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L_0626 | pathogens | T_3251 | Living things that cause human diseases include bacteria, fungi, and protozoa. Most infectious diseases caused by these organisms can be cured with medicines. For example, medicines called antibiotics can cure most diseases caused by bacteria. Bacteria are one-celled organisms without a nucleus. Although most bacteria are harmless, some cause diseases. Worldwide, the most common disease caused by bacteria is tuberculosis (TB). TB is a serious disease of the lungs. Another common disease caused by bacteria is strep throat. You may have had strep throat yourself. Bacteria that cause strep throat are shown below ( Figure 1.1). Some types of pneumonia and many cases of illnesses from food are also caused by bacteria. The structures that look like strings of beads are bacteria. They belong to the genus Streptococcus. Bacteria of this genus cause diseases such as strep throat and pneumonia. They are shown here 900 times bigger than their actual size. Fungi are simple eukaryotic organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athletes foot. Both are skin diseases that are not usually serious. A ringworm infection is pictured below ( Figure 1.2). A more serious fungus disease is histoplasmosis. It is a lung infection. Though fungal infections can be annoying, they are rarely as serious or deadly as bacterial or viral infections. Ringworm isnt a worm at all. Its a disease caused by a fungus. The fungus causes a ring-shaped rash on the skin, like the one shown here. Protozoa are one-celled organisms with a nucleus, making them eukaryotic organisms. They cause diseases such as malaria. Malaria is a serious disease that is common in warm climates. The protozoa infect people when they are bit by a mosquito. More than a million people die of malaria each year. Other protozoa cause diarrhea. An example is Giardia lamblia ( Figure 1.3). Viruses are nonliving collections of protein and DNA that must reproduce inside of living cells. Viruses cause many common diseases. For example, viruses cause colds and the flu. Cold sores are caused by the virus Herpes simplex This picture shows a one-celled organism called Giardia lamblia. It is a protozoan that causes diarrhea. ( Figure 1.4). Antibiotics do not affect viruses, because antibiotics only kill bacteria. But medicines called antiviral drugs can treat many diseases caused by viruses. Keep in mind that viruses are nonliving, so can they be killed? | text | null |
L_0626 | pathogens | T_3251 | Living things that cause human diseases include bacteria, fungi, and protozoa. Most infectious diseases caused by these organisms can be cured with medicines. For example, medicines called antibiotics can cure most diseases caused by bacteria. Bacteria are one-celled organisms without a nucleus. Although most bacteria are harmless, some cause diseases. Worldwide, the most common disease caused by bacteria is tuberculosis (TB). TB is a serious disease of the lungs. Another common disease caused by bacteria is strep throat. You may have had strep throat yourself. Bacteria that cause strep throat are shown below ( Figure 1.1). Some types of pneumonia and many cases of illnesses from food are also caused by bacteria. The structures that look like strings of beads are bacteria. They belong to the genus Streptococcus. Bacteria of this genus cause diseases such as strep throat and pneumonia. They are shown here 900 times bigger than their actual size. Fungi are simple eukaryotic organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athletes foot. Both are skin diseases that are not usually serious. A ringworm infection is pictured below ( Figure 1.2). A more serious fungus disease is histoplasmosis. It is a lung infection. Though fungal infections can be annoying, they are rarely as serious or deadly as bacterial or viral infections. Ringworm isnt a worm at all. Its a disease caused by a fungus. The fungus causes a ring-shaped rash on the skin, like the one shown here. Protozoa are one-celled organisms with a nucleus, making them eukaryotic organisms. They cause diseases such as malaria. Malaria is a serious disease that is common in warm climates. The protozoa infect people when they are bit by a mosquito. More than a million people die of malaria each year. Other protozoa cause diarrhea. An example is Giardia lamblia ( Figure 1.3). Viruses are nonliving collections of protein and DNA that must reproduce inside of living cells. Viruses cause many common diseases. For example, viruses cause colds and the flu. Cold sores are caused by the virus Herpes simplex This picture shows a one-celled organism called Giardia lamblia. It is a protozoan that causes diarrhea. ( Figure 1.4). Antibiotics do not affect viruses, because antibiotics only kill bacteria. But medicines called antiviral drugs can treat many diseases caused by viruses. Keep in mind that viruses are nonliving, so can they be killed? | text | null |
L_0626 | pathogens | T_3251 | Living things that cause human diseases include bacteria, fungi, and protozoa. Most infectious diseases caused by these organisms can be cured with medicines. For example, medicines called antibiotics can cure most diseases caused by bacteria. Bacteria are one-celled organisms without a nucleus. Although most bacteria are harmless, some cause diseases. Worldwide, the most common disease caused by bacteria is tuberculosis (TB). TB is a serious disease of the lungs. Another common disease caused by bacteria is strep throat. You may have had strep throat yourself. Bacteria that cause strep throat are shown below ( Figure 1.1). Some types of pneumonia and many cases of illnesses from food are also caused by bacteria. The structures that look like strings of beads are bacteria. They belong to the genus Streptococcus. Bacteria of this genus cause diseases such as strep throat and pneumonia. They are shown here 900 times bigger than their actual size. Fungi are simple eukaryotic organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athletes foot. Both are skin diseases that are not usually serious. A ringworm infection is pictured below ( Figure 1.2). A more serious fungus disease is histoplasmosis. It is a lung infection. Though fungal infections can be annoying, they are rarely as serious or deadly as bacterial or viral infections. Ringworm isnt a worm at all. Its a disease caused by a fungus. The fungus causes a ring-shaped rash on the skin, like the one shown here. Protozoa are one-celled organisms with a nucleus, making them eukaryotic organisms. They cause diseases such as malaria. Malaria is a serious disease that is common in warm climates. The protozoa infect people when they are bit by a mosquito. More than a million people die of malaria each year. Other protozoa cause diarrhea. An example is Giardia lamblia ( Figure 1.3). Viruses are nonliving collections of protein and DNA that must reproduce inside of living cells. Viruses cause many common diseases. For example, viruses cause colds and the flu. Cold sores are caused by the virus Herpes simplex This picture shows a one-celled organism called Giardia lamblia. It is a protozoan that causes diarrhea. ( Figure 1.4). Antibiotics do not affect viruses, because antibiotics only kill bacteria. But medicines called antiviral drugs can treat many diseases caused by viruses. Keep in mind that viruses are nonliving, so can they be killed? | text | null |
L_0626 | pathogens | T_3251 | Living things that cause human diseases include bacteria, fungi, and protozoa. Most infectious diseases caused by these organisms can be cured with medicines. For example, medicines called antibiotics can cure most diseases caused by bacteria. Bacteria are one-celled organisms without a nucleus. Although most bacteria are harmless, some cause diseases. Worldwide, the most common disease caused by bacteria is tuberculosis (TB). TB is a serious disease of the lungs. Another common disease caused by bacteria is strep throat. You may have had strep throat yourself. Bacteria that cause strep throat are shown below ( Figure 1.1). Some types of pneumonia and many cases of illnesses from food are also caused by bacteria. The structures that look like strings of beads are bacteria. They belong to the genus Streptococcus. Bacteria of this genus cause diseases such as strep throat and pneumonia. They are shown here 900 times bigger than their actual size. Fungi are simple eukaryotic organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athletes foot. Both are skin diseases that are not usually serious. A ringworm infection is pictured below ( Figure 1.2). A more serious fungus disease is histoplasmosis. It is a lung infection. Though fungal infections can be annoying, they are rarely as serious or deadly as bacterial or viral infections. Ringworm isnt a worm at all. Its a disease caused by a fungus. The fungus causes a ring-shaped rash on the skin, like the one shown here. Protozoa are one-celled organisms with a nucleus, making them eukaryotic organisms. They cause diseases such as malaria. Malaria is a serious disease that is common in warm climates. The protozoa infect people when they are bit by a mosquito. More than a million people die of malaria each year. Other protozoa cause diarrhea. An example is Giardia lamblia ( Figure 1.3). Viruses are nonliving collections of protein and DNA that must reproduce inside of living cells. Viruses cause many common diseases. For example, viruses cause colds and the flu. Cold sores are caused by the virus Herpes simplex This picture shows a one-celled organism called Giardia lamblia. It is a protozoan that causes diarrhea. ( Figure 1.4). Antibiotics do not affect viruses, because antibiotics only kill bacteria. But medicines called antiviral drugs can treat many diseases caused by viruses. Keep in mind that viruses are nonliving, so can they be killed? | text | null |
L_0626 | pathogens | T_3252 | Different pathogens spread in different ways. Some pathogens spread through food. They cause food borne illnesses, which are discussed in a previous concept. Some pathogens spread through water. Giardia lamblia is one example. Water can be boiled to kill Giardia and most other pathogens. Several pathogens spread through sexual contact. HIV is one example, which is discussed in the next concept. Other pathogens that spread through sexual contact are discussed in a separate concept. Many pathogens that cause respiratory diseases spread by droplets in the air. Droplets are released when a person sneezes or coughs. Thousands of tiny droplets are released when a person sneezes ( Figure 1.5). Each droplet can contain thousands of pathogens. Viruses that cause colds and the flu can spread in this way. You may get sick if you breathe in the pathogens. As this picture shows, thousands of tiny droplets are released into the air when a person sneezes. Each droplet may carry thousands of pathogens. You cant normally see the droplets from a sneeze because they are so small. However, you can breathe them in, along with any pathogens they carry. This is how many diseases of the respiratory system are spread. | text | null |
L_0626 | pathogens | T_3253 | Other pathogens spread when they get on objects or surfaces. A fungus may spread in this way. For example, you can pick up the fungus that causes athletes foot by wearing shoes that an infected person has worn. You can also pick up this fungus from the floor of a public shower or other damp areas. After acne, athletes foot is the most common skin disease in the United States. Therefore, the chance of coming in contact with the fungus in one of these ways is fairly high. Bacteria that cause the skin disease impetigo, which causes blisters, can spread when people share towels or clothes. The bacteria can also spread through direct skin contact in sports like wrestling. | text | null |
L_0626 | pathogens | T_3254 | Still other pathogens are spread by vectors. A vector is an organism that carries pathogens from one person or animal to another. Most vectors are insects, such as ticks and mosquitoes. These insects tend to transfer protozoan or viral parasites. When an insect bites an infected person or animal, it picks up the pathogen. Then the pathogen travels to the next person or animal it bites. Ticks carry the bacteria that cause Lyme disease. Mosquitoes ( Figure serious symptoms may develop. Other diseases spread by mosquitoes include Dengue Fever and Yellow Fever. The first case of West Nile virus in North America occurred in 1999. Within just a few years, the virus had spread throughout most of the United States. Birds as well as humans can be infected with the virus. Birds often fly long distances. This is one reason why West Nile virus spread so quickly. | text | null |
L_0627 | pedigree analysis | T_3255 | A pedigree is a chart that shows the inheritance of a trait over several generations. A pedigree is commonly created for families, and it outlines the inheritance patterns of genetic disorders and traits. A pedigree can help predict the probability that offspring will inherit a genetic disorder. Pictured below is a pedigree displaying recessive inheritance of a disorder through three generations ( Figure 1.1). From studying a pedigree, scientists can determine the following: If the trait is sex-linked (on the X or Y chromosome) or autosomal (on a chromosome that does not determine sex). If the trait is inherited in a dominant or recessive fashion. Sometimes pedigrees can also help determine whether individuals with the trait are heterozygous (two different alleles) or homozygous (two of the same allele). Some points to keep in mind when analyzing a pedigree are: 1. With autosomal recessive inheritance, all affected individuals will be homozygous recessive. 2. With dominant inheritance, all affected individuals will have at least one dominant allele. They will be either homozygous dominant or heterozygous. 3. With sex-linked inheritance, more males (XY) than females (XX) usually have the trait. Sex-linked inheritance is usually recessive. | text | null |
L_0628 | peripheral nervous system | T_3256 | There are other nerves in your body that are not found in the brain or spinal cord. The peripheral nervous system (PNS) ( Figure 1.1) contains all the nerves in the body that are found outside of the central nervous system. They include nerves of the hands, arms, feet, legs, and trunk. They also include nerves of the scalp, neck, and face. Nerves that send and receive messages to the internal organs are also part of the peripheral nervous system. The peripheral nervous system is divided into two parts, the sensory division and the motor division. How these divisions of the peripheral nervous system are related to the rest of the nervous system is shown below ( Figure 1.2). Refer to the figure as you read more about the peripheral nervous system in the text that follows. | text | null |
L_0628 | peripheral nervous system | T_3257 | The sensory division carries messages from sense organs and internal organs to the central nervous system. Human beings have several senses. They include sight, hearing, balance, touch, taste, and smell. We have special sense organs for each of these senses. What is the sense organ for sight? For hearing? Sensory neurons in each sense organ receive stimuli, or messages from the environment that cause a response in the body. For example, sensory neurons in the eyes send messages to the brain about light. Sensory neurons in the skin send messages to the brain about touch. Our sense organs recognize sensations, but they dont tell us what we are sensing. For example, when you breathe in chemicals given off by baking cookies, your nose does not tell you that you are smelling cookies. Thats your brains job. The sense organs send messages about sights, smells, and other stimuli to the brain ( Figure 1.3). The brain then reads the messages and tells you what they mean. A certain area of the brain receives and interprets information from each sense organ. For example, information from the nose is received and interpreted by the temporal lobe of the cerebrum. Which senses would be stimulated by these raspberries? | text | null |
L_0628 | peripheral nervous system | T_3257 | The sensory division carries messages from sense organs and internal organs to the central nervous system. Human beings have several senses. They include sight, hearing, balance, touch, taste, and smell. We have special sense organs for each of these senses. What is the sense organ for sight? For hearing? Sensory neurons in each sense organ receive stimuli, or messages from the environment that cause a response in the body. For example, sensory neurons in the eyes send messages to the brain about light. Sensory neurons in the skin send messages to the brain about touch. Our sense organs recognize sensations, but they dont tell us what we are sensing. For example, when you breathe in chemicals given off by baking cookies, your nose does not tell you that you are smelling cookies. Thats your brains job. The sense organs send messages about sights, smells, and other stimuli to the brain ( Figure 1.3). The brain then reads the messages and tells you what they mean. A certain area of the brain receives and interprets information from each sense organ. For example, information from the nose is received and interpreted by the temporal lobe of the cerebrum. Which senses would be stimulated by these raspberries? | text | null |
L_0628 | peripheral nervous system | T_3258 | The motor division of the peripheral system carries messages from the central nervous system to internal organs and muscles. The motor division is also divided into two parts ( Figure 1.2), the somatic nervous system and the autonomic nervous system. The somatic nervous system carries messages that control body movements. It is responsible for activities that are under your control, such as waving your hand or kicking a ball. The girl pictured below ( Figure 1.4) is using her somatic nervous system to control the muscles needed to play the violin. Her brain sends messages to motor neurons that move her hands so she can play. Without the messages from her brain, she would not be able to move her hands and play the violin. The autonomic nervous system carries nerve impulses to internal organs. It controls activities that are not under your control, such as sweating and digesting food. The autonomic nervous system has two parts: 1. The sympathetic division controls internal organs and glands during emergencies. It prepares the body for fight or flight ( Figure 1.5). For example, it increases the heart rate and the flow of blood to the legs, so you can run away from danger. 2. The parasympathetic division controls internal organs and glands during the rest of the time. It controls processes like digestion, heartbeat, and breathing when there is not an emergency. Have you ever become frightened and felt your heart start pounding? How does this happen? The answer is your autonomic nervous system. The sympathetic division prepared you to deal with a possible emergency by increasing | text | null |
L_0628 | peripheral nervous system | T_3258 | The motor division of the peripheral system carries messages from the central nervous system to internal organs and muscles. The motor division is also divided into two parts ( Figure 1.2), the somatic nervous system and the autonomic nervous system. The somatic nervous system carries messages that control body movements. It is responsible for activities that are under your control, such as waving your hand or kicking a ball. The girl pictured below ( Figure 1.4) is using her somatic nervous system to control the muscles needed to play the violin. Her brain sends messages to motor neurons that move her hands so she can play. Without the messages from her brain, she would not be able to move her hands and play the violin. The autonomic nervous system carries nerve impulses to internal organs. It controls activities that are not under your control, such as sweating and digesting food. The autonomic nervous system has two parts: 1. The sympathetic division controls internal organs and glands during emergencies. It prepares the body for fight or flight ( Figure 1.5). For example, it increases the heart rate and the flow of blood to the legs, so you can run away from danger. 2. The parasympathetic division controls internal organs and glands during the rest of the time. It controls processes like digestion, heartbeat, and breathing when there is not an emergency. Have you ever become frightened and felt your heart start pounding? How does this happen? The answer is your autonomic nervous system. The sympathetic division prepared you to deal with a possible emergency by increasing | text | null |
L_0629 | photosynthesis | T_3259 | If a plant gets hungry, it cannot walk to a local restaurant and buy a slice of pizza. So, how does a plant get the food it needs to survive? Plants are producers, which means they are able to make, or produce, their own food. They also produce the "food" for other organisms. Plants are also autotrophs. Autotrophs are the organisms that collect the energy from the sun and turn it into organic compounds. Using the energy from the sun, they produce complex organic compounds from simple inorganic molecules. So once again, how does a plant get the food it needs to survive? Through photosynthesis. Photosynthesis is the process plants use to make their own food from the suns energy, carbon dioxide, and water. During photosynthesis, carbon dioxide and water combine with solar energy to create glucose, a carbohydrate (C6 H12 O6 ), and oxygen. The process can be summarized as: in the presence of sunlight, carbon dioxide + water glucose + oxygen. Glucose, the main product of photosynthesis, is a sugar that acts as the "food" source for plants. The glucose is then converted into usable chemical energy, ATP, during cellular respiration. The oxygen formed during photosynthesis, which is necessary for animal life, is essentially a waste product of the photosynthesis process. Actually, almost all organisms obtain their energy from photosynthetic organisms. For example, if a bird eats a caterpillar, then the bird gets the energy that the caterpillar gets from the plants it eats. So the bird indirectly gets energy that began with the glucose formed through photosynthesis. Therefore, the process of photosynthesis is central to sustaining life on Earth. In eukaryotic organisms, photosynthesis occurs in chloroplasts. Only cells with chloroplastsplant cells and algal (protist) cellscan perform photosynthesis. Animal cells and fungal cells do not have chloroplasts and, therefore, cannot photosynthesize. That is why these organisms, as well as the non- photosynthetic protists, rely on other organisms to obtain their energy. These organisms are heterotrophs. The Photosynthesis Song explaining photosynthesis, can be heard at Click image to the left or use the URL below. URL: | text | null |
L_0629 | photosynthesis | T_3260 | Why do leaves change color each fall? This MIT video demonstrates an experiment about the different pigments in leaves. See the video at . Click image to the left or use the URL below. URL: | text | null |
L_0637 | polygenic traits | T_3277 | Another exception to Mendels rules is polygenic inheritance, which occurs when a trait is controlled by more than one gene. This means that each dominant allele "adds" to the expression of the next dominant allele. Usually, traits are polygenic when there is wide variation in the trait. For example, humans can be many different sizes. Height is a polygenic trait, controlled by at least three genes with six alleles. If you are dominant for all of the alleles for height, then you will be very tall. There is also a wide range of skin color across people. Skin color is also a polygenic trait, as are hair and eye color. Polygenic inheritance often results in a bell shaped curve when you analyze the population ( Figure 1.1). That means that most people fall in the middle of the phenotypic range, such as average height, while very few people are at the extremes, such as very tall or very short. At one end of the curve will be individuals who are recessive for all the alleles (for example, aabbcc); at the other end will be individuals who are dominant for all the alleles (for example, AABBCC). Through the middle of the curve will be individuals who have a combination of dominant and recessive alleles (for example, AaBbCc or AaBBcc). | text | null |
L_0638 | population growth patterns | T_3278 | What does population growth mean? You can probably guess that it means the number of individuals in a population is increasing. The population growth rate tells you how quickly a population is increasing or decreasing. What determines the population growth rate for a particular population? | text | null |
L_0638 | population growth patterns | T_3279 | Population growth rate depends on birth rates and death rates, as well as migration. First, we will consider the effects of birth and death rates. You can predict the growth rate by using this simple equation: growth rate = birth rate death rate. If the birth rate is larger than the death rate, then the population grows. If the death rate is larger than the birth rate, what will happen to the population? The population size will decrease. If the birth and death rates are equal, then the population size will not change. Factors that affect population growth are: 1. 2. 3. 4. 5. 6. Age of organisms at first reproduction. How often an organism reproduces. The number of offspring of an organism. The presence or absence of parental care. How long an organism is able to reproduce. The death rate of offspring. For an ecosystem to be stable, populations in that system must be healthy, and that usually means reproducing as much as their environment allows. Do organisms reproduce yearly or every few years? Do organisms reproduce for much of their life, or just part of their life? Do organisms produce many offspring at once, or just a few, or even just one? Do many newborn organisms die, or do the majority survive? All these factors play a role in the growth of a population. Organisms can use different strategies to increase their reproduction rate. Altricial organisms are helpless at birth, and their parents give them a lot of care. This care is often seen in bird species. ( Figure 1.1). Altricial birds are usually born blind and without feathers. Compared to precocial organisms, altricial organisms have a longer period of development before they reach maturity. Precocial organisms, such as the geese shown below, can take care of themselves at birth and do not require help from their parents ( Figure 1.1). In order to reproduce as much as possible, altricial and precocial organisms must use very different strategies. (left) A hummingbird nest with young il- lustrates an altricial reproductive strategy, with a few small eggs, helpless young, and intensive parental care. (right) The Canada goose shows a precocial repro- ductive strategy. It lays a large number of large eggs, producing well-developed young. | text | null |
L_0638 | population growth patterns | T_3280 | Migration is the movement of individual organisms into, or out of, a population. Migration affects population growth rate. There are two types of migration: 1. Immigration is the movement of individuals into a population from other areas. This increases the population size and growth rate. 2. Emigration is the movement of individuals out of a population. This decreases the population size and growth rate. The earlier growth rate equation can be modified to account for migration: growth rate = (birth rate + immigration rate) (death rate + emigration rate). One type of migration that you are probably familiar with is the migration of birds. Maybe you have heard that birds fly south for the winter. In the fall, birds fly thousands of miles to the south where it is warmer. In the spring, they return to their homes. ( Figure 1.2). Monarch butterflies also migrate from Mexico to the northern U.S. in the summer and back to Mexico in the winter. These types of migrations move entire populations from one location to another. A flock of barnacle geese fly in formation during the autumn migration. | text | null |
L_0638 | population growth patterns | T_3281 | Population growth can be described with two models, based on the size of the population and necessary resources. These two types of growth are known as exponential growth and logistic growth. If a population is given unlimited amounts of resources, such as food and water, land if needed, moisture, oxygen, and other environmental factors, it will grow exponentially. Exponential growth occurs as a population grows larger, dramatically increasing the growth rate. This is shown as a "J-shaped" curve below ( Figure 1.3). You can see that the population grows slowly at first, but as time passes, growth occurs more and more rapidly. Growth of populations according to ex- ponential (or J-curve) growth model (left) and logistic (or S-curve) growth model (right). Time is plotted on the x-axis, and population size is plotted on the y-axis. In nature, organisms do not usually have ideal environments with unlimited food. In nature, there are limits. Sometimes, there will be plenty of food. Sometimes, a fire will wipe out all of the available nutrients. Sometimes a predator will kill many individuals in a population. How do you think these limits affect the way organisms grow? | text | null |
L_0640 | pregnancy and childbirth | T_3283 | While a woman is pregnant, the developing baby may be called an embryo or a fetus. Do these mean the same thing? No, in the very early stages the developing baby is called an embryo, while in the later stages it is called a fetus. When the ball of cells first implants into the uterus, it is called an embryo. The embryo stage lasts until the end of the 8th week after fertilization. After that point until birth, the developing baby is called a fetus. | text | null |
L_0640 | pregnancy and childbirth | T_3284 | During the embryo stage, the baby grows in size. 3rd week after fertilization: Cells of different types start to develop. Cells that will form muscles and skin, for example, start to develop at this time. 4th week after fertilization: Body organs begin to form. 8th week after fertilization: All the major organs have started to develop. Pictured below are some of the changes that take place during the 4th and 8th weeks ( Figure 1.1). Look closely at the two embryos in the figure. Do you think that the older embryo looks more human? Notice that it has arms and legs and lacks a tail. The face has also started to form, and it is much bigger. Embryonic Development (Weeks 48). Most organs develop in the embryo during weeks four through eight. (Note: the drawings of the embryos are not to scale.) | text | null |
L_0640 | pregnancy and childbirth | T_3285 | There are also many changes that take place after the embryo becomes a fetus. Some of the differences between them are obvious. For example, the fetus has ears and eyelids. Its fingers and toes are also fully formed. The fetus even has fingernails and toenails. In addition, the reproductive organs have developed to make the baby a male or female. The brain and lungs are also developing quickly. The fetus has started to move around inside the uterus. This is usually when the mother first feels the fetus moving. By the 28th week, the fetus is starting to look much more like a baby. Eyelashes and eyebrows are present. Hair has started to grow on the head. The body of the fetus is also starting to fill out as muscles and bones develop. Babies born after the 28th week are usually able to survive. However, they need help breathing because their lungs are not yet fully mature. A baby should not be delivered prior to this time, unless absolutely necessary. A baby born prior to week 28 will need considerable medical intervention to survive. During the last several weeks of the fetal period, all of the organs become mature. The most obvious change, however, is an increase in body size. The fetus rapidly puts on body fat and gains weight during the last couple of months. By the end of the 38th week, all of the organs are working, and the fetus is ready to be born. This is when birth normally occurs. A baby born before this time is considered premature. | text | null |
L_0640 | pregnancy and childbirth | T_3286 | During pregnancy, other structures also develop inside the mothers uterus. They are the amniotic sac, placenta, and umbilical cord ( Figure 1.2). Surrounding the fetus is the fluid-filled amniotic sac. The placenta and umbilical cord are also shown here. They provide a connection between the mothers and fetuss blood for the transfer of nutrients and gases. The amniotic sac is a membrane that surrounds the fetus. It is filled with water and dissolved substances, known as amniotic fluid. Imagine placing a small plastic toy inside a balloon and then filling the balloon with water. The toy would be cushioned and protected by the water. It would also be able to move freely inside the balloon. The amniotic sac and its fluid are like a water-filled balloon. They cushion and protect the fetus. They also let the fetus move freely inside the uterus. The placenta is a spongy mass of blood vessels. Some of the vessels come from the mother. Some come from the fetus. The placenta is attached to the inside of the mothers uterus. The fetus is connected to the placenta by a tube called the umbilical cord. The cord contains two arteries and a vein. Substances pass back and forth between the mothers and fetuss blood through the placenta and cord. Oxygen and nutrients pass from the mother to the fetus. Carbon dioxide passes from the fetus to the mother. It is important for the mother to eat plenty of nutritious foods during pregnancy. She must take in enough nutrients for the fetus as well as for herself. She needs extra calories, proteins, and lipids. She also needs more vitamins and minerals. In addition to eating well, the mother must avoid substances that could harm the embryo or fetus. These include alcohol, illegal drugs, and some medicines. It is especially important for her to avoid these substances during the first eight weeks after fertilization. This is when all the major organs are forming. Exposure to harmful substances during this time could damage the developing body systems. | text | null |
L_0640 | pregnancy and childbirth | T_3287 | During childbirth, a baby passes from the uterus, through the vagina, and out of the mothers body. Childbirth usually starts when the amniotic sac breaks. Then, the muscles of the uterus start contracting. The contractions get stronger and closer together. They may go on for hours. Eventually, the contractions squeeze the baby out of the uterus. Once the baby enters the vagina, the mother starts pushing. She soon pushes the baby through the vagina and out of her body. As soon as the baby is born, the umbilical cord is cut. After the cord is cut, the baby can no longer get rid of carbon dioxide through the cord and placenta. As a result, carbon dioxide builds up in the babys blood. This triggers the baby to start breathing. The amniotic sac and placenta pass through the vagina and out of the body shortly after the birth of the baby. | text | null |
L_0641 | preserving water sources | T_3288 | It might seem like there is plenty of water on Earth, but thats not really the case. Water is a limited resource. That means that it is used faster than it is replaced. Theoretically, at some point in time, the supply of fresh water could run out. Though this is unlikely, it is possible. But it is a significant issue in parts of the world with large populations. As these populations continue to grow, the supply of water becomes an increasingly important issue. Even though we have lots of water in our oceans, we cannot use that water whenever we want. It takes special equipment, such as a desalination plant, and a lot of energy (and money) to convert salt water into fresh water. Of all the water on Earth, only about 1% can be used for drinking water. Almost all of the rest of the water is either salt water in the ocean or ice in glaciers and ice caps. As a result, there are water shortages many places in the world. Since we have such a limited supply of water, it is important to preserve our water supplies. Therefore, steps have been taken to prevent water pollution. Technologies have also been developed to conserve water and prevent water pollution. Sub-Saharan African countries have the most vulnerable water supplies. Some scientists believe of a potential future crisis in both Asia and Africa from pollution and depletion of natural water resources. Many countries in the Middle East are at an extreme risk of water shortages. Diminished water supplies could increase the risk of both internal conflicts or wars between countries. | text | null |
L_0641 | preserving water sources | T_3289 | In the U.S., concern over water pollution has resulted in many federal laws. Some of these laws go all the way back to the 1800s! The laws prohibit the disposal of any waste into the nations rivers, lakes, streams, and other bodies of water, unless a person first has a permit. Growing concern for controlling water pollutants led to the enactment of the Clean Water Act in 1972. The Clean Water Act set water quality standards. It also limits the pollution that can enter the waterways. Other countries are also actively preventing water pollution and purifying water ( Figure 1.1). A water purification station in France. Contaminants are removed to make clean water. | text | null |
L_0641 | preserving water sources | T_3290 | Fresh water is also preserved by purifying wastewater. Wastewater is water that has been used for cleaning, washing, flushing, or manufacturing. It includes the water that goes down your shower drain and that is flushed down your toilet. Instead of dumping wastewater directly into rivers, wastewater can be purified at a water treatment plant ( Figure 1.2). When wastewater is recycled, waterborne diseases caused by pathogens in sewage can be prevented. What are some ways you can save water in your own house? | text | null |
L_0642 | preventing infectious diseases | T_3291 | Infectious diseases are diseases that spread from person to person. They are caused by pathogens such as bacteria, viruses or fungi. What can you do to avoid infectious diseases? Eating right and getting plenty of sleep are a good start. These habits will help keep your immune system healthy. With a healthy immune system, you will be able to fight off many pathogens. The next best way is to avoid pathogens. Though this is difficult, there are steps you can take to limit your exposure to pathogens. Here are the ten best ways to prevent the spread of infectious diseases. 1. Wash your hands frequently. 2. Dont share personal items. 3. Cover your mouth when you cough or sneeze. 4. 5. 6. 7. 8. 9. 10. Get vaccinated. Use safe cooking practices. Be a smart traveler. Practice safe sex. Dont pick your nose (or your mouth or eyes either). Exercise caution with animals. Watch the news, and be aware of disease outbreaks. | text | null |
L_0642 | preventing infectious diseases | T_3292 | You can also take steps to avoid pathogens in the first place. The best way to avoid pathogens is to wash your hands often. You should wash your hands after using the bathroom or handling raw meat or fish. You should also wash your hands before eating or preparing food. In addition, you should also wash the food that your eat, and the utensils and countertop where food is prepared. In addition, you should wash your hands after being around sick people. The correct way to wash your hands is demonstrated below ( Figure 1.1). If soap and water arent available, use some hand sanitizer. The best way to prevent diseases spread by vectors is to avoid contact with the vectors. Recall that a vector is an organism that carries pathogens from one person or animal to another. For example, ticks and mosquitoes are vectors, so you should wear long sleeves and long pants when appropriate to avoid tick and mosquito bites. Using insect repellent can also reduce your risk of insect bites. Many infectious diseases can be prevented with vaccinations. Immunization can drastically reduce your chances of contracting many diseases. You will read more about vaccinations in another concept. Vaccinations can help prevent measles, mumps, chicken pox, and several other diseases. If you do develop an infectious disease, try to avoid infecting others. Stay home from school until you are well. Also, take steps to keep your germs to yourself. Cover your mouth and nose with a tissue when you sneeze or cough, Watching the news will allow you to make informed decisions. If an outbreak of bad beef due to a bacterial infection is in the news, dont buy beef for a while. If tomatoes are making people sick, dont eat tomatoes until the outbreak is over. If a place has an unhealthy water supply, boil the water or drink bottled water. Local news can tell you of restaurants to avoid due to unhealthy conditions. And so on. | text | null |
L_0643 | preventing noninfectious diseases | T_3293 | Noninfectious diseases cant be passed from one person to another. Instead, these types of diseases are caused by factors such as the environment, genetics, and lifestyle. Examples of inherited noninfectious conditions include cystic fibrosis and Down syndrome. If youre born with these conditions, you must learn how to manage the symptoms. Examples of conditions caused by environmental or lifestyle factors include heart disease and skin cancer. We cant change our genetic codes, but there are plenty of ways to prevent other noninfectious diseases. For example, cutting down on exposure to cigarette smoke and the suns rays will prevent certain types of cancer. It is a fact that most chronic noninfectious diseases can be prevented. The chronic noninfectious diseases that cause the most deaths in many developed countries are largely preventable. These diseases are heart disease, stroke, diabetes and cancer, and though they do have some genetic components, they also have many lifestyle components. For example, some cancers have genetic risks, but people at high risk for cancers can have screening examinations to catch them early or sometimes can take other steps to prevent the cancers. Heart disease, stroke and diabetes are mostly linked to lifestyle choices, even when family history puts a person at higher risk for the diseases. Most allergies can be prevented by avoiding the substances that cause them. For example, you can avoid pollens by staying indoors as much as possible. You can learn to recognize plants like poison ivy and not touch them. A good way to remember how to avoid poison ivy is "leaves of three, let it be." Some people receive allergy shots to help prevent allergic reactions. The shots contain tiny amounts of allergens, which are the substances that cause an allergic reaction. After many months or years of shots, the immune system gets used to the allergens and no longer responds to them. Type 1 diabetes and other autoimmune diseases cannot be prevented. But choosing a healthy lifestyle can help prevent type 2 diabetes. Getting plenty of exercise, avoiding high-fat foods, and staying at a healthy weight can reduce the risk of developing this type of diabetes. This is especially important for people who have family members with the disease. Making these healthy lifestyle choices can also help prevent some types of cancer. In addition, you can lower the risk of cancer by avoiding carcinogens, which are substances that cause cancer. For example, you can reduce your risk of lung cancer by not smoking. You can reduce your risk of skin cancer by using sunscreen. How to choose a sunscreen that offers the most protection is explained below ( Figure 1.1). Some people think that tanning beds are a safe way to get a tan. This is a myth. Tanning beds expose the skin to UV radiation. Any exposure to UV radiation increases the risk of skin cancer. It doesnt matter whether the radiation comes from tanning lamps or the sun. Overall, people in many developed countries are contributing to higher rates of noninfectious diseases (heart disease, stroke, diabetes and cancer) by taking advantage of technology and social environments that encourage a less active lifestyle, and also encourages faster and cheaper meals. For example, many children now spend more time on their computer or watching TV then playing outdoors. The "faster and cheaper" meals are usually less healthy than other meals. Even though many people are living longer, they can choose to live more healthily by adopting regular exercise routines and healthy eating habits. When you choose a sunscreen, select one with an SPF (sun protection factor) of 30 or higher. Also, choose a sunscreen that protects against both UVB and UVA radiation. | text | null |
L_0645 | process of cellular respiration | T_3298 | Cellular respiration is the process of extracting energy in the form of ATP from the glucose in the food you eat. How does cellular respiration happen inside of the cell? Cellular respiration is a three step process. Briefly: 1. In stage one, glucose is broken down in the cytoplasm of the cell in a process called glycolysis. 2. In stage two, the pyruvate molecules are transported into the mitochondria. The mitochondria are the organelles known as the energy "powerhouses" of the cells (Figure 1.1). In the mitochondria, the pyruvate, which have been converted into a 2-carbon molecule, enter the Krebs cycle. Notice that mitochondria have an inner membrane with many folds, called cristae. These cristae greatly increase the membrane surface area where many of the cellular respiration reactions take place. 3. In stage three, the energy in the energy carriers enters an electron transport chain. During this step, this energy is used to produce ATP. Oxygen is needed to help the process of turning glucose into ATP. The initial step releases just two molecules of ATP for each glucose. The later steps release much more ATP. Most of the reactions of cellular respira- tion are carried out in the mitochondria. | text | null |
L_0645 | process of cellular respiration | T_3299 | What goes into the cell? Oxygen and glucose are both reactants of cellular respiration. Oxygen enters the body when an organism breathes. Glucose enters the body when an organism eats. | text | null |
L_0645 | process of cellular respiration | T_3300 | What does the cell produce? The products of cellular respiration are carbon dioxide and water. Carbon dioxide is transported from your mitochondria out of your cell, to your red blood cells, and back to your lungs to be exhaled. ATP is generated in the process. When one molecule of glucose is broken down, it can be converted to a net total of 36 or 38 molecules of ATP. This only occurs in the presence of oxygen. | text | null |
L_0645 | process of cellular respiration | T_3301 | The overall chemical reaction for cellular respiration is one molecule of glucose (C6 H12 O6 ) and six molecules of oxygen (O2 ) yields six molecules of carbon dioxide (CO2 ) and six molecules of water (H2 O). Using chemical symbols the equation is represented as follows: C6 H12 O6 + 6O2 6CO2 + 6H2 O ATP is generated during the process. Though this equation may not seem that complicated, cellular respiration is a series of chemical reactions divided into three stages: glycolysis, the Krebs cycle, and the electron transport chain. | text | null |
L_0645 | process of cellular respiration | T_3302 | Stage one of cellular respiration is glycolysis. Glycolysis is the splitting, or lysis of glucose. Glycolysis converts the 6-carbon glucose into two 3-carbon pyruvate molecules. This process occurs in the cytoplasm of the cell, and it occurs in the presence or absence of oxygen. During glycolysis a small amount of NADH is made as are four ATP. Two ATP are used during this process, leaving a net gain of two ATP from glycolysis. The NADH temporarily holds energy, which will be used in stage three. | text | null |
L_0645 | process of cellular respiration | T_3303 | In the presence of oxygen, under aerobic conditions, pyruvate enters the mitochondria to proceed into the Krebs cycle. The second stage of cellular respiration is the transfer of the energy in pyruvate, which is the energy initially in glucose, into two energy carriers, NADH and FADH2 . A small amount of ATP is also made during this process. This process occurs in a continuous cycle, named after its discover, Hans Krebs. The Krebs cycle uses a 2-carbon molecule (acetyl-CoA) derived from pyruvate and produces carbon dioxide. | text | null |
L_0645 | process of cellular respiration | T_3304 | Stage three of cellular respiration is the use of NADH and FADH2 to generate ATP. This occurs in two parts. First, the NADH and FADH2 enter an electron transport chain, where their energy is used to pump, by active transport, protons (H+ ) into the intermembrane space of mitochondria. This establishes a proton gradient across the inner membrane. These protons then flow down their concentration gradient, moving back into the matrix by facilitated diffusion. During this process, ATP is made by adding inorganic phosphate to ADP. Most of the ATP produced during cellular respiration is made during this stage. For each glucose that starts cellular respiration, in the presence of oxygen (aerobic conditions), 36-38 ATP are generated. Without oxygen, under anaerobic conditions, much less (only two!) ATP are produced. | text | null |
L_0646 | processes of breathing | T_3305 | Breathing is only part of the process of bringing oxygen to where it is needed in the body. After oxygen enters the lungs, what happens? 1. The oxygen enters the bloodstream from the alveoli, tiny sacs in the lungs where gas exchange takes place ( Figure 1.1). The transfer of oxygen into the blood is through simple diffusion. 2. The oxygen-rich blood returns to the heart. 3. Oxygen-rich blood is then pumped through the aorta, the large artery that receives blood directly from the heart. 4. From the aorta, oxygen-rich blood travels to the smaller arteries and, finally, to the capillaries, the smallest type of blood vessel. 5. The oxygen molecules move, by diffusion, out of the capillaries and into the body cells. 6. While oxygen moves from the capillaries and into body cells, carbon dioxide moves from the cells into the capillaries. Gas exchange is the movement of oxygen into the blood and carbon dioxide out of the blood. 7. Carbon dioxide is brought, through the blood, back to the heart and then to the lungs. Then it is released into the air during exhalation. Why is oxygen needed by each cell in your body? To make ATP, the usable form of cellular energy. Oxygen is needed in the final stage of cellular respiration, which is the process of converting glucose into ATP. This process is much more efficient in the presence of oxygen. Without oxygen, much less ATP is produced. As ATP is needed for the cells to function properly, every cell in your body needs oxygen. Getting that oxygen begins with inhaling. The oxygen moves into your blood, where it travels to every cell in your body. | text | null |
L_0647 | producers | T_3306 | Energy is the ability to do work. In organisms, this work can be physical work, like walking or jumping, or it can be the work used to carry out the chemical processes in their cells. Every biochemical reaction that occurs in an organisms cells needs energy. All organisms need a constant supply of energy to stay alive. Some organisms can get the energy directly from the sun. Other organisms get their energy from other organisms. Through predator-prey relationships, the energy of one organism is passed on to another. Energy is constantly flowing through a community. With just a few exceptions, all life on Earth depends on the suns energy for survival. The energy of the sun is first captured by producers ( Figure 1.1), organisms that can make their own food. Many producers make their own food through the process of photosynthesis. The "food" the producers make is the sugar, glucose. Producers make food for the rest of the ecosystem. As energy is not recycled, energy must consistently be captured by producers. This energy is then passed on to the organisms that eat the producers, and then to the organisms that eat those organisms, and so on. Recall that the only required ingredients needed for photosynthesis are sunlight, carbon dioxide (CO2 ), and wa- ter (H2 O). From these simple inorganic ingredients, photosynthetic organisms produce the carbohydrate glucose (C6 H12 O6 ), and other complex organic compounds. Essentially, these producers are changing the energy from the sunlight into a usable form of energy. They are also making the oxygen that we breathe. Oxygen is a waste product of photosynthesis. The survival of every ecosystem is dependent on the producers. Without producers capturing the energy from the sun and turning it into glucose, an ecosystem could not exist. On land, plants are the dominant producers. Phytoplankton, tiny photosynthetic organisms, are the most common producers in the oceans and lakes. Algae, which is the green layer you might see floating on a pond, are an example of phytoplankton. There are also bacteria that use chemical processes to produce food. They get their energy from sources other than the sun, but they are still called producers. This process is known as chemosynthesis, and is common in ecosystems without sunlight, such as certain marine ecosystems. Producers include (a) plants, (b) algae, and (c) diatoms. | text | null |
L_0652 | puberty and adolescence | T_3317 | Puberty is the stage of life when a child becomes sexually mature. Puberty lasts from about 12 to 18 years of age in boys and from about 10 to 16 years of age in girls. The age when puberty begins is different from one child to another. Children that begin puberty much earlier or later than their peers may feel self-conscious. They may also worry that something is wrong with them. Usually, an early or late puberty is perfectly normal. In boys, puberty begins when the pituitary gland tells the testes to secrete testosterone. Testosterone causes the following to happen: 1. 2. 3. 4. The penis and testes grow. The testes start making sperm. Pubic and facial hair grow. The shoulders broaden, and the voice becomes deeper. In girls, puberty begins when the pituitary gland tells the ovaries to secrete estrogen. Estrogen causes the following to happen: 1. 2. 3. 4. 5. The uterus and ovaries grow. The ovaries start releasing eggs. The menstrual cycle begins. Pubic hair grows. The hips widen, and the breasts develop. Boys and girls are close to the same height during childhood. In both boys and girls, growth in height and weight is very fast during puberty. But boys grow faster than girls during puberty. Their period of fast growth also lasts longer. By the end of puberty, boys are an average of 10 centimeters (4 inches) taller than girls. | text | null |
L_0652 | puberty and adolescence | T_3318 | Adolescence is the period of life between the start of puberty and the beginning of adulthood. Adolescence includes the physical changes of puberty. It also includes many other changes, including significant mental, emotional, and social changes. During adolescence: Teenagers develop new thinking abilities. For example, they can think about abstract ideas, such as freedom. They are also better at thinking logically. They are usually better at solving problems as well. Teenagers try to establish a sense of who they are as individuals. They may try to become more independent from their parents. Most teens also have emotional ups and downs. This is partly due to changing hormone levels. Teenagers usually spend much more time with peers than with family members. | text | null |
L_0654 | recombinant dna | T_3320 | Recombinant DNA is the combination of DNA from two different sources. For example, it is possible to place a human gene into bacterial DNA. Recombinant DNA technology is useful in gene cloning and in identifying the function of a gene. Recombinant DNA technology can also be used to produce useful proteins, such as insulin. To treat diabetes, many people need insulin. Previously, insulin had been taken from animals. Through recombinant DNA technology, bacteria were created that carry the human gene which codes for the production of insulin. These bacteria become tiny factories that produce this protein. Recombinant DNA technology helps create insulin so it can be used by humans. Recombinant DNA technology is used in gene cloning. A clone is an exact genetic copy. Genes are cloned for many reasons, including use in medicine and in agriculture. Below are the steps used to copy, or clone, a gene: 1. A gene or piece of DNA is put in a vector, or carrier molecule, producing a recombinant DNA molecule. 2. The vector is placed into a host cell, such as a bacterium. 3. The gene is copied (or cloned) inside of the bacterium. As the bacterial DNA is copied, so is the vector DNA. As the bacteria divide, the recombinant DNA molecules are divided between the new cells. Over a 12- to 24-hour period, millions of copies of the cloned DNA are made. 4. The cloned DNA can produce a protein (like insulin) that can be used in medicine or in research. | text | null |
L_0654 | recombinant dna | T_3321 | Bacteria have small rings of DNA in the cytoplasm, called plasmids ( Figure 1.1). A plasmid is not part of the bacterial chromosome, but an additional pieced of DNA. When putting foreign DNA into a bacterium, the plasmids are often used as a vector. Viruses can also be used as vectors. The manipulation of the plasmid DNA, and then the insertion of the recombinant plasmid into a bacterium, is an invaluable tool in scientific research. This image shows a drawing of a plasmid. The plasmid has two large segments and one small segment depicted. The two large segments (green and blue) indicate antibiotic resistances usually used in a screening procedure. The antibiotic resis- tance segments ensure only bacteria with the plasmid will grow. The small segment (red) indicates an origin of replication. The origin of replication is where DNA replication starts, copying the plasmid. | text | null |
L_0655 | reduce reuse and recycle | T_3322 | Why conserve resources? During your lifetime, it is possible that the world may run out of some nonrenewable resources, especially as the population passes 8 then 9 billion people. So it is necessary to try to make these resources last as long as possible. You may have heard people say, "Reduce, Reuse, Recycle." You may know that this is the slogan of the campaign to conserve resources. But what do each one of those words truly mean? | text | null |
L_0655 | reduce reuse and recycle | T_3323 | What exactly does it mean to reduce? Reducing means decreasing the amount of waste we create. That could also mean cutting down on use of natural resources. In addition, many ways to reduce also result in saving money. Minimizing of waste may be difficult to achieve for individuals and households, but here are some starting points that you can include in your daily routine to reduce the use of resources: Turn lights off when not using them. Turn the television off when no one is watching. Replace burned out bulbs with ones that are more energy-efficient ( Figure 1.1). Reduce water use by turning off faucets when not using water. Use low-flow shower heads, which save on water and use less energy. Use low-flush and composting toilets. Put kitchen and garden waste into a compost pile. In the summer, change filters on your air conditioner and use as little air conditioning as possible. The use of air conditioning uses a lot of energy. In winter, make sure your furnace is working properly and make sure there is enough insulation on windows and doors. Mend broken or worn items instead of buying new ones. When you go shopping for items, buy quantities you know you will use without waste. Walk or bicycle instead of using an automobile, in order to save on fuel usage and costs, and to cut down on pollution. When buying a new vehicle, check into hybrid, semi-hybrid, or electric models to cut down on gas usage and air pollution. These fluorescent light bulbs are much more energy efficient than standard light bulbs. | text | null |
L_0655 | reduce reuse and recycle | T_3324 | Lets now look at what we can reuse. Reusing includes using the same item again for the same function and also using an item again for a new function. Reuse can have both economic and environmental benefits. New packaging regulations are helping society to move towards these goals. Water is a resource that can be reused for numerous purposes. You may not drink used water, but it is quite useful for other purposes. Some ways of reusing resources include: Use reusable bags when shopping. Use gray water. Water that has been used for laundry, for example, can be used to water the garden or flush toilets. At the town level, purified sewage water can be used for fountains, watering public parks or golf courses, fire fighting, and irrigating crops. Rain can be caught in rain barrels and used to water your garden. What are some other ways to reuse resources? | text | null |
L_0655 | reduce reuse and recycle | T_3325 | Now we move on to recycle. Sometimes it may be difficult to understand the differences between reusing and recycling. Recycling involves processing used materials in order to make them suitable for other uses. That usually means taking a used item, breaking it down, and reusing the pieces. Even though recycling requires extra energy, it does often make use of items which are broken, worn out, or cannot be reused. The things that are commonly recycled include: Batteries. Biodegradable waste. Electronics. Iron and steel. Aluminum ( Figure 1.2). Glass. Paper. Plastic. Textiles, such as clothing. Timber. Tires. Each type of recyclable requires a different recycling technique. Here are some things you can do to recycle in your home, school, or community: Laws can also be created to make sure people and companies reduce, reuse, and recycle. Individuals can vote for leaders who stand for sustainable ecological practices. They can also tell their leaders to make wise use of natural resources. You can also influence companies. If you and your family only buy from companies and restaurants that support recycling or eco-friendly packaging, then other companies will also change to be more environmentally friendly. | text | null |
L_0656 | renewable resources and alternative energy sources | T_3326 | A resource is renewable if it is remade by natural processes at the same rate that humans use it up. Sunlight and wind are renewable resources because they will not be used up ( Figure 1.1). The rising and falling of ocean tides is another example of a resource in unlimited supply. A sustainable resource is a resource that is used in a way that meets the needs of the present without keeping future generations from meeting their needs. People can sustainably harvest wood, cork, and bamboo. Farmers can also grow crops sustainably by not planting the same crop in their soil year after year. Planting the same crop each year can remove nutrients from the soil. This means that wood, cork, bamboo, and crops can be sustainable resources. | text | null |
L_0656 | renewable resources and alternative energy sources | T_3327 | A nonrenewable resource is one that cannot be replaced as easily as it is consumed. Fossil fuels are an example of nonrenewable resources. They take millions of years to form naturally, and so they cannot be replaced as fast as they are consumed. To take the place of fossil fuel use, alternative energy resources are being developed. These alternative energy sources often utilize renewable resources. The following are examples of sustainable alternative energy resources: Solar power, which uses solar cells to turn sunlight into electricity ( Figure 1.2). The electricity can be used to power anything that uses normal coal-generated electricity. Wind power, which uses windmills to transform wind energy into electricity. It is used for less than 1% of the worlds energy needs. But wind energy is growing fast. Every year, 30% more wind energy is used to create electricity. Hydropower ( Figure 1.3), which uses the energy of moving water to turn turbines (similar to windmills) or water wheels, that create electricity. This form of energy produces no waste or pollution. It is a renewable resource. Geothermal power, which uses the natural flow of heat from the Earths core to produce steam. This steam is used to turn turbines which create electricity. Biomass is the mass of biological organisms. It is usually used to describe the amount of organic matter in a trophic level of an ecosystem. Biomass production involves using organic matter ("biomass") from plants to create electricity. Using corn to make ethanol fuel is an example of biomass generated energy. Biomass is generally renewable. Tides in the ocean can also turn a turbine to create electricity. This energy can then be stored until needed ( Figure 1.4). Dam of the tidal power plant in the Rance River, Bretagne, France | text | null |
L_0656 | renewable resources and alternative energy sources | T_3327 | A nonrenewable resource is one that cannot be replaced as easily as it is consumed. Fossil fuels are an example of nonrenewable resources. They take millions of years to form naturally, and so they cannot be replaced as fast as they are consumed. To take the place of fossil fuel use, alternative energy resources are being developed. These alternative energy sources often utilize renewable resources. The following are examples of sustainable alternative energy resources: Solar power, which uses solar cells to turn sunlight into electricity ( Figure 1.2). The electricity can be used to power anything that uses normal coal-generated electricity. Wind power, which uses windmills to transform wind energy into electricity. It is used for less than 1% of the worlds energy needs. But wind energy is growing fast. Every year, 30% more wind energy is used to create electricity. Hydropower ( Figure 1.3), which uses the energy of moving water to turn turbines (similar to windmills) or water wheels, that create electricity. This form of energy produces no waste or pollution. It is a renewable resource. Geothermal power, which uses the natural flow of heat from the Earths core to produce steam. This steam is used to turn turbines which create electricity. Biomass is the mass of biological organisms. It is usually used to describe the amount of organic matter in a trophic level of an ecosystem. Biomass production involves using organic matter ("biomass") from plants to create electricity. Using corn to make ethanol fuel is an example of biomass generated energy. Biomass is generally renewable. Tides in the ocean can also turn a turbine to create electricity. This energy can then be stored until needed ( Figure 1.4). Dam of the tidal power plant in the Rance River, Bretagne, France | text | null |
L_0656 | renewable resources and alternative energy sources | T_3327 | A nonrenewable resource is one that cannot be replaced as easily as it is consumed. Fossil fuels are an example of nonrenewable resources. They take millions of years to form naturally, and so they cannot be replaced as fast as they are consumed. To take the place of fossil fuel use, alternative energy resources are being developed. These alternative energy sources often utilize renewable resources. The following are examples of sustainable alternative energy resources: Solar power, which uses solar cells to turn sunlight into electricity ( Figure 1.2). The electricity can be used to power anything that uses normal coal-generated electricity. Wind power, which uses windmills to transform wind energy into electricity. It is used for less than 1% of the worlds energy needs. But wind energy is growing fast. Every year, 30% more wind energy is used to create electricity. Hydropower ( Figure 1.3), which uses the energy of moving water to turn turbines (similar to windmills) or water wheels, that create electricity. This form of energy produces no waste or pollution. It is a renewable resource. Geothermal power, which uses the natural flow of heat from the Earths core to produce steam. This steam is used to turn turbines which create electricity. Biomass is the mass of biological organisms. It is usually used to describe the amount of organic matter in a trophic level of an ecosystem. Biomass production involves using organic matter ("biomass") from plants to create electricity. Using corn to make ethanol fuel is an example of biomass generated energy. Biomass is generally renewable. Tides in the ocean can also turn a turbine to create electricity. This energy can then be stored until needed ( Figure 1.4). Dam of the tidal power plant in the Rance River, Bretagne, France | text | null |
L_0656 | renewable resources and alternative energy sources | T_3327 | A nonrenewable resource is one that cannot be replaced as easily as it is consumed. Fossil fuels are an example of nonrenewable resources. They take millions of years to form naturally, and so they cannot be replaced as fast as they are consumed. To take the place of fossil fuel use, alternative energy resources are being developed. These alternative energy sources often utilize renewable resources. The following are examples of sustainable alternative energy resources: Solar power, which uses solar cells to turn sunlight into electricity ( Figure 1.2). The electricity can be used to power anything that uses normal coal-generated electricity. Wind power, which uses windmills to transform wind energy into electricity. It is used for less than 1% of the worlds energy needs. But wind energy is growing fast. Every year, 30% more wind energy is used to create electricity. Hydropower ( Figure 1.3), which uses the energy of moving water to turn turbines (similar to windmills) or water wheels, that create electricity. This form of energy produces no waste or pollution. It is a renewable resource. Geothermal power, which uses the natural flow of heat from the Earths core to produce steam. This steam is used to turn turbines which create electricity. Biomass is the mass of biological organisms. It is usually used to describe the amount of organic matter in a trophic level of an ecosystem. Biomass production involves using organic matter ("biomass") from plants to create electricity. Using corn to make ethanol fuel is an example of biomass generated energy. Biomass is generally renewable. Tides in the ocean can also turn a turbine to create electricity. This energy can then be stored until needed ( Figure 1.4). Dam of the tidal power plant in the Rance River, Bretagne, France | text | null |
L_0656 | renewable resources and alternative energy sources | T_3328 | Scientists at the Massachusetts of Technology are turning trash into coal, which can readily be used to heat homes and cook food in developing countries. This coal burns cleaner than that from fossil fuels. It also save a tremendous amount of energy. See http://youtu.be/GzhFgEYiVyY?list=PLzMhsCgGKd1hoofiKuifwy6qRXZs7NG6a for more information. Click image to the left or use the URL below. URL: | text | null |
L_0659 | reproductive system health | T_3336 | As was discussed in previous concepts, both infectious and noninfectious diseases of the reproductive system can be very serious. But there are ways to keep your reproductive system healthy. What can you do to keep your reproductive system healthy? You can start by making the right choices for overall good health. To be as healthy as you can be, you should: Eat a balanced diet that is high in fiber and low in fat. Drink plenty of water. Get regular exercise. Maintain a healthy weight. Get enough sleep. Avoid using tobacco, alcohol, or other drugs. Manage stress in healthy ways. Keeping your genitals clean is also very important. A daily shower or bath is all that it takes. Females do not need to use special feminine hygiene products. In fact, using them may do more harm than good because they can irritate the vagina or other reproductive structures. You should also avoid other behaviors that can put you at risk. Do not get into contact with another persons blood or other body fluids. For example, never get a tattoo or piercing unless you are sure that the needles have not been used before. This is one of the most important ways to prevent an STI. Of course, the only way to be fully protected against STIs is to refrain from sexual activity. If you are a boy, you should always wear a protective cup when you play contact sports. Contact sports include football, boxing, and hockey. Wearing a cup will help protect the testes from injury. You should also do a monthly self-exam to check for cancer of the testes. If you are a girl and use tampons, be sure to change them every four to six hours. Leaving tampons in for too long can put you at risk of toxic shock syndrome. This is a serious condition. Signs and symptoms of toxic shock syndrome develop suddenly, and the disease can be fatal. The disease involves fever, shock, and problems with the function of several body organs. Girls should also get in the habit of doing a monthly self-exam to check for breast cancer. Although breast cancer is rare in teens, its a good idea to start doing the exam when you are young. It will help you get to know what is normal for you. | text | null |
L_0661 | respiration | T_3340 | Most of the time, you breathe without thinking about it. Breathing is mostly an involuntary action that is controlled by a part of your brain that also controls your heart beat. If you swim, do yoga, or sing, you know you can control your breathing, however. Taking air into the body through the nose and mouth is called inhalation. Pushing air out of the body through the nose or mouth is called exhalation. The woman pictured below is exhaling before she surfaces from the pool water (Figure 1.1). How do lungs allow air in? Air moves into and out of the lungs by the movement of muscles. The most important muscle in the process of breathing is the diaphragm, a sheet of muscle that spreads across the bottom of the rib cage. The diaphragm and rib muscles contract and relax to move air into and out of the lungs. During inhalation, the diaphragm contracts and moves downward. The rib muscles contract and cause the ribs to move outward. This causes the chest volume to increase. Because the chest volume is larger, the air pressure inside the lungs is lower than the air pressure outside. This difference in air pressures causes air to be sucked into the lungs. When the diaphragm and rib muscles relax, air is pushed out of the lungs. Exhalation is similar to letting the air out of a balloon. How does the inhaled oxygen get into the bloodstream? The exchange of gasses between the lungs and the blood happens in tiny sacs called alveoli. The walls of the alveoli are very thin and allow gases to pass though them. The alveoli are lined with capillaries (Figure 1.2). Oxygen moves from the alveoli to the blood in the capillaries that surround the alveoli. At the same time, carbon dioxide moves in the opposite direction, from capillary blood to the alveoli. The gases move by simple diffusion, passing from an area of high concentration to an area of low concentration. For example, initially there is more oxygen in the alveoli than in the blood, so oxygen moves by diffusion from the alveoli into the blood. | text | null |
L_0661 | respiration | T_3340 | Most of the time, you breathe without thinking about it. Breathing is mostly an involuntary action that is controlled by a part of your brain that also controls your heart beat. If you swim, do yoga, or sing, you know you can control your breathing, however. Taking air into the body through the nose and mouth is called inhalation. Pushing air out of the body through the nose or mouth is called exhalation. The woman pictured below is exhaling before she surfaces from the pool water (Figure 1.1). How do lungs allow air in? Air moves into and out of the lungs by the movement of muscles. The most important muscle in the process of breathing is the diaphragm, a sheet of muscle that spreads across the bottom of the rib cage. The diaphragm and rib muscles contract and relax to move air into and out of the lungs. During inhalation, the diaphragm contracts and moves downward. The rib muscles contract and cause the ribs to move outward. This causes the chest volume to increase. Because the chest volume is larger, the air pressure inside the lungs is lower than the air pressure outside. This difference in air pressures causes air to be sucked into the lungs. When the diaphragm and rib muscles relax, air is pushed out of the lungs. Exhalation is similar to letting the air out of a balloon. How does the inhaled oxygen get into the bloodstream? The exchange of gasses between the lungs and the blood happens in tiny sacs called alveoli. The walls of the alveoli are very thin and allow gases to pass though them. The alveoli are lined with capillaries (Figure 1.2). Oxygen moves from the alveoli to the blood in the capillaries that surround the alveoli. At the same time, carbon dioxide moves in the opposite direction, from capillary blood to the alveoli. The gases move by simple diffusion, passing from an area of high concentration to an area of low concentration. For example, initially there is more oxygen in the alveoli than in the blood, so oxygen moves by diffusion from the alveoli into the blood. | text | null |
L_0661 | respiration | T_3341 | The process of getting oxygen into the body and releasing carbon dioxide is called respiration. Sometimes breathing is called respiration, but there is much more to respiration than just breathing. Breathing is only the movement of oxygen into the body and carbon dioxide out of the body. The process of respiration also includes the exchange of oxygen and carbon dioxide between the blood and the cells of the body. | text | null |
L_0662 | respiratory system diseases | T_3342 | Respiratory diseases are diseases of the lungs, bronchial tubes, trachea, nose, and throat ( Figure 1.1). These diseases can range from a mild cold to a severe case of pneumonia. Respiratory diseases are common. Many are easily treated, while others may cause severe illness or death. Some respiratory diseases are caused by bacteria or viruses, while others are caused by environmental pollutants, such as tobacco smoke. Some diseases are genetic and, therefore, are inherited. This boy is suffering from whooping cough (also known as pertussis), which gets its name from the loud whooping sound that is made when the person inhales during a coughing fit. | text | null |
L_0662 | respiratory system diseases | T_3343 | Bronchitis is an inflammation of the bronchi, the air passages that conduct air into the lungs. The bronchi become red and swollen with infection. Acute bronchitis is usually caused by viruses or bacteria, and may last several days or weeks. It is characterized by a cough that produces phlegm, or mucus. Symptoms include shortness of breath and wheezing. Acute bronchitis is usually treated with antibiotics. | text | null |
L_0662 | respiratory system diseases | T_3344 | Asthma is a chronic illness in which the bronchioles, the tiny branches into which the bronchi are divided, become inflamed and narrow ( Figure 1.2). The muscles around the bronchioles contract, which narrows the airways. Large amounts of mucus are also made by the cells in the lungs. People with asthma have difficulty breathing. Their chests feel tight, and they wheeze. Asthma can be caused by different things, such as allergies. Asthma can also be caused by cold air, warm air, moist air, exercise, or stress. The most common asthma triggers are illnesses, like the common cold. Asthma is not contagious and cannot be passed on to other people. Children and adolescents who have asthma can still lead active lives if they control their asthma. Asthma can be controlled by taking medication and by avoiding contact with environmental triggers for asthma, like smoking. | text | null |
L_0662 | respiratory system diseases | T_3345 | Pneumonia is an illness that occurs when the alveoli, the tiny sacs in the lungs where gas exchange takes place, become inflamed and filled with fluid. When a person has pneumonia, gas exchange cannot occur properly across the alveoli. Pneumonia can be caused by many things. Infection by bacteria, viruses, fungi, or parasites can cause pneumonia. An injury caused by chemicals or a physical injury to the lungs can also cause pneumonia. Symptoms of pneumonia include cough, chest pain, fever, and difficulty breathing. Treatment depends on the cause of pneumonia. Bacterial pneumonia is treated with antibiotics. Pneumonia is a common illness that affects people in all age groups. It is a leading cause of death among the elderly and people who are chronically and terminally ill. | text | null |
L_0662 | respiratory system diseases | T_3346 | Tuberculosis (TB) is a common and often deadly disease caused by a genus of bacterium called Mycobacterium. Tuberculosis most commonly attacks the lungs but can also affect other parts of the body. TB is a chronic disease, but most people who become infected do not develop the full disease. Symptoms include a cough, which usually contains mucus and coughing up blood. The TB bacteria are spread in the air when people who have the disease cough, sneeze, or spit, so it is very contagious. To help prevent the spread of the disease, public health notices, such as the one pictured below ( Figure 1.3), remind people how to stop the spread of the disease. A public health notice from the early 20th century reminded people that TB could be spread very easily. | text | null |
L_0662 | respiratory system diseases | T_3347 | Lung cancer is a disease in which the cells found in the lungs grow out of control. The growing mass of cells can form a tumor that pushes into nearby tissues. The tumor will affect how these tissues work. Lung cancer is the most common cause of cancer-related death in men, and the second most common in women. It is responsible for 1.3 million deaths worldwide every year ( Figure 1.4). The most common symptoms are shortness of breath, coughing (including coughing up blood), and weight loss. The most common cause of lung cancer is exposure to tobacco smoke. The inside of a lung showing cancerous tissue. | text | null |
L_0662 | respiratory system diseases | T_3348 | Emphysema is a chronic lung disease caused by the breakdown of the lung tissue. Symptoms of emphysema include shortness of breath, especially during exercise, and chronic cough, usually due to cigarette smoking, and wheezing, especially during expiration. Damage to the alveoli ( Figure 1.5), is not curable. Smoking is the leading cause of emphysema. | text | null |
L_0662 | respiratory system diseases | T_3349 | Many respiratory diseases are caused by pathogens. A pathogen is an organism that causes disease in another organism. Certain bacteria, viruses, and fungi are pathogens of the respiratory system. The common cold and flu are caused by viruses. The influenza virus that causes the flu is pictured below ( Figure 1.6). Tuberculosis, whooping cough, and acute bronchitis are caused by bacteria. The pathogens that cause colds, flu, and TB can be passed from person to person by coughing, sneezing, and spitting. Illnesses caused by bacteria can be treated with antibiotics. Those caused by viruses cannot. Pollution is another common cause of respiratory disease. The quality of the air you breathe can affect the health of your lungs. Asthma, heart and lung diseases, allergies, and several types of cancers are all linked to air quality. Air pollution is not just found outdoors; indoor air pollution can also be responsible for health problems. Smoking is the major cause of chronic respiratory disease as well as cardiovascular disease and cancer. Exposure to tobacco smoke by smoking or by breathing air that contains tobacco smoke is the leading cause of preventable death in the United States. Regular smokers die about 10 years earlier than nonsmokers do. The Centers for Disease Control and Prevention (CDC) describes tobacco use as "the single most important preventable risk to human health The lung of a smoker who had emphysema (left). Tar, a sticky, black substance found in tobacco smoke, is evident. Chronic obstructive pulmonary disease (right), is a tobacco-related disease that is characterized by emphysema. This represents the influenza virus that causes the swine flu, or H1N1. The Center for Disease Control and Prevention recommends that children between the ages of 6 months and 19 years get a flu vaccination each year. in developed countries and an important cause of [early] death worldwide." Simply stated: Stopping smoking can prevent many respiratory diseases. | text | null |
L_0662 | respiratory system diseases | T_3349 | Many respiratory diseases are caused by pathogens. A pathogen is an organism that causes disease in another organism. Certain bacteria, viruses, and fungi are pathogens of the respiratory system. The common cold and flu are caused by viruses. The influenza virus that causes the flu is pictured below ( Figure 1.6). Tuberculosis, whooping cough, and acute bronchitis are caused by bacteria. The pathogens that cause colds, flu, and TB can be passed from person to person by coughing, sneezing, and spitting. Illnesses caused by bacteria can be treated with antibiotics. Those caused by viruses cannot. Pollution is another common cause of respiratory disease. The quality of the air you breathe can affect the health of your lungs. Asthma, heart and lung diseases, allergies, and several types of cancers are all linked to air quality. Air pollution is not just found outdoors; indoor air pollution can also be responsible for health problems. Smoking is the major cause of chronic respiratory disease as well as cardiovascular disease and cancer. Exposure to tobacco smoke by smoking or by breathing air that contains tobacco smoke is the leading cause of preventable death in the United States. Regular smokers die about 10 years earlier than nonsmokers do. The Centers for Disease Control and Prevention (CDC) describes tobacco use as "the single most important preventable risk to human health The lung of a smoker who had emphysema (left). Tar, a sticky, black substance found in tobacco smoke, is evident. Chronic obstructive pulmonary disease (right), is a tobacco-related disease that is characterized by emphysema. This represents the influenza virus that causes the swine flu, or H1N1. The Center for Disease Control and Prevention recommends that children between the ages of 6 months and 19 years get a flu vaccination each year. in developed countries and an important cause of [early] death worldwide." Simply stated: Stopping smoking can prevent many respiratory diseases. | text | null |
L_0663 | respiratory system health | T_3350 | We know that many respiratory illnesses are caused by bacteria or viruses. There are steps you can take to help the spread of these pathogens, and also to prevent you from catching one. Furthermore, many respiratory illnesses are caused by poor habits, such as smoking. Many of the diseases related to smoking are called lifestyle diseases. Lifestyle diseases are diseases that are caused by choices that people make in their daily lives. For example, the choice to smoke can lead to emphysema, cancer and heart disease in later life. But you can make healthy choices instead. There are many things you can do to keep yourself healthy. | text | null |
L_0663 | respiratory system health | T_3351 | Cigarette smoking can cause serious diseases, so not smoking or quitting now are the most effective ways to reduce your risk of developing chronic respiratory diseases, such as lung cancer. Avoiding (or stopping) smoking is the single best way to prevent many respiratory and cardiovascular diseases. Also, do your best to avoid secondhand smoke. | text | null |
L_0663 | respiratory system health | T_3352 | Eating healthy foods, getting enough sleep, and being active every day can help keep your respiratory system, cardiovascular system and immune system strong. Getting enough exercise makes your lungs stronger and better at giving your body the oxygen it needs. It also helps to boost your body fight germs that could make you sick. These can also, of course, keep your skeletal and muscular systems strong. | text | null |
L_0663 | respiratory system health | T_3353 | Washing your hands often, especially after sneezing, coughing, or blowing your nose, helps to protect you and others from diseases. Washing your hands for 20 seconds with soap and warm water can help prevent colds and flu. In one respect, you can think of hand washing as a survival skill. Some viruses and bacteria can live from 20 minutes to two hours or more on surfaces like cafeteria tables, doorknobs, and desks. Washing your hands often can remove many of these pathogens. Never touch your mouth, nose, or eyes without washing your hands. | text | null |
L_0663 | respiratory system health | T_3354 | Do not go to school or to other public places when you are sick. You risk spreading your illness to other people. You may also get even sicker if you catch something else. Do not share food and other things that go in the mouth, as in guzzling milk from the carton or double dipping chips. You never know what pathogens can be lurking around. Cover your mouth with a tissue when you cough or sneeze and to dispose of the tissue yourself. No time to grab a tissue. Cough or sneeze into the inside of your elbow instead of your hands. | text | null |
L_0663 | respiratory system health | T_3355 | Getting the recommended vaccinations can help prevent diseases, such as whooping cough and flu. In fact, a yearly flu vaccine is recommended for everyone who is at least 6 months of age. The flu vaccine is especially important for people who are at high risk of developing serious complications (like pneumonia) if they get sick with the flu. People who have certain medical conditions including asthma, diabetes, and chronic lung disease, pregnant women, and people younger than 5 years (and especially those younger than 2), and people 65 years and older should also make sure they get the yearly flu vaccine. Seeking medical help for diseases like asthma can help stop the disease from getting worse. If you are unsure if you should go to the doctor, call the doctors office and ask. | text | null |
L_0664 | respiratory system organs | T_3356 | Your respiratory system is made up of the tissues and organs that allow oxygen to enter your body and carbon dioxide to leave your body. Organs in your respiratory system include your: Nose. Mouth. Larynx. Pharynx. Lungs. Diaphragm. The organs of the respiratory system move air into and out of the body. These structures are shown below (Figure 1.1). What do you think is the purpose of each of these organs? The nose and the nasal cavity filter, warm, and moisten the air you breathe. The nose hairs and the mucus produced by the cells in the nose catch particles in the air and keep them from entering the lungs. Behind the nasal cavity, air passes through the pharynx, a long tube. Both food and air pass through the pharynx. The larynx, also called the "voice box," is found just below the pharynx. Your voice comes from your larynx. Air from the lungs passes across thin tissues in the larynx and produces sound. The trachea, or windpipe, is a long tube that leads down to the lungs, where it divides into the right and left bronchi. The bronchi branch out into smaller bronchioles in each lung. There is small flap called the epiglottis that covers your trachea when you eat or drink. The muscle controlling the epiglottis is involuntary and prevents food from entering your lungs or wind pipe. The bronchioles lead to the alveoli. Alveoli are the little sacs at the end of the bronchioles (Figure 1.2). They look like little bunches of grapes. Oxygen is exchanged for carbon dioxide in the alveoli. That means oxygen enters the blood, and carbon dioxide moves out of the blood. The gases are exchanged between the blood and alveoli by simple diffusion. The diaphragm is a sheet of muscle that spreads across the bottom of the rib cage. When the diaphragm contracts, the chest volume gets larger, and the lungs take in air. When the diaphragm relaxes, the chest volume gets smaller, and air is pushed out of the lungs. "Grape-like" alveoli in the lungs. | text | null |
L_0664 | respiratory system organs | T_3356 | Your respiratory system is made up of the tissues and organs that allow oxygen to enter your body and carbon dioxide to leave your body. Organs in your respiratory system include your: Nose. Mouth. Larynx. Pharynx. Lungs. Diaphragm. The organs of the respiratory system move air into and out of the body. These structures are shown below (Figure 1.1). What do you think is the purpose of each of these organs? The nose and the nasal cavity filter, warm, and moisten the air you breathe. The nose hairs and the mucus produced by the cells in the nose catch particles in the air and keep them from entering the lungs. Behind the nasal cavity, air passes through the pharynx, a long tube. Both food and air pass through the pharynx. The larynx, also called the "voice box," is found just below the pharynx. Your voice comes from your larynx. Air from the lungs passes across thin tissues in the larynx and produces sound. The trachea, or windpipe, is a long tube that leads down to the lungs, where it divides into the right and left bronchi. The bronchi branch out into smaller bronchioles in each lung. There is small flap called the epiglottis that covers your trachea when you eat or drink. The muscle controlling the epiglottis is involuntary and prevents food from entering your lungs or wind pipe. The bronchioles lead to the alveoli. Alveoli are the little sacs at the end of the bronchioles (Figure 1.2). They look like little bunches of grapes. Oxygen is exchanged for carbon dioxide in the alveoli. That means oxygen enters the blood, and carbon dioxide moves out of the blood. The gases are exchanged between the blood and alveoli by simple diffusion. The diaphragm is a sheet of muscle that spreads across the bottom of the rib cage. When the diaphragm contracts, the chest volume gets larger, and the lungs take in air. When the diaphragm relaxes, the chest volume gets smaller, and air is pushed out of the lungs. "Grape-like" alveoli in the lungs. | text | null |
L_0665 | rna | T_3357 | DNA contains the instructions to create proteins, but it does not make proteins itself. DNA is located in the nucleus, which it never leaves, while proteins are made on ribosomes in the cytoplasm. So DNA needs a messenger to bring its instructions to a ribosome located outside of the nucleus. DNA sends out a message, in the form of RNA (ribonucleic acid), describing how to make the protein. There are three types of RNA directly involved in protein synthesis: Messenger RNA ( mRNA) carries the instructions from the nucleus to the cytoplasm. mRNA is produced in the nucleus, as are all RNAs. The other two forms of RNA, ribosomal RNA ( rRNA) and transfer RNA ( tRNA), are involved in the process of ordering the amino acids to make the protein. rRNA becomes part of the ribosome, which is the site of protein synthesis, and tRNA brings an amino acid to the ribosome so it can be added to a growing chain during protein synthesis. There are numerous tRNAs, as each tRNA is specific for an amino acid. The amino acid actually attaches to the tRNA during this process. More about RNAs will be discussed during the Transcription and Translation Concepts. All three RNAs are nucleic acids, made of nucleotides, similar to DNA ( Figure 1.1). The RNA nucleotide is different from the DNA nucleotide in the following ways: RNA contains a different kind of sugar, called ribose. In RNA, the base uracil (U) replaces the thymine (T) found in DNA. RNA is a single strand molecule. A comparison of DNA and RNA, with the bases of each shown. Notice that in RNA, uracil replaces thymine. | text | null |
L_0667 | roundworms | T_3362 | The word "worm" is not very scientific. This informal term describes animals (usually invertebrates) that have long bodies with no arms or legs. Worms with round, non-segmented bodies are known as nematodes or roundworms ( Figure 1.1). They are classified in the phylum Nematoda, which has over 28,000 known species. Some scientists believe there could be over a million species of Nematodes. Nematodes are slender bilaterally symmetrical worms, typically less than 2.5 mm long. The smallest nematodes are microscopic, while free-living species can reach as much as 5 cm, and some parasitic species are larger still, reaching over a meter in length. The worm body is often covered with ridges, rings, bristles, or other distinctive structures. The radially symmetrical head of a nematode also has distinct features. The head is covered with sensory bristles and, in many cases, solid "head-shields" around the mouth region. The mouth has either three or six lips arranged around the mouth opening, which often have a series of teeth on their inner edges. Nematodes can be parasites of plants and animals. | text | null |
L_0667 | roundworms | T_3363 | 1. Unlike the flatworms, the roundworms have a body cavity with internal organs. 2. A roundworm has a complete digestive system, which includes both a mouth and an anus. This is a significant difference from the incomplete digestive system of flatworms. The roundworm digestive system also include a large digestive organ known as the gut. Digestive enzymes that start to break down food are produced here. There is no stomach, but there is an intestine which produces enzymes that help absorb nutrients. The last portion of the intestine forms a rectum, which expels waste through the anus. 3. Roundworms also have a simple nervous system with a primitive brain. There are four nerves that run the length of the body and are connected from the top to the bottom of the body. At the anterior end of the animal (the head region), the nerves branch from a circular ring which serves as the brain. The head of a nematode has a few tiny sense organs, including chemoreceptors, which sense chemicals. Though still a relatively simple structure, the nervous system of roundworms is very different from that of the cnidarian nerve net. | text | null |
L_0667 | roundworms | T_3364 | Roundworms can be free-living organisms, but they are probably best known for their role as significant plant and animal parasites. Most Nematodes are parasitic, with over 16,000 parasitic species described. Heartworms, which cause serious disease in dogs while living in the heart and blood vessels, are a type of roundworm. Roundworms can also cause disease in humans. Elephantiasis, a disease characterized by the extreme swelling of the limbs ( Figure Most parasitic roundworm eggs or larvae are found in the soil and enter the human body when a person picks them up on the hands and then transfers them to the mouth. The eggs or larvae also can enter the human body directly through the skin. The best solution to these diseases is to try to prevent these diseases rather than treat or cure them. Diseases caused by roundworms are more common in developing countries. Many parasitic diseases caused by roundworms result from poor personal hygiene. Contributing factors may include lack of a clean water supply, inadequate sanitation measures, crowded living conditions, combined with a lack of access to health care and low levels of education. | text | null |
L_0675 | segmented worms | T_3388 | When you think of worms, you probably picture earthworms. There are actually many types of worms, including flatworms, roundworms, and segmented worms. Earthworms are segmented worms. Segmented worms are in the phylum Annelida, which has over 22,000 known species. These worms are known as the segmented worms because their bodies are segmented, or separated into repeating units. Besides the earthworm, the segmented worms also include leeches and some marine worms. Most segmented worms like the earthworm, feed on dead organic matter. Leeches (Figure 1.1), however, can live in fresh water and suck blood from their animal host. You may have noticed many earthworms in soil. Earthworms support terrestrial ecosystems both as prey and by aerating and enriching soil. | text | null |
L_0675 | segmented worms | T_3389 | Segmented worms have a number of characteristic features. 1. The basic form consists of multiple segments, each of which has the same sets of organs and, in most, a pair of parapodia that many species use for locomotion. 2. Segmented worms have a well-developed body cavity filled with fluid. This fluid-filled cavity serves as a hydroskeleton, a supportive structure that helps move the worms muscles. Only the most primitive worms (the flatworms) lack a body cavity. 3. Segmented worms also tend to have organ systems that are more developed than the roundworms or flat- worms. Earthworms, for example, have a complete digestive tract with two openings, as well as an esophagus and intestines. The circulatory system consists of paired hearts and blood vessels. Actually there are five pairs of hearts that pump blood along the two main vessels. And the nervous system consists of the brain and a ventral nerve cord. | text | null |
L_0675 | segmented worms | T_3390 | The following table compares the three worm phyla (Table 1.1). Phylum Platyhelminthes Nematoda Annelida Common Name Flatworm Roundworm Segmented worm Body Cavity Segmented No Yes Yes No No Yes Digestive System Incomplete Complete Complete | text | null |
L_0676 | sex linked inheritance | T_3391 | What determines if a baby is a male or female? Recall that you have 23 pairs of chromosomesand one of those pairs is the sex chromosomes. Everyone has two sex chromosomes. Your sex chromosomes can be X or Y. Females have two X chromosomes (XX), while males have one X chromosome and one Y chromosome (XY). If a baby inherits an X chromosome from the father and an X chromosome from the mother, what will be the childs sex? The baby will have two X chromosomes, so it will be female. If the fathers sperm carries the Y chromosome, the child will be male. Notice that a mother can only pass on an X chromosome, so the sex of the baby is determined by the father. The father has a 50 percent chance of passing on the Y or X chromosome, so there is a 50 percent chance that a child will be male, and there is a 50 percent chance a child will be female. This 50:50 chance occurs for each baby. A couples first five children could all be boys. The sixth child still has a 50:50 chance of being a girl. One special pattern of inheritance that doesnt fit Mendels rules is sex-linked inheritance, referring to the inher- itance of traits that are located on genes on the sex chromosomes. Since males and females do not have the same sex chromosomes, there will be differences between the sexes in how these sex-linked traitstraits linked to genes located on the sex chromosomesare expressed. Sex-linked traits usually refer to traits due to genes on the X chromosome. One example of a sex-linked trait is red-green colorblindness. People with this type of colorblindness cannot tell the difference between red and green. They often see these colors as shades of brown ( Figure 1.1). Boys are much more likely to be colorblind than girls ( Table 1.1). This is because colorblindness is a sex-linked, recessive trait. Boys only have one X chromosome, so if that chromosome carries the gene for colorblindness, they will be colorblind. As girls have two X chromosomes, a girl can have one X chromosome with the colorblind gene and one X chromosome with a normal gene for color vision. Since colorblindness is recessive, the dominant normal gene will mask the recessive colorblind gene. Females with one colorblindness allele and one normal allele are referred to as carriers. They carry the allele but do not express it. How would a female become colorblind? She would have to inherit two genes for colorblindness, which is very unlikely. Many sex-linked traits are inherited in a recessive manner. Xc Xc X (carrier female) Xc Y (colorblind male) X Y X XX (normal female) XY (normal male) According to this Punnett square ( Table 1.1), the son of a woman who carries the colorblindness trait and a male with normal vision has a 50% chance of being colorblind. | text | null |
L_0677 | sexually transmitted infections | T_3392 | A sexually transmitted infection (STI) is an infection that spreads through sexual contact. STIs are caused by pathogens, a living thing or virus that causes infection. The pathogens enter the body through the reproductive organs. Many STIs also spread through body fluids, such as blood. For example, a shared tattoo needle is one way an STI could spread. Some STIs can also spread from a mother to her baby during childbirth. STIs are more common in teens and young adults than in older people. One reason is that young people are more likely to take risks. They also may not know how STIs spread. They are likely to believe myths about STIs ( Table Myth If you are sexually active with just one person, you cant get STIs. If you dont have any symptoms, then you dont have an STI. Getting STIs is no big deal, because STIs can be cured with medicine. Fact The only way to avoid the risk of STIs is to practice abstinence from sexual activity. Many STIs do not cause symptoms, especially in fe- males. Only some STIs can be cured with medicine; other STIs cannot be cured. Most STIs are caused by bacteria or viruses. STIs caused by bacteria usually can be cured with drugs called antibiotics. But antibiotics are not effective against viruses. Therefore, STIs caused by viruses are not treated with antibiotics. Other drugs may be used to help control the symptoms of viral STIs, but they cannot be cured. Once you have a viral STI, you are usually infected for life. | text | null |
L_0677 | sexually transmitted infections | T_3393 | In the U.S., chlamydia is the most common STI caused by bacteria. Females are more likely than males to develop the infection. Rates of chlamydia among U.S. females in 2006 are shown below ( Figure 1.1). Rates were much higher in teens and young women than in other age groups. Chlamydia may cause a burning feeling during urination. It may also cause a discharge (leaking of fluids) from the vagina or penis. But in many cases it causes no symptoms. As a result, people do not know they are infected, so they dont go to the doctor for help. If chlamydia goes untreated, it may cause more serious problems in females. It may cause infections of the uterus, fallopian tubes, or ovaries. These infections may leave a woman unable to have children. Gonorrhea is another common STI. Gonorrhea may cause pain during urination. It may also cause a discharge from the vagina or penis. On the other hand, some people with gonorrhea have no symptoms. As a result, they dont seek treatment. Without treatment, gonorrhea may lead to infection of other reproductive organs. This can happen in males as well as females. Syphilis is a very serious STI. Luckily, it is less common than chlamydia or gonorrhea. Syphilis usually begins with a small sore on the genitals. This is followed a few months later by a rash and flu-like symptoms. If syphilis is not treated, it may damage the heart, brain, and other organs. It can even cause death. | text | null |
L_0677 | sexually transmitted infections | T_3394 | Genital warts are an STI caused by human papilloma virus, or HPV. They are one of the most common STIs in teenagers. HPV infections cannot be cured. But a new vaccine called Gardasil can prevent most HPV infections in females. Many doctors recommend that females between the ages of 9 and 26 years receive the vaccine. Preventing HPV infections in females is important because HPV can also cause cancer of the cervix. A related herpes virus causes cold sores on the lips ( Figure 1.2). Both viruses cause painful blisters. In the case of genital herpes, the blisters are on the penis or around the vaginal opening. The blisters go away on their own, but the virus remains in the body. The blisters may come back repeatedly, especially when a person is under stress. There is no cure for genital herpes. But drugs can help prevent or shorten outbreaks. Researchers are trying to find a vaccine to prevent genital herpes. Hepatitis B is a disease of the liver. It is caused by a virus called hepatitis B, which can be passed through sexual activity. Hepatitis B causes vomiting. It also causes yellowing of the skin and eyes. The disease goes away on its own in some people. Other people are sick for the rest of their lives. In these people, the virus usually damages the liver. It may also lead to liver cancer. Medicines can help prevent liver damage in these people. There is also a vaccine to protect against hepatitis B. HIV stands for "human immunodeficiency virus." It is the virus that causes AIDS. HIV and AIDS are described in a previous concept. HIV can spread through sexual contact. It can also spread through body fluids such as blood. There is no cure for HIV infection, and AIDS can cause death, although AIDS can be delayed for several years with medication. Researchers are trying to find a vaccine to prevent HIV infection. | text | null |
L_0678 | skeletal system joints | T_3395 | A joint is a point at which two or more bones meet. There are three main types of joints in the body: 1. Fixed joints do not allow any bone movement. Many of the joints in your skull are fixed ( Figure 1.1). There are eight bones that fuse together to form the cranium. The joints between these bones do not allow movement, which helps protect the brain. 2. Partly movable joints allow only a little movement. Your backbone has partly movable joints between the vertebrae ( Figure 1.2). The skull has fixed joints. Fixed joints do not allow any movement of the bones, which protects the brain from injury. 3. Movable joints allow the most movement. Movable joints are also the most common type of joint in your body. Your fingers, toes, hips, elbows, and knees all provide examples of movable joints. The surfaces of bones at movable joints are covered with a smooth layer of cartilage. The cartilage reduces friction between the bones. Ligaments often cross a joint, holding two nones together. For example, there are numerous ligaments connecting the leg bones across the knee joint. | text | null |
L_0678 | skeletal system joints | T_3395 | A joint is a point at which two or more bones meet. There are three main types of joints in the body: 1. Fixed joints do not allow any bone movement. Many of the joints in your skull are fixed ( Figure 1.1). There are eight bones that fuse together to form the cranium. The joints between these bones do not allow movement, which helps protect the brain. 2. Partly movable joints allow only a little movement. Your backbone has partly movable joints between the vertebrae ( Figure 1.2). The skull has fixed joints. Fixed joints do not allow any movement of the bones, which protects the brain from injury. 3. Movable joints allow the most movement. Movable joints are also the most common type of joint in your body. Your fingers, toes, hips, elbows, and knees all provide examples of movable joints. The surfaces of bones at movable joints are covered with a smooth layer of cartilage. The cartilage reduces friction between the bones. Ligaments often cross a joint, holding two nones together. For example, there are numerous ligaments connecting the leg bones across the knee joint. | text | null |
L_0678 | skeletal system joints | T_3396 | Four types of movable joints are discussed here. 1. In a ball-and-socket joint, the ball-shaped surface of one bone fits into the cup-like shape of another. Exam- ples of a ball-and-socket joint include the hip ( Figure 1.3) and the shoulder. 2. In a hinge joint, the ends of the bones are shaped in a way that allows motion in two directions, forward and backward. Examples of hinge joints are the knees ( Figure 1.4) and elbows. 3. The pivot joint ( Figure 1.5) only allows rotating movement. An example of a pivot joint is the joint between the radius and ulna that allows you to turn the palm of your hand up and down. 4. A gliding joint is a joint which allows only gliding movement. The gliding joint allows one bone to slide over the other. The gliding joint in your wrist allows you to flex your wrist. It also allows you to make very small side-to-side motions. There are also gliding joints in your ankles. | text | null |
L_0678 | skeletal system joints | T_3396 | Four types of movable joints are discussed here. 1. In a ball-and-socket joint, the ball-shaped surface of one bone fits into the cup-like shape of another. Exam- ples of a ball-and-socket joint include the hip ( Figure 1.3) and the shoulder. 2. In a hinge joint, the ends of the bones are shaped in a way that allows motion in two directions, forward and backward. Examples of hinge joints are the knees ( Figure 1.4) and elbows. 3. The pivot joint ( Figure 1.5) only allows rotating movement. An example of a pivot joint is the joint between the radius and ulna that allows you to turn the palm of your hand up and down. 4. A gliding joint is a joint which allows only gliding movement. The gliding joint allows one bone to slide over the other. The gliding joint in your wrist allows you to flex your wrist. It also allows you to make very small side-to-side motions. There are also gliding joints in your ankles. | text | null |
L_0678 | skeletal system joints | T_3396 | Four types of movable joints are discussed here. 1. In a ball-and-socket joint, the ball-shaped surface of one bone fits into the cup-like shape of another. Exam- ples of a ball-and-socket joint include the hip ( Figure 1.3) and the shoulder. 2. In a hinge joint, the ends of the bones are shaped in a way that allows motion in two directions, forward and backward. Examples of hinge joints are the knees ( Figure 1.4) and elbows. 3. The pivot joint ( Figure 1.5) only allows rotating movement. An example of a pivot joint is the joint between the radius and ulna that allows you to turn the palm of your hand up and down. 4. A gliding joint is a joint which allows only gliding movement. The gliding joint allows one bone to slide over the other. The gliding joint in your wrist allows you to flex your wrist. It also allows you to make very small side-to-side motions. There are also gliding joints in your ankles. | text | null |
L_0679 | skin | T_3397 | Did you know that you see the largest organ in your body every day? You wash it, dry it, cover it up to stay warm, and uncover it to cool off. Yes, your skin is your bodys largest organ. Your skin is part of your integumentary system ( Figure 1.1), which is the outer covering of your body. The integumentary system is made up of your skin, hair, and nails. Skin acts as a barrier that stops water and other things, like soap and dirt, from getting into your body. | text | null |
L_0679 | skin | T_3398 | The skin has many important functions. The skin: Provides a barrier. It keeps organisms that could harm the body out. It stops water from entering or leaving the body. Controls body temperature. It does this by making sweat (or perspiration), a watery substance that cools the body when it evaporates. Gathers information about your environment. Special nerve endings in your skin sense heat, pressure, cold, and pain. Helps the body get rid of some types of waste, which are removed in sweat. Acts as a sun block. A pigment called melanin blocks sunlight from getting to deeper layers of skin cells, which are easily damaged by sunlight. | text | null |
L_0679 | skin | T_3399 | Your skin is always exposed to your external environment, so it gets cut, scratched, and worn down. You also naturally shed many skin cells every day. Your body replaces damaged or missing skin cells by growing more of them. Did you know that the layer of skin you can see is actually dead? As the dead cells are shed or removed from the upper layer, they are replaced by the skin cells below them. Two different layers make up the skin: the epidermis and the dermis ( Figure 1.2). A fatty layer lies under the dermis, but it is not part of your skin. | text | null |
L_0679 | skin | T_3400 | The epidermis is the outermost layer of the skin. It forms the waterproof, protective wrap over the bodys surface. Although the top layer of epidermis is only about as thick as a sheet of paper, it is made up of 25 to 30 layers of cells. The epidermis also contains cells that produce melanin. Melanin is the brownish pigment that gives skin and hair their color. Melanin-producing cells are found in the bottom layer of the epidermis. The epidermis does not have any blood vessels. The lower part of the epidermis receives blood by diffusion from blood vessels of the dermis. Skin is made up of two layers, the epider- mis on top and the dermis below. The tissue below the dermis is called the hy- podermis, but it is not part of the skin. | text | null |
L_0679 | skin | T_3401 | The dermis is the layer of skin directly under the epidermis. It is made of a tough connective tissue. The dermis contains hair follicles, sweat glands, oil glands, and blood vessels ( Figure 1.2). It also holds many nerve endings that give you your sense of touch, pressure, heat, and pain. Do you ever notice how your hair stands up when you are cold or afraid? Tiny muscles in the dermis pull on hair follicles which cause hair to stand up. The resulting little bumps in the skin are commonly called "goosebumps" ( Figure 1.3). | text | null |
L_0679 | skin | T_3402 | Glands and hair follicles open out into the epidermis, but they start in the dermis. Oil glands ( Figure 1.2) release, or secrete an oily substance, called sebum, into the hair follicle. Sebum waterproofs hair and the skin surface to prevent them from drying out. It can also stop the growth of bacteria on the skin. It is odorless, but the breakdown of sebum by bacteria can cause odors. If an oil gland becomes plugged and infected, it develops into a pimple. Up to 85% of teenagers get pimples, which usually go away by adulthood. Frequent washing can help decrease the amount of sebum on the skin. Sweat glands ( Figure 1.2) open to the skin surface through skin pores. They are found all over the body. Evaporation of sweat from the skin surface helps to lower skin temperature. The skin also releases excess water, salts, sugars, and other wastes, such as ammonia and urea, in sweat. The Integumentary System Song can be heard at . Goosebumps are caused by tiny mus- cles in the dermis that pull on hair folli- cles, which causes the hairs to stand up straight. | text | null |
L_0680 | smooth skeletal and cardiac muscles | T_3403 | The muscular system consists of all the muscles in the body. This is the body system that allows us to move. You also depend on many muscles to keep you alive. Your heart, which is mostly muscle, pumps blood around your body. Each muscle in the body is made up of cells called muscle fibers. Muscle fibers are long, thin cells that can do something that other cells cannot dothey are able to get shorter. Shortening of muscle fibers is called contraction. Muscle fibers can contract because they are made of proteins, called actin and myosin, that form long filaments (or fibers). When muscles contract, these protein filaments slide or glide past one another, shortening the length of the cell. When your muscles relax, the length extends back to the previous position. Nearly all movement in the body is the result of muscle contraction. You can control some muscle movements. However, certain muscle movements happen without you thinking about them. Muscles that are under your conscious control are called voluntary muscles. Muscles that are not under your conscious control are called involuntary muscles. Muscle tissue is one of the four types of tissue found in animals. There are three different types of muscle in the body ( Figure 1.1): 1. Skeletal muscle is made up of voluntary muscles, usually attached to the skeleton. Skeletal muscles move the body. They can also contract involuntarily by reflexes. For example, you can choose to move your arm, but your arm would move automatically if you were to burn your finger on a stove top. This voluntary contraction begins with a thought process. A signal from your brain tells your muscles to contract or relax. Quickly contract and relax the muscles in your fingers a few times. Think about how quickly these signals must travel throughout your body to make this happen. 2. Smooth muscle is composed of involuntary muscles found within the walls of organs and structures such as the esophagus, stomach, intestines, and blood vessels. These muscles push materials like food or blood through organs. Unlike skeletal muscle, smooth muscle can never be under your control. 3. Cardiac muscle is also an involuntary muscle, found only in the heart. The cardiac muscle fibers all contract together, generating enough force to push blood throughout the body. What would happen if this muscle was under conscious or voluntary control? There are three types of muscles in the body: cardiac, skeletal, and smooth. | text | null |
L_0682 | sources of water pollution | T_3407 | While to many people clean water may seem limitless and everywhere, to many others this is not so. Water pollution is a serious issue facing hundreds of millions of people world-wide, having harmful effects on the lives of those people. Water is not in unlimited supply and cannot just be made fresh when it is wanted. Water is actually a limited resource, and for many people, fresh, unpolluted water is hard to find. A limited resource is one that we use faster than we can remake it. It is a resource that can be used up. Water pollution happens when contaminants enter water bodies. Contaminants are any substances that harm the health of the environment or humans. Most contaminants enter the water because of humans. Surface water (river or lake) can be exposed to and contaminated by acid rain, storm water runoff, pesticide runoff, and industrial waste. This water is cleaned somewhat by exposure to sunlight, aeration, and microorganisms in the water. Groundwater (private wells and some public water supplies) generally takes longer to become contaminated, but the natural clean- ing process also may take much longer. Groundwater can be contaminated by disease-producing pathogens, careless disposal of hazardous household chemical-containing products, agricultural chemicals, and leaking underground storage tanks. Water pollution can cause harmful effects to ecology and human health. Shown is the pollution in Jakarta, Indonesia. Natural events, like storms, volcanic eruptions and earthquakes can cause major changes in water quality. But human-caused contaminants have a much greater impact on the quality of the water supply. Water is considered polluted either when it does not support a human use, like clean drinking water, or a use for other animals and plants. The overgrowth of algae, known as an algal bloom, can result from the runoff of fertilizer into bodies of water. This excess of nutrients allows the algae to grow beyond control, bring harm to the rest of the ecosystem. The main sources of water pollution can be grouped into two categories: Point source pollution results from the contaminants that enter a waterway or water body through a single site. Examples of this include untreated sewage, wastewater from a sewage treatment plant, and leaking underground tanks. Nonpoint source pollution is contamination that does not come from a single point source. Instead, it happens when there is a buildup of small amounts of contaminants that collect from a large area. Examples of this include fertilizer runoff from many farms flowing into groundwater or streams. | text | null |
L_0688 | taste and smell | T_3422 | The senses of taste and smell are more complicated than many people might think and have a surprisingly large impact on behavior, perception and overall health. Imagine your sense of smell disappearing as you age. Though this doesnt usually happen, it could provide clues about diseases of the nervous system. What about differences in taste? Do all foods taste the same to all people? Are there some foods you would never eat because you dont like the taste? Does this food taste good to other people? Genetic differences in taste could help predict what we eat, how well our metabolism works, and even whether or not were overweight. These two senses actually work together to provide some of the basic sensations of everyday life. | text | null |
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