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L_0685 | succession | T_3412 | When you see an older forest, its easy to picture that the forest has been there forever. This is not the case. Ecosystems are "dynamic." This means that ecosystems change over time. That forest may lie on land that was once covered by an ocean millions of years ago. Lightning may have sparked a fire in a forest, destroying much of the plant life there. Or the forest may have been cut down at one point for agricultural use, then abandoned and allowed to re-grow over time. During the ice ages, glaciers once covered areas that are tropical rainforests today. Both natural forces and human actions cause ecosystems to change. If there is a big ecosystem change caused by natural forces or human actions, the plants and animals that live there may be destroyed. Or they may be forced to leave. Over time, a new community will develop, and then that community may be replaced by another. You may see several changes in the plant and animal composition of the community over time. Ecological succession is the constant replacement of one community by another. It happens after a big change in the ecosystem. And, of course, succession occurs on brand new land. | text | null |
L_0685 | succession | T_3413 | Primary succession is the type of ecological succession that happens on new landslands where life has not yet existed. Primary succession can take place after lava flow cools and hardens into new land, or a glacier recedes exposing new land. Since the land that results from these processes is completely new land, soil must first be produced. How is soil produced? Primary succession always starts with a pioneer species. This is the species that first lives in the habitat. If life is to begin on barren rock, which is typical of new land, the pioneer species would be an organism such as a lichen ( Figure 1.1). A lichen is actually an organism formed from two species. It results from a symbiotic relationship between a fungus and an algae or cyanobacteria. The lichen is able to thrive as both the fungus and the algae or bacteria contribute to the relationship. The fungus is able to absorb minerals and nutrients from the rock, while algae supplies the fungus with sugars through photosynthesis. Since lichens can photosynthesize and do not rely on soil, they can live in environments where other organisms cannot. As a lichen grows, it breaks down the rock, which is the first step of soil formation. Primary succession on a rock often be- gins with the growth of lichens. What do lichens help create? The pioneer species is soon replaced by other populations. Abiotic factors such as soil quality, water, and climate will determine the species that continue the process of succession. Mosses and grasses will be able to grow in the newly created soil. During early succession, plant species like grasses that grow and reproduce quickly will take over the landscape. Over time, these plants improve the soil and a few shrubs can begin to grow. Slowly, the shrubs are replaced by small trees. Small trees then are succeeded by larger trees. Since trees are more successful at competing for resources than shrubs and grasses, a forest may be the end result of primary succession. | text | null |
L_0685 | succession | T_3414 | Sometimes ecological succession occurs in areas where life has already existed. These areas already have soil full of nutrients. Secondary succession is the type of succession that happens after something destroys the habitat, such as a flood or other natural disaster. Abandoning a field that was once used for agriculture can also lead to secondary succession ( Figure 1.2). In this case, the pioneer species would be the grasses that first appear. Lichen would not be necessary as there is already nutrient-rich soil. Slowly, the field would return to its natural state. A forest fire can alter a habitat such that secondary succession occurs ( Figure 1.3 and Figure 1.4). Although the area will look devastated at first, the seeds of new plants are underground. They are waiting for their chance to grow. This land was once used for growing crops. Now that the field is abandoned, secondary succession has begun. Pio- neer species, such as grasses, appear first, and then shrubs begin to grow. Just like primary succession, the burned forest will go through a series of communities, starting with small grasses, then shrubs, and finally bigger trees. | text | null |
L_0685 | succession | T_3415 | A climax community ( Figure 1.5) is the end result of ecological succession. The climax community is a stable balance of all organisms in an ecosystem, and will remain stable unless a disaster strikes. After the disaster, succession will start all over again. Depending on the climate of the area, the climax community will look different. In the tropics, the climax community might be a tropical rainforest. At the other extreme, in northern parts of the world, the climax community might be a coniferous forest. Though climax communities are stable, are they truly the final community of the habitat? Or is it likely that sometime in the future, maybe a long time in the future, the community of populations will change, and another stable, climax community will thrive? | text | null |
L_0686 | symbiosis | T_3416 | Symbiosis describes a close and long-term relationship between different species. At least one species will benefit in a symbiotic relationship. These relationships are often necessary for the survival of one or both organisms. There are three types of symbiotic relationships: mutualism, communalism, and parasitism. Mutualism is a symbiotic relationship in which both species benefit. Commensalism is a symbiotic relationship in which one species benefits while the other is not affected. Parasitism is a symbiotic relationship in which the parasitic species benefits while the host species is harmed. An example of a mutualistic relationship is between herbivores (plant-eaters) and the bacteria that live in their intestines. The bacteria get a place to live. Meanwhile, the bacteria help the herbivore digest food. Both species benefit, so this is a mutualistic relationship. The clownfish and the sea anemones also have a mutualistic relationship. The clownfish protects the anemone from anemone-eating fish, and the stinging tentacles of the anemone protect the clownfish from predators ( Figure 1.1). Another example of this type of symbiotic relationship is the relationship between the plover bird and the African crocodile. The tiny blackbird acts as a toothpick for the fierce crocodile, and helps by removing tiny morsels of food that are stuck between the crocodiles teeth. These food remains are the source of food for the bird. Another example is between the ostrich and the zebra. The ostrich always moves with the herd of zebras since it has a poor sense of hearing and smell, whereas the zebra has very sharp senses. The ostrich has a keen sense of sight, which the zebra lacks. Hence, these two species depend on each other to warn one another of any nearby imposing dangers. Commensal relationships may involve an organism using another for transportation or housing. For example, spiders build their webs on trees. The spider gets to live in the tree, but the tree is unaffected. Other commensal relationships exist between cattle egrets and livestock. Cattle egrets are mostly found in meadows and grasslands are always seen near cattle, horses and other livestock. These birds feed on the insects that come out of the field due to the movement of the animals. They even eat ticks, fleas, and other insects off the back of animals. The relationship between tigers and golden jackals is also commensalism. The jackal alerts the tiger to a kill and feeds on the remains of the prey left by the tiger. This is not a mutualistic relationship as the tiger does not provide anything to the jackal. Parasites may live either inside or on the surface of their host. An example of a parasite is a hookworm. Hookworms are roundworms that affect the small intestine and lungs of a host organism. They live inside of humans and cause them pain. However, the hookworms must live inside of a host in order to survive. Parasites may even kill the host they live on, but then they also kill their host organism, so this is rare. Parasites are found in animals, plants, and fungi. Hookworms are common in the moist tropic and subtropic regions. There is very little risk of getting a parasite in industrialized nations. Clownfish in a sea anemone. | text | null |
L_0687 | symbiotic relationships of fungi | T_3417 | Fungi dont live in isolation. They often interact with other species. In fact, fungi can be dependent on another or- ganism for survival. When two species live close together and form a relationship, it is called symbiosis. Symbiosis can be beneficial to one or both organisms, or sometimes one organism hurts the other. Some of the partners in these relationships include plants, algae, insects and other animals, and even humans. | text | null |
L_0687 | symbiotic relationships of fungi | T_3418 | If it were not for fungi, many plants would go hungry. In the soil, fungi grow closely around the roots of plants, and they begin to help each other. The plant roots together with the special root-dwelling fungi are called mycorrhizae ( Figure 1.1). As plants and fungi form a close relationship, the plant and the fungus feed one another. The plant provides sugars to the fungus that the plant makes through photosynthesis, which the fungus cannot do. The fungus then provides minerals and water to the roots of the plant. Since the plant and the fungus are helping each other out, this is a mutualistic relationship, a type of symbiosis known as mutualism. In a mutualistic relationship, both organisms benefit. These roots (brown) and the mycorrhizae (white) help to feed one another. | text | null |
L_0687 | symbiotic relationships of fungi | T_3419 | Have you ever seen an organism called a lichen? Lichens are crusty, hard growths that you might find on trees, logs, walls, and rocks ( Figure 1.2). Although lichens may not be the prettiest organisms in nature, they are unique. A lichen is really two organisms, sometimes referred to as a composite organism, that live very closely together: a fungus and a bacterium or an alga. The cells from the alga or bacterium live inside the fungus. Besides providing a home, the fungus also provides nutrients. In turn, the bacterium or the alga provides energy to the fungus by performing photosynthesis, obtaining energy directly from the sun. A lichen is also an example of a mutualistic relationship. Because lichens can grow on rocks, these organisms are some of the earliest life forms in new ecosystems. | text | null |
L_0687 | symbiotic relationships of fungi | T_3420 | Many insects have a symbiotic relationship with certain types of fungi: Ants and termites grow fungi in underground fungus gardens that they create. When the ants or termites have eaten a big meal of wood or leaves, they also eat some fungi from their gardens. The fungi help them digest the wood or leaves. The fungi secrete certain enzymes that the ants or termites cannot produce on their own. Ambrosia beetles live in the bark of trees. Like ants and termites, they grow fungi inside the bark of trees and use it to help digest their food. | text | null |
L_0687 | symbiotic relationships of fungi | T_3421 | Although lots of symbiotic relationships help both organisms, sometimes one of the organisms is harmed. When that happens, the organism that benefits, and is not harmed, is called a parasite. This type of relationship is known as parasitism. Examples of parasitic fungi include the following: Beginning in 1950, Dutch Elm trees in the United States began to die. Since then, most of these trees have been eliminated. The disease was caused by a fungus that acted as a parasite. The fungus that killed the trees was carried by beetles to the trees. Some parasitic fungi cause human diseases such as athletes foot and ringworm. These fungi feed on the outer layer of warm, moist skin. Though its name may suggest otherwise, ringworm is not caused by a worm, but by a fungus. | text | null |
L_0689 | terrestrial biomes | T_3425 | A terrestrial biome is an area of land with a similar climate that includes similar communities of plants and animals. Different terrestrial biomes are usually defined in terms of their plants, such as trees, shrubs, and grasses. Factors such as latitude, humidity, and elevation affect biome type: Latitude means how far a biome is from the equator. Moving from the poles to the equator, you will find (in order) Arctic, boreal, temperate, subtropical, and tropical biomes. Humidity is the amount of water in the air. Air with a high concentration of water will be called humid. Moving away from the most humid climate, biomes will be called semi-humid, semi-arid, or arid (the driest). Elevation measures how high land is above sea level. It gets colder as you go higher above sea level, which is why you see snow-capped mountains. Terrestrial biomes include grasslands, forests, deserts, and tundra. Grasslands are characterized as lands dominated by grasses rather than large shrubs or trees and include the savanna and temperate grasslands. Forests are dominated by trees and other woody vegetation and are classified based on their latitude. Forests include tropical, temperate, and boreal forests (taiga). Deserts cover about one fifth of the Earths surface and occur where rainfall is less than 50 cm (about 20 inches) each year. Tundra is the coldest of all the biomes. The tundra is characterized for its frost-molded landscapes, extremely low temperatures, little precipitation, poor nutrients, and short growing seasons. There are two main types of tundra, Arctic and Alpine tundras. Terrestrial biomes ( Figure 1.1) lying within the Arctic and Antarctic Circles do not have very much plant or animal life. Biomes with the highest amount of biodiversity, that is the most variation in plant and animal life, are near the equator ( Figure 1.2). One of the terrestrial biomes, taiga, is an evergreen forest of the subarctic, covering extensive areas of northern North Amer- ica and Eurasia. This taiga is along the Denali Highway in Alaska. | text | null |
L_0690 | the biosphere | T_3426 | The highest level of ecological organization is the biosphere. It is the part of Earth, including the air, land, surface rocks, and water, where life is found. Parts of the lithosphere, hydrosphere, and atmosphere make up the biosphere. The lithosphere is the outermost layer of the Earths crust; essentially land is part of the lithosphere. The hydrosphere is composed of all the areas that contain water, which can be found on, under, and over the surface of Earth. The atmosphere is the layer of gas that surrounds the planet. The biosphere includes the area from about 11,000 meters below sea level to 15,000 meters above sea level. It overlaps with the lithosphere, hydrosphere, and atmosphere. Land plants and animals are found on the lithosphere, freshwater and marine plants and animals are found in the hydrosphere, and birds and other flying animals are found in the atmosphere. Of course, there are countless bacteria, protists, and fungi that are also found in the biosphere. | text | null |
L_0690 | the biosphere | T_3427 | The Gaia hypothesis states that the biosphere is its own living organism. The hypothesis suggests that the Earth is self-regulating and tends to achieve a stable state, known as homeostasis. For example the composition of our atmosphere stays fairly consistent, providing the ideal conditions for life. When carbon dioxide levels increase in the atmosphere, plants grow more quickly. As their growth continues, they remove more carbon dioxide from the atmosphere. In this way, the amount of carbon dioxide stays fairly constant without human intervention. For a better understanding of how the biosphere works and various dysfunctions related to human activity, scientists have simulated the biosphere in small-scale models. Biosphere 2 ( Figure 1.1) is a laboratory in Arizona that contains 3.15 acres of closed ecosystems. Ecosystems of Biosphere 2 are an ocean ecosystem with a coral reef, mangrove wetlands, a tropical rainforest, a savannah grassland and a fog desert. See for additional information. Additional biosphere projects include BIOS-3, a closed ecosystem in Siberia, and Biosphere J, located in Japan. | text | null |
L_0696 | tracing evolution | T_3441 | How fast is evolution? Can you actually see evolution happening within your lifetime? Usually evolution takes a long time. So how can we visualize how it has happened? | text | null |
L_0696 | tracing evolution | T_3442 | How long did it take for the giraffe to develop a long neck? How long did it take for the Galpagos finches to evolve? How long did it take for whales to evolve from land mammals? These, and other questions about the rate of evolution, are difficult to answer. The rate of evolution depends on how many of an organisms genes have changed over a period of time. Evolution is usually so gradual that we do not see the change for many, many generations. The rate of evolution also depends on the generation time of a particular species. Not all organisms evolve at the same rate. Humans took millions of years to evolve from a mammal that is now extinct. It is very difficult to observe evolution in humans. However, there are organisms that are evolving so fast that you can observe evolution! A human takes about 22 years to go through one generation. But some bacteria go through over a thousand generations in less than two months. Some bacteria go through many generations in a few days. And sometimes a bacterial generation is as fast as 20 minutes! We can actually trace their evolution as it is happening. | text | null |
L_0696 | tracing evolution | T_3443 | If evolution can take a very long time, how can we visualize how it happens? Charles Darwin came up with the idea of an evolutionary tree to represent the relationships between different species and their common ancestors ( Figure 1.1). The base of the tree represents the ancient ancestors of all life. The separation into large branches shows where these original species evolved into new species. The branches keep splitting into smaller and smaller branches as species continue to evolve into more and more species. Some species are represented by short twigs spurting out of the tree, then stopping. These are species that went extinct before evolving into new species. Other Trees of Life have been created by other scientists ( Figure would that be? Animal, plant, fungi protist, or none of those? Darwin drew this version of the Tree of Life on the left to represent how species evolve and diverge into separate direc- tions. Each point on the tree where one branch splits off from another represents the common ancestor of the species on the separate branches. Scientists have drawn many different versions of the Tree of Life to show different features of evo- lution. The Tree of Life on the right was made by Ernst Haeckel in 1879. | text | null |
L_0699 | tropisms | T_3446 | Plants may not be able to move to another location, but they are able to change how they grow in response to their environment. Growth toward or away from a stimulus is known as a tropism ( Table 1.1). Auxins, a class of plant hormones, allow plants to curve in specific directions as they grow. The auxin moves to one side of the stem, where it starts a chain of events that cause rapid cell growth on just that one side of the stem. With one side of the stem growing faster than the other, the plant begins to bend. Name Phototropism Gravitropism Thigmotropism Stimulus Light Gravity Touch | text | null |
L_0699 | tropisms | T_3447 | You might have noticed that plants bend toward the light. This is an example of a tropism where light is the stimulus, known as phototropism ( Figure 1.1). To obtain more light for photosynthesis, leaves and stems grow toward the light. On the other hand, roots grow away from light. This is beneficial for the roots, because they need to obtain water and nutrients from deep within the ground. | text | null |
L_0699 | tropisms | T_3448 | So, how do the roots of seeds underground know to grow downward? How do the roots deep in the soil know which way is up? Gravitropism is a growth toward or away from the pull of gravity ( Figure 1.2). Shoots, the new growth of a plant, also show a gravitropism, but in the opposite direction. If you place a plant on its side, the stem and new leaves will curve upward. | text | null |
L_0699 | tropisms | T_3449 | Plants also have a touch response called thigmotropism. If you have ever seen a morning glory or the tendrils of a pea plant twist around a pole, then you know that plants must be able to sense the pole. Thigmotropism works much like the other tropisms. The plant grows straight until it comes in contact with the pole. Then, the side of the stem that is in contact with the pole grows slower than the opposite side of the stem. This causes the stem to bend around the pole. | text | null |
L_0700 | turtles | T_3450 | Turtles are reptiles in the order Testudines. If you have seen turtles before, what is the most noticeable thing about them? Their shells. Most turtle bodies are covered by a special shell developed from their ribs. Their shells can be bony or cartilaginous, made from a more flexible supportive tissue. About 300 species are alive today, and some are highly endangered. Like other reptiles, turtles cannot regulate their body temperature, except with behavioral means, such as burrowing underground. The major difference between turtles and tortoises is that the land dwelling ones are called tortoises and water dwelling are called turtles. Turtles are broken down into two groups, based on how they bring their neck back into their shell: 1. Cryptodira, which can draw their neck inside and under their spine. 2. Pleurodira, which fold their necks to one side. | text | null |
L_0700 | turtles | T_3451 | Although many turtles spend large amounts of their lives underwater, they can also spend much of their lives on dry land and breathe air. Turtles cannot breathe in water, but can hold their breath for long periods of time. Turtles must surface at regular intervals to refill their lungs. The position of a turtles eyes can give a clue to their natural habitat. Most turtles that spend most of their lives on land have their eyes looking down at objects in front of them. Some aquatic turtles, such as snapping turtles and soft-shelled turtles, have eyes closer to the top of the head. These species of turtles can hide from predators in shallow water, where they lie entirely submerged in water except for their eyes and nostrils. Sea turtles ( Figure 1.1) have glands near their eyes that produce salty tears, which remove excess salt taken in from the water they drink. A species of sea turtle, showing place- ment of eyes, shell shape, and flippers. Turtles have exceptional night vision due to the unusually large number of cells that sense light in their eyes. This allows them to be active at any time of the day. Turtles also have color vision. Turtles dont lay eggs underwater. Turtles lay slightly soft and leathery eggs, like other reptiles. The eggs of the largest species are spherical, while the eggs of the rest are longer in shape. After internal fertilization, a female is ready to lay her eggs, she places a large numbers of eggs in holes dug into mud or sand. They are then covered and left to grow and develop by themselves. When the turtles hatch, they squirm their way to the surface and head toward the water. They need to get to the water as fast as possible before they are fed upon by animals such as seabirds, crabs, and raccoons. | text | null |
L_0700 | turtles | T_3452 | Turtles may appear slow and harmless when they are out of the water, but in the water is another story. Turtles can be either herbivores or carnivores, with most sea turtles carnivorous. Turtles have a rigid beak and use their jaws to cut and chew food. Instead of teeth, the upper and lower jaws of the turtle are covered by horny ridges. Carnivorous, or animal-eating turtles usually have knife-sharp ridges for slicing through their prey. But as the turtle is not a very fast animal, and it cannot quickly turn its head to snap at prey, it does have some limitations. Sea turtles typically feed on jellyfish, sponges and other soft-bodied organisms. Some species of sea turtle with stronger jaws eat shellfish, while other species, such as the green sea turtle, do not eat any meat at all. Herbivorous turtles have serrated ridges that help them cut through tough plants. | text | null |
L_0700 | turtles | T_3453 | The largest turtle is the great leatherback sea turtle ( Figure 1.2), which can have a shell length of seven feet and can weigh more than 2,000 pounds. The only surviving giant tortoises are on the Seychelles and Galpagos Islands and can grow to over four feet in length and weigh about 670 pounds ( Figure 1.3). The smallest turtle is the speckled padloper tortoise of South Africa, measuring no more than three inches in length, and weighing about five ounces. The largest ever turtle was the know extinct Archelon genus, a Late Cretaceous sea turtle known to have been up to 15 ft long, and 16 ft wide from flipper to flipper. The closest living relative of this genus is the leatherback sea turtle. It was the giant Galpagos tortoises that Charles Darwin studied during his voyage on the Beagle, providing significant evidence that he used to support his theory of evolution. A giant tortoise can grow to over feet ft in length and weigh about 670 lb. These animals can easily live over 100 years, spending their days grazing on grass, leaves, and cactus, basking in the sun, and napping nearly 16 hours each day. | text | null |
L_0700 | turtles | T_3453 | The largest turtle is the great leatherback sea turtle ( Figure 1.2), which can have a shell length of seven feet and can weigh more than 2,000 pounds. The only surviving giant tortoises are on the Seychelles and Galpagos Islands and can grow to over four feet in length and weigh about 670 pounds ( Figure 1.3). The smallest turtle is the speckled padloper tortoise of South Africa, measuring no more than three inches in length, and weighing about five ounces. The largest ever turtle was the know extinct Archelon genus, a Late Cretaceous sea turtle known to have been up to 15 ft long, and 16 ft wide from flipper to flipper. The closest living relative of this genus is the leatherback sea turtle. It was the giant Galpagos tortoises that Charles Darwin studied during his voyage on the Beagle, providing significant evidence that he used to support his theory of evolution. A giant tortoise can grow to over feet ft in length and weigh about 670 lb. These animals can easily live over 100 years, spending their days grazing on grass, leaves, and cactus, basking in the sun, and napping nearly 16 hours each day. | text | null |
L_0701 | types of archaea | T_3454 | The first archaea described could survive in extremely harsh environments in which no other organisms could survive. As a result, archaea are often distinguished by the environment in which they live. | text | null |
L_0701 | types of archaea | T_3455 | The halophiles, which means "salt-loving," live in environments with high levels of salt ( Figure 1.1). They have been identified in the Great Salt Lake in Utah and in the Dead Sea between Israel and Jordan, which have salt concentrations several times that of the oceans. | text | null |
L_0701 | types of archaea | T_3456 | The thermophiles live in extremely hot environments. For example, they can grow in hot springs, geysers, and near volcanoes. Unlike other organisms, they can thrive in temperatures near 100C, the boiling point of water! | text | null |
L_0701 | types of archaea | T_3457 | Methanogens can also live in some strange places, such as swamps and inside the guts of cows and termites. They help these animals break down cellulose, a tough carbohydrate made by plants ( Figure 1.2). This is an example of a mutualistic relationship. Methanogens are named for their waste product, a gas called methane. Cows are able to digest grass with the help of the methanogens in their gut. | text | null |
L_0701 | types of archaea | T_3458 | Although archaea are known for living in unusual environments, such as the Dead Sea, inside hot springs, and in the guts of cows, they also live in more common environments. For example, new research shows that archaea are abundant in the soil. They also live among the plankton in the ocean ( Figure 1.3). Therefore, scientists are just beginning to discover some of the important roles that archaea have in the environment. Thermococcus gammatolerans are another type of archaea. | text | null |
L_0703 | types of mollusks | T_3463 | There are approximately 160,000 living species and probably 70,000 extinct species of mollusks. They are typically divided into ten classes, of which two are extinct. The major classes of living mollusks include gastropods, bivalves, and cephalopods ( Figure 1.1). | text | null |
L_0703 | types of mollusks | T_3464 | Gastropods include snails and slugs. They use their foot to crawl. They have a well-developed head. There are many thousands of species of sea snails and sea slugs, as well as freshwater snails, freshwater limpets, land snails and land slugs. Gastropods live in many diverse habitats, from gardens to deserts and mountains. They also live in rivers, lakes and the ocean. Most shelled gastropods have a one-piece shell that is typically coiled or spiraled, but not all gastropods have shells. Gastropods have no sense of hearing, but they can see and have a keen sense of smell. In land-based gastropods, the olfactory organs (for smell) are the most important. These are located on the tentacles. | text | null |
L_0703 | types of mollusks | T_3465 | Bivalves include clams, scallops, oysters, and mussels. As their name implies, they have two parts of their shell, which can open and close. Bivalves live in both marine and freshwater habitats. Most bivalves have a pair of large gills that enable them to extract oxygen from the water (to breathe) and to capture food. Water is drawn into the bivalve and washes over the gills. Mucus on the gills helps capture food and cilia transfer the food particles to the mouth. Once in the mouth, food passes into the stomach to be digested. Bivalves have a mouth, heart, intestine, gills, and stomach, but no head. Bivalves have a muscular foot, which in many species such as clams, is used to anchor their body to a surface or dig down into the sand. | text | null |
L_0703 | types of mollusks | T_3466 | Cephalopods include the octopus and squid. They have a prominent head and a well-developed brain. Typically the foot has been modified into a set of arms or tentacles. Members of this class can change color. They can also change texture and body shape, and, and if those camouflage techniques dont work, they can still "disappear" in a cloud of ink. Cephalopods have three hearts that pump blue blood, theyre jet powered by their muscular foot, and theyre found in all oceans of the world. Cephalopods are thought to be the most intelligent of invertebrates. They have eyes and other senses that rival those of humans. Many cephalopods are active and efficient predators. What features do you think allows for this? (left) An example of a gastropod species, the ostrich foot. (right) A Caribbean reef squid, an example of a cephalopod. | text | null |
L_0706 | vascular seedless plants | T_3476 | For these plants, the name says it all. Vascular seedless plants have vascular tissue but do not have seeds. Remember that vascular tissue is specialized tissue that transports water and nutrients throughout the plant. The development of vascular tissue allowed these plants to grow much taller than nonvascular plants, forming ancient swamp forests. Most of these large vascular seedless plants are now extinct, but their smaller relatives still remain. Vascular tissue includes xylem, which transports water from the roots to the rest of the plant; and phloem, which transports sugars and nutrients from the leaves throughout the plant. Seedless vascular plants include: 1. 2. 3. 4. Clubmosses. Ferns. Horsetails. Whisk ferns. | text | null |
L_0706 | vascular seedless plants | T_3477 | Clubmosses are so named because they can look similar to mosses ( Figure 1.1). Clubmosses are not true mosses, though, because they have vascular tissue. The club part of the name comes from club-like clusters of sporangia found on the plants. One type of clubmoss is called the "resurrection plant" because it shrivels and turns brown when it dries out but then quickly turns green when watered again. Clubmosses can resemble mosses; how- ever, clubmosses have vascular tissue, while mosses do not. | text | null |
L_0706 | vascular seedless plants | T_3478 | Ferns are the most common seedless vascular plants ( Figure 1.2). They usually have large divided leaves called fronds. In most ferns, fronds develop from a curled-up formation called a fiddlehead ( Figure 1.3). The fiddlehead looks like the curled decoration on the end of a stringed instrument, such as a fiddle. Leaves unroll as the fiddleheads grow and expand. Ferns grow in a variety of habitats, ranging in size from tiny aquatic species to giant tropical plants. | text | null |
L_0706 | vascular seedless plants | T_3479 | Horsetails have hollow, ribbed stems and are often found in marshes ( Figure 1.4). Whorls of tiny leaves around the stem make the plant look like a horses tail, but these soon fall off and leave a hollow stem that can perform photosynthesis. This is unusual since photosynthesis most often occurs in leaves. The stems are rigid and rough to the touch because they are coated with a scratchy mineral. Because of their scratchy texture, these plants were once used as scouring pads for cleaning dishes. | text | null |
L_0706 | vascular seedless plants | T_3480 | Whisk ferns have green branching stems with no leaves, so they resemble a whisk broom ( Figure 1.5). Another striking feature of the whisk ferns is its spherical yellow sporangia. Ferns are common in the understory of the tropical rainforest. The first leaves of most ferns appear curled up into fiddleheads. | text | null |
L_0706 | vascular seedless plants | T_3480 | Whisk ferns have green branching stems with no leaves, so they resemble a whisk broom ( Figure 1.5). Another striking feature of the whisk ferns is its spherical yellow sporangia. Ferns are common in the understory of the tropical rainforest. The first leaves of most ferns appear curled up into fiddleheads. | text | null |
L_0707 | vertebrate characteristics | T_3481 | Vertebrates are animals with backbones. These include fish, amphibians, reptiles, birds, and mammals. | text | null |
L_0707 | vertebrate characteristics | T_3482 | The primary feature shared by all vertebrates is the vertebral column, or backbone. The vertebral column protects the spinal cord. Other typical vertebrate traits include: The cranium (skull) to protect the brain. The brain is attached to the spinal cord. An internal skeleton. The internal skeleton supports the animal, protects internal organs, and allows for movement. A defined head region with a brain. The head region has an accumulation of sense organs. Living vertebrates range in size from a carp species, as little as 0.3 inches, to the blue whale, which can be as large as 110 feet ( Figure 1.1). A species of carp and an image of the blue whale (a mammal), the largest liv- ing vertebrate, reaching up to 110 feet long. Shown below it is the smallest whale species, Hectors dolphin (about 5 feet in length), and beside it is a human. These images are not to scale. The carp is greatly exaggerated in size and is even smaller than depicted when compared to the blue whale. | text | null |
L_0707 | vertebrate characteristics | T_3483 | Vertebrates, or subphylum Vertebrata, are all members of the phylum Chordata. Although there is some disagreement on how to classify animals, the traditional system divides the vertebrates into seven classes ( Table 1.1). Class Agnatha Chondrichthyes Common Name Jawless fishes Cartilaginous fishes Osteichthyes Amphibia Bony fishes Amphibians Reptilia Reptiles Aves Birds Characteristics No jaws or scales. Skeletons consisting of hard, rubber-like carti- lage. Skeletons made of bone. Spend part of their lives under water and part on land Have lungs to breathe on land, skin that does not need to be kept wet, and produces a watertight (amniotic) egg. Produces watertight eggs and protects eggs from predators. Examples Lampreys, hagfish Sharks, rays Tuna, bass, salmon, trout Frogs, toads, salamanders Turtles, snakes, lizards, alligators Ostriches, penguins, flamingos, parrots Class Mammalia Common Name Mammals Characteristics Nourish young with milk through mammary glands. Examples Dogs, cats, bears, mon- keys, humans | text | null |
L_0711 | what are biomes | T_3494 | Tropical rainforests and deserts are two familiar types of biomes. A biome is an area with similar populations of organisms. This can easily be seen with a community of plants and animals. Remember that a community is all of the populations of different species that live in the same area and interact with one another. Different biomes, such as a forest ( Figure 1.1) or a desert, obviously have different communities of plants and animals. How are the plants and animals different in the rainforest than those in the desert? Why do you think they are so different? The differences in the biomes are due to differences in the abiotic factors, especially climate. Climate is the typical weather in an area over a long period of time. The climate includes the amount of rainfall and the average temperature in the region. Obviously, the climate in the desert is much different than the climate in the rainforest. As a result, different types of plants and animals live in each biome. There are into two major groups of biomes: 1. Terrestrial biomes, which are land-based, such as deserts and forests. 2. Aquatic biomes, which are water-based, such as ponds and lakes. The abiotic factors, such as the amount of rainfall and the temperature, are going to influence other abiotic factors, such as the quality of the soil. This, in turn, is going to influence the plants that migrate into the ecosystem and thrive Tropical rainforest landscape in Hawaii. Notice how the plants are different from those in the desert. in that biome. Recall that migration is the movement of an organism into or out of a population. It can also refer to a whole new species moving into a habitat. The type of plants that live in a biome are going to attract a certain type of animal to that habitat. It is the interaction of the abiotic and biotic factors that describe a biome and ecosystem. In aquatic biomes, abiotic factors such as salt, sunlight and temperature play significant roles. For example, a hot dry biome is going to be completely different from a moderate wet biome. The soil quality will be different. Together, these will result in different plants being able to occupy each biome. Different plants will attract different animals (herbivores) to eat these plants. These animals, in turn, will attract different (carnivores) animals to eat the herbivores. So it is the abiotic factors that determine the biotic factors of an ecosystem, and together these define the biome. | text | null |
L_0712 | what is science | T_3495 | Are you like the teen in Figure 1.1? Do you ever wonder why things happen? Do you like to find out how things work? If so, then you are already thinking like a scientist. Scientists also wonder how and why things happen. They are curious about the world. To answer their questions, they make many observations. Then they use logic to draw general conclusions. | text | null |
L_0712 | what is science | T_3496 | Drawing general conclusions from many individual observations is called induction. It is a hallmark of scientific thinking. To understand how induction works, think about this simple example. Assume you know nothing about gravity. In fact, pretend youve never even heard of gravity. Perhaps you notice that whenever you let go of an object it falls to the ground. For example, you drop a book, and it crashes to the floor. Your pencil rolls to the edge of the desk and down it goes. You throw a ball into the air, and it falls back down. Based on many such observations (Figure 1.2), you conclude that all objects fall to the ground. Now assume that someone gives you your first-ever helium balloon. You discover that it rises up into the air if you dont hold on to it. Based on this new observation, do you throw out your first idea about falling objects? No; you decide to observe more helium balloons and try to find other objects that fall up instead of down. Eventually, you come to a better understanding based on all your observations. You conclude that objects heavier than air fall to the ground but objects lighter than air do not. Your new conclusion is better because it applies to a wider range of observations. You can learn more about induction, including its limits, by watching the video at this link: http://w MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0712 | what is science | T_3496 | Drawing general conclusions from many individual observations is called induction. It is a hallmark of scientific thinking. To understand how induction works, think about this simple example. Assume you know nothing about gravity. In fact, pretend youve never even heard of gravity. Perhaps you notice that whenever you let go of an object it falls to the ground. For example, you drop a book, and it crashes to the floor. Your pencil rolls to the edge of the desk and down it goes. You throw a ball into the air, and it falls back down. Based on many such observations (Figure 1.2), you conclude that all objects fall to the ground. Now assume that someone gives you your first-ever helium balloon. You discover that it rises up into the air if you dont hold on to it. Based on this new observation, do you throw out your first idea about falling objects? No; you decide to observe more helium balloons and try to find other objects that fall up instead of down. Eventually, you come to a better understanding based on all your observations. You conclude that objects heavier than air fall to the ground but objects lighter than air do not. Your new conclusion is better because it applies to a wider range of observations. You can learn more about induction, including its limits, by watching the video at this link: http://w MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0712 | what is science | T_3497 | The above example shows how science generally advances. New evidence is usually used to improve earlier ideas rather than entirely replace them. In this way, scientists gradually refine their ideas and increase our understanding of the world. On the other hand, sometimes science advances in big leaps. This has happened when a scientist came up with a completely new way of looking at things. For example, Albert Einstein came up with a new view of gravity. He said it was really just a dent in the fabric of space and time. Different conclusions can be drawn from the same observations, and its not possible to tell which one is correct. For example, based on observations of the sun moving across the sky, people in the past couldnt tell whether the sun orbits Earth or Earth orbits the sun. Both models of the solar system are pictured in Figure 1.3. It wasnt until strong telescopes were invented that people could make observations that let them choose the correct idea. Not sure which idea is correct? You can learn more by watching the student-created video at this link: | text | null |
L_0712 | what is science | T_3498 | Some ideas in science gain the status of theories. Scientists use the term "theory" differently than it is used in everyday language. You might say, "I think the dog ate my homework, but its just a theory." In other words, its just one of many possible explanations for the missing work. However, in science, a theory is much more than that. | text | null |
L_0712 | what is science | T_3499 | A scientific theory is a broad explanation that is widely accepted because it is supported by a great deal of evidence. An example is the kinetic theory of matter. According to this theory, all matter consists of tiny particles that are in constant motion. Particles move at different speeds in matter in different states. You can see this in Figure 1.4 and at the following URL: http://preparatorychemistry.com/Bishop_KMT_frames.htm . Particles in solids move the least; particles in gases move the most. These differences in particle motion explain why solids, liquids, and gases look and act differently. Think about how ice and water differ, or how water vapor differs from liquid water. The kinetic theory of matter explains the differences. You can learn more about this theory in the chapter States of Matter. | text | null |
L_0712 | what is science | T_3500 | Scientific laws are often confused with scientific theories, but they are not the same thing. A scientific law is a statement describing what always happens under certain conditions in nature. It answers "how" questions but not "why" questions. An example of a scientific law is Newtons law of gravity. It describes how all objects attract each other. It states that the force of attraction is greater for objects that are closer together or have more mass. However, the law of gravity doesnt explain why objects attract each other in this way. Einsteins theory of general relativity explains why. You can learn more about Newtons law of gravity and Einsteins theory in the chapter Forces, and at the following link: . | text | null |
L_0712 | what is science | T_3501 | People have wondered about the natural world for as long as there have been people. So its no surprise that modern science has roots that go back thousands of years. The Table 1.1 describes just a few milestones in the history of science. A much more detailed timeline is available at the link below. Often, new ideas were not accepted at first because they conflicted with accepted views of the world. A good example is Copernicus idea that the sun is the center of the solar system. This idea was rejected at first because people firmly believed that Earth was the center of the solar system and the sun moved around it. Date Scientific Discovery Date 3500 BC Mesopotamian calendar 600 BC Thales 350 BC Aristotle 400 AD to 1000 AD Early Chinese Seismograph Scientific Discovery Several ancient civilizations studied astronomy. They recorded their observations of the movements of stars, the sun, and the moon. We still use the calendar developed by the Mesopotamians about 5500 years ago. It is based on cycles of the moon. The ancient Greek philosopher Thales proposed that natural events, such as lightning and earthquakes, have natural causes. Up until then, people blamed such events on gods or other supernatural causes. Thales has been called the "father of science" for his ideas about the natural world. The Greek philosopher Aristotle argued that truth about the natural world can be discovered through observa- tion and induction. This idea is called empiricism. Aristotles empiricism laid the foundation for the meth- ods of modern science. When Europe went through the Dark Ages, European science withered. However, in other places, science still flourished. For example: In North Africa, the scientist Alhazen studied light. He used experiments to test competing theories about light. In China, scientists invented compasses. They also invented seismographs to measure earth- quakes. They studied astronomy as well. Date Mid-1500s to late 1600s Scientific Discovery The Scientific Revolution occurred in Europe. This was the beginning of modern Western science. Many scientific advances were made during this time. Copernicus proposed that the sun, not Earth, is the center of the solar system. Galileo improved the telescope and made im- portant discoveries in astronomy. He discovered evidence that supported Copernicus theory. Newton proposed the law of gravity. Galileo 2001 Many scientists around the world worked together to complete the genetic sequence of human chromosomes. This amazing feat will help scientists understand, and perhaps someday cure, genetic diseases. Human Chromosomes | text | null |
L_0712 | what is science | T_3502 | Throughout history, women and people of color have rarely had the same chances as white males for education and careers in science. But they have still made important contributions to science. The Table 1.2 gives just a few examples of their contributions to physical science. More contributions are described at these links: Contributor Marie Curie (1867-1934) Description Marie Curie was the first woman to win a Nobel Prize. She won the 1903 Nobel Prize in physics for the discovery of radiation. She won the 1911 Nobel Prize in chemistry for discovering the elements radium and polonium. Contributor Lise Meitner (1878-1968) Description Lise Meitner was one of the scientists who discovered nuclear fission. This is the process that creates enor- mous amounts of energy in nuclear power plants. Irene Joliot-Curie (18971956) Irene Joliot-Curie, daughter of Marie Curie, won the 1935 Nobel prize in chemistry, along with her husband, for the synthesis of new radioactive elements. Maria Goeppert-Mayer (19061972) Maria Goeppert-Mayer was a co-winner of the 1963 Nobel prize in physics for discoveries about the struc- ture of the nucleus of the atom. Ada E. Yonath (1939present) Ada E. Yonath was a co-winner of the 2009 Nobel prize in chemistry. She made important discoveries about ribosomes, the structures in living cells where proteins are made. Contributor Shirley Ann Jackson (1946-present) Description Shirley Ann Jackson earned a doctoral degree in physics. She became the chair of the US Nuclear Regulatory Commission. Ellen Ochoa (1958-present) Ellen Ochoa is an inventor, research scientist, and NASA astronaut. She has flown several space missions. | text | null |
L_0713 | the scope of physical science | T_3503 | Physical science can be defined as the study of matter and energy. Matter refers to all the "stuff" that exists in the universe. It includes everything you can see and many things that you cannot see, including the air around you. Energy is what gives matter the ability to move and change. Energy can take many forms, such as electricity, heat, and light. Physical science can be divided into chemistry and physics. Chemistry focuses on matter and energy at the scale of atoms and molecules. Physics focuses on matter and energy at all scales, from atoms to outer space. | text | null |
L_0713 | the scope of physical science | T_3504 | Chemistry is the study of the structure, properties, and interactions of matter. Important concepts in chemistry include physical changes, such as water freezing, and chemical reactions, such as fireworks exploding. Chemistry concepts can answer all the questions on the left page of the notebook in Figure 1.5. Do you know the answers? | text | null |
L_0713 | the scope of physical science | T_3505 | Physics is the study of energy and how it interacts with matter. Important concepts in physics include motion, forces such as magnetism and gravity, and different forms of energy. Physics concepts can answer all the questions on the right page of the notebook in Figure 1.5. | text | null |
L_0713 | the scope of physical science | T_3506 | Physical science explains much of what you observe and do in your daily life. In fact, you depend on physical science for almost everything that makes modern life possible. You couldnt drive a car, text message, or send a tweet without decades of advances in chemistry and physics. You wouldnt even be able to turn on a light. Figure "hows" and "whys" about them as you read the rest of this book. | text | null |
L_0713 | the scope of physical science | T_3507 | People with training in physical science are employed in a variety of places. There are many career options. Just four are described in Figure 1.7. Many more are described at the URL below. Do any of these careers interest you? http://diplomaguide.com/article_directory/sh/page/Physical%20Science/sh/Job_Titles_and_Careers_List.html . | text | null |
L_0730 | pressure of fluids | T_3612 | All fluids exert pressure like the air inside a tire. The particles of fluids are constantly moving in all directions at random. As the particles move, they keep bumping into each other and into anything else in their path. These collisions cause pressure, and the pressure is exerted equally in all directions. When particles are crowded together in one part of their container, they quickly spread out to fill their container. They always move from an area of higher pressure to an area of lower pressure. Thats why air entering a tire quickly spreads throughout the tire. | text | null |
L_0730 | pressure of fluids | T_3613 | Pressure is the result of force acting on a given area. It can be represented by the equation: Pressure = Force Area Pressure shows how concentrated the force is on a given area. The smaller the area to which force is applied, the greater the pressure is. Think about pressing a pushpin, like the one in Figure 15.2, into a bulletin board. You apply force with your thumb to the broad head of the pushpin. However, the force that the pushpin applies to the bulletin board acts only over the tiny point of the pin. This is a much smaller area, so the pressure the point applies to the bulletin board is much greater than the pressure you apply with you thumb. As a result, the pin penetrates the bulletin board with ease. | text | null |
L_0730 | pressure of fluids | T_3614 | In the equation for pressure, force is expressed in newtons (N) and area is expressed in square meters (m2 ). Therefore, pressure is expressed in N/m2 , which is the SI unit for pressure. This unit is also called the pascal (Pa). It is named for the scientist Blaise Pascal, whose discovery about pressure in fluids is described later in this lesson. Pressure may also be expressed in the kilopascal (kPa), which equals 1000 pascals. For example, the correct air pressure inside a mountain bike tire is usually about 200 kPa. | text | null |
L_0730 | pressure of fluids | T_3615 | When you know how much force is acting on a given area, you can calculate the pressure that is being applied to the area using the equation for pressure given above. For example, assume that a big rock weighs 500 newtons and is resting on the ground on an area of 0.5 m2 . The pressure exerted on the ground by the rock is: Pressure = 500 N = 1000 N/m2 = 1000 Pa, or 1 kPa 0.5 m2 Sometimes pressure but not force is known. To calculate force, the equation for pressure can be rewritten as: Force = Pressure Area For example, suppose another rock exerts 2 kPa of pressure over an area of 0.3 m2 . How much does the rock weigh? Change 2 kPa to 2000 N/m2 and substitute it for pressure in the force equation: Force (Weight) = 2000 N/m2 0.3 m2 = 600 N Problem Solving Problem: A break dancer has a weight of 450 N. She is balancing on the ground on one hand. The palm of her hand has an area of 0.02 m2 . How much pressure does her hand exert on the ground? Solution: Use the equation Pressure = Force Area . Pressure = 450 N = 22500 Pa, or 22.5 kPa 0.02 m2 You Try It! Problem: If the break dancer lies down on the ground on her back, her weight is spread over an area of 0.75 m2 . How much pressure does she exert on the ground in this position? | text | null |
L_0730 | pressure of fluids | T_3616 | Both the water in the ocean and the air in the atmosphere exert pressure because of their moving particles. The ocean and atmosphere also illustrate two factors that affect pressure in fluids: depth and density. A fluid exerts more pressure at greater depths. Deeper in a fluid, all of the fluid above results in more weight pressing down. This causes greater pressure. Denser fluids such as water exert more pressure than less dense fluids such as air. The particles of denser fluids are closer together, so there are more collisions in a given area. This is illustrated in Figure 15.3 for water and air. | text | null |
L_0730 | pressure of fluids | T_3617 | As you go deeper in the ocean, the pressure exerted by the water increases steadily. The diagram in Figure 15.4 shows how pressure changes with depth. For every additional meter below the surface, pressure increases by 10 kPa. At 30 meters below the surface, the pressure is double the pressure at the surface. At a depth greater than 500 meters, the pressure is too great for humans to withstand without special equipment to protect them. Around 9000 meters below the surface, in the deepest part of the ocean, the pressure is tremendous. You can see a video demonstration of changes in water pressure with depth at this URL: (0:42). MEDIA Click image to the left or use the URL below. URL: Because of the pressure of the water, divers who go deeper than about 40 meters below the surface must return to the surface slowly and stop for several minutes at one or more points in their ascent. Thats what the divers in Figure water as they swim closer to the surface. If they were to rise to the surface too quickly, the gases dissolved in their blood would form bubbles and cause serious health problems. | text | null |
L_0730 | pressure of fluids | T_3618 | Like water in the ocean, air in the atmosphere exerts pressure that increases with depth. Most gas molecules in the atmosphere are pulled close to Earths surface by gravity. As a result, air pressure decreases quickly at lower altitudes and then more slowly at higher altitudes. This is illustrated in Figure 15.6. Air pressure is greatest at sea level, where the depth of the atmosphere is greatest. At higher altitudes, the pressure is less because the depth of the atmosphere is less. For example, on top of Mount Everest, the tallest mountain on Earth, air pressure is only about one-third of the pressure at sea level. At such high altitudes, low air pressure makes it hard to breathe and is dangerous to human health. The pressure of air in the atmosphere allows you to do many things, from sipping through a straw to simply breathing (see Figure 15.7). When you first suck on a straw, you remove air from the straw, so the air pressure in the straw is lower than For more examples of how we use air pressure, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0730 | pressure of fluids | T_3618 | Like water in the ocean, air in the atmosphere exerts pressure that increases with depth. Most gas molecules in the atmosphere are pulled close to Earths surface by gravity. As a result, air pressure decreases quickly at lower altitudes and then more slowly at higher altitudes. This is illustrated in Figure 15.6. Air pressure is greatest at sea level, where the depth of the atmosphere is greatest. At higher altitudes, the pressure is less because the depth of the atmosphere is less. For example, on top of Mount Everest, the tallest mountain on Earth, air pressure is only about one-third of the pressure at sea level. At such high altitudes, low air pressure makes it hard to breathe and is dangerous to human health. The pressure of air in the atmosphere allows you to do many things, from sipping through a straw to simply breathing (see Figure 15.7). When you first suck on a straw, you remove air from the straw, so the air pressure in the straw is lower than For more examples of how we use air pressure, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0730 | pressure of fluids | T_3618 | Like water in the ocean, air in the atmosphere exerts pressure that increases with depth. Most gas molecules in the atmosphere are pulled close to Earths surface by gravity. As a result, air pressure decreases quickly at lower altitudes and then more slowly at higher altitudes. This is illustrated in Figure 15.6. Air pressure is greatest at sea level, where the depth of the atmosphere is greatest. At higher altitudes, the pressure is less because the depth of the atmosphere is less. For example, on top of Mount Everest, the tallest mountain on Earth, air pressure is only about one-third of the pressure at sea level. At such high altitudes, low air pressure makes it hard to breathe and is dangerous to human health. The pressure of air in the atmosphere allows you to do many things, from sipping through a straw to simply breathing (see Figure 15.7). When you first suck on a straw, you remove air from the straw, so the air pressure in the straw is lower than For more examples of how we use air pressure, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0730 | pressure of fluids | T_3619 | Some of the earliest scientific research on fluids was conducted by a French mathematician and physicist named Blaise Pascal (16231662). Pascal was a brilliant thinker. While still a teen, he derived an important theorem in mathematics and also invented a mechanical calculator. One of Pascals contributions to our understanding of fluids is known as Pascals law. | text | null |
L_0730 | pressure of fluids | T_3620 | Pascals law states that a change in pressure at any point in an enclosed fluid is transmitted equally throughout the fluid. A simple example may help you understand Pascals law. Assume you have a small packet of ketchup, like the one in Figure 15.8. If you open one end of the packet and then apply pressure to the other end, what will happen? Ketchup will squirt out the open end. The pressure you exert on the packet is transmitted throughout the ketchup. When the pressure reaches the open end, it forces ketchup out of the packet. To see a video about Pascals law, go to this URL: (2:59). MEDIA Click image to the left or use the URL below. URL: The ability of fluids to transmit pressure in this way can be very useful besides providing ketchup for your French fries! For example, the hydraulic car lift in Figure 15.9 contains fluid that transmits pressure and raises a car so a mechanic can work on it from below. The fluid used, usually a type of oil, cant be compressed. Force is placed on the fluid in a narrow cylinder, and the fluid transmits the pressure throughout the hydraulic system. When the pressure reaches the fluid in the wide cylinder, it forces the cylinder upward, along with the car. The force applied to the car is much greater than the force applied to the fluid in the narrow cylinder. Why? When pressure acts over a wider area, it creates a larger force. Thats because force equals pressure multiplied by the area over which it acts, as you saw above in the equation Force = Pressure Area. Besides hydraulic car lifts, other equipment that uses hydraulic fluid to increase force ranges from brakes to bull- dozers. Even the controls in airplanes use hydraulics. Because of the force-multiplying effect, a flick of a switch can raise or lower heavy wing flaps or landing gear. You can see animations of hydraulic systems at these URLs: http://science.howstuffworks.com/transport/engines-equipment/hydraulic1.htm http://home.wxs.nl/~brink494/hydr_e.htm | text | null |
L_0730 | pressure of fluids | T_3620 | Pascals law states that a change in pressure at any point in an enclosed fluid is transmitted equally throughout the fluid. A simple example may help you understand Pascals law. Assume you have a small packet of ketchup, like the one in Figure 15.8. If you open one end of the packet and then apply pressure to the other end, what will happen? Ketchup will squirt out the open end. The pressure you exert on the packet is transmitted throughout the ketchup. When the pressure reaches the open end, it forces ketchup out of the packet. To see a video about Pascals law, go to this URL: (2:59). MEDIA Click image to the left or use the URL below. URL: The ability of fluids to transmit pressure in this way can be very useful besides providing ketchup for your French fries! For example, the hydraulic car lift in Figure 15.9 contains fluid that transmits pressure and raises a car so a mechanic can work on it from below. The fluid used, usually a type of oil, cant be compressed. Force is placed on the fluid in a narrow cylinder, and the fluid transmits the pressure throughout the hydraulic system. When the pressure reaches the fluid in the wide cylinder, it forces the cylinder upward, along with the car. The force applied to the car is much greater than the force applied to the fluid in the narrow cylinder. Why? When pressure acts over a wider area, it creates a larger force. Thats because force equals pressure multiplied by the area over which it acts, as you saw above in the equation Force = Pressure Area. Besides hydraulic car lifts, other equipment that uses hydraulic fluid to increase force ranges from brakes to bull- dozers. Even the controls in airplanes use hydraulics. Because of the force-multiplying effect, a flick of a switch can raise or lower heavy wing flaps or landing gear. You can see animations of hydraulic systems at these URLs: http://science.howstuffworks.com/transport/engines-equipment/hydraulic1.htm http://home.wxs.nl/~brink494/hydr_e.htm | text | null |
L_0730 | pressure of fluids | T_3621 | Another important law about pressure in fluids was described by Daniel Bernoulli, a Swiss mathematician who lived during the 1700s. Bernoulli used mathematics to arrive at his law. Bernoullis law states that pressure in a moving fluid is less when the fluid is moving faster. For an animation of this law, go to the URL below. Bernoullis law explains how the wings of both airplanes and birds create lift that allows flight (see Figure 15.10). The shape of the wings causes air to flow more quickly and air pressure to be lower above the wings than below them. This allows the wings to lift the plane or bird above the ground against the pull of gravity. A spoiler on a race car, like the one in Figure 15.10, works in the opposite way. Its shape causes air to flow more slowly and air pressure to be greater above the spoiler than below it. As a result, air pressure pushes the car downward, giving its wheels better traction on the track. | text | null |
L_0730 | pressure of fluids | T_3622 | Northern California has a storied, 500-year history of sailing. But despite this rich heritage, scientists and boat designers continue to learn more each day about what makes a sail boat move. Contrary to what you might expect, the physics of sailing still present some mysteries to modern sailors. For more information on the physics of sailing, see http://science.kqed.org/quest/video/the-physics-of-sailing/ . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0745 | scientific investigation | T_3737 | Scientists investigate the world in many ways. In different fields of science, researchers may use different methods and be guided by different theories and hypotheses. However, most scientists, including physical scientists, usually follow the general approach shown in Figure 2.1. This approach typically includes the following steps: Identify a research question or problem. Form a hypothesis. Gather evidence, or data, to test the hypothesis. Analyze the evidence. Decide whether the evidence supports the hypothesis Draw conclusions. Communicate the results. Scientists may follow these steps in a different sequence. Or they may skip or repeat some of the steps. Which steps are repeated in Figure 2.1? | text | null |
L_0745 | scientific investigation | T_3738 | A scientific investigation begins with a question or problem. Often, the question arises because a scientist is curious about something she has observed. An observation is any information that is gathered with the senses. People often have questions about things they see, hear, or observe in other ways. For example, a teen named Tara has a bracelet with a magnetic clasp, like the one shown in Figure 2.2. Tara has noticed that the two magnets in the clasp feel harder to pull apart on cold days than on warm days. She wonders whether temperature affects the strength of a magnet. | text | null |
L_0745 | scientific investigation | T_3739 | Tara is curious. She decides to investigate. She begins by forming a hypothesis. A hypothesis is a potential answer to a question that can be tested by gathering information. If it isnt possible to gather evidence to test an answer, then it cannot be used as a scientific hypothesis. In fact, the question it addresses may not even be answerable by science. For example, in the childrens television show Sesame Street, there was a large Snuffalufagus (kind of like an elephant). But Snuffy would disappear whenever people came around. So if someone said "Is there a Snuffy on Sesame Street?," that question would be unanswerable by science, since there isnt any test that can be performed because Snuffy would disappear as soon as a scientist showed up. Can you think of other examples of questions outside the realm of science? This important distinction, that evidence taken in by observation is experimented on by a scientist, is what separates legitimate science from other things which may pretend to be science. Fields which claim to be scientific but dont use the scientific method are called "pseudoscience." If a person cant gather data through some sort of instrument or sense information, they cant form a scientific conclusion. If there is no way to prove the hypothesis false, there is no scientific claim either. For example, if a friend told you that Snuffy visited him every day, but he was invisible whenever anyone walked into the room, this claim is not scientific, since there is no way to prove him false. Developing a hypothesis may require creativity as well as reason. However, in Taras case, the hypothesis is simple. She hypothesizes that a magnet is stronger at lower temperatures. Based on her hypothesis, Tara makes a prediction. If she cools a magnet, then it will pick up more metal objects, such as paper clips. Predictions are often phrased as "if-then" statements like this one. Is Taras prediction correct? She decides to do an experiment. | text | null |
L_0745 | scientific investigation | T_3740 | An experiment is a controlled scientific study of specific variables. A variable is a factor that can take on different values. There must be at least two variables in an experiment. They are called the manipulated variable and the responding variable. The manipulated variable (also called the "independent variable") is a factor that is changed by the re- searcher. For example, Tara will change the temperature of a magnet. Temperature is the manipulated variable in her experiment. The responding variable (also called the "dependent variable") is a factor that the researcher predicts will change if the manipulated variable changes. Tara predicts the number of paper clips attracted by the magnet will be greater at lower temperatures. Number of paper clips is the responding variable in her experiment. Tara wonders what other variables might affect the strength of a magnet. She thinks that the size and shape of a magnet might affect its strength. These are variables that must be controlled. A control is a variable that is held constant so it wont influence the outcome of an experiment. By using the same magnet at different temperatures, Tara is controlling for any magnet variables that might affect the results. What other variables should Tara control? (Hint: What about the paper clips?) | text | null |
L_0745 | scientific investigation | T_3740 | An experiment is a controlled scientific study of specific variables. A variable is a factor that can take on different values. There must be at least two variables in an experiment. They are called the manipulated variable and the responding variable. The manipulated variable (also called the "independent variable") is a factor that is changed by the re- searcher. For example, Tara will change the temperature of a magnet. Temperature is the manipulated variable in her experiment. The responding variable (also called the "dependent variable") is a factor that the researcher predicts will change if the manipulated variable changes. Tara predicts the number of paper clips attracted by the magnet will be greater at lower temperatures. Number of paper clips is the responding variable in her experiment. Tara wonders what other variables might affect the strength of a magnet. She thinks that the size and shape of a magnet might affect its strength. These are variables that must be controlled. A control is a variable that is held constant so it wont influence the outcome of an experiment. By using the same magnet at different temperatures, Tara is controlling for any magnet variables that might affect the results. What other variables should Tara control? (Hint: What about the paper clips?) | text | null |
L_0745 | scientific investigation | T_3741 | Not everything in physical science is as easy to study as magnets and paper clips. Sometimes its not possible or desirable to do experiments. There are some things with which a person simply cannot experiment. A distant star is a good example. Scientists study stars by making observations with telescopes and other devices. Often, its important to investigate a problem in the real world instead of in a lab. Scientists do field studies to gather real-world evidence. You can see an example of a field study in Figure 2.3. | text | null |
L_0745 | scientific investigation | T_3742 | Researchers should always communicate their results. By sharing their results, they may be able to get helpful feedback from other scientists. Reporting on research also lets other scientists repeat the investigation to see whether they get the same results. Getting the same results when an experiment is repeated is called replication. If results can be replicated, it means they are more likely to be correct. Replication of investigations is one way that a hypothesis may eventually become a theory. Scientists can share their results in various ways. For example, they can write articles for peer-reviewed science journals. Peer review means that the work is analyzed by peers, in this case other scientists. This is the best way to ensure that the results are accurate and reported honestly. Another way to share results with other scientists is with presentations at scientific meetings (see Figure 2.4). Creating websites and writing articles for newspapers and magazines are ways to share research with the public. Why might this be important? | text | null |
L_0745 | scientific investigation | T_3743 | Ethics refers to rules for deciding between right and wrong. Ethics is an important issue in science. Scientific research must be guided by ethical rules, including those listed below. The rules help ensure that the research is done safely and the results are reliable. Following the rules furthers both science and society. You can learn more about the role of ethics in science by following the links at this URL: Ethical Rules for Scientific Research Scientific research must be reported honestly. It is wrong and misleading to make up or change research results. Scientific researchers must try to see things as they really are. They should avoid being biased by the results they expect or want to get. Researchers must be careful. They should take pains to avoid errors in their data. Researchers studying human subjects must tell their subjects about any potential risks of the research. Subjects also must be told that they can refuse to participate in the research. Researchers must inform coworkers, students, and members of the community about any risks of the research. They should proceed with the research only if they have the consent of these groups. Researchers studying living animals must treat them humanely. They should provide for their needs and do what they can to avoid harming them (see Figure 2.5). Sometimes, science can help people make ethical decisions in their own lives, although science is unlikely to be the only factor involved. For example, scientific evidence shows that human actions are affecting Earths climate. Actions such as driving cars are causing Earth to get warmer. Does this mean that it is unethical to drive a car to work or school? What if driving is the only way to get there? As this example shows, ethical decisions are likely to be influenced by many factors, not just science. Can you think of other factors that might affect ethical decisions such as this one? | text | null |
L_0746 | science skills | T_3744 | One of the most important aspects of measuring is the system of units used for measurement. Remember the Mars Climate Orbiter that opened this chapter? It shows clearly why a single system of measurement units is needed in science. | text | null |
L_0746 | science skills | T_3745 | The measurement system used by most scientists is the International System of Units, or SI. Table 2.2 lists common units in this system. SI is easy to use because everything is based on the number 10. Basic units are multiplied or divided by powers of ten to arrive at bigger or smaller units. Prefixes are added to the names of the basic units to indicate the powers of ten. For example, the meter is the basic unit of length. The prefix kilo- means 1000, so a kilometer is 1000 meters. Can you infer what the other prefixes in the table mean? If not, you can find out at this URL: http://physics.nist.gov/cuu/Units/prefixes.html . Variable Length Volume Mass Basic SI Unit (English Equivalent) meter (m) (1 m = 39.37 in) cubic meter (m3 ) (1 m3 = 1.3 yd3 ) gram (g) (1 g = 0.04 oz) Related SI Units Equivalent Units kilometer (km) decimeter (dm) centimeter (cm) millimeter (mm) micrometer (m) nanometer (nm) liter (L) milliliter (mL) kilogram (kg) milligram (mg) = 1000 m = 0.1 m = 0.01 m = 0.001 m = 0.000001 m = 0.000000001 m = 1 dm3 = 1 cm3 = 1000 g = 0.001 g The SI system has units for other variables in addition to the three shown here in Table 2.2. Some of these other units are introduced in later chapters. Problem Solving Problem: Use information in Table 2.2 to convert 3 meters to inches. Solution: 3 m = 3 39.37 in = 118.11 in You Try It! Problem: Rod needs to buy 1 m of wire for a science experiment. The wire is sold by the yard, not the meter. If he buys 1 yd of wire, will he have enough? (Hint: How many inches are there in 1 yd? In 1 m?) | text | null |
L_0746 | science skills | T_3746 | The SI scale for measuring temperature is the Kelvin scale. However, some scientists use the Celsius scale instead. If you live in the U.S., you are probably more familiar with the Fahrenheit scale. Table 2.3 compares all three temperature scales. What is the difference between the boiling and freezing points of water on each of these scales? Scale Kelvin Celsius Fahrenheit Freezing Point of Water 273 K 0C 32F Boiling Point of Water 373 K 100C 212F Each 1-degree change on the Kelvin scale is equal to a 1-degree change on the Celsius scale. This makes it easy to convert measurements between Kelvin and Celsius. For example, to go from Celsius to Kelvin, just add 273. How would you convert a temperature from Kelvin to Celsius? Converting between Celsius and Fahrenheit is more complicated. The following conversion factors are used: Celsius ! Fahrenheit : ( C 1.8) + 32 = F Fahrenheit ! Celsius : ( F 32) 1.8 = C Problem Solving Problem: Convert 10C to Fahrenheit. Solution: (10C 1.8) + 32 = 50F You Try It! Problem: The weather forecaster predicts a high temperature today of 86F. What will the temperature be in Celsius? | text | null |
L_0746 | science skills | T_3747 | Measuring devices must be used correctly to get accurate measurements. Figure 2.6 shows the correct way to use a graduated cylinder to measure the volume of a liquid. Follow these steps when using a graduated cylinder to measure liquids: Place the cylinder on a level surface before adding liquid. Move so your eyes are at the same level as the top of the liquid in the cylinder. Read the mark on the glass that is at the lowest point of the curved surface of the liquid. This is called the meniscus. At the URLs below, you can see the correct way to use a metric ruler to measure length and a beam balance to measure mass. (beam balance) (5:14) | text | null |
L_0746 | science skills | T_3748 | Measurements should be both accurate and precise. Accuracy is how close a measurement is to the true value. For example, 66 mL is a fairly accurate measure- ment of the liquid in Figure 2.6. Precision is how exact a measurement is. A measurement of 65.5 mL is more precise than a measurement of 66 mL. But in Figure 2.6, it is not as accurate. You can think of accuracy and precision in terms of a game like darts. If you are aiming for the bulls-eye and get all of the darts close to it, you are being both accurate and precise. If you get the darts all close to each other somewhere else on the board, you are precise, but not accurate. And finally, if you get the darts spread out all over the board, you are neither accurate nor precise. | text | null |
L_0746 | science skills | T_3749 | Record keeping is very important in scientific investigations. Follow the tips below to keep good science records. Use a bound laboratory notebook so pages will not be lost. Write in ink for a permanent record. Record the steps of all procedures. Record all measurements and observations. Use drawings as needed. Date all entries, including drawings. | text | null |
L_0746 | science skills | T_3750 | Doing science often requires calculations. Converting units is just one example. Calculations are also needed to find derived quantities. | text | null |
L_0746 | science skills | T_3751 | Derived quantities are quantities that are calculated from two or more different measurements. Examples include area and volume. Its easy to calculate these quantities for a simple shape. For a rectangular solid, like the one in Figure 2.7, the formulas are: Area (of each side) = length width (l w) Volume = length width height (l w h) Helpful Hints When calculating area and volume, make sure that: all the measurements have the same units. answers have the correct units. Area should be in squared units, such as cm2 ; volume should be in cubed units, such as cm3 . Can you explain why? Naturally, not all derived quantities will have the same types of units. In the examples above, the only fundamental unit used was meters for the length of one of the sides of the box. However, if you had a quantity like speed (a derived quantity), it would be equal to distance traveled (which is meters) divided by the amount of time you spent traveling that distance (which is in seconds). Therefore your speed would be measured in meters per second. | text | null |
L_0746 | science skills | T_3752 | Assume you are finding the area of a rectangle with a length of 6.8 m and a width of 6.9 m. When you multiply the length by the width on your calculator, the answer you get is 46.92 m2 . Is this the correct answer? No; the correct answer is 46.9 m2 . The correct answer must be rounded down so there is just one digit to the right of the decimal point. Thats because the answer cannot have more digits to the right of the decimal point than any of the original measurements. Using extra digits implies a greater degree of precision than actually exists. The correct number of digits is called the number of significant figures. To learn more about significant figures and rounding, you can watch the videos at the URLs below. (3:20) (8:30) | text | null |
L_0746 | science skills | T_3753 | Quantities in science may be very large or very small. This usually requires many zeroes to the left or right of the decimal point. Such numbers can be hard to read and write accurately. Thats where scientific notation comes in. Scientific notation is a way of writing very large or small numbers that uses exponents. Numbers are written in this format: a 10b The letter a stands for a decimal number. The letter b stands for an exponent, or power, of 10. For example, the number 300 is written as 3.0 102 . The number 0.03 is written as 3.0 10 2 . Figure 2.8 explains how to convert numbers to and from scientific notation. For a review of exponents, watch: You Try It! Problem: Write the number 46,000,000 in scientific notation. | text | null |
L_0746 | science skills | T_3754 | In a scientific investigation, a researcher may make and record many measurements. These may be compiled in spreadsheets or data tables. In this form, it may be hard to see patterns or trends in the data. Descriptive statistics and graphs can help organize the data so patterns and trends are easier to spot. Example: A vehicle checkpoint was set up on a busy street. The number of vehicles of each type that passed by the checkpoint in one hour was counted and recorded in Table 2.4. These are the only types of vehicles that passed the checkpoint during this period. Type of Vehicle 4-door cars 2-door cars SUVs Number 150 50 80 Type of Vehicle vans pick-up trucks Number 50 70 | text | null |
L_0746 | science skills | T_3755 | A descriptive statistic sums up a set of data in a single number. Examples include the mean and range. The mean is the average value. It gives you an idea of the typical measurement. The mean is calculated by summing the individual measurements and dividing the total by the number of measurements. For the data in Table 2.4, the mean number of vehicles by type is: (150 + 50 + 80 + 50 + 70) 5 = 80. (There are two other words people can sometimes use when they use the word "average." They might be referring to a quantity called the "median" or the "mode." Youll see these quantities in later courses, but for now, well just say the average is the same thing as the mean.) The range is the total spread of values. It gives you an idea of the variation in the measurements. The range is calculated by subtracting the smallest value from the largest value. For the data in Table 2.4, the range in numbers of vehicles by type is: 150 - 50 = 100. | text | null |
L_0746 | science skills | T_3756 | Graphs can help you visualize a set of data. Three commonly used types of graphs are bar graphs, circle graphs, and line graphs. Figure 2.9 shows an example of each type of graph. The bar and circle graphs are based on the data in Table 2.4, while the line graph is based on unrelated data. You can see more examples at this URL: Bar graphs are especially useful for comparing values for different types of things. The bar graph in Figure Circle graphs are especially useful for showing percents of a whole. The circle graph in Figure 2.9 shows the percent of all vehicles counted that were of each type. Line graphs are especially useful for showing changes over time. The line graph in Figure 2.9 shows how distance from school changed over time when some students went on a class trip. Helpful Hints Circle graphs show percents of a whole. What are percents? Percents are fractions in which the denominator is 100. Example: 30% = 30/100 Percents can also be expressed as decimal numbers. Example: 30% = 0.30 You Try It! Problem: Show how to calculate the percents in the circle graph in Figure 2.9. Need a refresher on percents, fractions, and decimals? Go to this URL: | text | null |
L_0746 | science skills | T_3757 | Did you ever read a road map, sketch an object, or play with toy trucks or dolls? No doubt, the answer is yes. What do all these activities have in common? They all involve models. A model is a representation of an object, system, or process. For example, a road map is a representation of an actual system of roads on the ground. Models are very useful in science. They provide a way to investigate things that are too small, large, complex, or distant to investigate directly. Figure 2.10 shows an example of a model in chemistry. To be useful, a model must closely represent the real thing in important ways, but it must be simpler and easier to manipulate than the real thing. Do you think the model in Figure 2.10 meets these criteria? | text | null |
L_0746 | science skills | T_3758 | Research in physical science can be exciting, but it also has potential dangers. Whether in the lab or in the field, knowing how to stay safe is important. | text | null |
L_0746 | science skills | T_3759 | Lab procedures and equipment may be labeled with safety symbols. These symbols warn of specific hazards, such as flames or broken glass. Learn the symbols so you will recognize the dangers. A list of common safety symbols is shown in Figure 2.11. Do you know how to avoid each hazard? You can learn more at this URL: | text | null |
L_0746 | science skills | T_3759 | Lab procedures and equipment may be labeled with safety symbols. These symbols warn of specific hazards, such as flames or broken glass. Learn the symbols so you will recognize the dangers. A list of common safety symbols is shown in Figure 2.11. Do you know how to avoid each hazard? You can learn more at this URL: | text | null |
L_0746 | science skills | T_3760 | Following basic safety rules is the best way to stay safe in science. Safe practices help prevent accidents. Several lab safety rules are listed below. Different rules may apply when you work in the field. But in all cases, you should always follow your teachers instructions. Lab Safety Rules Wear safety gear, including goggles, an apron, and gloves. Wear a long-sleeved shirt and shoes that completely cover your feet. Tie back your hair if it is long. Do not eat or drink in the lab. Never work alone. Never perform unauthorized experiments. Never point the open end of a test tube at yourself or another person. Always add acid to water never water to acid and add the acid slowly. To smell a substance, use your hand to fan vapors toward your nose rather than smell it directly. This is demonstrated in Figure 2.12. When disposing of liquids in the sink, flush them down the drain with lots of water. Wash glassware and counters when you finish your lab work. Thoroughly wash your hands with soap and water before leaving the lab. Even when you follow the rules, accidents can happen. Immediately alert your teacher if an accident occurs. Report all accidents, even if you dont think they are serious. | text | null |
L_0747 | technology | T_3761 | Technology is the application of knowledge to real-world problems. It includes methods and processes as well as devices like computers and cars. An example is the Bessemer process. It is a cheap method of making steel that was invented in the 1850s. It is just one of many technological advances that have occurred in manufacturing. Technology is also responsible for most of the major advances in agriculture, transportation, communications, and medicine. Clearly, technology has had a huge impact on people and society. It is hard to imagine what life would be like without it. Professionals in technology are generally called engineers. Most engineers have a strong background in physical science. There are many different careers in engineering. You can learn about some of them at the URLs below. | text | null |
L_0747 | technology | T_3762 | The development of new technology is called technological design. It is similar to scientific investigation. Both processes use evidence and logic to solve problems. | text | null |
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