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L_0467 | blood types | T_2775 | The second most important blood group system in human blood is the Rhesus (Rh) factor. A person either has, or does not have, the Rh antigen on the surface of their RBCs. If they do have it, then the person is positive. If the person does not have the antigen, they are considered negative. | text | null |
L_0467 | blood types | T_2776 | Recall that people with type O blood do not have any antigens on their RBCs. As a result, type O blood can be given to people with blood types A, B, or AB. If there are no antigens on the RBCs, there cannot be an antibody reaction in the blood. People with type O blood are often called universal donors. The blood plasma of AB blood does not contain any anti-A or anti-B antibodies. People with type AB blood can receive any ABO blood type. People with type AB blood are called universal recipients because they can receive any blood type. The antigens and antibodies that define blood type are listed as follows ( Table 1.1). Blood Type Antigen Type Plasma Antibodies A B AB O A B A and B none anti-B anti-A none anti-A, anti-B Can Receive Blood from Types A,O B,O AB, A, B, O O Can Donate Blood to Types A, AB B, AB AB AB, A, B, O | text | null |
L_0468 | blood vessels | T_2777 | The blood vessels are an important part of the cardiovascular system. They connect the heart to every cell in the body. Arteries carry blood away from the heart, while veins return blood to the heart ( Figure 1.1). The right side of the heart pumps de- oxygenated blood into pulmonary circula- tion, while the left side pumps oxygenated blood into systemic circulation. | text | null |
L_0468 | blood vessels | T_2778 | There are specific veins and arteries that are more significant than others. The pulmonary arteries carry oxygen- poor blood away from the heart to the lungs. These are the only arteries that carry oxygen-poor blood. The aorta is the largest artery in the body. It carries oxygen-rich blood away from the heart. Further away from the heart, the aorta branches into smaller arteries, which eventually branch into capillaries. Capillaries are the smallest type of blood vessel; they connect very small arteries and veins. Gases and other substances are exchanged between cells and the blood across the very thin walls of capillaries. The veins that return oxygen-poor blood to the heart are the superior vena cava and the inferior vena cava. The pulmonary veins return oxygen-rich blood from the lungs to the heart. The pulmonary veins are the only veins that carry oxygen-rich blood. | text | null |
L_0468 | blood vessels | T_2779 | Pulmonary circulation is the part of the cardiovascular system that carries oxygen-poor blood away from the heart and brings it to the lungs. Oxygen-poor blood returns to the heart from the body and leaves the right ventricle through the pulmonary arteries, which carry the blood to each lung. Once at the lungs, the red blood cells release carbon dioxide and pick up oxygen when you breathe. The oxygen-rich blood then leaves the lungs through the pulmonary veins, which return it to the left side of the heart. This completes the pulmonary cycle. The oxygenated blood is then pumped to the body through systemic circulation, before returning again to pulmonary circulation. | text | null |
L_0468 | blood vessels | T_2780 | Systemic circulation is the part of the cardiovascular system that carries oxygen-rich blood away from the heart, to the body, and returns oxygen-poor blood back to the heart. Oxygen-rich blood leaves the left ventricle through the aorta. Then it travels to the bodys organs and tissues. The tissues and organs absorb the oxygen through the capillaries. Oxygen-poor blood is collected from the tissues and organs by tiny veins, which then flow into bigger veins, and, eventually, into the inferior vena cava and superior vena cava. This completes systemic circulation. The blood releases carbon dioxide and gets more oxygen in pulmonary circulation before returning to systemic circulation. The inferior vena cava returns blood from the body. The superior vena cava returns blood from the head. | text | null |
L_0469 | bony fish | T_2781 | There are about 27,000 species of bony fish ( Figure 1.1), which are divided into two classes: ray-finned fish and lobe-finned fish. Most bony fish are ray-finned. These thin fins consist of webs of skin over flexible spines. Lobe- finned fish, on the other hand, have fins that resemble stump-like appendages. Fins of bony fish: ray fin (left) and lobe fin (right). | text | null |
L_0469 | bony fish | T_2782 | Most fish are bony fish, making them the largest group of vertebrates in existence today. They are characterized by: 1. A head and pectoral girdles (arches supporting the forelimbs) that are covered with bones derived from the skin. 2. A lung or swim bladder, which helps the body create a balance between sinking and floating by either filling up with or emitting gases such as oxygen. Controlling the volume of this organ helps fish control their depth. 3. Jointed, segmented rods supporting the fins. 4. A cover over the gill called the operculum, which helps them breathe without having to swim. 5. The ability to see in color, unlike most other fish. | text | null |
L_0469 | bony fish | T_2783 | Most vertebrates are ray-finned fish, with close to 27,000 known species. By comparison, there are "only" about 10,000 species of birds. The ray-finned fish have fin rays, with fins supported by bony spines known as rays. The ray-finned fish are the dominant class of vertebrates, with nearly 99% of fish falling into this category. They live in all aquatic environments, from freshwater and marine environments from the deep sea to the highest mountain streams. | text | null |
L_0469 | bony fish | T_2784 | The lobe-finned fish are characterized by fleshy lobed fins, as opposed to the bony fins of the ray-finned fish. There are two types of living lobe-finned fish: the coelacanths and the lungfish. The pectoral and pelvic fins have joints resembling those of tetrapod (four-limbed land vertebrates) limbs. These fins evolved into legs of amphibians, the first tetrapod land vertebrates. They also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of ray-finned fish. All lobe-finned fishes possess teeth covered with true enamel. The lungfish also possess both gills and lungs, solidifying this class as the ancestors of amphibians. | text | null |
L_0469 | bony fish | T_2785 | The ocean sunfish is the most massive bony fish in the world, up to 11 feet long and weighing up to 5,070 pounds ( Figure 1.2). Other very large bony fish include the Atlantic blue marlin, the black marlin, some sturgeon species, the giant grouper, and the goliath grouper. The long-bodied oarfish can easily be over 30 feet long, but is not nearly as massive as the ocean sunfish. In contrast, the dwarf pygmy goby measures only 0.6 inches. Fish can also be quite valuable. In January 2013, at an auction in Tokyos Tsukiji fish market, a 222-kilogram (489-pound) tuna caught off northeastern Japan sold for 155.4 million yen, which is $1,760,000. An ocean sunfish, the most massive bony fish in the world, can reach up to 11 feet long and weigh up to 5,070 pounds! | text | null |
L_0470 | cancer | T_2786 | Cancer is a disease that causes cells to divide out of control. Normally, the body has systems that prevent cells from dividing out of control. But in the case of cancer, these systems fail. Cancer is usually caused by mutations. Mutations are random errors in genes. Mutations that lead to cancer usually happen to genes that control the cell cycle. Because of the mutations, abnormal cells divide uncontrollably. This often leads to the development of a tumor. A tumor is a mass of abnormal tissue. As a tumor grows, it may harm normal tissues around it. Anything that can cause cancer is called a carcinogen. Carcinogens may be pathogens, chemicals, or radiation. | text | null |
L_0470 | cancer | T_2787 | Pathogens that cause cancer include the human papilloma virus (HPV) ( Figure 1.1) and the hepatitis B virus. HPV is spread through sexual contact. It can cause cancer of the reproductive system in females. The hepatitis B virus is spread through sexual contact or contact with blood containing the virus. It can cause cancer of the liver. | text | null |
L_0470 | cancer | T_2788 | Many different chemical substances cause cancer. Dozens of chemicals in tobacco smoke, including nicotine, have been shown to cause cancer ( Figure 1.2). In fact, tobacco smoke is one of the main sources of chemical carcinogens. Smoking tobacco increases the risk of cancer of the lung, mouth, throat, and bladder. Using smokeless tobacco can also cause cancer. Other chemicals that cause cancer include asbestos, formaldehyde, benzene, cadmium, and nickel. | text | null |
L_0470 | cancer | T_2788 | Many different chemical substances cause cancer. Dozens of chemicals in tobacco smoke, including nicotine, have been shown to cause cancer ( Figure 1.2). In fact, tobacco smoke is one of the main sources of chemical carcinogens. Smoking tobacco increases the risk of cancer of the lung, mouth, throat, and bladder. Using smokeless tobacco can also cause cancer. Other chemicals that cause cancer include asbestos, formaldehyde, benzene, cadmium, and nickel. | text | null |
L_0470 | cancer | T_2789 | Forms of radiation that cause cancer include ultraviolet (UV) radiation and radon ( Figure 1.3). UV radiation is part of sunlight. It is the leading cause of skin cancer. Radon is a natural radioactive gas that seeps into buildings from the ground. It can cause lung cancer. | text | null |
L_0470 | cancer | T_2790 | Cancer is usually found in adults, especially in adults over the age of 50. The most common type of cancer in adult males is cancer of the prostate gland. The prostate gland is part of the male reproductive system. Prostate cancer makes up about one third of all cancers in men. The most common type of cancer in adult females is breast cancer. It makes up about one third of all cancers in women. In both men and women, lung cancer is the second most common type of cancer. Most cases of lung cancer happen in people who smoke. Cancer can also be found in children. But childhood cancer is rare. Leukemia is the main type of cancer in children. It makes up about one third of all childhood cancers. It happens when the body makes abnormal white blood cells. Sometimes cancer cells break away from a tumor. If they enter the bloodstream, they are carried throughout the body. Then, the cells may start growing in other tissues. This is usually how cancer spreads from one part of the body to another. Once this happens, cancer is very hard to stop or control. | text | null |
L_0470 | cancer | T_2791 | If leukemia is treated early, it usually can be cured. In fact, many cancers can be cured, which is known as remission, if treated early. Treatment of cancer often involves removing a tumor with surgery. This may be followed by other types of treatments. These treatments may include drugs (known as chemotherapy) and radiation therapy, which kill cancer cells. The sooner cancer is treated, the greater the chances of a cure. This is why it is important to know the warning signs of cancer. Having warning signs does not mean that you have cancer. However, you should see a doctor to be sure. Everyone should know the warning signs of cancer. Detecting and treating cancer early can often lead to a cure. Some warning signs of cancer include: Change in bowel or bladder habits. Sores that do not heal. Unusual bleeding or discharge. Lump in the breast or elsewhere. Chronic indigestion. Difficulty swallowing. Obvious changes in a wart or mole. Persistent cough or hoarseness. | text | null |
L_0471 | cardiovascular diseases | T_2792 | A cardiovascular disease (CVD) is any disease that affects the cardiovascular system. But the term is usually used to describe diseases that are linked to atherosclerosis. Atherosclerosis ( Figure 1.1) is an inflammation of the walls of arteries that causes swelling and a buildup of material called plaque. Plaque is made of cell pieces, fatty substances, calcium, and connective tissue that builds up around the area of inflammation. As a plaque grows, it stiffens and narrows the artery, which decreases the flow of blood through the artery. Atherosclerosis normally begins in late childhood and is typically found in most major arteries. It does not usually have any early symptoms. Causes of atherosclerosis include a high-fat diet, high cholesterol, smoking, obesity, and diabetes. Atherosclerosis becomes a threat to health when the plaque buildup prevents blood circulation in the heart or the brain. A blocked blood vessel in the heart can cause a heart attack. Blockage of the circulation in the brain can cause a stroke. Ways to prevent atherosclerosis include eating healthy foods, getting plenty of exercise and not smoking. These three factors are not as hard to control as you may think. If you smoke, STOP. Start a regular exercise program and watch what you eat. A diet high in saturated fat and cholesterol can raise your cholesterol levels, which makes more plaque available to line artery walls and narrow your arteries. Cholesterol and saturated fats are found mostly in animal products such Atherosclerosis is sometimes referred to as hardening of the arteries; plaque build- up decreases the blood flow through the artery. as meat, eggs, milk, and other dairy products. Check food labels to find the amount of saturated fat in a product. Also, avoid large amounts of salt and sugar. Be careful with processed foods, such as frozen dinners, as they can be high in fat, sugar, salt and cholesterol. Eat lots of fresh or frozen fruits and vegetables, smaller portions of lean meats and fish, and whole grains such as oats and whole wheat. Limit saturated fats like butter, instead choose unsaturated vegetable oils such as canola oil. | text | null |
L_0471 | cardiovascular diseases | T_2793 | Like any other muscle, your heart needs oxygen. Hearts have arteries that provide oxygen through the blood. They are known as coronary arteries. Coronary heart disease is the end result of the buildup of plaque within the walls of the coronary arteries. Coronary heart disease often does not have any symptoms. A symptom of coronary heart disease is chest pain. Occasional chest pain can happen during times of stress or physical activity. The pain of angina means the heart muscle fibers need more oxygen than they are getting. Most people with coronary heart disease often have no symptoms for many years until they have a heart attack. A heart attack happens when the blood cannot reach the heart because a blood vessel is blocked. If cardiac muscle is starved of oxygen for more than roughly five minutes, it will die. Cardiac muscle cells cannot be replaced, so once they die, they are dead forever. Coronary heart disease is the leading cause of death of adults in the United States. The image below shows the way in which a blocked coronary artery can cause a heart attack and cause part of the heart muscle to die ( Figure 1.2). Maybe one day stem cells will be used to replace dead cardiac muscle cells. | text | null |
L_0471 | cardiovascular diseases | T_2794 | Atherosclerosis in the arteries of the brain can also lead to a stroke. A stroke is a loss of brain function due to a blockage of the blood supply to the brain. Risk factors for stroke include old age, high blood pressure, having a previous stroke, diabetes, high cholesterol, and smoking. The best way to reduce the risk of stroke is to have low blood pressure. | text | null |
L_0472 | cardiovascular system | T_2795 | Your cardiovascular system has many jobs. At times the cardiovascular system can work like a pump, a heating system, or even a postal carrier. To do these tasks, your cardiovascular system works with other organ systems, such as the respiratory, endocrine, and nervous systems. The cardiovascular system (Figure 1.1) is made up of the heart, the blood vessels, and the blood. It moves nutrients, gases (like oxygen), and wastes to and from your cells. Every cell in your body depends on your cardiovascular system. If your cells dont receive nutrients, they cannot survive. The main function of the cardiovascular system is to deliver oxygen to each of your cells. Blood receives oxygen in your lungs (the main organs of the respiratory system) and then is pumped, by your heart, throughout your body. The oxygen then diffuses into your cells, and carbon dioxide, a waste product of cellular respiration, moves from your cells into your blood to be delivered back to your lungs and exhaled. Each cell in your body needs oxygen, as oxygen is used in cellular respiration to produce energy in the form of ATP. Without oxygen, lactic acid fermentation would occur in your cells, which can only be maintained for a brief period of time. Arteries carry blood full of oxygen ("oxygen-rich") away from the heart and veins return oxygen-poor blood back to the heart. The cardiovascular system also plays a role in maintaining body temperature. It helps to keep you warm by moving warm blood around your body. Your blood vessels also control your body temperature to keep you from getting too hot or too cold. When your brain senses that your body temperature is increasing, it sends messages to the blood vessels in the skin to increase in diameter. Increasing the diameter of the blood vessels increases the amount of blood and heat that moves near the skins surface. The heat is then released from the skin. This helps you cool down. What do you think your blood vessels do when your body temperature is decreasing? The blood also carries hormones, which are chemical messenger molecules produced by organs of the endocrine system, through your body. Hormones are produced in one area of your body and have an effect on another area. To get to that other area, they must travel through your blood. An example is the hormone adrenaline, produced by the adrenal glands on top of the kidneys. Adrenaline has multiple effects on the heart (it quickens the heart rate), on muscles and on the airway. | text | null |
L_0473 | cardiovascular system health | T_2796 | There are many risk factors that can cause a person to develop cardiovascular disease. A risk factor is anything that is linked to an increased chance of developing a disease. Some of the risk factors for cardiovascular disease you cannot control, but there are many risk factors you can control. Risk factors you cannot control include: Age: The older a person is, the greater their chance of developing a cardiovascular disease. Gender: Men under age 64 are much more likely to die of coronary heart disease than women, although the gender difference decreases with age. Genetics: Family history of cardiovascular disease increases a persons chance of developing heart disease. Risk factors you can control include many lifestyle factors: Tobacco smoking: Giving up smoking or never starting to smoke is the best way to reduce the risk of heart disease. Diabetes: Diabetes can cause bodily changes, such as high cholesterol levels, which are are risk factors for cardiovascular disease. High cholesterol levels: High amounts of "bad cholesterol," increase the risk of cardiovascular disease. Obesity: Having a very high percentage of body fat, especially if the fat is mostly found in the upper body, rather than the hips and thighs, increases risk significantly. High blood pressure: If the heart and blood vessels have to work harder than normal, this puts the cardiovas- cular system under a strain. Lack of physical activity: Aerobic activities, such as the one pictured below ( Figure 1.1), help keep your heart healthy. To reduce the risk of disease, you should be active for at least 60 minutes a day, five days a week. Poor eating habits: Eating mostly foods that do not have many nutrients other than fat or carbohydrate leads to high cholesterol levels, obesity, and cardiovascular disease ( Figure 1.2). 60 minutes a day of vigorous aerobic activity, such as basketball, is enough to help keep your cardiovascular system healthy. | text | null |
L_0473 | cardiovascular system health | T_2797 | Cholesterol cant dissolve in the blood. It has to be transported to and from the cells by carriers called lipoproteins. Low-density lipoprotein, or LDL, is known as "bad" cholesterol. High-density lipoprotein (HDL) is known as good cholesterol. When too much LDL cholesterol circulates in the blood, it can slowly build up in the inner walls of the The USDAs MyPyramid recommends that you limit the amount of such foods in your diet to occasional treats. arteries that feed the heart and brain. Together with other substances, it can form plaque, and lead to atherosclerosis. If a clot forms and blocks a narrowed artery, a heart attack or stroke can result. Cholesterol comes from the food you eat as well as being made by the body. To lower bad cholesterol, a diet low in saturated fat and dietary cholesterol should be followed. Regular aerobic exercise also lowers LDL cholesterol and increases HDL cholesterol. | text | null |
L_0474 | cartilaginous fish | T_2798 | The 1,000 or so species of cartilaginous fish are subdivided into two subclasses: the first includes sharks, rays, and skates; the second includes chimaera, sometimes called ghost sharks. Fish from this group range in size from the dwarf lanternshark, at 6.3 inches, to the over 50-foot whale shark. Sharks obviously have jaws, as do the other cartilaginous fish. These fish evolved from the jawless fish. So why did fish eventually evolve to have jaws? Such an adaptation would allow fish to eat a much wider variety of food, including plants and other organisms. Other characteristics of cartilaginous fish include: Paired fins. Paired nostrils. Scales. Two-chambered hearts. Skeletons made of cartilage rather than bone. Cartilage is supportive tissue that does not have as much calcium as bones, which makes bones rigid. Cartilage is softer and more flexible than bone. | text | null |
L_0474 | cartilaginous fish | T_2799 | Since they do not have bone marrow (as they have no bones), red blood cells are produced in the spleen, in special tissue around the reproductive organs, and in an organ called Leydigs organ, only found in cartilaginous fishes. The tough skin of this group of fish is covered with placoid scales, which are hard scales formed from modified teeth. The scales are covered with a hard enamel. The hard covering and the way the scales are arranged, gives the fish skin rough, sandpaper-like feel. The function of these scales is for protection against predators. The shape of sharks teeth differ according to their diet. Species that feed on mollusks and crustaceans have dense flattened teeth for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey, such as mammals, have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. Sharks continually shed and replace their teeth, with some shedding as much as 35,000 teeth in a lifetime. | text | null |
L_0474 | cartilaginous fish | T_2800 | The sharks, rays, and skates (which are similar to stingrays) are further broken into two superorders: 1. Rays and skates. 2. Sharks. Sharks are some of the most frequently studied cartilaginous fish. Sharks are distinguished by such features as: The number of gill slits. The number and type of fins. The type of teeth. The size of their jaws. Body shape. Their activity at night. An elongated, toothed snout used for slashing the fish that they eat, as seen in sawsharks. Teeth used for grasping and crushing shellfish, a characteristic of bullhead sharks. A whisker-like organ named barbels that help sharks find food, a characteristic of carpet sharks. A long snout (or nose-like area), characteristic of groundsharks. Ovoviviparous reproduction, where the eggs develop inside the mothers body after internal fertilization, and the young are born alive. This trait is characteristic of mackerel sharks. All sharks mate by internal fertilization. Some sharks then lay their eggs, others allow internal development. | text | null |
L_0481 | cellular respiration | T_2817 | How does the food you eat provide energy? When you need a quick boost of energy, you might reach for an apple or a candy bar. But cells do not "eat" apples or candy bars; these foods need to be broken down so that cells can use them. Through the process of cellular respiration, the energy in food is changed into energy that can be used by the bodys cells. Initially, the sugars in the food you eat are digested into the simple sugar glucose, a monosaccharide. Recall that glucose is the sugar produced by the plant during photosynthesis. The glucose, or the polysaccharide made from many glucose molecules, such as starch, is then passed to the organism that eats the plant. This organism could be you, or it could be the organism that you eat. Either way, it is the glucose molecules that holds the energy. | text | null |
L_0481 | cellular respiration | T_2818 | Specifically, during cellular respiration, the energy stored in glucose is transferred to ATP ( Figure 1.1). ATP, or adenosine triphosphate, is chemical energy the cell can use. It is the molecule that provides energy for your cells to perform work, such as moving your muscles as you walk down the street. But cellular respiration is slightly more complicated than just converting the energy from glucose into ATP. Cellular respiration can be described as the reverse or opposite of photosynthesis. During cellular respiration, glucose, in the presence of oxygen, is converted into carbon dioxide and water. Recall that carbon dioxide and water are the starting products of photosynthesis. What are the products of photosynthesis? The process can be summarized as: glucose + oxygen carbon dioxide + water. During this process, the energy stored in glucose is transferred to ATP. Energy is stored in the bonds between the phosphate groups (PO4 ) of the ATP molecule. When ATP is broken down into ADP (adenosine diphosphate) and inorganic phosphate, energy is released. When ADP and inorganic phosphate are joined to form ATP, energy is stored. During cellular respiration, about 36 to 38 ATP molecules are produced for every glucose molecule. The structural formula for adenosine triphosphate (ATP). During cellular respi- ration, energy from the chemical bonds of the food you eat must be transferred to ATP. | text | null |
L_0483 | central nervous system | T_2825 | The central nervous system (CNS) ( Figure 1.1) is the largest part of the nervous system. It includes the brain and the spinal cord. The bony skull protects the brain. The spinal cord is protected within the bones of the spine, which are called vertebrae. | text | null |
L_0483 | central nervous system | T_2826 | What weighs about three pounds and contains up to 100 billion cells? The answer is the human brain. The brain is the control center of the nervous system. Its like the pilot of a plane. It tells other parts of the nervous system what to do. The brain is also the most complex organ in the body. Each of its 100 billion neurons has synapses connecting it with thousands of other neurons. All those neurons use a lot of energy. In fact, the adult brain uses almost a quarter of the total energy used by the body. The developing brain of a baby uses an even greater amount of the bodys total energy. The brain is the organ that lets us understand what we see, hear, or sense in other ways. It also allows us to use language, learn, think, and remember. The brain controls the organs in our body and our movements as well. The brain consists of three main parts, the cerebrum, the cerebellum, and the brain stem ( Figure 1.2). 1. The cerebrum is the largest part of the brain. It sits on top of the brain stem. The cerebrum controls functions that we are aware of, such as problem-solving and speech. It also controls voluntary movements, like waving to a friend. Whether you are doing your homework or jumping hurdles, you are using your cerebrum. 2. The cerebellum is the next largest part of the brain. It lies under the cerebrum and behind the brain stem. The cerebellum controls body position, coordination, and balance. Whether you are riding a bicycle or writing with a pen, you are using your cerebellum. 3. The brain stem is the smallest of the three main parts of the brain. It lies directly under the cerebrum. The brain stem controls basic body functions, such as breathing, heartbeat, and digestion. The brain stem also carries information back and forth between the cerebrum and spinal cord. The cerebrum is divided into a right and left half ( Figure 1.2). Each half of the cerebrum is called a hemisphere. The two hemispheres are connected by a thick bundle of axons called the corpus callosum. It lies deep inside the brain and carries messages back and forth between the two hemispheres. Did you know that the right hemisphere controls the left side of the body, and the left hemisphere controls the right side of the body? By connecting the two hemispheres, the corpus callosum allows this to happen. Each hemisphere of the cerebrum is divided into four parts, called lobes. The four lobes are the: 1. 2. 3. 4. Frontal. Parietal. Temporal. Occipital. Each lobe has different jobs. Some of the functions are listed below ( Table 1.1). Side view of the brain (right). Can you find the locations of the three major parts of the brain? Top view of the brain (left). Lobe Frontal Parietal Temporal Occipital Main Function(s) Speech, thinking, touch Speech, taste, reading Hearing, smell Sight | text | null |
L_0483 | central nervous system | T_2826 | What weighs about three pounds and contains up to 100 billion cells? The answer is the human brain. The brain is the control center of the nervous system. Its like the pilot of a plane. It tells other parts of the nervous system what to do. The brain is also the most complex organ in the body. Each of its 100 billion neurons has synapses connecting it with thousands of other neurons. All those neurons use a lot of energy. In fact, the adult brain uses almost a quarter of the total energy used by the body. The developing brain of a baby uses an even greater amount of the bodys total energy. The brain is the organ that lets us understand what we see, hear, or sense in other ways. It also allows us to use language, learn, think, and remember. The brain controls the organs in our body and our movements as well. The brain consists of three main parts, the cerebrum, the cerebellum, and the brain stem ( Figure 1.2). 1. The cerebrum is the largest part of the brain. It sits on top of the brain stem. The cerebrum controls functions that we are aware of, such as problem-solving and speech. It also controls voluntary movements, like waving to a friend. Whether you are doing your homework or jumping hurdles, you are using your cerebrum. 2. The cerebellum is the next largest part of the brain. It lies under the cerebrum and behind the brain stem. The cerebellum controls body position, coordination, and balance. Whether you are riding a bicycle or writing with a pen, you are using your cerebellum. 3. The brain stem is the smallest of the three main parts of the brain. It lies directly under the cerebrum. The brain stem controls basic body functions, such as breathing, heartbeat, and digestion. The brain stem also carries information back and forth between the cerebrum and spinal cord. The cerebrum is divided into a right and left half ( Figure 1.2). Each half of the cerebrum is called a hemisphere. The two hemispheres are connected by a thick bundle of axons called the corpus callosum. It lies deep inside the brain and carries messages back and forth between the two hemispheres. Did you know that the right hemisphere controls the left side of the body, and the left hemisphere controls the right side of the body? By connecting the two hemispheres, the corpus callosum allows this to happen. Each hemisphere of the cerebrum is divided into four parts, called lobes. The four lobes are the: 1. 2. 3. 4. Frontal. Parietal. Temporal. Occipital. Each lobe has different jobs. Some of the functions are listed below ( Table 1.1). Side view of the brain (right). Can you find the locations of the three major parts of the brain? Top view of the brain (left). Lobe Frontal Parietal Temporal Occipital Main Function(s) Speech, thinking, touch Speech, taste, reading Hearing, smell Sight | text | null |
L_0483 | central nervous system | T_2827 | The spinal cord is a long, tube-shaped bundle of neurons, protected by the vertebrae. It runs from the brain stem to the lower back. The main job of the spinal cord is to carry nerve impulses back and forth between the body and brain. The spinal cord is like a two-way highway. Messages about the body, both inside and out, pass through the spinal cord to the brain. Messages from the brain pass in the other direction through the spinal cord to tell the body what to do. | text | null |
L_0485 | chemistry of life | T_2835 | If you pull a flower petal from a plant and break it in half, and then take that piece and break it in half again, and take the next piece and break it half, and so on, and so on, until you cannot even see the flower anymore, what do you think you will find? We know that the flower petal is made of cells, but what are cells made of? Scientists have broken down matter, or anything that takes up space and has masslike a cellinto the smallest pieces that cannot be broken down anymore. Every physical object, including rocks, animals, flowers, and your body, are all made up of matter. Matter is made up of a mixture of things called elements. Elements are substances that cannot be broken down into simpler substances. There are more than 100 known elements, and 92 occur naturally around us. The others have been made only in the laboratory. Inside of elements, you will find identical atoms. An atom is the simplest and smallest particle of matter that still has chemical properties of the element. Atoms are the building block of all of the elements that make up the matter in your body or any other living or non-living thing. Atoms are so small that only the most powerful microscopes can see them. Atoms themselves are composed of even smaller particles, including positively charged protons, uncharged neu- trons, and negatively charged electrons. Protons and neutrons are located in the center of the atom, or the nucleus, and the electrons move around the nucleus. How many protons an atom has determines what element it is. For example, hydrogen (H) has just one proton, helium (He) always has two protons ( Figure 1.1), while sodium (Na) always has 11. All the atoms of a particular element have the exact same number of protons, and the number of protons is that elements atomic number. An atom usually has the same number of protons and electrons, but sometimes an atom may gain or lose an electron, giving the atom a positive or negative charge. These atoms are known as ions and are depicted with a "+" or "-" sign. Ions, such as H+ , Na+ , K+ , or Cl have significant biological roles. An atom of Helium (He) contains two positively charged protons (red), two uncharged neutrons (blue), and two negatively charged electrons (yellow). | text | null |
L_0485 | chemistry of life | T_2836 | In 1869, a Russian scientist named Dmitri Mendeleev created the periodic table, which is a way of organizing elements according to their unique characteristics, like atomic number, density, boiling point, and other values ( Figure 1.2). Each element is represented by a one or two letter symbol. For example, H stands for hydrogen, and Au stands for gold. The vertical columns in the periodic table are known as groups, and elements in groups tend to have very similar properties. The table is also divided into rows, known as periods. | text | null |
L_0485 | chemistry of life | T_2837 | A molecule is any combination of two or more atoms. The oxygen in the air we breathe is two oxygen atoms connected by a chemical bond to form O2 , or molecular oxygen. A carbon dioxide molecule is a combination of one carbon atom and two oxygen atoms, CO2 . Because carbon dioxide includes two different elements, it is a compound as well as a molecule. A compound is any combination of two or more different elements. A compound has different properties from the elements that it contains. Elements and combinations of elements (compounds) make up all the many types of matter in the Universe. A chemical reaction is a process that breaks or forms the bonds between atoms of molecules and compounds. For example, two hydrogens and one oxygen bind together to form water, H2 O. The molecules that come together to start a chemical reaction are the reactants. So hydrogen and oxygen are the reactants. The product is the end result of a reaction. In this example, water is the product. Atoms also come together to form compounds much larger than water. It is some of these large compounds that come together to form the basis of the cell. So essentially, your cells are made out of compounds, which are made out of atoms. | text | null |
L_0488 | chromosomal disorders | T_2848 | Some children are born with genetic defects that are not carried by a single gene. Instead, an error in a larger part of the chromosome or even in an entire chromosome causes the disorder. Usually the error happens when the egg or sperm is forming. Having extra chromosomes or damaged chromosomes can cause disorders. | text | null |
L_0488 | chromosomal disorders | T_2849 | One common example of an extra-chromosome disorder is Down syndrome ( Figure 1.1). Children with Down syndrome are mentally disabled and also have physical deformities. Down syndrome occurs when a baby receives an extra chromosome 21 from one of his or her parents. Usually, a child will receive one chromosome 21 from the mother and one chromosome 21 from the father. In an individual with Down syndrome, however, there are three Chromosomes of a person with Down Syndrome. Notice the extra chromosome 21. copies of chromosome 21 ( Figure 1.2). Therefore, Down syndrome is also known as Trisomy 21. These people have 47 total chromosomes. Another example of a chromosomal disorder is Klinefelter syndrome, in which a male inherits an extra X chromosome. These individuals have an XXY genotype. They have underdeveloped sex organs and elongated limbs. They also have difficulty learning new things. | text | null |
L_0488 | chromosomal disorders | T_2849 | One common example of an extra-chromosome disorder is Down syndrome ( Figure 1.1). Children with Down syndrome are mentally disabled and also have physical deformities. Down syndrome occurs when a baby receives an extra chromosome 21 from one of his or her parents. Usually, a child will receive one chromosome 21 from the mother and one chromosome 21 from the father. In an individual with Down syndrome, however, there are three Chromosomes of a person with Down Syndrome. Notice the extra chromosome 21. copies of chromosome 21 ( Figure 1.2). Therefore, Down syndrome is also known as Trisomy 21. These people have 47 total chromosomes. Another example of a chromosomal disorder is Klinefelter syndrome, in which a male inherits an extra X chromosome. These individuals have an XXY genotype. They have underdeveloped sex organs and elongated limbs. They also have difficulty learning new things. | text | null |
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 |
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