blood vessels that filters waste products and excess water from the blood, while Bowman's capsule is a cup-shaped structure that surrounds the glomerulus and collects the filtered fluid, which is then further processed by the nephron to produce urine. Together, the glomerulus and Bowman's capsule form the first part of the nephron, the functional unit of the kidney, which is responsible for filtering and processing the blood to produce urine. The cortex and medulla are regions of the kidney that contain many nephrons, while the pelvis and pyramid are larger structures that help transport urine out of the kidney.

Détails de la réponse

Endangered species are organisms that are at risk of becoming extinct in the near future. This can happen for a variety of reasons, including habitat destruction, pollution, climate change, and overexploitation by humans. When a species becomes endangered, it means that there are very few individuals left in the wild, and their populations are declining rapidly. In order to prevent endangered species from going extinct, they need to be protected. This means that humans need to take measures to reduce the threats that are causing the species to decline. Protection can take many forms, including habitat conservation, legislation to regulate hunting and poaching, captive breeding programs, and public education campaigns to raise awareness about the importance of biodiversity and the need to protect endangered species. Therefore, the answer to this question is protected, as endangered species need to be protected in order to prevent them from becoming extinct.

Détails de la réponse

Sucrase does not belong to proteases. Proteases are enzymes that break down proteins into smaller peptides or amino acids. Examples of proteases include pepsin, trypsin, and erepsin. On the other hand, sucrase is an enzyme that breaks down sucrose into glucose and fructose, and it does not have a role in protein digestion. Therefore, sucrase is not a protease.

Détails de la réponse

Among the given options, "Conjugation in Spirogyra" is a form of sexual reproduction. Conjugation is a process where two haploid individuals (gametes) of Spirogyra, a filamentous green algae, come together and fuse their cytoplasmic contents, followed by the fusion of their nuclei to form a zygote. The zygote then undergoes meiosis to form haploid spores which germinate to form new filaments. On the other hand, the other options are forms of asexual reproduction. Budding in yeast is a process where a new individual grows out of the parent cell. Binary fission in Amoeba is a process where the parent cell divides into two identical daughter cells. Rhizome production in ginger is a vegetative reproduction where a new plant is formed from an underground stem of the parent plant without the involvement of gametes.

Détails de la réponse

Détails de la réponse

Yeast is added to the dough during the preparation of bread because it produces carbon dioxide. Yeast is a type of fungus that feeds on sugars and produces carbon dioxide gas as a byproduct. When added to bread dough, the yeast feeds on the sugars in the dough and produces carbon dioxide gas, which gets trapped in the dough and causes it to rise. This process is called fermentation, and it is what gives bread its light, airy texture. The carbon dioxide gas also helps to make the bread more flavorful by creating small pockets in the dough where flavor compounds can accumulate.

Détails de la réponse

Antibiotics are medications that are used to treat bacterial infections. However, not all infections are caused by bacteria, and some are caused by viruses or other types of microorganisms that antibiotics cannot treat. Out of the options given, Measles is caused by a virus and antibiotics are not effective against viral infections. Therefore, Measles would not respond to antibiotic treatment. Gonorrhoea, Diarrhoea, and Tuberculosis are bacterial infections that can be treated with antibiotics. It is important to note that the appropriate antibiotic needs to be selected for the specific bacterial strain causing the infection, and the course of treatment needs to be completed as directed by the healthcare provider to ensure effective treatment.

Détails de la réponse

The mode of nutrition common to green plants is autotrophic. Autotrophic nutrition is a mode of nutrition in which organisms synthesize their own food using inorganic substances, such as carbon dioxide and water, and energy from sunlight, through the process of photosynthesis. Green plants have chlorophyll in their leaves, which captures the energy from the sun and uses it to convert carbon dioxide and water into glucose and oxygen. This process not only provides energy for the plant but also produces oxygen, which is necessary for the survival of all other living organisms on Earth. Therefore, the mode of nutrition common to green plants is autotrophic.

Détails de la réponse

The bacteria that live in the root nodules of leguminous plants is Rhizobium. Rhizobium forms a symbiotic relationship with leguminous plants such as beans, peas, and clover. The bacteria invade the root hairs of the plant and form nodules, where they convert nitrogen gas from the atmosphere into a form that can be used by the plant. In return, the plant provides the bacteria with a source of energy in the form of carbohydrates. This mutually beneficial relationship is essential for the growth and survival of both the bacteria and the plant.

Détails de la réponse

The vector of the sleeping sickness disease parasite is the tse-tse fly. Tse-tse flies are blood-sucking insects that are found in sub-Saharan Africa. They are the sole vectors of the Trypanosoma parasite, which causes sleeping sickness in humans and animals. When infected tse-tse flies bite a person or an animal, they transmit the parasite to the host's bloodstream, causing sleeping sickness. Therefore, controlling the population of tse-tse flies is essential to prevent the spread of sleeping sickness.

Détails de la réponse

Enzymes can be inactivated by certain chemical substances in the body called inhibitors. Enzymes are biological catalysts that help to speed up chemical reactions in the body. They do this by lowering the activation energy required for the reaction to occur. However, enzymes can be inhibited by certain chemical substances that can bind to them and prevent them from functioning properly. These substances are called inhibitors. Inhibitors can be either competitive or non-competitive. Competitive inhibitors bind to the active site of the enzyme and prevent the substrate from binding. Non-competitive inhibitors bind to other parts of the enzyme and change its shape, making it unable to bind to the substrate. Inhibitors can have important therapeutic applications. For example, drugs that inhibit certain enzymes can be used to treat diseases such as cancer and viral infections. Therefore, enzymes can be inactivated by certain chemical substances in the body called inhibitors.

Détails de la réponse

The sun emits ultraviolet (UV) radiation that can damage the DNA in our cells. Exposure to excessive UV radiation can cause sunburn, premature aging of the skin, and increase the risk of developing skin cancer. Mammals have developed different mechanisms to protect their body cells against the harmful effects of UV radiation. One of the most important mechanisms is the production of melanin, a pigment that gives color to the skin, hair, and eyes. Melanin absorbs UV radiation and converts it into heat, which is then dissipated from the body. This process helps to prevent the UV radiation from penetrating the skin and damaging the DNA in our cells. Keratin, a fibrous protein, also provides some protection against UV radiation. It forms a protective barrier on the surface of the skin, which helps to prevent UV radiation from penetrating deeper into the skin. Sebum, an oily substance produced by the sebaceous glands in the skin, can also help to protect against UV radiation. Sebum forms a barrier on the skin's surface, which helps to prevent water loss and protect against UV radiation. Scales, on the other hand, are structures found on the skin of reptiles and fish. They provide protection against UV radiation, physical damage, and dehydration, but mammals do not have scales. In summary, the protection of body cells against UV radiation in mammals is mainly brought about by the production of melanin, which absorbs and converts UV radiation into heat, and by the presence of keratin and sebum that form protective barriers on the skin's surface.

Détails de la réponse

The transfer of pollen grains from the male part of a flower, called the anther, to the female part of the same flower, called the stigma, is known as self-pollination. This process is also sometimes referred to as self-fertilization. During self-pollination, the pollen grains land on the stigma and begin to germinate, growing a tube down through the style to reach the ovary. This tube delivers the male gametes, contained within the pollen grains, to the female gametes in the ovules, resulting in fertilization and the production of seeds. Self-pollination is common in plants that have both male and female reproductive organs within the same flower. It is a mechanism that ensures that the plant can reproduce even if there are no other plants nearby for cross-pollination. Therefore, the transfer of ripe pollen grains from the anther to the stigma of the same flower is termed self-pollination.

Détails de la réponse

The term "community" refers to different groups of plants and animals living in the same area and interacting with each other. In ecological terms, it describes the collection of living organisms that coexist and interact with each other in a particular habitat or ecosystem. These interactions include competition, predation, and mutualism, and they play a crucial role in shaping the structure and function of the community. The community also interacts with physical factors such as water, air, and soil in the environment, forming a complex web of relationships that make up the ecosystem.

Détails de la réponse

The site for production of ATP in a cell is mitochondrion. Mitochondria are the powerhouse of the cell where the process of cellular respiration occurs. Cellular respiration is a metabolic process that converts nutrients (glucose) into adenosine triphosphate (ATP), which is used as a source of energy for various cellular functions. The majority of ATP is produced during the electron transport chain, which occurs in the inner membrane of the mitochondria.

Détails de la réponse

Détails de la réponse

Détails de la réponse

Body weight is the form of variation that will give a normal distribution. A normal distribution, also known as a Gaussian distribution, is a type of probability distribution that follows a bell-shaped curve, where the majority of the values tend to cluster around the mean or average value. Body weight is a continuous variable, and the distribution of body weight in a large population tends to follow a normal distribution due to the combination of genetic and environmental factors influencing weight. On the other hand, blood groups, tongue rolling, and fingerprints are discrete variables, and their distribution does not follow a normal distribution.

Détails de la réponse

The fine adjustment of the light microscope is used to focus the object under high power. The fine adjustment knob moves the objective lens slightly to bring the object into sharp focus when using high magnification. This is because at high magnification, the depth of field is very shallow, meaning that only a small portion of the object will be in focus at any given time. The fine adjustment knob allows for small, precise movements of the objective lens to bring the object into sharp focus, making it easier to see and study the fine details of the specimen. It is important to use the fine adjustment knob carefully to avoid damaging the microscope or the specimen.

Détails de la réponse

The dominant stage in the life cycle of a fern is the sporophyte. This is because ferns, like other vascular plants, exhibit an alternation of generations, which involves the alternation between two distinct multicellular phases, the haploid gametophyte and the diploid sporophyte. In ferns, the sporophyte generation is the dominant phase and the one that is more visible and long-lived. The sporophyte produces the spores through meiosis, which then germinate to form the gametophyte. The gametophyte produces gametes, which then fuse during fertilization to form the sporophyte. Therefore, the sporophyte is the dominant stage in the fern life cycle.

Détails de la réponse

Détails de la réponse

A termite with a relatively large head and powerful jaws is likely to be a soldier. Soldiers in termite colonies have evolved to defend the colony from predators and other threats. Their large head and jaws are adapted for defense and can be used to attack enemies. Soldiers do not have reproductive functions and their primary role is defense.

Détails de la réponse

The endocrine system is responsible for producing and secreting hormones that regulate various bodily functions. The pituitary gland is often referred to as the "master gland" because it controls the activity of other endocrine glands in the body, and is also closely associated with the nervous system. The pituitary gland is located at the base of the brain and consists of two lobes - the anterior lobe and the posterior lobe. The anterior lobe produces and releases several hormones that regulate the activity of other endocrine glands, including the thyroid gland, adrenal glands, and gonads. The hormones secreted by the pituitary gland also play a role in growth and development, metabolism, and reproductive functions. In addition to its endocrine functions, the pituitary gland is also closely connected to the nervous system through the hypothalamus. The hypothalamus is a region of the brain that controls various bodily functions, including hunger, thirst, and body temperature, and it also plays a role in regulating the pituitary gland's hormone secretion. Therefore, the pituitary gland is the endocrine gland which co-ordinates the action of other glands and is also associated with the nervous system.

Détails de la réponse

Détails de la réponse

Détails de la réponse

The theory of survival of the fittest was propounded by Charles Darwin. In his book "On the Origin of Species," he described the process of natural selection as the mechanism behind the evolution of species. The theory states that individuals in a population with advantageous traits are more likely to survive and pass on those traits to their offspring, while individuals with less favorable traits are less likely to survive and reproduce. Over time, this leads to the gradual evolution of species as the advantageous traits become more prevalent in the population.

Détails de la réponse

The major pollutant around airport residential areas is noise. Airplanes taking off and landing produce a lot of noise, which can have negative effects on the health and well-being of people living nearby. Prolonged exposure to high levels of noise pollution can lead to stress, sleep disturbances, hearing damage, and other health problems. While airplanes do produce other forms of pollution such as soot and dust, noise pollution is typically the most significant concern for people living near airports. While oil spillage can also be a concern at airports, it is less common and typically affects a smaller area than noise pollution.

Détails de la réponse

Détails de la réponse

A population which exceeds its carrying capacity and then collapses is represented graphically as an S-shape curve. The carrying capacity is the maximum population size that can be sustained by the available resources in a given environment. When the population size surpasses the carrying capacity, resources become scarce and the population growth rate slows down. Eventually, the population reaches a point where it can no longer be sustained by the available resources, leading to a decline or collapse in population size. This pattern is shown in an S-shaped curve, where the population growth rate starts high, levels off as it approaches the carrying capacity, and then declines sharply after surpassing it.

Détails de la réponse

Détails de la réponse

The neurone that transmits impulses directly from sensory cells is called an "afferent neurone". Afferent neurones, also known as sensory neurones, carry sensory information from sensory receptors (such as in the skin, eyes, ears, etc.) towards the central nervous system (brain and spinal cord). These neurones play an important role in the process of sensation, as they help to detect stimuli and send signals to the brain, which then interprets and responds to the information received.

Détails de la réponse

Détails de la réponse

The smallest branches on the cell body of a neuron are called dendrites. Dendrites are thin, branched extensions that receive incoming signals from other neurons or sensory receptors. They act like tiny antennas that pick up chemical signals, called neurotransmitters, that are released by neighboring neurons. These signals are then transmitted to the cell body of the neuron, where they are processed and integrated with other signals. The more dendrites a neuron has, the more input it can receive and process. In contrast to dendrites, dendrons are not a common term used in neuroscience, while ganglia are clusters of nerve cell bodies located outside of the brain and spinal cord, and Schwann cells are specialized cells that wrap around and insulate axons.

Détails de la réponse

Organisms that interbreed to produce fertile offspring belong to the same species. A species is a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. When organisms belonging to the same species mate, they produce offspring that are also members of that same species and are able to reproduce. In contrast, organisms belonging to different species are unable to interbreed or produce fertile offspring. Therefore, the ability to interbreed and produce fertile offspring is a key characteristic used to define a species.

Détails de la réponse

Détails de la réponse

Détails de la réponse

Détails de la réponse

The statement "The cell body is always found at the end of the neurone" is not correct. Explanation: A nerve cell, also known as a neuron, consists of a cell body, dendrites, and an axon. The dendrites of a neuron receive signals from other neurons or sensory receptors and transmit those signals to the cell body. The cell body processes and integrates these signals and generates an electrical impulse that travels down the axon. The axon relays this impulse to other neurons, muscles, or glands. Therefore, the axon is responsible for transmitting impulses away from the cell body, not towards it.

Détails de la réponse

Fire is not a conservable natural resource because it is not a material substance that can be used repeatedly. While fire can be created and controlled for specific purposes, it cannot be stored or conserved for future use in the same way as minerals, soil, and water. In fact, the uncontrolled or accidental use of fire can lead to the destruction of other natural resources, such as forests and wildlife habitats, making it even more important to manage it carefully.

Détails de la réponse

The significance of adding dilute hydrochloric acid to the original sugar solution in a test for non-reducing sugars like sucrose is to hydrolyze the non-reducing sugar. Non-reducing sugars like sucrose cannot be detected by simple sugar tests because they do not have free aldehyde or ketone groups. However, they can be hydrolyzed into their component reducing sugars by heating them in the presence of an acid like dilute hydrochloric acid. This hydrolysis reaction breaks the glycosidic bond between the two monosaccharide units in the non-reducing sugar, producing two reducing sugars (glucose and fructose in the case of sucrose) that can be detected by simple sugar tests. Therefore, adding dilute hydrochloric acid to the original sugar solution is an essential step in the test for non-reducing sugars to convert the non-reducing sugars into reducing sugars for detection.

Détails de la réponse

Valves are flap-like structures that prevent the backward flow of blood in a vessel. Capillaries and arterioles do not have valves. Arteries carry oxygen-rich blood away from the heart and do not need valves to prevent backflow because the blood is under high pressure. Veins, on the other hand, carry oxygen-poor blood back to the heart and are under low pressure. To prevent the backflow of blood, veins have valves that keep the blood flowing in the right direction towards the heart. Therefore, the blood vessels that have valves are veins.

Détails de la réponse

None

Détails de la réponse

None

Détails de la réponse

None

Détails de la réponse

None

Détails de la réponse

None

Détails de la réponse

None