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L_0547 | human causes of extinction | T_3017 | In addition to habitat destruction, other human-caused problems are also threatening many species. These include issues associated with climate change, pollution, and over-population. | text | null |
L_0547 | human causes of extinction | T_3018 | Another major cause of extinction is global warming, which is also known as global climate change. During the past century, the Earths average temperature has risen by almost 1C (about 1.3F). You may not think that is significant, but to organisms that live in the wild and are constantly adapting to their environments, any climate change can be hazardous. Recall that burning fossil fuels releases gasses into the atmosphere that warm the Earth. Our increased use of fossil fuels, such as coal and oil, is changing the Earths climate. Any long-term change in the climate can destroy the habitat of a species. Even a brief change in climate may be too stressful for an organism to survive. For example, if the seas increase in temperature, even briefly, it may be too warm for certain types of fish to reproduce. | text | null |
L_0547 | human causes of extinction | T_3019 | Pollution adds chemicals, noise, heat, or even light to an environment. This can have many different harmful effects on all kinds of organisms. For example, the pesticide DDT nearly eliminated the peregrine falcon in some parts of the world. This pesticide caused falcons to lay eggs with thinner shells. As a result, fewer falcon eggs survived to hatching. Populations of peregrine falcons declined rapidly. DDT was then banned in the U.S. and peregrine falcon populations have recovered. Water pollution threatens vital freshwater and marine resources throughout the world ( Figure 1.1). Specifically, industrial and agricultural chemicals, waste, and acid rain threaten water. As water is essential for all ecosystems, water pollution can result in the extinction of species. A bird that was the victim of an oil spill. About 58,000 gallons of oil spilled from a South Korea-bound container ship when it struck a tower supporting the San Francisco-Oakland Bay Bridge in dense fog in November, 2007. Finally, soil contamination can also result in extinction. Soil contamination can come from toxic industrial and municipal wastes ( Figure 1.2), salts from irrigation, and pesticides from agriculture. These all degrade the soil as well. As soil is the foundation of terrestrial ecosystems, this can result in extinction. | text | null |
L_0547 | human causes of extinction | T_3020 | Human populations are on the rise. The human population passed the 7 billion mark in October of 2011, and will pass 8 and 9 billion probably before the middle of the century. All these people will need resources such as places to live, food to eat, and water to drink, and they will use energy and create waste. Essentially, human population growth can effect all other causes of extinction. For example, more people on the Earth means more people contributing to global warming and pollution. More people also means more clearing of land for agriculture and development. Recall that development by humans often causes habitats to be destroyed. This destruction can force species to go extinct, or move somewhere else. | text | null |
L_0548 | human digestive system | T_3021 | Nutrients in the foods you eat are needed by the cells of your body. How do the nutrients in foods get to your body cells? What organs and processes break down the foods and make the nutrients available to cells? The organs are those of the digestive system. The processes are digestion and absorption. The digestive system is the body system that breaks down food and absorbs nutrients. It also gets rid of solid food waste. The digestive system is mainly one long tube from the mouth to the anus, known as the gastrointestinal tract (GI tract). The main organs of the digestive system include the esophagus, stomach and the intestine, and are pictured below ( Figure 1.1). The intestine is divided into the small and large intestine. The small intestine has three segments. The ileum is the longest segment of the small intestine, which is well over 10 feet long. The large intestine is about 5 feet long. This drawing shows the major organs of the digestive system. The liver, pancreas and gallbladder are also organs of the digestive system. Digestion is the process of breaking down food into nutrients. There are two types of digestion, mechanical and chemical. In mechanical digestion, large chunks of food are broken down into small pieces. Mechanical digestion begins in the mouth and involves physical processes, such as chewing. This process continues in the stomach as the food is mixed with digestive juices. In chemical digestion, large food molecules are broken down into small nutrient molecules. This is a chemical process which also begins in the mouth as saliva begins to break down food and continues in the stomach as stomach enzymes further digest the food. Absorption is the process that allows substances you eat to be taken up by the blood. After food is broken down into small nutrient molecules, the molecules are absorbed by the blood. After absorption, the nutrient molecules travel in the bloodstream to cells throughout the body. This happens mostly in the small intestine. Some substances in food cannot be broken down into nutrients. They remain behind in the digestive system after the nutrients are absorbed. Any substances in food that cannot be digested and absorbed pass out of the body as solid waste. The process of passing solid food waste out of the body is called elimination. | text | null |
L_0550 | human genome project | T_3025 | A persons genome is all of his or her genetic information. In other words, the human genome is all the information that makes us human. And unless you have an identical twin, your genome is unique. No one else has a genome just like yours, though all our genomes are similar. The Human Genome Project ( Figure 1.1) was an international effort to sequence all 3 billion bases that make up our DNA and to identify within this code more than 20,000 human genes. Scientists also completed a chromosome map, identifying where the genes are located on each of the chromosomes. The Human Genome Project was completed in 2003. Though the Human Genome Project is finished, analysis of the data will continue for many years. To say the Human Genome Project has been beneficial to mankind would be an understatement. Exciting applications of the Human Genome Project include the following: The genetic basis for many diseases can be more easily determined. Now there are tests for over 1,000 genetic disorders. The technologies developed during this effort, and since the completion of this project, will reduce the cost of sequencing a persons genome. This may eventually allow many people to sequence their individual genome. Analysis of your own genome could determine if you are at risk for specific diseases. Knowing you might be genetically prone to a certain disease would allow you to make preventive lifestyle changes or have medical screenings. To complete the Human Genome Project, all 23 pairs of chromosomes in the human body were sequenced. Each chromo- some contains thousands of genes. This is a karyotype, a visual representation of an individuals chromosomes lined up by size. The video Our Molecular Selves discusses the human genome, and is available at or . Genome, Unlocking Lifes Code is the Smithsonian National Museum of Natural Historys exhibit on the human genome. See http://unlockinglifescode.org to visit the exhibit. Click image to the left or use the URL below. URL: | text | null |
L_0551 | human population | T_3026 | How quickly is the human population growing? If we look at worldwide human population growth from 10,000 BCE through today, our growth looks like exponential growth. It increased very slowly at first, but later grew faster and faster as the population increased in size ( Figure 1.1). And recently, the human population has increased at a faster pace than ever before. It has taken only 12 years for the worlds population to increase from six billion to seven billion. Considering that in the year 1804, there were just one billion people, and in 1927, there were just two billion people (thats 123 years to increase from 1 to 2 billion), the recent increase in the human population growth rate is characteristic of exponential growth. Does this mean there are unlimited resources? Worldwide human population growth from 10,000 BCE through today. | text | null |
L_0551 | human population | T_3027 | On the other hand, if you look at human population growth in specific countries, you may see a different pattern. On the level of a country, the history of human population growth can be divided into five stages, as described in Table 1.1. Some countries have very high birth rates, in some countries the growth rate has stabilized, and in some countries the growth rate is in decline. Stage 1 2 3 4 5 Description Birth and death rates are high and population growth is stable. This occurred in early human history. Significant drop in death rate, resulting in exponential growth. This occurred in 18th- and 19th-century Eu- rope. Population size continues to grow. Birth rates equal death rates and populations become stable. Total population size may level off. The United Nations and the U.S. Census Bureau predict that by 2050, the Earth will be populated by 9.4 billion people. Other estimates predict 10 to 11 billion. | text | null |
L_0551 | human population | T_3028 | There are two different beliefs about what type of growth the human population will undergo in the future: 1. Neo-Malthusians believe that human population growth cannot continue without destroying the environment, and maybe humans themselves. 2. Cornucopians believe that the Earth can give humans a limitless amount of resources. They also believe that technology can solve problems caused by limited resources, such as lack of food. The Cornucopians believe that a larger population is good for technology and innovation. The 5-stage model above predicts that when all countries are industrialized, the human population will eventually level out. But many scientists and other Neo-Malthusians believe that humans have already gone over the Earths carrying capacity. That means, we may have already reached the maximum population size that can be supported, without destroying our resources and habitat. If this is true, then human overpopulation will lead to a lack of food and other resources. Overpopulation may also lead to increased disease, and/or war. These problems may cause the population of humans to crash. If these issues are not controlled, could the human population go extinct? Which of the above theories makes sense to you? Why? | text | null |
L_0552 | human skeletal system | T_3029 | How important is your skeleton? Can you imagine your body without it? You would be a wobbly pile of muscle and internal organs, and you would not be able to move. The adult human skeleton has 206 bones, some of which are named below ( Figure 1.1). Bones are made up of living tissue. They contain many different types of tissues. Cartilage, a dense connective tissue, is found at the end of bones and is made of tough protein fibers. Cartilage creates smooth surfaces for the movement of bones that are next to each other, like the bones of the knee. Ligaments are made of tough protein fibers and connect bones to each other. Your bones, cartilage, and ligaments make up your skeletal system. | text | null |
L_0552 | human skeletal system | T_3030 | Your skeletal system gives shape and form to your body, but it also plays other important roles. The main functions of the skeletal system include: The skeletal system is made up of bones, cartilage, and ligaments. The skeletal system has many important functions in your body. What bones protect the heart and lungs? What protects the brain? Support. The skeleton supports the body against the pull of gravity, meaning you dont fall over when you stand up. The large bones of the lower limbs support the rest of the body when standing. Protection. The skeleton supports and protects the soft organs of the body. For example, the skull surrounds the brain to protect it from injury. The bones of the rib cage help protect the heart and lungs. Movement. Bones work together with muscles to move the body. Making blood cells. Blood cells are mostly made inside certain types of bones. | text | null |
L_0552 | human skeletal system | T_3031 | Bones come in many different shapes and sizes, but they are all made of the same materials. Bones are organs, and recall that organs are made up of two or more types of tissues. The two main types of bone tissue are compact bone and spongy bone ( Figure 1.2). Compact bone makes up the dense outer layer of bones. Spongy bone is found at the center of the bone and is lighter and more porous than compact bone. Bones look tough, shiny, and white because they are covered by a layer called the periosteum. Many bones also contain a soft connective tissue called bone marrow in the pores of the spongy bone. Bone marrow is where blood cells are made. Bones are made up of different types of tissues. | text | null |
L_0552 | human skeletal system | T_3032 | Early in human development, the skeleton consists of only cartilage and other connective tissues. At this point, the skeleton is very flexible. As the fetus develops, hard bone begins to replace the cartilage, and the skeleton begins to harden. Not all of the cartilage, however, is replaced by bone. Cartilage remains in many places in your body, including your joints, your rib cage, your ears, and the tip of your nose. A baby is born with zones of cartilage in its bones that allow growth of the bones. These areas, called growth plates, allow the bones to grow longer as the child grows. By the time the child reaches an age of about 18 to 25 years, all of the cartilage in the growth plate has been replaced by bone. This stops the bone from growing any longer. Even though bones stop growing in length in early adulthood, they can continue to increase in thickness throughout life. This thickening occurs in response to strain from increased muscle activity and from weight-lifting exercises. | text | null |
L_0568 | indoor air pollution | T_3086 | Recall that air pollution is due to chemical substances and particles released into the air mainly by human actions. When most people think of air pollution, they think of the pollution outdoors. But it is just as easy to have indoor air pollution. Your home or school classroom probably doesnt get much fresh air. Sealing up your home reduces heating and cooling costs. But this also causes air pollution to stay trapped indoors. And people today usually spend a majority of their time indoors. So exposure to indoor air pollution can become a significant health risk. Indoor air pollutants include both chemical and biological pollutants. Chemical pollutants include the following: Radon, a radioactive gas released from the Earth in certain locations. It can become trapped inside buildings and increase your risk of cancer. Formaldehyde, a toxic gas emitted from building materials, such as carpeting and plywood. Volatile organic compounds (VOCs), which are given off by paint and solvents as they dry. They can cause cause long-term health effects. Secondhand smoke, which comes from breathing the smoke release from tobacco products. Secondhand smoke is also the smoke exhaled by a cigarette smoker. This smoke is extremely dangerous to human health. Carbon monoxide (CO), a toxic gas released by burning fossil fuels. It is often released indoors by faulty chimneys, gas-powered generators, or burning charcoal; it can be extremely dangerous. Dry cleaning fluids, such as tetrachloroethylene, which can be released from clothing days after dry cleaning. The past use of asbestos in factories and in homes. Asbestos is a very dangerous material, and it was used in many buildings ( Figure 1.1). Asbestos can cause cancer and other lung diseases. The use of asbestos is not allowed today. The use of asbestos in industry and do- mestic environments in the past, as in the asbestos-covered pipes in the oil-refining plant pictured here, has left a potentially very dangerous material in many busi- nesses. Biological sources of air pollution are also found indoors. These are produced from: Pet dander. Dust from tiny skin flakes and decomposed hair. Dust mites. Mold from walls, ceilings, and other structures. Air conditioning systems that can incubate certain bacteria and mold. Pollen, dust, and mold from houseplants, soil, and surrounding gardens. | text | null |
L_0568 | indoor air pollution | T_3087 | Can you avoid indoor air pollution? You cant go to school outside. But it is possible to reduce your exposure to air pollution. Some tips to decrease your exposure to indoor air pollution include: Using less toxic chemicals when possible. Limiting your exposure to pesticides and cleaning fluids by keeping them in a garage or shed. When using toxic chemicals, allowing fresh air to circulate through open windows and doors. Having detectors for radon and carbon monoxide in your home. What else could you do to reduce your exposure to air pollution? | text | null |
L_0569 | infancy and childhood | T_3088 | The first year after birth is called infancy. Infancy is a period when the baby grows very fast. During infancy, the baby doubles in length and triples in weight. Other important changes also happen during infancy: The babys teeth start to come in, usually at about six months of age ( Figure 1.1). The baby starts smiling, paying attention to other people, and grabbing toys. The baby begins making babbling sounds. By the end of the first year, the baby is starting to say 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. Childhood begins after the babys first birthday and continues until the teen years. Between one and three years of age, a child is called a toddler. During the toddler stage, growth is still fast, but not as fast as it was during infancy. A toddler learns many new words. The child even starts putting together words in simple sentences. Motor skills also develop quickly during this stage. By age three, most children can run and climb steps. They can hold crayons and scribble with them. They can also feed themselves and use the toilet. From age three until the teens, growth is slower. The body also changes shape. The arms and legs get longer compared 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 also learn how to play games and sports ( Figure 1.2). By age six, children start losing their baby teeth. Their permanent teeth begin coming in to replace them. They also start school and learn how to read and write. They develop friendships and become less dependent on their parents. | text | null |
L_0569 | infancy and childhood | T_3089 | There are numerous milestones that occur during the first few years of childhood. These include the use of language, walking and running, understanding simple concepts, pretend play, the development of fine motor skills, the development of independence, Children develop better motor skills as they get older. having temper tantrums, demonstrating separation anxiety, becoming fully potty-trained, showing natural curiosity. | text | null |
L_0571 | influences on darwin | T_3093 | When Darwin returned to England five years later, in 1836, at the end of his voyage, he did not rush to announce his discoveries. Unlike other naturalists before him, Darwin did not want to present any ideas unless he had strong evidence supporting them. Instead, once Darwin returned to England, he spent over twenty years examining specimens, talking with other scientists and collecting more information before he presented his theories. Some of Darwins ideas conflicted with widely held beliefs, including those from religious leaders. At that time, many people believed that organisms never change and never go extinct, and that the world was only about 6,000 years old, always existing in the same way, never changing. These beliefs delayed Darwin in presenting his findings. How did Darwin come up with his theories? Charles Darwin was influenced by the ideas of several people. 1. Before the voyage of the Beagle, Jean-Baptiste Lamarck proposed the idea that species change over time. However, Darwin differed with Lamarck on several key points. Lamarck proposed that traits acquired during ones lifetime could be passed to the next generation. Darwin did not agree with this. 2. The findings of Charles Lyell, a well-known geologist, also influenced Darwin. Lyells writings taught Darwin about geology, paleontology, and the changing Earth. Lyells findings suggested the Earth must be much older than 6,000 years. And the evolution of life, as Darwin was developing his ideas, would definitely take much longer than just 6,000 years. During the Voyage of the Beagle, Darwin observed fossils of sea life high up in the mountains. What must happen to the Earth for this to occur? Darwin, using the readings of Lyell, took this as evidence of a constantly changing Earth. 3. After the Voyage of the Beagle, another naturalist, Alfred Russel Wallace ( Figure 1.1), developed a similar theory of evolution by natural selection. Wallace toured South America and made similar observations to Darwins. Darwin and Wallace presented their theories and evidence in public together. Due to the large number of observations and conclusions he made, Darwin is mostly credited and associated with this theory. Alfred Wallace developed a similar theory of evolution by natural selection. Imagine developing a theory that conflicted with widely held beliefs of the time, as Darwin did. Imagine pulling together material from all these different people, adding his own findings, and turning it all into his theory. Imag- ine the torment Darwin must have endured during this time, knowing the skepticism that would follow the release of his findings. But, upon his death, Darwin was given one of the highest honors in England. Darwin is buried in Westminster Abbey, the final resting place of many of Englands kings and queens. Why was he buried in such an important spot? | text | null |
L_0572 | injuries of the nervous system | T_3094 | Injuries to the central nervous system may damage tissues of the brain or spinal cord. If an injury is mild, a person may have a full recovery. If an injury is severe, it may cause permanent disability or even death. Brain and spinal cord injuries most commonly occur because of car crashes or sports accidents. The best way to deal with such injuries is to try to prevent them. | text | null |
L_0572 | injuries of the nervous system | T_3095 | Brain injuries can range from mild to extremely severe, but even mild injuries need medical attention. Brain injuries can result from falls, car accidents, violence, sports injuries, and war and combat. Falls are the most common cause of brain injuries, particularly in older adults and young children. The mildest and most common type of brain injury is a concussion. This is a bruise on the surface of the brain. It may cause temporary problems such as headache, drowsiness, and confusion. Most concussions in young people occur when they are playing sports, especially contact sports like football. Other sports, like soccer, boxing, baseball, lacrosse, skateboarding, and hockey can also result in concussions. A concussion normally heals on its own in a few days. A single concussion is unlikely to cause permanent damage. But repeated concussions may lead to lasting problems. People who have had two or more concussions may have life-long difficulties with memory, learning, speech, or balance. For this reason, concussions are treated very seriously among athletes and in professional sports. You can see an animation of how a concussion occurs by visiting A person with a serious brain injury usually suffers permanent brain damage. These brain injuries usually occur when an external mechanical force, such as a violent blow or jolt to the head or body, causes brain dysfunction. An object penetrating the skull, such as a bullet or a shattered piece of the skull, also can cause traumatic brain injury. As a result, the person may have trouble talking or controlling body movements. Symptoms depend on what part of the brain was injured. Serious brain injuries can also cause personality changes and problems with mental abilities such as memory. Medicines, counseling, and other treatments may help people with serious brain injuries recover from, or at least learn to cope with, their disabilities. Symptoms of severe brain injuries include the loss of consciousness from several minutes to hours, profound confusion, slurred speech, the inability to awaken from sleep, seizures, loss of coordination, persistent headache or headache that worsens. | text | null |
L_0572 | injuries of the nervous system | T_3096 | A spinal cord injury is damage to any part of the spinal cord or nerves at the end of the spinal canal. This injury often causes permanent changes in strength, sensation and other body functions below the site of the injury. Spinal cord injuries make it difficult for messages to travel between the brain and body. They may cause a person to lose the ability to feel or move parts of the body. This is called paralysis. Whether paralysis occursand what parts of the body are affected if it doesdepends on the location and seriousness of the injury. In addition to car crashes and sports injuries, diving accidents are a common cause of spinal cord injuries. Quadriplegia means your arms, hands, trunk, legs and pelvic organs are all affected by your spinal cord injury. Paraplegia means the paralysis affects all or part of the trunk, legs and pelvic organs. These people can still use their arms and hands. Some people recover from spinal cord injuries. But many people are paralyzed for life. Thanks to the work of Christopher Reeve ( Figure 1.1), more research is being done on spinal cord injuries now than ever before. For example, scientists are trying to discover ways to regrow damaged spinal cord neurons. If you suspect that someone has a back or neck injury: dont move the injured person as permanent paralysis and other serious complications may result, call 911 or your local emergency medical assistance number, keep the person very still, place heavy towels on both sides of the neck or hold the head and neck to prevent them from moving, until emergency care arrives, provide basic first aid, such as stopping any bleeding and making the person comfortable, without moving the head or neck. Former "man of steel" Superman star Christopher Reeve (September 25, 1952 October 10, 2004) was paralyzed from the neck down in a fall from a horse. The injury crushed his spinal cord so his brain could no longer communicate with his body. | text | null |
L_0579 | jawless fish | T_3111 | What defines a jawless fish? You can probably guess. A jawless fish is a fish without a jaw. But there are other features that are shared by this class of organisms. Why would such an organism evolve? These fish were the first vertebrates to evolve. Logically, this makes sense, in that the vertebral column would evolve first, with the more complex jaw bones evolving later. The early jawless fish are thought to have relied on filter feeding to capture their food, and most likely would have sucked water and debris from the seafloor into their mouth, releasing water and waste out of their gills. As other sea life evolved, these jawless fish began to feed on other fish species, and are now considered a pest in their habitat. Lampreys have no natural predators. | text | null |
L_0579 | jawless fish | T_3112 | Jawless fish are missing the following parts: 1. Jaws. 2. Paired fins. 3. A stomach. Characteristics they do have include: 1. A notochord, both in larvae and adults. Recall a notochord is a support rod that runs along the back of the fish. 2. Seven or more paired gill pouches. These organs take dissolved oxygen from water. 3. The branchial arches, a series of arches that support the gills of aquatic amphibians and fishes. They lie close to the bodys surface. 4. A light sensitive pineal eye, an eye-like structure that can detect light. 5. A cartilaginous skeleton, a skeleton made of a flexible rubber-like supportive material called cartilage. This is similar to the skeleton of cartilaginous fish, which includes sharks and rays. 6. A heart with two chambers. 7. Reproduction using external fertilization. 8. They are ectothermic. This means that their internal temperature depends on the temperature of their envi- ronment. | text | null |
L_0579 | jawless fish | T_3113 | Most scientists agree that the jawless fish are part of the the superclass Agnatha. They belong to the phylum Chordata, subphylum Vertebrata. There are two living groups of jawless fish, with about 100 species in total: lampreys and hagfish ( Figure 1.1). Although hagfish belong to the subphylum Vertebrata, they do not technically have vertebrae (though they do have a skull), whereas lampreys do have vertebrae. For this reason, scientists still disagree on the classification of jawless fish. A hagfish. | text | null |
L_0580 | keeping bones and joints healthy | T_3114 | You can help keep your bones and skeletal system healthy by eating well and getting enough exercise. Weight- bearing exercises help keep bones strong. Weight-bearing exercises and activities work against gravity. Such activities include basketball, tennis, gymnastics, karate, running, and walking. When the body is exercised regularly by performing weight-bearing activity, bones respond by adding more bone cells to increase their bone density. | text | null |
L_0580 | keeping bones and joints healthy | T_3115 | Did you know that what you eat as a teenager can affect how healthy your skeletal system will be in 30, 40, and even 50 years? Calcium and vitamin D are two of the most important nutrients for a healthy skeletal system. Your bones need calcium to grow properly. If you do not get enough calcium in your diet as a teenager, your bones may become weak and break easily later in life. Osteoporosis is a disease in which bones lose mass and become more fragile than they should be. Osteoporosis also makes bones more likely to break. Two of the easiest ways to prevent osteoporosis are eating a healthy diet that has the right amount of calcium and vitamin D and to do some sort of weight-bearing exercise every day. Foods that are a good source of calcium include milk, yogurt, and cheese. Non-dairy sources of calcium include Chinese cabbage, kale, and broccoli. Many fruit juices, fruit drinks, tofu, and cereals have calcium added to them. It is recommended that teenagers get 1300 mg of calcium every day. For example, one cup (8 fl. oz.) of milk provides about 300 mg of calcium, or about 30% of the daily requirement. Other sources of calcium are pictured in the Figure 1.1. There are many different sources of cal- cium. Getting enough calcium in your daily diet is important for good bone health. Vitamin D is unusual since you dont have to rely on your diet alone to get enough of this vitamin. Your skin makes vitamin D when exposed to sunlight. Pigments in the skin act like a filter that can prevent the skin from making vitamin D. As a result, people with darker skin need more time in the sun than people with lighter skin to make the same amount of vitamin D. You can also get vitamin D from foods. Fish is naturally rich in vitamin D. In the United States, vitamin D is added to other foods, including milk, soy milk, and breakfast cereals. Teenagers are recommended to get 5 micrograms (200 IU) of vitamin D every day. A 3 12 -ounce portion of cooked salmon provides 360 IU of vitamin D. A 8-ounce glass of milk is fortified with about 100 IU of vitamin D. | text | null |
L_0580 | keeping bones and joints healthy | T_3116 | Even though they are very strong, bones can fracture, or break. Fractures can happen at different places on a bone. They are usually caused by excess bending stress on the bone. Bending stress is what causes a pencil to break if you bend it too far. Soon after a fracture, the body begins to repair the break. The area becomes swollen and sore. Within a few days, bone cells travel to the break site and begin to rebuild the bone. It takes about two to three months before compact and spongy bone form at the break site. Sometimes the body needs extra help in repairing a broken bone. In such a case, a surgeon will piece a broken bone together with metal pins. Moving the broken pieces together will help keep the bone from moving and give the body a chance to repair the break. Below, a broken ulna has been repaired with pins ( Figure 1.2). The upper part of the ulna, just above the elbow joint, is broken, as you can see in the X-ray to the left. The x-ray to the right was taken after a surgeon inserted a system of pins and wires across the fracture to bring the two pieces of the ulna into close proximity. | text | null |
L_0580 | keeping bones and joints healthy | T_3117 | Osteoarthritis occurs when the cartilage at the ends of the bones breaks down. The break down of the cartilage leads to pain and stiffness in the joint. Decreased movement of the joint because of the pain may lead to weakening of the muscles that normally move the joint, and the ligaments surrounding the joint may become loose. Osteoarthritis is the most common form of arthritis. It has many contributing factors, including aging, sport injuries, fractures, and obesity. | text | null |
L_0580 | keeping bones and joints healthy | T_3118 | Recall that a ligament is a short band of tough connective tissue that connects bones together to form a joint. Ligaments can get injured when a joint gets twisted or bends too far. The protein fibers that make up a ligament can get strained or torn, causing swelling and pain. Injuries to ligaments are called sprains. Ankle sprains are a common type of sprain. | text | null |
L_0580 | keeping bones and joints healthy | T_3119 | Preventing injuries to your bones and ligaments is easier and much less painful than treating an injury. Wearing the correct safety equipment when performing activities that require such equipment can help prevent many common injuries. For example, wearing a bicycle helmet can help prevent a skull injury if you fall. Warming up and cooling down properly can help prevent ligament and muscle injuries. Stretching before and after activity also helps prevent injuries. | text | null |
L_0581 | keeping skin healthy | T_3120 | Your skin is your largest organ and constantly protects you from infections, so keeping your skin healthy is a good idea. | text | null |
L_0581 | keeping skin healthy | T_3121 | Some sunlight is good for your health. Vitamin D is made in the skin when it is exposed to sunlight. But getting too much sun can be unhealthy. A sunburn is a burn to the skin that is caused by overexposure to UV radiation from the suns rays or tanning beds. Light-skinned people, like the man pictured below ( Figure 1.1), get sunburned more quickly than people with darker skin. This is because pigments (melanin) in the skin act as a natural sunblock that help to protect the body from UV radiation. With over one million new cases each year, skin cancer, which is cancer that forms in the tissues of the skin, is the most common form of human cancer. Children and teens who have been sunburned are at a greater risk of developing skin cancer later in life. Long-term exposure to UV radiation is the leading cause of skin cancer. About 90 percent of skin cancers are linked to sun exposure. UV radiation damages the genetic material (DNA) of skin cells. This damage can cause the skin cells to grow out of control and form a tumor. Some of these tumors are very difficult to cure. For this reason you should always wear sunscreen with a high sun protection factor (SPF), a hat, and clothing when out in the sun. Sunburn is caused by overexposure to UV rays. Getting sunburned as a child or a teen, especially sunburn that causes blistering, increases the risk of developing skin cancer later in life. | text | null |
L_0581 | keeping skin healthy | T_3122 | Keeping your skin clean is important because dirty skin is more prone to infection. Bathing every day helps to keep your skin clean and healthy. Also, you know that taking a bath or shower helps prevent body odor. But where does body odor come from? During the day, sweat, oil, dirt, dust, and dead skin cells can build up on the skin surface. If not washed away, the mix of these materials can encourage the excess growth of bacteria. These bacteria feed on these substances and cause a smell that is commonly called body odor. | text | null |
L_0581 | keeping skin healthy | T_3123 | Conditions that irritate, clog or inflame your skin can cause symptoms such as redness, swelling, burning and itching. Allergies, irritants, your genetic background and certain diseases and immune system problems can cause numerous skin conditions. Many skin problems, such as acne, also affect your appearance. Acne Your skin has tiny holes called pores that that can become blocked by oil, bacteria, dead skin and dirt. When this occurs, you may develop a pimple. Acne is a skin condition that causes pimples, and is one of the more common skin problem among teenagers. A diet high in refined sugars or carbohydrates such as bread and chips can also lead to acne. Each pore on your skin is the opening to a follicle, which is made of a hair and sebaceous gland that releases sebum. Acne may result from too much sebum produced by the follicle, dead skin cells accumulating in the pore, or bacteria built up in the pore. Cleaning your skin daily with a mild soap to remove excess oil and dirt can help prevent acne. Cold Sores Cold sores are red, fluid-filled blisters that appear near the mouth or on other areas of the face, usually caused by herpes simplex virus type 1. Visible sores are contagious, but herpes may be spread even when sores cant be seen. You can catch the herpes simplex virus through kissing, sharing cosmetics, or sharing food with infected individuals. Once you catch herpes simplex virus, it cant be cured. Even after sores have healed, the virus remains in your body, and new cold sores can appear at any time. This is not to be confused with genital herpes, which is caused by herpes simplex virus type 2. Canker Sore A canker sore is a mouth ulcer or sore that is open and painful. They may be on the lips or inside of the lip or cheek. Canker sores are usually white or yellowish, surrounded by red, inflamed soft tissue. A canker sore can be either a simple canker or a complex canker. A simple canker sore reemerges about three to four times every year, and is the common type in people between the ages of 10 and 20. Canker sores are not contagious and usually heal on their own within a week or two. Causes of canker sores include a viral infection, stress, hormonal fluctuations, food allergies, immune system problems, or mouth injuries. | text | null |
L_0582 | keeping the nervous system healthy | T_3124 | The nervous system is such an important part of your body. You want it to work at its best so that you can be at your best. Your nervous system contains what is probably the most important part of your body, which, of course, is your brain. Your brain allows you to learn. It allows you to feel emotions like love, anger, and sadness. Your brain gives you the ability to see, hear, taste, touch, and smell. It works together with the nerves and spinal cord to send the signals that make your body move. Your nervous system lets you do things like run, jump, play sports, and do your homework. There are many choices you can make to keep your nervous system healthy. One obvious choice is to avoid using alcohol or other drugs. Not only will you avoid the injury that drugs themselves can cause, but you will also be less likely to get involved in other risky behaviors that could harm your nervous system. Another way to keep the nervous system healthy is to eat a variety of healthy foods. The minerals sodium, calcium, and potassium, and vitamins B1 and B12 are important for a healthy nervous system. Some foods that are good sources for these minerals and vitamins include milk, whole grains, beef steak, and kidney beans (shown in Figure 1.1). Your brain also needs healthy fats like those in nuts and fish. Recall that fats insulate the axons of neurons. These fats help build new connections between nerves and brain cells. These fats may improve memory and increase learning and intelligence. Water is also important for the nervous system, so drink plenty of water and other fluids. This helps prevent dehydration, which can cause confusion and memory problems. And get plenty of rest. Your brain requires plenty of rest so it can strengthen circuits that help with memory. A good nights sleep will help keep your brain functioning at its best. These foods are sources of nutrients needed for a healthy nervous system. Daily physical activity is also important for nervous system health. Regular exercise makes your heart more efficient at pumping blood to your brain. As a result, your brain gets more oxygen, which it needs to function normally. The saying use it or lose it applies to your brain as well as your body. This means that mental activity, not just physical activity, is important for nervous system health. Doing crossword puzzles, reading, and playing a musical instrument are just a few ways you can keep your brain active. You can also choose to practice safe behaviors to protect your nervous system from injury. To keep your nervous system safe, choose to: Bicycle helmets help protect from head injuries. Making healthy choices like this can help prevent nervous system injuries that could cause lifelong disability. Furthermore, make sure to exercise your nervous system on a daily basis. The simple act of writing requires that you use all the major components of your motor and sensory pathways. These include a number of different sensory receptors, peripheral nerves, synaptic connections within your spinal cord, major tracts within your spinal cord, and nerve tissue throughout your brain. All these components need to be utilized with great precision and coordination to produce neatly written words. What should you do? Spend a few minutes each day writing on paper as neatly as you can. This takes a lot more effort on the part of the nervous system than typing on a keyboard, as typing on a keyboard doesnt require as much fine motor control as writing on paper. If you dont want to write, then draw. Drawing with precision also requires use of all the major components of the sensory and motor divisions of the nervous system. | text | null |
L_0582 | keeping the nervous system healthy | T_3124 | The nervous system is such an important part of your body. You want it to work at its best so that you can be at your best. Your nervous system contains what is probably the most important part of your body, which, of course, is your brain. Your brain allows you to learn. It allows you to feel emotions like love, anger, and sadness. Your brain gives you the ability to see, hear, taste, touch, and smell. It works together with the nerves and spinal cord to send the signals that make your body move. Your nervous system lets you do things like run, jump, play sports, and do your homework. There are many choices you can make to keep your nervous system healthy. One obvious choice is to avoid using alcohol or other drugs. Not only will you avoid the injury that drugs themselves can cause, but you will also be less likely to get involved in other risky behaviors that could harm your nervous system. Another way to keep the nervous system healthy is to eat a variety of healthy foods. The minerals sodium, calcium, and potassium, and vitamins B1 and B12 are important for a healthy nervous system. Some foods that are good sources for these minerals and vitamins include milk, whole grains, beef steak, and kidney beans (shown in Figure 1.1). Your brain also needs healthy fats like those in nuts and fish. Recall that fats insulate the axons of neurons. These fats help build new connections between nerves and brain cells. These fats may improve memory and increase learning and intelligence. Water is also important for the nervous system, so drink plenty of water and other fluids. This helps prevent dehydration, which can cause confusion and memory problems. And get plenty of rest. Your brain requires plenty of rest so it can strengthen circuits that help with memory. A good nights sleep will help keep your brain functioning at its best. These foods are sources of nutrients needed for a healthy nervous system. Daily physical activity is also important for nervous system health. Regular exercise makes your heart more efficient at pumping blood to your brain. As a result, your brain gets more oxygen, which it needs to function normally. The saying use it or lose it applies to your brain as well as your body. This means that mental activity, not just physical activity, is important for nervous system health. Doing crossword puzzles, reading, and playing a musical instrument are just a few ways you can keep your brain active. You can also choose to practice safe behaviors to protect your nervous system from injury. To keep your nervous system safe, choose to: Bicycle helmets help protect from head injuries. Making healthy choices like this can help prevent nervous system injuries that could cause lifelong disability. Furthermore, make sure to exercise your nervous system on a daily basis. The simple act of writing requires that you use all the major components of your motor and sensory pathways. These include a number of different sensory receptors, peripheral nerves, synaptic connections within your spinal cord, major tracts within your spinal cord, and nerve tissue throughout your brain. All these components need to be utilized with great precision and coordination to produce neatly written words. What should you do? Spend a few minutes each day writing on paper as neatly as you can. This takes a lot more effort on the part of the nervous system than typing on a keyboard, as typing on a keyboard doesnt require as much fine motor control as writing on paper. If you dont want to write, then draw. Drawing with precision also requires use of all the major components of the sensory and motor divisions of the nervous system. | text | null |
L_0583 | kidneys | T_3125 | The kidneys ( Figure 1.1) are important organs in maintaining homeostasis, the ability of the body to maintain a stable internal environment despite a changing environment. Kidneys perform a number of homeostatic functions. They maintain the volume of body fluids. They maintain the balance of salt ions in body fluids. They excrete harmful nitrogen-containing molecules, such as urea, ammonia, and uric acid. There are many blood vessels in the kidneys ( Figure 1.1). The kidneys remove urea and other wastes from the blood through tiny filtering units called nephrons. Nephrons ( Figure 1.2) are tiny, tube-shaped structures found inside each kidney. Each kidney has up to a million nephrons. Each nephron collects a small amount of fluid and waste from a small group of capillaries. Structures of the kidney; fluid leaks from the capillaries and into the nephrons where the fluid forms urine then moves to the ureter and on to the bladder. Nitrogen-containing wastes, together with water and other wastes, form the urine as it passes through the nephrons and the kidney. The fluid within nephrons is carried out into a larger tube in the kidney called a ureter, which carries it to the bladder ( Figure 1.2). The kidneys never stop filtering waste products from the blood, so they are always producing urine. The amount of urine your kidneys produce is dependent on the amount of fluid in your body. Your body loses water through sweating, breathing, and urination. The water and other fluids you drink every day help to replace the lost water. This water ends up circulating in the blood because blood plasma is mostly water. | text | null |
L_0583 | kidneys | T_3126 | The process of urine formation is as follows: 1. Blood flows into the kidney through the renal artery. The renal artery connects to capillaries inside the kidney. Capillaries and nephrons lie very close to each other in the kidney. 2. The blood pressure within the capillaries causes water, salts, sugars, and urea to leave the capillaries and move into the nephron. 3. The water and salts move along through the tube-shaped nephron to a lower part of the nephron. 4. The fluid that remains in the nephron at this point is called urine. 5. The blood that leaves the kidney in the renal vein has much less waste than the blood that entered the kidney. 6. The urine is collected in the ureters and is moved to the urinary bladder, where it is stored. Nephrons filter about 14 cup of body fluid per minute. In a 24-hour period, nephrons filter 180 liters of fluid, and 1.5 liters of the fluid is released as urine. Urine enters the bladder through the ureters. Similar to a balloon, the walls of the bladder are stretchy. The stretchy walls allow the bladder to hold a large amount of urine. The bladder can hold about 1 12 to 2 21 cups of urine but may also hold more if the urine cannot be released immediately. How do you know when you have to urinate? Urination is the process of releasing urine from the body. Urine leaves the body through the urethra. Nerves in the bladder tell you when it is time to urinate. As the bladder first fills with urine, you may notice a feeling that you need to urinate. The urge to urinate becomes stronger as the bladder continues to fill up. The location of nephrons in the kidney. The fluid collects in the nephron tubules and moves to the bladder through the ureter. | text | null |
L_0583 | kidneys | T_3127 | The filtering action of the kidneys is controlled by the pituitary gland. The pituitary gland is about the size of a pea and is found below the brain ( Figure 1.3). The pituitary gland releases hormones that help the kidneys to filter water from the blood. The movement of water back into blood is controlled by a hormone called antidiuretic hormone (ADH). ADH is one of the hormones released from the pituitary gland in the brain. One of the most important roles of ADH is to control the bodys ability to hold onto water. If a person does not drink enough water, ADH is released. It causes the blood to reabsorb water from the kidneys. If the kidneys remove less water from the blood, what will the urine look like? It will look darker, because there is less water in it. When a person drinks a lot of water, then there will be a lot of water in the blood. The pituitary gland will then release a lower amount of ADH into the blood. This means less water will be reabsorbed by the blood. The kidneys then produce a large volume of urine. What color will this urine be? | text | null |
L_0586 | light reactions of photosynthesis | T_3135 | null | text | null |
L_0586 | light reactions of photosynthesis | T_3136 | Photosynthesis takes place in the organelle of the plant cell known as the chloroplasts. Chloroplasts are one of the main differences between plant and animal cells. Animal cells do not have chloroplasts, so they cannot photosynthesize. Photosynthesis occurs in two stages. During the first stage, the energy from sunlight is absorbed by the chloroplast. Water is used, and oxygen is produced during this part of the process. During the second stage, carbon dioxide is used, and glucose is produced. Chloroplasts contain stacks of thylakoids, which are flattened sacs of membrane. Energy from sunlight is absorbed by the pigment chlorophyll in the thylakoid membrane. There are two separate parts of a chloroplast: the space inside the chloroplast itself, and the space inside the thylakoids ( Figure 1.1). The inner compartments inside the thylakoids are called the thylakoid space (or lumen). This is the site of the first part of photosynthesis. The interior space that surrounds the thylakoids is filled with a fluid called stroma. This is where carbon dioxide is used to produce glucose, the second part of photosynthesis. The chloroplast is the photosynthesis fac- tory of the plant. | text | null |
L_0586 | light reactions of photosynthesis | T_3137 | What goes into the plant cell to start photosynthesis? The reactants of photosynthesis are carbon dioxide and water. These are the molecules necessary to begin the process. But one more item is necessary, and that is sunlight. All three components, carbon dioxide, water, and the suns energy are necessary for photosynthesis to occur. These three components must meet in the chloroplast of the leaf cell for photosynthesis to occur. How do these three components get to the cells in the leaf? Chlorophyll is the green pigment in leaves that captures energy from the sun. Chlorophyll molecules are located in the thylakoid membranes inside chloroplasts. The veins in a plant carry water from the roots to the leaves. Carbon dioxide enters the leaf from the air through special openings called stomata ( Figure 1.2). | text | null |
L_0586 | light reactions of photosynthesis | T_3138 | What is produced by the plant cell during photosynthesis? The products of photosynthesis are glucose and oxygen. This means they are produced at the end of photosynthesis. Glucose, the food of plants, can be used to store energy in the form of large carbohydrate molecules. Glucose is a simple sugar molecule which can be combined with other glucose molecules to form large carbohydrates, such as starch. Oxygen is a waste product of photosynthesis. It is released into the atmosphere through the stomata. As you know, animals need oxygen to live. Without photosynthetic organisms like plants, there would not be enough oxygen in the atmosphere for animals to survive. | text | null |
L_0586 | light reactions of photosynthesis | T_3139 | The overall chemical reaction for photosynthesis is 6 molecules of carbon dioxide (CO2 ) and 6 molecules of water (H2 O), with the addition of solar energy. This produces 1 molecule of glucose (C6 H12 O6 ) and 6 molecules of oxygen Stomata are special pores that allow gasses to enter and exit the leaf. (O2 ). Using chemical symbols, the equation is represented as follows: 6CO2 + 6H2 O C6 H12 O6 + 6O2 . Though this equation may not seem that complicated, photosynthesis is a series of chemical reactions divided into two stages, the light reactions and the Calvin cycle ( Figure 1.3). | text | null |
L_0586 | light reactions of photosynthesis | T_3140 | Photosynthesis begins with the light reactions. It is during these reactions that the energy from sunlight is absorbed by the pigment chlorophyll in the thylakoid membranes of the chloroplast. The energy is then temporarily transferred to two molecules, ATP and NADPH, which are used in the second stage of photosynthesis. ATP and NADPH are generated by two electron transport chains. During the light reactions, water is used and oxygen is produced. These reactions can only occur during daylight as the process needs sunlight to begin. | text | null |
L_0586 | light reactions of photosynthesis | T_3141 | The second stage of photosynthesis is the production of glucose from carbon dioxide. This process occurs in a continuous cycle, named after its discover, Melvin Calvin. The Calvin cycle uses CO2 and the energy temporarily stored in ATP and NADPH to make the sugar glucose. | text | null |
L_0587 | limiting factors to population growth | T_3142 | For a population to be healthy, factors such as food, nutrients, water and space, must be available. What happens when there are not resources to support the population? Limiting factors are resources or other factors in the environment that can lower the population growth rate. Limiting factors include a low food supply and lack of space. Limiting factors can lower birth rates, increase death rates, or lead to emigration. When organisms face limiting factors, they show logistic growth (S-shaped curve, curve B: Figure 1.1). Compe- tition for resources like food and space cause the growth rate to stop increasing, so the population levels off. This flat upper line on a growth curve is the carrying capacity. The carrying capacity (K) is the maximum population size that can be supported in a particular area without destroying the habitat. Limiting factors determine the carrying capacity of a population. Recall that when there are no limiting factors, the population grows exponentially. In exponential growth (J-shaped curve, curve A: Figure 1.1), as the population size increases, the growth rate also increases. Exponential and Logistic Growth. Curve A shows exponential growth. shows logistic growth. Curve B Notice that the carrying capacity (K) is also shown. | text | null |
L_0587 | limiting factors to population growth | T_3143 | If there are 12 hamburgers at a lunch table and 24 people sit down at a lunch table, will everyone be able to eat? At first, maybe you will split hamburgers in half, but if more and more people keep coming to sit at the lunch table, you will not be able to feed everyone. This is what happens in nature. But in nature, organisms that cannot get food will die or find a new place to live. It is possible for any resource to be a limiting factor, however, a resource such as food can have dramatic consequences on a population. In nature, when the population size is small, there is usually plenty of food and other resources for each individual. When there is plenty of food and other resources, organisms can easily reproduce, so the birth rate is high. As the population increases, the food supply, or the supply of another necessary resource, may decrease. When necessary resources, such as food, decrease, some individuals will die. Overall, the population cannot reproduce at the same rate, so the birth rates drop. This will cause the population growth rate to decrease. When the population decreases to a certain level where every individual can get enough food and other resources, and the birth and death rates become stable, the population has leveled off at its carrying capacity. | text | null |
L_0587 | limiting factors to population growth | T_3144 | Other limiting factors include light, water, nutrients or minerals, oxygen, the ability of an ecosystem to recycle nutrients and/or waste, disease and/or parasites, temperature, space, and predation. Can you think of some other factors that limit populations? Weather can also be a limiting factor. Whereas most plants like rain, an individual cactus-like Agave americana plant actually likes to grow when it is dry. Rainfall limits reproduction of this plant which, in turn, limits growth rate. Can you think of some other factors like this? Human activities can also limit the growth of populations. Such activities include use of pesticides, such as DDT, use of herbicides, and habitat destruction. | text | null |
L_0590 | male reproductive structures | T_3156 | The male reproductive organs include the penis, testes, and epididymis ( Figure 1.1). The figure also shows other parts of the male reproductive system. The penis is a cylinder-shaped organ. It contains the urethra. The urethra is a tube that carries urine out of the body. The urethra also carries sperm out of the body. This drawing shows the organs of the male reproductive system. It shows the organs from the side. Find each organ in the drawing as you read about it in the text. The two testes (singular, testis) are egg-shaped organs. They produce sperm and secrete testosterone. The testes are found inside of the scrotum. The scrotum is a sac that hangs down outside the body. The scrotum also contains the epididymis. The testes, being in the scrotum outside the body, allow the temperature of the sperm to be maintained at a few degrees lower than body temperature. This is necessary for the stability of these reproductive cells. The epididymis is a tube that is about six meters (20 feet) long in adults. It is tightly coiled, so it fits inside the scrotum. It rests on top of the testes. The epididymis is where sperm grow larger and mature. The epididymis also stores sperm until they leave the body. Other parts of the male reproductive system include the vas deferens and the prostate gland. Both of these structures are pictured below ( Figure 1.1). The vas deferens is a tube that carries sperm from the epididymis to the urethra. The prostate gland secretes a fluid that mixes with sperm to help form semen. The prostate gland is located beneath the bladder. Semen is a "milky" liquid that carries sperm through the urethra and out of the body. In addition to sperm cells, semen contains sugars (fructose) which provide energy to the sperm cells, and enzymes and other substances which help the sperm survive. | text | null |
L_0591 | male reproductive system | T_3157 | Dogs have puppies. Cats have kittens. All organisms reproduce, obviously including humans. Like other mammals, humans have a body system that controls reproduction. It is called the reproductive system. It is the only human body system that is very different in males and females. The male and female reproductive systems have different organs and different functions. The male reproductive system has two main functions: 1. Producing sperm. 2. Releasing testosterone into the body. Sperm are male gametes, or reproductive cells. When a male gamete meets a female gamete, they can form a new organism. Sperm form when certain cells in the male reproductive system divide by meiosis, resulting in cells with half the amount of DNA as a regular "body" cell. More precisely, sperm cells are haploid sex cells, having one set of chromosomes. Regular body cells are diploid, having two set of chromosomes. As there are 46 chromosomes in a diploid human cell, how many are in a human sperm cell? When males grow older, they produce millions of sperm each day. The male reproductive system also maintains and transports and delivers sperm and a protective fluid, known as semen. Testosterone is the main sex hormone in males. Hormones are chemicals that control many body processes. Testosterone has two major roles: During the teen years, testosterone causes the reproductive organs to mature. It also causes other male traits to develop. For example, it causes hair to grow on the face and allows for muscle growth. During adulthood, testosterone helps a man to produce sperm. When a hormone is released into the body, we say it is "secreted." Testosterone is secreted by males, but it is not the only sex hormone that males secrete. Males also secrete small amounts of estrogen. Even though estrogen is the main female sex hormone, scientists think that estrogen is needed for normal sperm production in males. | text | null |
L_0599 | menstrual cycle | T_3172 | The menstrual cycle is a series of changes in the reproductive system of mature females that repeats every month. While the egg and follicle are developing in the ovary, tissues are building up inside the uterus, the reproductive organ where the baby would develop. The uterus develops a thick lining covered in tiny blood vessels. This prepares the uterus to receive an egg that could develop into a child (a fertilized egg). The occurs during the first part of the cycle. Ovulation, the release of an egg from the ovary, occurs at about the midpoint of the cycle. This would be around day 14 of a 28 day cycle. The egg is swept into the fallopian tube. If sperm is present, fertilization may occur. As sperm can only survive in the fallopian tube for up to a few days, fertilization can only occur within those few days post-ovulation. If the egg is fertilized, the egg makes its way through the fallopian tube into the uterus, where it imbeds into the thick lining. When this occurs, the monthly cycle stops. The monthly cycle does not resume until the pregnancy is over. If a sperm does not enter an egg, the lining of the uterus breaks down. Blood and other tissues from the lining break off from the uterus. They pass through the vagina and out of the body. This is called menstruation. Menstruation is also called a menstrual period. It lasts about 4 days, on average. When the menstrual period ends, the cycle repeats. Some women feel discomfort during this process. Some people think that the average length of a menstrual period is the same as the normal length. They assume that shorter or longer menstrual periods are not normal. In fact, menstrual periods can vary from 1 to 8 days in length. This is usually normal. The average length of the cycle (time between menstrual periods) is about 28 days, but there is no normal cycle length. Some women experience cramping and pain before and during menstruation. | text | null |
L_0601 | microscopes | T_3176 | Microscopes, tools that you may get to use in your class, are some of the most important tools in biology ( Figure Microscopy is the study of small objects using microscopes. Look at your fingertips. Before microscopes were invented in 1595, the smallest things you could see on yourself were the tiny lines in your skin. But what else is hidden in your skin? | text | null |
L_0601 | microscopes | T_3177 | Over four hundred years ago, two Dutch spectacle makers, Zaccharias Janssen and his son Hans, were experimenting with several lenses in a tube. They discovered that nearby objects appeared greatly enlarged, or magnified. This was the forerunner of the compound microscope and of the telescope. In 1665, Robert Hooke, an English natural scientist, used a microscope to zoom in on a piece of cork - the stuff that makes up the stoppers in wine bottles, which is made from tree bark. Inside of cork, he discovered tiny structures, which he called cells. It turns out that cells are the smallest structural unit of living organisms. This finding eventually led to the development of the theory that all living things are made of cells. Without microscopes, this discovery would not have been possible, and the cell theory would not have been developed. Hookes discovery of the cell set the stage for other scientists to discover other types of organisms. After Hooke, the "father of microscopy," Dutch scientist Antoine van Leeuwenhoek ( Figure 1.2) taught himself to make one of the first microscopes. In one of his early experiments, van Leeuwenhoek took a sample of scum from his own teeth and used his microscope to discover bacteria, the smallest living organism on the planet. Using microscopes, van Leeuwenhoek also discovered one-celled protists and sperm cells. Today, microscopes are used by all types of scientists, including cell biologists, microbiologists, virologists, forensic scientists, entomologists, taxonomists, and many other types. Antoine van Leeuwenhoek, a Dutch cloth merchant with a passion for microscopy. | text | null |
L_0601 | microscopes | T_3177 | Over four hundred years ago, two Dutch spectacle makers, Zaccharias Janssen and his son Hans, were experimenting with several lenses in a tube. They discovered that nearby objects appeared greatly enlarged, or magnified. This was the forerunner of the compound microscope and of the telescope. In 1665, Robert Hooke, an English natural scientist, used a microscope to zoom in on a piece of cork - the stuff that makes up the stoppers in wine bottles, which is made from tree bark. Inside of cork, he discovered tiny structures, which he called cells. It turns out that cells are the smallest structural unit of living organisms. This finding eventually led to the development of the theory that all living things are made of cells. Without microscopes, this discovery would not have been possible, and the cell theory would not have been developed. Hookes discovery of the cell set the stage for other scientists to discover other types of organisms. After Hooke, the "father of microscopy," Dutch scientist Antoine van Leeuwenhoek ( Figure 1.2) taught himself to make one of the first microscopes. In one of his early experiments, van Leeuwenhoek took a sample of scum from his own teeth and used his microscope to discover bacteria, the smallest living organism on the planet. Using microscopes, van Leeuwenhoek also discovered one-celled protists and sperm cells. Today, microscopes are used by all types of scientists, including cell biologists, microbiologists, virologists, forensic scientists, entomologists, taxonomists, and many other types. Antoine van Leeuwenhoek, a Dutch cloth merchant with a passion for microscopy. | text | null |
L_0601 | microscopes | T_3178 | Some modern microscopes use light, as Hookes and van Leeuwenhoeks did. Others may use electron beams or sound waves. Researchers now use these four types of microscopes: 1. Light microscopes allow biologists to see small details of a specimen. Most of the microscopes used in schools and laboratories are light microscopes. Light microscopes use lenses, typically made of glass or plastic, to focus light either into the eye, a camera, or some other light detector. The most powerful light microscopes can make images up to 2,000 times larger. 2. Transmission electron microscopes (TEM) focus a beam of electrons through an object and can make an image up to two million times bigger, with a very clear image. 3. Scanning electron microscopes (SEM) allow scientists to find the shape and surface texture of extremely small objects, including a paperclip, a bedbug, or even an atom. These microscopes slide a beam of electrons across the surface of a specimen, producing detailed maps of the surface of objects. Magnification in a SEM can be controlled over a range from about 10 to 500,000 times. 4. Scanning acoustic microscopes use sound waves to scan a specimen. These microscopes are useful in biology and medical research. | text | null |
L_0601 | microscopes | T_3179 | Scanning Electron Microscope at (5:04) Click image to the left or use the URL below. URL: 1. How is the electron beam focused? 2. What part of a specimen does a scanning electron microscope look at? 3. Why is it important that a specimen for an electron microscope be placed in a vacuum? Why is this step unnecessary for a light microscope? | text | null |
L_0606 | mollusks | T_3188 | When you take a walk along a beach, what do you find there? Sand, the ocean, lots of sunlight. You may also find shells. The shells you find are most likely left by organisms in the phylum Mollusca. On the beach, you can find the shells of many different mollusks ( Figure 1.1), including clams, mussels, scallops, oysters, and snails. Mollusks are invertebrates that usually have a hard shell, a mantle, and a radula. Their glossy pearls, mother of pearl, and abalone shells are like pieces of jewelry. Some mollusks, such as squid and octopus, do not have shells. | text | null |
L_0606 | mollusks | T_3189 | The Mollusks body is often divided into different parts ( Figure 1.2): On the beach, you can find a wide variety of mollusk shells. 1. A head with eyes or tentacles. 2. In most species, a muscular foot, which helps the mollusk move. Some mollusks use the foot for burrowing into the sand, and others use it for jet-propulsion. 3. A mantle, or fold of the outer skin lining the shell. The mantle often releases calcium carbonate, which creates an external shell, just like the ones you find on the beach. The shell is made of chitin, a tough, semitransparent substance. 4. A mass housing the organs. 5. A complete digestive tract that begins at the mouth and runs to the anus. 6. Most ocean mollusks have a gill or gills to absorb oxygen from the water. 7. Many species have a feeding structure, the radula, found only in mollusks. The radula can be thought of as a "tongue-like" structure. The radula is made mostly of chitin. Types of radulae range from structures used to scrape algae off of rocks to the beaks of squid and octopuses. This is the basic body plan of a mollusk. Note the mantle, gills, and radula. Keep in mind the basic body plan can differ slightly among the mollusks. | text | null |
L_0606 | mollusks | T_3189 | The Mollusks body is often divided into different parts ( Figure 1.2): On the beach, you can find a wide variety of mollusk shells. 1. A head with eyes or tentacles. 2. In most species, a muscular foot, which helps the mollusk move. Some mollusks use the foot for burrowing into the sand, and others use it for jet-propulsion. 3. A mantle, or fold of the outer skin lining the shell. The mantle often releases calcium carbonate, which creates an external shell, just like the ones you find on the beach. The shell is made of chitin, a tough, semitransparent substance. 4. A mass housing the organs. 5. A complete digestive tract that begins at the mouth and runs to the anus. 6. Most ocean mollusks have a gill or gills to absorb oxygen from the water. 7. Many species have a feeding structure, the radula, found only in mollusks. The radula can be thought of as a "tongue-like" structure. The radula is made mostly of chitin. Types of radulae range from structures used to scrape algae off of rocks to the beaks of squid and octopuses. This is the basic body plan of a mollusk. Note the mantle, gills, and radula. Keep in mind the basic body plan can differ slightly among the mollusks. | text | null |
L_0606 | mollusks | T_3190 | Mollusks are probably most closely related to organisms in the phylum Annelida, also known as segmented worms. This phylum includes the earthworm and leech. Scientists believe these two groups are related because, when they are in the early stage of development, they look very similar. Mollusks also share features of their organ systems with segmented worms. Unlike segmented worms, however, mollusks do not have body segmentation. The basic mollusk body shape is usually quite different as well. | text | null |
L_0607 | muscles and exercise | T_3191 | Regular physical exercise is important in preventing lifestyle diseases such as cardiovascular disease, some types of cancer, type 2 diabetes, and obesity. Regular exercise also improves the health of the muscular system. Muscles that are exercised are bigger and stronger than muscles that are not exercised. Exercise improves both muscular strength and muscular endurance. Muscular strength is the ability of a muscle to use force during a contraction. Muscular endurance is the ability of a muscle to continue to contract over a long time without getting tired. Exercises are grouped into three types depending on the effect they have on the body: Aerobic exercises, such as cycling, walking, and running, increase muscular endurance and cardiovascular health. Anaerobic exercises, such as weight training or sprinting, increase muscle strength. Flexibility exercises, such as stretching, improve the range of motion of muscles and joints. Regular stretching helps people avoid activity-related injuries. | text | null |
L_0607 | muscles and exercise | T_3192 | Anaerobic exercises comprise brief periods of physical exertion and high-intensity, strength-training activities. Anaerobic exercises cause muscles to get bigger and stronger. Anaerobic exercises use a resistance against which the muscle has to work to lift or push away. The resistance can be a weight or a persons own body weight (Figure | text | null |
L_0607 | muscles and exercise | T_3193 | Aerobic exercises are exercises in which a low to moderate level of exertion can be sustained over long periods. These are exercises that cause your heart to beat faster and allow your muscles to use oxygen to contract. If you exercise aerobically, overtime, your muscles will not get easily tired, and you will use oxygen more efficiently. Aerobic exercise (Figure 1.2) also helps improve cardiac muscle. | text | null |
L_0607 | muscles and exercise | T_3194 | Sometimes muscles and tendons get injured when a person starts doing an activity before they have warmed up properly. A warm up is a slow increase in the intensity of a physical activity that prepares muscles for an activity. Warming up increases the blood flow to the muscles and increases the heart rate. Warmed-up muscles and tendons are less likely to get injured. For example, before running or playing soccer, a person might jog slowly to warm muscles and increase their heart rate. Even elite athletes need to warm up (Figure 1.3). When you dont do a proper warm-up, several types of injuries can occur. A strain happens when muscle or tendons tear. Strains are also known as "pulled muscles." Another common injury is tendinitis, the irritation of the tendons. Strains and tendinitis are usually treated with rest, cold compresses, and stretching exercises that a physical therapist designs for each patient. Injuries can also be prevented by proper rest and recovery. If you do not get enough rest, your body will become injured and will not react well to exercise, or improve. You can also rest by doing a different activity. For example, if you run, you can rest your running muscles and joints by swimming. Warming up before the game helps the players avoid injuries. Some warm-ups may include stretching exercises. | text | null |
L_0608 | muscles bones and movement | T_3195 | When skeletal muscles contract, bones move. But how do muscles make your bones move? A voluntary muscles usually works across a joint. It is attached to both the bones on either side of the joint by strong cords called tendons. A tendon is a tough band of connective tissue that connects a muscle to a bone. Tendons are similar to ligaments, except that ligaments join bones to each other. Muscles move the body by contracting against the skeleton. When muscles contract, they get shorter. By contracting, muscles pull on bones and allow the body to move. Muscles can only contract. They cannot actively extend, though they can move or relax back into the non-contracted neutral position. Therefore, to move bones in opposite directions, pairs of muscles must work in opposition. Each muscle in the pair works against the other to move bones at the joints of the body. The muscle that contracts to cause a joint to bend is called the flexor. The muscle that contracts to cause the joint to straighten is called the extensor. When one muscle is contracted, the other muscle from the pair is always elongated. For example, the biceps and triceps muscles work together to allow you to bend and straighten your elbow. When you want to bend your elbow, your biceps muscle contracts (Figure 1.1), and, at the same time, the triceps muscle relaxes. The biceps is the flexor, and the triceps is the extensor of your elbow joint. Other muscles that work together are the quadriceps and hamstrings used to bend and straighten the knee, and the pectorals and trapezius used to move the arms and shoulders forward and backward. During daily routines we do not use muscles equally. For example, we use our biceps more than our triceps due to lifting against gravity. | text | null |
L_0608 | muscles bones and movement | T_3196 | Smooth muscles and cardiac muscles are not attached to bone. Recall that these types of muscles are under involuntary control. Smooth muscle is responsible for the contractility of hollow organs, such as blood vessels, the gastrointestinal tract, the bladder, or the uterus. Like skeletal muscles, smooth muscle fibers do contract together, causing the muscle to shorten. Smooth muscles have numerous functions, including the following. The smooth muscle in the uterus helps a woman to push out her baby. In the bladder, smooth muscle helps to push out urine. Smooth muscles move food through the digestive tract. In arteries, smooth muscle movements maintain the arteries diameter. Smooth muscle regulates air flow in lungs. Smooth muscle in the lungs helps the airways to expand and contract as necessary. Smooth muscles in arteries and veins are largely responsible for regulation of blood pressure. Cardiac muscle also contracts and gets shorter. This muscle is found only in the heart. The sudden burst of contraction forces blood throughout your body. When the cardiac muscle relaxes, the heart fills with blood. This rhythmic contraction must continue for your whole life, luckily the heart muscle never gets tired. If your heart beats 75 times a minute, how many times does it beat in an hour? A day? A year? 85 years? | text | null |
L_0609 | mutations | T_3197 | The process of DNA replication is not always 100% accurate. Sometimes the wrong base is inserted in the new strand of DNA. This wrong base could become permanent. A permanent change in the sequence of DNA is known as a mutation. Small changes in the DNA sequence are usually point mutations, which is a change in a single nucleotide. Once DNA has a mutation, that mutation will be copied each time the DNA replicates. After cell division, each resulting cell will carry the mutation. A mutation may have no effect. However, sometimes a mutation can cause a protein to be made incorrectly. A defect in the protein can affect how well the protein works, or whether it works at all. Usually the loss of a protein function is detrimental to the organism. In rare circumstances, though, the mutation can be beneficial. Mutations are a mechanism for how species evolve. For example, suppose a mutation in an animals DNA causes the loss of an enzyme that makes a dark pigment in the animals skin. If the population of animals has moved to a light colored environment, the animals with the mutant gene would have a lighter skin color and be better camouflaged. So in this case, the mutation is beneficial. | text | null |
L_0609 | mutations | T_3198 | If a single base is deleted (called a deletion, which is also a point mutation), there can be huge effects on the organism, because this may cause a frameshift mutation. Remember that the bases in the mRNA are read in groups of three by the tRNA. If the reading frame is off by even one base, the resulting sequence will consist of an entirely different set of codons. The reading of an mRNA is like reading three-letter words of a sentence. Imagine the sentence: The big dog ate the red cat. If you take out the second letter from "big," the frame will be shifted so now it will read: The bgd oga tet her edc at. One single deletion makes the whole sentence impossible to read. A point mutation that adds a base (known as an insertion) would also result in a frameshift. | text | null |
L_0609 | mutations | T_3199 | Mutations may also occur in chromosomes ( Figure 1.1). These mutations are going to be fairly large mutations, possible affecting many genes. Possible types of mutations in chromosomes include: 1. Deletion: When a segment of DNA is lost, so there is a missing segment in the chromosome. These usually result in many genes missing from the chromosome. 2. Duplication: When a segment of DNA is repeated, creating a longer chromosome. These usually result in multiple copies of genes in the chromosome. 3. Inversion: When a segment of DNA is flipped and then reattached to the same chromosome. 4. Insertion: When a segment of DNA from one chromosome is added to another, unrelated chromosome. 5. Translocation: When two segments from different chromosomes change positions. | text | null |
L_0609 | mutations | T_3200 | Many mutations are not caused by errors in replication. Mutations can happen spontaneously, and they can be caused by mutagens in the environment. Some chemicals, such as those found in tobacco smoke, can be mutagens. Sometimes mutagens can also cause cancer. Tobacco smoke, for example, is often linked to lung cancer. | text | null |
L_0610 | nails and hair | T_3201 | Along with the skin, the integumentary system includes the nails and hair. Both the nails and hair contain the tough protein, keratin. The keratin forms fibers, which makes your nails and hair tough and strong. Keratin is similar in toughness to chitin, the carbohydrate found in the exoskeleton of arthropods. | text | null |
L_0610 | nails and hair | T_3202 | Nails are similar to claws in other animals. They cover the tips of fingers and toes. Fingernails and toenails both grow from nail beds. As the nail grows, more cells are added at the nail bed. Older cells get pushed away from the nail bed and the nail grows longer. There are no nerve endings in the nail. Otherwise cutting your nails would hurt a lot! Nails act as protective plates over the fingertips and toes. Fingernails also help in sensing the environment. The area under your nail has many nerve endings. These nerve endings allow you to receive more information about objects you touch. The Guinness Book of World Records began tracking record fingernail lengths in 1955. At that time the record was 1 foot 10.75 inches long. The current record-holder for men is from India, with a record of 20 feet 2.25 inches for all nails on his left hand, the longest being his thumbnail at 4 feet 9.6 inches. The record for women is held by an American woman. The record is 28 feet (850 cm) for all nails of both hands, with the longest nail on her right thumb at 2 feet 11 inches. Since adult nails grow at about 3 mm a month (1/10 of an inch), how long would it take to grow such long nails? | text | null |
L_0610 | nails and hair | T_3203 | Hair is one of the defining characteristics of mammals. In fact, mammals are the only animals to have hair. Hair sticks out from the epidermis, but it grows from the dermis ( Figure 1.1). Hair grows from inside the hair follicle. New cells grow in the bottom part of the hair, called the bulb. Older cells get pushed up, and the hair grows longer. The cells that make up the hair strand are dead and filled with the rope-like protein keratin. Hair, hair follicle, and oil glands. The oil, called sebum, helps to prevent water loss from the skin. The sebaceous gland secretes sebum, which waterproofs the skin and hair. In humans, hair grows everywhere on the body except the soles of the feet and the palms of the hands, the lips, and the eyelids (except for eyelashes). Hair grows at a rate of about half an inch (1.25 cm) each month, or about 6 inches (15 cm) a year. Hair, especially on the head, helps to keep the body warm. The air traps a layer of warm air near the skin and acts like a warm blanket. Hair can also act as a filter. Nose hair helps to trap particles in the air that may otherwise travel to the lungs. Eyelashes shield eyes from dust and sunlight. Eyebrows stop salty sweat and rain from flowing into the eye. The worlds longest documented hair, according to Guinness World Records, belongs to Xie Qiuping of China at just under 18 feet 6 inches (5.627 m) when measured on May 8, 2004. She had been growing her hair since 1973 when she was 13 years old. | text | null |
L_0613 | nervous system | T_3210 | Michelle was riding her scooter when she hit a hole in the street and started to lose control. She thought she would fall, but, in the blink of an eye, she shifted her weight and kept her balance. Her heart was pounding, but at least she didnt get hurt. How was she able to react so quickly? Michelle can thank her nervous system for that ( Figure 1.1). The nervous system, together with the endocrine system, controls all the other organ systems. The nervous system sends one type of signal around the body, and the endocrine system sends another type of signal around the body. The endocrine system makes and releases chemical messenger molecules, or hormones, which tell other body parts that a change or a reaction is necessary. So what type of signal does the nervous system send? Controlling muscles and maintaining balance are just two of the roles of the nervous system. The nervous system also lets you: Sense your surroundings with your eyes and other sense organs. Sense the environment inside of your body, including temperature. Control your internal body systems and keep them in balance. Staying balanced when riding a scooter requires control over the bodys muscles. The nervous system controls the muscles and maintains balance. Prepare your body to fight or flee in an emergency. Use language, think, learn, and remember. The nervous system works by sending and receiving electrical signals. The main organs of the nervous system are the brain and the spinal cord. The signals are carried by nerves in the body, similar to the wires that carry electricity all over a house. The signals travel from all over the body to the spinal cord and up to the brain, as well as moving in the other direction. For example, when Michelle started to fall off her scooter, her nervous system sensed that she was losing her balance. It responded by sending messages from her brain to muscles in her body. Some muscles tightened while others relaxed. Maybe these actions moved her hips or her arms. The nervous system, working together with the muscular and skeletal systems, allowed Michelle to react to the situation. As a result, Michelles body became balanced again. The messages released by the nervous system traveled through nerves. Just like the electricity that travels through wires, nerve quickly carry the electrical messages around the body. Think about how quickly all this happens. It has to be really fast, otherwise Michelle would not have been able to react. What would happen if a car pulled out unexpectedly in front of Michelle? A signal would have to go from her eyes to her brain and then to her muscles. What allows the nervous system to react so fast. It starts with the special cell of the nervous system, the neuron. | text | null |
L_0614 | non infectious reproductive system disorders | T_3211 | Many disorders of the reproductive system are not sexually transmitted infections. They are not caused by pathogens, so they dont spread from person to person. They develop for other reasons. The disorders are different between males and females. In both genders, the disorders could cause a little discomfort, or they could cause death. | text | null |
L_0614 | non infectious reproductive system disorders | T_3212 | Most common disorders of the male reproductive system involve the testes. For example, injuries to the testes are very common. In teenagers, injuries to the testes most often occur while playing sports. An injury such as a strike or kick to the testes can be very painful. It may also cause bruising and swelling. Such injuries do not usually last very long. Another disorder of the testes is cancer. Cancer of the testes is most common in males aged 15 to 35. It occurs when cells in the testes grow out of control. The cells form a lump called a tumor. If found early, cancer of the testes usually can be easily cured with surgery. | text | null |
L_0614 | non infectious reproductive system disorders | T_3213 | Disorders of the female reproductive system may affect the vagina, uterus, or ovaries. They may also affect the breasts. One of the most common disorders is vaginitis. This is redness and itching of the vagina. It may be due to irritation by soap or bubble bath. Another possible cause of vaginitis is a yeast infection. Yeast normally grow in the vagina. A yeast infection happens when the yeast multiply too fast and cause symptoms. A yeast infection can be treated with medication. Bubble baths may be fun, but for women and girls they can cause irritation to the vagina. A common disorder of the ovaries is an ovarian cyst. A cyst is a sac filled with fluid or other material. An ovarian cyst is usually harmless, but it may cause pain. Most cysts slowly disappear and do not need treatment. Very large or painful cysts can be removed with surgery. Many teen girls have painful menstrual periods. They typically have cramping in the lower abdomen. Generally, this is nothing to worry about. Taking a warm bath or using a heating pad often helps. Exercise can help as well. A pain reliever like ibuprofen may also work. If the pain is severe, a doctor can prescribe stronger medicine to relieve the pain. The most common type of cancer in females is breast cancer. The cancer causes the cells of the breast to grow out of control and form a tumor. Breast cancer is rare in teens. It becomes more common as women get older. If breast cancer is found early, it usually can be cured with surgery. | text | null |
L_0616 | nonrenewable resources | T_3217 | A nonrenewable resource is a natural resource that is consumed or used up faster than it can be made by nature. Two main types of nonrenewable resources are fossil fuels and nuclear power. Fossil fuels, such as petroleum, coal, and natural gas, formed from plant and animal remains over periods from 50 to 350 million years ago. They took millions of years to form. Humans have been consuming fossil fuels for less than 200 years, yet remaining reserves of oil can supply our needs only until around the year 2055. Natural gas can only supply us until around 2085. Coal will last longer, until around the year 2250. That is why it is so important to develop alternate forms of energy, especially for our cars. Today, electric cars are becoming more and more common. Considering the year 2055 is not that far away, what would happen if we ran out of gasoline? Alternative use of energy, especially in transportation, must become a standard feature of all cars and trucks and planes by the middle of the century. Nuclear power is the use of nuclear energy ( nuclear fission) to create energy inside of a nuclear reactor ( Figure uranium fuel supplies, which will last to about the year 2100 (or longer) at current rates of use. However, new technologies could make some uranium fuel reserves more useful. Population growth, especially in developing countries, should make people think about how fast they are consuming resources. Governments around the world should seriously consider these issues. Developing nations will also increase demands on natural resources as they build more factories ( Figure 1.2). Improvements in technology, conservation of resources, and controls in population growth could all help to decrease the demand on natural resources. Aerial photo of the Bruce Nuclear Gener- ating Station near Kincardine, Ontario. Per capita energy consumption (2003) shows the unequal distribution of wealth, technology, and energy use. | text | null |
L_0616 | nonrenewable resources | T_3217 | A nonrenewable resource is a natural resource that is consumed or used up faster than it can be made by nature. Two main types of nonrenewable resources are fossil fuels and nuclear power. Fossil fuels, such as petroleum, coal, and natural gas, formed from plant and animal remains over periods from 50 to 350 million years ago. They took millions of years to form. Humans have been consuming fossil fuels for less than 200 years, yet remaining reserves of oil can supply our needs only until around the year 2055. Natural gas can only supply us until around 2085. Coal will last longer, until around the year 2250. That is why it is so important to develop alternate forms of energy, especially for our cars. Today, electric cars are becoming more and more common. Considering the year 2055 is not that far away, what would happen if we ran out of gasoline? Alternative use of energy, especially in transportation, must become a standard feature of all cars and trucks and planes by the middle of the century. Nuclear power is the use of nuclear energy ( nuclear fission) to create energy inside of a nuclear reactor ( Figure uranium fuel supplies, which will last to about the year 2100 (or longer) at current rates of use. However, new technologies could make some uranium fuel reserves more useful. Population growth, especially in developing countries, should make people think about how fast they are consuming resources. Governments around the world should seriously consider these issues. Developing nations will also increase demands on natural resources as they build more factories ( Figure 1.2). Improvements in technology, conservation of resources, and controls in population growth could all help to decrease the demand on natural resources. Aerial photo of the Bruce Nuclear Gener- ating Station near Kincardine, Ontario. Per capita energy consumption (2003) shows the unequal distribution of wealth, technology, and energy use. | text | null |
L_0619 | organic compounds | T_3223 | The main chemical components of living organisms are known as organic compounds. Organic compounds are molecules built around the element carbon (C). Living things are made up of very large molecules. These large molecules are called macromolecules because macro means large; they are made by smaller molecules bonding together. Our body gets these smaller molecules, the "building blocks" or monomers, of organic molecules from the food we eat. Which organic molecules do you recognize from the list below? The four main types of macromolecules found in living organisms, shown in Table 1.1, are: 1. 2. 3. 4. Proteins. Carbohydrates. Lipids. Nucleic Acids. Proteins C, H, O, N, S Enzymes, muscle fibers, antibodies Elements Examples Monomer building molecule) (small block Amino acids Carbohydrates C, H, O Sugar, glucose, starch, glycogen, cellulose Monosaccharides (simple sugars) Lipids C, H, O, P Fats, oils, waxes, steroids, phospho- lipids in membranes Often include fatty acids Nucleic Acids C, H, O, P, N DNA, RNA, ATP Nucleotides | text | null |
L_0619 | organic compounds | T_3224 | Carbohydrates are sugars, or long chains of sugars. An important role of carbohydrates is to store energy. Glucose ( Figure 1.1) is an important simple sugar molecule with the chemical formula C6 H12 O6 . Simple sugars are known as monosaccharides. Carbohydrates also include long chains of connected sugar molecules. These long chains often consist of hundreds or thousands of monosaccharides bonded together to form polysaccharides. Plants store sugar in polysaccharides called starch. Animals store sugar in polysaccharides called glycogen. You get the carbohydrates you need for energy from eating carbohydrate-rich foods, including fruits and vegetables, as well as grains, such as bread, rice, or corn. A molecule of glucose, a type of carbohy- drate. | text | null |
L_0619 | organic compounds | T_3225 | Proteins are molecules that have many different functions in living things. All proteins are made of monomers called amino acids ( Figure 1.2) that connect together like beads on a necklace ( Figure 1.3). There are only 20 common amino acids needed to build proteins. These amino acids form in thousands of different combinations, making about 100,000 or more unique proteins in humans. Proteins can differ in both the number and order of amino acids. It is the number and order of amino acids that determines the shape of the protein, and it is the shape (structure) of the protein that determines the unique function of the protein. Small proteins have just a few hundred amino acids. The largest proteins have more than 25,000 amino acids. This model shows the general structure of all amino acids. Only the side chain, R, varies from one amino acid to another. KEY: H = hydrogen, N = nitrogen, C = carbon, O = oxygen, R = variable side chain. Many important molecules in your body are proteins. Examples include enzymes, antibodies, and muscle fiber. Enzymes are a type of protein that speed up chemical reactions. They are known as "biological catalysts." For example, your stomach would not be able to break down food if it did not have special enzymes to speed up the rate of digestion. Antibodies that protect you against disease are proteins. Muscle fiber is mostly protein ( Figure 1.4). Muscle fibers are made mostly of protein. Its important for you and other animals to eat food with protein, because we cannot make certain amino acids on our own. You can get proteins from plant sources, such as beans, and from animal sources, like milk or meat. When you eat food with protein, your body breaks the proteins down into individual amino acids and uses them to build new proteins. You really are what you eat! | text | null |
L_0619 | organic compounds | T_3225 | Proteins are molecules that have many different functions in living things. All proteins are made of monomers called amino acids ( Figure 1.2) that connect together like beads on a necklace ( Figure 1.3). There are only 20 common amino acids needed to build proteins. These amino acids form in thousands of different combinations, making about 100,000 or more unique proteins in humans. Proteins can differ in both the number and order of amino acids. It is the number and order of amino acids that determines the shape of the protein, and it is the shape (structure) of the protein that determines the unique function of the protein. Small proteins have just a few hundred amino acids. The largest proteins have more than 25,000 amino acids. This model shows the general structure of all amino acids. Only the side chain, R, varies from one amino acid to another. KEY: H = hydrogen, N = nitrogen, C = carbon, O = oxygen, R = variable side chain. Many important molecules in your body are proteins. Examples include enzymes, antibodies, and muscle fiber. Enzymes are a type of protein that speed up chemical reactions. They are known as "biological catalysts." For example, your stomach would not be able to break down food if it did not have special enzymes to speed up the rate of digestion. Antibodies that protect you against disease are proteins. Muscle fiber is mostly protein ( Figure 1.4). Muscle fibers are made mostly of protein. Its important for you and other animals to eat food with protein, because we cannot make certain amino acids on our own. You can get proteins from plant sources, such as beans, and from animal sources, like milk or meat. When you eat food with protein, your body breaks the proteins down into individual amino acids and uses them to build new proteins. You really are what you eat! | text | null |
L_0619 | organic compounds | T_3225 | Proteins are molecules that have many different functions in living things. All proteins are made of monomers called amino acids ( Figure 1.2) that connect together like beads on a necklace ( Figure 1.3). There are only 20 common amino acids needed to build proteins. These amino acids form in thousands of different combinations, making about 100,000 or more unique proteins in humans. Proteins can differ in both the number and order of amino acids. It is the number and order of amino acids that determines the shape of the protein, and it is the shape (structure) of the protein that determines the unique function of the protein. Small proteins have just a few hundred amino acids. The largest proteins have more than 25,000 amino acids. This model shows the general structure of all amino acids. Only the side chain, R, varies from one amino acid to another. KEY: H = hydrogen, N = nitrogen, C = carbon, O = oxygen, R = variable side chain. Many important molecules in your body are proteins. Examples include enzymes, antibodies, and muscle fiber. Enzymes are a type of protein that speed up chemical reactions. They are known as "biological catalysts." For example, your stomach would not be able to break down food if it did not have special enzymes to speed up the rate of digestion. Antibodies that protect you against disease are proteins. Muscle fiber is mostly protein ( Figure 1.4). Muscle fibers are made mostly of protein. Its important for you and other animals to eat food with protein, because we cannot make certain amino acids on our own. You can get proteins from plant sources, such as beans, and from animal sources, like milk or meat. When you eat food with protein, your body breaks the proteins down into individual amino acids and uses them to build new proteins. You really are what you eat! | text | null |
L_0619 | organic compounds | T_3226 | Have you ever tried to put oil in water? They dont mix. Oil is a type of lipid. Lipids are molecules such as fats, oils, and waxes. The most common lipids in your diet are probably fats and oils. Fats are solid at room temperature, whereas oils are fluid. Animals use fats for long-term energy storage and to keep warm. Plants use oils for long- term energy storage. When preparing food, we often use animal fats, such as butter, or plant oils, such as olive oil or canola oil. There are many more type of lipids that are important to life. One of the most important are the phospholipids that make up the protective outer membrane of all cells ( Figure 1.5). These lipid membranes are impermeable to most water soluble compounds. | text | null |
L_0619 | organic compounds | T_3227 | Nucleic acids are long chains of nucleotides. Nucleotides are made of a sugar, a nitrogen-containing base, and a phosphate group. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two main nucleic acids. DNA is a double-stranded nucleic acid. DNA is the molecule that stores our genetic information ( Figure 1.6). The single- stranded RNA is involved in making proteins. ATP (adenosine triphosphate), known as the "energy currency" of the cell, is also a nucleic acid. | text | null |
L_0621 | organization of the human body | T_3232 | Cells are grouped together to carry out specific functions. A group of cells that work together form a tissue. Your body has four main types of tissues, as do the bodies of other animals. These tissues make up all structures and contents of your body. An example of each tissue type is pictured in the Figure 1.1. Your body has four main types of tissue: nervous tissue, epithelial tissue, connective tissue, and muscle tissue. They are found throughout your body. 1. Epithelial tissue is made up of layers of tightly packed cells that line the surfaces of the body. Examples of epithelial tissue include the skin, the lining of the mouth and nose, and the lining of the digestive system. 2. Connective tissue is made up of many different types of cells that are all involved in supporting and binding other tissues of the body. Examples include tendon, cartilage, and bone. Blood is also classified as a specialized connective tissue. 3. Muscle tissue is made up of bands of cells that contract and allow movement. 4. Nervous tissue is made up of nerve cells that sense stimuli and transmit signals. Nervous tissue is found in nerves, the spinal cord, and the brain. | text | null |
L_0621 | organization of the human body | T_3233 | A single tissue alone cannot do all the jobs that are needed to keep you alive and healthy. Two or more tissues working together can do a lot more. An organ is a structure made of two or more tissues that work together. The heart ( Figure 1.2) is made up of the four types of tissues. The four different tissue types work to- gether in the heart as they do in the other organs. | text | null |
L_0621 | organization of the human body | T_3234 | Your heart pumps blood around your body. But how does your heart get blood to and from every cell in your body? Your heart is connected to blood vessels such as veins and arteries. Organs that work together form an organ system. Together, your heart, blood, and blood vessels form your cardiovascular system. What other organ systems can you think of? | text | null |
L_0621 | organization of the human body | T_3235 | Your bodys 12 organ systems are shown below ( Table 1.1). Your organ systems do not work alone in your body. They must all be able to work together. For example, one of the most important functions of organ systems is to provide cells with oxygen and nutrients and to remove toxic waste products such as carbon dioxide. A number of organ systems, including the cardiovascular and respiratory systems, all work together to do this. Organ System Cardiovascular Major Tissues and Organs Heart; blood vessels; blood Lymphatic Lymph nodes; lymph vessels Digestive Esophagus; stomach; small intes- tine; large intestine Pituitary gland, hypothalamus; adrenal glands; ovaries; testes Endocrine Function Transports oxygen, hormones, and nutrients to the body cells. Moves wastes and carbon dioxide away from cells. Defend against infection and dis- ease, moves lymph between tissues and the blood stream. Digests foods and absorbs nutrients, minerals, vitamins, and water. Produces hormones that communi- cate between cells. Organ System Integumentary Major Tissues and Organs Skin, hair, nails Muscular Cardiac (heart) muscle; skeletal muscle; smooth muscle; tendons Brain, spinal cord; nerves Nervous Reproductive Respiratory Female: uterus; vagina; fallopian tubes; ovaries Male: penis; testes; seminal vesi- cles Trachea, larynx, pharynx, lungs Skeletal Bones, cartilage; ligaments Urinary Kidneys; urinary bladder Immune Bone marrow; spleen; white blood cells Function Provides protection from injury and water loss, physical defense against infection by microorganisms, and temperature control. Involved in movement and heat pro- duction. Collects, transfers, and processes information. Produces gametes (sex cells) and sex hormones. Brings air to sites where gas ex- change can occur between the blood and cells (around body) or blood and air (lungs). Supports and protects soft tissues of body; produces blood cells; stores minerals. Removes extra water, salts, and waste products from blood and body; controls pH; controls water and salt balance. Defends against diseases. | text | null |
L_0623 | origins of life | T_3241 | There is good evidence that life has probably existed on Earth for most of Earths history. Fossils of blue-green algae found in Australia are the oldest fossils of life forms on Earth. They are at least 3.5 billion years old ( Figure 1.1). | text | null |
L_0623 | origins of life | T_3242 | How did life begin? In order to answer this question, scientists need to know what kinds of materials were available at that time. We know that the ingredients for life were present at the beginning of Earths history. Scientists believe early Earth did not contain oxygen gas (photosynthesis had yet to evolve), but did contain other gases, including: nitrogen gas, carbon dioxide, carbon monoxide, water vapor, hydrogen sulfide. Some of the oldest fossils on Earth were found along the coast of Australia, similar to the area shown here. Where did these ingredients come from? Some chemicals were in water and volcanic gases ( Figure 1.2). Other chemicals would have come from meteorites in space. Energy to drive chemical reactions was provided by volcanic eruptions and lightning. Today, we have evidence that life on Earth came from random reactions between chem- ical compounds, which formed molecules, or groups of atoms bonded together. Small molecules, such as those present in the early atmosphere, can provide the components (including the elements C, H, N, O and S) to make larger molecules. These early molecules further reacted and eventually formed even larger molecules and organic compounds, such as amino acids (which combine to form proteins), and nucleotides (which form nucleic acids - RNA or DNA). These organic molecules eventually came together in the right combinations to form basic cells. The components that were necessary for the formation of the first cells are still being studied. How long did it take to develop the first life forms? As much as 1 billion years. Many scientists still study the origin of the first life forms because there are many questions left unanswered, such as, "Did proteins or nucleic acids develop first?" or "What exactly were early Earths atmospheric conditions like?" There is a lot of work still left to answer these and similar questions. Some clues to the origins of life on Earth come from studying the early life forms that developed in hot springs, such as the Grand Prismatic Spring at Yellowstone National Park. This spring is approxi- mately 250 feet deep and 300 feet wide. | text | null |
L_0623 | origins of life | T_3242 | How did life begin? In order to answer this question, scientists need to know what kinds of materials were available at that time. We know that the ingredients for life were present at the beginning of Earths history. Scientists believe early Earth did not contain oxygen gas (photosynthesis had yet to evolve), but did contain other gases, including: nitrogen gas, carbon dioxide, carbon monoxide, water vapor, hydrogen sulfide. Some of the oldest fossils on Earth were found along the coast of Australia, similar to the area shown here. Where did these ingredients come from? Some chemicals were in water and volcanic gases ( Figure 1.2). Other chemicals would have come from meteorites in space. Energy to drive chemical reactions was provided by volcanic eruptions and lightning. Today, we have evidence that life on Earth came from random reactions between chem- ical compounds, which formed molecules, or groups of atoms bonded together. Small molecules, such as those present in the early atmosphere, can provide the components (including the elements C, H, N, O and S) to make larger molecules. These early molecules further reacted and eventually formed even larger molecules and organic compounds, such as amino acids (which combine to form proteins), and nucleotides (which form nucleic acids - RNA or DNA). These organic molecules eventually came together in the right combinations to form basic cells. The components that were necessary for the formation of the first cells are still being studied. How long did it take to develop the first life forms? As much as 1 billion years. Many scientists still study the origin of the first life forms because there are many questions left unanswered, such as, "Did proteins or nucleic acids develop first?" or "What exactly were early Earths atmospheric conditions like?" There is a lot of work still left to answer these and similar questions. Some clues to the origins of life on Earth come from studying the early life forms that developed in hot springs, such as the Grand Prismatic Spring at Yellowstone National Park. This spring is approxi- mately 250 feet deep and 300 feet wide. | text | null |
L_0624 | outdoor air pollution | T_3243 | Air is all around us. Air is essential for life. Sometimes, humans can pollute the air. For example, releasing smoke and dust from factories and cars can cause air pollution. Air pollution is due to chemical substances and particles released into the air mainly by human actions. This pollution affects entire ecosystems around the world. Pollution can also cause many human health problems, and it can also cause death. Air pollution can be found both outdoors and indoors. Outdoor air pollution is made of chemical particles. When smoke or other pollutants enter the air, the particles found in the pollution mix with the air. Air is polluted when it contains many large toxic particles. Outdoor air pollution changes the natural characteristics of the atmosphere. Primary pollutants are added directly to the atmosphere. Fires add primary pollutants to the air. Particles released from the fire directly enter the air and cause pollution ( Figure 1.1). Burning of fossil fuels such as oil and coal is a major source of primary pollutants ( Figure Secondary pollutants are formed when primary pollutants interact with sunlight, air, or each other. They do not directly cause pollution. However, when they interact with other parts of the air, they do cause pollution. For example, ozone is created when some pollutants interact with sunlight. High levels of ozone in the atmosphere can cause problems for humans. Wildfires, either natural or human-caused, release particles into the air, one of the many causes of air pollution. A major source of air pollution is the burn- ing of fossil fuels from factories, power plants, and motor vehicles. | text | null |
L_0624 | outdoor air pollution | T_3243 | Air is all around us. Air is essential for life. Sometimes, humans can pollute the air. For example, releasing smoke and dust from factories and cars can cause air pollution. Air pollution is due to chemical substances and particles released into the air mainly by human actions. This pollution affects entire ecosystems around the world. Pollution can also cause many human health problems, and it can also cause death. Air pollution can be found both outdoors and indoors. Outdoor air pollution is made of chemical particles. When smoke or other pollutants enter the air, the particles found in the pollution mix with the air. Air is polluted when it contains many large toxic particles. Outdoor air pollution changes the natural characteristics of the atmosphere. Primary pollutants are added directly to the atmosphere. Fires add primary pollutants to the air. Particles released from the fire directly enter the air and cause pollution ( Figure 1.1). Burning of fossil fuels such as oil and coal is a major source of primary pollutants ( Figure Secondary pollutants are formed when primary pollutants interact with sunlight, air, or each other. They do not directly cause pollution. However, when they interact with other parts of the air, they do cause pollution. For example, ozone is created when some pollutants interact with sunlight. High levels of ozone in the atmosphere can cause problems for humans. Wildfires, either natural or human-caused, release particles into the air, one of the many causes of air pollution. A major source of air pollution is the burn- ing of fossil fuels from factories, power plants, and motor vehicles. | text | null |
L_0624 | outdoor air pollution | T_3244 | Most air pollutants can be traced to the burning of fossil fuels. Fossil fuels are burned during many processes, including in power plants to create electricity, in factories to make machinery run, in power stoves and furnaces for heating, and in waste facilities. Perhaps one of the biggest uses of fossil fuels is in transportation. Fossil fuels are used in cars, trains, and planes. Air pollution can also be caused by agriculture, such as cattle ranching and the use of fertilizers and pesticides. Other sources of air pollution include the production of plastics, refrigerants, and aerosols, in nuclear power and defense, from landfills and mining, and from biological warfare. | text | null |
L_0624 | outdoor air pollution | T_3245 | One result of air pollution is acid rain. Acid rain is precipitation with a low (acidic) pH. This rain can be very destructive to wildlife. When acid rain falls in forests, freshwater habitats, or soils, it can kill insects and aquatic life. It causes this damage because of its very low pH. Sulfur oxides and nitrogen oxides in the air both cause acid rain to form ( Figure 1.3). Sulfur oxides are chemicals that are released from coal-fired power plants. Nitrogen oxides are released from motor vehicle exhaust. A forest in the Jizera Mountains of the Czech Republic shows effects caused by acid rain. What do you observe? | text | null |
L_0624 | outdoor air pollution | T_3246 | Pollutants also affect the atmosphere through their contribution to global warming. Global warming is an increase in the Earths temperature. It is thought to be caused mostly by the increase of greenhouse gases like carbon dioxide. Greenhouse gases can be released by factories that burn fossil fuels. Over the past 20 years, burning fossil fuels has produced about three-quarters of the carbon dioxide from human activity. The rest of the carbon dioxide in the atmosphere is there because of deforestation, or cutting down trees ( Figure 1.4). Trees absorb carbon dioxide during cellular respiration, so when trees are cut down, they cannot remove carbon dioxide from the air. This increase in global temperature will cause the sea level to rise. It is also expected to produce an increase in extreme weather events and change the amount of precipitation. Global warming may also cause food shortages and species extinction. | text | null |
L_0626 | pathogens | T_3250 | Has this ever happened to you? A student sitting next to you in class has a cold. The other student is coughing and sneezing, but you feel fine. Two days later, you come down with a cold, too. Diseases like colds are contagious. Contagious diseases are also called infectious diseases. An infectious disease is a disease that spreads from person to person. Infectious diseases are caused by pathogens. A pathogen is a living thing or virus that causes disease. Pathogens are commonly called germs. They can travel from one person to another. | text | null |
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