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L_0407 | reproduction and life stages | T_2344 | Pregnancy is the carrying of one or more offspring from the time of implantation until birth. It is the development of an embryo and fetus from the expectant mothers point of view. | text | null |
L_0407 | reproduction and life stages | T_2345 | The pregnant mother plays a critical role in the development of the embryo and fetus. She must avoid toxic substances such as alcohol, which can damage the developing offspring. She also must provide all the nutrients and other substances needed for normal growth and development. Most nutrients are needed in greater amounts by a pregnant woman because she is literally eating for two people. Thats why its important for a woman to eat plenty of nutritious foods during pregnancy. The pregnant woman in Figure 22.9 is eating a variety of fresh fruits, which provide energy, vitamins, and other nutrients. | text | null |
L_0407 | reproduction and life stages | T_2346 | Near the time of birth, the amniotic sac breaks in a gush of liquid. Labor usually begins within a day of this event. Labor involves contractions of the muscular walls of the uterus. With the mothers help, the contractions eventually push the fetus out of the uterus and through the vagina. Within seconds of birth, the umbilical cord is cut. Without this connection to the placenta, the baby cant exchange gases, so carbon dioxide quickly builds up in the babys blood. This stimulates the babys brain to trigger breathing, and the newborn takes her first breath. | text | null |
L_0407 | reproduction and life stages | T_2347 | For the first year after birth, a baby is referred to as an infant. Childhood begins at the age of two years and continues until puberty. Adolescence begins with puberty and lasts until adulthood. | text | null |
L_0407 | reproduction and life stages | T_2348 | The first year of life after birth is called infancy. During infancy, a baby grows very quickly. The babys length typically doubles and her weight triples by her first birthday. Many other important changes also occur during infancy: The baby starts smiling, usually by about 6 weeks of age (see Figure 22.10). The baby starts noticing people and grabbing toys and other objects The baby teeth start to come in, usually by 6 months of age. The baby begins making babbling sounds. By the end of the first year, the baby may be saying a few words, such as Mama and Dada. The baby learns to sit, crawl, and stand. By the end of the first year, the baby may be starting to walk. | text | null |
L_0407 | reproduction and life stages | T_2349 | Childhood begins after the babys first birthday and continues until puberty. Between 1 and 3 years of age, a child is called a toddler. During the toddler stage, growth is still very rapid, but not as rapid as it was during infancy. Toddlers learn many new words and starts putting them together in simple sentences. Motor skills also develop quickly during the toddler stage. By the age of 3 years, most children can run and climb steps. They can hold crayons and scribble with them. They can also feed themselves, and most can use the toilet. From age 3 until puberty, growth slows down. The body also changes shape. The arms and legs grow longer relative to the trunk. Children continue to develop new motor skills. For example, many young children learn how to ride a tricycle and then a bicycle. Most learn how to play games and sports. By the age of 6 years, children start losing their baby teeth. Permanent teeth come in to replace them. Most children have started school by this age. They typically start learning to read and write around age 6 or 7 (see Figure 22.11). During the later years of childhood, children also start to develop friendships and become less dependent on their parents. | text | null |
L_0407 | reproduction and life stages | T_2350 | Puberty is the stage of life when a child becomes sexually mature. Puberty lasts from about 10 to 16 years of age in girls and from about 12 to 18 years of age in boys. In both girls and boys, puberty begins when the pituitary gland signals the gonads (ovaries or testes) to start secreting sex hormones (estrogen in girls, testosterone in boys). Sex hormones, in turn, cause many other changes to take place. In girls, estrogen causes the following changes to occur: The uterus and ovaries grow. The ovaries start releasing eggs. The menstrual cycle begins. Pubic hair grows. The hips widen and the breasts develop. In boys, testosterone causes these changes to take place: The penis and testes grow. The testes start producing sperm. Pubic and facial hair grow. The shoulders broaden. The voice becomes deeper as the larynx in the throat grows larger (see Figure 22.12). Girls and boys of the same age are similar in height during childhood. In both girls and boys, growth in height and weight is very fast during puberty. But boys grow more quickly that girls do, and their period of rapid growth also lasts longer. In addition, boys generally start puberty later than girls, so they have a longer period of childhood growth. For all these reasons, by the end of puberty, the average height of boys is 10 centimeters (about 4 inches) greater than the average height of girls. | text | null |
L_0407 | reproduction and life stages | T_2351 | Adolescence is the stage of life between the start of puberty and the beginning of adulthood. Adolescence begins with the physical changes of puberty. It also includes many other changes, including mental, emotional, and social changes. During adolescence: Teens develop new thinking abilities. For example, they develop the ability to understand abstract ideas, such as honesty and freedom. Their ability to think logically also improves. They usually get better at problem solving as well. Teens try to establish a sense of identity. They typically become increasingly independent from their parents. Many teens have emotional ups and downs. This is at least partly due to their changing hormone levels. Teens usually start spending more time with their peers, like the girls in Figure 22.13. Adolescents usually spend much more time with their friends and classmates than they do with family members. | text | null |
L_0407 | reproduction and life stages | T_2351 | Adolescence is the stage of life between the start of puberty and the beginning of adulthood. Adolescence begins with the physical changes of puberty. It also includes many other changes, including mental, emotional, and social changes. During adolescence: Teens develop new thinking abilities. For example, they develop the ability to understand abstract ideas, such as honesty and freedom. Their ability to think logically also improves. They usually get better at problem solving as well. Teens try to establish a sense of identity. They typically become increasingly independent from their parents. Many teens have emotional ups and downs. This is at least partly due to their changing hormone levels. Teens usually start spending more time with their peers, like the girls in Figure 22.13. Adolescents usually spend much more time with their friends and classmates than they do with family members. | text | null |
L_0407 | reproduction and life stages | T_2352 | Adulthood doesnt have a definite starting point. Teens may become physically mature by the age 16 years, but they are not adults in a legal sense until they are older. For example, in the U.S., you must be 18 years old to vote or serve in the armed forces. You must be 21 years old before you can take on many legal and financial responsibilities. Once adulthood begins, it can be divided into three stages: early, middle, and late adulthood. | text | null |
L_0407 | reproduction and life stages | T_2353 | Early adulthood refers to the 20s and early 30s. During early adulthood, most people are at their physical peak, and they are usually in good health. Often, they are completing their education and getting established in the workforce. Many people become engaged or marry during this time. | text | null |
L_0407 | reproduction and life stages | T_2354 | Middle adulthood is the period from the mid-30s to the mid-60s. During this stage of life, people start showing signs of aging. Their hair may thin and slowly turn gray. Their skin develops wrinkles. The risk of serious health problems increases. For example, cardiovascular diseases, cancer, and type 2 diabetes become more common in people of middle age. This is also the stage when many people raise a family and strive to attain career goals. | text | null |
L_0407 | reproduction and life stages | T_2355 | Late adulthood begins in the mid-60s and continues until death. This is the stage of life when most people retire from work. This frees up their time for hobbies, grandchildren, or other interests. For example, the man in Figure During late adulthood, the risk of developing diseases such as cardiovascular diseases and cancer continues to rise. Most people also have a decline in strength and stamina. Their senses may start failing, and their reflex time typically increases. Their immune system also doesnt work as well as it used to. As a result, common diseases like the flu may become more serious and even lead to death. The majority of late adults develop arthritis, and as many as one in four develop Alzheimers disease. Despite problems such as these, many people remain healthy and active into their 80s and even 90s. Do you want | text | null |
L_0408 | reproductive system health | T_2356 | A sexually transmitted infection (STI) is a disease that spreads mainly through sexual contact. STIs are caused by pathogens that 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 that some STIs can spread. Some STIs can also spread from a mother to her infant during birth. | text | null |
L_0408 | reproductive system health | T_2357 | STIs are more common in teens and young adults than in older people. One reason is that young people are more likely to engage in risky behaviors. They also may not know how STIs spread. Instead, they may believe myths about STIs, like those in Table 22.1. Knowing the facts is important to prevent the spread of STIs. Myth If you are sexually active with just one person, then you cant get STIs. If you dont have any symptoms, then you dont have an STI. Getting STIs is no big deal, because they can be cured with medicines. Fact The only sure way to avoid getting 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 medicines; others cannot be cured. | text | null |
L_0408 | reproductive system health | T_2358 | A number of STIs are caused by bacteria. Bacterial STIs can usually be cured with antibiotics. However, some people with bacterial STIs may not have symptoms so they fail to get treatment. Left untreated, these infections may damage reproductive organs and lead to an inability to have children. Three bacterial STIs are chlamydia, gonorrhea, and syphilis. Chlamydia is the most common bacterial STI in the U.S. Females are more likely to develop it than males. Symptoms may include burning during urination and a discharge from the vagina or penis. Gonorrhea is another common bacterial STI. Symptoms may include painful urination and a discharge from the vagina or penis. Syphilis is a very serious STI but somewhat less common than chlamydia or gonorrhea. It 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 isnt treated, it can eventually damage the heart, brain, and other organs and even cause death. | text | null |
L_0408 | reproductive system health | T_2359 | Several STIs are caused by viruses. Viral STIs cant be cured with antibiotics. Other drugs may help control the symptoms of viral STIs, but the infections usually last for life. Three viral STIs are genital warts, genital herpes, and AIDS. Genital herpes is a common STI caused by a herpes virus. The virus causes painful blisters on the penis or near the vaginal opening. The blisters generally go away on their own, but they may return repeatedly throughout life. There is no cure for genital herpes, but medicines can help prevent or shorten outbreaks. Acquired Immunodeficiency Syndrome (AIDS) is caused by human immunodeficiency virus (HIV). HIV destroys lymphocytes that normally fight infections. AIDS develops if the number of lymphocytes drops to a very low level. People with AIDS come down with diseasessuch as certain rare cancersthat almost never occur in people with a healthy immune system. Medicines can delay the progression of an HIV infection and may prevent AIDS from developing. Genital warts is an STI caused by human papilloma virus (HPV), which is pictured in Figure 22.15. This is one of the most common STIs in U.S. teens. Genital warts cant be cured, but a vaccine can prevent most HPV infections. The vaccine is recommended for boys and girls starting at 11 or 12 years of age. Its important to prevent HPV infections because they may lead to cancer later in life. | text | null |
L_0408 | reproductive system health | T_2360 | Other reproductive system disorders include injuries and noninfectious diseases. These are different in males and females. | text | null |
L_0408 | reproductive system health | T_2361 | Most common disorders of the male reproductive system involve the testes. They include injuries and cancer. Injuries to the testes are very common. In teens, such injuries occur most often while playing sports. Injuries to the testes are likely to be very painful and cause bruising and swelling. However, they generally subside fairly quickly. Cancer of the testes is most common in males aged 15 to 35. It occurs when cells in the testes grow out of control and form a tumor. If found early, cancer of the testes usually can be cured with surgery. | text | null |
L_0408 | reproductive system health | T_2362 | Disorders of the female reproductive system may involve the vagina, uterus, or ovaries. They may also affect the breasts. Vaginitis is a very common disorder. Symptoms include redness and itching of the vagina. It may be caused by soap or bubble bath. Another possible cause is a yeast infection. Yeast normally grow in the vagina. If they multiple too quickly, they may cause irritation. A yeast infection can be treated with medication. Cysts may develop in the ovaries. A cyst is a sac filled with fluid or other material. Ovarian cysts are usually harmless and often disappear on their own. However, some cysts may be painful and require surgery. Many females experience abdominal cramps during menstruation. This is usually normal and not a cause for concern. Exercise, heat, or medication may help relieve the pain. In severe cases, prescription medicine may be needed. Breast cancer is the most common type of cancer in females. It occurs when cells in the breast grow out of control and form a tumor. Breast cancer is rare in teens but becomes more common as females get older. Regular screening is recommended for most women starting around age 40. If found early, breast cancer usually can be cured with surgery. | text | null |
L_0408 | reproductive system health | T_2363 | Maintaining overall good health will help keep your reproductive system healthy. You should eat right, get regular exercise, and follow other healthy lifestyle behaviors. In addition, the following practices will help keep the reproductive system healthy: Keep the genitals clean. A daily shower or bath is all thats needed. Avoid harsh soaps or other personal hygiene products that may be irritating. Avoid risky behaviors. This includes contact with blood or dirty needles as well as sexual activity. If you are a girl and use tampons, be sure to change them every 4 to 6 hours. This will reduce your risk of toxic shock syndrome. This is a very dangerous condition that may occur if tampons are left in too long. If you are a boy, wear a protective cup if you play a contact sport. This will help protect the testes from injury. You should also learn how to check yourself for testicular cancer (see Figure 22.16). You can learn how by watching this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0409 | what is ecology | T_2364 | Organisms are individual living things. They range from microscopic bacteria to gigantic blue whales (see Figure must be obtained from the environment. Biotic factors are all of the living or once-living aspects of the environment. They include all the organisms that live there as well as the remains of dead organisms. Abiotic factors are all of the aspects of the environment that have never been alive. They include factors such as sunlight, minerals in soil, temperature, and moisture. | text | null |
L_0409 | what is ecology | T_2365 | Ecologists study organisms and environments at several different levels, from the individual to the biosphere. The levels are depicted in Figure 23.2 and described below. For a video introduction to the levels of organization in ecology, click on this link: . MEDIA Click image to the left or use the URL below. URL: An individual is an organism, or single living thing. A population is a group of individuals of the same species that live in the same area. Members of the same population generally interact with each other. A community is made up of all the populations of all the species that live in the same area. Populations in a community also generally interact with each other. | text | null |
L_0410 | populations | T_2366 | Population size is the number of individuals in a population. Population size influences the chances of a species surviving or going extinct. If a species populations become very small, the species may be at risk of going extinct. | text | null |
L_0410 | populations | T_2367 | Another sign of a species state of health is the density of its populations. Population density is the average number of individuals in a population for a given area. Density is a measure of how crowded or spread out the individuals in a population are on average. For example, a population of 100 deer that live in an area of 10 square kilometers has a population density of 10 deer per square kilometer. Population density is an average measure. Often, individuals in a population are not spread out evenly. Instead, they may live in clumps or some other pattern. How individuals in a population are distributed, or spread throughout their area, is called population distribution. You can see different patterns of population distribution in Figure 23.3. Different patterns characterize different species and types of environments, as you can read in the figure. | text | null |
L_0410 | populations | T_2368 | Whether its populations are growing or shrinking in size may be another indicator of a species health. Individuals may be added to a population through births and the migration of individuals into the population. Individuals may be lost from a population through deaths and the migration of individuals out of the population. The population growth rate is how quickly a population changes in size over time. The rate of growth of a population may be positive or negative. A positive growth rate means that the population is increasing in size because more people are being added than lost. A negative growth rate means that the population is decreasing in size because more people are being lost than added. Populations may show different patterns of growth. The growth pattern depends partly on the conditions under which a population lives. Two common growth patterns are exponential growth and logistic growth. Both are represented in Figure 23.4. With exponential growth, the population starts out growing slowly. As population size increases, the growth rate also increases. The larger the population becomes, the more quickly it grows. This type of growth generally occurs only when a population is living under ideal conditions. However, it cant continue for very long. With logistic growth, the population starts out growing slowly, and then the rate of growth increasesbut only to a point. The rate of growth tapers off as the population size approaches its carrying capacity. Carrying capacity is the largest population size that can be supported in an area without harming the environment. This type of growth characterizes many populations. | text | null |
L_0410 | populations | T_2369 | Another way of describing a population is its age-sex structure. This refers to the numbers of individuals of each sex and age in the population. The age-sex structure of a population may influence the population growth rate. This is because only individuals of certain ages are able to reproduce, and because individuals of certain ages may be more likely to die. For example, if there are many individuals of reproductive age, there are likely to be many births, causing the population to grow rapidly. The age-sex structure of a population is often represented with a special bar graph called a population pyramid. You can see an example of a population pyramid in Figure 23.5. The graph in the figure actually has a pyramid shape because the bars become narrower from younger to older ages. However, this is not always the case. In some populations, for example, there may be more people at older than younger ages, resulting in a top-heavy population pyramid. Learn more about population pyramids and what you can learn from them, watch this TED video: http://w MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0410 | populations | T_2370 | Human beings have been called the most successful weed species on Earth. Like garden weeds, populations of human beings grow quickly and disperse rapidly. Human beings have colonized almost every terrestrial part of the planet. Overall, the human population has had a pattern of exponential growth, as you can see in Figure 23.6. The early human population grew very slowly. However, as the population grew larger, it started to grow more rapidly. | text | null |
L_0410 | populations | T_2370 | Human beings have been called the most successful weed species on Earth. Like garden weeds, populations of human beings grow quickly and disperse rapidly. Human beings have colonized almost every terrestrial part of the planet. Overall, the human population has had a pattern of exponential growth, as you can see in Figure 23.6. The early human population grew very slowly. However, as the population grew larger, it started to grow more rapidly. | text | null |
L_0410 | populations | T_2371 | The earliest members of the human species evolved around 200,000 years ago in Africa. Early humans lived in small populations of nomadic hunters and gatherers. Human beings remained in Africa until about 40,000 years ago. After that, they spread throughout Europe, Asia, and Australia. By 10,000 years ago, the first human beings colonized the Americas. During this long period of time, the total number of human beings increased very slowly. Birth rates were fairly high but so were death rates, producing low rates of population growth. Human beings invented agriculture about 10,000 years ago. This provided a bigger, more dependable food supply. It also allowed people to settle down in villages and cities for the first time. Birth rates went up because there was more food and settled life had other advantages. Death rates also rose because of crowded living conditions and diseases that spread from domestic animals. Because the higher birth rates were matched by higher death rates, the human population continued to grow very slowly. | text | null |
L_0410 | populations | T_2372 | Major changes in the human population first began in the 1700s. These changes occurred mainly in Europe, North America, and a few other places that became industrialized. First death rates fell. Then, somewhat later, birth rates also fell. These changes in death and birth rates affected the rate of population growth and are referred to as the demographic transition. The graph in Figure 23.7 shows the stages in which the demographic transition occurred. You can learn more about the stages by watching this video: http://education-portal.com/academy/lesson/what-is-d In Stage 1, both birth and death rates were high so population growth was slow. In Stage 2, death rates fell while birth rates remained high. Why did death rates fall? There were several reasons, including new scientific knowledge of the causes of disease. Water supplies were cleaned up and sewage was disposed of more safely. Better farming techniques and machines increased the food supply and the distribution of food. For all these reasons, death rates fell, especially in children. Birth rates, on the other hand, remained high. This resulted in faster population growth. Before long, birth rates also started to fall. People started having fewer children because large families became too expensive. For example, with better farming machines, farm families no longer needed as many children to work in the fields. Laws were also passed that required children to go to school. They could no longer work and help support the family. Having many children became too costly. Eventually, birth rates fell to match death rates (Stage 4). As a result, population growth slowed down. | text | null |
L_0410 | populations | T_2373 | Just as they did in Europe and North America, death rates have fallen throughout the world. No country today remains in Stage 1 of the demographic transition. However, birth rates are still high in many of the poorest countries of the world. These populations seem to be stuck in Stage 2 or 3 of the demographic transition. They have high population growth rates because low death rates are not matched by equally low birth rates. Whether these populations will ever enter Stage 4 and attain very low rates of population growth is uncertain. | text | null |
L_0410 | populations | T_2374 | As of 2014, there were more than 7 billion human beings on planet Earth. That number is increasing rapidly. More than 200,000 people are added to the human population each day! At this rate, the human population will pass 9 billion by 2050. Many experts think that the human population has reached its carrying capacity. It has already harmed the environ- ment. An even larger human population may cause severe environmental problems. It could also lead to devastating outbreaks of disease, starvation, and war. To solve these problems, two approaches may be needed: Slow down human population growth so there are fewer people. Distribute Earths resources more fairly so that everyone has enough. Hopefully, we will act before its too late. Otherwise, the planet may be ruined for future generations of human beings and other species. | text | null |
L_0413 | biomes | T_2389 | Terrestrial biomes are land-based biomes. They range from arctic tundra to tropical rainforests. Figure 23.18 shows the locations of the worlds major terrestrial biomes. | text | null |
L_0413 | biomes | T_2390 | Plants are the primary producers in terrestrial biomes. They make food for themselves and other organisms by photosynthesis. The major plants in a given biome, in turn, help determine the types of animals and other organisms that can live there. Which plants grow in a given biome depends mainly on climate. Climate is the average weather in a place over a long period of time. The major climatic factors affecting plant growth are temperature and moisture. | text | null |
L_0413 | biomes | T_2391 | You can read about three different terrestrial biomes in Figure 23.19: tropical rainforest, temperate grassland, and tundra. You can learn more about these and other terrestrial biomes by watching this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0413 | biomes | T_2392 | Aquatic biomes are water-based biomes. They include both freshwater biomes, such as rivers and lakes, and marine biomes, which are salt-water biomes in the ocean. The primary producers in most aquatic biomes are phytoplankton. Phytoplankton consist of microscopic bacteria and tiny algae that make food by photosynthesis. Unlike terrestrial biomes, which are determined mainly by temperature and moisture, aquatic biomes are determined mainly by sunlight and dissolved substances in the water. These factors, in turn, depend mainly on depth of water and distance from shore. | text | null |
L_0413 | biomes | T_2393 | Only the top 200 meters or so of water receive enough sunlight for photosynthesis. This part of the water is called the photic zone. Below 200 meters, there is too little sunlight for photosynthesis to take place. This part of the water is called the aphotic zone. In this zone, food must come from other sources. It may be made by chemosynthesis, in which microorganisms use energy in chemicals instead of sunlight to make food. Or, food may drift down from the water above. | text | null |
L_0413 | biomes | T_2394 | In addition to sunlight, aquatic producers also need dissolved oxygen and nutrients. Water near the surface generally contains more dissolved oxygen than deeper water. Many nutrients enter the water from the land. Therefore, water nearer shore usually contains more dissolved nutrients than water farther from shore. | text | null |
L_0413 | biomes | T_2395 | A lake is an example of a freshwater biome. Water in a lake generally forms three different zones based on water depth and distance from shore. The shallow water near the shore is called the littoral zone. It has diverse community of organisms. There is adequate light for photosynthesis and plenty of dissolved oxygen and nutrients. Producers include algae and aquatic plants (see Figure 23.20). Animals in this zone may include insects, crustaceans, fish, and turtles. The top layer of water farther from shore is called the limnetic zone. There is enough light for photosynthesis and plenty of dissolved oxygen. However, dissolved nutrients tend not to be as plentiful as they are in the littoral zone. Producers here are mainly phytoplankton. A variety of zooplankton and fish also occupy this zone. The deeper water of a lake makes up the profundal zone. There isnt enough light for photosynthesis in this zone, so most organisms here eat dead organisms that drift down from the water above. Organisms in the profundal zone may include clams, snails, and some species of fish. | text | null |
L_0413 | biomes | T_2396 | Zones in the oceans include the intertidal, pelagic, and benthic zones. The types of organisms found in these ocean zones are also determined by such factors as depth of water and distance from shore, among other factors. One of the most familiar ocean zones is the intertidal zone. This is the narrow strip along a coastline that is covered by water at high tide and exposed to air at low tide. You can see an example of an intertidal zone in Figure 23.21. There are plenty of nutrients and sunlight in the intertidal zone. Producers here include phytoplankton and algae. Other organisms include barnacles, snails, crabs, and mussels. They must have adaptations for the constantly changing conditions in this zone. Other ocean zones are farther from shore in the open ocean. All the water in the open ocean is called the pelagic zone. It is further divided by depth: The top 200 meters of water is the photic zone. Producers here include seaweeds and phytoplankton. Other organisms are plentiful. They include zooplankton and animals such as fish, whales, and dolphins. | text | null |
L_0413 | biomes | T_2396 | Zones in the oceans include the intertidal, pelagic, and benthic zones. The types of organisms found in these ocean zones are also determined by such factors as depth of water and distance from shore, among other factors. One of the most familiar ocean zones is the intertidal zone. This is the narrow strip along a coastline that is covered by water at high tide and exposed to air at low tide. You can see an example of an intertidal zone in Figure 23.21. There are plenty of nutrients and sunlight in the intertidal zone. Producers here include phytoplankton and algae. Other organisms include barnacles, snails, crabs, and mussels. They must have adaptations for the constantly changing conditions in this zone. Other ocean zones are farther from shore in the open ocean. All the water in the open ocean is called the pelagic zone. It is further divided by depth: The top 200 meters of water is the photic zone. Producers here include seaweeds and phytoplankton. Other organisms are plentiful. They include zooplankton and animals such as fish, whales, and dolphins. | text | null |
L_0415 | cycles of matter | T_2407 | The chemical elements and water that are needed by living things keep recycling on Earth. They pass back and forth through biotic and abiotic components of ecosystems. Thats why their cycles are called biogeochemical cycles. For example, a chemical element or water might move from organisms (bio) to the atmosphere or ocean (geo) and back to organisms again. Elements or water may be held for various periods of time in different parts of a biogeochemical cycle. An exchange pool is part of a cycle that holds a substance for a short period of time. For example, the atmosphere is an exchange pool for water. It usually holds water (as water vapor) for just a few days. A reservoir is part of a cycle that holds a substance for a long period of time. For example, the ocean is a reservoir for water. It may hold water for thousands of years. The rest of this lesson describes three biogeochemical cycles: water cycle, carbon cycle, and nitrogen cycle. | text | null |
L_0415 | cycles of matter | T_2408 | Water is an extremely important aspect of every ecosystem. Life cant exist without water. Most organisms contain a large amount of water, and many live in water. Therefore, the water cycle is essential to life on Earth. Water on Earth is billions of years old. However, individual water molecules keep moving through the water cycle. The water cycle is a global cycle. It takes place on, above, and below Earths surface, as shown in Figure 24.7. During the water cycle, water occurs in three different states: gas (water vapor), liquid (water), and solid (ice). Many processes are involved as water changes state to move through the cycle. Watch this video for an excellent visual introduction to the water cycle: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0415 | cycles of matter | T_2409 | Water changes to a gas by three different processes called evaporation, sublimation, and transpiration. Evaporation takes place when water on Earths surface changes to water vapor. The sun heats the water and gives water molecules enough energy to escape into the atmosphere. Most evaporation occurs from the surface of the ocean. Sublimation takes place when snow and ice on Earths surface change directly to water vapor without first melting to form liquid water. This also happens because of heat from the sun. Transpiration takes place when plants release water vapor through pores in their leaves called stomata. | text | null |
L_0415 | cycles of matter | T_2410 | Rising air currents carry water vapor into the atmosphere. As the water vapor rises in the atmosphere, it cools and condenses. Condensation is the process in which water vapor changes to tiny droplets of liquid water. The water droplets may form clouds. If the droplets get big enough, they fall as precipitation. Precipitation is any form of water that falls from the atmosphere. It includes rain, snow, sleet, hail, and freezing rain. Most precipitation falls into the ocean. Eventually, this water evaporates again and repeats the water cycle. Some frozen precipitation becomes part of ice caps and glaciers. These masses of ice can store frozen water for hundreds of years or even longer. Condensation may also form fog or dew. Some living things, like the lizard in Figure 24.8, depend directly on these sources of liquid water. | text | null |
L_0415 | cycles of matter | T_2411 | Precipitation that falls on land may flow over the surface of the ground. This water is called runoff. It may eventually flow into a body of water. Some precipitation that falls on land soaks into the ground. This water becomes groundwater. Groundwater may seep out of the ground at a spring or into a body of water such as the ocean. Some groundwater is taken up by plant roots. Some may flow deeper underground to an aquifer. An aquifer is an underground layer of rock that stores water. Water may be stored in an aquifer for thousands of years. | text | null |
L_0415 | cycles of matter | T_2412 | The element carbon is the basis of all life on Earth. Biochemical compounds consist of chains of carbon atoms and just a few other elements. Like water, carbon is constantly recycled through the biotic and abiotic factors of ecosystems. The carbon cycle includes carbon in sedimentary rocks and fossil fuels under the ground, the ocean, the atmosphere, and living things. The diagram in Figure 24.9 represents the carbon cycle. It shows some of the ways that carbon moves between the different parts of the cycle. You can see an animated carbon cycle at this link: http://commons.w | text | null |
L_0415 | cycles of matter | T_2413 | Major reservoirs of carbon include sedimentary rocks, fossil fuels, and the ocean. Sediments from dead organisms may form carbon-containing sedimentary rocks. Alternatively, the sediments may form carbon-rich fossil fuels, which include oil, natural gas, and coal. Carbon can be stored in these reservoirs for millions of years. However, if fossil fuels are extracted and burned, the stored carbon enters the atmosphere as carbon dioxide. Natural processes, such as volcanic eruptions, can also release underground carbon from rocks into the atmosphere. Water erosion by runoff, rivers, and streams dissolves carbon in rocks and carries it to the ocean. Ocean water near the surface dissolves carbon dioxide from the atmosphere. Dissolved carbon may be stored in the deep ocean for thousands of years. | text | null |
L_0415 | cycles of matter | T_2414 | Major exchange pools of carbon include organisms and the atmosphere. Carbon cycles more quickly between these components of the carbon cycle. Photosynthesis by plants and other producers removes carbon dioxide from the atmosphere to make organic compounds for living things. Cellular respiration by living things releases carbon into the atmosphere or ocean as carbon dioxide. Decomposition of dead organisms and organic wastes releases carbon back to the atmosphere, soil, or ocean. | text | null |
L_0415 | cycles of matter | T_2415 | Nitrogen is another common element found in living things. It is needed to form both proteins and nucleic acids such as DNA. Nitrogen gas makes up 78 percent of Earths atmosphere. In the nitrogen cycle, nitrogen flows back and forth between the atmosphere and living things. You can see how it happens in Figure 24.10. Several different types of bacteria play major roles in the cycle. Animals get nitrogen by eating plants or other organisms that eat plants. Where do plants get nitrogen? They cant use nitrogen gas in the air. The only form of nitrogen that plants can use is in chemical compounds called nitrates. Plants absorb nitrates through their roots. This is called assimilation. Most of the nitrates are produced by bacteria that live in soil or in the roots of plants called legumes. Nitrogen-fixing bacteria change nitrogen gas from the atmosphere to nitrates in soil. When organisms die and decompose, their nitrogen is returned to the soil as ammonium ions. Nitrifying bacteria change some of the ammonium ions into nitrates. The other ammonium ions are changed into nitrogen gas by denitrifying bacteria. | text | null |
L_0417 | air pollution | T_2421 | The major cause of outdoor air pollution is the burning of fossil fuels. Fossil fuels are burned in power plants, factories, motor vehicles, and home heating systems. Ranching and using chemicals such as fertilizers also cause outdoor air pollution. Erosion of soil in farm fields, mining activities, and construction sites adds dust particles to the air as well. Some specific outdoor air pollutants are described in Table 25.1. Air Pollutant Sulfur oxides Nitrogen oxides Carbon monoxide Carbon dioxide Particles (dust, smoke) Mercury Smog Ground-level ozone Source coal burning motor vehicle exhaust motor vehicle exhaust all fossil fuel burning wood and coal burning coal burning coal burning motor vehicle exhaust Problem acid rain acid rain poisoning global climate change respiratory problems nerve poisoning respiratory problems respiratory problems | text | null |
L_0417 | air pollution | T_2422 | Outdoor air pollution causes serious human health problems. For example, pollutants in the air are major contributors to respiratory and cardiovascular diseases. Air pollution may trigger asthma attacks and heart attacks in people with underlying health problems. In fact, more people die each year from air pollution than automobile accidents. | text | null |
L_0417 | air pollution | T_2423 | Air pollution may also cause acid rain. This is rain that is more acidic (has a lower pH) than normal rain. Acids form in the atmosphere when nitrogen and sulfur oxides mix with water in air. Nitrogen and sulfur oxides come mainly from motor vehicle exhaust and coal burning. If acid rain falls into lakes, it lowers the pH of the water and may kill aquatic organisms. If it falls on the ground, it may damage soil and soil organisms. If it falls on plants, it may make them sick or even kill them. Acid rain also damages stone buildings, bridges, and statues, like the one in Figure 25.1. | text | null |
L_0417 | air pollution | T_2424 | Another major problem caused by air pollution is global climate change. Gases such as carbon dioxide from the burning of fossil fuels increase the greenhouse effect and raise Earths temperature. The greenhouse effect is a natural feature of Earths atmosphere. It occurs when certain gases in the atmosphere, including carbon dioxide, radiate the suns heat back down to Earths surface. Figure 25.2 shows how this happens. Without greenhouse gases in the atmosphere, the heat would escape into space. The natural greenhouse effect of Earths atmosphere keeps the planets temperature within a range that can support life. The rise in greenhouse gases due to human actions is too much of a good thing. It increases the greenhouse effect and causes Earths average temperature to rise. Rising global temperatures, in turn, are melting polar ice caps and glaciers. Figure 25.3 shows how much smaller the Arctic ice cap was in 2012 than it was in 1984. With more liquid water on Earths surface, sea levels are rising. Adding more heat energy to Earths atmosphere also causes more extreme weather and changes in precipitation patterns. Global warming is already causing food and water shortages and species extinctions. These problems will only grow worse unless steps are taken to curb greenhouse gases and global climate change. | text | null |
L_0417 | air pollution | T_2424 | Another major problem caused by air pollution is global climate change. Gases such as carbon dioxide from the burning of fossil fuels increase the greenhouse effect and raise Earths temperature. The greenhouse effect is a natural feature of Earths atmosphere. It occurs when certain gases in the atmosphere, including carbon dioxide, radiate the suns heat back down to Earths surface. Figure 25.2 shows how this happens. Without greenhouse gases in the atmosphere, the heat would escape into space. The natural greenhouse effect of Earths atmosphere keeps the planets temperature within a range that can support life. The rise in greenhouse gases due to human actions is too much of a good thing. It increases the greenhouse effect and causes Earths average temperature to rise. Rising global temperatures, in turn, are melting polar ice caps and glaciers. Figure 25.3 shows how much smaller the Arctic ice cap was in 2012 than it was in 1984. With more liquid water on Earths surface, sea levels are rising. Adding more heat energy to Earths atmosphere also causes more extreme weather and changes in precipitation patterns. Global warming is already causing food and water shortages and species extinctions. These problems will only grow worse unless steps are taken to curb greenhouse gases and global climate change. | text | null |
L_0417 | air pollution | T_2425 | You may be able to avoid some of the health effects of outdoor air pollution by staying indoors on high-pollution days. However, some indoor air is just as polluted as outdoor air. | text | null |
L_0417 | air pollution | T_2426 | One source of indoor air pollution is radon gas. Radon is a radioactive gas that may seep into buildings from rocks underground. Exposure to radon gas may cause lung cancer. Another potential poison in indoor air is carbon monoxide. It may be released by faulty or poorly vented furnaces or other fuel-burning appliances. Indoor furniture, carpets, and paints may release toxic compounds into the air as well. Other possible sources of indoor air pollution include dust, mold, and pet dander. | text | null |
L_0417 | air pollution | T_2427 | Its easier to control the quality of indoor air than outdoor air. Steps home owners can take to improve indoor air quality include: keeping the home clean so it is as free as possible from dust, mold, and pet dander. choosing indoor furniture, flooring, and paints that are low in toxic compounds such as VOCs (volatile organic compounds). making sure that fuel-burning appliances are working correctly and venting properly. installing carbon monoxide alarms like the one in Figure 25.4 at every level of the home. | text | null |
L_0418 | water pollution | T_2428 | Water pollution has many causes. One of the biggest causes is fertilizer in runoff. Runoff dissolves fertilizer as it flows over farm fields, lawns, and golf courses. It carries the dissolved fertilizer into bodies of water. More dissolved fertilizer may enter a body of water at the mouth of a river, but there is generally no single point where this type of pollution enters the water. Thats why this type of water pollution is called nonpoint-source pollution. | text | null |
L_0418 | water pollution | T_2429 | When fertilizer ends up in bodies of water, the added nutrients cause excessive growth of algae. This is called an algal bloom. You can see one in Figure 25.5. The algae out-compete other water organisms. They may make the water unfit for human consumption or recreation. | text | null |
L_0418 | water pollution | T_2430 | Eventually, the algae in an algal bloom die and decompose. Their decomposition uses up oxygen in the water so that the water becomes hypoxic (without oxygen). This has occurred in many bodies of fresh water and large areas of the ocean, creating dead zones. Dead zones are areas where the hypoxic water cant support life. A very large dead zone exists in the Gulf of Mexico (see Figure 25.6). Nutrients carried into the Gulf by the Mississippi River caused this dead zone. Cutting down on the use of chemical fertilizers is one way to prevent dead zones in bodies of water. Preserving wetlands is also important. Wetlands are habitats such as swamps, marshes, and bogs where the ground is soggy or covered with water much of the year. Wetlands slow down and filter runoff before it reaches bodies of water. Wetlands also provide breeding grounds for many different species of organisms. | text | null |
L_0418 | water pollution | T_2431 | Unlike runoff, which enters bodies of water everywhere, some sources of pollution enter the water at a single point. This type of water pollution is called point-source pollution. | text | null |
L_0418 | water pollution | T_2432 | An example of point-source pollution is the release of pollution into a body of water through a pipe from a factory or sewage treatment plant. Waste water from a factory might contain dangerous chemicals such as strong acids, mercury, or lead. Water from a sewage treatment plant might contain untreated or partially treated sewage. Such pollution can make water dangerous for drinking or other uses. You can learn more about the problem of sewage contaminating the water in U.S. coastal communities by watching this video: MEDIA Click image to the left or use the URL below. URL: In poor nations, many people have no choice but to drink water from polluted sources. Drinking sewage-contaminated water causes waterborne diseases, due to pathogens such as protozoa, viruses, or bacteria. Most waterborne diseases cause diarrhea. | text | null |
L_0418 | water pollution | T_2433 | If heated water is released into a body of water, it may cause thermal pollution. Thermal pollution is a reduction in the quality of water because of an increase in water temperature. A common cause of thermal pollution is the use of water as a coolant by power plants and factories. This water is heated and then returned to the natural environment at a higher temperature. Warm water cant hold as much dissolved oxygen as cool water, so an increase in the temperature of water decreases the amount of oxygen it contains. Fish and other organisms adapted to a particular temperature range and oxygen concentration may be killed by the change in water temperature. | text | null |
L_0418 | water pollution | T_2434 | The ocean is huge but even this body of water is becoming seriously polluted. Climate change also affects the quality of ocean water for living things. | text | null |
L_0418 | water pollution | T_2435 | One way that the ocean is becoming polluted is with trash, mainly plastics. The waste comes from shipping accidents, landfill erosion, and the dumping of trash. Plastics may take hundreds or even thousands of years to break down. In the meantime, the waste can be very dangerous to aquatic organisms. Some organisms may swallow plastic bags, for example, and others may be strangled by plastic six-pack rings. You can see some of the trash that routinely washes up on coastlines in Figure 25.7. There are five massive garbage patches floating on the Pacific Ocean. Watch this video to learn more about them: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0418 | water pollution | T_2436 | Ocean water normally dissolves some of the carbon dioxide in the atmosphere. The burning of fossil fuels has increased the amount of carbon dioxide in the atmosphere. As a result, ocean water is also dissolving more carbon dioxide. When carbon dioxide dissolves in water, it forms a weak acid. With higher levels of dissolved carbon dioxide in ocean water, the water becomes more acidic. This process is called ocean acidification. Ocean acidification can kill some aquatic organisms, including corals and shellfish. It may make it more difficult for other aquatic organisms to reproduce. Both effects of acidification interfere with marine food webs, threatening the survival of many aquatic organisms. | text | null |
L_0419 | natural resources | T_2437 | From a human point of view, natural resources can be classified as either renewable or nonrenewable. | text | null |
L_0419 | natural resources | T_2438 | Renewable resources are natural resources that are remade by natural processes as quickly as people use them. Examples of renewable resources include sunlight and wind. They are in no danger of being used up. Metals and some other minerals are considered renewable as well because they are not destroyed when they are used. Instead, they can be recycled and used over and over again. Living things are also renewable resources. They can reproduce to replace themselves. However, living things can be over-used or misused to the point of extinction. For example, over-fishing has caused some of the best fishing spots in the ocean to be nearly depleted, threatening entire fish species with extinction. To be truly renewable, living things must be used wisely. They must be used in a way that meets the needs of the present generation but also preserves them for future generations. Using resources in this way is called sustainable use. | text | null |
L_0419 | natural resources | T_2439 | Nonrenewable resources are natural resources that cant be remade or else take too long to remake to keep up with human use. Examples of nonrenewable resources are coal, oil, and natural gas, all of which are fossil fuels. Fossil fuels form from the remains of plants and animals over hundreds of millions of years. We are using them up far faster than they can be replaced. At current rates of use, oil and natural gas will be used up in just a few decades, and coal will be used up in a couple of centuries. Uranium is another nonrenewable resource. It is used to produce nuclear power. Uranium is a naturally occurring chemical element that cant be remade. It will run out sooner or later if nuclear energy continues to be used. Soil is a very important natural resource. Plants need soil to grow, and plants are the basis of terrestrial ecosystems. Theoretically, soil can be remade. However, it takes millions of years for soil to form, so from a human point of view, it is a nonrenewable resource. Soil can be misused and eroded (see Figure 25.9). It must be used wisely to preserve it for the future. This means taking steps to avoid soil erosion and contamination of soil by toxins such as oil spills. | text | null |
L_0419 | natural resources | T_2440 | Some of the resources we depend on the most are energy resources. Whether its powering our lights and computers, heating our homes, or providing energy for cars and other vehicles, its hard to imagine what our lives would be like without a constant supply of energy. | text | null |
L_0419 | natural resources | T_2441 | Fossil fuels and nuclear energy are nonrenewable energy resources. People worldwide depend far more on these energy sources than any others. Figure 25.10 shows the worldwide consumption of energy sources by type in 2010. Nonrenewable energy sources accounted for 83 percent of the total energy used. Fossil fuels and the uranium needed for nuclear power will soon be used up if we continue to consume them at these rates. Using fossil fuels and nuclear energy creates other problems as well. The burning of fossil fuels releases carbon dioxide into the atmosphere. This is one of the major greenhouse gases causing global climate change. Nuclear power creates another set of problems, including the disposal of radioactive waste. | text | null |
L_0419 | natural resources | T_2442 | Switching to renewable energy sources solves many of the problems associated with nonrenewable energy. While it may be expensive to develop renewable energy sources, they are clearly the way of the future. Figure 25.11 represents three different renewable energy sources: solar, wind, and biomass energy. The three types are described below. You can watch Bill Nyes introduction to renewable energy resources in this video: MEDIA Click image to the left or use the URL below. URL: Solar energy is energy provided by sunlight. Solar cells can turn sunlight into electricity. The energy in sunlight is virtually limitless and free and creates no pollution to use. Wind energy is energy provided by the blowing wind. Wind turbines, like those in Figure 25.11, can turn wind energy into electricity. The wind blows because of differences in heating of Earths atmosphere by the sun. There will never be a shortage of wind. Biomass energy is energy provided by burning or decomposing organic matter. For example, when garbage decomposes in a landfill, it releases methane gas. This gas can be captured and burned to produce electricity. Crops such as corn can also be converted into a liquid fuel and added to gasoline. Although biomass is renewable, burning it produces carbon dioxide, similar to fossil fuels. | text | null |
L_0419 | natural resources | T_2443 | Especially when it comes to nonrenewable resources, conserving natural resources is important. Using less of them means that they will last longer. It also means they will impact the environment less. Everyone can help make a difference. There are three basic ways that all of us can conserve natural resources. They are referred to as the three Rs: reduce, reuse, and recycle. | text | null |
L_0419 | natural resources | T_2444 | Reducing the amount of natural resources you use is the best way to conserve resources. It takes energy to make new items, and even reusing or recycling items takes energy. You can reduce the amount of natural resources you use by not using the resources in the first place. Often, this involves just being less wasteful. Follow these tips to reduce your use of natural resources: Walk, bike, or use public transit instead of driving. If you must drive, a fuel-efficient vehicle will reduce energy use. Plan ahead to avoid making extra trips. Dont buy more than you need. For example, dont buy more fresh food than you can use without it going to waste. You will not only reduce your use of food. You will also reduce your use of energy resources. It takes a lot of energy to grow, process, and ship many of the foods we buy. When you shop, keep packaging in mind. "Precycle" by buying items with the least amount of wasted packaging. Use energy-efficient appliances and LED light bulbs. Also, turn off appliances and lights when you arent using them. Both steps will reduce the amount of energy resources you use. Keep the thermostat set low in the winter and high in the summer (see Figure 25.12). Instead of turning up the heat in cold weather, put on an extra layer of clothes to save energy resources. Open windows and use fans in hot weather rather than turning on the air conditioning. | text | null |
L_0419 | natural resources | T_2445 | Reusing means to use an item again rather than throwing it away and replacing it. Items can be reused for the same purpose or for a different purpose. Generally, it takes less energy to reuse an item than to recycle it, so choose this option over recycling when you can. Here are some specific tips for reusing natural resources: Consider mending or repairing worn or broken items rather than throwing them out and replacing them. Shop with reuse in mind. You can find great buys at flea markets and resale shops. You may be able to get free items online at free-cycle sites. Youll save money as well as natural resources. You can also sell (or give away) your own reusable items. Reuse cloth shopping bags. Instead of getting new plastic or paper bags for your purchases each time you shop, take your own reusable bag to the store each time. Even little steps can add up and help save natural resources. For example, unwrap gifts carefully and youll be able to reuse the gift wrap on a package for someone else. You can also reuse writing paper that has only been used on one side. Its great for notes and shopping lists. | text | null |
L_0419 | natural resources | T_2446 | If an item can no longer be used or reused, try to recycle it. Recycling means taking a used item, breaking it down, and reusing the components. It generally takes less energy to recycle materials than obtain new ones. Recycling also keeps waste out of landfills. Some of the items that can be recycled include: glass, paper, cardboard, plastic, aluminum, iron, steel, batteries, electronics, tires, and concrete. You can learn how some of these materials are recycled by watching this video: . MEDIA Click image to the left or use the URL below. URL: Even kitchen scraps and garden wastes can be recycled. They can be tossed into a compost bin, like the one in Figure 25.13. The recycled compost gradually breaks down to form rich humus that can be added to lawns and gardens to improve the soil. Encourage your family to recycle if they dont already. Even if you dont have curbside recycling where you live, there are likely to be recycling drop boxes or centers available for recycling many items. If you have recycling bins at school, be sure to use them. If not, raise the issue with your teacher or principal. You can also write a letter to the editor of your local newspaper encouraging everyone in your community to recycle. | text | null |
L_0424 | photosynthesis | T_2492 | Chemical energy that organisms need comes from food. The nearly universal food for life is the sugar glucose. Glucose is a simple carbohydrate with the chemical formula C6 H12 O6 . The glucose molecule stores chemical energy in a concentrated, stable form. In your body, glucose is the form of energy that is carried in your blood and taken up by each of your trillions of cells. | text | null |
L_0424 | photosynthesis | T_2493 | What is the source of glucose for living things? It is made by plants and certain other organisms. The process in which glucose is made using energy in light is photosynthesis. This process requires carbon dioxide and water. It produces oxygen in addition to glucose. Photosynthesis consists of many chemical reactions. Overall, the reactions of photosynthesis can be summed up by this chemical equation: 6CO2 + 6H2 O + light energy ! C6 H12 O6 + 6O2 In words, this means that six molecules of carbon dioxide (CO2 ) combine with six molecules of water (H2 O) in the presence of light energy. This produces one molecule of glucose (C6 H12 O6 ) and six molecules of oxygen (O2 ). Use this interactive animation to learn more about photosynthesis: Click on this link for a song about photosynthesis to reinforce the basic ideas: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0424 | photosynthesis | T_2494 | Types of organisms that make glucose by photosynthesis are pictured in Figure 4.7. They include plants, plant-like protists such as algae, and some kinds of bacteria. Living things that make glucose are called autotrophs ("self feeders"). All other living things obtain glucose by eating autotrophs (or organisms that eat autotrophs). These living things are called heterotrophs ("other feeders"). | text | null |
L_0424 | photosynthesis | T_2495 | In plants and algae, photosynthesis takes place in chloroplasts. (Photosynthetic bacteria have other structures for this purpose.) A chloroplast is a type of plastid, or plant organelle. It contains the green pigment known as chlorophyll. The presence of chloroplasts in plant cells is one of the major ways they differ from animal cells. You can see chloroplasts in plant cells Figure 4.8. | text | null |
L_0424 | photosynthesis | T_2496 | The structure of a chloroplast is shown in Figure 4.9. The chloroplast is surrounded by two membranes. Inside the chloroplast are stacks of flattened sacs of membrane, called thylakoids. The thylakoids contain chlorophyll. Surrounding the thylakoids is a space called the stroma. The stroma is filled with watery ("aqueous") fluid. | text | null |
L_0424 | photosynthesis | T_2497 | In plants, most chloroplasts are found in the leaves. Therefore, all the raw materials needed for photosynthesis must be present in the leaves. These materials include light, water, and carbon dioxide. The shape of the leaves gives them a lot of surface area to absorb light for photosynthesis. Roots take up water from the soil. Stems carry the water from the roots to the leaves. Carbon dioxide enters the leaves through tiny openings called stomata. (The oxygen released during photosynthesis also exits the leaves through the stomata.) | text | null |
L_0424 | photosynthesis | T_2498 | Photosynthesis occurs in two stages, called the light reactions and the Calvin cycle. Figure 4.10 sums up what happens in these two stages. Both stages are described below. | text | null |
L_0424 | photosynthesis | T_2499 | The light reactions occur in the first stage of photosynthesis. This stage takes place in the thylakoid membranes of the chloroplast. In the light reactions, energy from sunlight is absorbed by chlorophyll. This energy is temporarily transferred to two molecules: ATP and NADPH. These molecules are used to store the energy for the second stage of photosynthesis. The light reactions use water and produce oxygen. | text | null |
L_0424 | photosynthesis | T_2500 | The Calvin cycle occurs in the second stage of photosynthesis. This stage takes place in the stroma of the chloroplast. In the Calvin cycle, carbon dioxide is used to produce glucose (sugar) using the energy stored in ATP and NADPH. The energy is released from these molecules when ATP loses phosphate (Pi ) to become ADP and NADPH loses hydrogen (H) to become NADP+ . | text | null |
L_0425 | cellular respiration | T_2501 | Cellular respiration is the process in which cells break down glucose, release the stored energy, and use the energy to make ATP. For each glucose molecule that undergoes this process, up to 38 molecules of ATP are produced. Each ATP molecules forms when a phosphate is added to ADP, or adenosine diphosphate. This requires energy, which is stored in the ATP molecule. When cells need energy, a phosphate can be removed from ATP. This releases the energy and forms ADP again. | text | null |
L_0425 | cellular respiration | T_2502 | Cellular respiration involves many biochemical reactions. However, the overall process can be summed up in a single chemical equation: C6 H12 O6 + 6O2 ! 6CO2 + 6H2 O + energy (stored in ATP) Cellular respiration uses oxygen in addition to glucose. It releases carbon dioxide and water as waste products. Cellular respiration actually "burns" glucose for energy. However, it doesnt produce light or intense heat like burning a candle or log. Instead, it releases the energy slowly, in many small steps. The energy is used to form dozens of molecules of ATP. | text | null |
L_0425 | cellular respiration | T_2503 | Cellular respiration takes place in the cells of all organisms. It occurs in autotrophs such as plants as well as heterotrophs such as animals. Cellular respiration begins in the cytoplasm of cells. It is completed in mitochondria. The mitochondrion is a membrane-enclosed organelle in the cytoplasm. Its sometimes called the "powerhouse" of the cell because of its role in cellular respiration. Figure 4.12 shows the parts of the mitochondrion involved in cellular respiration. | text | null |
L_0425 | cellular respiration | T_2504 | Cellular respiration occurs in three stages. The flow chart in Figure dont purge me shows the order in which the stages occur and how much ATP forms in each stage. The names of the stages are glycolysis, the Krebs cycle, and electron transport. Each stage is described below. | text | null |
L_0425 | cellular respiration | T_2505 | Glycolysis is the first stage of cellular respiration. It takes place in the cytoplasm of the cell. The world glycolysis means "glucose splitting". Thats exactly what happens in this stage. Enzymes split a molecule of glucose into two smaller molecules called pyruvate. This results in a net gain of two molecules of ATP. Other energy-storing molecules are also produced. (Their energy will be used in stage 3 to make more ATP.) Glycolysis does not require oxygen. Anything that doesnt need oxygen is described as anaerobic. | text | null |
L_0425 | cellular respiration | T_2505 | Glycolysis is the first stage of cellular respiration. It takes place in the cytoplasm of the cell. The world glycolysis means "glucose splitting". Thats exactly what happens in this stage. Enzymes split a molecule of glucose into two smaller molecules called pyruvate. This results in a net gain of two molecules of ATP. Other energy-storing molecules are also produced. (Their energy will be used in stage 3 to make more ATP.) Glycolysis does not require oxygen. Anything that doesnt need oxygen is described as anaerobic. | text | null |
L_0425 | cellular respiration | T_2506 | The pyruvate molecules from glycolysis next enter the matrix of a mitochondrion. Thats where the second stage of cellular respiration takes place. This stage is called the Krebs cycle. During this stage, two more molecules of ATP are produced. Other energy-storing molecules are also produced (to be used to make more ATP in stage 3). The Krebs cycle requires oxygen. Anything that needs oxygen is described as aerobic. The oxygen combines with the carbon from the pyruvate molecules. This forms carbon dioxide, a waste product. | text | null |
L_0425 | cellular respiration | T_2507 | The third and final stage of cellular respiration is called electron transport. Remember the other energy-storing molecules from glycolysis and the Krebs cycle? Their energy is used in this stage to make many more molecules of ATP. In fact, during this stage, as many as 34 molecules of ATP are produced. Electron transport requires oxygen, so this stage is also aerobic. The oxygen combines with hydrogen from the energy-storing molecules. This forms water, another waste product. | text | null |
L_0425 | cellular respiration | T_2508 | Cellular respiration and photosynthesis are like two sides of the same coin. This is clear from the diagram in Figure needed for photosynthesis. Together, the two processes store and release energy in virtually all living things. | text | null |
L_0425 | cellular respiration | T_2509 | Some organisms can produce ATP from glucose anaerobically. One way this happens is called fermentation. Fermentation includes the glycolysis step of cellular respiration. However, it doesnt include the other, aerobic steps. There are two types of fermentation: lactic acid fermentation and alcoholic fermentation. | text | null |
L_0425 | cellular respiration | T_2510 | In lactic acid fermentation, glycolysis is followed by a step that produces lactic acid. This step forms additional molecules of ATP. Lactic acid fermentation occurs in some bacteria, including the bacteria in yogurt. The lactic acid gives unsweetened yogurt its sour taste. Your own muscle cells can also undertake lactic acid fermentation. This occurs when the cells are working very hard. They use fermentation because they cant get oxygen fast enough for aerobic respiration to supply them with all the energy they need. The muscle cells of the hurdlers in Figure 4.15 are using lactic acid fermentation by the time the athletes reach finish line. | text | null |
L_0425 | cellular respiration | T_2511 | In alcoholic fermentation, glycolysis is followed by a step that produces alcohol and carbon dioxide. This step also forms additional molecules of ATP. It occurs in yeast, such as the yeast in bread. Carbon dioxide from alcoholic fermentation creates gas bubbles in bread dough. The bubbles leave little holes in the bread after it bakes. You can see them in the bread in Figure 4.16. The holes make the bread light and fluffy. | text | null |
L_0425 | cellular respiration | T_2512 | Both aerobic and anaerobic respiration have certain advantages. Aerobic respiration releases far more energy than anaerobic respiration does. It results in the formation of many more molecules of ATP. Anaerobic respiration is much quicker than aerobic respiration. It also allows organisms to live in places where there is little or no oxygen, such as deep under water or soil. For an entertaining review of aerobic and anaerobic respiration, watch this creative music video: MEDIA Click image to the left or use the URL below. URL: | text | null |
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