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L_0434 | the scale of evolution | T_2607 | What happens when forces of evolution work over a long period of time? The answer is macroevolution. An example is the evolution of a new species. | text | null |
L_0434 | the scale of evolution | T_2608 | The evolution of a new species is called speciation. A species is a group of organisms that can mate and produce fertile offspring together but not with members of other such groups. What must happen for a new species to arise? Some members of an existing species must change so they can no produce fertile offspring with the rest of the species. Speciation often occurs when some members of a species break off from the rest. The splinter group evolves in isolation from the original species. The original species also continues to evolve. Sooner or later, the splinter group becomes too different to breed with members of the original species. At that point, a new species has formed. A good example of speciation involves anole lizards, like the one pictured in Figure 7.15. There are about 150 different species of anole lizards in the Caribbean Islands. Scientists think that a single species of lizard first colonized one of the islands about 50 million years ago. A few lizards from this original species eventually reached each of the other islands, where they evolved in isolation. Anoles in different habitats evolved traits that affected mating. For example, they evolved skin flaps of different colors. Females didnt respond to male anoles with the wrong color skin flap. This prevented them from mating. Eventually, all the different species of anoles known today evolved. Watch this interesting video to learn more about anole speciation in the Caribbean: | text | null |
L_0434 | the scale of evolution | T_2609 | Sometimes two species evolve the same traits. It happens because they live in similar habitats. This is called convergent evolution. Caribbean Anoles demonstrate this as well. On each Caribbean island, anoles in similar habitats evolved the same traits. For example, anoles that lived on the forest floor evolved long legs for leaping and running on the ground. Anoles that lived on tree branches evolved short legs that helped them cling to small branches and twigs. Anoles that lived at the tops of trees evolved large toe pads that allowed them to walk on leaves without falling. On each of the islands, there were anole species that evolved in each of these same ways. | text | null |
L_0434 | the scale of evolution | T_2610 | Two species may often interact with each other and have a close relationship. Examples include flowers and the animals that pollinate them. When one of the two species evolves new traits, the other species may evolve matching traits. This is called coevolution. You can see an example of this in Figure 7.16. The very long beak of this hummingbird co-evolved with the tubular flowers it pollinates. Only this species of hummingbird can reach nectar deep in the flowers. | text | null |
L_0434 | the scale of evolution | T_2611 | Darwin thought that evolution occurs very slowly. This is likely if conditions are stable. But what if conditions are changing rapidly? Evolution is likely to occur more rapidly as well. For example, the Grants showed that evolution occurred in just a couple of years in Darwins finches. This happened when a severe drought killed off a lot of the plants that the birds needed for food. Millions of fossils have been found since Darwins time. They show that evolution may occur in fits and starts. Long period of little or gradual change may be interrupted by bursts of rapid change. The rate of evolution is influenced by how the environment is changing. Today, Earths climate is changing rapidly. How do you think this might affect the rate of evolution? | text | null |
L_0435 | history of life on earth | T_2612 | Its hard to grasp the vast amounts of time since Earth formed and life first appeared. It may help to think of Earths history as a 24-hour day. | text | null |
L_0435 | history of life on earth | T_2613 | Figure 7.17 shows the history of Earth in a day. In this model, the planet forms at midnight. The first prokaryotes evolve around 3:00 am. Eukaryotes evolve at about 1:00 pm. Animals dont evolve until almost 8:00 pm. Humans appear only in the last minute of the day. Relating these major events in Earths history to a 24-hour day helps to put them in perspective. | text | null |
L_0435 | history of life on earth | T_2614 | Another tool for understanding the history of Earth and its life is the geologic time scale. You can see this time scale in Figure 7.18. It divides Earths history into eons, eras, and periods. These divisions are based on major changes in geology, climate, and the evolution of life. The geologic time scale organizes Earths history on the basis of important events instead of time alone. It also puts more focus on recent events, about which we know the most. | text | null |
L_0435 | history of life on earth | T_2615 | The Precambrian Supereon is the first major division of Earths history (see Figure 7.18). It covers the time from Earths formation 4.6 billion years ago to 544 million years ago. To see how life evolved during the Precambrian and beyond, watch this wonderful video. Its a good introduction to the rest of the lesson. MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0435 | history of life on earth | T_2616 | When Earth first formed, it was a fiery hot, barren ball. It had no oceans or atmosphere. Rivers of melted rock flowed over its surface. Gradually, the planet cooled and formed a solid crust. Gases from volcanoes formed an atmosphere, although it contained only a trace of oxygen. As the planet continued to cool, clouds formed and rain fell. Rainwater helped form oceans. The ancient atmosphere and oceans would be toxic to modern life, but they set the stage for life to begin. | text | null |
L_0435 | history of life on earth | T_2617 | All living things consist of organic molecules. Many scientists think that organic molecules evolved before cells, perhaps as early as 4 billion years ago. Its possible that lightning sparked chemical reactions in Earths early atmosphere. This could have created a soup of organic molecules from inorganic chemicals. Some scientists think that RNA was the first organic molecule to evolve. RNA can not only encode genetic instructions. Some RNA molecules can carry out chemical reactions. All living things are made of one or more cells. How the first cells evolved is not known for certain. Scientists speculate that lipid membranes grew around RNA molecules. The earliest cells may have consisted of little more than RNA inside a lipid membrane. You can see a model of such a cell in Figure 7.19. The first cells probably evolved between 3.8 and 4 billion years ago. Scientists think that one cell, called the Last Universal Common Ancestor (LUCA), gave rise to all of the following life on Earth. LUCA may have existed around 3.5 billion years ago. | text | null |
L_0435 | history of life on earth | T_2618 | The earliest cells were heterotrophs. They were unable to make food. Instead, they got energy by "eating" organic molecules in the soup around them. The earliest cells were also prokaryotes. They lacked a nucleus and other organelles. Gradually, these and other traits evolved. Photosynthesis evolved about 3 billion years ago. After that, certain cells could use sunlight to make food. These were the first autotrophs. They made food for themselves and other cells. They also added oxygen to the atmosphere. The oxygen was a waste product of photosynthesis. Oxygen was toxic to many cells. They had evolved in its absence. Many of them died out. The few that survived evolved a new way to use oxygen. They used it to get energy from food. This is the process of cellular respiration. The first eukaryotic cells probably evolved about 2 billion years ago. Thats when cells evolved organelles and a nucleus. Figure 7.20 shows one theory about the origin of organelles. According to this theory, a large cell engulfed small cells. The small cells took on special roles that helped the large cell function. In return, the small cells got nutrients from the large cell. Eventually, the large and small cells could no longer live apart. With their specialized organelles, eukaryotic cells were powerful and efficient. Eukaryotes would go on to evolve sexual reproduction. They would also evolve into multicellular organisms. The first multicellular organisms evolved about 1 billion years ago. | text | null |
L_0435 | history of life on earth | T_2619 | At the end of the Precambrian, a mass extinction occurred. In a mass extinction, the majority of species die out. The Precambrian mass extinction was the first of six mass extinctions that occurred on Earth. Its not certain what caused this first mass extinction. Changes in Earths geology and climate were no doubt involved. | text | null |
L_0435 | history of life on earth | T_2620 | The Paleozoic Era lasted from 544 to 245 million years ago. It is divided into six periods. | text | null |
L_0435 | history of life on earth | T_2621 | The Precambrian mass extinction opened up many niches for new organisms to fill. As a result, the Cambrian Period began with an explosion of new kinds of living things. For example, many types of simple animals called sponges evolved. Trilobites were also very common. Sponges and trilobites were small ocean invertebrates. These are animals without a backbone. You can see examples of them in Figure 7.21. | text | null |
L_0435 | history of life on earth | T_2622 | During the Ordovician Period, the oceans became filled with many kinds of invertebrates. The first fish also evolved. Plants colonized the land for the first time. However, animals remained in the water. | text | null |
L_0435 | history of life on earth | T_2623 | Corals appeared in the oceans during the Silurian period. Fish continued to evolve. On land, vascular plants appeared. These are plants that have special tissues to circulate water and other substances. This allowed plants to become larger and colonize drier habitats. | text | null |
L_0435 | history of life on earth | T_2624 | During the Devonian Period, the first seed plants evolved. Seeds have a protective coat and contain stored food. This was a big advantage over other types of plant reproduction. Seed plants eventually became the most common type of plants on land. In the oceans, fish with lobe fins evolved. These fish could breathe air when they raised their head above water. This was a step in the evolution of animals that could live on land. | text | null |
L_0435 | history of life on earth | T_2625 | In the Carboniferous Period, forests of huge ferns and trees were widespread. You can see how these first forests might have looked in Figure 7.22. After the ferns and trees died, their remains eventually turned to coal. The first amphibians also evolved during this period. They could live on land but had to return to the water to lay their eggs. After amphibians, the earliest reptiles appeared. They were the first animals that could reproduce on land and move away from the water. | text | null |
L_0435 | history of life on earth | T_2626 | During the Permian Period, all the major landmasses moved together to form one supercontinent. The supercontinent has been named Pangaea. You can see how it looked in Figure 7.23. At this time, temperatures were extreme and the climate became very dry. As a result, plants and animals evolved ways to cope with dryness. For example, reptiles evolved leathery skin. This helped prevent water loss. Plants evolved waxy leaves for the same purpose. The Permian Period ended with Earths second mass extinction. During this event, most of Earths species went extinct. It was the most massive extinction ever recorded. Its not clear why it happened. One possible reason is that a very large meteorite struck Earth. Another possibility is the eruption of enormous volcanoes. Either event could create a huge amount of dust. The dust might block out sunlight for months. This would cool the planet and prevent photosynthesis. | text | null |
L_0435 | history of life on earth | T_2627 | The Permian mass extinction paved the way for another burst of new life at the start of the Mesozoic Era. This era is known as the age of dinosaurs. It is divided into three periods. | text | null |
L_0435 | history of life on earth | T_2628 | During the Triassic Period, the first dinosaurs evolved from reptile ancestors. They eventually colonized the air and water in addition to the land. There were also forests of huge seed ferns and cone-bearing conifer trees in the Triassic Period. Modern corals, fish, and insects all evolved in this period as well. The supercontinent of Pangea started to break up. The Triassic Period ended in a mass extinction. The majority of species died out, but dinosaurs were spared. | text | null |
L_0435 | history of life on earth | T_2629 | The Triassic mass extinction gave dinosaurs the opportunity to really flourish during the Jurassic Period. Thats why this period is called the golden age of dinosaurs. The earliest birds also evolved during the Jurassic from dinosaur ancestors. In addition, all the major groups of mammals appeared. Flowering plants also appeared for the first time. New insects evolved to pollinate them. The continents continued to move apart. | text | null |
L_0435 | history of life on earth | T_2630 | During the Cretaceous Period, the dinosaurs reached their maximum size and distribution. For example, the well- known Tyrannosaurus rex weighed at least 7 tons! You can get an idea of how big it was from the T. rex skeleton in Figure 7.24. (Notice how small the person looks in the bottom left of the photo.) By the end of the Cretaceous, the continents were close to their present locations. The period ended with another mass extinction. This time, the dinosaurs went extinct. What happened to the dinosaurs? Some scientists think that a comet or asteroid may have crashed into Earth. This could darken the sky, shut down photosynthesis, and cause climate change. Other factors probably contributed to the mass extinction as well. | text | null |
L_0435 | history of life on earth | T_2631 | The extinction of the dinosaurs at the end of the Mesozoic Era paved the way for mammals to take over. Thats why the Cenozoic Era is called the age of mammals. They soon became the dominant land animals on Earth. The Cenozoic is divided into two periods. | text | null |
L_0435 | history of life on earth | T_2632 | During the Tertiary Period, many new kinds of mammals evolved. For example, primates and human ancestors first appeared during this period. Many mammals also increased in size. Modern rain forests and grasslands appeared. Flowering plants and insects increased in numbers. | text | null |
L_0435 | history of life on earth | T_2633 | During the Quaternary Period, the climate cooled. This caused a series of ice ages. Glaciers advanced southward from the North Pole. They reached as far south as Chicago and New York City. Sea levels fell because so much water was frozen in glaciers. This exposed land bridges between continents. The land bridges allowed land animals to move to new areas. Some mammals adapted to the cold by evolving very large size and thick fur. An example is the woolly mammoth, shown in Figure 7.25. Other mammals moved closer to the equator. Those that couldnt adapt or move went extinct, along with many plants. The last ice age ended about 12,000 years ago. By then, our own species, Homo sapiens, had evolved. After that, we were eyewitnesses to the story of life. As a result, the recent past is less of a mystery than the billions of years before it. | text | null |
L_0437 | bacteria | T_2649 | Bacteria are the most abundant living things on Earth. They live in almost all environments. They are found in the air, ocean, soil, and intestines of animals. They are even found in rocks deep below Earths surface. Any surface that has not been sterilized is likely to be covered with bacteria. The total number of bacteria in the world is amazing. Its estimated to be about 5 million trillion trillion. If you write that number in digits, it has 30 zeroes! | text | null |
L_0437 | bacteria | T_2650 | Bacteria are the most diverse organisms on Earth. Thousands of species of bacteria have been discovered. Many more are thought to exist. The known species are classified on the basis of various traits. For example, they may be classified by the shape of their cells. They may also be classified by how they react to a dye called Gram stain. | text | null |
L_0437 | bacteria | T_2651 | Bacteria come in several different shapes. The different shapes can be seen by examining bacteria under a light microscope. Therefore, its relatively easy to classify them by shape. There are three types of bacteria based on shape: bacilli (bacillus, singular), or rod shaped. cocci (coccus, singular), or sphere shaped. spirilli (spirillus, singular), or spiral shaped. You can see a common example of each type of bacteria in Figure 8.10. | text | null |
L_0437 | bacteria | T_2652 | Different types of bacteria stain a different color when Gram stain is applied to them. This makes them easy to identify. Some stain purple and some stain red, as you can see in Figure 8.11. The two types differ in their outer layers. This explains why they stain differently. Bacteria that stain purple are called gram-positive bacteria. They have a thick cell wall without an outer membrane. Bacteria that stain red are called gram-negative bacteria. They have a thin cell wall with an outer membrane. | text | null |
L_0437 | bacteria | T_2652 | Different types of bacteria stain a different color when Gram stain is applied to them. This makes them easy to identify. Some stain purple and some stain red, as you can see in Figure 8.11. The two types differ in their outer layers. This explains why they stain differently. Bacteria that stain purple are called gram-positive bacteria. They have a thick cell wall without an outer membrane. Bacteria that stain red are called gram-negative bacteria. They have a thin cell wall with an outer membrane. | text | null |
L_0437 | bacteria | T_2653 | Bacteria and people have many important relationships. Bacteria make our lives easier in a variety of ways. In fact, we could not survive without them. On the other hand, many bacteria can make us sick. Some of them are even deadly. For a dramatic overview of the many roles of bacteria, watch this stunning video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0437 | bacteria | T_2654 | Bacteria help usand all other living thingsby decomposing wastes. In this way, they recycle carbon and nitrogen in ecosystems. In addition, photosynthetic cyanobacteria are important producers. On ancient Earth, they added oxygen to the atmosphere and changed the course of evolution forever. There are billions of bacteria inside the human digestive tract. They help us digest food. They also make vitamins and play other important roles. We use bacteria in many other ways as well. For example, we use them to: create medical products such as vaccines. transfer genes in gene therapy. make fuels such as ethanol. clean up oil spills. kill plant pests. ferment foods. Do you eat any of the fermented foods pictured in Figure 8.12? If so, you are eating bacteria and their wastes. Yum! | text | null |
L_0437 | bacteria | T_2655 | You have ten times as many bacterial cells as human cells in your body. Luckily for you, most of these bacteria are harmless. However, some of them can cause disease. Any organism that causes disease is called a pathogen. Diseases caused by bacterial pathogens include food poisoning, strep throat, and Lyme disease. Bacteria that cause disease may spread directly from person to person. For example, they may spread when people shake hands with, or sneeze on, other people. Bacteria may also spread through food, water, or objects that have become contaminated with them. Some bacteria are spread by vectors. A vector is an organism that spreads bacteria or other pathogens. Most vectors are animals, commonly insects. For example, deer ticks like the one in Figure 8.13 spread Lyme disease. Ticks carry Lyme disease bacteria from deer to people when they bite them. | text | null |
L_0437 | bacteria | T_2656 | Bacteria in food or water usually can be killed by heating it to a high temperature. Generally, this temperature is at least 71 C (160 F). Bacteria on surfaces such as countertops and floors can be killed with disinfectants, such as chlorine bleach. Bacterial infections in people can be treated with antibiotic drugs. These drugs kill bacteria and may quickly cure the disease. If youve ever had strep throat, you were probably prescribed an antibiotic to treat it. Some bacteria have developed antibiotic resistance. They have evolved traits that make them resistant to one or more antibiotic drugs. You can see how this happens in Figure 8.14. Its an example of natural selection. Some bacteria are now resistant to most common antibiotic drugs. These infections are very hard to treat. | text | null |
L_0442 | adulthood and aging | T_2690 | When is a person considered an adult? That depends. Most teens become physically mature by the age of 16 or so. But they are not adults in a legal sense until they are older. For example, in the U.S., you must be 18 to vote. Once adulthood begins, it can be divided into three stages: (1) early, (2) middle, and (3) late adulthood. | text | null |
L_0442 | adulthood and aging | T_2691 | Early adulthood starts at age 18 or 21. It continues until the mid-30s. During early adulthood, people are at their physical peak. They are also usually in good health. The ability to have children is greatest during early adulthood, as well. This is the stage of life when most people complete their education. They are likely to begin a career or take a full-time job. Many people also marry and start a family during early adulthood. | text | null |
L_0442 | adulthood and aging | T_2692 | Middle adulthood begins in the mid-30s. It continues until the mid-60s. During middle adulthood, people start to show signs of aging. Their hair slowly turns gray. Their skin develops wrinkles. The risk of health problems also increases during middle adulthood. For example, heart disease, cancer, and diabetes become more common during this time. This is the stage of life when people are most likely to achieve career goals. Their children also grow up and may leave home during this stage. | text | null |
L_0442 | adulthood and aging | T_2693 | Late adulthood begins in the mid-60s. It continues until death. This is the stage of life when most people retire from work. They are also likely to reflect on their life. They may focus on their grandchildren. During late adulthood, people are not as physically able. For example, they usually have less muscle and slower reflexes. Their immune system also doesnt work as well as it used to. As a result, they have a harder time fighting diseases like the flu. The risk of developing diseases such as heart disease and cancer continues to rise. Arthritis is also common. In arthritis, joints wear out and become stiff and painful. As many as one in four late adults may develop Alzheimers disease. In this disease, brain changes cause mental abilities to decrease. This family picture shows females in each of the three stages of life. Which stage does each represent? Despite problems such as these, many people remain healthy and active into their 80s or even 90s. Do you want to be one of them? Then adopt a healthy lifestyle now and follow it for life. Doing so will increase your chances of staying healthy and active to an old age. Exercising the body and brain help prevent the physical and mental effects of aging. | text | null |
L_0449 | aquatic biomes | T_2716 | Recall that terrestrial biomes are defined by their climate. Thats because plants and animals are adapted for certain amounts of temperature and moisture. However, would aquatic biomes be classified in the same way? No, that wouldnt make much senseall parts of an aquatic environment have plenty of water. Aquatic biomes can be generally classified based on the amount of salt in the water. Freshwater biomes have less than 1% salt and are typical of ponds and lakes, streams and rivers, and wetlands. Marine biomes have more salt and are characteristic of the oceans, coral reefs, and estuaries. Most aquatic organisms do not have to deal with extremes of temperature or moisture. Instead, their main limiting factors are the availability of sunlight and the concentration of dissolved oxygen and nutrients in the water. | text | null |
L_0449 | aquatic biomes | T_2717 | Aquatic biomes in the ocean are called marine biomes. Organisms that live in marine biomes must be adapted to the salt in the water. For example, many have organs for excreting excess salt. Marine biomes include the oceans, coral reefs, and estuaries ( Figure 1.1). The oceans are the largest of all the ecosystems. They can be divided into four separate zones based on the amount of sunlight. Ocean zones are also divided based on their depth and their distance from land. Each zone has a great diversity of species. Within a coral reef, the dominant organisms are corals. Corals consist partially of algae, which provide nutrients via photosynthesis. Corals also extend tentacles to obtain plankton from the water. Coral reefs include several species of microorganisms, invertebrates, fishes, sea urchins, octopuses, and sea stars. Estuaries are areas where freshwater streams or rivers merge with the ocean. An example of a marine biome, a kelp for- est, from Anacapa Island in the Channel Islands National Marine Sanctuary. | text | null |
L_0449 | aquatic biomes | T_2718 | Freshwater biomes are defined by their low salt concentration, usually less than 1%. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration, such as the ocean. There are different types of freshwater biomes: ponds and lakes ( Figure 1.2), streams and rivers, and wetlands. Ponds and lakes range in size from just a few square meters to thousands of square kilometers. Streams and rivers are bodies of flowing water moving in one direction. They can be found everywhere. They get their starts at headwaters, which may be springs, melting snow, or even lakes, and then travel all the way to their mouths, emptying into another water channel or the ocean. Wetlands are areas of standing water that support aquatic plants. Wetlands include marshes, swamps, and bogs. Lake Tahoe in Northern California is a freshwater biome. | text | null |
L_0449 | aquatic biomes | T_2719 | In large bodies of water, such as the ocean and lakes, the water can be divided into zones based on the amount of sunlight it receives: 1. The photic zone extends to a maximum depth of 200 meters (656 feet) below the surface of the water. This is where enough sunlight penetrates for photosynthesis to occur. Algae and other photosynthetic organisms can make food and support food webs. 2. The aphotic zone is water deeper than 200 meters. This is where too little sunlight penetrates for photosyn- thesis to occur. As a result, producers must make "food" by chemosynthesis, or the food must drift down from the water above. | text | null |
L_0449 | aquatic biomes | T_2720 | Water in lakes and the ocean also varies in the amount of dissolved oxygen and nutrients it contains: 1. Water near the surface of lakes and the ocean usually has more dissolved oxygen than does deeper water. This is because surface water absorbs oxygen from the air above it. 2. Water near shore generally has more dissolved nutrients than water farther from shore. This is because most nutrients enter the water from land. They are carried by runoff, streams, and rivers that empty into a body of water. 3. Water near the bottom of lakes and the ocean may contain more nutrients than water closer to the surface. When aquatic organisms die, they sink to the bottom. Decomposers near the bottom of the water break down the dead organisms and release their nutrients back into the water. | text | null |
L_0454 | autoimmune diseases | T_2733 | The immune system usually protects you from pathogens and other causes of disease. When the immune system is working properly, it keeps you from getting sick. But the immune system is like any other system of the body. It can break down or develop diseases. AIDS is an infectious disease of the immune system caused by a virus. Some diseases of the immune system are noninfectious. They include autoimmune diseases and allergies. | text | null |
L_0454 | autoimmune diseases | T_2734 | Does it make sense for an immune system to attack the cells it is meant to protect? No, but an immune system that does not function properly will attack its own cells. An autoimmune disease is a disease in which the immune system attacks the bodys own cells. One example is type 1 diabetes. In this disease, the immune system attacks cells of the pancreas. Other examples are multiple sclerosis and rheumatoid arthritis. In multiple sclerosis, the immune system attacks nerve cells. This causes weakness and pain. In rheumatoid arthritis, the immune system attacks the cells of joints. This causes joint damage and pain. Autoimmune diseases cannot be cured. But they can be helped with medicines that weaken the immune systems attack on normal cells. Other autoimmune diseases include celiac disease (damages to the small intestine), inflam- matory bowel disease (damage to the digestive tract), psoriasis (damage to the skin), and lupus (damage to the joints, skin, kidneys, heart, and lungs). | text | null |
L_0454 | autoimmune diseases | T_2735 | An allergy occurs when the immune system attacks a harmless substance that enters the body from the outside. A substance that causes an allergy is called an allergen. It is the immune system, not the allergen, that causes the symptoms of an allergy. Did you ever hear of hay fever? Its not really a fever at all. Its an allergy to plant pollens. People with this type of allergy have symptoms such as watery eyes, sneezing, and a runny nose. A common cause of hay fever is the pollen of ragweed. Many people are also allergic to poison ivy ( Figure 1.2). Skin contact with poison ivy leads to an itchy rash in people who are allergic to the plant. Ragweed is a common roadside weed found throughout the United States. Many people are allergic to its pollen. Some people are allergic to certain foods. Nuts and shellfish are common causes of food allergies. Other common causes of allergies include: Drugs, such as penicillin. Mold. Dust. The dead skin cells of dogs and cats, called dander. Stings of wasps and bees. Most allergies can be treated with medicines. Medicines used to treat allergies include antihistamines and corticos- teroids. These medicines help control the immune system when it attacks an allergen. Sometimes, allergies cause severe symptoms, a condition known as anaphylaxis. For example, they may cause the throat to swell so it is hard to breathe. Severe allergies may be life threatening. They require emergency medical care. | text | null |
L_0457 | bacteria in the digestive system | T_2745 | Your large intestine is not just made up of cells. It is also an ecosystem, home to trillions of bacteria known as the "gut flora" ( Figure 1.1). But dont worry, most of these bacteria are helpful. Friendly bacteria live mostly in the large intestine and part of the small intestine. The acidic environment of the stomach does not allow bacterial growth. Gut bacteria have several roles in the body. For example, intestinal bacteria: Produce vitamin B12 and vitamin K. Control the growth of harmful bacteria. Break down poisons in the large intestine. Break down some substances in food that cannot be digested, such as fiber and some starches and sugars. Bacteria produce enzymes that digest carbohydrates in plant cell walls. Most of the nutritional value of plant material would be wasted without these bacteria. These help us digest plant foods like spinach. Your intestines are home to trillions of bacteria. A wide range of friendly bacteria live in the gut. Bacteria begin to populate the human digestive system right after birth. Gut bacteria include Lactobacillus, the bacteria commonly used in probiotic foods such as yogurt, and E. coli bacteria. About a third of all bacteria in the gut are members of the Bacteroides species. Bacteroides are key in helping us digest plant food. It is estimated that 100 trillion bacteria live in the gut. This is more than the human cells that make up you. It has also been estimated that there are more bacteria in your mouth than people on the planet. There are over 7 billion people on the planet. The bacteria in your digestive system are from anywhere between 300 and 1000 species. As these bacteria are helpful, your body does not attack them. They actually appear to the bodys immune system as cells of the digestive system, not foreign invaders. The bacteria actually cover themselves with sugar molecules removed from the actual cells of the digestive system. This disguises the bacteria and protects them from the immune system. As the bacteria that live in the human gut are beneficial to us, and as the bacteria enjoy a safe environment to live, the relationship that we have with these tiny organisms is described as mutualism, a type of symbiotic relationship. Lastly, keep in mind the small size of bacteria. Together, all the bacteria in your gut may weight just about 2 pounds. | text | null |
L_0458 | bacteria nutrition | T_2746 | Like all organisms, bacteria need energy, and they can acquire this energy through a number of different ways. | text | null |
L_0458 | bacteria nutrition | T_2747 | Photosynthetic bacteria use the energy of the sun to make their own food. In the presence of sunlight, carbon dioxide and water are turned into glucose and oxygen. The glucose is then turned into usable energy. Glucose is like the "food" for the bacteria. An example of photosynthetic bacteria is cyanobacteria, as seen in the opening image. These bacteria are sometimes called blue-green algae, although they are not algae, due to their numerous chlorophyll molecules. | text | null |
L_0458 | bacteria nutrition | T_2748 | Bacteria known as decomposers break down wastes and dead organisms into smaller molecules. These bacteria use the organic substrates they break down to get their energy, carbon, and nutrients they need for survival. | text | null |
L_0458 | bacteria nutrition | T_2749 | Bacteria can also be chemotrophs. Chemosynthetic bacteria, or chemotrophs, obtain energy by breaking down chemical compounds in their environment. An example of one of these chemicals broken down by bacteria is nitrogen-containing ammonia. These bacteria are important because they help cycle nitrogen through the environ- ment for other living things to use. Nitrogen cannot be made by living organisms, so it must be continually recycled. Organisms need nitrogen to make organic compounds, such as DNA. | text | null |
L_0458 | bacteria nutrition | T_2750 | Some bacteria depend on other organisms for survival. For example, some bacteria live in the roots of legumes, such as pea plants ( Figure 1.1). The bacteria turn nitrogen-containing molecules into nitrogen that the plant can use. Meanwhile, the root provides nutrients to the bacteria. In this relationship, both the bacteria and the plant benefit, so it is known as a mutualism. Other mutualistic bacteria include gut microbes. These are bacteria that live in the intestines of animals. They are usually beneficial bacteria, needed by the host organism. These microbes obviously dont kill their host, as that would kill the bacteria as well. | text | null |
L_0458 | bacteria nutrition | T_2751 | Other bacteria are parasitic and can cause illness. In parasitism, the bacteria benefit, and the other organism is harmed. Harmful bacteria will be discussed in another concept. | text | null |
L_0460 | barriers to pathogens | T_2755 | It is the immune systems job to protect the body. Your body has many ways to protect you from pathogens. Your bodys defenses are like a castle. The outside of a castle was protected by a moat and high walls. Inside the castle, soldiers were ready to fight off any enemies that made it across the moat and over the walls. Like a castle, your body has a series of defenses. Only pathogens that get through all the defenses can harm you. The first line of defence includes both physical and chemical barriers that are always ready and prepared to defend the body from infection. Pathogens must make it past this first line of defense to cause harm. If this defense is broken, the second line of defense within your body is activated. Your bodys first line of defense is like a castles moat and walls. It keeps most pathogens out of your body. This is a non-specific type of defense, in that it tries to keep all pathogens out. The first line of defense includes different types of barriers. Being the "first line", it starts with the skin. The first line also includes tears, mucus, cilia, stomach acid, urine flow, and friendly bacteria. | text | null |
L_0460 | barriers to pathogens | T_2756 | The skin is a very important barrier to pathogens. The skin is the bodys largest organ. In adults, it covers an area of about 16 to 22 square feet! The skin is also the bodys most important defense against disease. It forms a physical barrier between the body and the outside world. The skin has several layers that stack on top of each other ( Figure The mouth and nose are not lined with skin. Instead, they are lined with mucous membranes. Other organs that are exposed to the outside world, including the lungs and stomach, are also lined with mucous membranes. Mucous membranes are not tough like skin, but they have other defenses. One defense of mucous membranes is the mucus they release. Mucus is a sticky, moist substance that covers mucous membranes. Most pathogens get stuck in the mucus before they can do harm to the body. Many mucous membranes also have cilia. Cilia in the lungs are pictured below ( Figure 1.2). Cilia are tiny finger-like projections. They move in waves and sweep mucus and trapped pathogens toward body openings. When you clear your throat or blow your nose, you remove mucus and pathogens from your body. | text | null |
L_0460 | barriers to pathogens | T_2757 | Most body fluids that you release from your body contain chemicals that kill pathogens. For example, mucus, sweat, tears, and saliva contain enzymes called lysozymes that kill pathogens. These enzymes can break down the cell walls of bacteria to kill them. The stomach also releases a very strong acid, called hydrochloric acid. This acid kills most pathogens that enter the stomach in food or water. Urine is also acidic, so few pathogens can grow in it. This is what the cilia lining the lungs look like when they are magnified. Their movements constantly sweep mucus and pathogens out of the lungs. Do they remind you of brushes? | text | null |
L_0460 | barriers to pathogens | T_2758 | You are not aware of them, but your skin is covered by millions (or more!) of bacteria. Millions more live inside your body. Most of these bacteria help defend your body from pathogens. How do they do it? They compete with harmful bacteria for food and space. This prevents the harmful bacteria from multiplying and making you sick. | text | null |
L_0467 | blood types | T_2774 | Do you know what your blood type is? Maybe you have heard people say that they have type A or type O blood. Blood type is a way to describe the type of antigens, or proteins, on the surface of red blood cells (RBCs). There are four blood types; A, B, AB, and O. 1. Type A blood has type A antigens on the RBCs in the blood. 2. Type AB blood has A and B antigens on the RBCs. 3. Type B has B antigens on the RBCs. 4. Type O does not have either A or B antigens. The ABO blood group system is important if a person needs a blood transfusion. A blood transfusion is the process of putting blood or blood products from one person into the circulatory system of another person. The blood type of the recipient needs to be carefully matched to the blood type of the donor. Thats because different blood types have different types of antibodies, or proteins, released by the blood cells. Antibodies attack strange substances in the body. This is a normal part of your immune response, which is your defense against disease. For example, imagine a person with type O blood was given type A blood. First, what type of antibodies do people with type O blood produce? They produce anti-A and anti-B antibodies. This means, if a person with type O blood received type A blood, the anti-A antibodies in the persons blood would attack the A antigens on the RBCs in the donor blood ( Figure 1.1). The antibodies would cause the RBCs to clump together, and the clumps could block a blood vessel. This clumping of blood cells could cause death. A person with type O blood has A and B antibodies in his/her plasma; if the person was to get type A blood instead of type O, his/her A antibodies would attach to the antigens on the RBCs and cause them to clump together. People with type A blood produce anti-B antibodies, and people with type B blood produce anti-A antibodies. People with type AB blood do not produce either antibody. | text | null |
L_0467 | blood types | T_2775 | The second most important blood group system in human blood is the Rhesus (Rh) factor. A person either has, or does not have, the Rh antigen on the surface of their RBCs. If they do have it, then the person is positive. If the person does not have the antigen, they are considered negative. | text | null |
L_0467 | blood types | T_2776 | Recall that people with type O blood do not have any antigens on their RBCs. As a result, type O blood can be given to people with blood types A, B, or AB. If there are no antigens on the RBCs, there cannot be an antibody reaction in the blood. People with type O blood are often called universal donors. The blood plasma of AB blood does not contain any anti-A or anti-B antibodies. People with type AB blood can receive any ABO blood type. People with type AB blood are called universal recipients because they can receive any blood type. The antigens and antibodies that define blood type are listed as follows ( Table 1.1). Blood Type Antigen Type Plasma Antibodies A B AB O A B A and B none anti-B anti-A none anti-A, anti-B Can Receive Blood from Types A,O B,O AB, A, B, O O Can Donate Blood to Types A, AB B, AB AB AB, A, B, O | text | null |
L_0468 | blood vessels | T_2777 | The blood vessels are an important part of the cardiovascular system. They connect the heart to every cell in the body. Arteries carry blood away from the heart, while veins return blood to the heart ( Figure 1.1). The right side of the heart pumps de- oxygenated blood into pulmonary circula- tion, while the left side pumps oxygenated blood into systemic circulation. | text | null |
L_0468 | blood vessels | T_2778 | There are specific veins and arteries that are more significant than others. The pulmonary arteries carry oxygen- poor blood away from the heart to the lungs. These are the only arteries that carry oxygen-poor blood. The aorta is the largest artery in the body. It carries oxygen-rich blood away from the heart. Further away from the heart, the aorta branches into smaller arteries, which eventually branch into capillaries. Capillaries are the smallest type of blood vessel; they connect very small arteries and veins. Gases and other substances are exchanged between cells and the blood across the very thin walls of capillaries. The veins that return oxygen-poor blood to the heart are the superior vena cava and the inferior vena cava. The pulmonary veins return oxygen-rich blood from the lungs to the heart. The pulmonary veins are the only veins that carry oxygen-rich blood. | text | null |
L_0468 | blood vessels | T_2779 | Pulmonary circulation is the part of the cardiovascular system that carries oxygen-poor blood away from the heart and brings it to the lungs. Oxygen-poor blood returns to the heart from the body and leaves the right ventricle through the pulmonary arteries, which carry the blood to each lung. Once at the lungs, the red blood cells release carbon dioxide and pick up oxygen when you breathe. The oxygen-rich blood then leaves the lungs through the pulmonary veins, which return it to the left side of the heart. This completes the pulmonary cycle. The oxygenated blood is then pumped to the body through systemic circulation, before returning again to pulmonary circulation. | text | null |
L_0468 | blood vessels | T_2780 | Systemic circulation is the part of the cardiovascular system that carries oxygen-rich blood away from the heart, to the body, and returns oxygen-poor blood back to the heart. Oxygen-rich blood leaves the left ventricle through the aorta. Then it travels to the bodys organs and tissues. The tissues and organs absorb the oxygen through the capillaries. Oxygen-poor blood is collected from the tissues and organs by tiny veins, which then flow into bigger veins, and, eventually, into the inferior vena cava and superior vena cava. This completes systemic circulation. The blood releases carbon dioxide and gets more oxygen in pulmonary circulation before returning to systemic circulation. The inferior vena cava returns blood from the body. The superior vena cava returns blood from the head. | text | null |
L_0469 | bony fish | T_2781 | There are about 27,000 species of bony fish ( Figure 1.1), which are divided into two classes: ray-finned fish and lobe-finned fish. Most bony fish are ray-finned. These thin fins consist of webs of skin over flexible spines. Lobe- finned fish, on the other hand, have fins that resemble stump-like appendages. Fins of bony fish: ray fin (left) and lobe fin (right). | text | null |
L_0469 | bony fish | T_2782 | Most fish are bony fish, making them the largest group of vertebrates in existence today. They are characterized by: 1. A head and pectoral girdles (arches supporting the forelimbs) that are covered with bones derived from the skin. 2. A lung or swim bladder, which helps the body create a balance between sinking and floating by either filling up with or emitting gases such as oxygen. Controlling the volume of this organ helps fish control their depth. 3. Jointed, segmented rods supporting the fins. 4. A cover over the gill called the operculum, which helps them breathe without having to swim. 5. The ability to see in color, unlike most other fish. | text | null |
L_0469 | bony fish | T_2783 | Most vertebrates are ray-finned fish, with close to 27,000 known species. By comparison, there are "only" about 10,000 species of birds. The ray-finned fish have fin rays, with fins supported by bony spines known as rays. The ray-finned fish are the dominant class of vertebrates, with nearly 99% of fish falling into this category. They live in all aquatic environments, from freshwater and marine environments from the deep sea to the highest mountain streams. | text | null |
L_0469 | bony fish | T_2784 | The lobe-finned fish are characterized by fleshy lobed fins, as opposed to the bony fins of the ray-finned fish. There are two types of living lobe-finned fish: the coelacanths and the lungfish. The pectoral and pelvic fins have joints resembling those of tetrapod (four-limbed land vertebrates) limbs. These fins evolved into legs of amphibians, the first tetrapod land vertebrates. They also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of ray-finned fish. All lobe-finned fishes possess teeth covered with true enamel. The lungfish also possess both gills and lungs, solidifying this class as the ancestors of amphibians. | text | null |
L_0469 | bony fish | T_2785 | The ocean sunfish is the most massive bony fish in the world, up to 11 feet long and weighing up to 5,070 pounds ( Figure 1.2). Other very large bony fish include the Atlantic blue marlin, the black marlin, some sturgeon species, the giant grouper, and the goliath grouper. The long-bodied oarfish can easily be over 30 feet long, but is not nearly as massive as the ocean sunfish. In contrast, the dwarf pygmy goby measures only 0.6 inches. Fish can also be quite valuable. In January 2013, at an auction in Tokyos Tsukiji fish market, a 222-kilogram (489-pound) tuna caught off northeastern Japan sold for 155.4 million yen, which is $1,760,000. An ocean sunfish, the most massive bony fish in the world, can reach up to 11 feet long and weigh up to 5,070 pounds! | text | null |
L_0470 | cancer | T_2786 | Cancer is a disease that causes cells to divide out of control. Normally, the body has systems that prevent cells from dividing out of control. But in the case of cancer, these systems fail. Cancer is usually caused by mutations. Mutations are random errors in genes. Mutations that lead to cancer usually happen to genes that control the cell cycle. Because of the mutations, abnormal cells divide uncontrollably. This often leads to the development of a tumor. A tumor is a mass of abnormal tissue. As a tumor grows, it may harm normal tissues around it. Anything that can cause cancer is called a carcinogen. Carcinogens may be pathogens, chemicals, or radiation. | text | null |
L_0470 | cancer | T_2787 | Pathogens that cause cancer include the human papilloma virus (HPV) ( Figure 1.1) and the hepatitis B virus. HPV is spread through sexual contact. It can cause cancer of the reproductive system in females. The hepatitis B virus is spread through sexual contact or contact with blood containing the virus. It can cause cancer of the liver. | text | null |
L_0470 | cancer | T_2788 | Many different chemical substances cause cancer. Dozens of chemicals in tobacco smoke, including nicotine, have been shown to cause cancer ( Figure 1.2). In fact, tobacco smoke is one of the main sources of chemical carcinogens. Smoking tobacco increases the risk of cancer of the lung, mouth, throat, and bladder. Using smokeless tobacco can also cause cancer. Other chemicals that cause cancer include asbestos, formaldehyde, benzene, cadmium, and nickel. | text | null |
L_0470 | cancer | T_2788 | Many different chemical substances cause cancer. Dozens of chemicals in tobacco smoke, including nicotine, have been shown to cause cancer ( Figure 1.2). In fact, tobacco smoke is one of the main sources of chemical carcinogens. Smoking tobacco increases the risk of cancer of the lung, mouth, throat, and bladder. Using smokeless tobacco can also cause cancer. Other chemicals that cause cancer include asbestos, formaldehyde, benzene, cadmium, and nickel. | text | null |
L_0470 | cancer | T_2789 | Forms of radiation that cause cancer include ultraviolet (UV) radiation and radon ( Figure 1.3). UV radiation is part of sunlight. It is the leading cause of skin cancer. Radon is a natural radioactive gas that seeps into buildings from the ground. It can cause lung cancer. | text | null |
L_0470 | cancer | T_2790 | Cancer is usually found in adults, especially in adults over the age of 50. The most common type of cancer in adult males is cancer of the prostate gland. The prostate gland is part of the male reproductive system. Prostate cancer makes up about one third of all cancers in men. The most common type of cancer in adult females is breast cancer. It makes up about one third of all cancers in women. In both men and women, lung cancer is the second most common type of cancer. Most cases of lung cancer happen in people who smoke. Cancer can also be found in children. But childhood cancer is rare. Leukemia is the main type of cancer in children. It makes up about one third of all childhood cancers. It happens when the body makes abnormal white blood cells. Sometimes cancer cells break away from a tumor. If they enter the bloodstream, they are carried throughout the body. Then, the cells may start growing in other tissues. This is usually how cancer spreads from one part of the body to another. Once this happens, cancer is very hard to stop or control. | text | null |
L_0470 | cancer | T_2791 | If leukemia is treated early, it usually can be cured. In fact, many cancers can be cured, which is known as remission, if treated early. Treatment of cancer often involves removing a tumor with surgery. This may be followed by other types of treatments. These treatments may include drugs (known as chemotherapy) and radiation therapy, which kill cancer cells. The sooner cancer is treated, the greater the chances of a cure. This is why it is important to know the warning signs of cancer. Having warning signs does not mean that you have cancer. However, you should see a doctor to be sure. Everyone should know the warning signs of cancer. Detecting and treating cancer early can often lead to a cure. Some warning signs of cancer include: Change in bowel or bladder habits. Sores that do not heal. Unusual bleeding or discharge. Lump in the breast or elsewhere. Chronic indigestion. Difficulty swallowing. Obvious changes in a wart or mole. Persistent cough or hoarseness. | text | null |
L_0471 | cardiovascular diseases | T_2792 | A cardiovascular disease (CVD) is any disease that affects the cardiovascular system. But the term is usually used to describe diseases that are linked to atherosclerosis. Atherosclerosis ( Figure 1.1) is an inflammation of the walls of arteries that causes swelling and a buildup of material called plaque. Plaque is made of cell pieces, fatty substances, calcium, and connective tissue that builds up around the area of inflammation. As a plaque grows, it stiffens and narrows the artery, which decreases the flow of blood through the artery. Atherosclerosis normally begins in late childhood and is typically found in most major arteries. It does not usually have any early symptoms. Causes of atherosclerosis include a high-fat diet, high cholesterol, smoking, obesity, and diabetes. Atherosclerosis becomes a threat to health when the plaque buildup prevents blood circulation in the heart or the brain. A blocked blood vessel in the heart can cause a heart attack. Blockage of the circulation in the brain can cause a stroke. Ways to prevent atherosclerosis include eating healthy foods, getting plenty of exercise and not smoking. These three factors are not as hard to control as you may think. If you smoke, STOP. Start a regular exercise program and watch what you eat. A diet high in saturated fat and cholesterol can raise your cholesterol levels, which makes more plaque available to line artery walls and narrow your arteries. Cholesterol and saturated fats are found mostly in animal products such Atherosclerosis is sometimes referred to as hardening of the arteries; plaque build- up decreases the blood flow through the artery. as meat, eggs, milk, and other dairy products. Check food labels to find the amount of saturated fat in a product. Also, avoid large amounts of salt and sugar. Be careful with processed foods, such as frozen dinners, as they can be high in fat, sugar, salt and cholesterol. Eat lots of fresh or frozen fruits and vegetables, smaller portions of lean meats and fish, and whole grains such as oats and whole wheat. Limit saturated fats like butter, instead choose unsaturated vegetable oils such as canola oil. | text | null |
L_0471 | cardiovascular diseases | T_2793 | Like any other muscle, your heart needs oxygen. Hearts have arteries that provide oxygen through the blood. They are known as coronary arteries. Coronary heart disease is the end result of the buildup of plaque within the walls of the coronary arteries. Coronary heart disease often does not have any symptoms. A symptom of coronary heart disease is chest pain. Occasional chest pain can happen during times of stress or physical activity. The pain of angina means the heart muscle fibers need more oxygen than they are getting. Most people with coronary heart disease often have no symptoms for many years until they have a heart attack. A heart attack happens when the blood cannot reach the heart because a blood vessel is blocked. If cardiac muscle is starved of oxygen for more than roughly five minutes, it will die. Cardiac muscle cells cannot be replaced, so once they die, they are dead forever. Coronary heart disease is the leading cause of death of adults in the United States. The image below shows the way in which a blocked coronary artery can cause a heart attack and cause part of the heart muscle to die ( Figure 1.2). Maybe one day stem cells will be used to replace dead cardiac muscle cells. | text | null |
L_0471 | cardiovascular diseases | T_2794 | Atherosclerosis in the arteries of the brain can also lead to a stroke. A stroke is a loss of brain function due to a blockage of the blood supply to the brain. Risk factors for stroke include old age, high blood pressure, having a previous stroke, diabetes, high cholesterol, and smoking. The best way to reduce the risk of stroke is to have low blood pressure. | text | null |
L_0472 | cardiovascular system | T_2795 | Your cardiovascular system has many jobs. At times the cardiovascular system can work like a pump, a heating system, or even a postal carrier. To do these tasks, your cardiovascular system works with other organ systems, such as the respiratory, endocrine, and nervous systems. The cardiovascular system (Figure 1.1) is made up of the heart, the blood vessels, and the blood. It moves nutrients, gases (like oxygen), and wastes to and from your cells. Every cell in your body depends on your cardiovascular system. If your cells dont receive nutrients, they cannot survive. The main function of the cardiovascular system is to deliver oxygen to each of your cells. Blood receives oxygen in your lungs (the main organs of the respiratory system) and then is pumped, by your heart, throughout your body. The oxygen then diffuses into your cells, and carbon dioxide, a waste product of cellular respiration, moves from your cells into your blood to be delivered back to your lungs and exhaled. Each cell in your body needs oxygen, as oxygen is used in cellular respiration to produce energy in the form of ATP. Without oxygen, lactic acid fermentation would occur in your cells, which can only be maintained for a brief period of time. Arteries carry blood full of oxygen ("oxygen-rich") away from the heart and veins return oxygen-poor blood back to the heart. The cardiovascular system also plays a role in maintaining body temperature. It helps to keep you warm by moving warm blood around your body. Your blood vessels also control your body temperature to keep you from getting too hot or too cold. When your brain senses that your body temperature is increasing, it sends messages to the blood vessels in the skin to increase in diameter. Increasing the diameter of the blood vessels increases the amount of blood and heat that moves near the skins surface. The heat is then released from the skin. This helps you cool down. What do you think your blood vessels do when your body temperature is decreasing? The blood also carries hormones, which are chemical messenger molecules produced by organs of the endocrine system, through your body. Hormones are produced in one area of your body and have an effect on another area. To get to that other area, they must travel through your blood. An example is the hormone adrenaline, produced by the adrenal glands on top of the kidneys. Adrenaline has multiple effects on the heart (it quickens the heart rate), on muscles and on the airway. | text | null |
L_0473 | cardiovascular system health | T_2796 | There are many risk factors that can cause a person to develop cardiovascular disease. A risk factor is anything that is linked to an increased chance of developing a disease. Some of the risk factors for cardiovascular disease you cannot control, but there are many risk factors you can control. Risk factors you cannot control include: Age: The older a person is, the greater their chance of developing a cardiovascular disease. Gender: Men under age 64 are much more likely to die of coronary heart disease than women, although the gender difference decreases with age. Genetics: Family history of cardiovascular disease increases a persons chance of developing heart disease. Risk factors you can control include many lifestyle factors: Tobacco smoking: Giving up smoking or never starting to smoke is the best way to reduce the risk of heart disease. Diabetes: Diabetes can cause bodily changes, such as high cholesterol levels, which are are risk factors for cardiovascular disease. High cholesterol levels: High amounts of "bad cholesterol," increase the risk of cardiovascular disease. Obesity: Having a very high percentage of body fat, especially if the fat is mostly found in the upper body, rather than the hips and thighs, increases risk significantly. High blood pressure: If the heart and blood vessels have to work harder than normal, this puts the cardiovas- cular system under a strain. Lack of physical activity: Aerobic activities, such as the one pictured below ( Figure 1.1), help keep your heart healthy. To reduce the risk of disease, you should be active for at least 60 minutes a day, five days a week. Poor eating habits: Eating mostly foods that do not have many nutrients other than fat or carbohydrate leads to high cholesterol levels, obesity, and cardiovascular disease ( Figure 1.2). 60 minutes a day of vigorous aerobic activity, such as basketball, is enough to help keep your cardiovascular system healthy. | text | null |
L_0473 | cardiovascular system health | T_2797 | Cholesterol cant dissolve in the blood. It has to be transported to and from the cells by carriers called lipoproteins. Low-density lipoprotein, or LDL, is known as "bad" cholesterol. High-density lipoprotein (HDL) is known as good cholesterol. When too much LDL cholesterol circulates in the blood, it can slowly build up in the inner walls of the The USDAs MyPyramid recommends that you limit the amount of such foods in your diet to occasional treats. arteries that feed the heart and brain. Together with other substances, it can form plaque, and lead to atherosclerosis. If a clot forms and blocks a narrowed artery, a heart attack or stroke can result. Cholesterol comes from the food you eat as well as being made by the body. To lower bad cholesterol, a diet low in saturated fat and dietary cholesterol should be followed. Regular aerobic exercise also lowers LDL cholesterol and increases HDL cholesterol. | text | null |
L_0474 | cartilaginous fish | T_2798 | The 1,000 or so species of cartilaginous fish are subdivided into two subclasses: the first includes sharks, rays, and skates; the second includes chimaera, sometimes called ghost sharks. Fish from this group range in size from the dwarf lanternshark, at 6.3 inches, to the over 50-foot whale shark. Sharks obviously have jaws, as do the other cartilaginous fish. These fish evolved from the jawless fish. So why did fish eventually evolve to have jaws? Such an adaptation would allow fish to eat a much wider variety of food, including plants and other organisms. Other characteristics of cartilaginous fish include: Paired fins. Paired nostrils. Scales. Two-chambered hearts. Skeletons made of cartilage rather than bone. Cartilage is supportive tissue that does not have as much calcium as bones, which makes bones rigid. Cartilage is softer and more flexible than bone. | text | null |
L_0474 | cartilaginous fish | T_2799 | Since they do not have bone marrow (as they have no bones), red blood cells are produced in the spleen, in special tissue around the reproductive organs, and in an organ called Leydigs organ, only found in cartilaginous fishes. The tough skin of this group of fish is covered with placoid scales, which are hard scales formed from modified teeth. The scales are covered with a hard enamel. The hard covering and the way the scales are arranged, gives the fish skin rough, sandpaper-like feel. The function of these scales is for protection against predators. The shape of sharks teeth differ according to their diet. Species that feed on mollusks and crustaceans have dense flattened teeth for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey, such as mammals, have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. Sharks continually shed and replace their teeth, with some shedding as much as 35,000 teeth in a lifetime. | text | null |
L_0474 | cartilaginous fish | T_2800 | The sharks, rays, and skates (which are similar to stingrays) are further broken into two superorders: 1. Rays and skates. 2. Sharks. Sharks are some of the most frequently studied cartilaginous fish. Sharks are distinguished by such features as: The number of gill slits. The number and type of fins. The type of teeth. The size of their jaws. Body shape. Their activity at night. An elongated, toothed snout used for slashing the fish that they eat, as seen in sawsharks. Teeth used for grasping and crushing shellfish, a characteristic of bullhead sharks. A whisker-like organ named barbels that help sharks find food, a characteristic of carpet sharks. A long snout (or nose-like area), characteristic of groundsharks. Ovoviviparous reproduction, where the eggs develop inside the mothers body after internal fertilization, and the young are born alive. This trait is characteristic of mackerel sharks. All sharks mate by internal fertilization. Some sharks then lay their eggs, others allow internal development. | text | null |
L_0481 | cellular respiration | T_2817 | How does the food you eat provide energy? When you need a quick boost of energy, you might reach for an apple or a candy bar. But cells do not "eat" apples or candy bars; these foods need to be broken down so that cells can use them. Through the process of cellular respiration, the energy in food is changed into energy that can be used by the bodys cells. Initially, the sugars in the food you eat are digested into the simple sugar glucose, a monosaccharide. Recall that glucose is the sugar produced by the plant during photosynthesis. The glucose, or the polysaccharide made from many glucose molecules, such as starch, is then passed to the organism that eats the plant. This organism could be you, or it could be the organism that you eat. Either way, it is the glucose molecules that holds the energy. | text | null |
L_0481 | cellular respiration | T_2818 | Specifically, during cellular respiration, the energy stored in glucose is transferred to ATP ( Figure 1.1). ATP, or adenosine triphosphate, is chemical energy the cell can use. It is the molecule that provides energy for your cells to perform work, such as moving your muscles as you walk down the street. But cellular respiration is slightly more complicated than just converting the energy from glucose into ATP. Cellular respiration can be described as the reverse or opposite of photosynthesis. During cellular respiration, glucose, in the presence of oxygen, is converted into carbon dioxide and water. Recall that carbon dioxide and water are the starting products of photosynthesis. What are the products of photosynthesis? The process can be summarized as: glucose + oxygen carbon dioxide + water. During this process, the energy stored in glucose is transferred to ATP. Energy is stored in the bonds between the phosphate groups (PO4 ) of the ATP molecule. When ATP is broken down into ADP (adenosine diphosphate) and inorganic phosphate, energy is released. When ADP and inorganic phosphate are joined to form ATP, energy is stored. During cellular respiration, about 36 to 38 ATP molecules are produced for every glucose molecule. The structural formula for adenosine triphosphate (ATP). During cellular respi- ration, energy from the chemical bonds of the food you eat must be transferred to ATP. | text | null |
L_0483 | central nervous system | T_2825 | The central nervous system (CNS) ( Figure 1.1) is the largest part of the nervous system. It includes the brain and the spinal cord. The bony skull protects the brain. The spinal cord is protected within the bones of the spine, which are called vertebrae. | text | null |
L_0483 | central nervous system | T_2826 | What weighs about three pounds and contains up to 100 billion cells? The answer is the human brain. The brain is the control center of the nervous system. Its like the pilot of a plane. It tells other parts of the nervous system what to do. The brain is also the most complex organ in the body. Each of its 100 billion neurons has synapses connecting it with thousands of other neurons. All those neurons use a lot of energy. In fact, the adult brain uses almost a quarter of the total energy used by the body. The developing brain of a baby uses an even greater amount of the bodys total energy. The brain is the organ that lets us understand what we see, hear, or sense in other ways. It also allows us to use language, learn, think, and remember. The brain controls the organs in our body and our movements as well. The brain consists of three main parts, the cerebrum, the cerebellum, and the brain stem ( Figure 1.2). 1. The cerebrum is the largest part of the brain. It sits on top of the brain stem. The cerebrum controls functions that we are aware of, such as problem-solving and speech. It also controls voluntary movements, like waving to a friend. Whether you are doing your homework or jumping hurdles, you are using your cerebrum. 2. The cerebellum is the next largest part of the brain. It lies under the cerebrum and behind the brain stem. The cerebellum controls body position, coordination, and balance. Whether you are riding a bicycle or writing with a pen, you are using your cerebellum. 3. The brain stem is the smallest of the three main parts of the brain. It lies directly under the cerebrum. The brain stem controls basic body functions, such as breathing, heartbeat, and digestion. The brain stem also carries information back and forth between the cerebrum and spinal cord. The cerebrum is divided into a right and left half ( Figure 1.2). Each half of the cerebrum is called a hemisphere. The two hemispheres are connected by a thick bundle of axons called the corpus callosum. It lies deep inside the brain and carries messages back and forth between the two hemispheres. Did you know that the right hemisphere controls the left side of the body, and the left hemisphere controls the right side of the body? By connecting the two hemispheres, the corpus callosum allows this to happen. Each hemisphere of the cerebrum is divided into four parts, called lobes. The four lobes are the: 1. 2. 3. 4. Frontal. Parietal. Temporal. Occipital. Each lobe has different jobs. Some of the functions are listed below ( Table 1.1). Side view of the brain (right). Can you find the locations of the three major parts of the brain? Top view of the brain (left). Lobe Frontal Parietal Temporal Occipital Main Function(s) Speech, thinking, touch Speech, taste, reading Hearing, smell Sight | text | null |
L_0483 | central nervous system | T_2826 | What weighs about three pounds and contains up to 100 billion cells? The answer is the human brain. The brain is the control center of the nervous system. Its like the pilot of a plane. It tells other parts of the nervous system what to do. The brain is also the most complex organ in the body. Each of its 100 billion neurons has synapses connecting it with thousands of other neurons. All those neurons use a lot of energy. In fact, the adult brain uses almost a quarter of the total energy used by the body. The developing brain of a baby uses an even greater amount of the bodys total energy. The brain is the organ that lets us understand what we see, hear, or sense in other ways. It also allows us to use language, learn, think, and remember. The brain controls the organs in our body and our movements as well. The brain consists of three main parts, the cerebrum, the cerebellum, and the brain stem ( Figure 1.2). 1. The cerebrum is the largest part of the brain. It sits on top of the brain stem. The cerebrum controls functions that we are aware of, such as problem-solving and speech. It also controls voluntary movements, like waving to a friend. Whether you are doing your homework or jumping hurdles, you are using your cerebrum. 2. The cerebellum is the next largest part of the brain. It lies under the cerebrum and behind the brain stem. The cerebellum controls body position, coordination, and balance. Whether you are riding a bicycle or writing with a pen, you are using your cerebellum. 3. The brain stem is the smallest of the three main parts of the brain. It lies directly under the cerebrum. The brain stem controls basic body functions, such as breathing, heartbeat, and digestion. The brain stem also carries information back and forth between the cerebrum and spinal cord. The cerebrum is divided into a right and left half ( Figure 1.2). Each half of the cerebrum is called a hemisphere. The two hemispheres are connected by a thick bundle of axons called the corpus callosum. It lies deep inside the brain and carries messages back and forth between the two hemispheres. Did you know that the right hemisphere controls the left side of the body, and the left hemisphere controls the right side of the body? By connecting the two hemispheres, the corpus callosum allows this to happen. Each hemisphere of the cerebrum is divided into four parts, called lobes. The four lobes are the: 1. 2. 3. 4. Frontal. Parietal. Temporal. Occipital. Each lobe has different jobs. Some of the functions are listed below ( Table 1.1). Side view of the brain (right). Can you find the locations of the three major parts of the brain? Top view of the brain (left). Lobe Frontal Parietal Temporal Occipital Main Function(s) Speech, thinking, touch Speech, taste, reading Hearing, smell Sight | text | null |
L_0483 | central nervous system | T_2827 | The spinal cord is a long, tube-shaped bundle of neurons, protected by the vertebrae. It runs from the brain stem to the lower back. The main job of the spinal cord is to carry nerve impulses back and forth between the body and brain. The spinal cord is like a two-way highway. Messages about the body, both inside and out, pass through the spinal cord to the brain. Messages from the brain pass in the other direction through the spinal cord to tell the body what to do. | text | null |
L_0485 | chemistry of life | T_2834 | null | text | null |
L_0485 | chemistry of life | T_2835 | If you pull a flower petal from a plant and break it in half, and then take that piece and break it in half again, and take the next piece and break it half, and so on, and so on, until you cannot even see the flower anymore, what do you think you will find? We know that the flower petal is made of cells, but what are cells made of? Scientists have broken down matter, or anything that takes up space and has masslike a cellinto the smallest pieces that cannot be broken down anymore. Every physical object, including rocks, animals, flowers, and your body, are all made up of matter. Matter is made up of a mixture of things called elements. Elements are substances that cannot be broken down into simpler substances. There are more than 100 known elements, and 92 occur naturally around us. The others have been made only in the laboratory. Inside of elements, you will find identical atoms. An atom is the simplest and smallest particle of matter that still has chemical properties of the element. Atoms are the building block of all of the elements that make up the matter in your body or any other living or non-living thing. Atoms are so small that only the most powerful microscopes can see them. Atoms themselves are composed of even smaller particles, including positively charged protons, uncharged neu- trons, and negatively charged electrons. Protons and neutrons are located in the center of the atom, or the nucleus, and the electrons move around the nucleus. How many protons an atom has determines what element it is. For example, hydrogen (H) has just one proton, helium (He) always has two protons ( Figure 1.1), while sodium (Na) always has 11. All the atoms of a particular element have the exact same number of protons, and the number of protons is that elements atomic number. An atom usually has the same number of protons and electrons, but sometimes an atom may gain or lose an electron, giving the atom a positive or negative charge. These atoms are known as ions and are depicted with a "+" or "-" sign. Ions, such as H+ , Na+ , K+ , or Cl have significant biological roles. An atom of Helium (He) contains two positively charged protons (red), two uncharged neutrons (blue), and two negatively charged electrons (yellow). | text | null |
L_0485 | chemistry of life | T_2836 | In 1869, a Russian scientist named Dmitri Mendeleev created the periodic table, which is a way of organizing elements according to their unique characteristics, like atomic number, density, boiling point, and other values ( Figure 1.2). Each element is represented by a one or two letter symbol. For example, H stands for hydrogen, and Au stands for gold. The vertical columns in the periodic table are known as groups, and elements in groups tend to have very similar properties. The table is also divided into rows, known as periods. | text | null |
L_0485 | chemistry of life | T_2837 | A molecule is any combination of two or more atoms. The oxygen in the air we breathe is two oxygen atoms connected by a chemical bond to form O2 , or molecular oxygen. A carbon dioxide molecule is a combination of one carbon atom and two oxygen atoms, CO2 . Because carbon dioxide includes two different elements, it is a compound as well as a molecule. A compound is any combination of two or more different elements. A compound has different properties from the elements that it contains. Elements and combinations of elements (compounds) make up all the many types of matter in the Universe. A chemical reaction is a process that breaks or forms the bonds between atoms of molecules and compounds. For example, two hydrogens and one oxygen bind together to form water, H2 O. The molecules that come together to start a chemical reaction are the reactants. So hydrogen and oxygen are the reactants. The product is the end result of a reaction. In this example, water is the product. Atoms also come together to form compounds much larger than water. It is some of these large compounds that come together to form the basis of the cell. So essentially, your cells are made out of compounds, which are made out of atoms. | text | null |
L_0488 | chromosomal disorders | T_2848 | Some children are born with genetic defects that are not carried by a single gene. Instead, an error in a larger part of the chromosome or even in an entire chromosome causes the disorder. Usually the error happens when the egg or sperm is forming. Having extra chromosomes or damaged chromosomes can cause disorders. | text | null |
L_0488 | chromosomal disorders | T_2849 | One common example of an extra-chromosome disorder is Down syndrome ( Figure 1.1). Children with Down syndrome are mentally disabled and also have physical deformities. Down syndrome occurs when a baby receives an extra chromosome 21 from one of his or her parents. Usually, a child will receive one chromosome 21 from the mother and one chromosome 21 from the father. In an individual with Down syndrome, however, there are three Chromosomes of a person with Down Syndrome. Notice the extra chromosome 21. copies of chromosome 21 ( Figure 1.2). Therefore, Down syndrome is also known as Trisomy 21. These people have 47 total chromosomes. Another example of a chromosomal disorder is Klinefelter syndrome, in which a male inherits an extra X chromosome. These individuals have an XXY genotype. They have underdeveloped sex organs and elongated limbs. They also have difficulty learning new things. | text | null |
L_0488 | chromosomal disorders | T_2849 | One common example of an extra-chromosome disorder is Down syndrome ( Figure 1.1). Children with Down syndrome are mentally disabled and also have physical deformities. Down syndrome occurs when a baby receives an extra chromosome 21 from one of his or her parents. Usually, a child will receive one chromosome 21 from the mother and one chromosome 21 from the father. In an individual with Down syndrome, however, there are three Chromosomes of a person with Down Syndrome. Notice the extra chromosome 21. copies of chromosome 21 ( Figure 1.2). Therefore, Down syndrome is also known as Trisomy 21. These people have 47 total chromosomes. Another example of a chromosomal disorder is Klinefelter syndrome, in which a male inherits an extra X chromosome. These individuals have an XXY genotype. They have underdeveloped sex organs and elongated limbs. They also have difficulty learning new things. | text | null |
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