lessonID
stringlengths 6
6
| lessonName
stringlengths 3
52
| ID
stringlengths 6
21
| content
stringlengths 10
6.57k
| media_type
stringclasses 2
values | path
stringlengths 28
76
⌀ |
|---|---|---|---|---|---|
L_0650 | protist characteristics | T_3315 | For classification, the protists are divided into three groups: 1. Animal-like protists, which are heterotrophs and have the ability to move. 2. Plant-like protists, which are autotrophs that photosynthesize. 3. Fungi-like protists, which are heterotrophs, and they have cells with cell walls and reproduce by forming spores. But remember, protists are not animals, nor plants, nor fungi ( Figure 1.2). | text | null |
L_0651 | protists nutrition | T_3316 | The cells of protists need to perform all of the functions that other cells do, such as grow and reproduce, maintain homeostasis, and obtain energy. They also need to obtain "food" to provide the energy to perform these functions. Recall that protists can be plant-like, fungi-like, or animal-like. That means that protists can obtain food like plants, fungi, or animals do. There are many plant-like protists, such as algae, that get their energy from sunlight through photosynthesis. Some of the fungus-like protists, such as the slime molds ( Figure 1.1), decompose decaying matter. The animal-like protists must "eat" or ingest food. Some animal-like protists use their "tails" to eat. These protists are called filter-feeders. They acquire nutrients by constantly whipping their tails, called flagellum, back and forth. The whipping of the flagellum creates a current that brings food into the protist. Other animal-like protists must "swallow" their food through a process called endocytosis. Endocytosis happens when a cell takes in substances through its membrane. The process is described below: 1. The protist wraps around its prey, which is usually bacteria. 2. It creates a food vacuole, a sort of "food storage compartment," around the bacteria. 3. The protist produces toxins which paralyze its prey. 4. Once digested, the food material moves through the vacuole and into the cytoplasm of the protist. Also, some of the animal-like and fungi-like protists are parasitic, harming their hosts as they obtain nutrients. Fungi-like protists absorb nutrients meant for their host, harming the host in the process. Slime molds live on decaying plant life and in the soil. | text | null |
L_0653 | punnett squares | T_3319 | A Punnett square is a special tool derived from the laws of probability. It is used to predict the possible offspring from a cross, or mating between two parents. An example of a Punnett square ( Figure 1.1) shows the results of a cross between two purple flowers that each have one dominant factor and one recessive factor (Bb). The Punnett square of a cross between two purple flowers (Bb). A Punnett square can be used to calculate what percentage of offspring will have a certain trait. To create a Punnett square, perform the following steps: 1. 2. 3. 4. Take the factors from the first parent and place them at the top of the square (B and b). Take the factors from the second parent and line them up on the left side of the square (B and b). Pull the factors from the top into the boxes below. Pull the factors from the side into the boxes next to them. The possible offspring are represented by the letters in the boxes, with one factor coming from each parent. Results: Top left box: BB, or purple flowers Top right box: Bb, or purple flowers Lower left box: Bb, or purple flowers Lower right box: bb, or white flowers Only one of the plants out of the four, or 25% of the plants, has white flowers (bb). The other 75% have purple flowers (BB, Bb), because the purple factor (B) is the dominant factor. This shows that the color purple is the dominant trait in pea plants. Now imagine you cross one of the white flowers (bb) with a purple flower that has both a dominant and recessive factor (Bb). The only possible gamete in the white flower is recessive (b), while the purple flower can have gametes with either dominant (B) or recessive (b). Practice using a Punnett square with this cross (see Table 1.1). b Bb bb B b b Bb bb Did you find that 50% of the offspring will be purple, and 50% of the offspring will be white? | text | null |
L_0657 | reproduction in seedless plants | T_3329 | Seedless plants can reproduce asexually or sexually. Some seedless plants, like hornworts and liverworts, can reproduce asexually through fragmentation. When a small fragment of the plant is broken off, it can form a new plant. | text | null |
L_0657 | reproduction in seedless plants | T_3330 | Like all plants, nonvascular plants have an alternation of generations life cycle. That means they alternate between diploid cell stages (having two sets of chromosomes) and haploid cell stages (having one set of chromosomes) during their life cycle. Recall the haploid stage is called the gametophyte, and the diploid stage is called the sporophyte. In the life cycle of the nonvascular seedless plants, the gametophyte stage is the longest part of the cycle. The gametophyte is the green photosynthetic carpet that you would recognize as a moss. The life cycle of nonvascular seedless plants can be described as follows: 1. The male gametophyte produces flagellated sperm that must swim to the egg formed by the female game- tophyte. For this reason, sexual reproduction must happen in the presence of water. Therefore, nonvascular plants tend to live in moist environments. Though the life of a nonvascular seedless plant is a cycle, this can be considered the initial step in the life cycle. 2. Following fertilization, the sporophyte forms. The sporophyte is connected to, and dependent on, the gameto- phyte. 3. The sporophyte produces spores that will develop into gametophytes and start the cycle over again. | text | null |
L_0657 | reproduction in seedless plants | T_3331 | For the seedless vascular plants, the sporophyte stage is the longest part of the cycle, but the cycle is similar to nonvascular plants. For example, in ferns, the gametophyte is a tiny heart-shaped structure, while the leafy plant we recognize as a fern is the sporophyte. The ferns sporangia, where spores are produced, are often on the underside of the fronds ( Figure 1.1). Like nonvascular plants, ferns also have flagellated sperm that must swim to the egg. Unlike nonvascular plants, once fertilization takes place, the gametophyte will die, and the sporophyte will live independently. This fern is producing spores underneath its fronds. | text | null |
L_0658 | reproductive behavior of animals | T_3332 | Some of the most important animal behaviors involve mating. Mating is the pairing of an adult male and female to produce young. Adults that are most successful at attracting a mate are most likely to have offspring. Traits that help animals attract a mate and have offspring increase their fitness. As the genes that encode these traits are passed to the next generation, the traits will become more common in the population. | text | null |
L_0658 | reproductive behavior of animals | T_3333 | In many species, females choose the male they will mate with. For their part, males try to be chosen as mates. They show females that they would be a better mate than the other males. To be chosen as a mate, males may perform courtship behaviors. These are special behaviors that help attract a mate. Male courtship behaviors get the attention of females and show off a males traits. These behaviors are often observed as direct competition between males. Different species have different courtship behaviors. One example is a peacock raising his tail feathers. The colorful peacock is trying to impress females of his species with his beautiful feathers. Another example of courtship behavior in birds is the blue-footed booby. He is doing a dance to attract a female for mating. During the dance, he spreads out his wings and stamps his feet on the ground. You can watch the following video of a blue-footed booby doing his courtship dance at: . Click image to the left or use the URL below. URL: Courtship behaviors occur in many other species. For example, males in some species of whales have special mating songs to attract females as mates. Frogs croak for the same reason. Male deer clash antlers to court females. Male jumping spiders jump from side to side to attract mates. Courtship behaviors are one type of display behavior. A display behavior is a fixed set of actions that carries a specific message. Although many display behaviors are used to attract mates, some display behaviors have other purposes. For example, display behaviors may be used to warn other animals to stay away, as you will read below. | text | null |
L_0658 | reproductive behavior of animals | T_3334 | In most species of birds and mammals, one or both parents care for their offspring. Caring for the young may include making a nest or other shelter. It may also include feeding the young and protecting them from predators. Caring for offspring increases their chances of surviving. Birds called killdeers have an interesting way of protecting their chicks. When a predator gets too close to her nest, a mother killdeer pretends to have a broken wing. The mother walks away from the nest holding her wing as though it were injured ( Figure 1.1). The predator thinks she is injured and will be easy prey. The mother leads the predator away from the nest and then flies away. In most species of mammals, parents also teach their offspring important skills. For example, meerkat parents teach their pups how to eat scorpions without being stung. A scorpion sting can be deadly, so this is a very important skill. | text | null |
L_0658 | reproductive behavior of animals | T_3335 | Some species of animals are territorial. This means that they defend their area. The area they defend usually contains their nest and enough food for themselves and their offspring. A species is more likely to be territorial if there is not very much food in their area. Having a larger territory could mean more prey or food. Animals generally do not defend their territory by fighting. Instead, they are more likely to use display behavior. The behavior tells other animals to stay away. It gets the message across without the need for fighting. Display behavior is generally safer and uses less energy than fighting. Male gorillas use display behavior to defend their territory. They pound on their chests and thump the ground with their hands to warn other male gorillas to keep away from their area. The robin displays his red breast to warn other robins to stay away ( Figure 1.2). The red breast of this male robin is easy to see. The robin displays his bright red chest to defend his territory. It warns other robins to keep out of his area. Some animals deposit chemicals to mark the boundary of their territory. This is why dogs urinate on fire hydrants and other objects. Cats may also mark their territory by depositing chemicals. They have scent glands in their face. They deposit chemicals by rubbing their face against objects. | text | null |
L_0660 | reptiles | T_3337 | What reptiles can you name? Snakes, alligators, and crocodiles are all reptiles. Modern reptiles live on every continent except Antarctica. They range in size from the newly-discovered Jaragua Sphaero (a dwarf gecko), at 0.6 inches, to the saltwater crocodile, at up to 23 feet. There are four living orders of reptiles: 1. 2. 3. 4. Squamata, which includes lizards, snakes, and amphisbaenids (or worm-lizards). Crocodilia, which includes crocodiles, gharials ( Figure 1.1), caimans, and alligators. Testudines, which includes turtles and tortoises. Sphenodontia, which includes tuatara ( Figure 1.1). A gharial crocodile (left). A tuatara (right). | text | null |
L_0660 | reptiles | T_3338 | Reptiles are tetrapods (four-legged) and ectothermic, meaning their internal temperature depends on the temperature of their environment. This is why you may see reptiles sunbathing as they use the energy from the sun to warm their bodies. Usually the sense organs of reptiles, like ears, are well developed, though snakes do not have external ears. All reptiles have advanced eyesight. Reptiles also have a sense of smell. Crocodilians, turtles, and tortoises smell like most other land vertebrates. But, some lizards, and all snakes, smell with their tongues, which is flicked out of the mouth to pick up scent molecules from the air. Reptiles also have several adaptations for living on land. They have a skin covered in scales to protect them from drying out. All reptiles have lungs to breathe air. Reptiles are also amniotes, which means their embryos are surrounded by a thin membrane. This membrane protects the embryo from the harsh conditions of living on land. Reptile eggs are also surrounded by a protective shell, which may be either flexible or inflexible. | text | null |
L_0660 | reptiles | T_3339 | Most reptiles reproduce sexually, meaning there are two parents involved. In some families of lizards and one snake family, however, asexual reproduction is possible. This is when only one parent is involved in creating new life. For example, the gecko females can make tiny clones of themselves without the aid of a male. All reptiles have a cloaca, a single exit and entrance for sperm, eggs, and waste, located at the base of the tail. Most reptiles lay amniotic eggs covered with leathery or hard shell. These eggs can be placed anywhere as they dont have to be in a moist environment, like the eggs of amphibians. However, not all species lay eggs, as certain species of squamates can give birth to live young. Unlike the amphibians, there are no larval stages of development. The young reptiles look like miniature versions of the adult. The young reptiles are generally left to fend for themselves. However, some reptiles provide care for their young. For example, crocodiles and alligators may defend their young from predators. | text | null |
L_0666 | role of amphibians | T_3358 | Humans have used amphibians for a number of purposes for thousands of years, if not longer. Amphibians play significant roles in many food webs and are thus an important part of many ecosystems. For example, frogs keep insect populations stable. Extinction of frogs, or just significant decreases in the frog population, would probably have serious consequences for agricultural crops. Humans have also consumed amphibians, especially frogs, probably since they first ate meat. More recently, amphibians have been tremendously useful in research. | text | null |
L_0666 | role of amphibians | T_3359 | Amphibians play important roles in many ecosystems, especially as middle players in many food chains and food webs. In addition to consuming many worms and insects and other arthropods, and even some small reptiles and mammals and fish, they are prey for turtles and snakes, as well as some fish and birds. Tadpoles keep waterways clean by feeding on algae. Frogs are raised as a food source for humans. Frog legs are a delicacy in China, France, the Philippines, northern Greece, and the American south, especially the Frensh-speaking parts of Louisiana. Only the upper joint of the hind leg is served, which has a single bone similar to the upper joint of a chicken or turkey wing. They are commonly prepared by grilling or deep frying, sometimes breaded, though they can also be served with garlic, or turned into a soup or stew. Some estimates have well over a billion frogs harvested a year as food. Thats about one frog harvested for every seven people on the planet. | text | null |
L_0666 | role of amphibians | T_3360 | Amphibians have long been used in scientific research, especially developmental and physiological processes, largely due to their unique ability to undergo metamorphosis, and in some species, to regenerate limbs. Amphibians are also used in cloning research. Cloning involves making identical copies of a parent organism, and the large amphibian egg helps in this process. They are also used to study embryos because their eggs lack shells, so it is easy to watch their development. The African clawed frog, Xenopus laevis, is a species that is studied to understand aspects of developmental biology. It is a good model organism because it is easy to raise in a lab and has a large embryo, which is easy to study ( Figure 1.1). Many Xenopus genes have been identified and cloned, especially those involved in development. Developing Xenopus embryos can be easily observed and studied with a basic microscope, though the eggs are large enough to see without a microscope. Because of their size, the exact developmental stage after fertilization can be easily determined. This allows proteins that are used at a specific developmental time to be collected and analyzed. Identification of Xenopus genes and proteins has allowed the identification of corresponding genes and proteins from humans. Many environmental scientists believe that amphibians, including frogs, indicate when an environment is damaged. When species of frogs begin to decline, it often indicates that there is a bigger problem within the ecosystem. This could have dramatic effects on food webs and ecosystems. Frog embryos are often studied to better understand how development works. | text | null |
L_0666 | role of amphibians | T_3361 | Amphibians can be found in folklore, fairy tales, and popular culture. Numerous legends have developed over the centuries around the mystical properties of the salamander. Its name originates from the Persian words for fire and within," so many of these legends are related to fire. This connection likely originates from the tendency of many salamanders to live inside rotting logs. When placed into the fire, salamanders would escape from the logs, lending to the belief that the salamander was created from flames. Unforgettable amphibians Kermit the Frog ( Figure 1.2) and his popular saying Its not easy being green. Frogger, from the video game of the same name, has been teaching children about the dangers of the road and alligator-filled moats for years. And all it takes is a kiss from a princess to turn a frog into a prince, as told in The Frog Prince story. Kermit the Frog balloon is flown at the Annual Macys Thanksgiving Day Parade. | text | null |
L_0668 | safety in the life sciences | T_3365 | There can be some very serious safety risks in scientific research. If researchers are not careful, they could poison themselves or contract a deadly illness. The kinds of risks that scientists face depend on the kind of research they perform. For example, a scientist working with bacteria in a laboratory faces different risks than a scientist studying the behavior of lions in Africa, but both scientists must still follow safety guidelines. Safety practices must be followed when working with the hazardous things such as parasites, radiation and radioactive materials, toxins, and wild animals. Also, carcinogens, which are chemical that cause cancer, pathogens, which are disease-causing virus, bacteria or fungi, and teratogens, which are chemical that cause deformities in developing embryos, are extremely hazardous, and extreme care must be used when working with these items as well. For example, scientists studying dangerous organisms such as Yersinia pestis, the cause of bubonic plague, use special equipment that helps keep the organism from escaping the lab. A biohazard is any biological material that could make someone sick, including disease-causing organisms. There- fore, a used needle is a biohazard because it could harbor blood contaminated with a disease-causing organism. Bacteria grown in a laboratory are also biohazards if they could potentially cause disease. Science laboratory safety and chemical hazard signs. | text | null |
L_0668 | safety in the life sciences | T_3366 | If you perform an experiment in your classroom, your teacher will explain how to be safe. Professional scientists follow safety rules as well, especially for the study of dangerous organisms like the bacteria that cause bubonic plague ( Figure 1.2). Sharp objects, chemicals, heat, and electricity are all used at times in laboratories. Below is a list of safety guidelines that you should follow when in the laboratory: Be sure to obey all safety guidelines given in lab instructions and by your teacher. Follow directions carefully. Tie back long hair. Wear closed toe shoes with flat heels and shirts with no hanging sleeves, hoods, or drawstrings. Use gloves, goggles, or safety aprons when instructed to do so. Broken glass should only be cleaned up with a dust pan and broom. Never touch broken glass with your bare hands. Never eat or drink anything in the science lab. Table tops and counters could have dangerous substances on them. Be sure to completely clean materials like test tubes and beakers. Leftover substances could interact with other substances in future experiments. If you are using flames or heat plates, be careful when you reach. Be sure your arms and hair are kept far away from heat. Alert your teacher immediately if anything out of the ordinary occurs. An accident report may be required if someone is hurt. Also, the teacher must know if any materials are damaged or discarded. Scientists studying dangerous organisms such as Yersinia pestis, the cause of bubonic plague, use special equipment that helps keep the organism from escap- ing the lab. | text | null |
L_0668 | safety in the life sciences | T_3367 | A field scientist studies an organism in a natural setting, which is not usually an indoor laboratory. Scientists who work outdoors are also required to follow safety regulations. These safety regulations are designed to prevent harm to themselves, other humans, animals, and the environment. If scientists work outside the country, they are required to learn about and follow the laws and restrictions of the country in which they are doing research. For example, entomologists following monarch butterfly ( Figure 1.3) migrations between the United States and Mexico must follow regulations in both countries. Before biologists can study protected wildlife or plant species, they must apply for permission to do so, usually from the government. This is important to protect these fragile species. For example, if scientists collect rare butterflies, they must first get a permit. They must also be careful to not disturb the habitat. | text | null |
L_0669 | salamanders | T_3368 | Salamanders are characterized by slender bodies, short legs, and long tails. They are most closely related to the caecilians, little-known legless amphibians ( Figure 1.1). Most of the animals in the salamander order look like a cross between a lizard and a frog. They have moist, smooth skin like frogs and long tails like lizards. Salamanders are found in most moist or arid habitats in the Northern Hemisphere, but can also be found south of the equator. They live on all continents except Antarctica and Australia. Salamanders live in or near water or on moist ground, often in a swamp. Some species live in water most of their life, some live their entire adult life on land, and some live in both habitats. Some salamanders live in caves. These salamanders have pale skin and reduced eyes as they have adapted to living in complete darkness in underground pools of water. The reduced eyes are similar to other organisms that live in caves or underground. Salamanders are carnivorous, eating only other animals, not plants. They will eat almost any smaller animal, such as worms, centipedes, crickets, spiders, and slugs. Some will even eat small invertebrates. Finally, salamanders have the ability to grow back lost limbs, as well as other body parts. This process is known as regeneration. Salamanders have developed ways not to be eaten. Most salamanders have brightly colored, poisonous skin. The bold color tells predators not to eat the salamander. Many salamanders have glands on the back of the neck or on the tail that give off a poisonous or bad-tasting liquid. Some species can even shed their tail during an attack and grow a new one later. Some salamanders stand high on its legs and waves its tail to scare away danger. One particular salamander, the ribbed newt, has needle-like rib tips. It can squeeze its muscles to make the rib tips pierce through its skin and into its enemy, telling the predator to stay away, a feature unique among the animal kingdom. The marbled salamander (left) shows the typical salamander body plan: slender body, short legs, long tail, and moist skin. Caecilian (right) are a type of legless am- phibian most closely related to salaman- ders. | text | null |
L_0669 | salamanders | T_3369 | Different salamanders breathe in different ways. In those that have gills, breathing occurs through the gills as water passes over the gill slits. Sirens keep their gills all their lives, which allows them to breathe underwater. Species that live on land lose their gills as they grow older. These salamanders develop lungs that are used in breathing, much like breathing in mammals. Other land-living salamanders do not have lungs or gills. These are called lungless salamanders. Instead, they "breathe," or exchange gases, through their skin. This requires blood vessels that exchange gases to be spread throughout the skin. | text | null |
L_0669 | salamanders | T_3370 | Salamanders are generally small. However, some can reach a foot or more, as in the mudpuppy of North America. In Japan and China, the giant salamander reaches 6 feet and weighs up to 66 pounds ( Figure 1.2). | text | null |
L_0669 | salamanders | T_3371 | Salamanders belong to a group of approximately 500 species of amphibians. The order Urodela, containing sala- manders and newts, is divided into three suborders: 1. Giant salamanders, including the hellbender and Asiatic salamanders. 2. Advanced salamanders, including lungless salamanders, mudpuppies, and newts. Newts are salamanders that spend most of each year living on land. 3. Sirens. Sirens are salamanders that have lungs as well as gills and never develop beyond the larval stage. Sirens have only two legs, but the other salamander species develop four legs as adults, with fleshy toes at the end of each foot. The legs on four-legged salamanders are so short that the salamander belly drags on the ground as the animal walks. Sirens have long, strong tails that are flat to help sirens swim like a fish, with the tail swinging from side to side. The Pacific giant salamander can reach up to 6 feet in length and weigh up to 66 pounds. | text | null |
L_0670 | scientific investigation | T_3372 | The scientific method is a process used to investigate the unknown ( Figure 1.1). It is the general process of a scientific investigation. This process uses evidence and testing. Scientists use the scientific method so they can find information. A common method allows all scientists to answer questions in a similar way. Scientists who use this method can reproduce another scientists experiments. Almost all versions of the scientific method include the following steps, although some scientists do use slight variations. 1. 2. 3. 4. 5. 6. 7. Make observations. Identify a question you would like to answer based on the observation. Find out what is already known about your observation (research). Form a hypothesis. Test the hypothesis. Analyze your results and draw conclusions. Communicate your results. | text | null |
L_0670 | scientific investigation | T_3373 | Imagine that you are a scientist. While collecting water samples at a local pond, you notice a frog with five legs instead of four ( Figure 1.2). As you start to look around, you discover that many of the frogs have extra limbs, Steps of a Scientific Investigation. A scientific investigation typically has these steps. extra eyes, or no eyes. One frog even has limbs coming out of its mouth. These are your observations, or things you notice about an environment using your five senses. A frog with an extra leg. | text | null |
L_0670 | scientific investigation | T_3373 | Imagine that you are a scientist. While collecting water samples at a local pond, you notice a frog with five legs instead of four ( Figure 1.2). As you start to look around, you discover that many of the frogs have extra limbs, Steps of a Scientific Investigation. A scientific investigation typically has these steps. extra eyes, or no eyes. One frog even has limbs coming out of its mouth. These are your observations, or things you notice about an environment using your five senses. A frog with an extra leg. | text | null |
L_0670 | scientific investigation | T_3374 | The next step is to ask a question about the frogs. You may ask, "Why are so many frogs deformed?" Or, "Is there something in their environment causing these defects, like water pollution?" Yet, you do not know if this large number of deformities is "normal" for frogs. What if many of the frogs found in ponds and lakes all over the world have similar deformities? Before you look for causes, you need to find out if the number and kind of deformities is unusual. So besides finding out why the frogs are deformed, you should also ask: "Is the percentage of deformed frogs in this pond greater than the percentage of deformed frogs in other places?" | text | null |
L_0670 | scientific investigation | T_3375 | No matter what you observe, you need to find out what is already known about your questions. For example, is anyone else doing research on deformed frogs? If yes, what did they find out? Do you think that you should repeat their research to see if it can be duplicated? During your research, you might learn something that convinces you to change or refine your question. From this, you will construct your hypothesis. A pond with frogs. | text | null |
L_0670 | scientific investigation | T_3376 | A hypothesis is a proposed explanation that tries to explain an observation. A good hypothesis allows you to make more predictions. For example, you might hypothesize that a pesticide from a nearby farm is running into the pond and causing frogs to have extra legs. If thats true, then you can predict that the water in a pond of non-deformed frogs will have lower levels of that pesticide. Thats a prediction you can test by measuring pesticide levels in two sets of ponds, those with deformed frogs and those with nothing but healthy frogs. Every hypothesis needs to be written in a way that it can: 1. 2. 3. 4. Be tested using experiments to collect evidence. Be proven wrong. Provide measurable results. Provide yes or no answers. For example, do you think the following hypothesis meets the four criteria above? Lets see. Hypothesis: "The number of deformed frogs in five ponds that are polluted with chemical X is higher than the number of deformed frogs in five ponds without chemical X." Of course, next you will have to test your hypothesis. | text | null |
L_0670 | scientific investigation | T_3377 | To test the hypothesis, an experiment will be done. You would count the healthy and deformed frogs and measure the amount of chemical X in all of the ponds. The hypothesis will be either true or false. Doing an experiment will test most hypotheses. The experiment may generate evidence in support of the hypothesis. The experiment may also generate evidence proving the hypothesis false. Once you collect your data, it will need to be analyzed. | text | null |
L_0670 | scientific investigation | T_3378 | If a hypothesis and experiment are well designed, the experiment will produce results that you can measure, collect, and analyze. The analysis should tell you if the hypothesis is true or false. Refer to the table for the experimental results ( Table 1.1). Polluted Pond 1 2 3 4 5 Average: Number of Deformed Frogs 20 23 25 26 21 23 Non-Polluted Pond 1 2 3 4 5 Average: Number of Deformed Frogs 23 25 30 16 20 22.8 Your results show that pesticide levels in the two sets of ponds are different, but the average number of deformed frogs is almost the same. Your results demonstrate that your hypothesis is false. The situation may be more complicated than you thought. This gives you new information that will help you decide what to do next. Even if the results supported your hypothesis, you would probably ask a new question to try to better understand what is happening to the frogs and why. | text | null |
L_0670 | scientific investigation | T_3379 | If a hypothesis and experiment are well designed, the results will indicate whether your hypothesis is true or false. If a hypothesis is true, scientists will often continue testing the hypothesis in new ways to learn more. If a hypothesis is false, the results may be used to come up with and test a new hypothesis. A scientist will then communicate the results to the scientific community. This will allow others to review the information and extend the studies. The scientific community can also use the information for related studies. Scientists communicate their results in a number of ways. For example, they may talk to small groups of scientists and give talks at large scientific meetings. They will also write articles for scientific journals. Their findings may also be communicated to journalists. If you conclude that frogs are deformed due to a pesticide not previously measured, you would publish an article and give talks about your research. Your conclusion could eventually help find solutions to this problem. | text | null |
L_0670 | scientific investigation | T_3380 | A summery video of the scientific method, using the identification of DNA structure as an example, is shown in this video by MIT students: . | text | null |
L_0671 | scientific theories | T_3381 | One goal of a scientist is to find answers to scientific questions. To do this, scientists first develop a hypothesis, which is a proposed explanation that tries to explain an observation. To collect evidence to support (or disprove) their hypothesis, scientists must do experiments. Evidence is: 1. A direct, physical observation of something or a process over time. 2. Usually something measurable or "quantifiable." 3. The data resulting from an experiment. For example, an apple falling to the ground is evidence in support of the law of gravity. A bear skeleton in the woods would be evidence of the presence of bears. Looking at the image below might be confusing at first because this evidence seems to defy the law of gravity ( Figure 1.1). Of course water cannot be poured out of bottle and flow upward. The law of gravity is a scientific law, which is a statement describing what always happens under certain conditions in nature. Scientific laws are developed from lots of collected information. If many experiments are performed, and lots of evidence is collected in support of a general hypothesis, a scientific theory can be developed. Scientific theories are well established explanations of evidence, usually tested and confirmed by many different people. Scientific theories usually have a lot of evidence in support of the theory, and no evidence disproving the theory. Scientific theories produce information that helps us understand our world. For example, the idea that matter is made up of atoms is a scientific theory. Scientists accept this theory as a fundamental principle of basic science. A scientific theory must stand up to all scientific testing. Thus, when scientists find new evidence, they can change their theories. In addition to the germ theory of disease, other scientific theories are the cell theory and the theory of evolution. | text | null |
L_0672 | scientific ways of thinking | T_3382 | Modern science is a way of understanding the physical world, based on observable evidence, reasoning, and repeated testing. That means scientists explain the world based on their own observations. If they develop new ideas about the way the world works, they set up a way to test these new ideas. | text | null |
L_0672 | scientific ways of thinking | T_3383 | A scientist is always trying to find the truth and discover new truths. How can you think like a scientist? Thinking like a scientist is based on asking and answering questions. Though you may not know it, you do this all day long. Scientists ask questions, and then make detailed observations to try to ask more specific questions and develop a hypothesis. They may design and perform an experiment to try to answer their question and test their hypothesis. From the results of their experiment, scientists draw conclusions. A conclusion describes what the evidence tells the scientist. Scientists ask questions: The key to being a great scientist is to ask questions. Imagine you are a scientist in the African Congo. While in the field, you observe one group of healthy chimpanzees on the north side of the jungle. On the other side of the jungle, you find a group of chimpanzees that are mysteriously dying. What questions might you ask? A good scientist might ask the following two questions: 1. "What differs between the two environments where the chimpanzees live?" 2. "Are there differences in behavior between the two groups of chimpanzees?" Scientists make detailed observations: To observe means to watch and study attentively. A person untrained in the sciences may only observe, "The chimps on one side of the jungle are dying, while chimps on the other side of the jungle are healthy." A scientist, however, will make more detailed observations. Can you think of ways to make this observation more detailed? What about the number of chimps? Are they male or female? Young or old? What do they eat? A good scientist may observe, "While all seven adult females and three adult males on the north side of the jungle are healthy and show normal behavior, four female and five male chimps under the age of five on the south side have died." Detailed observations can ultimately help scientists design their experiments and answer their questions. From these observations, a scientist will develop a hypothesis to explain the observations. A hypothesis is the scientists proposed explanation for his observations. The scientists hypothesis may be that "Young chimps on the south side die due to a lack of nutrients in their diet." An adult and infant chimpanzee (Pan troglodytes). Scientists find answers using tests: When scientists want to answer a question, they search for evidence using experiments. An experiment is a test to see if their explanation is right or wrong. Evidence is made up of the observations a scientist makes during an experiment. To study the cause of death in the chimpanzees, scientists may give the chimps nutrients in the form of nuts, berries, and vitamins to see if they are dying from a lack of food. This test is the experiment. If fewer chimps die, then the experiment shows that the chimps may have died from not having enough food. This is the evidence. Scientists question the answers: Good scientists are skeptical. Scientists never use only one piece of evidence to form a conclusion. For example, the chimpanzees in the experiment may have died from a lack of food, but can you think of another explanation for their death? They may have died from a virus, or from another less obvious cause. More experiments need to be completed before scientists can be sure. Science is about finding the truth, no matter what. So good scientists constantly question their own conclusions. They also find other scientists to confirm or disagree with their evidence. | text | null |
L_0673 | seasonal changes in plants | T_3384 | Have you seen the leaves of plants change colors? During what time of year does this happen? What causes it to happen? Plants can sense changes in the seasons. Leaves change color and drop each autumn in some climates ( Figure 1.1). Certain flowers, like poinsettias, only bloom during the winter. And, in the spring, the winter buds on the trees break open, and the leaves start to grow. How do plants detect time of year? Although you might detect seasonal changes by the change in temperature, this is not the way in which plants know the seasons are changing. Plants determine the time of year by the length of daylight, known as the photoperiod. Because of the tilt of the Earth, during winter days, there are less hours of light than during summer days. Thats why, in the winter, it starts getting dark very early in the evening, and then stays dark while youre getting ready for school the next morning. But in the summer it will be bright early in the morning, and the sun will not set until late that night. With a light-sensitive chemical, plants can sense the differences in day length. For example, in the fall, when the days start to get shorter, the trees sense that there is less sunlight. The plant is stimulated, and it sends messages telling the leaves to change colors and fall. This is an example of photoperiodism, the reaction of organisms, such as plants, to the length of day or night. Photoperiodism is also the reaction of plants to the length of light and dark periods. Many flowering plants sense the length of night, a dark period, as a signal to flower. Each plant has a different photoperiod, or night length. When the plant senses the appropriate length of darkness, resulting in an appropriate length of daylight, it flowers. Flowering plants are classified as long-day plants or short-day plants. Long-day plants flower when the length of daylight exceeds the necessary photoperiod, and short-day plants flower when the day length is shorter than the necessary photoperiod. Long-day plants include carnations, clover, lettuce, wheat, and turnips. Short-day plants include cotton, rice, and sugar cane. | text | null |
L_0674 | seeds and seed dispersal | T_3385 | Plants seem to grow wherever they can. How? Plants cant move on their own. So how does a plant start growing in a new area? | text | null |
L_0674 | seeds and seed dispersal | T_3386 | If youve ever seen a plant grow from a tiny seed, then you might realize that seeds are amazing structures. A seed is a plant ovule containing an embryo. The seed allows a plant embryo to survive droughts, harsh winters, and other conditions that would kill an adult plant. The tiny plant embryo can simply stay dormant, in a resting state, and wait for the perfect environment to begin to grow. In fact, some seeds can stay dormant for hundreds of years! Another impressive feature of the seed is that it stores food for the young plant after it sprouts. This greatly increases the chances that the tiny plant will survive. So being able to produce a seed is a beneficial adaptation, and, as a result, seed plants have been very successful. Although the seedless plants were here on Earth first, today there are many more seed plants than seedless plants. Learn more about seeds in the Seeds Massachusetts Institute of Technology video at | text | null |
L_0674 | seeds and seed dispersal | T_3387 | For a seed plant species to be successful, the seeds must be dispersed, or scattered around in various directions. If the seeds are spread out in many different areas, there is a better chance that some of the seeds will find the right conditions to grow. But how do seeds travel to places they have never been before? To aid with seed dispersal, some plants have evolved special features that help their seeds travel over long distances. One such strategy is to allow the wind to carry the seeds. With special adaptations in the seeds, the seeds can be carried long distances by the wind. For example, you might have noticed how the "fluff" of a dandelion moves in the wind. Each piece of fluff carries a seed to a new location. If you look under the scales of pine cone, you will see tiny seeds with "wings" that allow these seeds to be carried away by the wind. Maple trees also have specialized fruits with wing-like parts that help seed dispersal ( Figure 1.1). Maple trees have fruits with wings that help the wind disperse the seeds. Some flowering plants grow fleshy fruit that helps disperse their seeds. When animals eat the fruit, the seeds pass through an animals digestive tract unharmed. The seeds germinate after they are passed out with the animals feces. Berries, citrus fruits, cherries, apples, and a variety of other types of fruits are all adapted to be attractive to animals, so the animals will eat them and disperse the seed ( Figure 1.2). Some non-fleshy fruits are specially adapted for animals to carry them on their fur. You might have returned from a walk in the woods to find burrs stuck to your socks. These burrs are actually specialized fruits designed to carry seeds to a new location. | text | null |
L_0681 | social behavior of animals | T_3404 | Why is animal communication important? Without it, animals would not be able to live together in groups. Animals that live in groups with other members of their species are called social animals. Social animals include many species of insects, birds, and mammals. Specific examples of social animals are ants, bees, crows, wolves, lions, and humans. To live together with one another, these animals must be able to share information. | text | null |
L_0681 | social behavior of animals | T_3405 | Some species of animals are very social. In these species, members of the group depend completely on one another. Different animals within the group have different jobs. Therefore, group members must work together for the good of all. Most species of ants and bees are highly social animals. Ants live together in large groups called colonies ( Figure 1.1). A colony may have millions of ants, making communication among the ants very important. All of the ants in the colony work together as a single unit. Each ant has a specific job, and most of the ants are workers. Their job is to build and repair the colonys nest. Worker ants also leave the nest to find food for themselves and other colony members. The workers care for the young as well. Other ants in the colony are soldiers. They defend the colony against predators. Each colony also has a queen. Her only job is to lay eggs. She may lay millions of eggs each month. A few ants in the colony are called drones. They are the only male ants in the colony. Their job is to mate with the queen. Honeybees and bumblebees also live in colonies ( Figure 1.2). Each bee in the colony has a particular job. Most of the bees are workers. Young worker bees clean the colonys hive and feed the young. Older worker bees build the waxy honeycomb or guard the hive. The oldest workers leave the hive to find food. Each colony usually has one queen that lays eggs. The colony also has a small number of male drones. They mate with the queen. | text | null |
L_0681 | social behavior of animals | T_3405 | Some species of animals are very social. In these species, members of the group depend completely on one another. Different animals within the group have different jobs. Therefore, group members must work together for the good of all. Most species of ants and bees are highly social animals. Ants live together in large groups called colonies ( Figure 1.1). A colony may have millions of ants, making communication among the ants very important. All of the ants in the colony work together as a single unit. Each ant has a specific job, and most of the ants are workers. Their job is to build and repair the colonys nest. Worker ants also leave the nest to find food for themselves and other colony members. The workers care for the young as well. Other ants in the colony are soldiers. They defend the colony against predators. Each colony also has a queen. Her only job is to lay eggs. She may lay millions of eggs each month. A few ants in the colony are called drones. They are the only male ants in the colony. Their job is to mate with the queen. Honeybees and bumblebees also live in colonies ( Figure 1.2). Each bee in the colony has a particular job. Most of the bees are workers. Young worker bees clean the colonys hive and feed the young. Older worker bees build the waxy honeycomb or guard the hive. The oldest workers leave the hive to find food. Each colony usually has one queen that lays eggs. The colony also has a small number of male drones. They mate with the queen. | text | null |
L_0681 | social behavior of animals | T_3406 | Ants, bees, and other social animals must cooperate. Cooperation means working together with others. Members of the group may cooperate by sharing food. They may also cooperate by defending each other. Look at the ants pictured below ( Figure 1.3). They show very clearly why cooperation is important. A single ant would not be able to carry this large bee back to the nest to feed the other ants. With cooperation, the job is easy. Animals in many other species cooperate. For example, lions live in groups called prides ( Figure 1.4). All the lions in the pride cooperate, though there is still serious competition among the males. Male lions work together to defend the other lions in the pride. Female lions work together to hunt. Then, they share the meat with other pride members. Another example of cooperation is seen with meerkats. Meerkats are small mammals that live in Africa. They also live in groups and cooperate with one another. For example, young female meerkats act as babysitters. They take care of the baby meerkats while their parents are away looking for food. Members of this lion pride work together. Males cooperate by defending the pride. Females cooperate by hunting and shar- ing the food. | text | null |
L_0681 | social behavior of animals | T_3406 | Ants, bees, and other social animals must cooperate. Cooperation means working together with others. Members of the group may cooperate by sharing food. They may also cooperate by defending each other. Look at the ants pictured below ( Figure 1.3). They show very clearly why cooperation is important. A single ant would not be able to carry this large bee back to the nest to feed the other ants. With cooperation, the job is easy. Animals in many other species cooperate. For example, lions live in groups called prides ( Figure 1.4). All the lions in the pride cooperate, though there is still serious competition among the males. Male lions work together to defend the other lions in the pride. Female lions work together to hunt. Then, they share the meat with other pride members. Another example of cooperation is seen with meerkats. Meerkats are small mammals that live in Africa. They also live in groups and cooperate with one another. For example, young female meerkats act as babysitters. They take care of the baby meerkats while their parents are away looking for food. Members of this lion pride work together. Males cooperate by defending the pride. Females cooperate by hunting and shar- ing the food. | text | null |
L_0684 | structural evidence for evolution | T_3409 | Even though two different species may not look similar, they may have similar internal structures that suggest they have a common ancestor. That means both evolved from the same ancestor organism a long time ago. Common ancestry can also be determined by looking at the structure of the organism as it first develops. | text | null |
L_0684 | structural evidence for evolution | T_3410 | Some of the most interesting kinds of evidence for evolution are body parts that have lost their use through evolution ( Figure 1.1). For example, most birds need their wings to fly. But the wings of an ostrich have lost their original use. Structures that have lost their use through evolution are called vestigial structures. They provide evidence for evolution because they suggest that an organism changed from using the structure to not using the structure, or using it for a different purpose. Penguins do not use their wings, known as flippers, to fly in the air. However, they do use them to move in the water. The theory of evolution suggests that penguins evolved to use their wings for a different purpose. A whales pelvic bones, which were once attached to legs, are also vestigial structures. Whales are descended from land-dwelling ancestors that had legs. Homologous structures are structures that have a common function and suggest common ancestry. For example, homologous structures include the limbs of mammals, such as bats, lions, whales, and humans, which all have a common ancestor. Different mammals may use their limbs for walking, running, swimming or flying. The method the mammal uses to move is considered a common function. | text | null |
L_0684 | structural evidence for evolution | T_3411 | Some of the oldest evidence of evolution comes from embryology, the study of how organisms develop. An embryo is an animal or plant in its earliest stages of development. This means looking at a plant or animal before it is born or hatched. Centuries ago, people recognized that the embryos of many different species have similar appearances. The embryos of some species are even difficult to tell apart. Many of these animals do not differ much in appearance until they develop further. Some unexpected traits can appear in animal embryos. For example, human embryos have gill slits just like fish! In fish they develop into gills, but in humans they disappear before birth. The presence of the gill slits suggests that a long time ago humans and fish shared a common ancestor. The similarities between embryos suggests that these animals are related and have common ancestors. For example, humans did not evolve from chimpanzees. But the similarities between the embryos of both species suggest that we have an ancestor in common with chimpanzees. As our common ancestor evolved, humans and chimpanzees went down different evolutionary paths and developed different traits. | text | null |
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 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.