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L_0488 | chromosomal disorders | T_2850 | Chromosomal disorders also occur when part of a chromosome becomes damaged. For example, if a tiny portion of chromosome 5 is missing, the individual will have cri du chat (cats cry) syndrome. These individuals have misshapen facial features, and the infants cry resembles a cats cry. | text | null |
L_0489 | circulation and the lymphatic system | T_2851 | The lymphatic system is a network of vessels and tissues that carry a clear fluid called lymph. The lymphatic system ( Figure 1.1) spreads all around the body and filters and cleans the lymph of any debris, abnormal cells, or pathogens. Lymph vessels are tube-shaped, just like blood vessels, with about 500-600 lymph nodes (in an adult) attached. The lymphatic system works with the cardiovascular system to return body fluids to the blood. The lymphatic system and the cardiovascular system are often called the bodys two "circulatory systems." Organs of the lymphatic system include the tonsils, thymus gland and spleen. The thymus gland produces T cells or T-lymphocytes (see below) and the spleen and tonsils help in fighting infections. The spleens main function is to filter the blood, removing unwanted red blood cells. The spleen also detects viruses and bacteria and triggers the release of pathogen fighting cells. The lymphatic system helps return fluid that leaks from the blood vessels back to the cardiovascular system. | text | null |
L_0489 | circulation and the lymphatic system | T_2852 | You may think that your blood vessels have thick walls without any leaks, but thats not true. Blood vessels can leak just like any other pipe. The lymphatic system makes sure leaked blood returns back to the bloodstream. When a small amount of fluid leaks out from the blood vessels, it collects in the spaces between cells and tissues. Some of the fluid returns to the cardiovascular system, and the rest is collected by the lymph vessels of the lymphatic system ( Figure 1.2). The fluid that collects in the lymph vessels is called lymph. The lymphatic system then returns the lymph to the cardiovascular system. Unlike the cardiovascular system, the lymphatic system is not closed (meaning it is an open circulatory system that releases and collects fluid) and has no central pump (or heart). Lymph moves slowly in lymph vessels. It is moved along in the lymph vessels by the squeezing action of smooth muscles and skeletal muscles. Lymph capillaries collect fluid that leaks out from blood capillaries. The lymphatic vessels return the fluid to the cardiovas- cular system. | text | null |
L_0489 | circulation and the lymphatic system | T_2853 | The lymphatic system also plays an important role in the immune system. For example, the lymphatic system makes white blood cells that protect the body from diseases. Cells of the lymphatic system produce two types of white blood cells, T cells and B cells, that are involved in fighting specific pathogens. Lymph nodes, which are scattered throughout the lymphatic system, act as filters or traps for foreign particles and are important in the proper functioning of the immune system. The role of the lymphatic system in the immune response is discussed in additional concepts. | text | null |
L_0494 | connecting cellular respiration and photosynthesis | T_2865 | Photosynthesis and cellular respiration are connected through an important relationship. This relationship enables life to survive as we know it. The products of one process are the reactants of the other. Notice that the equation for cellular respiration is the direct opposite of photosynthesis: Cellular Respiration: C6 H12 O6 + 6O2 6CO2 + 6H2 O Photosynthesis: 6CO2 + 6H2 O C6 H12 O6 + 6O2 Photosynthesis makes the glucose that is used in cellular respiration to make ATP. The glucose is then turned back into carbon dioxide, which is used in photosynthesis. While water is broken down to form oxygen during photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water. While photosynthesis requires carbon dioxide and releases oxygen, cellular respiration requires oxygen and releases carbon dioxide. It is the released oxygen that is used by us and most other organisms for cellular respiration. We breathe in that oxygen, which is carried through our blood to all our cells. In our cells, oxygen allows cellular respiration to proceed. Cellular respiration works best in the presence of oxygen. Without oxygen, much less ATP would be produced. Cellular respiration and photosynthesis are important parts of the carbon cycle. The carbon cycle is the pathways through which carbon is recycled in the biosphere. While cellular respiration releases carbon dioxide into the environment, photosynthesis pulls carbon dioxide out of the atmosphere. The exchange of carbon dioxide and oxygen during photosynthesis ( Figure 1.1) and cellular respiration worldwide helps to keep atmospheric oxygen and carbon dioxide at stable levels. Cellular respiration and photosynthesis are direct opposite reactions. Energy from the sun enters a plant and is con- verted into glucose during photosynthe- sis. Some of the energy is used to make ATP in the mitochondria during cellular respiration, and some is lost to the envi- ronment as heat. | text | null |
L_0499 | diabetes | T_2879 | Diabetes is a non-infectious disease in which the body is unable to control the amount of sugar in the blood. People with diabetes have high blood sugar, either because their bodies do not produce enough insulin, or because their cells do not respond to insulin. Insulin is a hormone that helps cells take up sugar from the blood. Without enough insulin, the blood contains too much sugar. This can damage blood vessels and other cells throughout the body. The kidneys work hard to filter out and remove some of the extra sugar. This leads to frequent urination and excessive thirst. There are two main types of diabetes, type 1 diabetes and type 2 diabetes. Type 1 diabetes makes up about 5-10% of all cases of diabetes in the United States. Type 2 diabetes accounts for most of the other cases. Both types of diabetes are more likely in people that have certain genes. Having a family member with diabetes increases the risk of developing the disease. Either type of diabetes can increase the chances of having other health problems. For example, people with diabetes are more likely to develop heart disease and kidney disease. Type 1 and type 2 diabetes are similar in these ways. However, the two types of diabetes have different causes. | text | null |
L_0499 | diabetes | T_2880 | Type 1 diabetes occurs when the immune system attacks normal cells of the pancreas. Since the cells in the pancreas are damaged, the pancreas cannot make insulin. Type 1 diabetes usually develops in childhood or adolescence. People with type 1 diabetes must frequently check the sugar in their blood. They use a meter to monitor their blood sugar ( Figure 1.1). Whenever their blood sugar starts to get too high, they need a shot of insulin. The insulin brings their blood sugar back to normal. There is no cure for type 1 diabetes. Therefore, insulin shots must be taken for life. Most people with this type of diabetes learn how to give themselves insulin shots. This is one type of meter used by people with diabetes to measure their blood sugar. Modern meters like this one need only a drop of blood and take less than a minute to use. | text | null |
L_0499 | diabetes | T_2881 | Type 2 diabetes occurs when body cells are no longer sensitive to insulin. The pancreas may still make insulin, but the cells of the body cannot use it efficiently. Being overweight and having high blood pressure increase the chances of developing type 2 diabetes. Type 2 diabetes usually develops in adulthood, but it is becoming more common in teens and children. This is because more young people are overweight, due to a high sugar and fat diet, now than ever before. Some cases of type 2 diabetes can be cured with weight loss. However, most people with the disease need to take medicine to control their blood sugar. Regular exercise and balanced eating also help, and should be a regular part of the treatment for these people. Like people with type 1 diabetes, people with type 2 diabetes must frequently check their blood sugar. | text | null |
L_0499 | diabetes | T_2882 | Common symptoms of diabetes include the following: frequent urination feeling very thirsty feeling very hungry, even though you are eating extreme fatigue blurry vision cuts or bruises that are slow to heal weight loss, even though you are eating more (type 1) tingling, pain, or numbness in the hands or feet (type 2) | text | null |
L_0499 | diabetes | T_2883 | Complications of diabetes can include the following: eye complications foot complications skin complications high blood pressure hearing issues nerve damage kidney disease artery disease stroke stress | text | null |
L_0501 | digestive system organs | T_2887 | The mouth and stomach are just two of the organs of the digestive system. Other digestive system organs are the esophagus, small intestine, and large intestine. Below, you can see that the digestive organs form a long tube ( Figure 1.1). In adults, this tube is about 30 feet long! At one end of the tube is the mouth. At the other end is the anus. Food enters the mouth and then passes through the rest of the digestive system. Food waste leaves the body through the anus. The organs of the digestive system are lined with muscles. The muscles contract, or tighten, to push food through the system ( Figure 1.2). The muscles contract in waves. The waves pass through the digestive system like waves through a slinky. This movement of muscle contractions is called peristalsis. Without peristalsis, food would not be able to move through the digestive system. Peristalsis is an involuntary process, which means that it occurs without your conscious control. The liver, gallbladder, and pancreas are also organs of the digestive system ( Figure 1.1). Food does not pass through these three organs. However, these organs are important for digestion. They secrete or store enzymes or other chemicals that are needed to help digest food chemically. | text | null |
L_0501 | digestive system organs | T_2888 | The mouth is the first organ that food enters. But digestion may start even before you put the first bite of food into your mouth. Just seeing or smelling food can cause the release of saliva and digestive enzymes in your mouth. This diagram shows how muscles push food through the digestive system. Muscle contractions travel through the system in waves, pushing the food ahead of them. This is called peristalsis. Once you start eating, saliva wets the food, which makes it easier to break up and swallow. Digestive enzymes, including the enzyme amylase, start breaking down starches into sugars. Your tongue helps mix the food with the saliva and enzymes. Your teeth also help digest food. Your front teeth are sharp. They cut and tear food when you bite into it. Your back teeth are broad and flat. They grind food into smaller pieces when you chew. Chewing is part of mechanical digestion. Your tongue pushes the food to the back of your mouth so you can swallow it. When you swallow, the lump of chewed food passes down your throat to your esophagus. The esophagus is a narrow tube that carries food from the throat to the stomach. Food moves through the esophagus because of peristalsis. At the lower end of the esophagus, a circular muscle controls the opening to the stomach. The muscle relaxes to let food pass into the stomach. Then the muscle contracts again to prevent food from passing back into the esophagus. Some people think that gravity moves food through the esophagus. If that were true, food would move through the esophagus only when you are sitting or standing upright. In fact, because of peristalsis, food can move through the esophagus no matter what position you are ineven upside down! Just dont try to swallow food when you are upside downyou could choke! The stomach is a sac-like organ at the end of the esophagus. It has thick muscular walls. The muscles contract and relax. This moves the food around and helps break it into smaller pieces. Mixing the food around with the enzyme pepsin and other chemicals helps digest proteins. Water, salt, and simple sugars can be absorbed into the blood from the stomach. Most other substances are broken down further in the small intestine before they are absorbed. The stomach stores food until the small intestine is ready to receive it. A circular muscle controls the opening between the stomach and small intestine. When the small intestine is empty, the muscle relaxes. This lets food pass from the stomach into the small intestine. | text | null |
L_0501 | digestive system organs | T_2889 | The small intestine a is narrow tube that starts at the stomach and ends at the large intestine ( Figure 1.1). In adults, the small intestine is about 23 feet long. Chemical digestion takes place in the first part of the small intestine. Many enzymes and other chemicals are secreted here. The small intestine is also where most nutrients are absorbed into the blood. The later sections of the small intestines are covered with tiny projections called villi ( Figure 1.3). Villi contain very tiny blood vessels. Nutrients are absorbed into the blood through these tiny vessels. There are millions of villi, so, altogether, there is a very large area for absorption to take place. In fact, villi make the inner surface area of the small intestine 1,000 times larger than it would be without them. The entire inner surface area of the small intestine is about as big as a basketball court! The small intestine is much longer than the large intestine. So why is it called small? If you compare small and large intestines ( Figure 1.1), you will see the small intestine is smaller in width than the large intestine. | text | null |
L_0501 | digestive system organs | T_2890 | The large intestine is a wide tube that connects the small intestine with the anus. In adults, it is about five feet long. Waste enters the large intestine from the small intestine in a liquid state. As the waste moves through the large intestine, excess water is absorbed from it. After the excess water is absorbed, the remaining solid waste is called feces. Circular muscles control the anus. They relax to let the feces pass out of the body through the anus. After feces pass out of the body, they are called stool. Releasing the stool from the body is referred to as a bowel movement. | text | null |
L_0502 | diseases of the nervous system | T_2891 | The nervous system controls sensing, feeling, and thinking. It also controls movement and just about every other body function. Thats why problems with the nervous system can affect the entire body. Diseases of the nervous system include brain and spinal cord infections. Other problems of the nervous system range from very serious diseases, such as tumors, to less serious problems, such as tension headaches. Some of these diseases are present at birth. Others begin during childhood or adulthood. | text | null |
L_0502 | diseases of the nervous system | T_2892 | When you think of infections, you probably think of an ear infection or strep throat. You probably dont think of a brain or spinal cord infection. But bacteria and viruses can infect these organs as well as other parts of the body. Infections of the brain and spinal cord are not very common. But when they happen, they can be very serious. Thats why its important to know their symptoms. | text | null |
L_0502 | diseases of the nervous system | T_2893 | Encephalitis is a brain infection ( Figure 1.1). If you have encephalitis, you are likely to have a fever and headache or feel drowsy and confused. The disease is most often caused by viruses. The immune system tries to fight off a brain infection, just as it tries to fight off other infections. But sometimes this can do more harm than good. The immune systems response may cause swelling in the brain. With no room to expand, the brain pushes against the skull. This may injure the brain and even cause death. Medicines can help fight some viral infections of the brain, but not all infections. | text | null |
L_0502 | diseases of the nervous system | T_2894 | Meningitis is an infection of the membranes that cover the brain and spinal cord. If you have meningitis, you are likely to have a fever and a headache. Another telltale symptom is a stiff neck. Meningitis can be caused by viruses or bacteria. Viral meningitis often clears up on its own after a few days. Bacterial meningitis is much more serious ( Figure 1.2). It may cause brain damage and death. People with bacterial meningitis need emergency medical treatment. They are usually given antibiotics to kill the bacteria. A vaccine to prevent meningitis recently became available. It can be given to children as young as two years old. Many doctors recommend that children receive the vaccine no later than age 12 or 13, or before they begin high school. | text | null |
L_0502 | diseases of the nervous system | T_2895 | A condition called Reyes syndrome can occur in young people that take aspirin when they have a viral infection. The syndrome causes swelling of the brain and may be fatal. Fortunately, Reyes syndrome is very rare. The best way to prevent it is by not taking aspirin when you have a viral infection. Products like cold medicines often contain aspirin. So, read labels carefully when taking any medicines ( Figure 1.3). Since 1988, the U.S. Food and Drug Ad- ministration has required that all aspirin and aspirin-containing products carry a warning about Reyes syndrome. | text | null |
L_0502 | diseases of the nervous system | T_2896 | Like other parts of the body, the nervous system may develop tumors. A tumor is a mass of cells that grows out of control. A tumor in the brain may press on normal brain tissues. This can cause headaches, difficulty speaking, or other problems, depending on where the tumor is located. Pressure from a tumor can even cause permanent brain damage. In many cases, brain tumors can be removed with surgery. In other cases, tumors cant be removed without damaging the brain even more. In those cases, other types of treatments may be needed. Cerebral palsy is a disease caused by injury to the developing brain. The injury occurs before, during, or shortly after birth. Cerebral palsy is more common in babies that have a low weight at birth. But the cause of the brain injury is not often known. The disease usually affects the parts of the brain that control body movements. Symptoms range from weak muscles in mild cases to trouble walking and talking in more severe cases. There is no known cure for cerebral palsy. Epilepsy is a disease that causes seizures. A seizure is a period of lost consciousness that may include violent muscle contractions. It is caused by abnormal electrical activity in the brain. The cause of epilepsy may be an infection, a brain injury, or a tumor. The seizures of epilepsy can often be controlled with medicine. There is no known cure for the disease, but children with epilepsy may outgrow it by adulthood. A headache is a very common nervous system problem. Headaches may be a symptom of serious diseases, but they are more commonly due to muscle tension. A tension headache occurs when muscles in the shoulders, neck, and head become too tense. This often happens when people are stressed out. Just trying to relax may help relieve this type of headache. Mild pain relievers such as ibuprofen may also help. Sometimes relaxation is the best medicine for a tension headache and to help muscles get rid of pain. A migraine is a more severe type of headache. It occurs when blood vessels in the head dilate, or expand. This may be triggered by certain foods, bright lights, weather changes, or other factors. People with migraines may also have nausea or other symptoms. Fortunately, migraines can often be relieved with prescription drugs. There are many other nervous system diseases. They include multiple sclerosis, Huntingtons disease, Parkinsons disease, and Alzheimers disease. However, these diseases rarely, if ever, occur in young people. Their causes and symptoms are listed below ( Table 1.1). The diseases have no known cure, but medicines may help control their symptoms. Disease Multiple sclerosis Cause The immune system attacks and damages the central nervous sys- tem so neurons cannot function nor- mally. Symptoms Muscle weakness, difficulty mov- ing, problems with coordination, difficulty keeping the body bal- anced Parkinsons disease Alzheimers disease | text | null |
L_0505 | dna the genetic material | T_2901 | DNA is the material that makes up our chromosomes and stores our genetic information. When you build a house, you need a blueprint, a set of instructions that tells you how to build. The DNA is like the blueprint for living organisms. The genetic information is a set of instructions that tell your cells what to do. DNA is an abbreviation for deoxyribonucleic acid. As you may recall, nucleic acids are a type of macromolecule that store information. The deoxyribo part of the name refers to the name of the sugar that is contained in DNA, deoxyribose. DNA may provide the instructions to make up all living things, but it is actually a very simple molecule. DNA is made of a very long chain of nucleotides. In fact, in you, the smallest DNA molecule has well over 20 million nucleotides. | text | null |
L_0505 | dna the genetic material | T_2902 | Nucleotides are composed of three main parts: 1. a phosphate group. 2. a 5-carbon sugar (deoxyribose in DNA). 3. a nitrogen-containing base. The only difference between each nucleotide is the identity of the base. There are only four possible bases that make up each DNA nucleotide: adenine (A), guanine (G), thymine (T), and cytosine (C). | text | null |
L_0505 | dna the genetic material | T_2903 | The various sequences of the four nucleotide bases make up the genetic code of your cells. It may seem strange that there are only four letters in the alphabet of DNA. But since your chromosomes contain millions of nucleotides, there are many, many different combinations possible with those four letters. But how do all these pieces fit together? James Watson and Francis Crick won the Nobel Prize in 1962 for piecing together the structure of DNA. Together with the work of Rosalind Franklin and Maurice Wilkins, they determined that DNA is made of two strands of nucleotides formed into a double helix, or a two-stranded spiral, with the sugar and phosphate groups on the outside, and the paired bases connecting the two strands on the inside of the helix (Figure 1.1). | text | null |
L_0505 | dna the genetic material | T_2904 | The bases in DNA do not pair randomly. When Erwin Chargaff looked closely at the bases in DNA, he noticed that the percentage of adenine (A) in the DNA always equaled the percentage of thymine (T), and the percentage of guanine (G) always equaled the percentage of cytosine (C). Watson and Cricks model explained this result by suggesting that A always pairs with T, and G always pairs with C in the DNA helix. Therefore A and T, and G and C, are "complementary bases," or bases that always pair together, known as a base-pair. The base-pairing rules state that A will always bind to T, and G will always bind to C (Figure 1.2). For example, if one DNA strand reads ATGCCAGT, the other strand will be made up of the complementary bases: TACGGTCA. Hydrogen bonds hold the complementary bases together, with two bonds forming between an A and a T, and three bonds between a G and a C. The chemical structure of DNA includes a chain of nucleotides consisting of a 5- carbon sugar, a phosphate group, and a nitrogen base. Notice how the sugar and phosphate group form the backbone of DNA (strands highlighted in pink), with the hydrogen bonds between the bases joining the two strands. | text | null |
L_0507 | echinoderms | T_2908 | Youre probably familiar with starfish and sand dollars ( Figure 1.1). They are both echinoderms. Sea urchins and sea cucumbers are also echinoderms. Whats similar between these three organisms? They all have radial symmetry. This means that the body is arranged around a central point. Echinoderms belong to the phylum Echinodermata. This phylum includes 7,000 living species. It is the largest animal phylum without freshwater or land-living members. | text | null |
L_0507 | echinoderms | T_2909 | As mentioned earlier, echinoderms show radial symmetry. Other key echinoderm features include an internal skeleton and spines, as well as a few organs and organ systems. Although echinoderms look like they have a hard exterior, they do not have an external skeleton. Instead, a thin outer skin covers an internal skeleton made of tiny plates and spines. This provides rigid support. Some groups of echinoderms, such as sea urchins ( Figure 1.2), have spines that protect the organism. Sea cucumbers use these spines to help them move. A starfish (left) and a keyhole sand dollar (right), showing the radial symmetry char- acteristic of the echinoderms. Starfish are also known as sea stars. Another echinoderm, a sea urchin (Echi- nus esculentus), showing its spines. Echinoderms have a unique water vascular system. This network of fluid-filled tubes helps them to breathe, eat, and move. Therefore, they can function without gill slits. Echinoderms also have a very simple digestive system, circulatory system, and nervous system. The digestive system often leads directly from the mouth to the anus. The echinoderms have an open circulatory system, meaning that fluid moves freely in the body cavity. But echinoderms have no heart. This may be due to their simple radial symmetry - a heart is not needed to pump the freely moving fluid. The echinoderm nervous system is a nerve net, or interconnected neurons with no central brain. Many echinoderms have amazing powers of regeneration. For example, some sea stars (starfish) are capable of regenerating lost arms. In some cases, lost arms have been observed to regenerate a second complete sea star! Sea cucumbers often release parts of their internal organs if they perceive danger. The released organs and tissues are then quickly regenerated. | text | null |
L_0507 | echinoderms | T_2909 | As mentioned earlier, echinoderms show radial symmetry. Other key echinoderm features include an internal skeleton and spines, as well as a few organs and organ systems. Although echinoderms look like they have a hard exterior, they do not have an external skeleton. Instead, a thin outer skin covers an internal skeleton made of tiny plates and spines. This provides rigid support. Some groups of echinoderms, such as sea urchins ( Figure 1.2), have spines that protect the organism. Sea cucumbers use these spines to help them move. A starfish (left) and a keyhole sand dollar (right), showing the radial symmetry char- acteristic of the echinoderms. Starfish are also known as sea stars. Another echinoderm, a sea urchin (Echi- nus esculentus), showing its spines. Echinoderms have a unique water vascular system. This network of fluid-filled tubes helps them to breathe, eat, and move. Therefore, they can function without gill slits. Echinoderms also have a very simple digestive system, circulatory system, and nervous system. The digestive system often leads directly from the mouth to the anus. The echinoderms have an open circulatory system, meaning that fluid moves freely in the body cavity. But echinoderms have no heart. This may be due to their simple radial symmetry - a heart is not needed to pump the freely moving fluid. The echinoderm nervous system is a nerve net, or interconnected neurons with no central brain. Many echinoderms have amazing powers of regeneration. For example, some sea stars (starfish) are capable of regenerating lost arms. In some cases, lost arms have been observed to regenerate a second complete sea star! Sea cucumbers often release parts of their internal organs if they perceive danger. The released organs and tissues are then quickly regenerated. | text | null |
L_0507 | echinoderms | T_2910 | Feeding strategies vary greatly among the different groups of echinoderms. Theres no one food or technique thats shared by all echinoderms. Different eating-methods include: 1. Passive filter-feeders, which are organisms that absorb suspended nutrients from passing water. Some echino- derms use their long arms to capture food particles floating past in the currents. 2. Grazers, such as sea urchins, are organisms that feed on available plants. Sea urchins are omnivorous, eating both plant and animals. The sea urchin mainly feeds on algae on the coral and rocks, along with decomposing matter such as dead fish, mussels, sponges, and barnacles. 3. Deposit feeders, which are organisms that feed on small pieces of organic matter, usually in the top layer of soil. Sea cucumbers are deposit feeders, living on the ocean floor. They eat the tiny scrap particles that are usually abundant in the environments that they inhabit. 4. Active hunters, which are organisms that actively hunt their prey. Many sea stars are predators, feeding on mollusks like clams by prying apart their shells and actually placing their stomach inside the mollusk shell to digest the meat. | text | null |
L_0507 | echinoderms | T_2911 | Echinoderms reproduce sexually. In most echinoderms, eggs and sperm cells are released into open water, and fertilization takes place when the eggs and sperm meet. This is called external fertilization, and is typical of many marine animals. The release of sperm and eggs often occurs when organisms are in the same place at the same time. Internal fertilization takes place in only a few species. Some species even take care of their offspring, like parents! | text | null |
L_0509 | effects of water pollution | T_2913 | Water pollutants can have an effect on both the ecology of ecosystems and on humans. As a result of water pollution, humans may not be able to use a waterway for recreation and fishing. Drinking water can also be affected if a toxin enters the groundwater. | text | null |
L_0509 | effects of water pollution | T_2914 | In a marine ecosystem, algae are the producers. Through photosynthesis, they provide glucose for the ecosystem. So, can too much algae be a bad thing? Eutrophication is an over-enrichment of chemical nutrients in a body of water. Usually these nutrients are the nitrogen and phosphorous found in fertilizers. Run-off from lawns or farms can wash fertilizers into rivers or coastal waters. Plants are not the only things that grow more quickly with added fertilizers. Algae like the excess nutrients in fertilizers too. When there are high levels of nutrients in the water, algae populations will grow large very quickly. This leads to overgrowths of algae called algal blooms. However, these algae do not live very long. They die and begin to decompose. This process uses oxygen, removing the oxygen from the water. Without oxygen, fish and shellfish cannot live, and this results in the death of these organisms ( Figure 1.1). Certain types of algal blooms can also create toxins. These toxins can enter shellfish. If humans eat these shellfish, then they can get very sick. These toxins cause neurological problems in humans. | text | null |
L_0509 | effects of water pollution | T_2915 | Ocean acidification occurs when excess carbon dioxide in the atmosphere causes the oceans to become acidic. Burning fossil fuels has led to an increase in carbon dioxide in the atmosphere. This carbon dioxide is then absorbed by the oceans, which lowers the pH of the water. Ocean acidification can kill corals and shellfish. It may also cause marine organisms to reproduce less, which could harm other organisms in the food chain. As a result, there also may be fewer marine organisms for humans to consume. | text | null |
L_0509 | effects of water pollution | T_2916 | Aquatic debris is trash that gets into fresh- and saltwater waterways. It comes from shipping accidents, landfill erosion, or the direct dumping of trash. Debris can be very dangerous to aquatic wildlife. Some animals may swallow plastic bags, mistaking them for food. Other animals can be strangled by floating trash like plastic six-pack rings. Wildlife can easily get tangled in nets ( Figure 1.2). Marine trash can harm different types of aquatic life. Pictured here is a marine turtle entangled in a net. How can you keep this from happening? | text | null |
L_0509 | effects of water pollution | T_2917 | Unsafe water supplies have drastic effects on human health. Waterborne diseases are diseases due to microscopic pathogens in fresh water. These diseases can be caused by protozoa, viruses, bacteria, and intestinal parasites. In many parts of the world there are no water treatment plants. If sewage or animal manure gets into a river, then people downstream will get sick when they drink the water. According to the World Health Organization (WHO), diarrheal disease is responsible for the deaths of 1.8 million people every year. It was estimated that 88% of the cases of diarrheal disease are caused by unsafe water supplies. | text | null |
L_0510 | energy pyramids | T_2918 | When an herbivore eats a plant, the energy in the plant tissues is used by the herbivore. But how much of that energy is transferred to the herbivore? Remember that plants are producers, bringing the energy into the ecosystem by converting sunlight into glucose. Does the plant use some of the energy for its own needs? Recall the energy is the ability to do work, and the plant has plenty or "work" to do. So of course it needs and uses energy. It converts the glucose it makes into ATP through cellular respiration just like other organisms. After the plant uses the energy from glucose for its own needs, the excess energy is available to the organism that eats the plant. The herbivore uses the energy from the plant to power its own life processes and to build more body tissues. However, only about 10% of the total energy from the plant gets stored in the herbivores body as extra body tissue. The rest of the energy is used by the herbivore and released as heat. The next consumer on the food chain that eats the herbivore will only store about 10% of the total energy from the herbivore in its own body. This means the carnivore will store only about 1% of the total energy that was originally in the plant. In other words, only about 10% of energy of one step in a food chain is stored in the next step in the food chain. The majority of the energy is used by the organism or released to the environment. Every time energy is transferred from one organism to another, there is a loss of energy. This loss of energy can be shown in an energy pyramid. An example of an energy pyramid is pictured below ( Figure 1.1). Since there is energy loss at each step in a food chain, it takes many producers to support just a few carnivores in a community. Each step of the food chain in the energy pyramid is called a trophic level. Plants or other photosynthetic organisms ( autotrophs) are found on the first trophic level, at the bottom of the pyramid. The next level will be the herbivores, and then the carnivores that eat the herbivores. The energy pyramid ( Figure 1.1) shows four levels of a food chain, from producers to carnivores. Because of the high rate of energy loss in food chains, there are usually only 4 or 5 trophic levels in the food chain or energy pyramid. There just is not enough energy to support any additional trophic levels. Heterotrophs are found in all levels of an energy pyramid other than the first level. | text | null |
L_0511 | enzymes in the digestive system | T_2919 | Chemical digestion could not take place without the help of digestive enzymes. An enzyme is a protein that speeds up chemical reactions in the body. Digestive enzymes speed up chemical reactions that break down large food molecules into small molecules. Did you ever use a wrench to tighten a bolt? You could tighten a bolt with your fingers, but it would be difficult and slow. If you use a wrench, you can tighten a bolt much more easily and quickly. Enzymes are like wrenches. They make it much easier and quicker for chemical reactions to take place. Like a wrench, enzymes can also be used over and over again. But you need the appropriate size and shape of the wrench to efficiently tighten the bolt, just like each enzyme is specific for the reaction it helps. Digestive enzymes are released, or secreted, by the organs of the digestive system. These enzymes include proteases that digest proteins, and nucleases that digest nucleic acids. Examples of digestive enzymes are: Amylase, produced in the mouth. It helps break down large starch molecules into smaller sugar molecules. Pepsin, produced in the stomach. Pepsin helps break down proteins into amino acids. Trypsin, produced in the pancreas. Trypsin also breaks down proteins. Pancreatic lipase, produced in the pancreas. It is used to break apart fats. Deoxyribonuclease and ribonuclease, produced in the pancreas. They are enzymes that break bonds in nucleic acids like DNA and RNA. Bile salts are bile acids that help to break down fat. Bile acids are made in the liver. When you eat a meal, bile is secreted into the intestine, where it breaks down the fats ( Figure 1.1). | text | null |
L_0511 | enzymes in the digestive system | T_2920 | If you are a typical teenager, you like to eat. For your body to break down, absorb and spread the nutrients from your food throughout your body, your digestive system and endocrine system need to work together. The endocrine system sends hormones around your body to communicate between cells. Essentially, hormones are chemical messenger molecules. Digestive hormones are made by cells lining the stomach and small intestine. These hormones cross into the blood where they can affect other parts of the digestive system. Some of these hormones are listed below. Gastrin, which signals the secretion of gastric acid. Cholecystokinin, which signals the secretion of pancreatic enzymes. Secretin, which signals secretion of water and bicarbonate from the pancreas. Ghrelin, which signals when you are hungry. Gastric inhibitory polypeptide, which stops or decreases gastric secretion. It also causes the release of insulin in response to high blood glucose levels. | text | null |
L_0512 | evolution acts on the phenotype | T_2921 | Natural selection acts on the phenotype (the traits or characteristics) of an individual. On the other hand, natural selection does not act on the underlying genotype (the genetic makeup) of an individual. For many traits, the homozygous genotype, AA, for example, has the same phenotype as the heterozygous Aa genotype. If both an AA and Aa individual have the same phenotype, the environment cannot distinguish between them. So natural selection cannot select for a homozygous individual over a heterozygous individual. Even if the "aa" phenotype is lethal, the recessive a allele, will be maintained in the population through heterozygous Aa individuals. Furthermore, the mating of two heterozygous individuals can produce homozygous recessive (aa) individuals. However, natural selection can and does differentiate between dominant and recessive phenotypes. | text | null |
L_0512 | evolution acts on the phenotype | T_2922 | Since natural selection acts on the phenotype, if an allele causes death in a homozygous individual, aa, for example, it will not cause death in a heterozygous Aa individual. These heterozygous Aa individuals will then act as carriers of the a allele, meaning that the a allele could be passed down to offspring. People who are carriers do not express the recessive phenotype, as they have a dominant allele. This allele is said to be kept in the populations gene pool. The gene pool is the complete set of genes and alleles within a population. For example, Tay-Sachs disease is a recessive human genetic disorder. That means only individuals with the homozygous recessive genotype, rr will be affected. Affected individuals usually die from complications of the disease in early childhood, at an age too young to reproduce. The two parents are each heterozygous (Rr) for the Tay-Sachs gene; they will not die in childhood and will be carriers of the disease gene. This deadly allele is kept in the gene pool even though it does not help humans adapt to their environment. This happens because evolution acts on the phenotype, not the genotype ( Figure 1.1). Tay-Sachs disease is inherited in the au- tosomal recessive pattern. Each parent is an unaffected carrier of the lethal allele. | text | null |
L_0513 | excretion | T_2923 | So what happens to your bodys wastes? Obviously, you must get rid of them. This is the job of the excretory system. You remove waste as a gas (carbon dioxide), as a liquid (urine and sweat), and as a solid. Excretion is the process of removing wastes and excess water from the body. Recall that carbon dioxide travels through the blood and is transferred to the lungs where it is exhaled. In the large intestine, the remains of food are turned into solid waste for excretion. How is waste other than carbon dioxide removed from the blood? That is the role of the kidneys. Urine is a liquid waste formed by the kidneys as they filter the blood. If you are getting plenty of fluids, your urine should be almost clear. But you might have noticed that sometimes your urine is darker than usual. Do you know why this happens? Sometimes your body is low on water and trying to reduce the amount of water lost in urine. Therefore, your urine gets darker than usual. Your body is striving to maintain homeostasis through the process of excretion. Urine helps remove excess water, salts, and nitrogen from your body. Your body also needs to remove the wastes that build up from cell activity and from digestion. If these wastes are not removed, your cells can stop working, and you can get very sick. The organs of your excretory system help to release wastes from the body. The organs of the excretory system are also parts of other organ systems. For example, your lungs are part of the respiratory system. Your lungs remove carbon dioxide from your body, so they are also part of the excretory system. More organs of the excretory system are listed below ( Table 1.1). Organ(s) Function Lungs Skin Remove carbon dioxide. Sweat glands remove water, salts, and other wastes. Removes solid waste and some wa- ter in the form of feces. Remove urea, salts, and excess wa- ter from the blood. Large intestine Kidneys Component of Other Organ Sys- tem Respiratory system Integumentary system Digestive system Urinary system | text | null |
L_0514 | excretory system problems | T_2924 | The urinary system controls the amount of water in the body and removes wastes. Any problem with the urinary system can also affect many other body systems. | text | null |
L_0514 | excretory system problems | T_2925 | In some cases, certain mineral wastes can form kidney stones ( Figure 1.1). Stones form in the kidneys and may be found anywhere in the urinary system. Often, stones form when the urine becomes concentrated, allowing minerals to crystallize and stick together. They can vary in size, from small stones that can flow through your urinary system, to larger stones that cannot. Some stones cause great pain, while others cause very little pain. Some stones may need to be removed by surgery or ultrasound treatments. What are the symptoms of kidney stones? You may have a kidney stone if you have pain while urinating, see blood in your urine, and/or feel a sharp pain in your back or lower abdomen (the area between your chest and hips). The pain may last for a long or short time. You may also have nausea and vomiting with the pain. If you have a small stone that passes on its own easily, you may not experience any symptoms. If you have some of these symptoms, you should see your doctor. A kidney stone. The stones can form anywhere in the urinary system. | text | null |
L_0514 | excretory system problems | T_2926 | Kidney failure happens when the kidneys cannot remove wastes from the blood. If the kidneys are unable to filter wastes from the blood, the wastes build up in the body. Kidney failure can be caused by an accident that injures the kidneys, the loss of a lot of blood, or by some drugs and poisons. Kidney failure may lead to permanent loss of kidney function. But if the kidneys are not seriously damaged, they may recover. Chronic kidney disease is the slow decrease in kidney function that may lead to permanent kidney failure. A person who has lost kidney function may need to get kidney dialysis. Kidney dialysis is the process of filtering the blood of wastes using a machine. A dialysis machine ( Figure 1.2) filters waste from the blood by pumping the blood through a fake kidney. The filtered blood is then returned to the patients body. | text | null |
L_0514 | excretory system problems | T_2927 | Urinary tract infections (UTIs) are bacterial infections of any part of the urinary tract. When bacteria get into the bladder or kidney and produce more bacteria in the urine, they cause a UTI. The most common type of UTI is a bladder infection. Women get UTIs more often than men. UTIs are often treated with antibiotics. Most UTIs are not serious, but some infections can lead to serious problems. Long lasting kidney infections can cause permanent damage, including kidney scars, poor kidney function, high blood pressure, and other problems. Some sudden kidney infections can be life threatening, especially if the bacteria enter the bloodstream, a condition called septicemia. What are the signs and symptoms of a UTI? a burning feeling when you urinate, frequent or intense urges to urinate, even when you have little urine to pass, pain in your back or side below the ribs, cloudy, dark, bloody, or foul-smelling urine, fever or chills. You should see your doctor if you have signs of a UTI. Your doctor will diagnose a UTIs by asking about your symptoms and then testing a sample of your urine. | text | null |
L_0515 | features of populations | T_2928 | A population is a group of organisms of the same species, all living in the same area and interacting with each other. Since they live together in one area, members of the same species reproduce together. Ecologists who study populations determine how healthy or stable the populations are. They also study how the individuals of a species interact with each other and how populations interact with the environment. If a group of similar organisms in the same area cannot reproduce with members of the other group, then they are members of two distinct species and form two populations. Ecologists look at many factors that help to describe a population. First, ecologists can measure the number of individuals that make up the population, known as population size. They can then determine the population density, which is the number of individuals of the same species in an area. Population density can be expressed as number per area, such as 20 mice/acre, or 50 rabbits/square mile. Ecologists also study how individuals in a population are spread across an environment. This spacing of individuals within a population is called dispersion. Some species may be clumped or clustered ( Figure 1.1) in an area. Others may be evenly spaced ( Figure 1.2). Still others may be spaced randomly within an area. The population density and dispersion have an effect on reproduction and population size. What do you think the relationship is between population density, dispersion and size? Clumped species are closer together. This may allow for easier reproduction. A population of cacti in the Sonoran Desert generally shows even dispersion due to competition for water. Ecologists also study the birth and death rates of the population. Together these give the growth rate (the birth rate minus the death rate), which tells how fast (or slow) the population size is changing. The birth rate is the number of births within a population during a specific time period. The death rate is the number of deaths within a population during a specific time period. Knowing the birth and death rates of populations gives you information about a populations health. For example, when a population is made up of mostly young organisms and the birth rate is high, the population is growing. A population with equal birth and death rates will remain the same size. Populations that are decreasing in size have a higher death rate than birth rate. | text | null |
L_0515 | features of populations | T_2928 | A population is a group of organisms of the same species, all living in the same area and interacting with each other. Since they live together in one area, members of the same species reproduce together. Ecologists who study populations determine how healthy or stable the populations are. They also study how the individuals of a species interact with each other and how populations interact with the environment. If a group of similar organisms in the same area cannot reproduce with members of the other group, then they are members of two distinct species and form two populations. Ecologists look at many factors that help to describe a population. First, ecologists can measure the number of individuals that make up the population, known as population size. They can then determine the population density, which is the number of individuals of the same species in an area. Population density can be expressed as number per area, such as 20 mice/acre, or 50 rabbits/square mile. Ecologists also study how individuals in a population are spread across an environment. This spacing of individuals within a population is called dispersion. Some species may be clumped or clustered ( Figure 1.1) in an area. Others may be evenly spaced ( Figure 1.2). Still others may be spaced randomly within an area. The population density and dispersion have an effect on reproduction and population size. What do you think the relationship is between population density, dispersion and size? Clumped species are closer together. This may allow for easier reproduction. A population of cacti in the Sonoran Desert generally shows even dispersion due to competition for water. Ecologists also study the birth and death rates of the population. Together these give the growth rate (the birth rate minus the death rate), which tells how fast (or slow) the population size is changing. The birth rate is the number of births within a population during a specific time period. The death rate is the number of deaths within a population during a specific time period. Knowing the birth and death rates of populations gives you information about a populations health. For example, when a population is made up of mostly young organisms and the birth rate is high, the population is growing. A population with equal birth and death rates will remain the same size. Populations that are decreasing in size have a higher death rate than birth rate. | text | null |
L_0516 | female reproductive structures | T_2929 | The female reproductive organs include the vagina, uterus, fallopian tubes, and ovaries ( Figure 1.1). The breasts are not shown in this figure. They are not considered reproductive organs, even though they are involved in reproduction. They contain mammary glands that give milk to feed a baby. The milk leaves the breast through the nipple when the baby sucks on it. The vagina is a cylinder-shaped organ found inside of the female body. One end of the vagina opens at the outside of the body. The other end joins with the uterus. During sexual intercourse, sperm may be released into the vagina. If this occurs, the sperm will move through the vagina and into the uterus. During birth, a baby passes from the uterus to the vagina to leave the body. The uterus is a hollow organ with muscular walls. The part that connects the vagina with the uterus is called the cervix. The uterus is where a baby develops until birth. The walls of the uterus grow bigger as the baby grows. The muscular walls of the uterus push the baby out during birth. This drawing shows the organs of the female 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 ovaries are small, oval organs on either side of the uterus. Each ovary contains thousands of eggs, with about 1-2 million immature eggs present at birth and 40,000 immature eggs present at puberty, as most of the eggs die off. The eggs do not fully develop until a female has gone through puberty. About once a month, on average one egg completes development and is released by the ovary. The ovaries also secrete estrogen, the main female sex hormone. The two fallopian tubes are narrow tubes that open off from the uterus. Each tube reaches for one of the ovaries, but the tubes are not attached to the ovaries. The end of each fallopian tube by the ovary has fingers ( Figure 1.1). They sweep an egg into the fallopian tube. Then the egg passes through the fallopian tube to the uterus. If an egg is to be fertilized, this will occur in the fallopian tube. A fertilized egg then implants into the wall of the uterus, where it begins to develop. An unfertilized egg will flow through the uterus and be excreted from the body. | text | null |
L_0517 | female reproductive system | T_2930 | Most of the male reproductive organs are outside of the body. But female reproductive organs are inside of the body. The male and female organs also look very different and have different jobs. Two of the functions of the female reproductive system are similar to the functions of the male reproductive system. The female system: 1. Produces gametes, the reproductive cells, which are called eggs in females. 2. Secretes a major sex hormone, estrogen. One of the main roles of the female reproductive system is to produce eggs. Eggs ( Figure 1.1) are female gametes, and they are made in the ovaries. After puberty, females release only one egg at a time. Eggs are actually made in the body before birth, but they do not fully develop until later in life. Like sperm, eggs are produced by meiosis, so they contain half the number of chromosomes as the original cell. Another role of the female system is to secrete estrogen. Estrogen is the main sex hormone in females. Estrogen has two major roles: 1. During the teen years, estrogen causes the reproductive organs to develop. It also causes other female traits to develop. For example, it causes the breasts to grow. 2. During adulthood, estrogen is needed for a woman to release eggs. On average, a woman releases one egg each month from her ovaries. The female reproductive system has another important function. After puberty, the female reproductive system must prepare itself to accept a fertilized egg each cycle (about every month). This cycle is controlled by a well-planned and very complex interplay of hormones. If an egg is not fertilized, the system must prepare itself again the next cycle. The female reproductive system also supports a baby as it develops before birth, and it facilitates the babys birth at the end of pregnancy. | text | null |
L_0518 | fermentation | T_2931 | Sometimes cells need to obtain energy from sugar, but there is no oxygen present to complete cellular respiration. In this situation, cellular respiration can be anaerobic, occurring in the absence of oxygen. In this process, called fermentation, only the first step of respiration, glycolysis, occurs, producing two ATP; no additional ATP is produced. Therefore, the organism only obtains the two ATP molecules per glucose molecule from glycolysis. Compared to the 36-38 ATP produced under aerobic conditions, anaerobic respiration is not a very efficient process. Fermentation allows the first step of cellular respiration to continue and produce some ATP, even without oxygen. Yeast (single-celled eukaryotic organisms) perform alcoholic fermentation in the absence of oxygen. The products of alcoholic fermentation are ethyl alcohol (drinking alcohol) and carbon dioxide gas. This process is used to make common food and drinks. For example, alcoholic fermentation is used to bake bread. The carbon dioxide bubbles allow the bread to rise and become fluffy. Meanwhile, the alcohol evaporates. In wine making, the sugars of grapes are fermented to produce wine. The sugars are the starting materials for glycolysis. Animals and some bacteria and fungi carry out lactic acid fermentation. Lactic acid is a waste product of this process. Our muscles perform lactic acid fermentation during strenuous exercise, since oxygen cannot be delivered to the muscles quickly enough. The buildup of lactic acid is believed to make your muscles sore after exercise. Bacteria that produce lactic acid are used to make cheese and yogurt. The lactic acid causes the proteins in milk to thicken. Lactic acid also causes tooth decay, because bacteria use the sugars in your mouth for energy. Pictured below are some products of fermentation ( Figure 1.1). Products of fermentation include cheese (lactic acid fermentation) and wine (alco- holic fermentation). | text | null |
L_0518 | fermentation | T_2932 | Behind every fart is an army of gut bacteria undergoing some crazy biochemistry. These bacteria break down the remains of digested food through fermentation, creating gas in the process. Learn what these bacteria have in common with beer brewing at http://youtu.be/R1kxajH629A?list=PLzMhsCgGKd1hoofiKuifwy6qRXZs7NG6a . Click image to the left or use the URL below. URL: | text | null |
L_0521 | fish | T_2936 | What exactly is a fish? You probably think the answer is obvious. You may say that a fish is an animal that swims in the ocean or a lake, using fins. But as we saw with the mudskipper, not all fish spend all their time in water. So how do scientists define fish? Some characteristics of fish include: 1. They are ectothermic, meaning their temperature depends on the temperature of their environment. Ectother- mic animals are cold-blooded in that they cannot raise their body temperature on their own. This is unlike humans, whose temperature is controlled from inside the body. 2. They are covered with scales. 3. They have two sets of paired fins and several unpaired fins. 4. They also have a streamlined body that allows them to swim rapidly. Fish are aquatic vertebrates, meaning they have backbones. They became a dominant form of sea life and eventually evolved into land vertebrates. There are three classes of fish: Class Agnatha (the jawless fish), Class Chondrichthyes (the cartilaginous fish), and Class Osteichthyes (the bony fish). All have the characteristics of fish in common, though there are differences unique to each class. | text | null |
L_0521 | fish | T_2937 | In order to absorb oxygen from the water, fish use gills ( Figure 1.2). Gills take dissolved oxygen from water as the water flows over the surface of the gill. Gills help a fish breathe. | text | null |
L_0521 | fish | T_2938 | Fish reproduce sexually. They lay eggs that can be fertilized either inside or outside of the body. In most fish, the eggs develop outside of the mothers body. In the majority of these species, fertilization also takes place outside the mothers body. The male and female fish release their gametes into the surrounding water, where fertilization occurs. Female fish release very high numbers of eggs to increase the chances of fertilization. | text | null |
L_0521 | fish | T_2939 | Fish range in size from the 65-foot, 75,000 pound whale shark ( Figure 1.3) to the stout infantfish, which is about 0.33 inches (8.4 mm), and the Paedocypris progenetica carp species of the Indonesian island of Sumatra, which is about 0.31 inches (7.9 mm) long, making it also the smallest known vertebrate animal. The second-largest fish is the basking shark, which grows to about 40 feet and 8,000 pounds. Both of the large sharks may look ferocious, and would probably scare anyone who comes across one in the water, but both species are filter-feeders, and feed on tiny fish and plankton. The tiny carp species is unique in that it has the appearance of larvae, with a reduced skeleton lacking a cranium, which leaves the brain unprotected by bone. The fish lives in dark acidic waters, having a pH of 3. Keep in mind that whales are not fish, they are mammals. | text | null |
L_0521 | fish | T_2940 | There are exceptions to many of these fish traits. For example, tuna, swordfish, and some species of shark show some warm-blooded adaptations and are able to raise their body temperature significantly above that of the water around them. Some species of fish have a slower, more maneuverable swimming style, like eels and rays ( Figure 1.4). Body shape and the arrangement of fins are highly variable, and the surface of the skin may be naked, as in moray eels, or covered with scales. Scales can be of a variety of different types. | text | null |
L_0521 | fish | T_2941 | How are fish important? Of course, they are used as food ( Figure 1.5). In fact, people all over the world either catch fish in the wild or farm them in much the same way as cattle or chickens. Farming fish is known as aquaculture. Fish are also caught for recreation to display in the home or in a public aquarium. | text | null |
L_0522 | flatworms | T_2942 | The word "worm" is not very scientific. But it is a word that informally describes animals (usually invertebrates) that have long bodies with no arms or legs. (Snakes are vertebrates, so they are not usually described as worms.) Worms are the first significant group of animals with bilateral symmetry, meaning that the right side of their bodies is a mirror of the left. One type of worm is the flatworm. Worms in the phylum Platyhelminthes are called flatworms because they have flattened bodies. There are more than 18,500 known species of flatworms. | text | null |
L_0522 | flatworms | T_2943 | The main characteristics of flatworms ( Figure 1.1) include: 1. Flatworms have no true body cavity, but they do have bilateral symmetry. Due to the lack of a body cav- ity,flatworms are known as acoelomates. 2. Flatworms have an incomplete digestive system. This means that the digestive tract has only one opening. Digestion takes place in the gastrovascular cavity. 3. Flatworms do not have a respiratory system. Instead, they have pores that allow oxygen to enter through their body. Oxygen enters the pores by diffusion. 4. There are no blood vessels in the flatworms. Their gastrovascular cavity helps distribute nutrients throughout the body. 5. Flatworms have a ladder-like nervous system; two interconnected parallel nerve cords run the length of the body. 6. Most flatworms have a distinct head region that includes nerve cells and sensory organs, such as eyespots. The development of a head region, called cephalization, evolved at the same time as bilateral symmetry in animals. This process does not occur in cnidarians, which evolved prior to flatworms and have radial symmetry. Marine flatworms can be brightly colored, such as this one from the class Turbel- laria. These worms are mostly carnivores or scavengers. | text | null |
L_0522 | flatworms | T_2944 | Flatworms live in a variety of environments. Some species of flatworms are free-living organisms that feed on small organisms and rotting matter. These types of flatworms include marine flatworms and freshwater flatworms, such as Dugesia. Other types of flatworms are parasitic. That means they live inside another organism, called a host, in order to get the food and energy they need. For example, tapeworms have a head-like area with tiny hooks and suckers (known as the scolex) that help the worm attach to the intestines of an animal host ( Figure 1.2). There are over 11,000 species of parasitic flatworms. | text | null |
L_0523 | food and nutrients | T_2945 | Did you ever hear the old saying, An apple a day keeps the doctor away? Do apples really prevent you from getting sick? Probably not, but eating apples and other fresh fruits can help keep you healthy. Do you eat your vegetables? Maybe you do, but you may have friends who wont touch a piece of broccoli or asparagus. Should you eat these foods and food like them? The girls pictured in the Figure 1.1 are eating salads. Why do you need foods like these for good health? What role does food play in the body? Your body needs food for three reasons: 1. Food gives your body energy. You need energy for everything you do. Remember that cellular respiration converts the glucose in the food you eat into ATP, or cellular energy. Which has more glucose, a salad or a piece of meat? Do you remember what types of foods produce glucose? Recall that glucose is the product of photosynthesis. These girls are eating leafy green vegetables. Fresh vegetables such as these are excellent food choices for good health. 2. Food provides building materials for your body. Your body needs building materials so it can grow and repair itself. Specifically, it needs these materials to produce more cells and its components. 3. Food contains substances that help control body processes. Your body processes must be kept in balance for good health. For all these reasons, you must have a regular supply of nutrients. Nutrients are chemicals in food that your body needs. There are five types of nutrients. 1. 2. 3. 4. 5. Carbohydrates Proteins Lipids Vitamins Minerals Carbohydrates, proteins, and lipids are categories of organic compounds. They give your body energy, though carbohydrates are the main source of energy. Proteins provide building materials, such as amino acids to build your own proteins. Proteins, vitamins, and minerals also help control body processes. Carbohydrates include sugars such as the glucose made by photosynthesis. Often glucose is stored in large molecules such as starch. Proteins are found in foods like meats and nuts. Lipids includes fats and oils. Though you should stay away from many types of fats, others are needed by your body. Important vitamins include vitamins A, B (multiple types) C, D, and E. Important minerals include calcium and potassium. What should you drink to get calcium? Milk is a good source. | text | null |
L_0525 | fossils | T_2947 | Fossils are the preserved remains of animals, plants, and other organisms from the distant past. Examples of fossils include bones, teeth, and impressions. By studying fossils, evidence for evolution is revealed. Paleontologists are scientists who study fossils to learn about life in the past. Fossils allow these scientists to determine the features of extinct species. Paleontologists compare the features of species from different periods in history. With this information, they try to understand how species have evolved over millions of years ( Figure below). Until recently, fossils were the main source of evidence for evolution ( Figure below). Through studying fossils, we now know that todays organisms look much different in many cases than those that were alive in the past. Scientists have also shown that organisms were spread out differently across the planet. Earthquakes, volcanoes, shifting seas, and other movements of the continents have all affected where organisms live and how they adapted to their changing environments. | text | null |
L_0525 | fossils | T_2948 | There are many layers of rock in the Earths surface. Newer layers form on top of the older layers; the deepest rock layers are the oldest. Therefore, you can tell how old a fossil is by observing in which layer of rock it was found. Evolution of the horse. Fossil evi- dence, depicted by the skeletal frag- ments, demonstrates evolutionary mile- stones in this process. Notice the 57 million year evolution of the horse leg bones and teeth. Especially obvious is the transformation of the leg bones from having four distinct digits to that of todays horse. The fossils and the order in which fossils appear is called the fossil record. The fossil record provides evidence for when organisms lived on Earth, how species evolved, and how some species have gone extinct. Geologists use a method called radiometric dating to determine the exact age of rocks and fossils in each layer of rock. This technique, which is possible because radioactive materials decay at a known rate, measures how much of the radioactive materials in each rock layer have broken down ( Figure 1.3). Radiometric dating has been used to determine that the oldest known rocks on Earth are between 4 and 5 billion years old. The oldest fossils are between 3 and 4 billion years old. Remember that during Darwins time, people believed the Earth was just about 6,000 years old. The fossil record proves that Earth is much older than people once thought. | text | null |
L_0525 | fossils | T_2948 | There are many layers of rock in the Earths surface. Newer layers form on top of the older layers; the deepest rock layers are the oldest. Therefore, you can tell how old a fossil is by observing in which layer of rock it was found. Evolution of the horse. Fossil evi- dence, depicted by the skeletal frag- ments, demonstrates evolutionary mile- stones in this process. Notice the 57 million year evolution of the horse leg bones and teeth. Especially obvious is the transformation of the leg bones from having four distinct digits to that of todays horse. The fossils and the order in which fossils appear is called the fossil record. The fossil record provides evidence for when organisms lived on Earth, how species evolved, and how some species have gone extinct. Geologists use a method called radiometric dating to determine the exact age of rocks and fossils in each layer of rock. This technique, which is possible because radioactive materials decay at a known rate, measures how much of the radioactive materials in each rock layer have broken down ( Figure 1.3). Radiometric dating has been used to determine that the oldest known rocks on Earth are between 4 and 5 billion years old. The oldest fossils are between 3 and 4 billion years old. Remember that during Darwins time, people believed the Earth was just about 6,000 years old. The fossil record proves that Earth is much older than people once thought. | text | null |
L_0525 | fossils | T_2948 | There are many layers of rock in the Earths surface. Newer layers form on top of the older layers; the deepest rock layers are the oldest. Therefore, you can tell how old a fossil is by observing in which layer of rock it was found. Evolution of the horse. Fossil evi- dence, depicted by the skeletal frag- ments, demonstrates evolutionary mile- stones in this process. Notice the 57 million year evolution of the horse leg bones and teeth. Especially obvious is the transformation of the leg bones from having four distinct digits to that of todays horse. The fossils and the order in which fossils appear is called the fossil record. The fossil record provides evidence for when organisms lived on Earth, how species evolved, and how some species have gone extinct. Geologists use a method called radiometric dating to determine the exact age of rocks and fossils in each layer of rock. This technique, which is possible because radioactive materials decay at a known rate, measures how much of the radioactive materials in each rock layer have broken down ( Figure 1.3). Radiometric dating has been used to determine that the oldest known rocks on Earth are between 4 and 5 billion years old. The oldest fossils are between 3 and 4 billion years old. Remember that during Darwins time, people believed the Earth was just about 6,000 years old. The fossil record proves that Earth is much older than people once thought. | text | null |
L_0533 | genetic disorders | T_2968 | Many genetic disorders are caused by mutations in one or a few genes. Others are caused by chromosomal mutations. Some human genetic disorders are X-linked or Y-linked, which means the faulty gene is carried on these sex chromosomes. Other genetic disorders are carried on one of the other 22 pairs of chromosomes; these chromosomes are known as autosomes or autosomal (non-sex) chromosomes. Some genetic disorders are due to new mutations, others can be inherited from your parents. | text | null |
L_0533 | genetic disorders | T_2969 | Some genetic disorders are caused by recessive alleles of a single gene on an autosome. An example of autosomal recessive genetic disorders are Tay-Sachs disease and cystic fibrosis. Children with cystic fibrosis have excessively thick mucus in their lungs, which makes it difficult for them to breathe. The inheritance of this recessive allele is the same as any other recessive allele, so a Punnett square can be used to predict the probability that two carriers of the disease will have a child with cystic fibrosis. Recall that carriers have the recessive allele for a trait but do not express the trait. What are the possible genotypes of the offspring in the following table ( Table 1.1)? What are the possible phenotypes? F FF (normal) Ff (carrier) F f f Ff (carrier) ff (affected) According to this Punnett square, two parents that are carriers (Ff ) of the cystic fibrosis gene have a 25% chance of having a child with cystic fibrosis (ff ). The affected child must inherit two recessive alleles. The carrier parents are not affected. Tay-Sachs disease is a severe genetic disorder in which affected children do not live to adulthood, so the gene is not passed from an affected individual. Carriers of the Tay-Sachs gene are not affected. How does a child become affected with Tay-Sachs? | text | null |
L_0533 | genetic disorders | T_2970 | Huntingtons disease is an example of an autosomal dominant disorder. This means that if the dominant allele is present, then the person will express the disease. A child only has to inherit one dominant allele to have the disease. The disease causes the brains cells to break down, leading to muscle spasms and personality changes. Unlike most other genetic disorders, the symptoms usually do not become apparent until middle age. You can use a simple Punnett square to predict the inheritance of a dominant autosomal disorder, like Huntingtons disease. If one parent has Huntingtons disease, what is the chance of passing it on to the children? If you draw the Punnett square, you will find that there is a 50 percent chance of the disorder being passed on to the children. | text | null |
L_0537 | hardy weinberg theorem | T_2985 | Sometimes understanding how common a gene is within a population is necessary. Or, more specifically, you may want to know how common a certain form of that gene is within the population, such as a recessive form. This can be done using the Hardy-Weinberg model, but it can only be done if the frequencies of the genes are not changing. The Hardy-Weinberg model describes how a population can remain at genetic equilibrium, referred to as the Hardy-Weinberg equilibrium. Genetic equilibrium occurs when there is no evolution within the population. In other words, the frequency of alleles (variants of a gene) will be the same from one generation to another. At genetic equilibrium, the gene or allele frequencies are stablethey do not change. For example, lets assume that red hair is determined by the inheritance of a gene with two allelesR and r. The dominant allele, R, encodes for non-red hair, while the recessive allele, r, encodes for red hair. If a populations gene pool contains 90% R and 10% r alleles, then the next generation would also have 90% R and 10% r alleles. However, this only works under a strict set of conditions. The five conditions that must be met for genetic equilibrium to occur include: 1. 2. 3. 4. 5. No mutation (change) in the DNA sequence. No migration (moving into or out of a population). A very large population size. Random mating. No natural selection. These five conditions rarely occur in nature. When one or more of the conditions does not exist, then evolution can occur. As a result, allele frequencies are constantly changing, and populations are constantly evolving. As mutations and natural selection occur frequently in nature, it is difficult for a population to be at genetic equilibrium. The Hardy-Weinberg model also serves a mathematical formula used to predict allele frequencies in a population at genetic equilibrium. If you know the allele frequencies of one generation, you can use this formula to predict the next generation. Again, this only works if all five conditions are being met in a population. | text | null |
L_0538 | harmful bacteria | T_2986 | With so many species of bacteria, some are bound to be harmful. Harmful bacteria can make you sick. They can also ruin food and be used to hurt people. | text | null |
L_0538 | harmful bacteria | T_2987 | There are also ways that bacteria can be harmful to humans and other animals. Bacteria are responsible for many types of human illness ( Figure 1.1), including: Strep throat Tuberculosis Pneumonia Leprosy Lyme disease Luckily most of these can be treated with antibiotics, which kill the bacteria. It is important that when a medical doctor prescribes antibiotics for you, you take the medicine exactly as the doctor tells you. You need to make sure the bacteria is killed. | text | null |
L_0538 | harmful bacteria | T_2988 | Bacterial contamination of foods can lead to digestive problems, an illness known as food poisoning. Raw eggs and undercooked meats commonly carry the bacteria that can cause food poisoning. Food poisoning can be prevented by cooking meat thoroughly, which kills most microbes, and washing surfaces that have been in contact with raw meat. Washing your hands before and after handling food also helps prevent contamination. | text | null |
L_0538 | harmful bacteria | T_2989 | Some bacteria also have the potential to be used as biological weapons by terrorists. An example is anthrax, a disease caused by the bacterium Bacillus anthracis. Inhaling the spores of this bacterium can lead to a deadly infection, and, therefore, it is a dangerous weapon. In 2001, an act of terrorism in the United States involved B. anthracis spores sent in letters through the mail. | text | null |
L_0538 | harmful bacteria | T_2990 | KidsHealth Food Poisoning at http://kidshealth.org/kid/ill_injure/sick/food_poisoning.html . 1. What are the common bacteria that cause food poisoning? 2. What steps can you take to keep your food safe? | text | null |
L_0539 | health hazards of air pollution | T_2991 | The World Health Organization (WHO) reports that 2.4 million people die each year from causes directly related to air pollution. This includes both outdoor and indoor air pollution. Worldwide, there are more deaths linked to air pollution each year than to car accidents. Research by the WHO also shows that the worst air quality is in countries with high poverty and population rates, such as Egypt, Sudan, Mongolia, and Indonesia. Respiratory system disorders are directly related to air pollution. These disorders have severe effects on human health, some leading to death directly related to air pollution. Air pollution related respiratory disorders include asthma, bronchitis, and emphysema. Asthma is a respiratory disorder characterized by wheezing, coughing, and a feeling of constriction in the chest. Bronchitis is inflammation of the membrane lining of the bronchial tubes of the lungs. Emphysema is a deadly lung disease characterized by abnormal enlargement of air spaces in the lungs and destruction of the lung tissue. Additional lung and heart diseases are also related to air pollution, as are respiratory allergies. Air pollution can also indirectly cause other health issues and even deaths. Air pollutants can cause an increase in cancer including lung cancer, eye problems, and other conditions. For example, using certain chemicals on farms, such as the insecticide DDT (dichlorodiphenyltrichloroethane) and toxic PCBs (polychlorinated biphenyl), can cause cancer. Indoors, pollutants such as radon or asbestos can also increase your cancer risk. Lastly, air pollution can lead to heart disease, including heart attack and stroke. | text | null |
L_0539 | health hazards of air pollution | T_2992 | Certain respiratory conditions can be made worse in people who live closer to or in large cites. Some studies have shown that people in urban areas suffer lower levels of lung function and more chronic bronchitis and emphysema. If you live in a city, you have seen smog. It is a low-hanging, fog-like cloud that seems to never leave the city ( Figure 1.1). Smog is caused by coal burning and by ozone produced by motor vehicle exhaust. Smog can cause eye irritation and respiratory problems. A layer of smog is typical for Cairo, Egypt. | text | null |
L_0539 | health hazards of air pollution | T_2993 | After reading about the effects of air pollution, both indoors and outdoors, you may wonder how you can avoid it. As for outdoor air pollution, if you hear in the news that the outdoor air quality is particularly bad, then it might make sense to wear a mask outdoors or to stay indoors. Because you have more control over your indoor air quality than the outdoor air quality, there are some simple steps you can take indoors to make sure the air quality is less polluted. These include: 1. 2. 3. 4. Make sure that vents and chimneys are working properly, and never burn charcoal indoors. Place carbon monoxide detectors in the home. Keep your home as clean as possible from pet dander, dust, dust mites, and mold. Make sure air conditioning systems are working properly. Are there any other ways you can think of to protect yourself from air pollution? | text | null |
L_0540 | health of the digestive system | T_2994 | Most of the time, you probably arent aware of your digestive system. It works well without causing any problems. But most people have problems with their digestive system at least once in a while. Did you ever eat something that didnt agree with you? Maybe you had a stomachache or felt sick to your stomach? Maybe you had diarrhea? These could be symptoms of foodborne illness, food allergies, or a food intolerance. | text | null |
L_0540 | health of the digestive system | T_2995 | Harmful bacteria can enter your digestive system in food and make you sick. This is called foodborne illness or food poisoning. The bacteria, or the toxins they produce, may cause vomiting or cramping, in addition to the symptoms mentioned above. Foodborne illnesses can also be caused by viruses and parasites. The most common foodborne illnesses happen within a few minutes to a few hours, and make you feel really sick, but last for only about a day or so. Others can take longer for the illness to appear. Some people believe that the taste of food will tell you if it is bad. As a rule, you probably should not eat bad tasting food, but many contaminated foods can still taste good. You can help prevent foodborne illness by following a few simple rules. Keep hot foods hot and cold foods cold. This helps prevent any bacteria in the foods from multiplying. Wash your hands before you prepare or eat food. This helps prevent bacteria on your hands from getting on the food. This is the easiest way to prevent foodborne illnesses. Wash your hands after you touch raw foods, such as meats, poultry, fish, or eggs. These foods often contain bacteria that your hands could transfer to your mouth. Cook meats, poultry, fish, and eggs thoroughly before eating them. The heat of cooking kills any bacteria the foods may contain, so they cannot make you sick. Refrigerate cooked food soon after a meal. Cooked food can be left out for up to two hours before they need to be placed in the cold. This will prevent the spread of bacteria. Cooked foods should not be left out all day. Bacteria that cause foodborne illnesses include Salmonella, a bacterium found in many foods, including raw and undercooked meat, poultry, dairy products, and seafood. Campylobacter jejuni is found in raw or undercooked chicken and unpasteurized milk. Several strains of E. coli can cause illnesses, and are found in raw or undercooked hamburger, unpasteurized fruit juices and milk, and even fresh produce. Vibrio is a bacterium that may contaminate fish or shellfish. Listeria has been found in raw and undercooked meats, unpasteurized milk, soft cheeses, and ready- to-eat deli meats and hot dogs. Most of these bacterial illnesses can be prevented with proper cooking of food and washing of hands. Common foodborne viruses include norovirus and hepatitis A virus. Norovirus, which causes inflammation of the stomach and intestines, has been a recent issue on cruise ships, infecting hundreds of passengers and crew on certain voyages. Hepatitis A causes inflammation of the liver, which is treated with rest and diet changes. Parasites are tiny organisms that live inside another organism. Giardia is a parasite spread through water contaminated with the stools of people or animals who are infected. Food preparers who are infected with parasites can also contaminate food if they do not thoroughly wash their hands after using the bathroom and before handling food. Trichinella is a type of roundworm parasite. People may be infected with this parasite by consuming raw or undercooked pork or wild game. | text | null |
L_0540 | health of the digestive system | T_2996 | Food allergies are like other allergies. They occur when the immune system reacts to harmless substances as though they were harmful. Almost ten percent of children have food allergies. Some of the foods most likely to cause allergies are shown below ( Figure 1.1). Eating foods you are allergic to may cause vomiting, diarrhea, or skin rashes. Some people are very allergic to certain foods. Eating even tiny amounts of the foods causes them to have serious symptoms, such as difficulty breathing. If they eat the foods by accident, they may need emergency medical treatment. Some of the foods that commonly cause allergies are shown here. They include nuts, eggs, grains, milk, and shellfish. Are you allergic to any of these foods? The most common food allergy symptoms include: tingling or itching in the mouth hives, itching or eczema, swelling of the lips, face, tongue and throat, or other parts of the body, wheezing, nasal congestion or trouble breathing, abdominal pain, diarrhea, nausea or vomiting, dizziness, lightheadedness or fainting. In some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can cause a coma or death. Anaphylaxis is vary rare. The vast majority of people will never have an anaphylactic reaction. The life-threatening symptoms of anaphylaxis include: constriction and tightening of the airway, a swollen throat or the sensation of a lump in your throat that makes it difficult to breathe, shock, with a severe drop in blood pressure, a rapid pulse, dizziness, lightheadedness or loss of consciousness. | text | null |
L_0540 | health of the digestive system | T_2997 | A food intolerance, or food sensitivity, is different from a food allergy. A food intolerance happens when the digestive system is unable to break down a certain type of food. This can result in stomach cramping, diarrhea, tiredness, and weight loss. Food intolerances are often mistakenly called allergies. Lactose intolerance is a food intolerance. A person who is lactose intolerant does not make enough lactase, the enzyme that breaks down the milk sugar, lactose. Lactose intolerance may be as high as 75% in some populations, but overall the percentage of affected individuals is much less. Still, well over 10% of the worlds population is lactose intolerant. | text | null |
L_0541 | hearing and balance | T_2998 | What do listening to music and riding a bike have in common? It might surprise you to learn that both activities depend on your ears. The ears do more than just detect sound. They also sense the position of the body and help maintain balance. | text | null |
L_0541 | hearing and balance | T_2999 | Hearing is the ability to sense sound. Sound travels through the air in waves, much like the waves you see in the water pictured below ( Figure 1.1). Sound waves in air cause vibrations inside the ears. The ears sense the vibrations. The human ear is pictured below ( Figure 1.2). As you read about it, trace the path of sound waves through the ear. Assume a car horn blows in the distance. Sound waves spread through the air from the horn. Some of the sound waves reach your ear. The steps below show what happens next. They explain how your ears sense the sound. 1. The sound waves travel to the ear canal (external auditory canal in the figure). This is a tube-shaped opening in the ear. Sound waves travel through the air in all directions away from a sound, like waves traveling through water away from where a pebble was dropped. Read the names of the parts of the ear in the text; then find each of the parts in the diagram. Note that the round window is distinct from the oval window. 2. At the end of the ear canal, the sound waves hit the eardrum (tympanic membrane). This is a thin membrane that vibrates like the head of a drum when sound waves hit it. 3. The vibrations pass from the eardrum to the hammer (malleus). This is the first of three tiny bones that pass vibrations through the ear. 4. The hammer passes the vibrations to the anvil (incus), the second tiny bone that passes vibrations through the ear. 5. The anvil passes the vibrations to the stirrup (stapes), the third tiny bone that passes vibrations through the ear. 6. From the stirrup, the vibrations pass to the oval window. This is another membrane like the eardrum. 7. The oval window passes the vibrations to the cochlea. The cochlea is filled with liquid that moves when the vibrations pass through, like the waves in water when you drop a pebble into a pond. Tiny hair cells line the cochlea and bend when the liquid moves. When the hair cells bend, they release neurotransmitters. 8. The neurotransmitters trigger nerve impulses that travel to the brain through the auditory nerve (cochlear No doubt youve been warned that listening to loud music or other loud sounds can damage your hearing. Its true. In fact, repeated exposure to loud sounds is the most common cause of hearing loss. The reason? Very loud sounds can kill the tiny hair cells lining the cochlea. The hair cells do not generally grow back once they are destroyed, so this type of hearing loss is permanent. You can protect your hearing by avoiding loud sounds or wearing earplugs or other ear protectors. | text | null |
L_0541 | hearing and balance | T_2999 | Hearing is the ability to sense sound. Sound travels through the air in waves, much like the waves you see in the water pictured below ( Figure 1.1). Sound waves in air cause vibrations inside the ears. The ears sense the vibrations. The human ear is pictured below ( Figure 1.2). As you read about it, trace the path of sound waves through the ear. Assume a car horn blows in the distance. Sound waves spread through the air from the horn. Some of the sound waves reach your ear. The steps below show what happens next. They explain how your ears sense the sound. 1. The sound waves travel to the ear canal (external auditory canal in the figure). This is a tube-shaped opening in the ear. Sound waves travel through the air in all directions away from a sound, like waves traveling through water away from where a pebble was dropped. Read the names of the parts of the ear in the text; then find each of the parts in the diagram. Note that the round window is distinct from the oval window. 2. At the end of the ear canal, the sound waves hit the eardrum (tympanic membrane). This is a thin membrane that vibrates like the head of a drum when sound waves hit it. 3. The vibrations pass from the eardrum to the hammer (malleus). This is the first of three tiny bones that pass vibrations through the ear. 4. The hammer passes the vibrations to the anvil (incus), the second tiny bone that passes vibrations through the ear. 5. The anvil passes the vibrations to the stirrup (stapes), the third tiny bone that passes vibrations through the ear. 6. From the stirrup, the vibrations pass to the oval window. This is another membrane like the eardrum. 7. The oval window passes the vibrations to the cochlea. The cochlea is filled with liquid that moves when the vibrations pass through, like the waves in water when you drop a pebble into a pond. Tiny hair cells line the cochlea and bend when the liquid moves. When the hair cells bend, they release neurotransmitters. 8. The neurotransmitters trigger nerve impulses that travel to the brain through the auditory nerve (cochlear No doubt youve been warned that listening to loud music or other loud sounds can damage your hearing. Its true. In fact, repeated exposure to loud sounds is the most common cause of hearing loss. The reason? Very loud sounds can kill the tiny hair cells lining the cochlea. The hair cells do not generally grow back once they are destroyed, so this type of hearing loss is permanent. You can protect your hearing by avoiding loud sounds or wearing earplugs or other ear protectors. | text | null |
L_0541 | hearing and balance | T_3000 | Did you ever try to stand on one foot with your eyes closed? Try it and see what happens, but be careful! Its harder to keep your balance when you cant see. Your eyes obviously play a role in balance. But your ears play an even bigger role. The gymnast pictured below ( Figure 1.3) may not realize it, but her earsalong with her cerebellumare mostly responsible for her ability to perform on the balance beam. The parts of the ears involved in balance are the semicircular canals. Above, the semicircular canals are colored purple ( Figure 1.2). The canals contain liquid and are like the bottle of water pictured below ( Figure 1.4). When the bottle tips, the water surface moves up and down the sides of the bottle. When the body tips, the liquid in the semicircular canals moves up and down the sides of the canals. Tiny hair cells line the semicircular canals. Movement of the liquid inside the canals causes the hair cells to send nerve impulses. The nerve impulses travel to the cerebellum in the brain along the vestibular nerve. In response, the cerebellum sends commands to muscles to contract or relax so that the body stays balanced. | text | null |
L_0542 | heart | T_3001 | What does the heart look like? How does it pump blood? The heart is divided into four chambers ( Figure 1.1), or spaces: the left and right atria, and the left and right ventricles. An atrium (singular for atria) is one of the two small, thin-walled chambers on the top of the heart where the blood first enters. A ventricle is one of the two muscular V-shaped chambers that pump blood out of the heart. You can remember they are called ventricles because they are shaped like a "V." The atria receive the blood, and the ventricles pump the blood out of the heart. Each of the four chambers of the heart has a specific job. The right atrium receives oxygen-poor blood from the body. The right ventricle pumps oxygen-poor blood toward the lungs, where it receives oxygen. The left atrium receives oxygen-rich blood from the lungs. The left ventricle pumps oxygen-rich blood out of the heart to the rest of the body. | text | null |
L_0542 | heart | T_3002 | Blood flows through the heart in two separate loops. You can think of them as a left side loop and a right side loop. The right side of the heart collects oxygen-poor blood from the body and pumps it into the lungs, where it releases carbon dioxide and picks up oxygen. (Recall that carbon dioxide is a waste product that must be removed. It is removed when we exhale.) The left side carries the oxygen-rich blood back from the lungs into the left side of the heart, which then pumps the oxygen-rich blood to the rest of the body. The blood delivers oxygen to the cells of the body, where it is needed for cellular respiration, and returns to the heart oxygen-poor. To move blood through the heart, the cardiac muscle needs to contract in an organized way. Blood first enters the atria ( Figure 1.2). When the atria contract, blood is pushed into the ventricles. After the ventricles fill with blood, they contract, and blood is pushed out of the heart. The heart is mainly composed of cardiac muscle. These muscle cells contract in unison, causing the heart itself to contract and generating enough force to push the blood out. So how is the blood kept from flowing back on itself? Valves ( Figure 1.2) in the heart keep the blood flowing in one direction. The valves do this by opening and closing in one direction only. Blood only moves forward through the heart. The valves stop the blood from flowing backward. There are four valves of the heart. The two atrioventricular (AV) valves stop blood from moving from the ventricles to the atria. The two semilunar (SL) valves are found in the arteries leaving the heart, and they prevent blood from flowing back from the arteries into the ventricles. Why does a heart beat? The lub-dub sound of the heartbeat is caused by the closing of the AV valves ("lub") and SL valves ("dub") after blood has passed through them. | text | null |
L_0543 | helpful bacteria | T_3003 | Can we survive without bacteria? Could bacteria survive without us? No and yes. No, we could not survive without bacteria. And yes, bacteria could survive without us. | text | null |
L_0543 | helpful bacteria | T_3004 | Bacteria can be used to make cheese from milk. The bacteria turn the milk sugars into lactic acid. The acid is what causes the milk to curdle to form cheese. Bacteria are also involved in producing other foods. Yogurt is made by using bacteria to ferment milk ( Figure 1.1). Fermenting cabbage with bacteria produces sauerkraut. Yogurt is made from milk fermented with bacteria. The bacteria ingest natural milk sugars and release lactic acid as a waste product, which causes proteins in the milk to form into a solid mass, which becomes the yogurt. | text | null |
L_0543 | helpful bacteria | T_3005 | In the laboratory, bacteria can be changed to provide us with a variety of useful materials. Bacteria can be used as tiny factories to produce desired chemicals and medicines. For example, insulin, which is necessary to treat people with diabetes, can be produced using bacteria. Through the process of transformation, the human gene for insulin is placed into bacteria. The bacteria then use that gene to make a protein. The protein can be separated from the bacteria and then used to treat patients. The mass production of insulin by bacteria made this medicine much more affordable. During transformation, bacteria can take up any DNA from the environment. Therefore, transformation allows scientists to insert any DNA into a bacteria, potentially producing many different proteins. This makes the bacteria greatly useful to people. | text | null |
L_0543 | helpful bacteria | T_3006 | Bacteria also help you digest your food. Several species of bacteria, such as E. coli, are found in your digestive tract. In fact, in your gut, bacteria cells greatly outnumber your own cells! | text | null |
L_0543 | helpful bacteria | T_3007 | Bacteria are important in practically all ecosystems because many bacteria are decomposers. They break down dead materials and waste products and recycle nutrients back into the environment. The recycling of nutrients, such as nitrogen, by bacteria, is essential for living organisms. Organisms cannot produce nutrients, so they must come from other sources. We get nutrients from the food we eat; plants get them from the soil. How do these nutrients get into the soil? One way is from the actions of decomposers. Without decomposers, we would eventually run out of the materials we need to survive. We also depend on bacteria to decompose our wastes in sewage treatment plants. | text | null |
L_0544 | hiv and aids | T_3008 | HIV, or human immunodeficiency virus, causes AIDS. AIDS stands for "acquired immune deficiency syndrome." It is a condition that causes death and does not have a known cure. AIDS usually develops 10 to 15 years after a person is first infected with HIV. The development of AIDS can be delayed with proper medicines. The delay can be well over 20 years with the right medicines. Today, individuals who acquire HIV after 50 years of age can expect to reach an average human life span. | text | null |
L_0544 | hiv and aids | T_3009 | HIV spreads through contact between an infected persons body fluids and another persons bloodstream or mucus membranes, which are found in the mouth, nose, and genital areas. Body fluids that may contain HIV are blood, semen, vaginal fluid, and breast milk. The virus can spread through sexual contact or shared drug needles. It can also spread from an infected mother to her baby during childbirth or breastfeeding. Saliva can carry the HIV virus, but it wont spread it, unless the saliva gets into the bloodstream. Other body fluids such as urine and sweat do not contain the virus. HIV does not spread in any fluid in which the host cells cannot survive. Some people think they can become infected with HIV by donating blood or receiving donated blood. This is not true. The needles used to draw blood for donations are always new. Therefore, they cannot spread the virus. Donated blood is also tested to make sure it is does not contain HIV. HIV is not transmitted by day-to-day contact in the workplace, schools, or social settings. HIV is not transmitted through shaking hands, hugging, or a casual kiss. You cannot become infected from a toilet seat, a drinking fountain, a door knob, dishes, drinking glasses, food, or pets. | text | null |
L_0544 | hiv and aids | T_3010 | How does an HIV infection develop into AIDS? HIV destroys white blood cells called helper T cells. The cells are produced by the immune system. This is the body system that fights infections and other diseases. HIV invades helper T cells and uses them to produce more virus particles ( Figure 1.1). Then, the virus kills the helper T cells. As the number of viruses in the blood rises, the number of helper T cells falls. Without helper T cells, the immune system is unable to protect the body. The infected person cannot fight infections and other diseases because they do not have T cells. This is why people do not die from HIV. Instead, they die from another illness, like the common cold, that they cannot fight because they do not have helper T cells. Medications can slow down the increase of viruses in the blood. But the medications cannot remove the viruses from the body. At present, there is no cure for HIV infection. A vaccine against HIV could stop this disease, and such a vaccine is in development, though it could take many years before it can be given to prevent this virus. | text | null |
L_0544 | hiv and aids | T_3011 | AIDS is not really a single disease. It is a set of symptoms and other diseases. It results from years of damage to the immune system by HIV. AIDS occurs when helper T cells fall to a very low level, making it difficult for the affected person to fight various diseases and other infections. These people develop infections or cancers that people with a healthy immune systems can easily resist. These diseases are usually the cause of death of people with AIDS. The first known cases of AIDS occurred in 1981. Since then, AIDS has led to the deaths of more than 35 million people worldwide. Many of them were children. The greatest number of deaths occurred in Africa. It is also where medications to control HIV are least available. There are currently more people infected with HIV in Africa than any other part of the world. Well over 30 million people are living with HIV worldwide. | text | null |
L_0545 | homeostasis | T_3012 | When you walk outside on a cool day, does your body temperature drop? No, your body temperature stays stable at around 98.6 degrees Fahrenheit. Even when the temperature around you changes, your internal temperature stays the same. This ability of the body to maintain a stable internal environment despite a changing environment is called home- ostasis. Homeostasis doesnt just protect against temperature changes. Other aspects of your internal environment also stay stable. For example, your body closely regulates your fluid balance. You may have noticed that if you are slightly dehydrated, your urine is darker. Thats because the urine is more concentrated and less water is mixed in with it. | text | null |
L_0545 | homeostasis | T_3013 | So how does your body maintain homeostasis? The regulation of your internal environment is done primarily through negative feedback. Negative feedback is a response to a stimulus that keeps a variable close to a set value ( Figure For example, your body has an internal thermostat. During a winter day, in your house a thermostat senses the temperature in a room and responds by turning on or off the heater. Your body acts in much the same way. When body temperature rises, receptors in the skin and the brain sense the temperature change. The temperature change triggers a command from the brain. This command can cause several responses. If you are too hot, the skin makes sweat and blood vessels near the skin surface dilate. This response helps decrease body temperature. Another example of negative feedback has to do with blood glucose levels. When glucose (sugar) levels in the blood are too high, the pancreas secretes insulin to stimulate the absorption of glucose and the conversion of glucose into glycogen, which is stored in the liver. As blood glucose levels decrease, less insulin is produced. When glucose levels are too low, another hormone called glucagon is produced, which causes the liver to convert glycogen back to glucose. For additional information, see Homeostasis at . Feedback Regulation. If a raise in body temperature (stimulus) is detected (recep- tor), a signal will cause the brain to main- tain homeostasis (response). Once the body temperature returns to normal, neg- ative feedback will cause the response to end. This sequence of stimulus-receptor- signal-response is used throughout the body to maintain homeostasis. | text | null |
L_0545 | homeostasis | T_3014 | Some processes in the body are regulated by positive feedback. Positive feedback is when a response to an event increases the likelihood of the event to continue. An example of positive feedback is milk production in nursing mothers. As the baby drinks her mothers milk, the hormone prolactin, a chemical signal, is released. The more the baby suckles, the more prolactin is released, which causes more milk to be produced. Other examples of positive feedback include contractions during childbirth. When constrictions in the uterus push a baby into the birth canal, additional contractions occur. | text | null |
L_0546 | how the eye works | T_3015 | Carbon is one of the most common elements found in living organisms. Chains of carbon molecules form the backbones of many organic molecules, such as carbohydrates, proteins, and lipids. Carbon is constantly cycling between living organisms and the atmosphere ( Figure 1.1). The cycling of carbon occurs through the carbon cycle. Living organisms cannot make their own carbon, so how is carbon incorporated into living organisms? In the atmosphere, carbon is in the form of carbon dioxide gas (CO2 ). Recall that plants and other producers capture the carbon dioxide and convert it to glucose (C6 H12 O6 ) through the process of photosynthesis. Then as animals eat plants or other animals, they gain the carbon from those organisms. The chemical equation of photosynthesis is 6CO2 + 6H2 O C6 H12 O6 + 6O2 . How does this carbon in living things end up back in the atmosphere? Remember that we breathe out carbon dioxide. This carbon dioxide is generated through the process of cellular respiration, which has the reverse chemical reaction as photosynthesis. That means when our cells burn food (glucose) for energy, carbon dioxide is released. We, like all animals, exhale this carbon dioxide and return it back to the atmosphere. Also, carbon is released to the atmosphere as an organism dies and decomposes. Cellular respiration and photosynthesis can be described as a cycle, as one uses carbon dioxide (and water) and makes oxygen (and glucose), and the other uses oxygen (and glucose) and makes carbon dioxide (and water). The carbon cycle. The cycling of carbon dioxide in photosynthesis and cellular res- piration are main components of the car- bon cycle. Carbon is also returned to the atmosphere by the burning of fossil fuels and decomposition of organic matter. | text | null |
L_0546 | how the eye works | T_3016 | Millions of years ago, there were so many dead plants and animals that they could not completely decompose before they were buried. They were covered over by soil or sand, tar or ice. These dead plants and animals are organic matter made out of cells full of carbon-containing organic compounds (carbohydrates, lipids, proteins and nucleic acids). What happened to all this carbon? When organic matter is under pressure for millions of years, it forms fossil fuels. Fossil fuels are coal, oil, and natural gas. When humans dig up and use fossil fuels, we have an impact on the carbon cycle ( Figure 1.2). This carbon is not recycled until it is used by humans. The burning of fossil fuels releases more carbon dioxide into the atmosphere than is used by photosynthesis. So, there is more carbon dioxide entering the atmosphere than is coming out of it. Carbon dioxide is known as a greenhouse gas, since it lets in light energy but does not let heat escape, much like the panes of a greenhouse. The increase of greenhouse gasses in the atmosphere is contributing to a global rise in Earths temperature, known as global warming or global climate change. | text | null |
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