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L_0346 | volcanic landforms | T_1848 | The most obvious landforms created by lava are volcanoes, most commonly as cinder cones, composite volcanoes, and shield volcanoes. Eruptions also take place through other types of vents, commonly from fissures (Figure 1.1). The eruptions that created the entire ocean floor are essentially fissure eruptions. | text | null |
L_0346 | volcanic landforms | T_1849 | Viscous lava flows slowly. If there is not enough magma or enough pressure to create an explosive eruption, the magma may form a lava dome. Because it is so thick, the lava does not flow far from the vent. (Figure 1.2). Lava flows often make mounds right in the middle of craters at the top of volcanoes, as seen in the Figure 1.3. A fissure eruption on Mauna Loa in Hawaii travels toward Mauna Kea on the Big Is- land. Lava domes are large, round landforms created by thick lava that does not travel far from the vent. Lava domes may form in the crater of composite volcanoes as at Mount St. He- lens. | text | null |
L_0346 | volcanic landforms | T_1849 | Viscous lava flows slowly. If there is not enough magma or enough pressure to create an explosive eruption, the magma may form a lava dome. Because it is so thick, the lava does not flow far from the vent. (Figure 1.2). Lava flows often make mounds right in the middle of craters at the top of volcanoes, as seen in the Figure 1.3. A fissure eruption on Mauna Loa in Hawaii travels toward Mauna Kea on the Big Is- land. Lava domes are large, round landforms created by thick lava that does not travel far from the vent. Lava domes may form in the crater of composite volcanoes as at Mount St. He- lens. | text | null |
L_0346 | volcanic landforms | T_1849 | Viscous lava flows slowly. If there is not enough magma or enough pressure to create an explosive eruption, the magma may form a lava dome. Because it is so thick, the lava does not flow far from the vent. (Figure 1.2). Lava flows often make mounds right in the middle of craters at the top of volcanoes, as seen in the Figure 1.3. A fissure eruption on Mauna Loa in Hawaii travels toward Mauna Kea on the Big Is- land. Lava domes are large, round landforms created by thick lava that does not travel far from the vent. Lava domes may form in the crater of composite volcanoes as at Mount St. He- lens. | text | null |
L_0346 | volcanic landforms | T_1850 | A lava plateau forms when large amounts of fluid lava flow over an extensive area (Figure 1.4). When the lava solidifies, it creates a large, flat surface of igneous rock. Layer upon layer of basalt have created the Columbia Plateau, which covers more than 161,000 square kilometers (63,000 square miles) in Washington, Oregon, and Idaho. | text | null |
L_0346 | volcanic landforms | T_1851 | Lava creates new land as it solidifies on the coast or emerges from beneath the water (Figure 1.5). Lava flowing into the sea creates new land in Hawaii. Over time the eruptions can create whole islands. The Hawaiian Islands are formed from shield volcano eruptions that have grown over the last 5 million years (Figure 1.6). The island of Hawaii was created by hotspot volcanism. You can see some of the volcanoes (both active and extinct) in this mosaic of false-color composite satellite images. | text | null |
L_0346 | volcanic landforms | T_1851 | Lava creates new land as it solidifies on the coast or emerges from beneath the water (Figure 1.5). Lava flowing into the sea creates new land in Hawaii. Over time the eruptions can create whole islands. The Hawaiian Islands are formed from shield volcano eruptions that have grown over the last 5 million years (Figure 1.6). The island of Hawaii was created by hotspot volcanism. You can see some of the volcanoes (both active and extinct) in this mosaic of false-color composite satellite images. | text | null |
L_0346 | volcanic landforms | T_1852 | Magma intrusions can create landforms. Shiprock in New Mexico is the neck of an old volcano that has eroded away (Figure 1.7). The volcanic neck is the remnant of the conduit the magma traveled up to feed an eruption. The aptly named Shiprock in New Mexico. | text | null |
L_0347 | volcano characteristics | T_1853 | A volcano is a vent from which the material from a magma chamber escapes. Volcanic eruptions can come from peaky volcanic cones, fractured domes, a vent in the ground, or many other types of structures. | text | null |
L_0347 | volcano characteristics | T_1854 | Volcanoes are a vibrant manifestation of plate tectonics processes. Volcanoes are common along convergent and di- vergent plate boundaries. Volcanoes are also found within lithospheric plates away from plate boundaries. Wherever mantle is able to melt, volcanoes may be the result. What is the geological reason for the locations of all the volcanoes in the figure? Does it resemble the map of earthquake epicenters? Are all of the volcanoes located along plate boundaries? Why are the Hawaiian volcanoes located away from any plate boundaries? World map of active volcanoes (red dots). | text | null |
L_0347 | volcano characteristics | T_1855 | Volcanoes erupt because mantle rock melts. This is the first stage in creating a volcano. Remember from the chapter Materials of Earths Crust that mantle may melt if temperature rises, pressure lowers, or water is added. Be sure to think about how and why melting occurs in the settings where there is volcanism mentioned in the next few concepts. | text | null |
L_0347 | volcano characteristics | T_1856 | Of all the volcanoes in the world, very few are erupting at any given time. Scientists question whether a volcano that is not erupting will ever erupt again and then describe it as active, dormant, or extinct. Active: currently erupting or showing signs of erupting soon. Dormant: no current activity, but has erupted recently. Extinct: no activity for some time; will probably not erupt again. Click image to the left or use the URL below. URL: | text | null |
L_0348 | volcanoes at hotspots | T_1857 | Although most volcanoes are found at convergent or divergent plate boundaries, intraplate volcanoes may be found in the middle of a tectonic plate. These volcanoes rise at a hotspot above a mantle plume. Melting at a hotspot is due to pressure release as the plume rises through the mantle. Earth is home to about 50 known hotspots. Most of these are in the oceans because they are better able to penetrate oceanic lithosphere to create volcanoes. But there are some large ones in the continents. Yellowstone is a good example of a mantle plume erupting within a continent. | text | null |
L_0348 | volcanoes at hotspots | T_1858 | The South Pacific has many hotspot volcanic chains. The hotspot is beneath the youngest volcano in the chain and older volcanoes are found to the northwest. A volcano forms above the hotspot, but as the Pacific Plate moves, that volcano moves off the hotspot. Without its source of volcanism, it no longer erupts. The crust gets cooler and the volcano erodes. The result is a chain of volcanoes and seamounts trending northwest from the hotspot. Prominent hotspots of the world. (a) The Society Islands formed above a hotspot that is now beneath Mehetia and two submarine volcanoes. (b) The satellite image shows how the islands become smaller and coral reefs became more developed as the volcanoes move off the hotspot and grow older. The most famous example of a hotspot in the oceans is the Hawaiian Islands. Forming above the hotspot are massive shield volcanoes that together create the islands. The lavas are mafic and have low viscosity. These lavas produce beautiful ropy flows of pahoehoe and clinkery flows of aa, which will be described in more detail in Effusive Eruptions. | text | null |
L_0348 | volcanoes at hotspots | T_1858 | The South Pacific has many hotspot volcanic chains. The hotspot is beneath the youngest volcano in the chain and older volcanoes are found to the northwest. A volcano forms above the hotspot, but as the Pacific Plate moves, that volcano moves off the hotspot. Without its source of volcanism, it no longer erupts. The crust gets cooler and the volcano erodes. The result is a chain of volcanoes and seamounts trending northwest from the hotspot. Prominent hotspots of the world. (a) The Society Islands formed above a hotspot that is now beneath Mehetia and two submarine volcanoes. (b) The satellite image shows how the islands become smaller and coral reefs became more developed as the volcanoes move off the hotspot and grow older. The most famous example of a hotspot in the oceans is the Hawaiian Islands. Forming above the hotspot are massive shield volcanoes that together create the islands. The lavas are mafic and have low viscosity. These lavas produce beautiful ropy flows of pahoehoe and clinkery flows of aa, which will be described in more detail in Effusive Eruptions. | text | null |
L_0348 | volcanoes at hotspots | T_1859 | The hotspots that are known beneath continents are extremely large. The reason is that it takes a massive mantle plume to generate enough heat to penetrate through the relatively thick continental crust. The eruptions that come from these hotspots are infrequent but massive, often felsic and explosive. All thats left at Yellowstone at the moment is a giant caldera and a very hot spot beneath. | text | null |
L_0348 | volcanoes at hotspots | T_1860 | How would you be able to tell hotspot volcanoes from island arc volcanoes? At island arcs, the volcanoes are all about the same age. By contrast, at hotspots the volcanoes are youngest at one end of the chain and oldest at the other. Click image to the left or use the URL below. URL: | text | null |
L_0349 | volcanoes at plate boundaries | T_1861 | Converging plates can be oceanic, continental, or one of each. If both are continental they will smash together and form a mountain range. If at least one is oceanic, it will subduct. A subducting plate creates volcanoes. In the chapter Plate Tectonics we moved up western North America to visit the different types of plate boundaries there. Locations with converging in which at least one plate is oceanic at the boundary have volcanoes. | text | null |
L_0349 | volcanoes at plate boundaries | T_1862 | Melting at convergent plate boundaries has many causes. The subducting plate heats up as it sinks into the mantle. Also, water is mixed in with the sediments lying on top of the subducting plate. As the sediments subduct, the water rises into the overlying mantle material and lowers its melting point. Melting in the mantle above the subducting plate leads to volcanoes within an island or continental arc. | text | null |
L_0349 | volcanoes at plate boundaries | T_1863 | Volcanoes at convergent plate boundaries are found all along the Pacific Ocean basin, primarily at the edges of the Pacific, Cocos, and Nazca plates. Trenches mark subduction zones, although only the Aleutian Trench and the Java Trench appear on the map in the previous concept, "Volcano Characteristics." The Cascades are a chain of volcanoes at a convergent boundary where an oceanic plate is subducting beneath a continental plate. Specifically the volcanoes are the result of subduction of the Juan de Fuca, Gorda, and Explorer Plates beneath North America. The volcanoes are located just above where the subducting plate is at the right depth in the mantle for there to be melting (Figure 1.1). The Cascades have been active for 27 million years, although the current peaks are no more than 2 million years old. The volcanoes are far enough north and are in a region where storms are common, so many are covered by glaciers. | text | null |
L_0349 | volcanoes at plate boundaries | T_1864 | At divergent plate boundaries hot mantle rock rises into the space where the plates are moving apart. As the hot mantle rock convects upward it rises higher in the mantle. The rock is under lower pressure; this lowers the melting temperature of the rock and so it melts. Lava erupts through long cracks in the ground, or fissures. | text | null |
L_0349 | volcanoes at plate boundaries | T_1865 | Volcanoes erupt at mid-ocean ridges, such as the Mid-Atlantic ridge, where seafloor spreading creates new seafloor in the rift valleys. Where a hotspot is located along the ridge, such as at Iceland, volcanoes grow high enough to create islands (Figure 1.3). | text | null |
L_0349 | volcanoes at plate boundaries | T_1866 | Eruptions are found at divergent plate boundaries as continents break apart. The volcanoes in Figure 1.4 are in the East African Rift between the African and Arabian plates. Remember from the chapter Plate Tectonics that Baja California is being broken apart from mainland Mexico as another example of continental rifting. Click image to the left or use the URL below. URL: The Cascade Range is formed by volca- noes created from subduction of oceanic crust beneath the North American conti- nent. | text | null |
L_0369 | sponges and cnidarians | T_1983 | Sponges are aquatic invertebrates that make up Phylum Porifera. The word porifera means pore-bearing. As you can see from the close-up view in Figure 12.3, a sponge has a porous body with many small holes in it. There are at least 5000 living species of sponges. Almost all of them inhabit the ocean. Most live on coral reefs or the ocean floor. Adult sponges are unable to move from place to place. They have root-like projections that anchor them to surfaces. They may live in colonies of many sponges. You can visit the incredible world of sponges by watching this short video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0369 | sponges and cnidarians | T_1983 | Sponges are aquatic invertebrates that make up Phylum Porifera. The word porifera means pore-bearing. As you can see from the close-up view in Figure 12.3, a sponge has a porous body with many small holes in it. There are at least 5000 living species of sponges. Almost all of them inhabit the ocean. Most live on coral reefs or the ocean floor. Adult sponges are unable to move from place to place. They have root-like projections that anchor them to surfaces. They may live in colonies of many sponges. You can visit the incredible world of sponges by watching this short video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0369 | sponges and cnidarians | T_1983 | Sponges are aquatic invertebrates that make up Phylum Porifera. The word porifera means pore-bearing. As you can see from the close-up view in Figure 12.3, a sponge has a porous body with many small holes in it. There are at least 5000 living species of sponges. Almost all of them inhabit the ocean. Most live on coral reefs or the ocean floor. Adult sponges are unable to move from place to place. They have root-like projections that anchor them to surfaces. They may live in colonies of many sponges. You can visit the incredible world of sponges by watching this short video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0369 | sponges and cnidarians | T_1984 | Sponges have several different types of specialized cells, although they lack tissues. You can see the basic sponge body plan and specialized cells in Figure 12.4. Some of the specialized cells grow short, sharp projections called spicules. Spicules make up the sponges internal skeleton, or endoskeleton. The endoskeleton helps to support and protect the sponge. Other specialized cells are involved in feeding. Sponges are filter feeders. They filter food out of the water as it flows through them. Sponges pump water into their body through specialized pore cells called porocytes. The water flows through a large central cavity. As it flows by, specialized cells called collar cells trap and digest food particles in the water. Specialized cells called amebocytes carry nutrients from the digested food to the rest of the cells in the sponge. As water flows through the sponge, oxygen diffuses from the water to the sponges cells. The cells also expel wastes into the water. The water then flows out of the sponge through an opening called the osculum. | text | null |
L_0369 | sponges and cnidarians | T_1985 | Sponges reproduce both asexually and sexually. Asexual reproduction occurs by budding. Sexual reproduction occurs by the production of eggs and sperm. Males release sperm into the water through the osculum. Sperm may enter a female sponge through a pore and fertilize her eggs. The resulting zygotes develop into larvae. Unlike sponge adults, sponge larvae can swim. They have cilia that propel them through the water. As larvae develop and grow, they become more similar to an adult sponge and lose their ability to swim. | text | null |
L_0369 | sponges and cnidarians | T_1986 | Many sponges live on coral reefs, like the one in Figure 12.5. Reef sponges typically have symbiotic relationships with other reef species. For example, the sponges provide shelter for algae, shrimp, and crabs. In return, they get nutrients from the metabolism of the organisms they shelter. Sponges are a source of food for many species of fish. Because sponges are anchored to a reef or rock, they cant run away from predators. However, their sharp spicules provide some defense. They also produce toxins that may poison predators that try to eat them. | text | null |
L_0369 | sponges and cnidarians | T_1987 | Cnidarians are invertebrates such as jellyfish and corals. They belong to Phylum Cnidaria. All cnidarians are aquatic. Most of them live in the ocean. Cnidarians are a little more complex than sponges. Besides specialized cells, they have tissues and radial symmetry. There are more than 10,000 cnidarian species, see Figure 12.6. | text | null |
L_0369 | sponges and cnidarians | T_1988 | An interesting feature of all cnidarians is one or more stingers called nematocysts. You can see a nematocyst in the sketch of a hydra in Figure 12.7. The nematocyst is long and thin and has a poison barb on the end. When not in use, it lies coiled inside a special cell. Nematocysts are used to attack prey or defend against predators. Watch this awesome animation to see a nematocyst in action: http://commons.wikimedia.org/wiki/File:Nematocyst.gif Another interesting feature of many cnidarians is the ability to produce light. The production of light by living things is called bioluminescence. A more familiar example of bioluminescence is the light produced by fireflies. In cnidarians, bioluminescence may be used to startle predators or to attract prey or mates. Watch this short video to see an amazing light show put on by a jellyfish at the Monterey Aquarium in Monterey, California: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0369 | sponges and cnidarians | T_1988 | An interesting feature of all cnidarians is one or more stingers called nematocysts. You can see a nematocyst in the sketch of a hydra in Figure 12.7. The nematocyst is long and thin and has a poison barb on the end. When not in use, it lies coiled inside a special cell. Nematocysts are used to attack prey or defend against predators. Watch this awesome animation to see a nematocyst in action: http://commons.wikimedia.org/wiki/File:Nematocyst.gif Another interesting feature of many cnidarians is the ability to produce light. The production of light by living things is called bioluminescence. A more familiar example of bioluminescence is the light produced by fireflies. In cnidarians, bioluminescence may be used to startle predators or to attract prey or mates. Watch this short video to see an amazing light show put on by a jellyfish at the Monterey Aquarium in Monterey, California: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0369 | sponges and cnidarians | T_1989 | Cnidarians have two basic body forms, called medusa and polyp: The medusa (medusae, plural) is a bell-shaped form. It is typically able to move. The polyp is a tubular form. It is usually attached to a surface and unable to move. As you can see in Figure 12.8, both body plans have radial symmetry. Some cnidarian species alternate between medusa and polyp forms. Other species exist in just one form or the other. | text | null |
L_0369 | sponges and cnidarians | T_1990 | Cnidarians have an incomplete digestive system with a single opening. The opening is surrounded by tentacles, which are covered with nematocyst cells and used to capture prey. Digestion takes place in the digestive cavity. Nutrients are absorbed and gases are exchanged through the cells lining this cavity. Fluid in the cavity supports and stiffens the cnidarian body. Cnidarians have a simple nervous system. It consists of a net of nerves that can sense touch. You can see a sketch of the nerve net in a hydra in Figure 12.9. Some cnidarians also have other sensory structures. For example, jellyfish have light-sensing structures and gravity-sensing structures. | text | null |
L_0369 | sponges and cnidarians | T_1991 | Cnidarians in the polyp form usually reproduce asexually. One type of asexual reproduction in polyps leads to the formation of new medusae. Medusae usually reproduce sexually with sperm and eggs. Fertilization forms a zygote. The zygote develops into a larva, and the larva develops into a polyp. There are many variations on this general life cycle. Obviously, species that exist only as polyps or medusae have a life cycle without the other form. | text | null |
L_0369 | sponges and cnidarians | T_1992 | Cnidarians can be found in almost all ocean habitats. A few species live in fresh water. Jellyfish spend most of their lives as medusae. They live virtually everywhere in the ocean. They prey on zooplankton, other invertebrates, and the eggs and larvae of fish. Corals form large colonies in shallow tropical water. They are confined to shallow water because they have a symbiotic relationship with algae that live inside of them. The algae need sunlight for photosynthesis, so they must stay relatively close to the surface of the water to get enough light. Corals exist only as polyps. They catch plankton with their tentacles. Many corals form a hard, mineral exoskeleton. Over time, this builds up to become a coral reef. A coral reef is pictured in Figure 12.10. Coral reefs provide food and shelter to many other ocean organisms. Watch this beautiful National Geographic video to learn more about corals, coral reefs, and coral reef life: http://video MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0395 | characteristics of living organisms | T_2231 | Five characteristics are used to define life. All living things share these characteristics. All living things: 1. 2. 3. 4. 5. are made of one or more cells. need energy to stay alive. respond to stimuli in their environment. grow and reproduce. maintain a stable internal environment. | text | null |
L_0395 | characteristics of living organisms | T_2232 | Cells are the basic building blocks of life. They are like tiny factories where virtually all life processes take place. Some living things, like the bacteria in Figure 2.1, consist of just one cell. They are called single-celled organisms. You can see other single-celled organisms in Figure 2.2. Some living things are composed of a few to many trillions of cells. They are called multicellular organisms. Your body is composed of trillions of cells. Regardless of the type of organism, all living cells share certain basic structures. For example, all cells are enclosed by a membrane. The cell membrane separates the cell from its environment. It also controls what enters or leaves the cell. | text | null |
L_0395 | characteristics of living organisms | T_2233 | Everything you do takes energy. Energy is the ability to change or move matter. Whether its reading these words or running a sprint, it requires energy. In fact, it takes energy just to stay alive. Where do you get energy? You probably know the answer. You get energy from food. Figure {{ref|MS-LS-SE-02-03-Food|below}] shows some healthy foods that can provide you with energy. Just like you, other living things need a source of energy. But they may use a different source. Organisms may be grouped on the basis of the source of energy they use. In which group do you belong? Producers such as the tree in Figure 2.1 use sunlight for energy to produce their own food. The process is called photosynthesis, and the food is sugar. Plants and other organisms use this food for energy. Consumers such as the raccoon in Figure 2.1 eat plantsor other consumers that eat plantsas a source of energy. Some consumers such as the mushroom in Figure 2.1 get their energy from dead organic matter. For example, they might consume dead leaves on a forest floor. | text | null |
L_0395 | characteristics of living organisms | T_2234 | When a living thing responds to its environment, it is responding to a stimulus. A stimulus (stimuli, plural) is something in the environment that causes a reaction in an organism. The reaction a stimulus produces is called a response. Imagine how you would respond to the following stimuli: Youre about to cross a street when the walk light turns red. You hear a smoke alarm go off in the kitchen. You step on an upturned tack with a bare foot. You smell the aroma of your favorite food. You taste something really sour. It doesnt take much imagination to realize that responding appropriately to such stimuli might help keep you safe. It might even help you survive. Like you, all other living things sense and respond to stimuli in their environment. In general, their responses help them survive or reproduce. Watch this amazing time-lapse video to see how a plant responds to the stimuli of light and gravity as it grows. Why do you think it is important for a plant to respond appropriately to these stimuli for proper growth? MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0395 | characteristics of living organisms | T_2235 | Like plants, all living things have the capacity for growth. The ducklings in Figure 2.4 have a lot of growing to do to catch up in size to their mother. Multicellular organisms like ducks grow by increasing the size and number of their cells. Single-celled organisms just grow in size. As the ducklings grow, they will develop and mature into adults. By adulthood, they will be able to reproduce. Reproduction is the production of offspring. The ability to reproduce is another characteristic of living things. Many organisms reproduce sexually. In sexual reproduction, parents of different sexes mate to produce offspring. The offspring have some combination of the traits of the two parents. Ducks are examples of sexually reproducing organisms. Other organisms reproduce asexually. In asexual reproduction, a single parent can produce offspring alone. For example, a bacterial cell reproduces by dividing into two daughter cells. The daughter cells are identical to each other and to the parent cell. | text | null |
L_0395 | characteristics of living organisms | T_2236 | The tennis player in Figure 2.5 has really worked up a sweat. Do you know why we sweat? Sweating helps to keep us cool. When sweat evaporates from the skin, it uses up some of the bodys heat energy. Sweating is one of the ways that the body maintains a stable internal environment. It helps keep the bodys internal temperature constant. When the bodys internal environment is stable, the condition is called homeostasis. All living organisms have ways of maintaining homeostasis. They have mechanisms for controlling such factors as their internal temperature, water balance, and acidity. Homeostasis is necessary for normal life processes that take place inside cells. If an organism cant maintain homeostasis, normal life processes are disrupted. Disease or even death may result. | text | null |
L_0397 | classification of living things | T_2251 | Like you, scientists also group together similar organisms. The science of classifying living things is called taxon- omy. Scientists classify living things in order to organize and make sense of the incredible diversity of life. Modern scientists base their classifications mainly on molecular similarities. They group together organisms that have similar proteins and DNA. Molecular similarities show that organisms are related. In other words, they are descendants of a common ancestor in the past. | text | null |
L_0397 | classification of living things | T_2252 | Carl Linnaeus (1707-1778) is called the father of taxonomy. You may already be familiar with the classification system Linnaeus introduced. | text | null |
L_0397 | classification of living things | T_2253 | You can see the main categories, or taxa (taxon, singular), of the Linnaean system in Figure 2.16. As an example, the figure applies the Linnaean system to classify our own species, Homo sapiens. Although the Linnaean system has been revised, it forms the basis of modern classification systems. The broadest category in the Linnaean system is the kingdom. Figure 2.16 shows the Animal Kingdom because Homo sapiens belongs to that kingdom. Other kingdoms include the Plant Kingdom, Fungus Kingdom, and Protist Kingdom. Kingdoms are divided, in turn, into phyla (phylum, singular). Each phylum is divided into classes, each class into orders, each order into families, and each family into genera (genus, singular). Each genus is divided into one or more species. The species is the narrowest category in the Linnaean system. A species is defined as a group of organisms that can breed and produce fertile offspring together. | text | null |
L_0397 | classification of living things | T_2254 | Linnaeus is also famous for his method of naming species, which is still used today. The method is called binomial nomenclature. Every species is given a unique two-word name. Usually written in Latin, it includes the genus name followed by the species name. Both names are always written in italics, and the genus name is always capitalized. For example, the human species is named Homo sapiens. The species of the family dog is named Canis familiaris. Coming up with a scientific naming method may not seem like a big deal, but it really is. Prior to Linnaeus, there was no consistent way to name species. Names given to organisms by scientists were long and cumbersome. Often, different scientists came up with different names for the same species. Common names also differed, generally from one place to another. A single, short scientific name for each species avoided a lot of mistakes and confusion. | text | null |
L_0397 | classification of living things | T_2255 | When Linnaeus was naming and classifying organisms in the 1700s, almost nothing was known of microorganisms. With the development of powerful microscopes, scientists discovered many single-celled organisms that didnt fit into any of Linnaeus kingdoms. As a result, a new taxon, called the domain, was added to the classification system. The domain is even broader than the kingdom, as you can see in Figure 2.17. Most scientists think that all living things can be classified in three domains: Archaea, Bacteria, and Eukarya. These domains are compared in Table 2.3. The Archaea Domain includes only the Archaea Kingdom, and the Bacteria Domain includes only the Bacteria Kingdom. The Eukarya Domain includes the Animal, Plant, Fungus, and Protist Kingdoms. Trait Multicellularity Archaea No Bacteria No Cell Wall Yes Without peptidoglycan Yes With peptidoglycan Cell Nucleus (DNA inside a membrane) No No Eukarya Yes except for many pro- tists Yes for plants, fungi, and some protists No for animals and other protists Yes Trait Cell Organelles structures membranes) (other inside Archaea No Bacteria No Eukarya Yes The Archaea and Bacteria Domains contain only single-celled organisms. Both Archaea and Bacteria have cells walls, but their cell walls are made of different materials. The cells of Archaea and Bacteria lack a nucleus. A nucleus is membrane-enclosed structure for holding a cells DNA. Some Eukarya are also single-celled, but many are multicellular. Some have a cell wall; others do not. However, the cells of all Eukarya have a nucleus and other organelles. Archaea and Bacteria may seem more similar to each other than either is to Eukarya. However, scientists think that Archaea may actually be more closely related to Eukarya than Bacteria are. This view is based on similarities in their DNA. | text | null |
L_0397 | classification of living things | T_2256 | This question was posed at the beginning of the chapter. Should viruses be placed in one of the three domains of life? Are viruses living things? Before considering these questions, you need to know the characteristics of viruses. A virus is nothing more than some DNA or RNA surrounded by a coat of proteins. A virus is not a cell. A virus cannot use energy, respond to stimuli, grow, or maintain homeostasis. A virus cannot reproduce on its own. However, a virus can reproduce by infecting the cell of a living host. Inside the host cell, the virus uses the cells structures, materials, and energy to make copies of itself. Because they have genetic material and can reproduce, viruses can evolve. Their DNA or RNA can change through time. The ability to evolve is a very lifelike attribute. Many scientists think that viruses should not be classified as living things because they lack most of the defining traits of living things. Other scientists arent so sure. They think that the ability of viruses to evolve and interact with living cells earns them special consideration. Perhaps a new category of life should be created for viruses. What do you think? | text | null |
L_0403 | first two lines of defense | T_2311 | Your bodys first line of defense is like a castles moat and walls. It keeps most pathogens out of your body. The first line of defense includes physical, chemical, and biological barriers. | text | null |
L_0403 | first two lines of defense | T_2312 | The skin is a very important barrier to pathogens. It is the bodys largest organ and the most important defense against disease. It forms a physical barrier between the body and the outside environment. The outer layer of the skin, called the epidermis, consists of dead cells filled with the protein keratin. These cells form a tough, waterproof covering on the body. It is very difficult for pathogens to get through the epidermis. The inside of the mouth and nose are lined with mucous membranes. Other organs that are exposed to substances from the environment are also lined with mucous membranes. These include the respiratory and digestive organs. Mucous membranes arent tough like skin, but they have other ways of keeping out pathogens. One way mucous membranes protect the body is by producing mucus. Mucus is a sticky, moist secretion that covers mucous membranes. The mucus traps pathogens and particles so they cant enter the body. Many mucous membranes are also covered with cilia. These are tiny, hair-like projections. Cilia move in waves and sweep mucus and trapped pathogens toward body openings. You can see this in the diagram in Figure 21.10. When you clear your throat or blow your nose, you remove mucus and pathogens from your body. | text | null |
L_0403 | first two lines of defense | T_2313 | In addition to mucus, your body releases a variety of fluids, including tears, saliva, and sweat. These fluids contain enzymes called lysozymes. Lysozymes break down the cell walls of bacteria and kill them. Your stomach contains a very strong acid, called hydrochloric acid. This acid kills most pathogens that enter the stomach in food or water. Urine is also acidic, so few pathogens are able to grow in it. | text | null |
L_0403 | first two lines of defense | T_2314 | Your skin is covered by millions of bacteria. Millions more live inside your body, mainly in your gastrointestinal tract. Most of these bacteria are helpful. For one thing, they help defend your body from pathogens. They do it by competing with harmful bacteria for food and space. They prevent the harmful bacteria from multiplying and making you sick. | text | null |
L_0403 | first two lines of defense | T_2315 | Did you ever get a splinter in your skin, like the one in Figure 21.11? It doesnt look like a serious injury, but even a tiny break in the skin may let pathogens enter the body. If bacteria enter through the break, for example, they could cause an infection. These bacteria would then face the bodys second line of defense. | text | null |
L_0403 | first two lines of defense | T_2316 | If bacteria enter the skin through a splinter or other wound, the area may become red, warm, and painful. These are signs of inflammation. Inflammation is one way the body reacts to infections or injuries. It occurs due to chemicals that are released when tissue is damaged. The chemicals cause nearby blood vessels to dilate, increasing blood flow to the area. The chemicals also attract white blood cells to the area. The white blood cells leak out of the blood vessels and into the damaged tissue. You can see an animation of the inflammatory response by watching this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0403 | first two lines of defense | T_2317 | The white blood cells that go to a site of inflammation and leak into damaged tissue are called phagocytes. They start eating pathogens and dead cells by engulfing and destroying them. This process is called phagocytosis. You can see how it happens in Figure ??. You can see it in action in the animation at this link: http://commons.wikim | text | null |
L_0403 | first two lines of defense | T_2318 | Phagocytes also release chemicals that cause a fever. A fever is a higher-than-normal body temperature. Normal human body temperature is 98.6 F (37 C). Most bacteria and viruses that infect people reproduce quickly at this temperature. When the temperature rises higher, the pathogens cant reproduce as quickly. Therefore, a fever helps to limit the infection. A fever also causes the immune system to make more white blood cells to fight the infection. | text | null |
L_0404 | immune system defenses | T_2319 | The immune system is the body system that fights to protect the body from specific pathogens. It has a special response for each type of pathogen. The immune systems specific reaction to a pathogen is called an immune response. The immune system is shown in Figure 21.13. It includes several organs and a network of vessels that carry lymph. Lymph is a yellowish liquid that normally leaks out of tiny blood vessels into spaces between cells in tissues. When inflammation occurs, more lymph leaks into tissues, and the lymph is likely to contain pathogens. | text | null |
L_0404 | immune system defenses | T_2320 | Immune system organs include bone marrow, the thymus gland, the spleen, and the tonsils. Each organ has a different job in the immune system. Bone marrow is found inside many bones. Its role in the immune system is to produce white blood cells called lymphocytes. The thymus gland is in the chest behind the breast bone. It stores some types of lymphocytes while they mature. The spleen is in the abdomen below the lungs. Its job is to filter pathogens out of the blood. The two tonsils are located on either side of the throat. They trap pathogens that enter the body through the mouth or nose. | text | null |
L_0404 | immune system defenses | T_2321 | Lymph vessels make up a circulatory system that is similar to the blood vessels of the cardiovascular system. However, lymph vessels circulate lymph instead of blood, and the heart does not pump lymph through the vessels. Lymph that collects in tissues slowly passes into tiny lymph vessels. Lymph then travels from smaller to larger lymph vessels. Muscles around the lymph vessels contract and squeeze the lymph through the vessels. The lymph vessels also contract to help move the lymph along. Eventually, lymph reaches the main lymph vessels, which are located in the chest. From these vessels, lymph drains into two large veins of the cardiovascular system. This is how lymph returns to the blood. Before lymph reaches the bloodstream, it passes through small oval structures called lymph nodes, which are located along the lymph vessels. Figure 21.14 shows where some of the bodys many lymph nodes are concentrated. Lymph nodes act like filters and remove pathogens from lymph. | text | null |
L_0404 | immune system defenses | T_2322 | A lymphocyte is the type of white blood cell involved in an immune system response. You can see what a lymphocyte looks like, greatly magnified, in Figure 21.15. Lymphocytes make up about one quarter of all white blood cells, but there are trillions of them in the human body. Usually, fewer than half of the bodys lymphocytes are in the blood. The majority are in the lymph, lymph nodes, and lymph organs. There are two main types of lymphocytes, called B cells and T cells. Both types of lymphocytes are produced in bone marrow. They are named for the sites where they grow and mature. The B in B cells stands for bone marrow, where B cells mature. The T in T cells stands for thymus gland, where T cells mature. Both B cells and T cells must be switched on in order to fight a specific pathogen. Once this happens, they produce an army of cells that are ready to fight that particular pathogen. How can B and T cells recognize specific pathogens? Pathogens have unique antigens, often located on their cell surface. Antigens are proteins that the body recognizes either as self or nonself. Self antigens include those found on red blood cells that determine a persons blood type. Generally, the immune system doesnt respond to self antigens. Nonself antigens include those found on bacteria, viruses, and other pathogens. Nonself antigens are also found on other cells, such as pollen cells and cancer cells. It is these antigens that trigger an immune response. | text | null |
L_0404 | immune system defenses | T_2323 | There are two different types of immune responses. Both types involve lymphocytes. However, one type of response involves B cells. The other type involves T cells. | text | null |
L_0404 | immune system defenses | T_2323 | There are two different types of immune responses. Both types involve lymphocytes. However, one type of response involves B cells. The other type involves T cells. | text | null |
L_0404 | immune system defenses | T_2324 | B cells respond to pathogens in the blood and lymph. Most B cells fight infections by making antibodies. An antibody is a large, Y-shaped molecule that binds to an antigen. Each antibody can bind with just one specific type of antigen. The antibody and antigen fit together like a lock and key. You can see how this works in Figure 21.16. The antibody in the figure can bind only with the type of antigen that is colored yellow. Once the antibody binds with the antigen, it signals a phagocyte to engulf and destroy them, along with the pathogen that carries the antigen on its surface. You can watch an animation of the antibody-antigen binding process at this link: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0404 | immune system defenses | T_2325 | There are different types of T cells, including killer T cells and helper T cells. Killer T cells destroy infected, damaged, or cancerous body cells. Figure 21.17 shows how a killer T cells destroys an infected cell. When the killer T cell comes into contact with the infected cell, it releases toxins. The toxins make tiny holes in the infected cells membrane. This causes the cell to burst open. Both the infected cell and the pathogens inside it are destroyed. Helper T cells do not destroy infected, damaged, or cancerous body cells. However, they are still needed for an immune response. They help by releasing chemicals that control other lymphocytes. The chemicals released by helper T cells switch on B cells and killer T cells so they can recognize and fight specific pathogens. | text | null |
L_0404 | immune system defenses | T_2326 | Most B cells and T cells die after an infection has been brought under control. But some of them survive for many years. They may even survive for a persons lifetime. These long-lasting B and T cells are called memory cells Memory cells allow the immune system to remember a pathogen after the infection is over. If the pathogen invades the body again, the memory cells will start dividing in order to fight it. They will quickly produce a new army of B or T cells to fight the pathogen. They will begin a faster, stronger attack than the first time the pathogen invaded the body. As a result, the immune system will be able to destroy the pathogen before it can cause an infection. Being able to fight off and resist a pathogen in this way is called immunity. You dont have to suffer through an infection to gain immunity to some diseases. Immunity can also come about by vaccination. Vaccination is the process of exposing a person to pathogens on purpose so the person will develop immunity to them. In vaccination, the pathogens are usually injected under the skin. Only part of the pathogens are injected, or else weakened or dead pathogens are used. This causes an immune response without causing the disease. Diseases you are likely to have been vaccinated against include measles, mumps, and chicken pox. | text | null |
L_0421 | lifes building blocks | T_2455 | Cells were first discovered in the mid-1600s. The cell theory came about some 200 years later. You can see a re- enactment of some of the discoveries that led to the cell theory in this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0421 | lifes building blocks | T_2456 | British scientist Robert Hooke first discovered cells in 1665. He was one of the earliest scientists to study living things under a microscope. He saw that cork was divided into many tiny compartments, like little rooms. (Do the cells in Figure 3.1 look like little rooms to you too?) Hooke called these little rooms cells. Cork comes from trees, so what Hooke observed was dead plant cells. In the late 1600s, Dutch scientist Anton van Leeuwenhoek made more powerful microscopes. He used them to observe cells of other organisms. For example, he saw human blood cells and bacterial cells. Over the next century, microscopes were improved and more cells were observed. | text | null |
L_0421 | lifes building blocks | T_2457 | By the early 1800s, scientists had seen cells in many different types of organisms. Every organism that was examined was found to consist of cells. From all these observations, German scientists Theodor Schwann and Matthias Schleiden drew two major conclusions about cells. They concluded that: cells are alive. all living things are made of cells. Around 1850, a German doctor named Rudolf Virchow was observing living cells under a microscope. As he was watching, one of the cells happened to divide. Figure 3.2 shows a cell dividing, like the cell observed by Virchow. This was an aha moment for Virchow. He realized that living cells produce new cells by dividing. This was evidence that cells arise from other cells. The work of Schwann, Schleiden, and Virchow led to the cell theory. This is one of the most important theories in life science. The cell theory can be summed up as follows: All organisms consist of one or more cells. Cells are alive and the site of all life processes. All cells come from pre-existing cells. | text | null |
L_0421 | lifes building blocks | T_2458 | All cells have certain parts in common. These parts include the cell membrane, cytoplasm, DNA, and ribosomes. The cell membrane is a thin coat of phospholipids that surrounds the cell. Its like the skin of the cell. It forms a physical boundary between the contents of the cell and the environment outside the cell. It also controls what enters and leaves the cell. The cell membrane is sometimes called the plasma membrane. Cytoplasm is the material inside the cell membrane. It includes a watery substance called cytosol. Besides water, cytosol contains enzymes and other substances. Cytoplasm also includes other cell structures suspended in the cytosol. DNA is a nucleic acid found in cells. It contains genetic instructions that cells need to make proteins. Ribosomes are structures in the cytoplasm where proteins are made. They consist of RNA and proteins. These four components are found in all cells. They are found in the cells of organisms as different as bacteria and people. How did all known organisms come to have such similar cells? The answer is evolution. The similarities show that all life on Earth evolved from a common ancestor. | text | null |
L_0421 | lifes building blocks | T_2459 | Besides the four parts listed above, many cells also have a nucleus. The nucleus of a cell is a structure enclosed by a membrane that contains most of the cells DNA. Cells are classified in two major groups based on whether or not they have a nucleus. The two groups are prokaryotic cells and eukaryotic cells. | text | null |
L_0421 | lifes building blocks | T_2460 | Prokaryotic cells are cells that lack a nucleus. The DNA in prokaryotic cells is in the cytoplasm, rather than enclosed within a nuclear membrane. All the organisms in the Bacteria and Archaea Domains have prokaryotic cells. No other organisms have this type of cell. Organisms with prokaryotic cells are called prokaryotes. They are all single-celled organisms. They were the first type of organisms to evolve. They are still the most numerous organisms today. You can see a model of a prokaryotic cell in Figure 3.3. The cell in the figure is a bacterium. Notice how it contains a cell membrane, cytoplasm, ribosomes, and several other structures. However, the cell lacks a nucleus. The cells DNA is circular. It coils up in a mass called a nucleoid that floats in the cytoplasm. | text | null |
L_0421 | lifes building blocks | T_2461 | Eukaryotic cells are cells that contain a nucleus. They are larger than prokaryotic cells. They are also more complex. Living things with eukaryotic cells are called eukaryotes. All of them belong to the Eukarya Domain. This domain includes protists, fungi, plants, and animals. Many protists consist of a single cell. However, most eukaryotes have more than one cell. You can see a model of a eukaryotic cell in Figure 3.4. The cell in the figure is an animal cell. The nucleus is an example of an organelle. An organelle is any structure inside a cell that is enclosed by a membrane. Eukaryotic cells may contain many different organelles. Each does a special job. For example, the mitochondrion is an organelle that provides energy to the cell. You can see a mitochondrion and several other organelles in the animal cell in Figure 3.4. Organelles allow eukaryotic cells to carry out more functions than prokaryotic cells can. | text | null |
L_0421 | lifes building blocks | T_2462 | All living cells have certain things in common. Besides having the basic parts described above, all cells can perform the same basic functions. For example, all cells can use energy, respond to their environment, and reproduce. However, cells may also have special functions. Multicellular organisms such as you have many different types of specialized cells. Each specialized cell has a particular job. Cells with special functions generally have a shape that suits them for that job. Figure 3.5 shows four examples of specialized cells. Each type of cell in the figure has a different function. It also has a shape that helps it perform that function. The function of a nerve cell is to carry messages to other cells. It has many long arms that extend outward from the cell. The "arms" let the cell pass messages to many other cells at once. The function of a red blood cell is to carry oxygen to other cells. A red blood cell is small and smooth. This helps it slip through small blood vessels. A red blood cell is also shaped like a fattened disc. This gives it a lot of surface area for transferring oxygen. The function of a sperm cell is to swim through fluid to an egg cell. A sperm cell has a long tail that helps it swim. The function of a pollen cell is to pollinate flowers. The pollen cells in the figure have tiny spikes that help them stick to insects such as bees. The bees then carry the pollen cells to other flowers for pollination. | text | null |
L_0421 | lifes building blocks | T_2463 | Cells and organelles are made of biochemical molecules. These include nucleic acids and proteins. Molecules, in turn, are made of atoms. Figure 3.6 shows these different levels of organization in living things. As you can see in Figure 3.6, living things also have levels of organization higher than the cell. These higher levels are found only in multicellular organisms with specialized cells. Specialized cells may be organized into tissues. A tissue is a group of cells of the same kind that performs the same function. For example, muscle cells are organized into muscle tissue. The function of muscle tissue is to contract in order to move the body or its parts. Tissues may be organized into organs. An organ is a structure composed of two or more types of tissue that work together to do a specific task. For example, the heart is an organ. It consists of muscle, nerve, and other types of tissues. Its task is to pump blood. Organs may be organized into organ systems. An organ system is a group of organs that work together to do the same job. For example, the heart is part of the cardiovascular system. This system also includes blood vessels and blood. The job of the cardiovascular system is to transport substances in blood to and from cells throughout the body. Organ systems are organized into the organism. The different organ systems work together to carry out all the life functions of the individual. For example, cardiovascular and respiratory systems work together to provide the individual with oxygen and rid it of carbon dioxide. | text | null |
L_0421 | lifes building blocks | T_2464 | Cells with different functions often vary in shape. They may also vary in size. However, all cells are very small. Even the largest organisms have microscopic cells. Cells are so small that their diameter is measured in micrometers. A micrometer is just one-millionth of a meter. Use the sliding scale at the following link to see how small cells and cell parts are compared with other objects. Why are cells so small? The answer has to do with the surface area and volume of cells. To carry out life processes, a cell must be able to pass substances into and out of the cell. For example, it must be able to pass nutrients into the cell and waste products out of the cell. Anything that enters or leaves a cell has to go through the cell membrane on the surface of the cell. A bigger cell needs more nutrients and creates more wastes. As the size of a cell increases, its volume increases more quickly that its surface area. If the volume of a cell becomes too great, it wont have enough surface area to transfer all of its nutrients and wastes. | text | null |
L_0422 | cell structures | T_2465 | The cell membrane is like the bag holding the Jell-O. It encloses the cytoplasm of the cell. It forms a barrier between the cytoplasm and the environment outside the cell. The function of the cell membrane is to protect and support the cell. It also controls what enters or leaves the cell. It allows only certain substances to pass through. It keeps other substances inside or outside the cell. | text | null |
L_0422 | cell structures | T_2466 | The structure of the cell membrane explains how it can control what enters and leaves the cell. The membrane is composed mainly of two layers of phospholipids. Figure 3.8 shows how the phospholipids are arranged in the cell membrane. Each phospholipid molecule has a head and two tails. The heads are water loving (hydrophilic), and the tails are water fearing (hydrophobic). The water-loving heads are on the outer surfaces of the cell membrane. They point toward the watery cytoplasm within the cell or the watery fluid that surrounds the cell. The water-fearing tails are in the middle of the cell membrane. | text | null |
L_0422 | cell structures | T_2467 | Hydrophobic molecules like to be near other hydrophobic molecules. They fear being near hydrophilic molecules. The opposite is true of hydrophilic molecules. They like to be near other hydrophilic molecules. They fear being near hydrophobic molecules. These likes and fears explain why some molecules can pass through the cell membrane while others cannot. Hydrophobic molecules can pass through the cell membrane. Thats because they like the hydrophobic interior of the membrane and fear the hydrophilic exterior of the membrane. Hydrophilic molecules cant pass through the cell membrane. Thats because they like the hydrophilic exterior of the membrane and fear the hydrophobic interior of the membrane. You can see how this works in the video at this link: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0422 | cell structures | T_2468 | Cytoplasm is everything inside the cell membrane (except the nucleus if there is one). It includes the watery, gel-like cytosol. It also includes other structures. The water in the cytoplasm makes up about two-thirds of the cells weight. It gives the cell many of its properties. | text | null |
L_0422 | cell structures | T_2469 | Why does a cell have cytoplasm? Cytoplasm has several important functions. These include: suspending cell organelles. pushing against the cell membrane to help the cell keep its shape. providing a site for many of the biochemical reactions of the cell. | text | null |
L_0422 | cell structures | T_2470 | Crisscrossing the cytoplasm is a structure called the cytoskeleton. It consists of thread-like filaments and tubules. The cytoskeleton is like a cellular skeleton. It helps the cell keep its shape. It also holds cell organelles in place within the cytoplasm. Figure 3.9 shows several cells. In the figure, the filaments of their cytoskeletons are colored green. The tubules are colored red. The blue dots are the cell nuclei. | text | null |
L_0422 | cell structures | T_2471 | Eukaryotic cells contain a nucleus and several other types of organelles. These structures carry out many vital cell functions. | text | null |
L_0422 | cell structures | T_2472 | The nucleus is the largest organelle in a eukaryotic cell. It contains most of the cells DNA. DNA, in turn, contains the genetic code. This code tells the cell which proteins to make and when to make them. You can see a diagram of a cell nucleus in Figure 3.10. Besides DNA, the nucleus contains a structure called a nucleolus. Its function is to form ribosomes. The membrane enclosing the nucleus is called the nuclear envelope. The envelope has tiny holes, or pores, in it. The pores allow substances to move into and out of the nucleus. | text | null |
L_0422 | cell structures | T_2473 | The mitochondrion (mitochondria, plural) is an organelle that makes energy available to the cell. Its like the power plant of a cell. It uses energy in glucose to make smaller molecules called ATP (adenosine triphosphate). ATP packages energy in smaller amounts that cells can use. Think about buying a bottle of water from a vending machine. The machine takes only quarters, and you have only dollar bills. The dollar bills wont work in the vending machine. Glucose is like a dollar bill. It contains too much energy for cells to use. ATP is like a quarter. It contains just the right amount of energy for use by cells. | text | null |
L_0422 | cell structures | T_2474 | A ribosome is a small organelle where proteins are made. Its like a factory in the cell. It gathers amino acids and joins them together into proteins. Unlike other organelles, the ribosome is not surrounded by a membrane. As a result, some scientists do not classify it as an organelle. Ribosomes may be found floating in the cytoplasm. Some ribosomes are located on the surface of another organelle, the endoplasmic reticulum. | text | null |
L_0422 | cell structures | T_2475 | The endoplasmic reticulum (ER) is an organelle that helps make and transport proteins and lipids. Its made of folded membranes. Bits of membrane can pinch off to form tiny sacs called vesicles. The vesicles carry proteins or lipids away from the ER. There are two types of endoplasmic reticulum. They are called rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). Both types are shown in Figure 3.11. NOTE: Crop to include only part a of the original image.] | text | null |
L_0422 | cell structures | T_2475 | The endoplasmic reticulum (ER) is an organelle that helps make and transport proteins and lipids. Its made of folded membranes. Bits of membrane can pinch off to form tiny sacs called vesicles. The vesicles carry proteins or lipids away from the ER. There are two types of endoplasmic reticulum. They are called rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). Both types are shown in Figure 3.11. NOTE: Crop to include only part a of the original image.] | text | null |
L_0422 | cell structures | T_2476 | The Golgi apparatus is a large organelle that sends proteins and lipids where they need to go. Its like a post office. It receives molecules from the endoplasmic reticulum. It packages and labels the molecules. Then it sends them where they are needed. Some molecules are sent to different parts of the cell. Others are sent to the cell membrane for transport out of the cell. Small bits of membrane pinch off the Golgi apparatus to enclose and transport the proteins and lipids. You can see a Golgi apparatus at work in this animation: | text | null |
L_0422 | cell structures | T_2477 | Both vesicles and vacuoles are sac-like organelles. They store and transport materials in the cell. They are like movable storage containers. Some vacuoles are used to isolate materials that are harmful to the cell. Other vacuoles are used to store needed substances such as water. Vesicles are much smaller than vacuoles and have a variety of functions. Some vesicles pinch off from the membranes of the endoplasmic reticulum and Golgi apparatus. These vesicles store and transport proteins and lipids. Other vesicles are used as chambers for biochemical reactions. | text | null |
L_0422 | cell structures | T_2478 | A lysosome is an organelle that recycles unneeded molecules. It uses enzymes to break down the molecules into their components. Then the components can be reused to make new molecules. Lysosomes are like recycling centers. | text | null |
L_0422 | cell structures | T_2479 | Centrioles are organelles that are found only in animal cells. They are located near the nucleus. They help organize the DNA in the nucleus before cell division takes place. They ensure that the DNA divides correctly when the cell divides. | text | null |
L_0422 | cell structures | T_2480 | All but one of the structures described above are found in plant cells as well as animal cells. The only exception is centrioles, which are not found in plant cells. Plant cells have three additional structures that are not found in animals cells. These include a cell wall, large central vacuole, and organelles called plastids. You can see these structures in the model of a plant cell in Figure 3.12. You can also see them in the interactive plant cell at this link: | text | null |
L_0422 | cell structures | T_2481 | The cell wall is a rigid layer that surrounds the cell membrane of a plant cell. Its made mainly of the complex carbohydrate called cellulose. The cell wall supports and protects the cell. The cell wall isnt solid like a brick wall. It has tiny holes in it called pores. The pores let water, nutrients, and other substances move into and out of the cell. | text | null |
L_0422 | cell structures | T_2482 | Most plant cells have a large central vacuole. It can make up as much as 90 percent of a plant cells total volume. The central vacuole is like a large storage container. It may store substances such as water, enzymes, and salts. It may have other roles as well. For example, the central vacuole helps stems and leaves hold their shape. It may also contain pigments that give flowers their colors. | text | null |
L_0422 | cell structures | T_2483 | Plastids are organelles in plant cells that may have various jobs. The main types of plastids are chloroplasts, chromoplasts, and leucoplasts. Chloroplasts are plastids that contain chlorophyll. Chlorophyll is a green pigment. It gives plants their green color. Photosynthesis takes place in chloroplasts. They capture sunlight and use its energy to make glucose. Chromoplasts are plastids that contain other pigments. These other pigments give flowers and fruits their colors. Leucoplasts are plastids that make or store other molecules. For example, some leucoplasts make amino acids. Other leucoplasts store starch or oil. | text | null |
L_0423 | transport | T_2484 | Youve probably blown soap bubbles like the child in Figure 4.1. In some ways, the thin film of soap molecules that forms a bubble resembles the cell membrane. Like the soap film, the cell membrane consists of a thin skin of molecules. You can see a model of the cell membrane in Figure below. The molecules that make up the cell membrane are mainly phospholipids. There are two layers of phospholipids. They are arranged so the lipid tails are on the inside of the membrane. They make the interior of the membrane hydrophobic, or "water fearing". The lipid heads point toward the outside of the membrane. The make the outer surfaces of the membrane hydrophilic, or "water loving". Different types of proteins are embedded in the lipid layers. The proteins are needed to help transport many substances across the membrane. The passage of a substance through a cell membrane is called transport. There are two basic ways that transport can occur: passive transport and active transport. For a good video introduction to passive and active transport, click on this link: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0423 | transport | T_2485 | Passive transport occurs when a substance passes through the cell membrane without needing any energy to pass through. This happens when a substance moves from an area where it is more concentrated to an area where it is less concentrated. Concentration is the number of particles of a substance in a given volume. Lets say you dissolve a teaspoon of salt in a cup of water. Then you dissolve two teaspoons of salt in another cup of water. The second solution will have a higher concentration of salt. Why does passive transport require no energy? A substance naturally moves from an area of higher to lower concentration. This is known as moving down the concentration gradient. The process is called diffusion. Its a little like a ball rolling down a hill. The ball naturally rolls from a higher to lower position without any added energy. You can see diffusion if you place a few drops of food coloring in a pan of water. Even without shaking or stirring, the food coloring gradually spreads throughout the water in the pan. Some substances can also diffuse through a cell membrane. This can occur in two ways: simple diffusion or facilitated diffusion. | text | null |
L_0423 | transport | T_2486 | Simple diffusion occurs when a substance diffuses through a cell membrane without any help from other molecules. The substance simply passes through tiny spaces in the membrane. It moves from the side of the membrane where it is more concentrated to the side where it is less concentrated. You can see how this happens in Figure 4.2. Substances that cross cell membranes by simple diffusion must squeeze between the lipid molecules in the mem- brane. As a result, the diffusing molecules must be very small. Oxygen (O2 ) and carbon dioxide (CO2 ) are examples of molecules that can cross cell membranes this way. When you breathe in, oxygen is more concentrated in the air in your lungs than it is in your blood. So oxygen diffuses from your lungs to your blood. The reverse happens with carbon dioxide. Carbon dioxide is more concentrated in your blood than it is in the air in your lungs. So carbon dioxide diffuses out of your blood to your lungs. | text | null |
L_0423 | transport | T_2487 | Hydrophilic molecules and very large molecules cant pass through the cell membrane by simple diffusion. They need help to pass through the membrane. The help is provided by proteins called transport proteins. This process is known as facilitated diffusion. There are two types of transport proteins: channel proteins and carrier proteins. They work in different ways. You can see how they work in Figure 4.3. A channel protein forms a tiny hole called a pore in the cell membrane. This allows water or hydrophilic molecules to bypass the hydrophobic interior of the membrane. A carrier protein binds with a diffusing molecule. This causes the carrier protein to change shape. As it does, it carries the molecule across the membrane. This allows large molecules to pass through the cell membrane. | text | null |
L_0423 | transport | T_2488 | Osmosis is the special case of the diffusion of water. Its an important means of transport in cells because the fluid inside and outside cells is mostly water. Water can pass through the cell membrane by simple diffusion, but it can happen more quickly with the help of channel proteins. Water moves in or out of a cell by osmosis until its concentration is the same on both sides of the cell membrane. | text | null |
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