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L_0430 | introduction to genetics | T_2557 | When gametes unite during fertilization, the resulting zygote inherits two alleles for each gene. One allele comes from each parent. | text | null |
L_0430 | introduction to genetics | T_2558 | The two alleles that an individual inherits make up the individuals genotype. The two alleles may be the same or different. Look at Table 6.1. It shows alleles for the flower-color gene in peas. The alleles are represented by the letters B (purple flowers) and b (white flowers). A plant with two alleles of the same type (BB or bb) is called a homozygote. A plant with two different alleles (Bb) is called a heterozygote. Genotypes BB (homozygote) Bb (heterozygote) bb (homozygote) Phenotypes purple flowers purple flowers white flowers | text | null |
L_0430 | introduction to genetics | T_2559 | The expression of an organisms genotype is called its phenotype. The phenotype refers to the organisms traits, such as purple or white flowers. Different genotypes may produce the same phenotype. This will be the case if one allele is dominant to the other. Both BB and Bb genotypes in Table 6.1 have purple flowers. Thats because the B allele is dominant to the b allele, which is recessive. The terms dominant and recessive are the terms Mendel used to describe his "factors." Today we use them to describe alleles. In a Bb heterozygote, only the dominant B allele is expressed. The recessive b allele is expressed only in the bb genotype. | text | null |
L_0430 | introduction to genetics | T_2560 | Each trait Mendel studied was controlled by one gene with two alleles. In each case, one of the alleles was dominant to the other. This resulted in just two possible phenotypes for each trait. Each trait Mendel studied was also controlled by a gene on a different chromosome. As a result, each trait was inherited independently of the others. With traits like these, its easy to predict which forms of a trait will show up in the offspring of a given set of parents. | text | null |
L_0430 | introduction to genetics | T_2561 | Consider a purple-flowered pea plant with the genotype Bb. Half the gametes produced by this parent will have a B allele. The other half will have a b allele. You can see this in Figure 6.7. This is similar to tossing a coin. There is a 50 percent chance of a head and a 50 percent chance of a tail. Like a head or tail, there is a 50 percent chance that any gamete from this parent will have the B allele. There is also a 50 percent chance that any gamete will have the b allele. | text | null |
L_0430 | introduction to genetics | T_2562 | Now lets see what happens if two parent pea plants have the Bb genotype. What genotypes are possible for their offspring? And what ratio of genotypes would you expect? The easiest way to find the answer to these questions is with a Punnett square. A Punnett square is a chart that makes it easy to find the possible genotypes in offspring of two parents. Figure of the chart. The gametes produced by the female parent are along the left side of the chart. The different possible combinations of alleles in their offspring can be found by filling in the cells of the chart. If the parents had four offspring, their most likely genotypes would be one BB, two Bb, and one bb. But the genotype ratios of their actual offspring may differ. Thats because which gametes happen to unite is a matter of chance, like a coin toss. The Punnett square just shows the possible genotypes and their most likely ratios. | text | null |
L_0430 | introduction to genetics | T_2563 | You know that the B allele is dominant to the b allele. Therefore, you can also use the Punnett square in Figure 6.8 to predict the most likely offspring phonotypes. If the parents had four offspring, their most likely phenotypes would be three with purple flowers (1 BB + 2 Bb) and one with white flowers (1 bb). | text | null |
L_0430 | introduction to genetics | T_2564 | Inheritance is often more complex than it is for traits like those Mendel studied. Several factors can complicate it. | text | null |
L_0430 | introduction to genetics | T_2565 | If a gene has two alleles, one may not be dominant to the other. There are other possibilities. One possibility is called codominance. Another is called incomplete dominance. With codominance, both alleles are expressed equally in heterozygotes. The red and white flower in Figure With incomplete dominance, a dominant allele is not completely dominant. Instead, it is influenced by the recessive allele in heterozygotes. The pink flower in Figure 6.9 is an example. It has an incompletely dominant allele for red petals. It also has a recessive allele for white petals. This results in a flower with pink petals. | text | null |
L_0430 | introduction to genetics | T_2566 | Many genes have more than two alleles. An example is ABO blood type in people. There are three common alleles for the gene that controls this trait. The allele for type A is codominant with the allele for type B. Both of these alleles are dominant to the allele for type O. The possible genotypes and phenotypes for this trait are shown in Table below Genotype AA AO BB BO AB OO Phenotype Type A Type A Type B Type B Type AB Type O | text | null |
L_0430 | introduction to genetics | T_2567 | Some traits are controlled by more than one gene. They are called polygenic traits. Each gene for a polygenic trait may have two or more alleles. The genes may be on the same or different chromosomes. Polygenic traits may have many possible phenotypes. Skin color and adult height are examples of polygenic traits in humans. Think about all the variation in the heights of adults you know. Normal adults may range from less than 5 feet tall to more than 7 feet tall. There are people at every gradation of height in between these extremes. | text | null |
L_0430 | introduction to genetics | T_2568 | Genes play an important role in determining an organisms traits. However, for many traits, phenotype is influenced by the environment as well. For example, skin color is controlled by genes but also influenced by exposure to sunlight. You can see the effect of sunlight on skin in Figure 6.10. | text | null |
L_0430 | introduction to genetics | T_2569 | Animals and most plants have two special chromosomes. They are called sex chromosomes. These are chromo- somes that determine the sex of the organism. All of the other chromosomes are called autosomes. Genes on sex chromosomes may be inherited differently than genes on autosomes. | text | null |
L_0430 | introduction to genetics | T_2570 | In people, the sex chromosomes are called X and Y chromosomes. Individuals with two X chromosomes are normally females. Individuals with one X and one Y chromosome are normally males. As you can see in Figure sons. | text | null |
L_0430 | introduction to genetics | T_2571 | Traits controlled by genes on the sex chromosomes are called sex-linked traits. One gene on the Y chromosome determines male sex. There are very few other genes on the Y chromosome, which is the smallest human chromo- some. There are hundreds of genes on the much larger X chromosome. None is related to sex. Traits controlled by genes on the X chromosome are called X-linked traits. X-linked traits have a different pattern of inheritance than traits controlled by genes on autosomes. With just one X chromosome, males have only one allele for any X-linked trait. Therefore, a recessive X-linked allele is always expressed in males. With two X chromosomes, females have two alleles for any X-linked trait, just as they do for autosomal traits. Therefore, a recessive X-linked allele is expressed in females only when they inherit two copies of it. This explains why X-linked recessive traits show up less often in females than males. | text | null |
L_0430 | introduction to genetics | T_2572 | An example of a recessive X-linked trait is red-green color blindness. People with this trait cant see red or green colors. This trait is fairly common in males but rare in females. Figure 6.12 is a pedigree for this trait. A pedigree is a chart that shows how a trait is inherited in a family. The mother has one allele for color blindness. She doesnt have color blindness because she also has a dominant normal allele for the gene. Instead, she is called a carrier for the trait. She passes the allele to half of her children. One daughter is a carrier, and one son has the color blindness trait. No matter how many children this couple has, none of the daughters will have color blindness, but half of the sons, on average, will have the trait. Can you explain why? | text | null |
L_0431 | advances in genetics | T_2573 | A species genome consists of all of its genetic information. The human genome consists of the complete set of genes in the human organism. Its all the DNA of a human being. | text | null |
L_0431 | advances in genetics | T_2574 | The Human Genome Project was launched in 1990. It was an international effort to sequence all 3 billion bases in human DNA. Another aim of the project was to identify the more than 20,000 human genes and map their locations on chromosomes. The logo of the Human Genome Project in Figure 6.13 shows that the project brought together experts in many fields. The Human Genome Project was completed in 2003. It was one of the greatest feats of modern science. It provides a complete blueprint for a human being. Its like having a very detailed manual for making a human organism. | text | null |
L_0431 | advances in genetics | T_2575 | Knowing the sequence of the human genome is very useful. For example, it helps us understand how humans evolved. Another use is in medicine. It is helping researchers identify and understand genetic disorders. You can learn more about the Human Genome Project and its applications by watching this funny, fast-paced video: http://w MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0431 | advances in genetics | T_2576 | Sequencing the human genome has increased our knowledge of genetic disorders. Genetic disorders are diseases caused by mutations. Many genetic disorders are caused by mutations in a single gene. Others are caused by abnormal numbers of chromosomes. | text | null |
L_0431 | advances in genetics | T_2577 | Table 6.3 lists some genetic disorders caused by mutations in just one gene. It include autosomal and X-linked disorders. It also includes dominant and recessive disorders. Genetic Disorder Marfan syndrome Cystic fibrosis Sickle Cell Anemia Hemophilia A Effect of Mutation Defective protein in tis- sues such as cartilage and bone Defective protein needed to make mucus Defective hemoglobin protein that is needed to transport oxygen in red blood cells Reduced activity of a pro- tein needed for blood to clot Signs of the Disorder Heart and bone defects; unusually long limbs Type of Trait Autosomal dominant Unusually thick mucus that clogs airways in lungs and ducts in other organs Sickle-shaped red blood cells that block blood ves- sels and interrupt blood flow Excessive bleeding that is difficult to control Autosomal recessive Autosomal recessive X-linked recessive Relatively few genetic disorders are caused by dominant alleles. A dominant allele is expressed in everybody who inherits even one copy of it. If it causes a serious disorder, affected people may die young and fail to reproduce. They wont pass the allele to the next generation. As a result, the allele may die out of the population. One of the exceptions is Marfan syndrome. It is thought to have affected Abraham Lincoln. Hes pictured in Figure 6.14. His very long limbs are one reason for the suspicion of Marfan syndrome in this former U.S. president. Recessive disorders are more common than dominant ones. Why? A recessive allele is not expressed in heterozy- gotes. These people are called carriers. They dont have the genetic disorder but they carry the recessive allele. They can also pass this allele to their offspring. A recessive allele is more likely than a dominant allele to pass to the next generation rather than die out. | text | null |
L_0431 | advances in genetics | T_2578 | In the process of meiosis, paired chromosomes normally separate from each other. They end up in different gametes. Sometimes, however, errors occur. The paired chromosomes fail to separate. When this happens, some gametes get an extra copy of a chromosome. Other gametes are missing a chromosome. If one of these gametes is fertilized and survives, a chromosomal disorder results. You can see examples of such disorders in Table 6.4 Genetic Disorder Down syndrome Genotype Extra copy (complete or partial) of chromosome 21 Turners syndrome One X chromosome and no other sex chromosome (XO) One Y chromosome and two or more X chromosomes (XXY, XXXY) Klinefelters syndrome Phenotypic Effects Developmental delays, distinctive facial appearance, and other abnor- malities Female with short height and inabil- ity to reproduce Male with abnormal sexual devel- opment and reduced level of male sex hormone Most chromosomal disorders involve the sex chromosomes. Can you guess why? The X and Y chromosomes are very different in size. The X is much larger than the Y. This difference in size creates problems. It increases the chances that the two chromosomes will fail to separate properly during meiosis. | text | null |
L_0431 | advances in genetics | T_2579 | Treating genetic disorders is one use of biotechnology. Biotechnology is the use of technology to change the genetic makeup of living things for human purposes. Its also called genetic engineering. Besides treating genetic disorders, biotechnology is used to change organisms so they are more useful to people. | text | null |
L_0431 | advances in genetics | T_2580 | Biotechnology uses a variety of methods, but some are commonly used in many applications. A common method is the polymerase chain reaction. Another common method is gene cloning. The polymerase chain reaction is a way of making copies of a gene. It uses high temperatures and an enzyme to make new DNA molecules. The process keeps cycling to make many copies of a gene. Gene cloning is another way of making copies of a gene. A gene is inserted into the DNA of a bacterial cell. Figure 6.15 shows how this is done. Bacteria multiply very rapidly by binary fission. Each time a bacterial cell divides, the inserted gene is copied. | text | null |
L_0431 | advances in genetics | T_2581 | Biotechnology has many uses. It is especially useful in medicine and agriculture. Biotechnology is used to treat genetic disorders. For example, copies of a normal gene might be inserted into a patient with a defective gene. This is called gene therapy. Ideally, it can cure a genetic disorder. create genetically modified organisms (GMOs). Many GMOs are food crops such as corn. Genes are inserted into plants to give them desirable traits. This might be the ability to get by with little water. Or it might be the ability to resist insect pests. The modified plants are likely to be healthier and produce more food. They may also need less pesticide. produce human proteins. Insulin is one example. This protein is needed to treat diabetes. The human insulin gene is inserted into bacteria. The bacteria reproduce rapidly. They can produce large quantities of the human protein. You can see another example in Figure 6.16. | text | null |
L_0431 | advances in genetics | T_2582 | Biotechnology has many benefits. Its pros are obvious. It helps solve human problems. However, biotechnology also raises many concerns. For example, some people worry about eating foods that contain GMOs. They wonder if GMOs might cause health problems. The person in Figure 6.17 favors the labeling of foods that contain GMOs. That way, consumers can know which foods contain them and decide for themselves whether to eat them. Another concern about biotechnology is how it may affect the environment. Negative effects on the environment have already occurred because of some GMOs. For example, corn has been created that has a gene for a pesticide. The corn plants have accidentally cross-pollinated nearby milkweeds. Monarch butterfly larvae depend on milkweeds for food. When they eat milkweeds with the pesticide gene, they are poisoned. This may threaten the survival of the monarch species as well as other species that eat monarchs. Do the benefits of the genetically modified corn outweigh the risks? What do you think? | text | null |
L_0438 | archaea | T_2657 | Archaeans are prokaryotes in the Archaea Domain. They were first discovered in extreme environments such as hot springs. For a long time, they were classified as bacteria. As more was learned about them, they were found to be quite different from bacteria. They were finally placed in their own domain in the late 1970s. You can see the incredible story of their discovery in this brief video: . MEDIA Click image to the left or use the URL below. URL: The study of archaeans is in its infancy. Scientists still know relatively little about them. New species of archaeans are being discovered all the time. | text | null |
L_0438 | archaea | T_2658 | Many archaeans are extremophiles. Extremophiles are organisms that live in extreme conditions. For example, some archaeans live around hydrothermal vents. A hydrothermal vent is a crack on the ocean floor. You can see one in Figure 8.16. Boiling hot, highly acidic water pours out of the vent. These extreme conditions dont deter archaeans. They have evolved adaptations for coping with them. These conditions are like those on ancient Earth. This suggests that archaeans may have evolved very early in Earths history. There are four types of archaean extremophiles. Each type is described below. Extreme conditions pose many challenges to living cells. Archaeans have evolved adaptations that allow them to deal with the challenges. | text | null |
L_0438 | archaea | T_2659 | Halophiles are organisms that "love" salt. They can survive in very salty water. For example, they have been found in the Great Salt Lake in Utah and the Dead Sea between Israel and Jordan. Both of these bodies of water are much saltier than the ocean. | text | null |
L_0438 | archaea | T_2660 | Hyperthermophiles are organisms that "love" heat. Some archaeans can survive at very high temperatures. For example, they can grow in hot springs and geysers. One archaean species can even reproduce at 122 C (252 F). This is higher than the boiling point of water. It is the highest recorded temperature for any organism. | text | null |
L_0438 | archaea | T_2661 | Acidophiles are organisms that "love" acids. They live in very acidic environments, such as acid mine drainage. They are also found near vents of volcanoes. The most acidophilic archaeans can thrive at negative pH values. No other organisms can survive in such acidic conditions. | text | null |
L_0438 | archaea | T_2662 | Alkaliphiles are organisms that "love" bases. Bases are like the opposite of acids. Basic environments where archaeans are found include Mono Lake in California, pictured in Figure 8.17. Mono Lake is the oldest lake in North America. The water is not only unusually basic. Its also saltier than the ocean. So archaeans that live in the water of Mono Lake must have adaptations to both salty and basic conditions. They are haloalkaliphiles. | text | null |
L_0438 | archaea | T_2663 | Not all archaeans live in extreme conditions. In fact, archaeans are now known to live just about everywhere on Earth. They make up as much as 20 percent of Earths total mass of living things. | text | null |
L_0438 | archaea | T_2664 | Archaeans have been found in a broad range of habitats. For example, they live in soils, bodies of water, and marshlands. They even live in the human belly button! Archaeans are very common in the ocean. Archaeans in plankton may be some of the most abundant organisms on Earth. | text | null |
L_0438 | archaea | T_2665 | Like bacteria, archaeans are important decomposers. For example, archaeans help break down sewage in waste treatment plants. As decomposers, they help recycle carbon and nitrogen. Many archaeans live in close relationships with other organisms. For example, large numbers live inside animals, including humans. Unlike many bacteria, archaeans dont harm their hosts. None of them is known to cause human disease. Archaeans are more likely to help their hosts. For example, archaeans called methanogens live inside the gut of cows (see Figure 8.18). They help cows digest tough plant fibers made of cellulose. They produce methane gas as a waste product. | text | null |
L_0443 | alligators and crocodiles | T_2694 | Crocodilia, containing both alligators and crocodiles, is an order of large reptiles. Reptiles belonging to Crocodilia are the closest living relatives of birds. Reptiles and birds are the only known living descendants of the dinosaurs. Some would day that alligators and crocodiles actually look like small dinosaurs. Dinosaurs that evolved wings are the ancestors of birds. The basic crocodilian body plan ( Figure 1.1) is a very successful one and has changed little over time. Modern species actually look very similar to their Cretaceous ancestors of 84 million years ago. All species of crocodilians have similar body structures, including an elongated snout, powerful jaws, muscular tail, large protective scales, streamlined body, and eyes and nostrils that are positioned on top of the head. | text | null |
L_0443 | alligators and crocodiles | T_2695 | Crocodilians have a flexible, semi-erect posture. They can walk either in a low, sprawled belly walk, or hold their legs more directly underneath them to perform the high walk. Most other reptiles can only walk in a sprawled position. All crocodilians have, like humans, teeth set in bony sockets. But unlike mammals, they replace their teeth through- out life. Crocodiles and gharials (large crocodilians with longer jaws) have salivary glands on their tongue, which are used to remove salt from their bodies. This helps with life in a saltwater environment. Crocodilians are often seen lying with their mouths open, a behavior called gaping. One of its functions is probably to cool them down. The crocodilian digestive system is highly adapted to their lifestyle. Crocodilians are known to swallow stones, known as gastroliths, which help digest their prey. The crocodilian stomach is divided into two chambers. The first is powerful and muscular. The other stomach is the most acidic digestive system of any animal. It can digest mostly everything from their prey, including bones, feathers, and horns! All crocodilians are carnivores. They feed on live animals such as birds, small mammals and fish. Crocodilians use several methods of attack when pursuing live prey. One approach is that of the ambush. The crocodilian lies motionless beneath the waters surface with only their nostrils above the water line. This keeps them concealed while they watch for prey that approaches the waters edge. The crocodilian then lunges out of the water, taking their prey by surprise and dragging it from the shoreline into deep water where the prey is killed. The sex of developing crocodilians is determined by the temperature of the eggs during incubation, when eggs are kept warm before they hatch. This means that the sex of crocodilians is not determined genetically. If the eggs are kept at a cold or a hot temperature, then their offspring may be all male or all female. To get both male and female offspring, the temperature must be kept within a narrow range. Female crocodilians care for the young after they hatch, providing them with protection until they grow large enough to defend themselves. In many species of crocodilians, the female carries her tiny offspring in her mouth. | text | null |
L_0443 | alligators and crocodiles | T_2696 | Like all reptiles, crocodilians have a relatively small brain, but the crocodilian brain is more advanced than those of other reptiles. Because of their aquatic habitat, the eyes, ears, and nostrils are all located on the same "face" in a line one after the other. The crocodiles have advanced sensory organs. They see well during the day and may even have color vision, and they also have excellent night vision. A third transparent eyelid, the nictitating membrane, protects their eyes underwater. The eardrums are located behind the eyes and are covered by a movable flap of skin. This flap closes, along with the nostrils and eyes, when they dive. This prevents water from entering their external head openings. Their jaws are covered with sensory pits, which hold bundles of nerve fibers that respond to the slightest disturbance in surface water. Crocodiles can detect vibrations and small pressure changes in water. This makes it possible for them to sense prey and danger even in total darkness, and becomes very useful when the animal is submerged in the water. Like mammals and birds, and unlike other reptiles, crocodiles have a four-chambered heart. But, unlike mammals, blood with and without oxygen can be mixed. See Supersize Crocs at | text | null |
L_0444 | amphibians | T_2697 | What group of animals begins its life in the water, but then spends most of its life on land? Amphibians! Amphibians are a group of vertebrates that has adapted to live in both water and on land. Amphibian larvae are born and live in water, and they breathe using gills. The adults live on land for part of the time and breathe both through their skin and with their lungs as their lungs are not sufficient to provide the necessary amount of oxygen. There are approximately 6,000 species of amphibians. They have many different body types, physiologies, and habitats, ranging from tropical to subarctic regions. Frogs, toads, salamanders ( Figure 1.1), newts, and caecilians are all types of amphibians. | text | null |
L_0444 | amphibians | T_2698 | Transition to life on land meant significant changes to both external and internal features. In order to live on land, amphibians replaced gills with another respiratory organ, the lungs. Other adaptations include: One of the many species of amphibian is this dusky salamander. Skin that prevents loss of water. Eyelids that allow them to adapt to vision outside of the water. An eardrum developed to separate the external ear from the middle ear. A tail that disappears in adulthood (in frogs and toads). | text | null |
L_0444 | amphibians | T_2699 | Like fish, amphibians are ectothermic vertebrates. They belong to the class Amphibia. There are three orders: 1. Urodela, containing salamanders and newts. 2. Anura, containing frogs and toads. 3. Apoda, containing caecilians. | text | null |
L_0444 | amphibians | T_2700 | Most amphibians live in fresh water, not salt water. Their habitats can include areas close to springs, streams, rivers, lakes, swamps and ponds. They can be found in moist areas in forests, meadows and marshes. Amphibians can be found almost anywhere there is a source of fresh water. Although there are no true saltwater amphibians, a few can live in brackish (slightly salty) water. Some species do not need any water at all, and several species have also adapted to live in drier environments. Most amphibians still need water to lay their eggs. | text | null |
L_0444 | amphibians | T_2701 | Amphibians reproduce sexually. The life cycle of amphibians happens in the following stages: 1. Egg Stage: Amphibian eggs are fertilized in a number of ways. External fertilization, employed by most frogs and toads, involves a male gripping a female across her back, almost as if he is squeezing the eggs out of her. The male releases sperm over the females eggs as they are laid. Another method is used by salamanders, whereby the male deposits a packet of sperm onto the ground. The female then pulls it into her cloaca, a single opening for her internal organ systems. Therefore, fertilization occurs internally. By contrast, caecilians and tailed frogs use internal fertilization, just like reptiles, birds, and mammals. The male deposits sperm directly into the females cloaca. 2. Larval stage: When the egg hatches, the organism is legless, lives in water, and breathes with gills, resembling their evolutionary ancestors (fish). 3. During the larval stage, the amphibian slowly transforms into an adult by losing its gills and growing four legs. Once development is complete, it can live on land. | text | null |
L_0445 | angiosperms | T_2702 | Angiosperms, in the phylum Anthophyta, are the most successful phylum of plants. This category also contains the largest number of individual plants ( Figure 1.1). Angiosperms evolved the structure of the flower, so they are also called the flowering plants. Angiosperms live in a variety of different environments. A water lily, an oak tree, and a barrel cactus, although different, are all angiosperms. | text | null |
L_0445 | angiosperms | T_2703 | Even though flowers may look very different from each other, they do have some structures in common. The structures are explained in the picture below ( Figure 1.2). The green outside of a flower that often looks like a leaf is called the sepal ( Figure 1.3). All of the sepals together are called the calyx, which is usually green and protects the flower before it opens. All of the petals ( Figure 1.3) together are called the corolla. They are bright and colorful to attract a particular pollinator, an animal that carries pollen from one flower to another. Examples of pollinators include birds and insects. Angiosperms are the flowering plants. A complete flower has sepals, petals, sta- mens, and one or more carpels. The next structure is the stamen, consisting of the stalk-like filament that holds up the anther, or pollen sac. The pollen, which is found at the top of the stamen, is the male gametophyte. At the very center is the carpel, which is divided into three different parts: (1) the sticky stigma, where the pollen lands, (2) the tube of the style, and (3) the large, bottom part, known as the ovary. The ovary holds the ovules, the female gametophytes. When the ovules are fertilized, the ovule becomes the seed and the ovary becomes the fruit. The following table summarizes the parts of the flower ( Table 1.1). Part sepals calyx corolla stamens filament anther carpel Definition The green outside of the flower. All of the sepals together, or the outside of the flower. The petals of a flower collectively. The part of the flower that produces pollen. Stalk that holds up the anther. The structure that contains pollen in a flower. Female part of the flower; includes the stigma, style, and ovary. style ovary ovules This image shows the difference between a petal and a sepal. | text | null |
L_0445 | angiosperms | T_2703 | Even though flowers may look very different from each other, they do have some structures in common. The structures are explained in the picture below ( Figure 1.2). The green outside of a flower that often looks like a leaf is called the sepal ( Figure 1.3). All of the sepals together are called the calyx, which is usually green and protects the flower before it opens. All of the petals ( Figure 1.3) together are called the corolla. They are bright and colorful to attract a particular pollinator, an animal that carries pollen from one flower to another. Examples of pollinators include birds and insects. Angiosperms are the flowering plants. A complete flower has sepals, petals, sta- mens, and one or more carpels. The next structure is the stamen, consisting of the stalk-like filament that holds up the anther, or pollen sac. The pollen, which is found at the top of the stamen, is the male gametophyte. At the very center is the carpel, which is divided into three different parts: (1) the sticky stigma, where the pollen lands, (2) the tube of the style, and (3) the large, bottom part, known as the ovary. The ovary holds the ovules, the female gametophytes. When the ovules are fertilized, the ovule becomes the seed and the ovary becomes the fruit. The following table summarizes the parts of the flower ( Table 1.1). Part sepals calyx corolla stamens filament anther carpel Definition The green outside of the flower. All of the sepals together, or the outside of the flower. The petals of a flower collectively. The part of the flower that produces pollen. Stalk that holds up the anther. The structure that contains pollen in a flower. Female part of the flower; includes the stigma, style, and ovary. style ovary ovules This image shows the difference between a petal and a sepal. | text | null |
L_0445 | angiosperms | T_2703 | Even though flowers may look very different from each other, they do have some structures in common. The structures are explained in the picture below ( Figure 1.2). The green outside of a flower that often looks like a leaf is called the sepal ( Figure 1.3). All of the sepals together are called the calyx, which is usually green and protects the flower before it opens. All of the petals ( Figure 1.3) together are called the corolla. They are bright and colorful to attract a particular pollinator, an animal that carries pollen from one flower to another. Examples of pollinators include birds and insects. Angiosperms are the flowering plants. A complete flower has sepals, petals, sta- mens, and one or more carpels. The next structure is the stamen, consisting of the stalk-like filament that holds up the anther, or pollen sac. The pollen, which is found at the top of the stamen, is the male gametophyte. At the very center is the carpel, which is divided into three different parts: (1) the sticky stigma, where the pollen lands, (2) the tube of the style, and (3) the large, bottom part, known as the ovary. The ovary holds the ovules, the female gametophytes. When the ovules are fertilized, the ovule becomes the seed and the ovary becomes the fruit. The following table summarizes the parts of the flower ( Table 1.1). Part sepals calyx corolla stamens filament anther carpel Definition The green outside of the flower. All of the sepals together, or the outside of the flower. The petals of a flower collectively. The part of the flower that produces pollen. Stalk that holds up the anther. The structure that contains pollen in a flower. Female part of the flower; includes the stigma, style, and ovary. style ovary ovules This image shows the difference between a petal and a sepal. | text | null |
L_0445 | angiosperms | T_2704 | Flowering plants can reproduce two different ways: 1. Self-pollination: Pollen falls on the stigma of the same flower. This way, a seed will be produced that can turn into a genetically identical plant. 2. Cross-fertilization: Pollen from one flower travels to a stigma of a flower on another plant. Pollen travels from flower to flower by wind or by animals. Flowers that are pollinated by animals such as birds, butterflies, or bees are often colorful and provide nectar, a sugary reward, for their animal pollinators. | text | null |
L_0445 | angiosperms | T_2705 | Angiosperms are important to humans in many ways, but the most significant role of angiosperms is as food. Wheat, rye, corn, and other grains are all harvested from flowering plants. Starchy foods, such as potatoes, and legumes, such as beans, are also angiosperms. And, as mentioned previously, fruits are a product of angiosperms that increase seed dispersal and are nutritious. There are also many non-food uses of angiosperms that are important to society. For example, cotton and other plants are used to make cloth, and hardwood trees are used for lumber. | text | null |
L_0446 | animal behaviors | T_2706 | Barking, purring, and playing are just some of the ways in which dogs and cats behave. These are examples of animal behaviors. Animal behavior is any way that animals act, either alone or with other animals. | text | null |
L_0446 | animal behaviors | T_2707 | Can you think of examples of animal behaviors? What about insects and birds? How do they behave? Pictured below are just some of the ways in which these, and other animals act ( Figure 1.1). Look at the pictures and read about the behaviors. Think about why the animal is behaving that way. These pictures show examples of animal behaviors. Why do the animals behave these ways? | text | null |
L_0446 | animal behaviors | T_2708 | Why do animals behave the way they do? The answer to this question depends on what the behavior is. A cat chases a mouse to catch it. A mother dog nurses her puppies to feed them. All of these behaviors have the same purpose: getting or providing food. All animals need food for energy. They need energy to move around. In fact, they need energy just to stay alive. Energy allows all the processes inside cells to occur. Baby animals also need energy to grow and develop. Birds and wasps build nests to have a safe place to store their eggs and raise their young. Many other animals build nests for the same reason. Animals protect their young in other ways, as well. For example, a mother dog not only nurses her puppies. She also washes them with her tongue and protects them from strange people or other animals. All of these behaviors help the young survive and grow up to be adults. Rabbits run away from foxes and other predators to stay alive. Their speed is their best defense. Lizards sun themselves on rocks to get warm because they cannot produce their own body heat. When they are warmer, they can move faster and be more alert. This helps them escape from predators and also find food. All of these animal behaviors are important. They help the animals get food for energy, make sure their young survive, or ensure that they, themselves, survive. Behaviors that help animals or their young survive, increase the animals fitness. Animals with higher fitness have a better chance of passing their genes on to the next generation. If genes control behaviors that increase fitness, the behaviors become more common in the species. This occurs through the process of evolution by natural selection. | text | null |
L_0447 | animal communication | T_2709 | What does the word "communication" make you think of? Talking on a cell phone? Texting? Writing? Those are just a few of the ways in which human beings communicate. Most other animals also communicate. Communication is any way in which animals share information, and they do this in many different ways. Do all animals talk to each other? Probably not, but many do communicate. Like human beings, many other animals live together in groups. Some insects, including ants and bees, are well known for living in groups. In order for animals to live together in groups, they must be able to communicate with each other. Animal communication, like most other animal behaviors, increases the ability to survive and have offspring. This is known as fitness. Communication increases fitness by helping animals find food, defend themselves from predators, mate, and care for offspring. | text | null |
L_0447 | animal communication | T_2710 | Some animals communicate with sound. Most birds communicate this way. Birds use different calls to warn other birds of danger, or to tell them to flock together. Many other animals also use sound to communicate. For example, monkeys use warning cries to tell other monkeys in their troop that a predator is near. Frogs croak to attract female frogs as mates. Gibbons use calls to tell other gibbons to stay away from their area. | text | null |
L_0447 | animal communication | T_2711 | Another way some animals communicate is with sight. By moving in certain ways or by making faces, they show other animals what they mean. Most primates communicate in this way. For example, a male chimpanzee may raise his arms and stare at another male chimpanzee. This warns the other chimpanzee to keep his distance. The chimpanzee pictured below may look like he is smiling, but he is really showing fear ( Figure 1.1). He is communicating to other chimpanzees that he will not challenge them. Look at the peacock pictured below ( Figure 1.2). Why is he raising his beautiful tail feathers? He is also communicating. He is showing females of his species that he would be a good mate. This peacock is using his tail feathers to communicate. What is he "saying"? | text | null |
L_0447 | animal communication | T_2711 | Another way some animals communicate is with sight. By moving in certain ways or by making faces, they show other animals what they mean. Most primates communicate in this way. For example, a male chimpanzee may raise his arms and stare at another male chimpanzee. This warns the other chimpanzee to keep his distance. The chimpanzee pictured below may look like he is smiling, but he is really showing fear ( Figure 1.1). He is communicating to other chimpanzees that he will not challenge them. Look at the peacock pictured below ( Figure 1.2). Why is he raising his beautiful tail feathers? He is also communicating. He is showing females of his species that he would be a good mate. This peacock is using his tail feathers to communicate. What is he "saying"? | text | null |
L_0447 | animal communication | T_2712 | Some animals communicate with scent. They release chemicals that other animals of their species can smell or detect in some other way. Ants release many different chemicals. Other ants detect the chemicals with their antennae. This explains how ants are able to work together. The different chemicals that ants produce have different meanings. Some of the chemicals signal to all of the ants in a group to come together. Other chemicals warn of danger. Still other chemicals mark trails to food sources. When an ant finds food, it marks the trail back to the nest by leaving behind a chemical on the ground. Other ants follow the chemical trail to the food. Many other animals also use chemicals to communicate. You have probably seen male dogs raise their leg to urinate on a fire hydrant or other object. Did you know that the dogs were communicating? They mark their area with a chemical in their urine. Other dogs can smell the chemical. The scent of the chemical tells other dogs to stay away. | text | null |
L_0447 | animal communication | T_2713 | Like other animals, humans communicate with one another. They mainly use sound and sight to share information. The most important way in which humans communicate is with language. Language is the use of symbols to communicate. In human languages, the symbols are words. They stand for many different things. Words stand for things, people, actions, feelings, or ideas. Think of several common words. What does each word stand for? Another important way in which humans communicate is with facial expressions. Look at the face of the young child pictured below ( Figure 1.3). Can you tell from her face how she is feeling? Humans also use gestures to communicate. What are people communicating when they shrug their shoulders? When they shake their head? These are just a few examples of the ways in which humans share information without using words. What does this girls face say about how she is feeling? | text | null |
L_0448 | animal like protists | T_2714 | Animal-like protists are called protozoa. Protozoa are single-celled eukaryotes that share some traits with animals. Like animals, they can move, and they are heterotrophs. That means they eat things outside of themselves instead of producing their own food. Animal-like protists are very small, measuring only about 0.010.5mm. Animal-like protists include the flagellates, ciliates, and the sporozoans. | text | null |
L_0448 | animal like protists | T_2715 | There are many different types of animal-like protists. They are different because they move in different ways. Flagellates have long flagella, or tails. Flagella rotate in a propeller-like fashion, pushing the protist through its environment ( Figure 1.1). An example of a flagellate is Trypanosoma, which causes African sleeping sickness. Other protists have what are called transient pseudopodia, which are like temporary feet. The cell surface extends out to form feet-like structures that propel the cell forward. An example of a protist with pseudopodia is the amoeba. The ciliates are protists that move by using cilia. Cilia are thin, very small tail-like projections that extend outward from the cell body. Cilia beat back and forth, moving the protist along. Paramecium has cilia that propel it. The sporozoans are protists that produce spores, such as the toxoplasma. These protists do not move at all. The spores develop into new protists. These flagellates all cause diseases in humans. A video of the animal-like amoeba can be viewed at: http://commons.wikimedia.org/wiki/File:Amoeba_engulfing_ | text | null |
L_0450 | arachnids | T_2721 | Arachnids are a class of joint-legged invertebrates in the subphylum Chelicerata. They live mainly on land but are also found in fresh water and in all marine environments, except for the open ocean. There are over 100,000 named species, including many species of spiders, scorpions, daddy-long-legs, ticks, and mites ( Figure 1.1). There may be up to 600,000 species in total, including unknown ones. | text | null |
L_0450 | arachnids | T_2722 | Arachnids have the following characteristics: 1. Four pairs of legs (eight total). You can tell the difference between an arachnid and an insect because insects have three pairs of legs (six total). 2. Arachnids also have two additional pairs of appendages. The first pair, the chelicerae, serve in feeding and defense. The next pair, the pedipalps, help the organisms feed, move, and reproduce. (left) A daddy-long-legs spider. (right) Various diseases are caused by bacteria that are spread to humans by arachnids, like the tick shown here. 3. 4. 5. 6. 7. 8. 9. Arachnids do not have antennae or wings. The arachnid body is organized into the cephalothorax, a fusion of the head and thorax, and the abdomen. To adapt to living on land, arachnids have internal breathing systems, like a trachea or a book lung. Arachnids are mostly carnivorous, feeding on the pre-digested bodies of insects and other small animals. Several groups are venomous. They release the venom from specialized glands to kill prey or enemies. Several mites are parasitic, and some of those are carriers of disease. Arachnids usually lay eggs, which hatch into immature arachnids that are similar to adults. Scorpions, however, give birth to live young. | text | null |
L_0450 | arachnids | T_2723 | The arachnids are divided into eleven subgroups. Below are the four most familiar subgroups, with a description of each ( Table 1.1). Subgroup Representative Organisms Approximate Number of Species Characteristics Subgroup Araneae Representative Organisms Spiders Approximate Number of Species 40,000 Characteristics Found all over the world, ranging from tropics to the Arctic, some in extreme environments. All produce silk, which is used for trapping insects in webs, aiding in climbing, producing egg sacs, and wrapping prey. Nearly all spiders inject venom to protect themselves or to kill prey. Only about 200 species have bites that can be harmful to humans. Subgroup Opiliones Representative Organisms Daddy-long-legs Approximate Number of Species 6,300 Characteristics Known for extremely long walking legs. No silk nor poison glands. Many are omnivores, eating small insects, plant material, and fungi. Some are scavengers, eating decaying animal and other matter. Mostly nocturnal (come out at night) and colored in hues of brown. A number of diurnal (come out during the day) species have vivid patterns of yellow, green, and black. Subgroup Scorpiones Representative Organisms Scorpions Approximate Number of Species 2,000 Characteristics Characterized by a tail with six segments, the last bearing a pair of venom glands and a venom-injecting barb. Predators of small arthropods and insects. They use pincers to catch prey. Then they either crush it or inject it with a fast-acting venom, which is used to kill or paralyze the prey. Only a few species are harmful to humans. Nocturnal; during the day, they find shelter in holes or under rocks. Unlike the majority of arachnids, scorpions produce live young. The young are carried about on the mothers back until they have molted at least once. They reach an age of between four to 25 years. Subgroup Acarina Representative Organisms Mites and ticks Approximate Number of Species 30,000 Characteristics Most are small (no more than 1.0 mm in length), but some ticks, and one species of mite, may grow to be 10-20 mm in length. Live in nearly ev- ery habitat, includ- ing aquatic and ter- restrial. Many are parasitic, affecting both in- vertebrates and ver- tebrates. They may transmit diseases to humans and other mammals. Those that feed on plants may damage crops. | text | null |
L_0452 | arthropods | T_2727 | How often do you think you see an arthropod? Well, have you ever looked up close at an ant? A spider? A fly? A moth? With over a million described species (and many more yet to be described) in the phylum containing arthro- pods, chances are, you encounter one of these organisms every day, without even leaving your house. Arthropods are a very diverse group of animals. In fact, they are the biggest group of animals on the planet, with upwards of 5 million distinct species. | text | null |
L_0452 | arthropods | T_2728 | Arthropods belong to the phylum Arthropoda, which means jointed feet, and includes four living subphyla. Chelicerata, which includes spiders ( Figure 1.1), mites, and scorpions. In these animals, the first pair of appendages are often modified as fangs or pincers, and are used to manipulate food. Spiders have eight legs. Myriapoda, which includes centipedes and millipedes. All of these animals live on land, and can have anywhere from ten to nearly 200 pairs of appendages. Hexapoda, which includes the insects. These animals dominate the land. All hexapods have three pairs (six appendages) of walking appendages. Crustacea, which includes lobsters, crabs, barnacles, crayfish, and shrimp. These animals dominate the ocean, and usually have a set of anterior appendages that are modified as mandibles, which function in grasping, biting, and chewing food. Spiders are one type of arthropod. | text | null |
L_0452 | arthropods | T_2729 | Characteristics of arthropods include: 1. A segmented body ( Figure 1.2) with a head, a thorax, and abdomen segments. 2. Appendages on at least one segment. They can be used for feeding, sensory reception, defense, and locomo- tion. In addition to legs, antennas and mouth parts are considered modified appendages. 3. A nervous system. 4. A hard exoskeleton made of chitin, which gives them physical protection and resistance to drying out. In order to grow, arthropods shed this outer covering in a process called molting. 5. An open circulatory system with hemolymph, a blood-like fluid. A series of hearts move the hemolymph into the body cavity where it comes in direct contact with the tissues. Hemolymph is involved with oxygen distribution. 6. A complete digestive system with a mouth and an anus. 7. Aquatic arthropods use gills to exchange gases. These gills have a large surface area in contact with the water, so they can absorb more oxygen. 8. Land-living arthropods have internal surfaces that help exchange gasses. Insects and most other terrestrial species have a tracheal system, where air sacs lead into the body from pores in the exoskeleton. These pores cover a large part of their external body surface. Others use book lungs, gills modified for breathing air, as seen in species like the coconut crab. Some areas of the legs of soldier crabs are covered with an oxygen absorbing skin. Land crabs sometimes have two different structures: one used for breathing underwater, and another used to absorb oxygen from the air. | text | null |
L_0461 | basic and applied science | T_2759 | Science can be "basic" or "applied." The goal of basic science is to understand how things workwhether it is a single cell, an organism made of trillions of cells, or a whole ecosystem. Scientists working on basic science questions are simply looking to increase human knowledge of nature and the world around us. The knowledge obtained through the study of the subspecialties of the life sciences is mostly basic science. Basic science is the source of most scientific theories. For example, a scientist that tries to figure out how the body makes cholesterol, or what causes a particular disease, is performing basic science. This is also known as basic research. Additional examples of basic research would be investigating how glucose is turned into cellular energy or determining how elevated blood glucose levels can be harmful. The study of the cell (cell biology), the study of inheritance (genetics), the study of molecules (molecular biology), the study of microorganisms and viruses (microbiology and virology), the study of tissues and organs (physiology) are all types of basic research, and have all generated lots of information that is applied to humans and human health. Applied science is using scientific discoveries, such as those from basic research, to solve practical problems. For example, medicine, and all that is known about how to treat patients, is applied science based on basic research ( Figure 1.1). A doctor administering a drug to lower a persons cholesterol is an example of applied science. Applied science also creates new technologies based on basic science. For example, designing windmills to capture wind energy is applied science ( Figure 1.2). This technology relies, however, on basic science. Studies of wind patterns and bird migration routes help determine the best placement for the windmills. Surgeons operating on a person, an example of applied science. Windmills capturing energy, an example of applied science. | text | null |
L_0461 | basic and applied science | T_2759 | Science can be "basic" or "applied." The goal of basic science is to understand how things workwhether it is a single cell, an organism made of trillions of cells, or a whole ecosystem. Scientists working on basic science questions are simply looking to increase human knowledge of nature and the world around us. The knowledge obtained through the study of the subspecialties of the life sciences is mostly basic science. Basic science is the source of most scientific theories. For example, a scientist that tries to figure out how the body makes cholesterol, or what causes a particular disease, is performing basic science. This is also known as basic research. Additional examples of basic research would be investigating how glucose is turned into cellular energy or determining how elevated blood glucose levels can be harmful. The study of the cell (cell biology), the study of inheritance (genetics), the study of molecules (molecular biology), the study of microorganisms and viruses (microbiology and virology), the study of tissues and organs (physiology) are all types of basic research, and have all generated lots of information that is applied to humans and human health. Applied science is using scientific discoveries, such as those from basic research, to solve practical problems. For example, medicine, and all that is known about how to treat patients, is applied science based on basic research ( Figure 1.1). A doctor administering a drug to lower a persons cholesterol is an example of applied science. Applied science also creates new technologies based on basic science. For example, designing windmills to capture wind energy is applied science ( Figure 1.2). This technology relies, however, on basic science. Studies of wind patterns and bird migration routes help determine the best placement for the windmills. Surgeons operating on a person, an example of applied science. Windmills capturing energy, an example of applied science. | text | null |
L_0462 | biotechnology in agriculture | T_2760 | Energy must constantly flow through an ecosystem for the system to remain stable. What exactly does this mean? Essentially, it means that organisms must eat other organisms. Food chains ( Figure 1.1) show the eating patterns in an ecosystem. Food energy flows from one organism to another. Arrows are used to show the feeding relationship between the animals. The arrow points from the organism being eaten to the organism that eats it. For example, an arrow from a plant to a grasshopper shows that the grasshopper eats the leaves. Energy and nutrients are moving from the plant to the grasshopper. Next, a bird might prey on the grasshopper, a snake may eat the bird, and then an owl might eat the snake. The food chain would be: plant grasshopper bird snake owl. A food chain cannot continue to go on and on. For example the food chain could not be: plant grasshopper spider frog lizard fox hawk. Food chains only have 4 or 5 total levels. Therefore, a chain has only 3 or 4 levels for energy transfer. This food chain includes producers and consumers. How could you add decom- posers to the food chain? In an ocean ecosystem, one possible food chain might look like this: phytoplankton krill fish shark. The producers are always at the beginning of the food chain, bringing energy into the ecosystem. Through photosynthesis, the producers create their own food in the form of glucose, but also create the food for the other organisms in the ecosystem. The herbivores come next, then the carnivores. When these consumers eat other organisms, they use the glucose in those organisms for energy. In this example, phytoplankton are eaten by krill, which are tiny, shrimp-like animals. The krill are eaten by fish, which are then eaten by sharks. Could decomposers be added to a food chain? Each organism can eat and be eaten by many different types of organisms, so simple food chains are rare in nature. There are also many different species of fish and sharks. So a food chain cannot end with a shark; it must end with a distinct species of shark. A food chain does not contain the general category of "fish," it will contain specific species of fish. In ecosystems, there are many food chains. Since feeding relationships are so complicated, we can combine food chains together to create a more accurate flow of energy within an ecosystem. A food web ( Figure 1.2) shows the feeding relationships between many organisms in an ecosystem. If you expand our original example of a food chain, you could add deer that eat clover and foxes that hunt chipmunks. A food web shows many more arrows, but still shows the flow of energy. A complete food web may show hundreds of different feeding relationships. | text | null |
L_0463 | bird reproduction | T_2761 | How do birds reproduce? We know that chickens lay eggs. But how do they do that? It all starts with behavior aimed at attracting a mate. In birds, this will involve a type of display, usually performed by the male. Some displays are very elaborate and may include dancing, aerial flights, or wing or tail drumming. Most male birds also sing a type of song to attract females. If they are successful at attracting a female, it will lead to breeding. Birds reproduce by internal fertilization, during which the egg is fertilized inside the female. Like reptiles, birds have cloaca, or a single exit and entrance for sperm, eggs, and waste. The male brings his sperm to the female cloaca. The sperm fertilizes the egg. Then the hard-shelled egg develops within the female. The hard-shelled eggs have a fluid-filled amnion, a thin membrane forming a closed sac around the embryo. Eggs are usually laid in a nest. | text | null |
L_0463 | bird reproduction | T_2762 | Why do you think eggs come in so many different colors? Birds that make nests in the open have camouflaged eggs ( Figure 1.1). This gives the eggs protection against predation. Some species, like ground-nesting nightjars, have pale eggs, but the birds camouflage the eggs with their feathers. To protect their young, different species of birds make different nests. Birds of all types, from hummingbirds to ostriches, make nests. Many can be elaborate, shaped like cups, domes, plates, mounds, or burrows. However, some birds, like the common guillemot, do not use nests. Instead, they lay their eggs on bare cliffs. Emperor penguins do not have a nest at all; they sit on eggs to keep them warm before they hatch, a process called incubation. How else might a bird help protect its young from predators? Most species locate their nests in areas that are hidden, in order to avoid predators. Large birds, or those that nest in groups, may build nests in the open, since they are more capable of defending their young. Nest and eggs of the common moorhen, showing camouflaged eggs. | text | null |
L_0463 | bird reproduction | T_2763 | In birds, 90% to 95% of species are monogamous, meaning the male and female remain together for breeding for a few years or until one mate dies. Birds of all types, from parrots to eagles and falcons, are monogamous. Usually, the parents take turns incubating the eggs. Birds usually incubate their eggs after the last one has been laid. In polygamous species, where there is more than one mate, one parent does all of the incubating. The wild turkey is an example of a polygamous bird. The length and type of parental care varies widely amongst different species of birds. At one extreme, in a group of birds called the magapodes (which are chicken-like birds), parental care ends at hatching. In this case, the newly- hatched chick digs itself out of the nest mound without parental help and can take care of itself right away. These birds are called precocial. Other precocial birds include the domestic chicken and many species of ducks and geese. At the other extreme, many seabirds care for their young for extended periods of time. For example, the chicks of the Great Frigatebird receive intensive parental care for six months, or until they are ready to fly, and then take an additional 14 months of being fed by the parents ( Figure 1.2). These birds are the opposite of precocial birds and are called altricial. In most animals, male parental care is rare. But it is very common in birds. Often both parents share tasks such as defense of territory and nest site, incubation, and the feeding of chicks. Since birds often take great care of their young, some birds have evolved a behavior called brood parasitism. This happens when a bird leaves her eggs in another birds nest. The host bird often accepts and raises the parasite birds eggs. Great Frigatebird adults are known to care for their young for up to 20 months after hatching, the longest in a bird species. Here, a young bird is begging for food. | text | null |
L_0464 | birds | T_2764 | How many different types of birds can you think of? Robins, ostriches, hummingbirds, chickens, and eagles. All of these are birds, but they are very different from one another. There is an amazingly wide variety of birds. Like amphibians, reptiles, mammals, and fish, birds are vertebrates. What does that mean? It means they have a backbone. Almost all birds have forelimbs modified as wings, but not all birds can fly. In some birds, the wings have evolved into other structures. Birds are in the class Aves. All birds have the following key features: they are endothermic (warm-blooded), have two legs, and lay eggs. Birds range in size from the tiny two-inch bee hummingbird to the nine-foot ostrich ( Figure 1.1). With approxi- mately 10,000 living species, birds are the most numerous vertebrates with four limbs. They live in diverse habitats around the globe, from the Arctic to the Antarctic. The ostrich can reach a height of nine feet! Pictured here is an ostrich with her young in the Negev Desert, southern Israel. | text | null |
L_0464 | birds | T_2765 | The digestive system of birds is unique, with a gizzard that contains swallowed stones for grinding food. Birds do not have teeth. What do you think the stones do? They help them digest their food. Defining characteristics of modern birds also include: Feathers. High metabolism. A four-chambered heart. A beak with no teeth. A lightweight but strong skeleton. Production of hard-shelled eggs. Which of the above traits do you think might be of importance to flight? | text | null |
L_0464 | birds | T_2766 | In comparing birds with other vertebrates, what do you think distinguishes them the most? In most birds, flight is the obvious difference. Birds have adapted their body plan for flight: Their skeleton is especially lightweight, with large, air-filled spaces connecting to their respiratory system. Their neck bones are flexible. Birds that fly have a bony ridge along the breastbone that the flight muscles attach to ( Figure 1.2). This allows them to remain stable in the air as they fly. Birds also have wings that function as an aerofoil. The surface of the aerofoil is curved to help the bird control and use the air currents to fly. Aerofoils are also found on the wings of airplanes. A bony ridge along the breastbone (green) allows birds to remain stable as they fly. What other traits do you think might be important for flight? Feathers help because theyre more lightweight than scales or fur. A birds wing shape and size will determine how a species flies. For example, many birds have powered flight at certain times, requiring the flapping of their wings, while at other times they soar, using up less energy ( Figure 1.3). One birds flight. A flightless cormorant can no longer fly, but it uses its wings for swimming. | text | null |
L_0464 | birds | T_2766 | In comparing birds with other vertebrates, what do you think distinguishes them the most? In most birds, flight is the obvious difference. Birds have adapted their body plan for flight: Their skeleton is especially lightweight, with large, air-filled spaces connecting to their respiratory system. Their neck bones are flexible. Birds that fly have a bony ridge along the breastbone that the flight muscles attach to ( Figure 1.2). This allows them to remain stable in the air as they fly. Birds also have wings that function as an aerofoil. The surface of the aerofoil is curved to help the bird control and use the air currents to fly. Aerofoils are also found on the wings of airplanes. A bony ridge along the breastbone (green) allows birds to remain stable as they fly. What other traits do you think might be important for flight? Feathers help because theyre more lightweight than scales or fur. A birds wing shape and size will determine how a species flies. For example, many birds have powered flight at certain times, requiring the flapping of their wings, while at other times they soar, using up less energy ( Figure 1.3). One birds flight. A flightless cormorant can no longer fly, but it uses its wings for swimming. | text | null |
L_0464 | birds | T_2766 | In comparing birds with other vertebrates, what do you think distinguishes them the most? In most birds, flight is the obvious difference. Birds have adapted their body plan for flight: Their skeleton is especially lightweight, with large, air-filled spaces connecting to their respiratory system. Their neck bones are flexible. Birds that fly have a bony ridge along the breastbone that the flight muscles attach to ( Figure 1.2). This allows them to remain stable in the air as they fly. Birds also have wings that function as an aerofoil. The surface of the aerofoil is curved to help the bird control and use the air currents to fly. Aerofoils are also found on the wings of airplanes. A bony ridge along the breastbone (green) allows birds to remain stable as they fly. What other traits do you think might be important for flight? Feathers help because theyre more lightweight than scales or fur. A birds wing shape and size will determine how a species flies. For example, many birds have powered flight at certain times, requiring the flapping of their wings, while at other times they soar, using up less energy ( Figure 1.3). One birds flight. A flightless cormorant can no longer fly, but it uses its wings for swimming. | text | null |
L_0466 | blood pressure | T_2772 | The health of your whole body depends on the good health of your cardiovascular system. One measure of the health of your cardiovascular system is blood pressure. Blood pressure occurs when circulating blood puts pressure on the walls of blood vessels. Since blood pressure is primarily caused by the beating of your heart, the walls of the arteries move in a rhythmic fashion. Blood in arteries is under the greatest amount of pressure. The pressure of the circulating blood slowly decreases as blood moves from the arteries and into the smaller blood vessels. Blood in veins is not under much pressure. | text | null |
L_0466 | blood pressure | T_2773 | Blood pressure is read as two numbers. The first number is the systolic pressure. The systolic pressure is the pressure on the blood vessels when the heart beats. This is the time when there is the highest pressure in the arteries. The diastolic pressure, which is the second number, is when your blood pressure is lowest, when the heart is resting between beats. Healthy ranges for blood pressure are: Systolic: less than 120 Diastolic: less than 80 Blood pressure is written as systolic/diastolic. For example, a reading of 120/80 is said as "one twenty over eighty." These measures of blood pressure can change with each heartbeat and over the course of the day. Pressure varies with exercise, emotions, sleep, stress, nutrition, drugs, or disease. Studies have shown that people whose systolic pressure is around 115, rather than 120, have fewer health problems. Clinical trials have shown that people who have blood pressures at the low end of these ranges have much better long term cardiovascular health. Blood pressure is measured with a sphygmomanometer ( Figure 1.1). A digital sphygmomanometer is made of an inflatable cuff and a pressure meter to measure blood pressure. This reading shows a blood pressure of 126/70. Hypertension, which is also called "high blood pressure," occurs when a persons blood pressure is always high. Hypertension is said to be present when a persons systolic blood pressure is always 140 or higher, and/or if the persons diastolic blood pressure is always 90 or higher. Having hypertension increases a persons chance for developing heart disease, having a stroke, or suffering from other serious cardiovascular diseases. Hypertension often does not have any symptoms, so a person may not know that he or she has high blood pressure. For this reason, hypertension is often called the "silent killer." Treatments for hypertension include diet changes, exercise, and medication. Foods thought to lower blood pressure include skim milk, spinach, beans, bananas and dark chocolate. Some health conditions, as well as a persons lifestyle and genetic background, can put someone at a higher risk for developing high blood pressure. As a person cannot alter their genetic background, lifestyle changes may be necessary to reduce the chance of developing high blood pressure. These changes include getting enough exercise, limiting the amount of sodium (salt) in the diet, not being overweight, not drinking alcohol to excess, and not smoking. Low blood pressure is not usually a concern, as long as there are no problems associated with the low pressure. Symptoms associated with low blood pressure include dizziness or lightheadedness, fainting, dehydration and unusual thirst, lack of concentration, blurred vision, nausea, and fatigue. | text | null |
L_0482 | centipedes and millipedes | T_2819 | Centipedes and millipedes belong to the subphylum Myriapoda, which contains 13,000 species. They all live on land, which makes sense as all those legs are more adapted to a terrestrial lifestyle, as opposed to an aquatic lifestyle. The Myriapoda are divided among four classes: (1) Chilopoda (centipedes), (2) Diplopoda (millipedes), (3) Sym- phyla (symphylans), and (4) Pauropoda (pauropods). They range from having over 750 legs to having fewer than ten legs. They have a single pair of antennae and simple eyes. | text | null |
L_0482 | centipedes and millipedes | T_2820 | Myriapoda are mostly found in moist forests, where they help to break down decaying plant material. A few live in grasslands, semi-arid habitats, or even deserts. Most myriapods are decomposers, with the majority herbivores breaking down decaying plant material, but centipedes are nighttime predators. Centipedes roam around looking for small animals to bite and eat; their prey includes insects, spiders, and other small invertebrates. If the centipede is large enough, it will even attack small vertebrates, like lizards. Although not generally considered dangerous to humans, many from this group can cause temporary blistering and discoloration of the skin. | text | null |
L_0482 | centipedes and millipedes | T_2821 | Centipedes ("hundred feet") ( Figure 1.1) are fast, predatory carnivores, and venomous. There are around 3,300 described species, ranging from one tiny species (less than half an inch in length) to one giant species (the Peruvian giant yellow-leg centipede or Amazonian giant centipede), which may grow larger than 12 inches. This giant centipede has been known to attack, kill and eat much larger animals, including tarantulas. Centipedes have one pair of legs per body segment, with the first pair of legs behind the head modified into a pair of fangs containing a poison gland. Many centipedes also guard their eggs and young by curling around them. Centipede. | text | null |
L_0482 | centipedes and millipedes | T_2822 | Most millipedes are slower than centipedes and feed on leaf litter and loose organic material. They can be distin- guished from centipedes by looking at the number of legs per body segment. Millipedes have two pairs of legs per body segment, while centipedes have a single pair of legs per body segment. Millipedes protect their eggs from predators by using a nest of hard soil. Millipedes are not poisonous. They lack the pair of fangs containing a poison gland that centipedes have. | text | null |
L_0482 | centipedes and millipedes | T_2823 | The third class, Symphyla, contains 200 species. Symphylans resemble centipedes but are smaller and translucent. These arthropods have an elongated body, with three pairs of thoracic legs and about nine pairs of abdominal legs, giving this class 12 pairs total. Many spend their lives in soil feeding on plant roots, but some do live in trees. | text | null |
L_0482 | centipedes and millipedes | T_2824 | The pauropods are typically 0.5-2.0 mm long and live on all continents except Antarctica. They are usually found in soil, leaf litter, or other moist places. They feed on fungi and decaying organic matter, and are essentially harmless. Adult pauropods have 11 or 12 body segments and 9-11 pairs of legs. They also possess unique forked antennae and a distinctive pattern of movement characterized by rapid burst of movement and frequent abrupt changes in direction. Over 700 species have been described, and they are believed to be closely related to millipedes. | text | null |
L_0486 | choosing healthy foods | T_2838 | Foods such as whole grain breads, fresh fruits, and fish provide nutrients you need for good health. But different foods give you different types of nutrients. You also need different amounts of each nutrient. How can you choose the right mix of foods to get the proper balance of nutrients? Three tools can help you choose foods wisely: MyPyramid, MyPlate, and food labels. | text | null |
L_0486 | choosing healthy foods | T_2839 | MyPyramid ( Figure 1.1) is a diagram that shows how much you should eat each day of foods from six different food groups. It recommends the amount of nutrients you need based on your age, your gender, and your level of activity. The six food groups in MyPyramid are: Grains, such as bread, rice, pasta, and cereal. Vegetables, such as spinach, broccoli, carrots, and sweet potatoes. Fruits, such as oranges, apples, bananas, and strawberries. Oils, such as vegetable oil, canola oil, olive oil, and peanut oil. Dairy, such as milk, yogurt, cottage cheese, and other cheeses. Meat and beans, such as chicken, fish, soybeans, and kidney beans. MyPyramid can help you choose foods wisely for good health. Each colored band represents a different food group. The key shows which food group each color represents. Which colored band of MyPyramid is widest? Which food group does it represent? In MyPyramid, each food group is represented by a band of a different color. For example, grains are represented by an orange band, and vegetables are represented by a green band. The wider the band, the more foods you should choose from that food group each day. The orange band in MyPyramid is the widest band. This means that you should choose more foods from the grain group than from any other single food group. The green, blue, and red bands are also relatively wide. Therefore, you should choose plenty of foods from the vegetable, dairy, and fruit groups as well. You should choose the fewest foods from the food group with the narrowest band. Which band is narrowest? Which food group does it represent? Are you wondering where foods like ice cream, cookies, and potato chips fit into MyPyramid? The white tip of MyPyramid represents foods such as these. These are foods that should be eaten only in very small amounts and not very often. Such foods contain very few nutrients and are called nutrient-poor. Instead, they are high in fats, sugars, and sodium, which are nutrients that you should limit in a healthy eating plan. Ice cream, cookies, and potato chips are also high in calories. Eating too much of them may lead to unhealthy weight gain. | text | null |
L_0486 | choosing healthy foods | T_2840 | Make at least half your daily grain choices whole grains. Examples of whole grains are whole wheat bread, whole wheat pasta, and brown rice. Choose a variety of different vegetables each day. Be sure to include both dark green vegetables, such as spinach and broccoli, and orange vegetables, such as carrots and sweet potatoes. Choose a variety of different fruits each day. Select mainly fresh fruits rather than canned fruits, and whole fruits instead of fruit juices. When choosing oils, choose unsaturated oils, such as olive oil, canola oil, or vegetable oil. Choose low-fat or fat-free milk and other dairy products. For example, select fat-free yogurt and low-fat cheese. For meats, choose fish, chicken, and lean cuts of beef. Also, be sure to include beans, nuts, and seeds. | text | null |
L_0486 | choosing healthy foods | T_2841 | In June 2011, the United States Department of Agriculture replaced My Pyramid with MyPlate. MyPlate depicts the relative daily portions of various food groups ( Figure 1.2). See for more information. MyPlate is a visual guideline for balanced eating, replacing MyPyramid in 2011. The following guidelines accompany MyPlate: 1. Balancing Calories Enjoy your food, but eat less. Avoid oversized portions. 2. Foods to Increase Make half your plate fruits and vegetables. Make at least half your grains whole grains. Switch to fat-free or low-fat (1%) milk. 3. Foods to Reduce | text | null |
L_0486 | choosing healthy foods | T_2842 | In the United States and other nations, packaged foods are required by law to have nutrition facts labels. A nutrition facts label ( Figure 1.3) shows the nutrients in a food. Packaged foods are also required to list their ingredients. The information listed at the right of the label tells you what to look for. At the top of the label, look for the serving size. The serving size tells you how much of the food you should eat to get the nutrients listed on the label. A cup of food from the label pictured below is a serving. The calories in one serving are listed next. In this food, there are 250 calories per serving. Reading nutrition facts labels can help you choose healthy foods. Look at the nutrition facts label shown here. Do you think this food is a good choice for a healthy eating plan? Why or why not? Next on the nutrition facts label, look for the percent daily values (% DV) of nutrients. Remember the following tips when reading a food label: A food is low in a nutrient if the percent daily value of the nutrient is 5% or less. The healthiest foods are low in nutrients such as fats and sodium. A food is high in a nutrient if the percent daily value of the nutrient is 20% or more. The healthiest foods are high in nutrients such as fiber and proteins. | text | null |
L_0486 | choosing healthy foods | T_2843 | Look at MyPyramid ( Figure 1.1). Note the person walking up the side of the pyramid. This shows that exercise is important for balanced eating. Exercise helps you use any extra energy in the foods you eat. The more active you are, the more energy you use. You should try to get at least an hour of physical activity just about every day. Pictured below are some activities that can help you use extra energy ( Figure 1.4). | text | null |
L_0486 | choosing healthy foods | T_2844 | Any unused energy in food is stored in the body as fat. This is true whether the extra energy comes from carbohy- drates, proteins, or lipids. What happens if you take in more energy than you use, day after day? You will store more and more fat and become overweight. Eventually, you may become obese. Obesity is having a very high percentage of body fat. Obese people are at least 20 percent heavier than their healthy weight range. The excess body fat of obesity is linked to many diseases. Obese people often have serious health problems, such as diabetes, high blood pressure, and high cholesterol. They are also more likely to develop arthritis and some types of cancer. People who remain obese during their entire adulthood usually do not live as long as people who stay within a healthy weight range. The current generation of children and teens is the first generation in our history that may have a shorter life than their parents. The reason is their high rate of obesity and the health problems associated with obesity. You can avoid gaining weight and becoming obese. The choice is yours. Choose healthy foods by using MyPyramid and reading food labels. Then get plenty of exercise to balance the energy in the foods you eat. | text | null |
L_0487 | chordates | T_2845 | Did you know that fish, amphibians, reptiles, birds, and mammals are all related? They are all chordates. Chordates are a group of animals that includes vertebrates, as well as several closely related invertebrates. Chordates (phylum Chordata) are named after a feature they all share, a notochord. A notochord is a hollow nerve cord along the back. | text | null |
L_0487 | chordates | T_2846 | Chordates are defined by a set of four characteristics that are shared by these animals at some point during their development. In some chordates, all four traits are present in the adult animal and serve important functions. However, in many chordates, including humans, some traits are present only during the embryonic stage. After that, these traits may disappear. All chordates have four main traits ( Figure 1.1): 1. Post-anal tail: The tail is opposite the head and extends past the anus. 2. Dorsal hollow nerve cord: "Dorsal" means that the nerve cord runs along the top of the animal. In some animals, the nerve cord develops into the brain and spinal cord. 3. Notochord: The notochord lies below the nerve cord. It is a rigid structure where muscles attach. 4. Pharyngeal slits: Pharyngeal slits are used to filter out food from water by some simple chordates. In most chordates, however, they are only present during the embryonic stages and serve no apparent purpose. Body Plan of a Typical Chordate. The body plan of a chordate includes a post- anal tail, notochord, dorsal hollow nerve cord, and pharyngeal slits. | text | null |
L_0487 | chordates | T_2847 | The chordates are divided into nine classes. Five of the classes are the fish, amphibians, reptiles, birds, and mammals. There are actually five classes of marine chordates (for example, sharks are cartilaginous fish which are distinct from bony fish), and these will be discussed in additional concepts. The chordate phylum is broken down into three subphyla: 1. Urochordata: The tunicates, pictured in the introduction, make up this group. The urochordates are sessile (non-moving) marine animals with sack-like bodies and tubes for water movement. Urochordates have a notochord and nerve cord only during the larval stage. 2. Cephalochordata: Cephalochordates include the lancelets ( Figure 1.2), fish-like marine animals often found half-buried in the sand. Cephalochordates have a notochord and nerve cord but no backbone. 3. Vertebrata: Humans and other mammals, along with fish, amphibians, reptiles, and birds, fall in this category. In vertebrates, the notochord is typically smaller and surrounded by a backbone. The lancelet, an example of a chordate, is found in shallow ocean waters. | text | null |
L_0491 | cnidarians | T_2856 | Cnidarians, in the phylum Cnidaria, include organisms such as the jellyfish, corals, and sea anemones. These animals are found in shallow ocean water. You might know that these animals can give you a painful sting if you step on them. Thats because cnidarians have stinging cells known as nematocysts. Cnidarians use nematocysts to catch their food. When touched, the nematocysts release a thread of poison that can be used to paralyze prey. Cnidarians are among the simplest of the so-called "higher" organisms, but are also among the most beautiful. | text | null |
L_0491 | cnidarians | T_2857 | The body plan of cnidarians is unique because these organisms show radial symmetry, making these animals very different from those that evolved before them. Radial symmetry means that they have a circular body plan, and any cut through the center of the animal leaves two equal halves. The cnidarians have two basic body forms: 1. Polyp: The polyp is a cup-shaped body with the mouth facing upward, such as a sea anemone and coral. 2. Medusa: The medusa is a bell-shaped body with the mouth and tentacles facing downward, such as a jellyfish. Unlike the sponges which evolved prior to cnidarians, the cnidarians are made up of true tissues. The inside of a cnidarian is called the gastrovascular cavity, a large space that helps the organism digest and move nutrients around the body. The cnidarians also have nerve tissue organized into a net-like structure, known as a nerve-net, with connected nerve cells dispersed throughout the body. Cnidarians do not have true organs, however. Reproduction is by asexual budding (polyps) or sexual formation of gametes (medusae, some polyps). The result of sexual reproduction is a larva, which can swim on its own. | text | null |
L_0491 | cnidarians | T_2858 | Some types of cnidarians are also known to form colonies. Two examples are described below. 1. The Portuguese Man o War ( Figure 1.1) looks like a single organism but is actually a colony of polyps. One polyp is filled with air to help the colony float, while several feeding polyps hang below with tentacles. The tentacles are full of nematocysts. The Portuguese Man o War is known to cause extremely painful stings to swimmers and surfers who accidentally brush up against it in the water. 2. Coral reefs ( Figure below) look like big rocks, but they are actually alive. They are built from cnidarians called corals. The corals are sessile (non-moving) polyps that can use their tentacles to feed on ocean creatures that pass by. Their skeletons are made up of calcium carbonate, which is also known as limestone. Over long periods of time, their skeletons build on each other to produce large structures known as coral reefs. Coral reefs are important habitats for many different types of ocean life. Corals are colonial cnidarians. | text | null |
L_0492 | competition | T_2859 | Recall that ecology is the study of how living organisms interact with each other and with their environment. But how do organisms interact with each other? Organisms interact with each other through various mechanisms, one of which is competition. Competition occurs when organisms strive for limited resources. Competition can be for food, water, light, or space. This interaction can be between organisms of the same species (intraspecific) or between organisms of different species (interspecific). Intraspecific competition happens when members of the same species compete for the same resources. For example, two trees may grow close together and compete for light. One may out-compete the other by growing taller to get more available light. As members of the same species are usually genetically different, they have different characteristics, and in this example, one tree grows taller than the other. The organism that is better adapted to that environment is better able to survive. The other organism may not survive. In this example, it is the taller tree that is better adapted to the environment. Interspecific competition happens when individuals of different species strive for a limited resource in the same area. Since any two species have different traits, one species will be able to out-compete the other. One species will be better adapted to its environment, and essentially "win" the competition. The other species will have lower reproductive success and lower population growth, resulting in a lower survival rate. For example, cheetahs and lions feed on similar prey. If prey is limited, then lions may catch more prey than cheetahs. This will force the cheetahs to either leave the area or suffer a decrease in population. Looking at different types of competition, ecologists developed the competitive exclusion principle. The principle states that species less suited to compete for resources will either adapt, move from the area, or die out. In order for two species within the same area to coexist, they may adapt by developing different specializations. This is known as character displacement. An example of character displacement is when different birds adapt to eating different types of food. They can develop different types of bills, like Darwins Finches ( Figure 1.1). Therefore, competition for resources within and between species plays an important role in evolution through natural selection. An example of character displacement, showing different types of bill for eating different types of foods, in Darwins or Galapagos Finches. | text | null |
L_0495 | consumers and decomposers | T_2866 | Recall that producers make their own food through photosynthesis. But many organisms are not producers and cannot make their own food. So how do these organisms obtain their energy? They must get their energy from other organisms. They must eat other organisms, or obtain their energy from these organisms some other way. The organisms that obtain their energy from other organisms are called consumers. All animals are consumers, and they eat other organisms. Fungi and many protists and bacteria are also consumers. But, whereas animals eat other organisms, fungi, protists, and bacteria "consume" organisms through different methods. The consumers can be placed into different groups, depending on what they consume. Herbivores are animals that eat producers to get energy. For example, rabbits and deer are herbivores that eat plants. The caterpillar pictured below ( Figure 1.1) is a herbivore. Animals that eat phytoplankton in aquatic environments are also herbivores. Carnivores feed on animals, either herbivores or other carnivores. Snakes that eat mice are carnivores. Hawks that eat snakes are also carnivores ( Figure 1.1). Omnivores eat both producers and consumers. Most people are omnivores, since they eat fruits, vegetables, and grains from plants, and also meat and dairy products from animals. Dogs, bears, and raccoons are also omnivores. Examples of consumers are caterpillars (herbivores) and hawks (carnivore). | text | null |
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