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L_0597 | mendels laws and genetics | T_3169 | This law explains what Mendel had seen in the F1 generation when a tall plant was crossed with a short plant. The two heredity factors in this case were the short and tall factors. Each individual in the F1 would have one of each factor, and as the tall factor is dominant to the short factor (the recessive factor), all the plants appeared tall. In describing genetic crosses, letters are used. The dominant factor is represented with a capital letter (T for tall) while the recessive factor is represented by a lowercase letter (t). For the T and t factors, three combinations are possible: TT, Tt, and tt. TT plants will be tall, while plants with tt will be short. Since T is dominant to t, plants that are Tt will be tall because the dominant factor masks the recessive factor. In this example, we are crossing a TT tall plant with a tt short plant. As each parent gives one factor to the F1 generation, all of the F1 generation will be Tt tall plants. When the F1 generation (Tt) is allowed to self-pollinate, each parent will give one factor (T or t) to the F2 generation. So the F2 offspring will have four possible combinations of factors: TT, Tt, tT, or tt. According to the laws of probability, 25% of the offspring would be tt, so they would appear short. And 75% would have at least one T factor and would be tall. | text | null |
L_0598 | mendels pea plants | T_3170 | What does the word "inherit" mean? You may have inherited something of value from a grandparent or another family member. To inherit is to receive something from someone who came before you. You can inherit objects, but you can also inherit traits. For example, you can inherit a parents eye color, hair color, or even the shape of your nose and ears! Genetics is the study of inheritance. The field of genetics seeks to explain how traits are passed on from one generation to the next. In the late 1850s, an Austrian monk named Gregor Mendel ( Figure 1.1) performed the first genetics experiments. To study genetics, Mendel chose to work with pea plants because they have easily identifiable traits ( Figure 1.2). For example, pea plants are either tall or short, which is an easy trait to observe. Furthermore, pea plants grow quickly, so he could complete many experiments in a short period of time. Mendel also used pea plants because they can either self-pollinate or be cross-pollinated. Self-pollination means that only one flower is involved; the flowers own pollen lands on the female sex organs. Cross pollination is done by hand by moving pollen from one flower to the stigma of another (just like bees do naturally). As a result, one plants sex cells combine with another plants sex cells. This is called a "cross." These crosses produce offspring Gregor Mendel, the "father" of genetics. Characteristics of pea plants. (or "children"), just like when male and female animals mate. Since Mendel could move pollen between plants, he could carefully control and then observe the results of crosses between two different types of plants. He studied the inheritance patterns for many different traits in peas, including round seeds versus wrinkled seeds, white flowers versus purple flowers, and tall plants versus short plants. Because of his work, Mendel is considered the "Father of Genetics." | text | null |
L_0598 | mendels pea plants | T_3170 | What does the word "inherit" mean? You may have inherited something of value from a grandparent or another family member. To inherit is to receive something from someone who came before you. You can inherit objects, but you can also inherit traits. For example, you can inherit a parents eye color, hair color, or even the shape of your nose and ears! Genetics is the study of inheritance. The field of genetics seeks to explain how traits are passed on from one generation to the next. In the late 1850s, an Austrian monk named Gregor Mendel ( Figure 1.1) performed the first genetics experiments. To study genetics, Mendel chose to work with pea plants because they have easily identifiable traits ( Figure 1.2). For example, pea plants are either tall or short, which is an easy trait to observe. Furthermore, pea plants grow quickly, so he could complete many experiments in a short period of time. Mendel also used pea plants because they can either self-pollinate or be cross-pollinated. Self-pollination means that only one flower is involved; the flowers own pollen lands on the female sex organs. Cross pollination is done by hand by moving pollen from one flower to the stigma of another (just like bees do naturally). As a result, one plants sex cells combine with another plants sex cells. This is called a "cross." These crosses produce offspring Gregor Mendel, the "father" of genetics. Characteristics of pea plants. (or "children"), just like when male and female animals mate. Since Mendel could move pollen between plants, he could carefully control and then observe the results of crosses between two different types of plants. He studied the inheritance patterns for many different traits in peas, including round seeds versus wrinkled seeds, white flowers versus purple flowers, and tall plants versus short plants. Because of his work, Mendel is considered the "Father of Genetics." | text | null |
L_0598 | mendels pea plants | T_3171 | In one of Mendels early experiments, he crossed a short plant and a tall plant. What do you predict the offspring of these plants were? Medium-sized plants? Most people during Mendels time would have said medium-sized. But an unexpected result occurred. Mendel observed that the offspring of this cross (called the F1 generation) were all tall plants! Next, Mendel let the F1 generation self-pollinate. That means the tall plant offspring were crossed with each other. He found that 75% of their offspring (the F2 generation) were tall, while 25% were short. Shortness skipped a generation. But why? In all, Mendel studied seven characteristics, with almost 20,000 F2 plants analyzed. All of his results were similar to the first experimentabout three out of every four plants had one trait, while just one out of every four plants had the other. For example, he crossed purple flowered-plants and white flowered-plants. Do you think the colors blended? No, they did not. Just like the previous experiment, all offspring in this cross (the F1 generation) were one color: purple. In the F2 generation, 75% of plants had purple flowers and 25% had white flowers ( Figure 1.3). There was no blending of traits in any of Mendels experiments. The results of Mendels experiment with purple flowered and white flowered-plants numerically matched the results of his experiments with other pea plant traits. | text | null |
L_0600 | microevolution and macroevolution | T_3173 | Does evolution only happen gradually through small changes? Or is it possible that drastic environmental changes can cause new species to evolve? Or can both small and large changes occur? Evolutionary changes can be both big and small. Some evolutionary changes do not create new species, but result in changes at the population level. A population is a group of organisms of the same species that live in the same area ( Figure 1.1). But what exactly is the definition of a species? A species is a group of organisms that have similar characteristics (they are genetically similar) and can mate with one another to produce fertile offspring. This school of fish are considered mem- bers of the same species because they are able to mate with one another. They are also considered a population because they live in the same part of the ocean. | text | null |
L_0600 | microevolution and macroevolution | T_3174 | You already know that evolution is the change in species over time. Most evolutionary changes are small and do not lead to the creation of a new species. When populations change in small ways over time, the process is called microevolution. Microevolution results in changes within a species. An example of microevolution is the evolution of mosquitoes that cannot be killed by pesticides, called pesticide- resistant mosquitoes. Imagine that you have a pesticide that kills most of the mosquitoes in your state. Through a random mutation, some of the mosquitoes have resistance to the pesticide. As a result of the widespread use of this pesticide, most of the remaining mosquitoes are the pesticide-resistant mosquitoes. When these mosquitoes repro- duce the next year, they produce more mosquitoes with the pesticide-resistant trait. Soon, most of the mosquitoes in your state are resistant to the pesticide. This is an example of microevolution because the number of mosquitoes with this trait changed. However, this evolutionary change did not create a new species of mosquito because the pesticide-resistant mosquitoes can still reproduce with other non-pesticide-resistant mosquitoes. | text | null |
L_0600 | microevolution and macroevolution | T_3175 | Macroevolution refers to much bigger evolutionary changes that result in new species. Macroevolution may happen: 1. When microevolution occurs repeatedly over a long period of time and leads to the creation of a new species. 2. As a result of a major environmental change, such as a volcanic eruption, earthquake, or an asteroid hitting Earth, which changes the environment so much that natural selection leads to large changes in the traits of a species. After thousands of years of isolation from each other, Darwins finch populations have experienced both microevo- lution and macroevolution. These finch populations cannot breed with other finch populations when they are brought together. Since they do not breed together, they are classified as separate species. | text | null |
L_0604 | modern genetics | T_3184 | Mendel laid the foundation for modern genetics, but there were still a lot of questions he left unanswered. What exactly are the dominant and recessive factors that determine how all organisms look? And how do these factors work? Since Mendels time, scientists have discovered the answers to these questions. Genetic material is made out of DNA. It is the DNA that makes up the hereditary factors that Mendel identified. By applying our modern knowledge of DNA and chromosomes, we can explain Mendels findings and build on them. In this concept, we will explore the connections between Mendels work and modern genetics. | text | null |
L_0604 | modern genetics | T_3185 | Recall that our DNA is wound into chromosomes. Each of our chromosomes contains a long chain of DNA that encodes hundreds, if not thousands, of genes. Each of these genes can have slightly different versions from individual to individual. These variants of genes are called alleles. Each parent only donates one allele for each gene to an offspring. For example, remember that for the height gene in pea plants there are two possible factors. These factors are alleles. There is a dominant allele for tallness (T) and a recessive allele for shortness (t). | text | null |
L_0604 | modern genetics | T_3186 | Genotype is a way to describe the combination of alleles that an individual has for a certain gene ( Table 1.1). For each gene, an organism has two alleles, one on each chromosome of a homologous pair of chromosomes (think of it as one allele from Mom, one allele from Dad). The genotype is represented by letter combinations, such as TT, Tt, and tt. When an organism has two of the same alleles for a specific gene, it is homozygous (homo means "same") for that gene. An organism can be either homozygous dominant (TT) or homozygous recessive (tt). If an organism has two different alleles (Tt) for a certain gene, it is known as heterozygous (hetero means different). Genotype Homozygous Heterozygous Homozygous dominant Homozygous recessive Definition Two of the same allele One dominant allele and one reces- sive allele Two dominant alleles Two recessive alleles Example TT or tt Tt TT tt Phenotype is a way to describe the traits you can see. The genotype is like a recipe for a cake, while the phenotype is like the cake made from the recipe. The genotype expresses the phenotype. For example, the phenotypes of Mendels pea plants were either tall or short, or they were purple-flowered or white-flowered. Can organisms with different genotypes have the same phenotypes? Lets see. What is the phenotype of a pea plant that is homozygous dominant (TT) for the tall trait? Tall. What is the phenotype of a pea plant that is heterozygous (Tt)? It is also tall. The answer is yes, two different genotypes can result in the same phenotype. Remember, the recessive phenotype will be expressed only when the dominant allele is absent, or when an individual is homozygous recessive (tt) ( Figure 1.1). Different genotypes (AA, Aa, aa or TT, Tt, tt) will lead to different phenotypes, or different appearances of the organism. | text | null |
L_0605 | molecular evidence for evolution | T_3187 | Arguably, some of the best evidence of evolution comes from examining the molecules and DNA found in all living things. Beginning in the 1940s, scientists studying molecules and DNA have confirmed conclusions about evolution drawn from other forms of evidence. Molecular clocks are used to determine how closely two species are related by calculating the number of differences between the species DNA sequences or amino acid sequences. These clocks are sometimes called gene clocks or evolutionary clocks. The fewer the differences, the less time since the species split from each other and began to evolve into different species ( Figure 1.1). A chicken and a gorilla will have more differences between their DNA and amino acid sequences than a gorilla and an orangutan. That means the chicken and gorilla had a common ancestor a very long time ago, while the gorilla and orangutan shared a more recent common ancestor. This provides additional evidence that the gorilla and orangutan are more closely related than the gorilla and the chicken. Which pair of organisms would have more molecular differences, a mammal and a bird, a mammal and a frog, or a mammal and a fish? On the other hand, animals may look similar but can have very different DNA sequences and evolutionary ancestry. Which would have more DNA sequences in common, a whale and a horse, or a whale and a shark? Almost all organisms are made from DNA with the same building blocks. The genomes (all of the genes in an organism) of all mammals are almost identical. The genomes, or all the DNA sequences of all the genes of an organism, have been determined for many different organisms. The comparison of genomes provides new information about the relationships among species and how evolution occurs ( Figure 1.2). Molecular evidence for evolution also includes: 1. The same biochemical building blocks, such as amino acids and nucleotides, are found in all organisms, from bacteria to plants and animals. Recall that amino acids are the building blocks of proteins, and nucleotides are the building blocks of DNA and RNA. 2. DNA and RNA determine the development of all organisms. 3. The similarities and differences between the genomes confirm patterns of evolution. | text | null |
L_0611 | natural selection | T_3204 | The theory of evolution by natural selection means that the inherited traits of a population change over time. Inherited traits are features that are passed from one generation to the next. For example, your eye color is an inherited trait. You inherited your eye color from your parents. Inherited traits are different from acquired traits, or traits that organisms develop over a lifetime, such as strong muscles from working out ( Figure 1.1). Natural selection explains how organisms in a population develop traits that allow them to survive and reproduce. Natural selection means that traits that offer an advantage will most likely be passed on to offspring; individuals with those traits have a better chance of surviving. Evolution occurs by natural selection. Take the giant tortoises on the Galpagos Islands as an example. If a short-necked tortoise lives on an island with fruit located at a high level, will the short-necked tortoise survive? No, it will not, because it will not be able to reach the food it needs to survive. If all of the short necked tortoises die, and the long-necked tortoises survive, then, over time, only the long-necked trait will be passed down to offspring. All of the tortoises with long-necks will be Human earlobes may be attached or free. You inherited the particular shape of your earlobes from your parents. Inherited traits are influenced by genes, which are passed on to offspring and future genera- tions. Things not influenced by genes are not passed on to your offspring. Natural selection only operates on traits like ear- lobe shape that have a genetic basis, not on traits that are acquired, like a summer tan. "naturally selected" to survive. Organisms that are not well-adapted, for whatever reason, to their environment, will naturally have less of a chance of surviving and reproducing. Every plant and animal depends on its traits to survive. Survival may include getting food, building homes, and attracting mates. Traits that allow a plant, animal, or other organism to survive and reproduce in its environment are called adaptations. Natural selection occurs when: 1. There is some variation in the inherited traits of organisms within a species. Without this variation, natural selection would not be possible. 2. Some of these traits will give individuals an advantage over others in surviving and reproducing. 3. These individuals will be likely to have more offspring. Imagine how in the Arctic, dark fur makes a rabbit easy for foxes to spot and catch in the snow. Therefore, white fur is a beneficial trait that improves the chance that a rabbit will survive, reproduce, and pass the trait of white fur on to its offspring ( Figure 1.2). Through this process of natural selection, dark fur rabbits will become uncommon over time. Rabbits will adapt to have white fur. In essence, the selection of rabbits with white fur - the beneficial trait - is a natural process. | text | null |
L_0611 | natural selection | T_3205 | Scientists estimate that there are between 5 million and 30 million species on the planet. But why are there so many? Different species are well-adapted to live and survive in many different types of environments. As environments change over time, organisms must constantly adapt to those environments. Diversity of species increases the chance that at least some organisms adapt and survive any major changes in the environment. For example, if a natural disaster kills all of the large organisms on the planet, then the small organisms will continue to survive. | text | null |
L_0617 | nonvascular plants | T_3218 | Nonvascular seedless plants, as their name implies, lack vascular tissue. Vascular tissue is specialized tissue that transports water, nutrients, and food in plants. As they lack vascular tissue, they also do not have true roots, stems, or leaves. Nonvascular plants do often have a leafy appearance, though, and they can have stem-like and root-like structures. These plants are very short because they cannot move nutrients and water up a stem. Nonvascular seedless plants, also known as bryophytes, are classified into three phyla: 1. Mosses 2. Hornworts 3. Liverworts | text | null |
L_0617 | nonvascular plants | T_3219 | Mosses are most often recognized as the green fuzz on damp rocks and trees in a forest. If you look closely, you will see that most mosses have tiny stem-like and leaf-like structures. This is the gametophyte stage. Remember that a gametophyte is haploid, having only one set of chromosomes. The gametophyte produces the gametes that, after fertilization, develop into the diploid sporophyte with two sets of chromosomes. The sporophyte forms a capsule, called the sporangium, which releases spores ( Figure 1.1). Sporophytes sprout up on stalks from this bed of moss gametophytes. Notice that both the sporophytes and gametophytes exist at the same time. | text | null |
L_0617 | nonvascular plants | T_3220 | Hornworts are named for their appearance. The "horn" part of the name comes from their hornlike sporophytes, and wort comes from the Anglo-Saxon word for herb. The hornlike sporophytes grow from a base of flattened lobes, which are the gametophytes ( Figure 1.2). They usually grow in moist and humid areas. In hornworts, the horns are the sporo- phytes that rise up from the leaflike ga- metophyte. | text | null |
L_0617 | nonvascular plants | T_3221 | Liverworts have two distinct appearances: they can either be leafy like mosses or flattened and ribbon-like. Liver- worts get their name from the type with the flattened bodies, which can resemble a liver ( Figure 1.3). Liverworts can often be found along stream beds. Liverworts with a flattened, ribbon-like body are called thallose liverworts. | text | null |
L_0620 | organization of living things | T_3228 | When you see an organism that you have never seen before, you probably put it into a group without even thinking. If it is green and leafy, you probably call it a plant. If it is long and slithers, you probably call it as a snake. How do you make these decisions? You look at the physical features of the organism and think about what it has in common with other organisms. Scientists do the same thing when they classify, or put into categories, living things. Scientists classify organisms not only by their physical features, but also by how closely related they are. Lions and tigers look like each other more than they look like bears, but are lions and tigers related? Evolutionarily speaking, yes. Evolution is the change in a species over time. Lions and tigers both evolved from a common ancestor. So it turns out that the two cats are actually more closely related to each other than to bears. How an organism looks and how it is related to other organisms determines how it is classified. | text | null |
L_0620 | organization of living things | T_3229 | People have been concerned with classifying organisms for thousands of years. Over 2,000 years ago, the Greek philosopher Aristotle developed a classification system that divided living things into several groups that we still use today, including mammals, insects, and reptiles. Carolus (Carl) Linnaeus (1707-1778) ( Figure 1.1) built on Aristotles work to create his own classification system. He invented the way we name organisms today, with each organism having a two word name. Linnaeus is considered the inventor of modern taxonomy, the science of naming and grouping organisms. In the 18th century, Carl Linnaeus invented the two-name system of naming organisms (genus and species) and introduced the most complete classification system then known. Linnaeus developed binomial nomenclature, a way to give a scientific name to every organism. In this system, each organism receives a two-part name in which the first word is the genus (a group of species), and the second word refers to one species in that genus. For example, a coyotes species name is Canis latrans. Latrans is the species and Canis is the genus, a larger group that includes dogs, wolves, and other dog-like animals. Here is another example: the red maple, Acer rubra, and the sugar maple, Acer saccharum, are both in the same genus and they look similar ( Figure 1.2). Notice that the genus is capitalized and the species is not, and that the whole scientific name is in italics. Tigers (Panthera tigris) and lions (Panthera leo) have the same genus name, but are obviously different species. The names may seem strange, but the names are written in a language called Latin. These leaves are from two different species of trees in the Acer, or maple, genus. The green leaf (far left) is from the sugar maple, and the red leaf (center ) are from the red maple. One of the character- istics of the maple genus is winged seeds (far right). | text | null |
L_0620 | organization of living things | T_3229 | People have been concerned with classifying organisms for thousands of years. Over 2,000 years ago, the Greek philosopher Aristotle developed a classification system that divided living things into several groups that we still use today, including mammals, insects, and reptiles. Carolus (Carl) Linnaeus (1707-1778) ( Figure 1.1) built on Aristotles work to create his own classification system. He invented the way we name organisms today, with each organism having a two word name. Linnaeus is considered the inventor of modern taxonomy, the science of naming and grouping organisms. In the 18th century, Carl Linnaeus invented the two-name system of naming organisms (genus and species) and introduced the most complete classification system then known. Linnaeus developed binomial nomenclature, a way to give a scientific name to every organism. In this system, each organism receives a two-part name in which the first word is the genus (a group of species), and the second word refers to one species in that genus. For example, a coyotes species name is Canis latrans. Latrans is the species and Canis is the genus, a larger group that includes dogs, wolves, and other dog-like animals. Here is another example: the red maple, Acer rubra, and the sugar maple, Acer saccharum, are both in the same genus and they look similar ( Figure 1.2). Notice that the genus is capitalized and the species is not, and that the whole scientific name is in italics. Tigers (Panthera tigris) and lions (Panthera leo) have the same genus name, but are obviously different species. The names may seem strange, but the names are written in a language called Latin. These leaves are from two different species of trees in the Acer, or maple, genus. The green leaf (far left) is from the sugar maple, and the red leaf (center ) are from the red maple. One of the character- istics of the maple genus is winged seeds (far right). | text | null |
L_0620 | organization of living things | T_3230 | Modern taxonomists have reordered many groups of organisms since Linnaeus. The main categories that biologists use are listed here from the most specific to the least specific category ( Figure 1.3). All organisms can be classified into one of three domains, the least specific grouping. The three domains are Bacteria, Archaea, and Eukarya. The Kingdom is the next category after the Domain. All life is divided among six kingdoms: Kingdom Bacteria, Kingdom Archaea, Kingdom Protista, Kingdom Plantae, Kingdom Fungi, and Kingdom Animalia. This diagram illustrates the classification categories for organisms, with the broad- est category (kingdom) at the bottom, and the most specific category (species) at the top. We are Homo sapiens. Homo is the genus of great apes that includes modern humans and closely related species, and sapiens is the only living species of the genus. | text | null |
L_0620 | organization of living things | T_3231 | Even though naming species is straightforward, deciding if two organisms are the same species can sometimes be difficult. Linnaeus defined each species by the distinctive physical characteristics shared by these organisms. But two members of the same species may look quite different. For example, people from different parts of the world sometimes look very different, but we are all the same species ( Figure 1.4). So how is a species defined? A species is defined as a group of similar individuals that can interbreed with one another and produce fertile offspring. A species does not produce fertile offspring with other species. | text | null |
L_0622 | origin of species | T_3236 | The creation of a new species is called speciation. Most new species develop naturally. But humans have also artificially created new breeds and species for thousands of years. New species develop naturally through the process of natural selection. Due to natural selection, organisms with traits that better enable them to adapt to their environment will tend to survive and reproduce in greater numbers. Natural selection causes beneficial heritable traits to become more common in a population and unfavorable heritable traits to become less common. For example, a giraffes neck is beneficial because it allows the giraffe to reach leaves high in trees. Natural selection caused this beneficial trait to become more common than short necks. As new changes in the DNA sequence are constantly being generated in a populations gene pool (changing the populations allele frequencies), some of these changes will be beneficial and result in traits that allow adaptation and survival. Natural selection causes evolution of a species as these beneficial traits become more common within a population. Evolution can occur within a species without completely resulting in a new species. Therefore, evolution and speciation are not the same. | text | null |
L_0622 | origin of species | T_3237 | Artificial selection occurs when humans select which plants or animals to breed in order to pass on specific traits to the next generation. For example, a farmer may choose to breed only cows that produce the best milk. Farmers would also avoid breeding cows that produce less milk. In this way, selective breeding of the cows would increase milk quality and quantity. Humans have also artificially bred dogs to create new breeds ( Figure 1.1). Artificial Selection: Humans used artificial selection to create these different breeds. Both dog breeds are descended from the same wolves, and their genes are almost identical. | text | null |
L_0622 | origin of species | T_3238 | There are two main ways that speciation happens naturally. Both processes create new species by reproductively isolating populations of the same species from each other. Organisms can be geographically isolated or isolated by a behavior. Either way, they will no longer be able to mate. Over a long period of time, usually thousands of years, each of the isolated populations evolves in a different direction, forming distinct species. How do you think scientists test whether two populations are separate species? They bring species from two populations back together again. If the two populations do not mate and produce fertile offspring, they are separate species. | text | null |
L_0622 | origin of species | T_3239 | Allopatric speciation occurs when groups from the same species are geographically isolated for long periods. Imagine all the ways that plants or animals could be isolated from each other: Emergence of a mountain range. Formation of a canyon. New rivers or streams. Here are two examples of allopatric speciation: Darwin observed thirteen distinct finch species on the Galpagos Islands that had evolved from the same ancestor. Different finch populations lived on separate islands with different environments. They evolved to best adapt to those particular environments. Later, scientists were able to determine which finches had evolved into distinct species by bringing members of each population together. The birds that could not mate were a separate species. When the Grand Canyon in Arizona formed, two populations of one squirrel species were separated by the giant canyon. After thousands of years of isolation from each other, the squirrel populations on the northern wall of the canyon looked and behaved differently from those on the southern wall ( Figure 1.2). North rim squirrels have white tails and black bellies. Squirrels on the south rim have white bellies and dark tails. They cannot mate with each other, so they are different species. Abert squirrel (left) on the southern rim of the Grand Canyon. Kaibab squirrel (right) found on northern rim of the Grand Canyon. | text | null |
L_0622 | origin of species | T_3240 | Sympatric speciation occurs when groups from the same species stop mating because of something other than physical or geographic separation. The behavior of two groups that live in the same region is an example of such separation. The separation may be caused by different mating seasons, for example. Sympatric speciation is more difficult to identify. Here are two examples of sympatric speciation: Some scientists suspect that two groups of orcas (killer whales) live in the same part of the Pacific Ocean part of the year but do not mate. The two groups hunt different prey species, eat different foods, sing different songs, and have different social interactions ( Figure 1.3). Two groups of Galpagos Island finch species lived in the same space, but each had his or her own distinct mating signals. Members of each group selected mates according to different beak structures and bird calls. The behavioral differences kept the groups separated until they formed different species. | text | null |
L_0631 | plant characteristics | T_3265 | Plants have adapted to a variety of environments, from the desert to the tropical rain forest to lakes and oceans. In each environment, plants have become crucial to supporting animal life. Plants are the food that animals eat. Plants also provide places for animals, such as insects and birds, to live; many birds build nests in plants. From tiny mosses to gorgeous rose bushes to extremely large redwood trees ( Figure 1.1), the organisms in this kingdom, Kingdom Plantae, have three main features. They are all: 1. Eukaryotic. 2. Photosynthetic. 3. Multicellular. Recall that eukaryotic organisms also include animals, protists, and fungi. Eukaryotes have cells with nuclei that contain DNA, and membrane-bound organelles, such as mitochondria. Photosynthesis is the process by which plants capture the energy of sunlight and use carbon dioxide from the air (and water) to make their own food, the carbohydrate glucose. Plants have chloroplasts, the organelle of photosynthesis, and are known as producers and autotrophs. Other organisms are heterotrophic consumers, meaning they must obtain their nutrients from another organism, as these organisms lack chloroplasts. Lastly, plants must be multicellular, composed of more than one cell. There are no single-celled plants. Recall that some protists, such as algae, are eukaryotic and photosynthetic but are not considered plants. Unlike plants, algae is mostly unicellular. | text | null |
L_0632 | plant classification | T_3266 | Plants are formally divided into 12 phyla (plural for phylum), and these phyla are gathered into four groups ( Figure 1. Nonvascular plants evolved first. They are distinct from the algae because they keep the embryo inside of the reproductive structure after fertilization. These plants do not have vascular tissue, xylem or phloem, to transport nutrients, water, and food. Examples include mosses, liverworts, and hornworts. Without vascular tissue, these plants do not grow very tall. 2. Seedless vascular plants evolved to have vascular tissue after the nonvascular plants but do not have seeds. Examples include the ferns, whisk ferns, club mosses, and horsetails. Vascular tissue allowed these plants to grow taller. 3. Gymnosperms evolved to have seeds but do not have flowers. Examples of gymnosperms include the Redwood, Fir, and Cypress trees. Gymnos means "naked" in Greek; the seeds of gymnosperms are naked, not protected by flowers. 4. Flowering plants, or angiosperms, evolved to have vascular tissue, seeds, and flowers. Examples of an- giosperms include magnolia trees, roses, tulips, and tomatoes. The plant kingdom contains a diversity of organisms. | text | null |
L_0633 | plant hormones | T_3267 | Plants may not move, but that does not mean they dont respond to their environment. Plants can sense gravity, light, touch, and seasonal changes. For example, you might have noticed how a house plant bends toward a bright window. Plants can sense and then grow toward the source of light. Scientists say that plants are able to respond to "stimuli," or somethingusually in the environmentthat results in a response. For instance, light is the stimulus, and the plant moving toward the light is the "response." Hormones are special chemical messengers molecules that help organisms, including plants, respond to stimuli in their environment. In order for plants to respond to the environment, their cells must be able to communicate with other cells. Hormones send messages between the cells. Animals, like humans, also have hormones, such as testosterone or estrogen, to carry messages from cell to cell. In both plants and animals, hormones travel from cell to cell in response to a stimulus; they also activate a specific response. | text | null |
L_0633 | plant hormones | T_3268 | Five different types of plant hormones are involved in the main responses of plants, and they each have different functions ( Table 1.1). Hormone Ethylene Gibberellins Cytokinins Abscisic Acid Auxins Function Fruit ripening and abscission Break the dormancy of seeds and buds; promote growth Promote cell division; prevent senescence Close the stomata; maintain dormancy Involved in tropisms and apical dominance | text | null |
L_0633 | plant hormones | T_3269 | The hormone ethylene has two functions. It (1) helps ripen fruit and (2) is involved in the process of abscission, the dropping of leaves, fruits, and flowers. When a flower is done blooming or a fruit is ripe and ready to be eaten, ethylene causes the petals or fruit to fall from a plant ( Figure 1.1 and Figure 1.2). Ethylene is an unusual plant hormone because it is a gas. That means it can move through the air, and a ripening apple can cause another apple to ripen, or even over-ripen. Thats why one rotten apple spoils the whole barrel! Some farmers spray their green peppers with ethylene gas to cause them to ripen faster and become red peppers. You can try to see how ethylene works by putting a ripe apple or banana with another unripe fruit in a closed container or paper bag. What do you think will happen to the unripe fruit? | text | null |
L_0633 | plant hormones | T_3270 | Gibberellins are hormones that cause the plant to grow. When gibberellins are applied to plants by scientists, the stems grow longer. Some gardeners or horticulture scientists add gibberellins to increase the growth of plants. The hormone ethylene causes flower petals to fall from a plant, a process known as abscission. Dwarf plants (small plants), on the other hand, have low levels of gibberellins ( Figure 1.3). Another function of gibberellins is to stop dormancy (resting time) of seeds and buds. Gibberellins signal that its time for a seed to germinate (sprout) or for a bud to open. Dwarf plants like this bonsai tree often have unusually low concentrations of gib- berellins. | text | null |
L_0633 | plant hormones | T_3270 | Gibberellins are hormones that cause the plant to grow. When gibberellins are applied to plants by scientists, the stems grow longer. Some gardeners or horticulture scientists add gibberellins to increase the growth of plants. The hormone ethylene causes flower petals to fall from a plant, a process known as abscission. Dwarf plants (small plants), on the other hand, have low levels of gibberellins ( Figure 1.3). Another function of gibberellins is to stop dormancy (resting time) of seeds and buds. Gibberellins signal that its time for a seed to germinate (sprout) or for a bud to open. Dwarf plants like this bonsai tree often have unusually low concentrations of gib- berellins. | text | null |
L_0633 | plant hormones | T_3271 | Cytokinins are hormones that cause plant cells to divide. Cytokinins were discovered from attempts to grow plant tissue in artificial environments ( Figure 1.4). Cytokinins prevent the process of aging (senescence). So florists sometimes apply cytokinins to cut flowers, so they do not get old and die. Cytokinins promote cell division and are necessary for growing plants in tissue cul- ture. A small piece of a plant is placed in sterile conditions to regenerate a new plant. | text | null |
L_0633 | plant hormones | T_3272 | Abscisic acid is misnamed because it was once believed to play a role in abscission (the dropping of leaves, fruits, and flowers), but we now know abscission is caused by ethylene. The actual role of abscisic acid is to close the stomata, the tiny openings in leaves that allow substances to enter and leave, and to maintain dormancy. When a plant is stressed due to lack of water, abscisic acid tells the stomata to close. This prevents water loss through the stomata. When the environment is not good for a seed to germinate, abscisic acid signals for the dormancy period of the seed to continue. Abscisic acid also tells the buds of plants to stay in the dormancy stage. When conditions improve, the levels of abscisic acid drop and the levels of gibberellins increase, signaling that is time to break dormancy ( Figure | text | null |
L_0633 | plant hormones | T_3273 | Auxins are hormones that play a role in plant growth. Auxins produced at the tip of the plant are involved in apical dominance, when the main central stem grows more strongly than other stems and branches. When the tip of the plant is removed, the auxins are no longer present, and the side branches begin to grow. This is why pruning a plant by cutting off the main branches helps produce a fuller plant with more branches. You actually need to cut branches off of a plant for it to grow more branches! Auxins are also involved in tropisms, responses to stimuli in the environment | text | null |
L_0634 | plant like protists | T_3274 | Plant-like protists are known as algae ( Figure 1.1). They are a large and diverse group. Plant-like protists are autotrophs. This means that they produce their own food. They perform photosynthesis to produce sugar by using carbon dioxide and water, and the energy from sunlight, just like plants. Unlike plants, however, plant-like protists do not have true stems, roots, or leaves. Most plant-like protists live in oceans, ponds, or lakes. Protists can be unicellular (single-celled) or multicellular (many-celled). Seaweed and kelp are examples of multicellular, plant-like protists. Kelp can be as large as trees and form a "forest" in the ocean ( Figure 1.2). Plant-like protists are essential to the ecosystem. They are the base of the marine food chain, and they produce oxygen through photosynthesis for animals to breathe. They are classified into a number of basic groups ( Table Red algae are a very large group of protists making up about 5,0006,000 species. They are mostly multicellular and live in the ocean. Many red algae are seaweeds and help create coral reefs. Macrocystis pyrifera (giant kelp) is a type of multicellular, plant-like protist. Phylum Description Chlorophyta Green algae (related to higher plants) Red algae Brown algae Diatoms, golden-brown algae, yellow-green algae Dinoflagellates Euglenoids Rhodophyta Phaeophyta Chrysophyta Pyrrophyta Euglenophyta Approximate Number of Species 7,500 5,000 1,500 12,000 Chlamydomnas, Volvox Porphyra Macrocystis Cyclotella 4,000 1,000 Gonyaulax Euglena | text | null |
L_0634 | plant like protists | T_3274 | Plant-like protists are known as algae ( Figure 1.1). They are a large and diverse group. Plant-like protists are autotrophs. This means that they produce their own food. They perform photosynthesis to produce sugar by using carbon dioxide and water, and the energy from sunlight, just like plants. Unlike plants, however, plant-like protists do not have true stems, roots, or leaves. Most plant-like protists live in oceans, ponds, or lakes. Protists can be unicellular (single-celled) or multicellular (many-celled). Seaweed and kelp are examples of multicellular, plant-like protists. Kelp can be as large as trees and form a "forest" in the ocean ( Figure 1.2). Plant-like protists are essential to the ecosystem. They are the base of the marine food chain, and they produce oxygen through photosynthesis for animals to breathe. They are classified into a number of basic groups ( Table Red algae are a very large group of protists making up about 5,0006,000 species. They are mostly multicellular and live in the ocean. Many red algae are seaweeds and help create coral reefs. Macrocystis pyrifera (giant kelp) is a type of multicellular, plant-like protist. Phylum Description Chlorophyta Green algae (related to higher plants) Red algae Brown algae Diatoms, golden-brown algae, yellow-green algae Dinoflagellates Euglenoids Rhodophyta Phaeophyta Chrysophyta Pyrrophyta Euglenophyta Approximate Number of Species 7,500 5,000 1,500 12,000 Chlamydomnas, Volvox Porphyra Macrocystis Cyclotella 4,000 1,000 Gonyaulax Euglena | text | null |
L_0636 | plants adaptations for life on land | T_3276 | The first photosynthetic organisms were bacteria that lived in the water. So, where did plants come from? Evidence shows that plants evolved from freshwater green algae, a protist ( Figure 1.1). The similarities between green algae and plants is one piece of evidence. They both have cellulose in their cell walls, and they share many of the same chemicals that give them color. So what separates green algae from green plants? There are four main ways that plants adapted to life on land and, as a result, became different from algae: The ancestor of plants is green algae. This picture shows a close up of algae on the beach. 1. In plants, the embryo develops inside of the female plant after fertilization. Algae do not keep the embryo inside of themselves but release it into water. This was the first feature to evolve that separated plants from green algae. This is also the only adaptation shared by all plants. 2. Over time, plants had to evolve from living in water to living on land. In early plants, a waxy layer called a cuticle evolved to help seal water in the plant and prevent water loss. However, the cuticle also prevents gases from entering and leaving the plant easily. Recall that the exchange of gassestaking in carbon dioxide and releasing oxygenoccurs during photosynthesis. 3. To allow the plant to retain water and exchange gases, small pores (holes) in the leaves called stomata also evolved ( Figure 1.2). The stomata can open and close depending on weather conditions. When its hot and dry, the stomata close to keep water inside of the plant. When the weather cools down, the stomata can open again to let carbon dioxide in and oxygen out. 4. A later adaption for life on land was the evolution of vascular tissue. Vascular tissue is specialized tissue that transports water, nutrients, and food in plants. In algae, vascular tissue is not necessary since the entire body is in contact with the water, and the water simply enters the algae. But on land, water may only be found deep in the ground. Vascular tissues take water and nutrients from the ground up into the plant, while also taking food down from the leaves into the rest of the plant. The two vascular tissues are xylem and phloem. Xylem is responsible for the transport of water and nutrients from the roots to the rest of the plant. Phloem carries the sugars made in the leaves to the parts of the plant where they are needed. | text | null |
L_0639 | predation | T_3282 | Predation is another mechanism in which species interact with each other. Predation is when a predator organism feeds on another living organism or organisms, known as prey. The predator always lowers the preys fitness. It does this by keeping the prey from surviving, reproducing, or both. Predator-prey relationships are essential to maintaining the balance of organisms in an ecosystem. Examples of predator-prey relationships include the lion and zebra, the bear and fish, and the fox and rabbit. There are different types of predation, including: true predation. grazing. parasitism. True predation is when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large prey. They tear it apart and chew it before eating it. Others, like bottlenose dolphins or snakes, may eat their prey whole. In some cases, the prey dies in the mouth or the digestive system of the predator. Baleen whales, for example, This lion is an example of a predator on the hunt. eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for prey, or they may sit and wait for prey to get within striking distance. Certain traits enable organisms to be effective hunters. These include camouflage, speed, and heightened senses. These traits also enable certain prey to avoid predators. In grazing, the predator eats part of the prey but does not usually kill it. You may have seen cows grazing on grass. The grass they eat grows back, so there is no real effect on the population. In the ocean, kelp (a type of seaweed) can regrow after being eaten by fish. Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could become dominant over others. Grazers on a grassland keep grass from growing out of control. Predators can be keystone species. These are species that can have a large effect on the balance of organisms in an ecosystem. For example, if all of the wolves are removed from a population, then the population of deer or rabbits may increase. If there are too many deer, then they may decrease the amount of plants or grasses in the ecosystem. Decreased levels of producers may then have a detrimental effect on the whole ecosystem. In this example, the wolves would be a keystone species. Prey also have adaptations for avoiding predators. Prey sometimes avoid detection by using camouflage ( Figure background. Mimicry is a related adaptation in which a species uses appearance to copy or mimic another species. For example, a non-poisonous dart frog may evolve to look like a poisonous dart frog. Why do you think this is an adaptation for the non-poisonous dart frog? Mimicry can be used by both predators and prey ( Figure 1.3). Parasitism is a type of symbiotic relationship and will be described in the Symbiosis concept. Camouflage by the dead leaf mantis makes it less visible to both its predators and prey. If alarmed, it lies motionless on the rainforest floor of Madagascar, Africa, camouflaged among the actual dead leaves. It eats other animals up to the size of small lizards. An example of mimicry, where the Viceroy butterfly (right) mimics the unpleasant Monarch butterfly (left). Both butterfly species are avoided by predators to a greater degree than either one would be without mimicry. | text | null |
L_0639 | predation | T_3282 | Predation is another mechanism in which species interact with each other. Predation is when a predator organism feeds on another living organism or organisms, known as prey. The predator always lowers the preys fitness. It does this by keeping the prey from surviving, reproducing, or both. Predator-prey relationships are essential to maintaining the balance of organisms in an ecosystem. Examples of predator-prey relationships include the lion and zebra, the bear and fish, and the fox and rabbit. There are different types of predation, including: true predation. grazing. parasitism. True predation is when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large prey. They tear it apart and chew it before eating it. Others, like bottlenose dolphins or snakes, may eat their prey whole. In some cases, the prey dies in the mouth or the digestive system of the predator. Baleen whales, for example, This lion is an example of a predator on the hunt. eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for prey, or they may sit and wait for prey to get within striking distance. Certain traits enable organisms to be effective hunters. These include camouflage, speed, and heightened senses. These traits also enable certain prey to avoid predators. In grazing, the predator eats part of the prey but does not usually kill it. You may have seen cows grazing on grass. The grass they eat grows back, so there is no real effect on the population. In the ocean, kelp (a type of seaweed) can regrow after being eaten by fish. Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could become dominant over others. Grazers on a grassland keep grass from growing out of control. Predators can be keystone species. These are species that can have a large effect on the balance of organisms in an ecosystem. For example, if all of the wolves are removed from a population, then the population of deer or rabbits may increase. If there are too many deer, then they may decrease the amount of plants or grasses in the ecosystem. Decreased levels of producers may then have a detrimental effect on the whole ecosystem. In this example, the wolves would be a keystone species. Prey also have adaptations for avoiding predators. Prey sometimes avoid detection by using camouflage ( Figure background. Mimicry is a related adaptation in which a species uses appearance to copy or mimic another species. For example, a non-poisonous dart frog may evolve to look like a poisonous dart frog. Why do you think this is an adaptation for the non-poisonous dart frog? Mimicry can be used by both predators and prey ( Figure 1.3). Parasitism is a type of symbiotic relationship and will be described in the Symbiosis concept. Camouflage by the dead leaf mantis makes it less visible to both its predators and prey. If alarmed, it lies motionless on the rainforest floor of Madagascar, Africa, camouflaged among the actual dead leaves. It eats other animals up to the size of small lizards. An example of mimicry, where the Viceroy butterfly (right) mimics the unpleasant Monarch butterfly (left). Both butterfly species are avoided by predators to a greater degree than either one would be without mimicry. | text | null |
L_0639 | predation | T_3282 | Predation is another mechanism in which species interact with each other. Predation is when a predator organism feeds on another living organism or organisms, known as prey. The predator always lowers the preys fitness. It does this by keeping the prey from surviving, reproducing, or both. Predator-prey relationships are essential to maintaining the balance of organisms in an ecosystem. Examples of predator-prey relationships include the lion and zebra, the bear and fish, and the fox and rabbit. There are different types of predation, including: true predation. grazing. parasitism. True predation is when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large prey. They tear it apart and chew it before eating it. Others, like bottlenose dolphins or snakes, may eat their prey whole. In some cases, the prey dies in the mouth or the digestive system of the predator. Baleen whales, for example, This lion is an example of a predator on the hunt. eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for prey, or they may sit and wait for prey to get within striking distance. Certain traits enable organisms to be effective hunters. These include camouflage, speed, and heightened senses. These traits also enable certain prey to avoid predators. In grazing, the predator eats part of the prey but does not usually kill it. You may have seen cows grazing on grass. The grass they eat grows back, so there is no real effect on the population. In the ocean, kelp (a type of seaweed) can regrow after being eaten by fish. Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could become dominant over others. Grazers on a grassland keep grass from growing out of control. Predators can be keystone species. These are species that can have a large effect on the balance of organisms in an ecosystem. For example, if all of the wolves are removed from a population, then the population of deer or rabbits may increase. If there are too many deer, then they may decrease the amount of plants or grasses in the ecosystem. Decreased levels of producers may then have a detrimental effect on the whole ecosystem. In this example, the wolves would be a keystone species. Prey also have adaptations for avoiding predators. Prey sometimes avoid detection by using camouflage ( Figure background. Mimicry is a related adaptation in which a species uses appearance to copy or mimic another species. For example, a non-poisonous dart frog may evolve to look like a poisonous dart frog. Why do you think this is an adaptation for the non-poisonous dart frog? Mimicry can be used by both predators and prey ( Figure 1.3). Parasitism is a type of symbiotic relationship and will be described in the Symbiosis concept. Camouflage by the dead leaf mantis makes it less visible to both its predators and prey. If alarmed, it lies motionless on the rainforest floor of Madagascar, Africa, camouflaged among the actual dead leaves. It eats other animals up to the size of small lizards. An example of mimicry, where the Viceroy butterfly (right) mimics the unpleasant Monarch butterfly (left). Both butterfly species are avoided by predators to a greater degree than either one would be without mimicry. | text | null |
L_0644 | primates | T_3294 | If primates are mammals, what makes them seem so different from most mammals? Primates, including humans, have several unique features. Some adaptations give primates advantages that allow them to live in certain habitats, such as in trees. Other features have allowed them to adapt to complex social and cultural situations. Primates are mostly omnivorous, meaning many primate species eat both plant and animal material. The order contains all of the species commonly related to lemurs, monkeys, and apes. The order also includes humans ( Figure 1.1). Key features of primates include: Five fingers, known as pentadactyl. Several types of teeth. Certain eye orbit characteristics, such as a postorbital bar, or a bone that runs around the eye socket. An opposable thumb, a finger that allows a grip that can hold objects. (top left) Ring-tailed lemurs. Lemurs be- long to the prosimian group of primates. (top right) One of the New World mon- keys, a squirrel monkey. (bottom left) Chimpanzees belong to the great apes, one of the groups of primates. (bottom right) Reconstruction of a Neanderthal man, belonging to an extinct subspecies of Homo sapiens. This subspecies of humans lived in Europe and western and central Asia from about 100,000 40,000 BCE. Whats the difference between monkeys and apes? The easiest way to distinguish monkeys from the other primates is to look for a tail. Most monkey species have tails, but no apes or humans do. Monkeys are much more like other mammals than apes and humans are. | text | null |
L_0644 | primates | T_3295 | In intelligent mammals, such as primates, the cerebrum is larger compared to the rest of the brain. A larger cerebrum allows primates to develop higher levels of intelligence. Primates have the ability to learn new behaviors. They also engage in complex social interactions, such as fighting and play. | text | null |
L_0644 | primates | T_3296 | Old World species, such as apes and some monkeys ( Figure 1.1 and Figure 1.2), tend to have significant size differences between the sexes. This is known as sexual dimorphism. Males tend to be slightly more than twice as heavy as females. This dimorphism may have evolved when one male had to defend many females. Old World generally refers to monkeys of Africa and Asia. New World refers to monkeys of the Americas. New World species, including tamarins (squirrel-sized monkeys) and marmosets (very small primitive monkeys) ( Figure 1.2), form pair bonds, which is a partnership between a mating pair that lasts at least one season. The pair cooperatively raise the young and generally do not show a significant size difference between the sexes. Old World monkeys do not tend to form monogamous relationships. (left) An Old World monkey, a species of macaque, in Japan. (center ) A New World species of monkey, a tamarin. (right) Another New World species of monkey, the pygmy marmoset. | text | null |
L_0644 | primates | T_3297 | Non-human primates live mostly in Central and South America, Africa, and South Asia. Since primates evolved from animals living in trees, many modern species still live mostly in trees. Other species live on land most of the time, such as baboons ( Figure 1.3) and the Patas monkey. Only a few species live on land all of the time, such as the gelada and humans. Primates live in a diverse number of forested habitats, including rain forests, mangrove forests and mountain forests to altitudes of over 9,800 feet. The combination of opposable thumbs, short fingernails, and long, inward-closing fingers has allowed some species to develop the ability to move by swinging their arms from one branch to another ( Figure 1.4). Another feature for climbing are expanded finger-like parts, such as those in tarsiers, which improve grasping ( Figure 1.4). A few species, such as the proboscis monkey, De Brazzas monkey, and Allens swamp monkey, evolved webbed fingers so they can swim and live in swamps and aquatic habitats. Some species, such as the rhesus macaque and the Hanuman langur, can even live in cities by eating human garbage. (left) A gibbon shows how its limbs are modified for hanging from trees. (right) A species of tarsier, with expanded digits used for grasping branches. | text | null |
L_0644 | primates | T_3297 | Non-human primates live mostly in Central and South America, Africa, and South Asia. Since primates evolved from animals living in trees, many modern species still live mostly in trees. Other species live on land most of the time, such as baboons ( Figure 1.3) and the Patas monkey. Only a few species live on land all of the time, such as the gelada and humans. Primates live in a diverse number of forested habitats, including rain forests, mangrove forests and mountain forests to altitudes of over 9,800 feet. The combination of opposable thumbs, short fingernails, and long, inward-closing fingers has allowed some species to develop the ability to move by swinging their arms from one branch to another ( Figure 1.4). Another feature for climbing are expanded finger-like parts, such as those in tarsiers, which improve grasping ( Figure 1.4). A few species, such as the proboscis monkey, De Brazzas monkey, and Allens swamp monkey, evolved webbed fingers so they can swim and live in swamps and aquatic habitats. Some species, such as the rhesus macaque and the Hanuman langur, can even live in cities by eating human garbage. (left) A gibbon shows how its limbs are modified for hanging from trees. (right) A species of tarsier, with expanded digits used for grasping branches. | text | null |
L_0650 | protist characteristics | T_3312 | Protists are eukaryotes, which means their cells have a nucleus and other membrane-bound organelles. Most, but not all, protists are single-celled. Other than these features, they have very little in common. You can think about protists as all eukaryotic organisms that are neither animals, nor plants, nor fungi. Although Ernst Haeckel set up the Kingdom Protista in 1866, this kingdom was not accepted by the scientific world until the 1960s. These unique organisms can be so different from each other that sometimes Protista is called the junk drawer" kingdom. Just like a junk drawer, which contains items that dont fit into any other category, this kingdom contains the eukaryotes that cannot be put into any other kingdom. Therefore, protists can seem very different from one another. | text | null |
L_0650 | protist characteristics | T_3313 | Most protists are so small that they can be seen only with a microscope. Protists are mostly unicellular (one-celled) eukaryotes. A few protists are multicellular (many-celled) and surprisingly large. For example, kelp is a multicellular protist that can grow to be over 100-meters long ( Figure 1.1). Multicellular protists, however, do not show cellular specialization or differentiation into tissues. That means their cells all look the same and, for the most part, function the same. On the other hand, your cells often are much different from each other and have special jobs. Kelp is an example of a muticellular pro- tist. | text | null |
L_0650 | protist characteristics | T_3314 | A few characteristics are common between protists. 1. 2. 3. 4. They are eukaryotic, which means they have a nucleus. Most have mitochondria. They can be parasites. They all prefer aquatic or moist environments. | text | null |
L_0650 | protist characteristics | T_3315 | For classification, the protists are divided into three groups: 1. Animal-like protists, which are heterotrophs and have the ability to move. 2. Plant-like protists, which are autotrophs that photosynthesize. 3. Fungi-like protists, which are heterotrophs, and they have cells with cell walls and reproduce by forming spores. But remember, protists are not animals, nor plants, nor fungi ( Figure 1.2). | text | null |
L_0651 | protists nutrition | T_3316 | The cells of protists need to perform all of the functions that other cells do, such as grow and reproduce, maintain homeostasis, and obtain energy. They also need to obtain "food" to provide the energy to perform these functions. Recall that protists can be plant-like, fungi-like, or animal-like. That means that protists can obtain food like plants, fungi, or animals do. There are many plant-like protists, such as algae, that get their energy from sunlight through photosynthesis. Some of the fungus-like protists, such as the slime molds ( Figure 1.1), decompose decaying matter. The animal-like protists must "eat" or ingest food. Some animal-like protists use their "tails" to eat. These protists are called filter-feeders. They acquire nutrients by constantly whipping their tails, called flagellum, back and forth. The whipping of the flagellum creates a current that brings food into the protist. Other animal-like protists must "swallow" their food through a process called endocytosis. Endocytosis happens when a cell takes in substances through its membrane. The process is described below: 1. The protist wraps around its prey, which is usually bacteria. 2. It creates a food vacuole, a sort of "food storage compartment," around the bacteria. 3. The protist produces toxins which paralyze its prey. 4. Once digested, the food material moves through the vacuole and into the cytoplasm of the protist. Also, some of the animal-like and fungi-like protists are parasitic, harming their hosts as they obtain nutrients. Fungi-like protists absorb nutrients meant for their host, harming the host in the process. Slime molds live on decaying plant life and in the soil. | text | null |
L_0653 | punnett squares | T_3319 | A Punnett square is a special tool derived from the laws of probability. It is used to predict the possible offspring from a cross, or mating between two parents. An example of a Punnett square ( Figure 1.1) shows the results of a cross between two purple flowers that each have one dominant factor and one recessive factor (Bb). The Punnett square of a cross between two purple flowers (Bb). A Punnett square can be used to calculate what percentage of offspring will have a certain trait. To create a Punnett square, perform the following steps: 1. 2. 3. 4. Take the factors from the first parent and place them at the top of the square (B and b). Take the factors from the second parent and line them up on the left side of the square (B and b). Pull the factors from the top into the boxes below. Pull the factors from the side into the boxes next to them. The possible offspring are represented by the letters in the boxes, with one factor coming from each parent. Results: Top left box: BB, or purple flowers Top right box: Bb, or purple flowers Lower left box: Bb, or purple flowers Lower right box: bb, or white flowers Only one of the plants out of the four, or 25% of the plants, has white flowers (bb). The other 75% have purple flowers (BB, Bb), because the purple factor (B) is the dominant factor. This shows that the color purple is the dominant trait in pea plants. Now imagine you cross one of the white flowers (bb) with a purple flower that has both a dominant and recessive factor (Bb). The only possible gamete in the white flower is recessive (b), while the purple flower can have gametes with either dominant (B) or recessive (b). Practice using a Punnett square with this cross (see Table 1.1). b Bb bb B b b Bb bb Did you find that 50% of the offspring will be purple, and 50% of the offspring will be white? | text | null |
L_0657 | reproduction in seedless plants | T_3329 | Seedless plants can reproduce asexually or sexually. Some seedless plants, like hornworts and liverworts, can reproduce asexually through fragmentation. When a small fragment of the plant is broken off, it can form a new plant. | text | null |
L_0657 | reproduction in seedless plants | T_3330 | Like all plants, nonvascular plants have an alternation of generations life cycle. That means they alternate between diploid cell stages (having two sets of chromosomes) and haploid cell stages (having one set of chromosomes) during their life cycle. Recall the haploid stage is called the gametophyte, and the diploid stage is called the sporophyte. In the life cycle of the nonvascular seedless plants, the gametophyte stage is the longest part of the cycle. The gametophyte is the green photosynthetic carpet that you would recognize as a moss. The life cycle of nonvascular seedless plants can be described as follows: 1. The male gametophyte produces flagellated sperm that must swim to the egg formed by the female game- tophyte. For this reason, sexual reproduction must happen in the presence of water. Therefore, nonvascular plants tend to live in moist environments. Though the life of a nonvascular seedless plant is a cycle, this can be considered the initial step in the life cycle. 2. Following fertilization, the sporophyte forms. The sporophyte is connected to, and dependent on, the gameto- phyte. 3. The sporophyte produces spores that will develop into gametophytes and start the cycle over again. | text | null |
L_0657 | reproduction in seedless plants | T_3331 | For the seedless vascular plants, the sporophyte stage is the longest part of the cycle, but the cycle is similar to nonvascular plants. For example, in ferns, the gametophyte is a tiny heart-shaped structure, while the leafy plant we recognize as a fern is the sporophyte. The ferns sporangia, where spores are produced, are often on the underside of the fronds ( Figure 1.1). Like nonvascular plants, ferns also have flagellated sperm that must swim to the egg. Unlike nonvascular plants, once fertilization takes place, the gametophyte will die, and the sporophyte will live independently. This fern is producing spores underneath its fronds. | text | null |
L_0658 | reproductive behavior of animals | T_3332 | Some of the most important animal behaviors involve mating. Mating is the pairing of an adult male and female to produce young. Adults that are most successful at attracting a mate are most likely to have offspring. Traits that help animals attract a mate and have offspring increase their fitness. As the genes that encode these traits are passed to the next generation, the traits will become more common in the population. | text | null |
L_0658 | reproductive behavior of animals | T_3333 | In many species, females choose the male they will mate with. For their part, males try to be chosen as mates. They show females that they would be a better mate than the other males. To be chosen as a mate, males may perform courtship behaviors. These are special behaviors that help attract a mate. Male courtship behaviors get the attention of females and show off a males traits. These behaviors are often observed as direct competition between males. Different species have different courtship behaviors. One example is a peacock raising his tail feathers. The colorful peacock is trying to impress females of his species with his beautiful feathers. Another example of courtship behavior in birds is the blue-footed booby. He is doing a dance to attract a female for mating. During the dance, he spreads out his wings and stamps his feet on the ground. You can watch the following video of a blue-footed booby doing his courtship dance at: . Click image to the left or use the URL below. URL: Courtship behaviors occur in many other species. For example, males in some species of whales have special mating songs to attract females as mates. Frogs croak for the same reason. Male deer clash antlers to court females. Male jumping spiders jump from side to side to attract mates. Courtship behaviors are one type of display behavior. A display behavior is a fixed set of actions that carries a specific message. Although many display behaviors are used to attract mates, some display behaviors have other purposes. For example, display behaviors may be used to warn other animals to stay away, as you will read below. | text | null |
L_0658 | reproductive behavior of animals | T_3334 | In most species of birds and mammals, one or both parents care for their offspring. Caring for the young may include making a nest or other shelter. It may also include feeding the young and protecting them from predators. Caring for offspring increases their chances of surviving. Birds called killdeers have an interesting way of protecting their chicks. When a predator gets too close to her nest, a mother killdeer pretends to have a broken wing. The mother walks away from the nest holding her wing as though it were injured ( Figure 1.1). The predator thinks she is injured and will be easy prey. The mother leads the predator away from the nest and then flies away. In most species of mammals, parents also teach their offspring important skills. For example, meerkat parents teach their pups how to eat scorpions without being stung. A scorpion sting can be deadly, so this is a very important skill. | text | null |
L_0658 | reproductive behavior of animals | T_3335 | Some species of animals are territorial. This means that they defend their area. The area they defend usually contains their nest and enough food for themselves and their offspring. A species is more likely to be territorial if there is not very much food in their area. Having a larger territory could mean more prey or food. Animals generally do not defend their territory by fighting. Instead, they are more likely to use display behavior. The behavior tells other animals to stay away. It gets the message across without the need for fighting. Display behavior is generally safer and uses less energy than fighting. Male gorillas use display behavior to defend their territory. They pound on their chests and thump the ground with their hands to warn other male gorillas to keep away from their area. The robin displays his red breast to warn other robins to stay away ( Figure 1.2). The red breast of this male robin is easy to see. The robin displays his bright red chest to defend his territory. It warns other robins to keep out of his area. Some animals deposit chemicals to mark the boundary of their territory. This is why dogs urinate on fire hydrants and other objects. Cats may also mark their territory by depositing chemicals. They have scent glands in their face. They deposit chemicals by rubbing their face against objects. | text | null |
L_0660 | reptiles | T_3337 | What reptiles can you name? Snakes, alligators, and crocodiles are all reptiles. Modern reptiles live on every continent except Antarctica. They range in size from the newly-discovered Jaragua Sphaero (a dwarf gecko), at 0.6 inches, to the saltwater crocodile, at up to 23 feet. There are four living orders of reptiles: 1. 2. 3. 4. Squamata, which includes lizards, snakes, and amphisbaenids (or worm-lizards). Crocodilia, which includes crocodiles, gharials ( Figure 1.1), caimans, and alligators. Testudines, which includes turtles and tortoises. Sphenodontia, which includes tuatara ( Figure 1.1). A gharial crocodile (left). A tuatara (right). | text | null |
L_0660 | reptiles | T_3338 | Reptiles are tetrapods (four-legged) and ectothermic, meaning their internal temperature depends on the temperature of their environment. This is why you may see reptiles sunbathing as they use the energy from the sun to warm their bodies. Usually the sense organs of reptiles, like ears, are well developed, though snakes do not have external ears. All reptiles have advanced eyesight. Reptiles also have a sense of smell. Crocodilians, turtles, and tortoises smell like most other land vertebrates. But, some lizards, and all snakes, smell with their tongues, which is flicked out of the mouth to pick up scent molecules from the air. Reptiles also have several adaptations for living on land. They have a skin covered in scales to protect them from drying out. All reptiles have lungs to breathe air. Reptiles are also amniotes, which means their embryos are surrounded by a thin membrane. This membrane protects the embryo from the harsh conditions of living on land. Reptile eggs are also surrounded by a protective shell, which may be either flexible or inflexible. | text | null |
L_0660 | reptiles | T_3339 | Most reptiles reproduce sexually, meaning there are two parents involved. In some families of lizards and one snake family, however, asexual reproduction is possible. This is when only one parent is involved in creating new life. For example, the gecko females can make tiny clones of themselves without the aid of a male. All reptiles have a cloaca, a single exit and entrance for sperm, eggs, and waste, located at the base of the tail. Most reptiles lay amniotic eggs covered with leathery or hard shell. These eggs can be placed anywhere as they dont have to be in a moist environment, like the eggs of amphibians. However, not all species lay eggs, as certain species of squamates can give birth to live young. Unlike the amphibians, there are no larval stages of development. The young reptiles look like miniature versions of the adult. The young reptiles are generally left to fend for themselves. However, some reptiles provide care for their young. For example, crocodiles and alligators may defend their young from predators. | text | null |
L_0666 | role of amphibians | T_3358 | Humans have used amphibians for a number of purposes for thousands of years, if not longer. Amphibians play significant roles in many food webs and are thus an important part of many ecosystems. For example, frogs keep insect populations stable. Extinction of frogs, or just significant decreases in the frog population, would probably have serious consequences for agricultural crops. Humans have also consumed amphibians, especially frogs, probably since they first ate meat. More recently, amphibians have been tremendously useful in research. | text | null |
L_0666 | role of amphibians | T_3359 | Amphibians play important roles in many ecosystems, especially as middle players in many food chains and food webs. In addition to consuming many worms and insects and other arthropods, and even some small reptiles and mammals and fish, they are prey for turtles and snakes, as well as some fish and birds. Tadpoles keep waterways clean by feeding on algae. Frogs are raised as a food source for humans. Frog legs are a delicacy in China, France, the Philippines, northern Greece, and the American south, especially the Frensh-speaking parts of Louisiana. Only the upper joint of the hind leg is served, which has a single bone similar to the upper joint of a chicken or turkey wing. They are commonly prepared by grilling or deep frying, sometimes breaded, though they can also be served with garlic, or turned into a soup or stew. Some estimates have well over a billion frogs harvested a year as food. Thats about one frog harvested for every seven people on the planet. | text | null |
L_0666 | role of amphibians | T_3360 | Amphibians have long been used in scientific research, especially developmental and physiological processes, largely due to their unique ability to undergo metamorphosis, and in some species, to regenerate limbs. Amphibians are also used in cloning research. Cloning involves making identical copies of a parent organism, and the large amphibian egg helps in this process. They are also used to study embryos because their eggs lack shells, so it is easy to watch their development. The African clawed frog, Xenopus laevis, is a species that is studied to understand aspects of developmental biology. It is a good model organism because it is easy to raise in a lab and has a large embryo, which is easy to study ( Figure 1.1). Many Xenopus genes have been identified and cloned, especially those involved in development. Developing Xenopus embryos can be easily observed and studied with a basic microscope, though the eggs are large enough to see without a microscope. Because of their size, the exact developmental stage after fertilization can be easily determined. This allows proteins that are used at a specific developmental time to be collected and analyzed. Identification of Xenopus genes and proteins has allowed the identification of corresponding genes and proteins from humans. Many environmental scientists believe that amphibians, including frogs, indicate when an environment is damaged. When species of frogs begin to decline, it often indicates that there is a bigger problem within the ecosystem. This could have dramatic effects on food webs and ecosystems. Frog embryos are often studied to better understand how development works. | text | null |
L_0666 | role of amphibians | T_3361 | Amphibians can be found in folklore, fairy tales, and popular culture. Numerous legends have developed over the centuries around the mystical properties of the salamander. Its name originates from the Persian words for fire and within," so many of these legends are related to fire. This connection likely originates from the tendency of many salamanders to live inside rotting logs. When placed into the fire, salamanders would escape from the logs, lending to the belief that the salamander was created from flames. Unforgettable amphibians Kermit the Frog ( Figure 1.2) and his popular saying Its not easy being green. Frogger, from the video game of the same name, has been teaching children about the dangers of the road and alligator-filled moats for years. And all it takes is a kiss from a princess to turn a frog into a prince, as told in The Frog Prince story. Kermit the Frog balloon is flown at the Annual Macys Thanksgiving Day Parade. | text | null |
L_0668 | safety in the life sciences | T_3365 | There can be some very serious safety risks in scientific research. If researchers are not careful, they could poison themselves or contract a deadly illness. The kinds of risks that scientists face depend on the kind of research they perform. For example, a scientist working with bacteria in a laboratory faces different risks than a scientist studying the behavior of lions in Africa, but both scientists must still follow safety guidelines. Safety practices must be followed when working with the hazardous things such as parasites, radiation and radioactive materials, toxins, and wild animals. Also, carcinogens, which are chemical that cause cancer, pathogens, which are disease-causing virus, bacteria or fungi, and teratogens, which are chemical that cause deformities in developing embryos, are extremely hazardous, and extreme care must be used when working with these items as well. For example, scientists studying dangerous organisms such as Yersinia pestis, the cause of bubonic plague, use special equipment that helps keep the organism from escaping the lab. A biohazard is any biological material that could make someone sick, including disease-causing organisms. There- fore, a used needle is a biohazard because it could harbor blood contaminated with a disease-causing organism. Bacteria grown in a laboratory are also biohazards if they could potentially cause disease. Science laboratory safety and chemical hazard signs. | text | null |
L_0668 | safety in the life sciences | T_3366 | If you perform an experiment in your classroom, your teacher will explain how to be safe. Professional scientists follow safety rules as well, especially for the study of dangerous organisms like the bacteria that cause bubonic plague ( Figure 1.2). Sharp objects, chemicals, heat, and electricity are all used at times in laboratories. Below is a list of safety guidelines that you should follow when in the laboratory: Be sure to obey all safety guidelines given in lab instructions and by your teacher. Follow directions carefully. Tie back long hair. Wear closed toe shoes with flat heels and shirts with no hanging sleeves, hoods, or drawstrings. Use gloves, goggles, or safety aprons when instructed to do so. Broken glass should only be cleaned up with a dust pan and broom. Never touch broken glass with your bare hands. Never eat or drink anything in the science lab. Table tops and counters could have dangerous substances on them. Be sure to completely clean materials like test tubes and beakers. Leftover substances could interact with other substances in future experiments. If you are using flames or heat plates, be careful when you reach. Be sure your arms and hair are kept far away from heat. Alert your teacher immediately if anything out of the ordinary occurs. An accident report may be required if someone is hurt. Also, the teacher must know if any materials are damaged or discarded. Scientists studying dangerous organisms such as Yersinia pestis, the cause of bubonic plague, use special equipment that helps keep the organism from escap- ing the lab. | text | null |
L_0668 | safety in the life sciences | T_3367 | A field scientist studies an organism in a natural setting, which is not usually an indoor laboratory. Scientists who work outdoors are also required to follow safety regulations. These safety regulations are designed to prevent harm to themselves, other humans, animals, and the environment. If scientists work outside the country, they are required to learn about and follow the laws and restrictions of the country in which they are doing research. For example, entomologists following monarch butterfly ( Figure 1.3) migrations between the United States and Mexico must follow regulations in both countries. Before biologists can study protected wildlife or plant species, they must apply for permission to do so, usually from the government. This is important to protect these fragile species. For example, if scientists collect rare butterflies, they must first get a permit. They must also be careful to not disturb the habitat. | text | null |
L_0669 | salamanders | T_3368 | Salamanders are characterized by slender bodies, short legs, and long tails. They are most closely related to the caecilians, little-known legless amphibians ( Figure 1.1). Most of the animals in the salamander order look like a cross between a lizard and a frog. They have moist, smooth skin like frogs and long tails like lizards. Salamanders are found in most moist or arid habitats in the Northern Hemisphere, but can also be found south of the equator. They live on all continents except Antarctica and Australia. Salamanders live in or near water or on moist ground, often in a swamp. Some species live in water most of their life, some live their entire adult life on land, and some live in both habitats. Some salamanders live in caves. These salamanders have pale skin and reduced eyes as they have adapted to living in complete darkness in underground pools of water. The reduced eyes are similar to other organisms that live in caves or underground. Salamanders are carnivorous, eating only other animals, not plants. They will eat almost any smaller animal, such as worms, centipedes, crickets, spiders, and slugs. Some will even eat small invertebrates. Finally, salamanders have the ability to grow back lost limbs, as well as other body parts. This process is known as regeneration. Salamanders have developed ways not to be eaten. Most salamanders have brightly colored, poisonous skin. The bold color tells predators not to eat the salamander. Many salamanders have glands on the back of the neck or on the tail that give off a poisonous or bad-tasting liquid. Some species can even shed their tail during an attack and grow a new one later. Some salamanders stand high on its legs and waves its tail to scare away danger. One particular salamander, the ribbed newt, has needle-like rib tips. It can squeeze its muscles to make the rib tips pierce through its skin and into its enemy, telling the predator to stay away, a feature unique among the animal kingdom. The marbled salamander (left) shows the typical salamander body plan: slender body, short legs, long tail, and moist skin. Caecilian (right) are a type of legless am- phibian most closely related to salaman- ders. | text | null |
L_0669 | salamanders | T_3369 | Different salamanders breathe in different ways. In those that have gills, breathing occurs through the gills as water passes over the gill slits. Sirens keep their gills all their lives, which allows them to breathe underwater. Species that live on land lose their gills as they grow older. These salamanders develop lungs that are used in breathing, much like breathing in mammals. Other land-living salamanders do not have lungs or gills. These are called lungless salamanders. Instead, they "breathe," or exchange gases, through their skin. This requires blood vessels that exchange gases to be spread throughout the skin. | text | null |
L_0669 | salamanders | T_3370 | Salamanders are generally small. However, some can reach a foot or more, as in the mudpuppy of North America. In Japan and China, the giant salamander reaches 6 feet and weighs up to 66 pounds ( Figure 1.2). | text | null |
L_0669 | salamanders | T_3371 | Salamanders belong to a group of approximately 500 species of amphibians. The order Urodela, containing sala- manders and newts, is divided into three suborders: 1. Giant salamanders, including the hellbender and Asiatic salamanders. 2. Advanced salamanders, including lungless salamanders, mudpuppies, and newts. Newts are salamanders that spend most of each year living on land. 3. Sirens. Sirens are salamanders that have lungs as well as gills and never develop beyond the larval stage. Sirens have only two legs, but the other salamander species develop four legs as adults, with fleshy toes at the end of each foot. The legs on four-legged salamanders are so short that the salamander belly drags on the ground as the animal walks. Sirens have long, strong tails that are flat to help sirens swim like a fish, with the tail swinging from side to side. The Pacific giant salamander can reach up to 6 feet in length and weigh up to 66 pounds. | text | null |
L_0670 | scientific investigation | T_3372 | The scientific method is a process used to investigate the unknown ( Figure 1.1). It is the general process of a scientific investigation. This process uses evidence and testing. Scientists use the scientific method so they can find information. A common method allows all scientists to answer questions in a similar way. Scientists who use this method can reproduce another scientists experiments. Almost all versions of the scientific method include the following steps, although some scientists do use slight variations. 1. 2. 3. 4. 5. 6. 7. Make observations. Identify a question you would like to answer based on the observation. Find out what is already known about your observation (research). Form a hypothesis. Test the hypothesis. Analyze your results and draw conclusions. Communicate your results. | text | null |
L_0670 | scientific investigation | T_3373 | Imagine that you are a scientist. While collecting water samples at a local pond, you notice a frog with five legs instead of four ( Figure 1.2). As you start to look around, you discover that many of the frogs have extra limbs, Steps of a Scientific Investigation. A scientific investigation typically has these steps. extra eyes, or no eyes. One frog even has limbs coming out of its mouth. These are your observations, or things you notice about an environment using your five senses. A frog with an extra leg. | text | null |
L_0670 | scientific investigation | T_3373 | Imagine that you are a scientist. While collecting water samples at a local pond, you notice a frog with five legs instead of four ( Figure 1.2). As you start to look around, you discover that many of the frogs have extra limbs, Steps of a Scientific Investigation. A scientific investigation typically has these steps. extra eyes, or no eyes. One frog even has limbs coming out of its mouth. These are your observations, or things you notice about an environment using your five senses. A frog with an extra leg. | text | null |
L_0670 | scientific investigation | T_3374 | The next step is to ask a question about the frogs. You may ask, "Why are so many frogs deformed?" Or, "Is there something in their environment causing these defects, like water pollution?" Yet, you do not know if this large number of deformities is "normal" for frogs. What if many of the frogs found in ponds and lakes all over the world have similar deformities? Before you look for causes, you need to find out if the number and kind of deformities is unusual. So besides finding out why the frogs are deformed, you should also ask: "Is the percentage of deformed frogs in this pond greater than the percentage of deformed frogs in other places?" | text | null |
L_0670 | scientific investigation | T_3375 | No matter what you observe, you need to find out what is already known about your questions. For example, is anyone else doing research on deformed frogs? If yes, what did they find out? Do you think that you should repeat their research to see if it can be duplicated? During your research, you might learn something that convinces you to change or refine your question. From this, you will construct your hypothesis. A pond with frogs. | text | null |
L_0670 | scientific investigation | T_3376 | A hypothesis is a proposed explanation that tries to explain an observation. A good hypothesis allows you to make more predictions. For example, you might hypothesize that a pesticide from a nearby farm is running into the pond and causing frogs to have extra legs. If thats true, then you can predict that the water in a pond of non-deformed frogs will have lower levels of that pesticide. Thats a prediction you can test by measuring pesticide levels in two sets of ponds, those with deformed frogs and those with nothing but healthy frogs. Every hypothesis needs to be written in a way that it can: 1. 2. 3. 4. Be tested using experiments to collect evidence. Be proven wrong. Provide measurable results. Provide yes or no answers. For example, do you think the following hypothesis meets the four criteria above? Lets see. Hypothesis: "The number of deformed frogs in five ponds that are polluted with chemical X is higher than the number of deformed frogs in five ponds without chemical X." Of course, next you will have to test your hypothesis. | text | null |
L_0670 | scientific investigation | T_3377 | To test the hypothesis, an experiment will be done. You would count the healthy and deformed frogs and measure the amount of chemical X in all of the ponds. The hypothesis will be either true or false. Doing an experiment will test most hypotheses. The experiment may generate evidence in support of the hypothesis. The experiment may also generate evidence proving the hypothesis false. Once you collect your data, it will need to be analyzed. | text | null |
L_0670 | scientific investigation | T_3378 | If a hypothesis and experiment are well designed, the experiment will produce results that you can measure, collect, and analyze. The analysis should tell you if the hypothesis is true or false. Refer to the table for the experimental results ( Table 1.1). Polluted Pond 1 2 3 4 5 Average: Number of Deformed Frogs 20 23 25 26 21 23 Non-Polluted Pond 1 2 3 4 5 Average: Number of Deformed Frogs 23 25 30 16 20 22.8 Your results show that pesticide levels in the two sets of ponds are different, but the average number of deformed frogs is almost the same. Your results demonstrate that your hypothesis is false. The situation may be more complicated than you thought. This gives you new information that will help you decide what to do next. Even if the results supported your hypothesis, you would probably ask a new question to try to better understand what is happening to the frogs and why. | text | null |
L_0670 | scientific investigation | T_3379 | If a hypothesis and experiment are well designed, the results will indicate whether your hypothesis is true or false. If a hypothesis is true, scientists will often continue testing the hypothesis in new ways to learn more. If a hypothesis is false, the results may be used to come up with and test a new hypothesis. A scientist will then communicate the results to the scientific community. This will allow others to review the information and extend the studies. The scientific community can also use the information for related studies. Scientists communicate their results in a number of ways. For example, they may talk to small groups of scientists and give talks at large scientific meetings. They will also write articles for scientific journals. Their findings may also be communicated to journalists. If you conclude that frogs are deformed due to a pesticide not previously measured, you would publish an article and give talks about your research. Your conclusion could eventually help find solutions to this problem. | text | null |
L_0670 | scientific investigation | T_3380 | A summery video of the scientific method, using the identification of DNA structure as an example, is shown in this video by MIT students: . | text | null |
L_0671 | scientific theories | T_3381 | One goal of a scientist is to find answers to scientific questions. To do this, scientists first develop a hypothesis, which is a proposed explanation that tries to explain an observation. To collect evidence to support (or disprove) their hypothesis, scientists must do experiments. Evidence is: 1. A direct, physical observation of something or a process over time. 2. Usually something measurable or "quantifiable." 3. The data resulting from an experiment. For example, an apple falling to the ground is evidence in support of the law of gravity. A bear skeleton in the woods would be evidence of the presence of bears. Looking at the image below might be confusing at first because this evidence seems to defy the law of gravity ( Figure 1.1). Of course water cannot be poured out of bottle and flow upward. The law of gravity is a scientific law, which is a statement describing what always happens under certain conditions in nature. Scientific laws are developed from lots of collected information. If many experiments are performed, and lots of evidence is collected in support of a general hypothesis, a scientific theory can be developed. Scientific theories are well established explanations of evidence, usually tested and confirmed by many different people. Scientific theories usually have a lot of evidence in support of the theory, and no evidence disproving the theory. Scientific theories produce information that helps us understand our world. For example, the idea that matter is made up of atoms is a scientific theory. Scientists accept this theory as a fundamental principle of basic science. A scientific theory must stand up to all scientific testing. Thus, when scientists find new evidence, they can change their theories. In addition to the germ theory of disease, other scientific theories are the cell theory and the theory of evolution. | text | null |
L_0672 | scientific ways of thinking | T_3382 | Modern science is a way of understanding the physical world, based on observable evidence, reasoning, and repeated testing. That means scientists explain the world based on their own observations. If they develop new ideas about the way the world works, they set up a way to test these new ideas. | text | null |
L_0672 | scientific ways of thinking | T_3383 | A scientist is always trying to find the truth and discover new truths. How can you think like a scientist? Thinking like a scientist is based on asking and answering questions. Though you may not know it, you do this all day long. Scientists ask questions, and then make detailed observations to try to ask more specific questions and develop a hypothesis. They may design and perform an experiment to try to answer their question and test their hypothesis. From the results of their experiment, scientists draw conclusions. A conclusion describes what the evidence tells the scientist. Scientists ask questions: The key to being a great scientist is to ask questions. Imagine you are a scientist in the African Congo. While in the field, you observe one group of healthy chimpanzees on the north side of the jungle. On the other side of the jungle, you find a group of chimpanzees that are mysteriously dying. What questions might you ask? A good scientist might ask the following two questions: 1. "What differs between the two environments where the chimpanzees live?" 2. "Are there differences in behavior between the two groups of chimpanzees?" Scientists make detailed observations: To observe means to watch and study attentively. A person untrained in the sciences may only observe, "The chimps on one side of the jungle are dying, while chimps on the other side of the jungle are healthy." A scientist, however, will make more detailed observations. Can you think of ways to make this observation more detailed? What about the number of chimps? Are they male or female? Young or old? What do they eat? A good scientist may observe, "While all seven adult females and three adult males on the north side of the jungle are healthy and show normal behavior, four female and five male chimps under the age of five on the south side have died." Detailed observations can ultimately help scientists design their experiments and answer their questions. From these observations, a scientist will develop a hypothesis to explain the observations. A hypothesis is the scientists proposed explanation for his observations. The scientists hypothesis may be that "Young chimps on the south side die due to a lack of nutrients in their diet." An adult and infant chimpanzee (Pan troglodytes). Scientists find answers using tests: When scientists want to answer a question, they search for evidence using experiments. An experiment is a test to see if their explanation is right or wrong. Evidence is made up of the observations a scientist makes during an experiment. To study the cause of death in the chimpanzees, scientists may give the chimps nutrients in the form of nuts, berries, and vitamins to see if they are dying from a lack of food. This test is the experiment. If fewer chimps die, then the experiment shows that the chimps may have died from not having enough food. This is the evidence. Scientists question the answers: Good scientists are skeptical. Scientists never use only one piece of evidence to form a conclusion. For example, the chimpanzees in the experiment may have died from a lack of food, but can you think of another explanation for their death? They may have died from a virus, or from another less obvious cause. More experiments need to be completed before scientists can be sure. Science is about finding the truth, no matter what. So good scientists constantly question their own conclusions. They also find other scientists to confirm or disagree with their evidence. | text | null |
L_0673 | seasonal changes in plants | T_3384 | Have you seen the leaves of plants change colors? During what time of year does this happen? What causes it to happen? Plants can sense changes in the seasons. Leaves change color and drop each autumn in some climates ( Figure 1.1). Certain flowers, like poinsettias, only bloom during the winter. And, in the spring, the winter buds on the trees break open, and the leaves start to grow. How do plants detect time of year? Although you might detect seasonal changes by the change in temperature, this is not the way in which plants know the seasons are changing. Plants determine the time of year by the length of daylight, known as the photoperiod. Because of the tilt of the Earth, during winter days, there are less hours of light than during summer days. Thats why, in the winter, it starts getting dark very early in the evening, and then stays dark while youre getting ready for school the next morning. But in the summer it will be bright early in the morning, and the sun will not set until late that night. With a light-sensitive chemical, plants can sense the differences in day length. For example, in the fall, when the days start to get shorter, the trees sense that there is less sunlight. The plant is stimulated, and it sends messages telling the leaves to change colors and fall. This is an example of photoperiodism, the reaction of organisms, such as plants, to the length of day or night. Photoperiodism is also the reaction of plants to the length of light and dark periods. Many flowering plants sense the length of night, a dark period, as a signal to flower. Each plant has a different photoperiod, or night length. When the plant senses the appropriate length of darkness, resulting in an appropriate length of daylight, it flowers. Flowering plants are classified as long-day plants or short-day plants. Long-day plants flower when the length of daylight exceeds the necessary photoperiod, and short-day plants flower when the day length is shorter than the necessary photoperiod. Long-day plants include carnations, clover, lettuce, wheat, and turnips. Short-day plants include cotton, rice, and sugar cane. | text | null |
L_0674 | seeds and seed dispersal | T_3385 | Plants seem to grow wherever they can. How? Plants cant move on their own. So how does a plant start growing in a new area? | text | null |
L_0674 | seeds and seed dispersal | T_3386 | If youve ever seen a plant grow from a tiny seed, then you might realize that seeds are amazing structures. A seed is a plant ovule containing an embryo. The seed allows a plant embryo to survive droughts, harsh winters, and other conditions that would kill an adult plant. The tiny plant embryo can simply stay dormant, in a resting state, and wait for the perfect environment to begin to grow. In fact, some seeds can stay dormant for hundreds of years! Another impressive feature of the seed is that it stores food for the young plant after it sprouts. This greatly increases the chances that the tiny plant will survive. So being able to produce a seed is a beneficial adaptation, and, as a result, seed plants have been very successful. Although the seedless plants were here on Earth first, today there are many more seed plants than seedless plants. Learn more about seeds in the Seeds Massachusetts Institute of Technology video at | text | null |
L_0674 | seeds and seed dispersal | T_3387 | For a seed plant species to be successful, the seeds must be dispersed, or scattered around in various directions. If the seeds are spread out in many different areas, there is a better chance that some of the seeds will find the right conditions to grow. But how do seeds travel to places they have never been before? To aid with seed dispersal, some plants have evolved special features that help their seeds travel over long distances. One such strategy is to allow the wind to carry the seeds. With special adaptations in the seeds, the seeds can be carried long distances by the wind. For example, you might have noticed how the "fluff" of a dandelion moves in the wind. Each piece of fluff carries a seed to a new location. If you look under the scales of pine cone, you will see tiny seeds with "wings" that allow these seeds to be carried away by the wind. Maple trees also have specialized fruits with wing-like parts that help seed dispersal ( Figure 1.1). Maple trees have fruits with wings that help the wind disperse the seeds. Some flowering plants grow fleshy fruit that helps disperse their seeds. When animals eat the fruit, the seeds pass through an animals digestive tract unharmed. The seeds germinate after they are passed out with the animals feces. Berries, citrus fruits, cherries, apples, and a variety of other types of fruits are all adapted to be attractive to animals, so the animals will eat them and disperse the seed ( Figure 1.2). Some non-fleshy fruits are specially adapted for animals to carry them on their fur. You might have returned from a walk in the woods to find burrs stuck to your socks. These burrs are actually specialized fruits designed to carry seeds to a new location. | text | null |
L_0681 | social behavior of animals | T_3404 | Why is animal communication important? Without it, animals would not be able to live together in groups. Animals that live in groups with other members of their species are called social animals. Social animals include many species of insects, birds, and mammals. Specific examples of social animals are ants, bees, crows, wolves, lions, and humans. To live together with one another, these animals must be able to share information. | text | null |
L_0681 | social behavior of animals | T_3405 | Some species of animals are very social. In these species, members of the group depend completely on one another. Different animals within the group have different jobs. Therefore, group members must work together for the good of all. Most species of ants and bees are highly social animals. Ants live together in large groups called colonies ( Figure 1.1). A colony may have millions of ants, making communication among the ants very important. All of the ants in the colony work together as a single unit. Each ant has a specific job, and most of the ants are workers. Their job is to build and repair the colonys nest. Worker ants also leave the nest to find food for themselves and other colony members. The workers care for the young as well. Other ants in the colony are soldiers. They defend the colony against predators. Each colony also has a queen. Her only job is to lay eggs. She may lay millions of eggs each month. A few ants in the colony are called drones. They are the only male ants in the colony. Their job is to mate with the queen. Honeybees and bumblebees also live in colonies ( Figure 1.2). Each bee in the colony has a particular job. Most of the bees are workers. Young worker bees clean the colonys hive and feed the young. Older worker bees build the waxy honeycomb or guard the hive. The oldest workers leave the hive to find food. Each colony usually has one queen that lays eggs. The colony also has a small number of male drones. They mate with the queen. | text | null |
L_0681 | social behavior of animals | T_3405 | Some species of animals are very social. In these species, members of the group depend completely on one another. Different animals within the group have different jobs. Therefore, group members must work together for the good of all. Most species of ants and bees are highly social animals. Ants live together in large groups called colonies ( Figure 1.1). A colony may have millions of ants, making communication among the ants very important. All of the ants in the colony work together as a single unit. Each ant has a specific job, and most of the ants are workers. Their job is to build and repair the colonys nest. Worker ants also leave the nest to find food for themselves and other colony members. The workers care for the young as well. Other ants in the colony are soldiers. They defend the colony against predators. Each colony also has a queen. Her only job is to lay eggs. She may lay millions of eggs each month. A few ants in the colony are called drones. They are the only male ants in the colony. Their job is to mate with the queen. Honeybees and bumblebees also live in colonies ( Figure 1.2). Each bee in the colony has a particular job. Most of the bees are workers. Young worker bees clean the colonys hive and feed the young. Older worker bees build the waxy honeycomb or guard the hive. The oldest workers leave the hive to find food. Each colony usually has one queen that lays eggs. The colony also has a small number of male drones. They mate with the queen. | text | null |
L_0681 | social behavior of animals | T_3406 | Ants, bees, and other social animals must cooperate. Cooperation means working together with others. Members of the group may cooperate by sharing food. They may also cooperate by defending each other. Look at the ants pictured below ( Figure 1.3). They show very clearly why cooperation is important. A single ant would not be able to carry this large bee back to the nest to feed the other ants. With cooperation, the job is easy. Animals in many other species cooperate. For example, lions live in groups called prides ( Figure 1.4). All the lions in the pride cooperate, though there is still serious competition among the males. Male lions work together to defend the other lions in the pride. Female lions work together to hunt. Then, they share the meat with other pride members. Another example of cooperation is seen with meerkats. Meerkats are small mammals that live in Africa. They also live in groups and cooperate with one another. For example, young female meerkats act as babysitters. They take care of the baby meerkats while their parents are away looking for food. Members of this lion pride work together. Males cooperate by defending the pride. Females cooperate by hunting and shar- ing the food. | text | null |
L_0681 | social behavior of animals | T_3406 | Ants, bees, and other social animals must cooperate. Cooperation means working together with others. Members of the group may cooperate by sharing food. They may also cooperate by defending each other. Look at the ants pictured below ( Figure 1.3). They show very clearly why cooperation is important. A single ant would not be able to carry this large bee back to the nest to feed the other ants. With cooperation, the job is easy. Animals in many other species cooperate. For example, lions live in groups called prides ( Figure 1.4). All the lions in the pride cooperate, though there is still serious competition among the males. Male lions work together to defend the other lions in the pride. Female lions work together to hunt. Then, they share the meat with other pride members. Another example of cooperation is seen with meerkats. Meerkats are small mammals that live in Africa. They also live in groups and cooperate with one another. For example, young female meerkats act as babysitters. They take care of the baby meerkats while their parents are away looking for food. Members of this lion pride work together. Males cooperate by defending the pride. Females cooperate by hunting and shar- ing the food. | text | null |
L_0684 | structural evidence for evolution | T_3409 | Even though two different species may not look similar, they may have similar internal structures that suggest they have a common ancestor. That means both evolved from the same ancestor organism a long time ago. Common ancestry can also be determined by looking at the structure of the organism as it first develops. | text | null |
L_0684 | structural evidence for evolution | T_3410 | Some of the most interesting kinds of evidence for evolution are body parts that have lost their use through evolution ( Figure 1.1). For example, most birds need their wings to fly. But the wings of an ostrich have lost their original use. Structures that have lost their use through evolution are called vestigial structures. They provide evidence for evolution because they suggest that an organism changed from using the structure to not using the structure, or using it for a different purpose. Penguins do not use their wings, known as flippers, to fly in the air. However, they do use them to move in the water. The theory of evolution suggests that penguins evolved to use their wings for a different purpose. A whales pelvic bones, which were once attached to legs, are also vestigial structures. Whales are descended from land-dwelling ancestors that had legs. Homologous structures are structures that have a common function and suggest common ancestry. For example, homologous structures include the limbs of mammals, such as bats, lions, whales, and humans, which all have a common ancestor. Different mammals may use their limbs for walking, running, swimming or flying. The method the mammal uses to move is considered a common function. | text | null |
L_0684 | structural evidence for evolution | T_3411 | Some of the oldest evidence of evolution comes from embryology, the study of how organisms develop. An embryo is an animal or plant in its earliest stages of development. This means looking at a plant or animal before it is born or hatched. Centuries ago, people recognized that the embryos of many different species have similar appearances. The embryos of some species are even difficult to tell apart. Many of these animals do not differ much in appearance until they develop further. Some unexpected traits can appear in animal embryos. For example, human embryos have gill slits just like fish! In fish they develop into gills, but in humans they disappear before birth. The presence of the gill slits suggests that a long time ago humans and fish shared a common ancestor. The similarities between embryos suggests that these animals are related and have common ancestors. For example, humans did not evolve from chimpanzees. But the similarities between the embryos of both species suggest that we have an ancestor in common with chimpanzees. As our common ancestor evolved, humans and chimpanzees went down different evolutionary paths and developed different traits. | text | null |
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