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BIOLOGY II REVIEW High School Graduation Test Beneficial: Harmful: decomposers of matter, in digestive system, nitrogenfixers can cause diseases like strep throat, pneumonia LINNAEAN SYSTEM In the mid-1700’s, Carolus Linnaeus developed a new classification system that revolutionized taxonomy. He suggested that organisms be classified with other organisms that had similar structures. Organisms are known by their common name, such as red maple. Organisms have been given a scientific name, the genus followed by the species. The genus and species for the red maple tree is Acer rubrum. The genus begins with a capital letter and the second name is always lower case. All scientific names are written in Latin, and are italicized or underlined. PROTISTA Examples: A classification key can be used as an aid to identify organism. It uses an organisms general characteristics and special features to find its appropriate placement. Growth: Reproduction: Beneficial: Harmful: Characteristics: Structures: Most unicellular organisms - protozoa, amoeba, zooplankton, euglena, paramecium, and algae Animal-like organism, distinguished by method of locomotion, eukaryotes, mainly microscopic, single celled or multicellular; some are autotrophic (algae) and many are heterotrophic (protozoans) flagella, capsules, cell organelles, membrane bound, some are photosynthetic cell membrane, availability of food set growth limit. asexual or sexual some are harmless sleeping sickness, malaria TAXONOMY Scientists these days study chromosome structure, reproductive potential, biochemical similarities, and embryology to determine the relationships among organisms. The classification levels are: Kingdom-Phylum-Class-Order-Family-Genus-Species (King Philip Came Over For Great Spaghetti) KINGDOMS MONERA includes Eubacteria and Archae Examples: Bacteria, blue-green bacteria, and other microorganisms that lack nuclei Characteristics: prokaryote, microscopic, lives as a single cell or in colonies in water. Most are autotrophic (producers), a few are heterotrophic (consumers) Structures: flagella, capsules Growth: cell membrane and availability of food set growth limit; keep moist and warm for optimal conditions Reproduction: binary fission (splits in two) FUNGI Examples: Characteristics: Structures: Growth: Reproduction: Beneficial: Harmful: PLANTS Examples: Characteristics: Structures: Functions: Systems: Growth: mushrooms, bread molds, slime molds, rusts and smuts, yeast Animal-like organism, cannot move, eukaryotes, mainly multicellular, parasitic, heterotrophic, root-like, caps, filaments based on food source and availability asexual, sexual yeast, penicillin, decompose organic material cereal rusts, ringworm, athlete’s foot, All multicellular plants - Mosses, liverworts, hornworts, ferns, gymnosperms (pine cone plants), angiosperms (flower-bearing plants) eukaryotes, mainly multicellular, can’t move, autotrophic cellulose cell walls based on cell and tissue chemistry all present and functioning based on hormone action Reproduction: ANIMALS Examples: Characteristics: Structures: Functions: Systems: Growth: Reproduction: asexual, sexual by spores, seeds, flowers, and cones All multicellular animals - Invertebrates (sponges, jellyfish, coral, sea anemones, planarian, fluke, tapeworm, hookworm, earthworm, mollusks, starfish, insects, crustacean); vertebrates (fish – cartilaginous and bony); amphibians – frogs, salamanders; reptiles – snakes, lizards, turtles; birds; and mammals eukaryotes, multicellular, heterotrophic, most are motile at some point in their lifetime all present and unique to the organism based on nutrition, cell and tissue chemistry, and individual demands all present and functioning based on hormone action and nutrition asexual, sexual PLANTS One of the major ways that land plants differ is the way they transport water and nutrients throughout the plant body. The majority of land plants have an internal system of connected tubes and vessels called vascular tissues. These plants, called vascular plants, are the plants that you are the most familiar with –maple trees, grasses, roses, and house plants. Vascular plants have roots, stems, and leaves. The other group of plants is called bryophytes. They lack vascular tissue. They transport water and nutrients by osmosis and diffusion. NONVASCULAR PLANTS Bryophytes need a lot of water to survive. Remember that they transport materials by osmosis and diffusion. This requires a lot of water. Almost all bryophytes are small plants and they grow close to the ground. Gravity can restrict the processes of osmosis and diffusion. Bryophytes do not have true stems, leaves, and roots. What you think are their “roots” are actually rhizoids. They anchor the plant to the ground, but they do not absorb water like real roots do. The part of the bryophyte that is above the ground gets its water from the air through its leaves. Bryophyte leaves are usually only two cells thick. The main type if Bryophytes are: mosses, liverworts, and hornworts VASCULAR PLANTS Plants with vascular tissue are called tracheophytes. They have true roots, stems, and leaves. They have an internal network of tubes that carry water, nutrients and glucose made from photosynthesis throughout the plant. The roots absorb water and nutrients from the soil and they anchor the plant. The roots also store food that was made in the leaves. The stem contains vascular tissue that transports substances between the roots and the leaves. The stem also supports plant growth above the ground. It is the backbone of the plant. There are two types of vascular tissue: xylem and phloem. Xylem transports water and minerals absorbed by the roots up to those parts of the plant that are above the ground. The phloem carries sugar and other soluble organic materials produced by photosynthesis from the leaves to the rest of the plant. The leaves use sunlight, water, and carbon dioxide to carry out photosynthesis. They also transport the food they produce to the rest of the plant in a process called translocation. In addition leaves exchange gases and water vapor with the atmosphere. The outside of the leave is covered with a waxy layer that slows the evaporation of water from the leaf. The waxy layer covers the epidermis, a single transparent layer of cells. The epidermis has openings called stomata. Each stomata has a guard cell on each side. The guard cells change shape to control the exit and entry of water and gases. Most guard cells are located on the underside of the leaf where the surface is shaded. Ninety percent of the water that enters the roots is lost through the leaves in a process called transpiration. The middle portion of the cell is called mesophyll. The cells of the mesophyll contain the chlorophyll and other pigments. Vascular bundles extend into the tissue of the mesophyll. They are seen in the leaves as veins. The vascular plants can be divided into those that have seeds and those that have spores. Ferns, horsetails, whisk ferns, and club mosses all have spores. All other plants have seed – either in a cone or in a fruit. FERNS Ferns are seedless plants that contain vascular tissue. Other seedless plant groups include whisk ferns, horsetails, and club mosses. Ferns have underground rhizomes (underground stem) that produce roots. Each fern frond has a stem (called a stipe) many leaf blades that make up the frond. Fern fronds spread out over a large area and so ferns are able to survive in dim sunlight. GYMNOSPERMS Gymnosperms are one of two groups of vascular plants. Gymnosperms produce their seeds in cones and generally keep their leaves throughout the year (evergreen). The main gymnosperms alive today – are Conifers. Conifers means “cone-bearer”. Pines, spruce, fir, and other conifers are characterized by their stiff cones and needle-like leaves. Conifers can thrive in harsh conditions because they have special adaptations. Their needles are covered in a hard waxy cuticle and have little exposed surface area. This means that they do not lose much moisture. They shed their needles throughout the year instead of once a year. They send their roots out into a wide area of soil instead of deep into the soil. This allows them to survive in areas where the soil is not very deep. ANGIOSPERMS Angiosperms are flowering plants. They produce seeds enclosed in fruits. (Gymnosperm seeds are uncovered in their cones.) Angiosperms are deciduous plants. That means that they lose their leaves every fall. Angiosperms produce seeds with a cotyledon (seed leaf) inside. A cotyledon provides food for the plant embryo in the seed when it begins to grow. Angiosperms can be divided into one of two groups. This group is based on characteristics of their seeds: monocot and dicot. Monocots are plants with only one cotyledon. Monocots also have vascular tissue that is scattered in separate bundles throughout the stem. The leaves have parallel veins and the root system is fibrous with string-like branches. Dicots have two cotyledons. Dicots have vascular tissue arranged in a circle around the outside of the stem. The leaves have net-like veins. The root is a large central taproot. REPRODUCTION Vascular plant life is different from non-vascular plant life. Nonvascular plants spend the majority of their life in the gametophyte phase. In vascular plants, the sporophyte generation is the dominant generation. The sporophyte is physically larger and shows more complex development. The reproductive cycle of a conifer involves separate male and female cones that are grown on the same tree. The male pollen cones produce the pollen grains. The female seed cones contain egg cells. Both pollen and eggs are gametophytes. When the egg cells mature, the female cells produce a sticky sap that traps the pollen grain. The pollen grain produces sperm, which fertilize the eggs. A conifer embryo develops, enclosed in the seed. Reproduction in angiosperms is different. All angiosperms produce flowers. Some flowers have both male and female parts and some have just one sex. The flower attracts insects for pollination and thus fertilization to make a seed. After fertilization, the flower petals die and the remaining flower structures form a fruit. The fruit protects the seed and helps to disperse them in various ways. Then, an animal eats the fruit and leaves the seed in its feces elsewhere. SEXUAL REPRODUCTION In plants that produce them, the flower functions in sexual reproduction. Flowers consist of modified leaves. The essential flower parts are the ones that produce gametes and carry out sexual reproduction. These include male parts called stamens and female parts call pistils. Most flowers have three, four, or five stamens. The thin stem-like portion of a stamen is called the filament. Pollen is produced at the tip of the filament, generally in an oblong structure called the anther. Most flowers have a single pistil. The pistil contains three parts. The swollen base of the pistil is called the ovary. Within the ovary, one or more ovules produce the egg cells. The slender middle part of the pistil is called the style. At the tip of the style is the stigma. The stigma produces a sticky substance to which pollen grains become attached. During pollination, pollen grains stick to the top of the stigma. From there, the pollen grain grows a pollen tube down through the style to the ovary where it fertilizes the egg. In cross-pollination, the pollen from one flower sticks to insects, which in turn deposit, it on other flowers. In self-pollination, the pollen is transferred to the stigma of the same flower. In the anther and the ovary, cell division takes place, which reduces the number of chromosomes in half. Animals, wind, and water all transport pollen from flower to flower. The nonessential flower parts are modified to aid the specific type of pollination a plant undergoes. In flowers that are pollinated by animals, the stem and receptacle hold the flower out where its colors and scent are most obvious. Some flowers produce nectar, a sweet liquid. Fruits are formed when the egg is fertilized and the ovary begins to swell and ripen. It changes color and becomes fleshy or dry. Animals eat the fruit and pass the seed out to new places through their waste. ASEXUAL REPRODUCTION Many plants can produce new plants without the aid of fertilization.. Asexual reproduction is common in strawberries, potatoes, irises, spider plants, and grasses. Remember that any plant produced asexually has the same genes as its parent plant. Asexual reproduction can be accomplished naturally through vegetative propagation. This means that the plant sends out runners or long modified stems (rhizomes) and grows new plants from these parts. Artificial propagation involves things like cuttings and graftings. With cuttings, pieces of stem are cut from the parent plant and kept in soil or water until roots grow. Then the plant is placed in soil to grow. Grafting is a method used to propagate fruit trees, roses, and grapes. Sections of one plant’s stem are cut and attached to another plant’s stem that is already rooted in the soil. SEEDS Seeds gave the animal world a new high-energy food source. They provide food for mammals that need lots of food to help maintain their body temperature. People have depended upon angiosperms for food, lumber, fibers, clothing, and medicines. The development of plants that have seeds really helped plants to survive in a variety of places. Seeds can lie dormant (asleep) if the conditions aren’t right for growing. Some seeds, because they have burrs or stickers, can travel a long way on animals or in the wind before developing into a plant. This spreading of seeds, called dispersal, is good for plants. It helps to spread the plant’s genes over a wider area. INVERTEBRATES The major difference between animals and plants is that animals can move. Animals cannot produce their own food so they must move to find it. The arrangement of body parts is related to how a particular animal species meets the challenges of living, which includes gathering food, protecting itself, and reproducing. Differences in body structure are useful in classifying animals. Invertebrates make up 97% of the animal kingdom. Invertebrate are animal that do not have a backbone such as: worms, octopus and all insects. VERTEBRATES Vertebrates have a strong flexible backbone. Three classes live entirely in water - jawless fish, cartilaginous fish, and bony fish. Amphibians are adapted to life on land as well as the water. Reptiles and mammals are primarily land animals. All but a few birds can fly. Vertebrates have a number of characteristics in common. They have bilateral symmetry. The major sense organs are located in the head. All vertebrates have a closed circulatory system and a coelom (large central body cavity that contains the important organs). They all have an endoskeleton which supports and protects them. A distinctive feature of the skeleton is the backbone - vertebral column. The endoskeleton can be made of cartilage or bone. They have pairs of muscles that work in opposite directions to push and pull the bones. Their bodies are covered with scales, skin, feathers, or hair. There is contractile tissue attached to the bone or cartilage. They have a digestive tube that goes from mouth to anus. They have gills or lungs for breathing and have a closed circulatory system with two-, three-, or four-chambered hearts. They have arteries to take the blood from the heart and veins to take it back to the heart. Their excretory (waste) system consist of kidneys, and associated tubes. Heir nervous system includes a spinal cord, brain, nerves, and sense organs. There are male and female sexes. Fish Most of the world’s fishes have skeletons made of bone, and have jaws and scaly skin. They get their oxygen from the water through gills. They have a swim bladder to help with buoyancy and a two-chambered heart. They are ectothermic. They have separate sexes and the eggs are fertilized outside the body. Class Amphibia Amphibians live on land and in the water. They have internal lungs that are not very efficient and they also get oxygen through their moist skin. They keep their skin moist with a mucus and they can never venture too far from water. They return to the water to lay their eggs and their young pass through a larval stage in the water before beginning their life on land. Adult amphibians are carnivores. They have a three chambered heart and are ectothermic. They have a brain which is the central part of their nervous system. They have separate sexes and have external fertilization. Amphibians include frogs, toads, and salamanders. In frogs, the young are called tadpoles and live in the water. The tadpoles go through metamorphosis, or change, as it develops into an adult. A tadpole begins life with a short tail and breathes through gills. Gradually it develops arms and legs and its tail begins to disappear. The lungs replace the gills and the frog leaves the water. Class Reptilia Reptiles were the first animals that were truly independent of the water. They do not need to keep their body moist for their skin is thick and covered with scales. They do not need to return to water to have babies for their young are laid in eggs. These eggs hold food for the embryo to live off of while it is growing. Some are herbivores and some are carnivores. They have strong, bony skeletons and their feet have toes with claws. They have welldeveloped lungs and a three chambered heart (except for crocodiles). They are ectothermic. The reptile’s nervous system is similar to that of amphibians and they have a small brains. Reptiles include the extinct dinosaurs, turtles, tortoises, alligators, crocodiles, lizards, and snakes. Class Aves This is the class of all birds. Birds arose from reptiles and they grew feathers instead of scales to insulate themselves. The feathers distinguish birds from other classes of vertebrates. Birds are endothermic warm-blooded - their body temperature remains constant. They have a four-chambered heart. They have wings and can fly. The body is divided into a head, neck, trunk, and tail. They do not have teeth - they have a horny beak. Their front limbs are modified into wings. They lay eggs and incubate them in the nest. There are four common bird types: flightless birds (penguins, ostriches), water birds (ducks, geese, swans), perching birds (sparrows, robins), and birds of prey (hawks, eagles, owls). Class Mammalia Mammals have several characteristics not found in other vertebrates. They nurse their young using milk from mammary glands. Mammals have live births - the young are born live after spending time in their parents developing. They have body hair that acts as insulation and also protects the body from injury. Mammals have a large well-developed brain and they are the only animals that have an external outer ear for hearing. Their body is divided into two parts - the chest and the abdomen. The diaphragm separates the two parts. They are endothermic. They have a four-chambered heart and an efficient, closed circulatory system. Mammals have a well-developed cerebral cortex and have a complex nervous system. Mammals include monotremes (duck-billed platypus, spiny anteater). They have mammary glands, which make them mammals, but they lay eggs. Mammals also include marsupials (kangaroos, koalas, opossums). They bear live young, but the young are not as developed as other mammals. These babies complete their development inside a pouch attached to the mother. Placental mammals include 95% of all mammals. The embryo of a placental mammal is implanted in the mother’s uterus - the mother’s reproductive organ. The placenta forms, connecting the young mammal directly to the mother. ECOLOGY ECOSYSTEMS Life on earth extends from the ocean depths to a few kilometers above the earth’s surface. The area where life exists is called the biosphere. The biosphere can be more easily understood by breaking it into smaller components called ecosystems. An ecosystem is a physically distinct, self-supporting unit of interacting organisms and their surrounding environment. It is made up of biotic and abiotic interactions. The biotic factors of an ecosystem are the living organisms in the area. The abiotic factors are the non-living, or physical, components of the area like light, soil, water, temperature, wind, and nutrients. The essential factors that make an ecosystem successful are a source of energy, a storage of water, and the ability to recycle water, oxygen, carbon, and nitrogen. Ecosystems must maintain an ecological balance. This can be helpful or harmful to the members that make up the community depending upon whether they are predators or prey. A predator is an animal that feeds on other living things. The animal it feeds upon is the prey. Lions (predator) hunt down and kill antelope (prey). Each of the biotic organisms in an ecosystem interrelate with the others. A symbiotic relationship between two members of a community is one in which one or both parties benefit. Commensalism is a relationship in which one member is the host, but causes no harm to the other organism (barnacles on whales). Mutualism is a relationship in which two living organisms live together in dependency on each other (the protozoa in the human intestine). Parasitism is a relationship that involves a host organism which is harmed by the presence of the other organism (fleas on dogs and cats). COMMUNITIES An ecosystem’s biotic factors interact with each other and compose a community of living things that coexist. Each community is composed of populations. A population is a group of small individuals of a single species that occupy a common area and share common resources. The number of populations within a community varies. A tropical rain forest community may have thousands of populations while a desert community may have very few. Just like communities are made up of populations, each populations is composed of interacting individuals. Each individual organism lives in a specific environment and pursues a particular way of life. The surroundings in which a particular species can be found is called its habitat. An organism can inhabit an entire ecosystem like a woodpecker might occupy the whole oak forest. But the spider may only inhabit the trunk of one of the oak trees. The way of life that a species pursues within its habitat is called its ecological niche. An organism’s niche is composed of biotic and abiotic factors. Some niches can be very broad (rats) while others can be very limited (panda). THE FLOW OF MATERIALS Each ecosystem has its producers, consumers, and decomposers. They make up a cycle called a food chain. Food passes from one organism to another in the food chain. Energy is used up by each consumer in the food chain. Plants make food, animals eat plants, some animals eat other animals, and some animals eat plants and other animals. Herbivores are animals that eat only plants. Carnivores are animals that each only other animals. Omnivores are animals that eat both plants and animals. A Saprophyte is an organisms that feeds on dead organisms. There are many food chains in an ecosystem. The least amount of energy consumed is the item highest in the food chain. In the preceding example that would be the human. All the food chains in an ecosystem make up the food web of the area. Most food chains overlap because many organism can eat more than one type of food. All organisms need certain chemicals in order to live. The most important ones are water, oxygen, carbon, and nitrogen. The continuous movement of chemicals throughout an ecosystem is called recycling. ECOLOGICAL SUCCESSION An ecosystem goes through a series of changes known as ecological succession. Succession occurs when one community slowly replaces another as the environment changes. As succession in a community continues, it finally reaches a climax community. A few organisms establish themselves and become the dominant species in the area. The complete process of succession may take anywhere from a hundred to thousands of years, depending upon the communities. POPULATIONS IN ECOSYSTEMS The population of an area is affected by the new offspring produced in the area. New plants and animals moving in from other places increase the size of the population. The death of organisms Evoluti and animals moving out of the on area decrease the size of the population. There is a direct relationship between the number of plants and animals in an area which is in ecological balance. If the number of one of them is increased or decreased, it will affect the numbers of the other. During deer season, the number of deer is reduced by man. The plants that the deer eats will increase during this season. A change in populations may be helpful or harmful to the community. If insects are killed by insecticide, the animals that depend on they for food must move elsewhere. Even the human population changes as he seasons change. In the summertime, the coastal area is more widely populated by vacationing people. In the wintertime, the snowy, mountainous areas are more populated by snow skiers. BIOMES Communities are members of a larger ecological unit called a biome. A biome is an extensive area of similar climate and vegetation. A biome’s abiotic (non-living) factors determine what plants and animals live there. The major influences are temperature, light intensity, and patterns of rainfall, which determine the availability of water. There are six basic biomes on earth: tundra, taiga, grassland, deciduous forest, desert, tropical rain forest. Biomes that are closest to the poles experience the coldest weather conditions for they are furthest away from the sun due to the tilting of the earth. ECOLOGICAL PROBLEMS Natural resources are necessary for human survival and the making of necessary products. The natural resources are water, air, soil, wildlife, and forests. Problems that are now being faced are related to erosion, soil depletion, species extinction, deforestation, desertification, and water shortages. Efforts to reverse these problems and their environmental damages are found in the planned programs of reforestation, captive breeding, and planned farming through efficient plowing and planting procedures. Disruptive changes can easily upset the stability of an ecosystem. Destructive acts of nature can occur. A forest fire can destroy all plant and ---animal life in a forest, along a river, and around the shore of a pond. It can also pollute a pond with ash. Humans are unique in our ability to modify our ecosystem. Pollution from human acts can also affect an ecosystem. A chemical spill or pesticides sprayed overhead can kill all plant and animal life with which it comes in contact with. A housing development along the bank of a river or on the shore of a pond can bring both garbage and noise pollution, in addition to direct physical destruction of these habitats. Pollution is damaging to both the ecosystems and living organisms. Air, soil, and food resources are being affected by pollution. Pollutants include automobile exhaust, fertilizers, pesticides, industrial wastes, radioactive wastes, and household wastes. Pesticides like DDT become absorbed by the animal and concentrated in their bodies. Acid rain forms from the exhausts of automobiles which emit sulfur and nitrogen oxides. These combine with water in the air to form sulfuric and nitric acids. The growing population and modern conveniences greatly contribute to the problems of pollution. Government regulations, community efforts, and changes in habits of industries and individuals are necessary to solve pollution problems. EVOLUTION Evolution means change over time. The theory of evolution begins with the origin of life on the early Earth. The conditions of early Earth were very different - there was no oxygen, the continents were connected, and constant lightning and volcanoes provided a great deal of energy. A scientist named Oparin hypothesized that is was these conditions that made it possible for life to begin. The idea of life coming from nonliving material is called spontaneous generation, or abiogenesis. Miller and Urey tested Oparin's "primordial soup" hypothesis and were able to generate amino acids (the building blocks of protein) from simple gases such as carbon dioxide and methane. With the conditions of the Earth today, scientists do not believe life can come from non-living matter. The idea that life can only come from life is called biogenesis. This idea was supported by the experiments of Redi (who showed the flies laying eggs are responsible for maggots, not rotting meat) and Pasteur (who showed that microorganisms present in the air are responsible for new microorganisms, not the air itself.) The evolution of the cell would have led to the first organism (living thing) on Earth. The first cells to evolve would have most likely been prokaryotic cells (a cell with no nucleus and no complex organelles). The evolution of the cell is described in the "heterotroph hypothesis" which states that the first cell would have also been heterotrophic and anaerobic. The eventual evolution of a photosynthetic cell released oxygen into the atmosphere and led to the formation of the ozone layer. As prokaryotic cells evolved, some may have begun to live symbiotically within each other. The "endosymbiotic theory" describes the evolution of the eukaryotic cell (a cell with a nucleus and complex organelles) as the result of a aerobic prokaryotic cell (which became the mitochondia) and a photosynthetic cell (which became the chloroplast) living together inside a larger cell (which developed a nucleus for protection). Evidence for evolution includes: J. Fossil record 2. Comparative biochemistry (comparing DNA; proteins, or cell processes) 3. Comparative anatomy (examining body structures for similarities) 4. Comparative embryology (examining developing embryos for similarities). In general, the more characteristics two species share, the more related those two species are in terms of evolution. The evolutionary history of a species, which is usually theorized based on these types of evidence, is called that specie's phylogeny. For example, the arm of a human and the flipper of a whale have a similar bone arrangement. We call these structures homologous structures because of that similarity. Both animals are mammals, and share similar embryological development. Both animals have similar proteins the cells use. Thus, the phylogeny of humans and whales may be more similar than the phylogeny of humans and insects. These types of evidence have led scientists to make several conclusions about the way evolution works: I. Evolution tends to move from simple organisms/structures to complex organisms/structures. For example, the first organisms were the simplest cells (prokaryotes) and the last organisms were complex, multicellular organisms (mammals). 2. Evolution may happen gradually over a long period of time (gradualism) or it may happen quickly, followed by a long period of no change (punctuated equilibrium). Often, sudden changes such as climate shifts (ice age) or a natural disaster (Earth hit by a meteorite) seem to be followed by punctuated equilibrium. 3. The development of new species (speciation) may be caused by natural selection. Natural selection occurs when the following happens: A. Variation within a population's gene pool. Variation means differences, and may be due to mutations or natural genetic differences. All of the genes in a population are called the gene pool. B. Overproduction of offspring. Evolution can only act on a population, not on an individual, because the genes of a population may change but the genes of an individual will not. C. Competition for resources D. Survival or greater reproduction of the best adapted. An adaptation is any heritable trait (it may be physical, physiological or behavioral) that allows an organism to better survive or reproduce. . For example, different tooth lengths in a rat population arc caused by differences in the genes of the rats. If many rats are born within a population, competition for food may occur. If the rats with longer teeth are better able to eat the food source, these rats will be healthier and have more offspring. The offspring will inherit the long tooth gene, and he better eaters. Eventually the rat population will have more long-tooth rats than it did before. Darwin is credited with the theory of natural selection. He developed this theory after noticing similarities among different species of finches and tortoises in the Galapagos Islands. Darwin theorized that all of the finch species evolved from a common ancestor. As the birds spread to nearby islands, different environmental conditions caused different traits to be more successful. Over a long period of time, the birds changed enough to become different species. This process of evolution from a common ancestor is called adaptive radiation.