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Key Idea 3 - Organic Evolution: Individual organisms and species change over time.
In modern classification, protozoa and algae are known as molds, and bacteria are known as bryophytes plants protists animals
Most modern biologists agree that an ideal classification system should reflect nutritional similarities among organisms habitat requirements of like groups distinctions between organisms based on size evolutionary relationships among species
Which term includes the other three? genus species kingdom phylum
In one modern classification system, organisms are grouped into three kingdoms phyla genera species
Which is one basic assumption of the heterotroph hypothesis? More complex organisms appeared before less complex organisms. Living organisms did not appear until there was oxygen in the atmosphere. Large autotrophic organisms appeared before small photosynthesizing organisms. Autotrophic activity added molecular oxygen to the environment.
According to the heterotroph hypothesis, scientists believe that life arose in a desert environment a forest environment a vacuum an ocean environment
From an evolutionary standpoint, the greatest advantage of sexual reproduction is the variety of organisms produced appearance of similar traits generation after generation continuity within a species small number of offspring produced
According to modern theories of evolution, which of the following factors would be least effective in bringing about species changes? geographic isolation changing environments genetic recombination asexual reproduction
A factor that tends to cause species to change is a stable environment lack of migration recombination of genes decrease in mutations
If a fossil mammoth were discovered frozen in ice, its cells could be analyzed to determine whether its proteins were similar to those of the modern elephant. This type of investigation is known as comparative anatomy embryology biochemistry ecology
If members of the same species have been geographically isolated from each other for an extended period of time, which will they most likely exhibit? mutations identical to each other random recombination occurring in the same manner evolution of traits of high adaptive value for their particular environments evolution into two new species which will have no problem interbreeding
Skeletal similarities between two animals of different species are probably due to the fact that both species live in the same environment perform the same functions are genetically related to a common ancestor have survived until the present time
The best means of discovering if there is a close evolutionary relationship between animals is to compare blood proteins use of forelimbs foods consumed habitats occupied
In the process of evolution, the effect of the environment is to prevent the occurrence of mutations act as a selective force on variations in species provide conditions favorable for the formation of fossils provide stable conditions favorable to the survival of all species
In a stable population in which the gene frequencies have been constant for a long time, the rate of evolution increases decreases remains the same increases, then decreases
Certain strains of bacteria that were susceptible to penicillin in the past have now become resistant. The probable explanation for this is that the mutation rate must have increased naturally the strains have become resistant because they needed to do so for survival a mutation was retained and passed on to succeeding generations because it had high survival value the principal forces influencing the pattern of survival in a population are isolation and mating
The frequency of traits that presently offer high adaptive value to a population may decrease markedly in future generations if conditions remain stable the environment changes all organisms with these traits survive mating remains random
Since the publication of Darwin’s theory, evolutionists have developed the concept that a species produces more offspring than can possibly survive the individuals that survive are those best fitted to the environment through time, favorable variations are retained in a species mutations are partially responsible for the variations within a species
One factor that Darwin was unable to explain satisfactorily in his theory of evolution was natural selection overproduction survival of the fittest the source of variations
Key Idea 3—Organic Evolution: Answers and Explanations
3 The protists include all unicellular organisms and organisms that have both plant and animal features within one cell. Protozoa and algae are protists. Wrong Choices Explained: (1) Bryophytes are multicellular green plants that do not have vascular tissue. Mosses are examples of bryophytes. (2) Multicellular photosynthetic organisms make up the plant kingdom, which includes both vascular and nonvascular plants. (4) The animal kingdom is composed of multicellular organisms that cannot manufacture their own food. The organisms within this kingdom lack cell walls, and most are capable of some type of locomotion.
4 A classification system should reflect evolutionary relationships among species. Evolutionary relationships are determined on the basis of the similarities in the anatomy, embryology, and biochemistry among organisms. Wrong Choices Explained: (1) All animals from protozoans to humans utilize the same nutrients in a similar manner. The process of photosynthesis is the same in tree cells and unicellular algae. Nutritional similarities among organisms are not useful in a system of classification. (2) Both the whale and the fish live in an ocean environment. However, the whale is a mammal. Other than sharing the same habitat, the whale has no fish characteristics. (3) Algae and protozoans are both microscopic organisms. However, algae have plant characteristics and protozoans have animal characteristics. Size cannot be used as the basis for a system of classification.
3 According to the classification system, the largest grouping of organisms is the kingdom. Following this, the other groups, in order, are phylum, class, order, family, genus, species. Depending on its chief characteristics, an organism is placed in one of five kingdoms, Monera, Protist, Fungi, Animal, or Plant. 1 In one modern classification system, organisms are grouped into three kingdoms: Animal, Plant, and Protist. Organisms that are not typical plants or animals are classified as protists. Examples are protozoa, slime molds, and bacteria. Wrong Choices Explained: (2) A phylum (plural phyla) is a large grouping that consists of classes, orders, families, genera, and species. (3) A genus (plural genera) is a classification group composed of species. Members of a genus are more closely related than groups belonging to a given phylum. (4) The species is the unit of classification. All members of a species are so closely related that they can mate and produce viable offspring.
4 A heterotroph is an organism that must get its food from a source outside its own body cells; it cannot synthesize its food from inorganic materials. The heterotroph hypothesis proposes that the first living things on Earth were heterotrophs that obtained their food from the organic materials in the primitive seas. Autotrophs are organisms, such as green plants, that can synthesize their own food. At some stage in Earth’s history, autotrophic activity used up the carbon dioxide in the air and, as a consequence of photosynthesis, added molecular oxygen to the atmosphere. Wrong Choices Explained: (1) Coacervates and then relatively simple cells developed before more complex organisms. (2) Living heterotrophs appeared before molecular oxygen was added to the atmosphere. (3) Small cells that carried on photosynthesis appeared before the more complex vascular and seed plants. The course of evolution is from the simple to the complex.
4 According to the heterotroph hypothesis, life on earth evolved through a sequence of stages. The gases of the primitive atmosphere, such as methane, ammonia, and hydrogen, were washed down by heavy rains into the early oceans. They were acted on by ultraviolet radiation, cosmic rays, the earth’s heat, and radioactivity. The bonding together of the molecules resulted in the formation of larger organic molecules. Wrong Choices Explained: (1) A desert environment could not support “first” life. The intense heat and the rapid evaporation of water are conditions that do not allow for the movement or maintenance of molecules in a fluid medium. (2) A forest environment does not provide the pools of warm water on a continuous basis necessary for aggregate molecules to form. (3) A vacuum, a place without air, cannot support life.
1 Sexual reproduction helps to maximize the number of different allelic combinations that occur in offspring, leading to a greater variety of organisms produced within the species’ population as a whole. Individuals displaying favorable traits in a changing environment are more likely to survive and to pass these traits on to their offspring, a fact that helps to promote evolutionary change. Wrong Choices Explained: (2), (3) Appearance of similar traits generation after generation and continuity within a species describe conditions that promote stability and uniformity within species, both of which are maximized during asexual reproduction. (4) Evolutionarily speaking, the larger the number of offspring produced during reproduction, the more successful a particular species variety tends to be in competing with other varieties of the same species. Small number of offspring produced, therefore, is not an evolutionary advantage of sexual or any other type of reproduction.
4 Variations among organisms are necessary for speciation. Asexual reproduction is least effective in bringing about changes in species. There are no variations among organisms that are reproduced asexually. These organisms are genetically like their parents. Wrong Choices Explained: (1) Geographic isolation increases the chance that a group of organisms will develop a new gene pool, which will give rise to a new species. (2) Changes in the environment cause shifts in the gene pool. The genes that ensure the survival of organisms increase in the pool. Thus, the environment changes the characteristics of the original population, and a new species is formed. (3) Genetic recombination occurs during meiosis and fertilization. The shuffling of genes results in the appearance of new characteristics in a population.
3 The recombination of genes is one factor that tends to cause species to change. Mutations are changes in genes. When like mutations combine in the fertilized egg, the new characteristic will be expressed in the offspring. If this mutation adds to the survival value of the organism, the gene change will be passed on to progeny because individuals having this mutation will live to reproduce. Wrong Choices Explained: (1) A stable environment will probably not cause species to change. Beneficial mutations become effective in changing environments. For example, the mutations that produced white fur in the polar bear were beneficial. At one time, the polar regions were tropical. A change to a glacial environment was accompanied by a change or changes in the animal species that inhabited the region. Bears with a dark coat color became immediate targets for natural enemies. (2) Migration aids the recombination of genes because organisms have greater opportunities for interbreeding. (4) A decrease in mutations does not aid speciation but slows it.
3 Biochemistry is the study of the chemistry of living organisms. Proteins are compounds found only in living organisms. Wrong Choices Explained: (1) Anatomy is the study of the structure of organisms. (2) Embryology is the study of the development of embryos. (4) Ecology is the study of the relationship of living organisms to each other and to their environment.
3 Geographic isolation involves the separation of organisms by natural barriers. Each group of isolated individuals develops its own gene pool because each group lives under different environmental conditions. In the case of members of the same species who have been geographically isolated from each other, the selection for individuals with special survival traits is different in each environment. Wrong Choices Explained: (1) Mutations are the raw materials for evolution. Although mutations might have been the same in each group, they do not have the same adaptive value in each group. (2) Random recombination occurs in the same manner in each group. However, the recombination process operates on two distinctly different gene pools. (4) Usually, different species cannot mate. If their mating happens to be successful, their offspring will not be fertile.
3 Morphology is the study of the structure and form of living things. When the arm of a human and the wing of a bird are studied, they are seen to have similar bone structure. This indicates that both organisms descended from a common ancestor. They have both undergone many changes since then and are now very different from each other. However, they still retain some of the same genes and therefore show a similarity in many parts of their bodies, including the arrangement of the bones in their forelimbs.
1 A close evolutionary relationship between animals can be shown by a study of their blood proteins. The precipitin test is used to show such a relationship. A rabbit can be sensitized to human blood by being injected with human serum. When the sensitized rabbit serum is mixed with human serum, a white precipitate forms. If the sensitized rabbit serum is mixed with serum from a chicken, there is no reaction. However, a precipitate does form when the sensitized rabbit serum is mixed with the serum of a chimpanzee. In a like manner, the serum of a dog and a wolf show precipitation with serum sensitized to dog serum. Wrong Choices Explained: (2) The forelimbs of many unrelated animals may be used for the same purpose. (3) Many unrelated animals consume similar food. (4) Many unrelated animals live in the same habitat.
2 There are many variations among the organisms of a species. Some variations allow an organism to survive best in a particular environment. Such factors as climate, food supply, and type of predators determine which organisms are best adapted to that environment. Wrong Choices Explained: (1) Mutations occur naturally and randomly. Mutations increase the variations among organisms. (3) Fossils are the remains of organisms that lived in the past. They present evidence that evolution has occurred. (4) There are many factors in an environment that influence the survival of different species. A stable environment preserves the species that have already adapted to that environment.
3 Stable gene pools are a hallmark of nonevolving populations. The rate of evolution in such populations neither increases nor decreases, but remain the same. Wrong Choices Explained: (1), (2), and (4) all refer to changing rates of evolution that do not occur. 3 Bacteria resistant to penicillin developed as a result of mutation. Organisms that did not receive the mutated gene were killed by the antibiotic. Those in which gene mutation occurred survived and passed the mutation on to succeeding generations. Wrong Choices Explained: (1) The mutation rate did not increase. The survivors had the mutated gene that allowed the bacteria to resist the effects of penicillin. These resistant strains reproduced, creating populations that replaced the nonresistant strains. (2) Need does not determine mutation. Mutations are chance occurrences. (4) Survival of a species depends on the ability of its members to obtain food, carry out respiration, and reproduce successfully. Isolation does not increase species survival.
2 As long as environmental conditions remain stable, the alleles controlling traits that promote individual survival in that environment tend to be maintained at a high level in the population’s gene pool. When the environment changes, however, the factors that promoted survival may no longer be present. Selection pressure may then operate to reduce the frequency of the once-prevailing alleles in favor of alleles controlling other, contrasting traits that increase individuals’ chances for survival in the new environment. Wrong Choices Explained: (1) As long as conditions remain stable, selection pressures on individuals displaying favorable traits remain low, promoting the maintenance of a high frequency of alleles controlling these traits. (3) If all organisms with these traits survive, their genes will be passed on to future generations at a high rate. This will help to maintain a high frequency of alleles controlling these traits in the population. (4) If mating remains random, the probability that alleles will pair in unrestricted combinations will remain high, helping to ensure that the laws of probability will operate freely and that gene frequencies for existing traits will remain stable.
4 Darwin proposed his theory of evolution in 1856. His theory did not explain how variation arose in organisms. In 1901, Hugo De Vries discovered the existence of mutations. Mutations accounted for the rise of variations in organisms. Wrong Choices Explained: (1) One of the principles of Darwin’s theory of evolution stated that a species produced more offspring than could possibly survive. (2) Another principle stated that the individuals that survived were those best suited to the environment. (3) The variations favored by the environment are retained within a species. It is the environment that determines which variations are favorable.
4 Darwin’s theory of evolution was completed and published before Mendel completed his study of inheritance in the garden pea. Darwin could not explain how variations occurred or how they were passed on from parent to offspring. Wrong Choices Explained: (1) Darwin’s theory of natural selection was divided into five distinct principles that formulated his concept of evolution. These ideas were set forth in his book The Origin of the Species by Natural Selection. (2) Overproduction was one of the principles of Darwin’s theory. He explained that for a species to continue in existence, it must overproduce in order to maintain the species number. For example, one female codfish lays about 9 million eggs. Not all of these eggs are fertilized and not all codfish lay about 9 million eggs. Not all of these eggs are fertilized and not all codfish fry reach adulthood. If the 9 million eggs per female were fertilized and if these zygotes developed into adult fish, the seas would be overrun with codfish. However, if the number of gametes produced by codfish were greatly reduced, the species would die out. This overproduction of gametes is necessary to maintain codfish survival. (3) Another of Darwin’s principles was survival of the fittest. No two organisms are alike; each has variations. These variations may either help or hinder the organism in its struggle for existence. An organism with variations that help it reach food faster is more fit and has a better potential for survival than a slower, less fit member of the species.
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