Biology 102 Exam Two Study Material
Biology 102 Exam Two Study Material Bio 102
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This 34 page Study Guide was uploaded by Amanda Merritt on Saturday March 12, 2016. The Study Guide belongs to Bio 102 at University of Rhode Island taught by Serena Moseman-Valitierra in Spring 2016. Since its upload, it has received 107 views. For similar materials see Principles Biology II in Biology at University of Rhode Island.
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Date Created: 03/12/16
Pages 580596 (Starting with 31.2) 31.2 How Do Biologists Study Green Algae and Land Plants? To understand how green pants originated and diversified, biologists analyze: o Morphological traits o Fossil record o Phylogenetic trees estimated from similarities and differences in DNA sequences from homologous genes and whole genomes Analyzing Morphological Traits Green algae includes species that are o unicellular o colonial o multicellular Live in o marine o freshwater o moist terrestrial Similarities Between Green Algae and Land Plants Chloroplasts contain the photosynthetic pigments chlorophyll a and b and accessory B carotene Similar arrangements of internal, membranous sacs: thylakoids Cell walls, sperm, peroxisomes are similar in structure and composition Chloroplasts synthesize starch Two most similar: o Coleochaetohyceae o Charophyceae Hypothesize land plants evolved from multicellular green algae and lived in freshwater habitats More Morphological Difference Among Land Plants Land plants clustered into broad 3 categories o Nonvascular Plants bryophytes lack vascular tissue Ex. Mosses o Seedless vascular plants Do not make seeds make microscopic pores that are carried by wind Ex. Ferns o Vascular seed plants Seed consist of embryo and a store of nutritive tissue, surrounded by a tough protective layer Flowering plants: angiosperms Using a Fossil Record First green plants on fossil record: green algae Supports hypothesis that land plants are derived from green algae Reasonable to hypothesize that the evolution of green algae contributed to the ride of oxygen levels Origin of Land Plants Most fossils are microscopic o consist of reproductive cells (spores) and cuticles (waxy coating0 Observations of fossils from green plants o Cuticle helps them resist drying o Fossilized spores are surrounded by sheetlike coating Sporopollenin; encases spores and pollen from modern land plants and help resist drying o Fossilized spores have been found in association with sporeproducing structure Sporangia SilurianDevonian Explosion Second major interval in fossil records Biologists found fossil records from most major plant lineages Virtually all adaptations that allow plants to occupy dy, terrestrial habitats are present o including waterconducting tissue and roots Plants colonized the land conjunction with fungi and grew in mutually beneficial symbiosis o Fungi provided nutrients from below the surface o plants provided sugars and other products of photosynthesis The Carboniferous Period Third integral in fossil records Extensive deposits of coal o Carbon rich rock packed with fossil spores,branches, leaves, and tree trunks Most fossils were derived from seedless vascular plants Coal formation is thought to start only in the presence of water, Carboniferous fossils indicate the presence of extensive forested swamps Diversification of Gymnosperms Fourth interval of land plant history Characterized by seed plants: gymnosperms Five major groups o Ginkgophyta o Cycadophyta o Cupressophyta o Pinophyta o Gnetophyta Continents became blanketed with green plants for the first time during this period Diversification of Angiosperms Fifth interval in history of land plants Still underway Age of flowering plants o Angiosperms Plants that first produced flowers are the ancestors of today’s grasses, orchids, daises, oaks, maples, and roses According to fossil record o Green algae appear first o Nonvascular plants o Seedless vascular plants o Seed plants Organisms that appear late in the fossil record are often less dependent on moist habitats o Support hypothesis that green plants evolved from green algae an land plants evolved to colonize dry habitats Evaluating Molecular Phylogenies Green plants are monophyletic o single common ancestor gave rise to them Green algae are paraphyletic Charophyceae are the closest living relative to land plants Land plants are monophyletic Nonvascular plants are the earliestbranching groups among land plants Nonvascular plants are paraphyletic Seedless vascular plants are paraphyletic, but the vascular plants as a whole are monophyletic Seed plants are monophyletic Gymnosperms and angiosperms are a monophyletic group Land plant evolution began with nonvascular plants, proceeded to seedless vascular plants, and continued with the evolution of seeds 31.1 What Themes Occur in the Diversification of Land Plants? The most ancient groups in the lineage are dependent on wet habitats More recently evolved groups can live and reproduce in dry, or even desert, conditions The story of land plants is the story of adaptations that allowed photosynthetic organisms to move from aquatic to terrestrial environments The Transition to Land: How Did Plants Adapt to Dry Conditions with Intense Sunlight? Once green plants made the transition to survive out of water, growth on land offered many resources o Light Amount of light is reduced for photosynthesis when it has to penetrate water On land that isn’t the case = more light for photosynthesis o Carbon Dioxide most important molecule required by photosynthetic organisms More abundant in the atmosphere and diffuses more readily than it does in water Adaptations that solved the drying out problem o Preventing water loss which kept cells from drying out and dying o Providing protection from harmful UV radiation o Moving water from tissues with direct access to water to tissues without direct access Preventing Water Loss: Cuticle and Stomata Cuticle: sheets of a waxy substance that coats the plant and prevents water loss by transpiration o Made the transition to land possible Coverings in wax creates a problem though: makes it harder for carbon dioxide to diffuse Stomata: opening surrounded by guard cells: pore that lets gasses flow in and out but can be regulated with the guard cells Guard cells gave land plants the ability to regulate gas exchange and control water loss Providing Protection From UV Radiation Exposed to higher light intensities, could photosynthesize faster UV rays known to damage DNA Most plants today accumulate UVabsorbing compounds: flavonoids o protects DNA from damage o Plant pigments that act as sunscreen The importance of Upright Growth Hypothesize the first land plants were small or had low, sprawling growth habit Competition for space would have become intense Individuals that can grow erect have better access to sunlight Two problems have to be overcome for plant growth to be erect o Transporting water from tissues that are in contact with wet soil to tissues exposed to dry air against gravity o becoming rigid enough to avoid falling over in response to gravity and wind o Vascular tissues solved both The Origin of Vascular Tissue Established a species containing elongated cells that were organized into tissues along the length of the plant o hypothesized that the elongated cells move from the base of tha plants upward to erect portions through water conducting cells Some has a simple cellulose containing cells some water conducting cells had cell walls with thickened rings containing a molecule called lignin Lignin o extremely effective in resisting gravity Hypothesis: lignified cell walls face stem tissues the strength to remain erect in the face of wind and gravity Defining feature in vascular tissue Elaboration of Vascular Tissue: Tracheids and Vessels Natural selection favored more complex tissues that were more efficient in providing support and transport Tracheids o long, thin, tapering cells that have thickened, lignincontaining secondary cell wall in addition to cellulose based primary cell wall pits in the sides and ends of cell where secondary cell wall is absent, where water can flow efficiently from one to the next Secondary cell wall gave tracheids ability to provide better structural support Vessel Elements o Most advanced type of water conducting cells o shorter and wider o Upper and lower ends have gaps where both primary and secondary cell walls are missing o Continuous pipelike structure Wood o combination of tracheids and vessels o Extremely strong supportive material o ability to make lignified vascular tissues allows them to grow tall and transport water from soil to the top Mapping Evolutionary Changes on the Phylogenetic Tree Fundamentally important adaptations to dry conditions (cuticle, pores, stomata, vascular tissue, tracheids) evolved once Convergent evolution occurred: vessels evolved independently in gnetophytes and angiosperms Transition to Land, II: How Do Plants Reproduce in Dry Conditions? Functions of sexually reproducing eukaryotes (including plants) o increase genetic variability as a result of meiosis and fertilization o increase number of individuals o disperse individuals to new habitats Plants are sessle Key adaptations for reproducing on land: spores that resist drying o encased in a tough coat of sporopollenin o One of the innovations that made the initial colonization of land possible Two other innovations occurring early were instrumental for efficiency in dry environments o gametes were produced in complex, multicellular structures o embryo was retained on the parent plant and was nourished by it Producing Gametes in Protected Structures Gametangia o protected gametes from drying and mechanical damage o present in all land plants except angiosperms Antheridia: spermproducing gametangium Archegonium: eggproducing gametangium Retaining Offspring: Land Plant Embryos are Nourished by Their Parent Instead of land plants shedding their eggs into water or soul, their retaining them Aquatic o Zygote stays attached to mom where it receives nutrient o When the mom dies during fall, the zygote remains on the parent tissue, settles to the bottom of lake or pond in spring meiosis occurs resulting spores turn into haploid adult plants Terrestrial o Zygote is retained by mom called Embryophyta o begin to develop on the living parent plant o forms multicellular embryo that remains attached to parent and can be nourished by it o embryos don't have to manufacture their own food early in life Alternation of Generations Individuals represent a multicellular haploid phase (gametophyte) or multicellular diploid phase (sporophyte) Two phases of life are connected by distinct types of reproductive cells) gametes and spores After dispersion with aid of flagella, spores begin dividing by mitosis Suggests alteration of generations of originated in land plants independently o Male gametes no longer needed to swim o no need for freeliving gametophytes Alternation of generations sequence: o Sporophyte produces spores by meiosis (haploid) o Spores germinate and divide by mitosis to develop into multicellular, haploid gametophytes o Gametophytes produce gametes by mitosis (gametophytes are unicellular and haploid) o Two gametes unite during fertilization to form diploid zygote o Zygote divides by mitosis and develops into multicellular, diploid sporophytes Zygotes vs Spores o Both singles cancelled and divide by mitosis to form multicellular individual o Zygotes develop into sporophytes o Spores develop into gametophytes o Zygotes are diploid, spores are haploid o Zygotes result from the fusion of two haploid cells o Spores are not formed by the fusion of gametes o Spores are produced by meiosis inside structures (sporangia) o Gametes are produced by mitosis inside gametangia LEARNING CATALYTICS NOTES Make sure to check power point slides (2/18) Look at the phylogeny: Be able to label the tick marks with the adaptations Why are they important? Which organism has which adaptations sporopollenin is one of the most chemically inert biological polymers. It is a major component of the tough outer (exine) walls of plant spores and pollen grains Seed: Embryo plus nutritive tissue (2n) Spore: Single cell produced by mitosis or meiosis (n) that can develop into an adult plant, found in algae and many eukaryotes Multicellularhaploid: gametophyte Multicellulardiploid: sporophyte Summary of Alternation of Generations: Sporophyte makes spores via meiosis Gametophytes makes gametes via mitosis Pages 590596 The GametophyteDominant To SporophyteDominant Trend in Life Cycles (Sporophyte Dominated Life cycle) (Gametophyte Dominated Life Cycle) oCcurs in all species with alternation of generations In land plants, the relationship between gametophyte and sporophyte is highly variable Nonvascular plants o Sporophyte is small and short lived o Largely dependent on the gametophyte for nutrition o Gametophytes are long lived and produce most of the food required considered the dominant part of the life cycle Vascular Plants o Sporophyte is the larger and longer lived o Said to have a sporophytedominated life cycle Transition of gametophytedominated to sporophytedominated life cycles is one of the most striking of all trends in plant evolution Hypothesised sporophytedominated life cycles were advantageous because diploid cells can responds to varying environmental conditions more efficiently than haploid cells o particularly if the individual is heterozygous at many genes Heterospory Definition: the production of two distinct types of spores by different structures All non vascular plants and most seedless vascular plants are homosporous o Homospory: production of a single type of spore Homosporois species produc spores that develop into biosexual gametophytes that prodice both eggs and sperm o If they are isolated in nature, they can selffertilize o If two bisexuals are close to each other, outcrossing is favored for genetic variation Two types of sporeproducing structures in heterosporous species are often found in the same individual o Microsporangia: sporeproducing structures that produce megaspores Microspores: develop into male gametophytes: → produce sperm o Magaporangia: sporeproducing structures that produce megaspores Megaspores develop into female gametophytes → produce eggs Gametophytes of seed plants are either male or female, never both Evolution of heterospory was a key event in land plant evolution o made pollen possible Pollen Nonvascular Plants: Has to be a continuous sheet of water for sperm to swim to the egg Species that live in dry environments, pollen is used to move gametes without aid of water Heterosporous seed plants: microspore germinates to form tiny male gametophytes that are surrounded by a tough coat of sporopollenin in a pollen grain Pollen grains o can be exposed to air for a long period of time without dying from dehydration o Tiny enough to be carried to female gametophytes by wind or animal Seeds Retaining embryos has a downside In ferns and horsetails: sporophytes have to live in the same place as their parent gametophytes o Seed plants overcome this limitation embryos are portable can disperse to new locations Dispersal stage of the life cycle shifted from the haploid spore to the young diploid sporophyte Structure that includes an embryo, food supply, surrounded by a touch coating allowing effective dispersal of the embryo Spore are an effective dispersal stage for some plants, but lack stored nutrients, unlike seeds Flowers Angiosperms Most diverse of land plants Flower o Two reproductive structures: stamen and carpels Both are responsible for heterospory o Stamen: includes an anther: where microsporangia develop. Meiosis occurs inside this to form microspores, these then divide by mitosis to pollen grains o Carpel: contains a protective structure: ovary. Ovules are found here Ovules contain the megasporangia Cell inside megasporangium divides by meiosis to form megaspore o then that divides by mitosis to form the gametophytes After pollen grain lands on carpel and produces sperm, fertilization takes place Fertilization requires two sperm cells o One fuses with the egg to form the diploid zygote o One fuses with two nuclei in the female gametophyte to form a triploid nutritive tissue called endosperm o This is all called double fertilization Key innovation was the ovary: helps helps protect female gametophytes from insects and other predators Pollination by Insects and Other Animals Once stamens and carpels evolves, they became enclosed by modified leaves called sepals and petals Hypothesize that flowers are adaptations to increase the probability that an animal will perform pollination o transfer of pollen from one individual’s steman to another’s carpel o That natural selection favored structures that reward an animal (usually an insect) for carrying pollen directly from one flower to another Pollinator: an organism that transfers pollen o attracted to flowers because of their pollen or nectar Evidence: characteristics of the flower correlate with characteristics of the pollinator o scent o flower shape o flower color Fruits evolution of ovary was an important event in land plant diversification o made fruit possible Structure that is derived from the ovary and encloses one or more seeds Animals eat the fruit and disperse the seeds in their feces The Angiosperm Radiation Adaptive Radiation: occurs when a single lineage produces a large number of descendant species that are adapted to a wide variety of habitats Diversification of angiosperms is associated with three key adaptations o Waterconducting vessels o Flowers o Fruits Classified into two major groups o monocotyledons/monocots o dicotyledons/dicots Names were derived by the differences in their cotyledon o COTYLEDON STORES NUTRIENTS AND SUPPLIES THE, WITH THE DEVELOPING EMBRYONIC PLANT Monocots have a single cotyledon Dicots have two Differences also include: o arrangement of vascular tissue o arrangement of leaf veins o characteristics of flowers Doesn’t mean each plant fits into description of either monocots or dicots monocots are monophyletic Dictos are paraphyletic Eudicots o monophyletic lineage o includes most of the plants once considered dicots 26.3 Pages 472474 Natural Selection Occurs when heritable variation leads to differential success in survival and reproduction If certain alleles are associated with the favored phenotypes, they increase in frequency while other phenotypes decrease in frequency o results in evolution How Does Selection Affect Genetic Variation? Genetic variation: the number and relative frequency of alleles that are present in a particular population Selection can only occur if heritable variation exists in a population Natural selection occurs in a wide variety of patterns, or modes, each with different consequences to genetic variation o Directional Selection: changes the average value of a trai o Stabilizing Selection: reduces variation in a trait o Disruptive Selection: increases variation in a trait o Balancing Selection: maintains variation in a trait Directional Selection Average phenotype of a population changes in one direction Directional selection tends to reduce the genetic diversity of a population If this continues over time, the favored alleles will eventually approach a frequency of 1.0 while disadvantageous alleles will approach a frequency of 0.0 o alleles that reach 1.0 are said to be fixed o alleles that reach 0.0 are said to be lost Purifying selection: disadvantageous alleles decline in frequency Stabilizing Selection Selection reduced one extreme in the range of phenotypes and resulted in directional change in the average characteristics of the population Selection can also reduce both extremes in the population: stabilizing selection Two important consequences of stabilizing selection: o No change in the average value of a trait over time o genetic variation in the population is reduced Disruptive Selection Has the opposite effect of stabilizing selection Eliminates phenotypes near the average value and favors extreme phenotypes The overall genetic amount of genetic variation in the population is increased Sometimes plays a part in speciation Balancing Selection when no single allele has a different advantage Balancing among several alleles in terms of their fitness and frequency Occurs when o Heterozygous individuals have higher fitness: heterozygous advantage o Certain alleles are favored by selection at different times or in different places As a result, overall genetic variation in the population is maintained or increased o Certain alleles are favored when they are rare, not when they are common: frequency dependent selection 26.4 Pages 478479 Genetic Drift Genetic Drift: any change in allele frequencies in a population that is due to chance Causes allele frequencies to drift up and down randomly over time When it occurs: allele frequencies change due to blind luck: Sampling error Sampling error occurs when the allele frequencies of a chosen subset of a population are different from those in the total population, by chance Occurs especially in smaller populations Simulation Studies of Genetic Drift Computer Simulations Given enough time, drift can be an important factor even in large populations Key Points About Genetic Drift Genetic drift is random with respect to fitness, the changes in allele frequency that it produces are not adaptive Genetic drift is most pronounced in small populations Over time, genetic drift can lead to random loss or fixation of alleles 37.237.3 Pages 740747 Primary Growth Extends the Plant Body Meristems: populations of undifferentiated cells that retain the ability to undergo mitosis and produce new cells o Some specialize o Some help the meristem grow Apical Meristems: located at the tip of each roots and shoot, they elongate and allow the structure to explore Primary growth: increase the length of the root and shoot systems (in this case) How Do Apical Meristems Produce the Primary Plant Body? Primary Meristem distinct populations: o Protoderm o Ground Meristem o Procambium o All give rise to major tissue systems Protoderm: gives rise to dermal tissue system o epidermis o single layer of cells that covers the plant body and protects it Ground Meristem: Ground tissue system o makes up bulk of plant o Photosynthesis o storange Procambium: Vascular Tissue System o provides support o transports water, nutrients, and photosynthetic products between roots and shoots How is the Primary Root System Organized? Root Cap: protects the root apical meristem o sense gravity o determine direction of growth o Synthesize and secrete polysaccharidesubstance that helps lubricate the root tip, reduces friction and protecting the meristem as it is pushed through the soil Zone of Cellular Division: contain the apical meristem, protoderm, ground meristem, and procambium Zone of cellular elongation: made up of cells that are recently derived from the primary meristematic tissues and increase in length `most responsible for the growth of roots through soil Zone of Cellular Maturation: older cells complete their differentiation into dermal, vascular, or ground tissue o Most important for water and nutrient absorption Root Hairs: increase surface area of the dermal tissue Root system o structural support o conducts water and ions to the shoot o stores products of photosynthesis o anchors the plant to the soil How is the Primary Shoot System Organized? Pith: ground tissue that is inside vascular bundles Cortex: ground tissue that is outside the vascular bundles Start of 37.3 Cells and Tissue of the Primary Plant Body Features absent in animals cells o Cell wall supports cell and defines shape o Plasmodesmata cytoplasm of adjacent plant cells are connected by this o Chloroplasts o Vacuole contains cell sap stores wastes and can digest them store water and nutrients o Plant cells don’t change position once they form The Dermal Tissue System interface between organism and environment protects plant body o water loss o diseasecausing agents o herbivores Epidermal Cells Protect the Surface Secrete cuticle: a waxy layer that forms a continuous sheet over the surface o Reduces the amount of water lost o forms a barrier to protect the plant from viruses, bacteria, spores, or growing hyphae or parasitic fungi o Defense against pathogens Waxes in the cuticle can also be detrimental o reduces gas exchange o solved by stomata Stomata Regulate Gas Exchange and Water Loss Stomata: o allow carbon dioxide to enter photosynthetically active tissues o consists of two guard cells change shape and open/close the pore Trichomes Perform an Array of Functions Trichomes o hairlike appendages made up of specialized epidermal cells o Keep the leaf surface cool by reflecting sunlight o reduce water loss by forming a dense mat that limits transpiration o provide barbs, or store toxic compounds that thwart herbivores o trap and digest insects The Ground Tissue System Most photosynthesis and carbohydrate storage occurs here Responsible for most of the synthesis and storage of specialized products o colorful pigments o hormones o toxins required for defense Producing and storing valuable molecules Made up of three tissue types o Parenchyma o Collenchyma o Sclerenchyma Parenchyma Are “Workhorse” Cells Relatively thin cell walls Most abundant and versatile Cells filled with chloroplasts Primary site of photosynthesis In other organs, cells store starch granules Mant cells are totipotent: retain the capacity to divide and develop into a complete, mature plant o important for healing wounds o reproducing asexually via stolons and rhizomes o Callus: a mass of undifferentiated cells Collenchyma Cells Function Primarily in Shoot Support Cells walls are thicker in some areas Overall the cells are longer and thinner than parenchyma Supports plant body Often found just under the epidermis of stems, especially outside vascular bundles Ability to stretch allows the stems to flex in the wind without breaking Sclerenchyma: Two Types of Specialized Support Cells These cells produce a thick secondary cell wall in addition to the primary cell wall Secondary cell wall o contains the tough, rigid compound lignin in addition to cellulose Can support actively growing parts of the plant o have an expandable primary cell wall o Nonexpandable secondary cell wall supporting stems and other structures where growing has ceased Cells usually dead at maturity, contain no cytoplasm o THINK OF THIS AS A SKELETON Ground Tissue typically contains 2 types of sclerenchyma cells o Fibers o Sclereids Fibers: o extremely elongated o in paper, fabrics Sclereids o relatively short o variable shapes o often function as protection o make up the tough coats of seeds The Vascular Tissue System Functions in support and in longdistance transport of water and dissolved nutrients Moves the products of photosynthesis that are made and stored in ground tissue Simple tissues: plant tissues that consist of a single cell type Complex Tissues: tissues that contain several types of cells Vascular system is made up of two tissues o Xylem o Phloem Xylem: conducts water and dissolved ions in one direction: from root to the shoot Phloem conducts sugar, amino acids, chemical signals, and other substances in two directions: root to shoot and shoot to root Xylem Structure Cell types o Tracheids o Vessel Elements Tracheids: waterconducting cells o long, slender cells o tapered ends o sides and ends have pits gaps in the secondary cell wall where only the primary cell wall is present water moves both vertically and horizontally when moving up the plant where resistance to flow is lowest Vessel Elements: o Water conducting cells o shorter and wider o have pits and perforations openings that lack both primary and secondary cell walls o the ends of vessel elements lack any cell wall o stacked cells form open pipes called vessel o Vessel elements conduct water more efficiently because of their width and perforations offer less resistance to flow Both are dead at maturity Both have thick, lignin containing secondary cell walls No membranes Filled with the fluids that they conduct In angiosperms: both found adjacent to each other in the plant Phloem Structure Phloem is made up of two specialized parenchyma cells o sieve tube elements o companion cells Both alive at maturity lack lignin secondary cell walls arise from the division of a common precursor cell Sieve Tube Elements: o long, thin cells o have perforated ends: sieve plates responsible for transporting sugars and other nutrients o lack nuclei and most other organelles o Companion Cells o not conducting cells o provide materials to maintain the cytoplasm and plasma membrane of sievetube elements o Have most organelles o support function of sieve tubes o involved in loading and unloading carbohydrates and other nutrients into and out of sievetube elements Both are directly connected to adjacent companion cells Pages 465472 4 Processes that can shift allele frequencies in a population over time o Natural Selection: increases frequencies of certain alleles, leads to adaptation o Genetic Drift: causes allele frequencies to change randomly may cause alleles that decrease fitness to increase in frequency o Gene Flow: occurs when individuals leave a population, join another, nd breed o Mutation: modifies allele frequencies by continually introducing new alleles, alleles created by mutation can either be advantageous or detrimental HardyWeinberg Principle: mathematical null hypothesis for the study of evolutionary processes 26.1 Analyzing Change in Allele Frequencies: The HardyWeinberg Principle Wanted to know what happened in an entire population when all of the individuals (all possible genotypes) bred The Gene Pool Concept Gene Pool: all of the alleles from the gamete produced in each generation Calculations predict the genotypes of the offspring that would be produced, and the frequencies of each genotype Principle makes two claims o Frequencies of p and q can be given as p^2 + 2pq + q^2 =1 allele frequencies = p + q = 1 o When alleles are transmitted via meiosis and random combinations of gamete, their frequencies do not change over time for evolution to occur, some other factor(s) must come into play The HardyWeinberg Model Makes Important Assumptions Five assumptions must be met o Random Mating o No Natural Selection o No genetic drift (random allele frequency change) o No gene flow o No mutation How Does the HardyWeiberg Principle Serve as a Null Hypothesis? Null Hypothesis: predicts there are no difference among the treatment of the groups in the experiment Predicts what genotype frequencies will occur when mating is random with the respect to that gene CASE STUDIES IN BOOK (page 468) Review Worksheet 26.2 Nonrandom Mating Inbreeding: the mating between relatives Mating isn’t always nonrandom, organisms may have a higher rate in possibility to mate due to location, religion, and more How Does Inbreeding Affect Allele Frequencies and Genotype Frequencies? Selffertilization is the most extreme form of inbreeding Homozygous parents that self fertilize produce all homozygous offspring Heterozygous parents produce both homo and heterozygous offspring in a 1:2:1 ratio Two fundamental points about inbreeding o Inbreeding increases homozygosity o Inbreeding itself doesn’t cause evolution, because allele frequencies do no change in the population as a whole Nonrandom mating changes only genotype frequencies, not allele frequencies o not an evolutionary process itself How Does Inbreeding Influence Evolution? Can speed up the rate of evolutionary change Increases the rate at which natural selection eliminates recessive deleterious alleles (alleles that lower fitness) from the population Inbreeding depression: the decline in average fitness that take place when homozygosity increases and heterozygosity decreases in population o Results from 2 causes Many recessive alleles represent lossoffunction mutations Many genes especially those involved with fighting disease are under intense selection for heterozygote advantage, a selection process that favors genetic diversity Pages 444454 25.125.3 The Evolution of Evolutionary Thought A scientific revolution: overturns of an existing idea about how nature works and replaces it with another, radically different idea Plato and Typological Thinking Typological thinking: based on the idea that species are unchanging types and variations within a species are unimportant or even misleading Aristotle and the Great Chain of Being Also called teh scale of nature Species were organized intp a sequence based on increasing size and complexity, with humans at the top Claimed characteristics of species were fixed Lamarck and the Idea of Evolution as Change through Time Initially based on the great chain of being Evolution was progressive in the sense of always producing larger and more complex, or “better” species Contended that species change through time via the inheritance of acquired characteristics Idea here that an individual develops in response to challenges posed by the environment o Giraffes getting longer necks because the previous generation stretched to reach higher leaves Darwin and Wallace and Evolution by Natural Selection Evolution occurs because traits vary among individuals in a population, and because individuals with certain traits leave more offspring than others do Variation among individuals in a population was the key to understanding the nature of species o Population thinking 25.2 The Pattern of Evolution Have Species CHanged, and Are They Related? Described evolution as descent with modification o species that lived in the past are the ancestors of the species existing today and the species change through time Evidence for Change Through Time Extant species (those living today) support the claim that they are modified forms of ancestral species due to fossil record The Vastness of Geologic Time Researchers used sedimentary rocks to base the fossil’s relative position in time As they collected and compared, they created a geologic time scale o a sequence of names intervals called eons, era, and periods that represented the major events in earth history o realized it takes a long time for the rock layers to form Discovery of radioactive decay allowed to pinpoint exact ages Extinction Changes the Species Present Over Time Darwin interpreted extinct forms as evidence that species are not static, immutable entities, unchanged since the moment of special creation If species have gone extinct, then the array of species living on Earth has changed through time Transitional Features Link Older and Younger Species Law of Succession o extinct species in the fossil record were succeeded, in the same region, by similar species Transitional Feature: a trait in a fossil species that is intermediate between those of ancestral and derived species Vestigial Traits Are Evidence of Change Through Time Vestigial Trait: a reduced or incompletely developed structure that has no function, or reduced function, but is clearly similar to functioning organs or structures in closely related species Evidence that characteristics change over time Current Examples of Change Through Time Can be measured directly Species are dynamic not static, unchanging, and fixed types Evidence of Descent from a Common Ancestor Data from the fossil record and contemporary species refute the hypothesis that species are immutable Similar Species Are Found in the Same Geographic Area Some species descend from one common ancestor, but colonize separately through time and became a new species Similar Species Share Homologies Homology: a similarity that exists in species because they inherited the trait from a common ancestor Homology can be studied in 3 levels o Genetic homology occurs in DNA, RNA, and amino acid sequences o Developmental Homology recognized in embryos o Structural Homology similarity in adult morphology or form 3 levels interact Genetic homologies cause the developmental homologies observed in embryos, which then lead to the structural homologies recognized in adults Most fundamental of all homologies is the genetic code Homology is a key component in contemporary biology Current Examples of Descent from a Common Ancestor Speciation: a process that results in one species splitting into two or more descendant species Supports the claims that all organisms are related by descent from a common ancestor Evolution’s “Internal Consistency” The Importance of Independent Data Sets Data supports the idea that species have descended, with modification, from a common ancestor Internal Consistency: observation that data from independent sources agree in supporting predictions made by a theory o Examples: whales and dolphins are called cetaceans SUMMARY TABLE ON PAGE 452 Many independent line of evidence coverage on the same conclusion: Whales gradually evolved from a terrestrial ancestor 50 million years ago No single observation of experiment instantly “proved” this, but the accumulation over all data found Darwin’s Inspiration Pigeon breeding Artificial Selection: choose certain individuals with desirable traits to reproduce, thus manipulating the composition of the population Since many more individuals are born than can survive, a “struggle for existence” occurs are organisms compete for food and places to live Darwin’s Four Postulates Process of evolution by natural selection in 4 postulates o Individual organisms that make up a population vary in the traits they possess, such as size and shape o Some of the trait differences are heritable o In each generation, many more offspring are produced that can survive, only some individuals survive long enough to reproduce, and among those individuals, some will produce more that others o Subset of individuals that survive best and produce the most offspring is not a random sample of the population natural selection occurs when individuals with certain characteristics produce more offspring than do individuals without those characteristics Individuals are selected naturally = by the environment Because the selected traits are passed on to offspring, the frequency of the selected traits increases from one generation to the next Natural selection is the change in allele frequencies in a population over time Variation among individuals in a population is essential if evolution is to occur Evolution by natural selection occurs when heritable variation leads to differential reproductive success The Biological Definitions of Fitness, Adaptation, and Selection Fitness: the ability of an individual to produce surviving, fertile offspring relative to that ability in other individuals in the population o MEasurable quantity o Counting the number of surviving offspring each individual produces and comparing the data o Compact way of formally defining adaptation Adaptation: a heritable trait that increases the fitness of an individual in a particular environment relative to individuals lacking the trait o Increase fitness Artificial Selection: breeders choose which characteristics they want to keep or get rid of in their species o Differential reproduction as a result of heritable variation Pages 762766 Cohesion is the molecular attraction among like molecules o H atoms in water Because water molecules cohere, the upward pull by adhesion is transmitted to the rest of the water column Meniscus: effects of adhesion, cohesion, and gravity to form a concave surface Surface tension: force that exists among water molecules o Surface molecules share stronger attractive forces o Enhanced attraction results in tension that minimizes the total SA Capillary action: adhesion, cohesion, and surface tension counteract gravity and result in capillarity o Can only carry water a limited distance The CohesionTension Theory Hypothesis for longdistance water movement in vascular plants States that the water is pulled to the tops of trees along a waterpotential gradient vis forces generated by transpiration at leaf surfaces The Role of Surface Tension in Water Transport Key concept in the theory: negative force or pull (tension) generated at the airwater interface is transmitted through the water outside of leaf cells to the water is xylem to the water in the vascular tissue of the roots and then to the soil This is possible because o Continuous column of water throughout the plant o All the water molecules present hydrogen bonds to on another (cohesion) o Doesn’t expel energy*** Driven by the sun Creating a Water Potential Gradient Because tracheids and vessels are dead at maturity: water in xylem doesn’t cross a plasma membrane Resulting in water not moving between cells by osmosis In xylem water is driven entirely by differences in pressure potential o Moves by bulk flow: a mass of movement of molecules along a pressure gradient Menisci allow the plant to overcome the force of gravity since it is happening all around the plant, pulls waters up long distances The Importance of Secondary Cell Walls The secondary thickenings characteristic of the cell walls in tracheids and vessel elements o Reinforced with lignin molecules Allowed vascular tissue to withstand extreme negative pressures o Resulted in tall trees What Evidence Do Biologists Have for the CohesionTension Theory? Xylem pressure changed as the researchers changed light levels Light intensity increased → xylem pressure probe documented increased tension, or pull = negative pressure Higher light levels reduced the weight on the overall plant o Suggested higher transpiration rates caused water loss Water Absorption and Water Loss (38.3) To absorb water, the roots need to expend to accumulate the ions that maintains a solute potential is lower than the soil Once water with dissolved nutrients is in the root xylem, the sun furnishes the energy required to pull the solution up o Energy from sun heats water molecules at the airwater interface inside leaves enough the break the hydrogen bonds and cause transpiration o Creates deep minisci in the walls of the leaf, causing tension that lowers the water potential of the leaf o Hydrogen bonding between water molecules transmits this tension down to the water molecules in the roots Xylem allows water to move from a region of high water potential (roots) to a region of low water potential (the leaves) When the roots dry o Becomes harder for the plant to replenish the lost water o Closes stomata o Which inhibits the plant’s ability to carry out photosynthesis Photosynthesistranspiration compromise: balance between conserving water and maximizing photosynthesis o Particularly delicate for species that grow on dry sites Limiting Water Loss Special features for plants that live in dry environments to limit water loss o Thick cuticle on the top of leaf in direct sunlight o Stomata are located on underside of leaf o Trichomes shield pit of stomata limiting water loss by creating a layer of still air o Cacti: thorn like leaves to reduce SA to reduce transpiration Obtaining Carbon Dioxide Under Water Stress Crassulacean Acid Metabolism (CAM) C4 Photosynthesis Both allow plants to increase carbon dioxide concentration in their leaves and conserve water CAM plants o Open their stomata at night o Store the carbon dioxide that diffuses into their tissues by adding the carbon dioxide molecules to organic acids o When sunlight is available, carbon dioxide molecules are released from the acids and converted to sugars by rubisco Enzyme found in all green plants that initiates the calvin cycle o Plants can grow and photosynthesis even when stomata are closed during the day C4 plants o Minimize the extent to which their stomata are open o Use CO2 so efficiently o Mesophyll take up CO2 and add it to organic acids o Co2 then transferred to specialized cells: bundlesheath cells Where the calvin cycle operates o Concentrating carbon dioxide in cells deep inside the leaf so stomata do not have to be wide open continuously Both have adaptations that help them conserve water by limiting transpiration Pages 781788 What Factors Affect Nutrient Availability? Elements required for plant growth are found in the soil as ions Ome exist as elemental ions, while others are molecular ions Anions and Cations Behave Differently Anion negative charge o Usually dissolve in soil o Interact with water molecules via hydrogen bonding o Phosphate ions exception insoluble complexes with positively charged cations o Exist as solutes Readily available to plants for absorption Easily washed out by rain Leaching: the loss of nutrients via the movement of water through soil Cation positive charge o Dissolved in solid water o Not immediately available o In solutions, interact with negative charges found in two types of soil particles Organic matter that is rich in negatively charged organic acids The surfaces of clay which are rich in mineral anions o Organic soils that contain clay tend to retain nutrients Because few positively charged cations leach away Because these soils hold water (and this anions) better than sandy soil o Presence of clay makes it harder for plants to extract cations and use them The Role of Soil pH Concentration of hydrogen ions in a solution Acidic soils found in regions: conifer forests o Where the decomposition or organic matter produces carbonic acid, phosphoric acid, or nitric acid Alkaline soils are common in regions: where limestone is abundant o Limestone interacts with water, the calcium ions that are released take the place of protons that cling to soil particles o Protons then react with CO3 2 to form bicarbonate ions Lowers the hydrogen ion concentration of the soul and raises its pH Most plants thrive in relatively neutral pH soils Cation Exchange Soil pH affects the availability of plant nutrients o Presence of protons in soil water can release of cations that are bound to soil particles Cation exchange Occurs when protons or other soluble cations bind to negative charges on soil particles and cause bound cations to be released from the soil Nutrients then become available for uptake by nearby plant roots Plants influence this process because roots cells release CO2 and it reacts with water to form carbonic acid, which releases protons If soil is too acidic, rain may leach cations away before the roots can take up the nutrients Deforestation or agriculture has resulted in acidic, nutrientpoor soils that are not productive Most productive oils are a mixture of sand, clay, and organic matter Nutrients are found at extremely low concentrations in soil High concentrations in plant cells Nutrient Uptake Root system is typically the site of nutrient uptake Most nutrient uptake occurs just above the growing root tip : zone of maturation o Have extensions: root hairs Root hairs o Increase SA of root o Cause a “zone of nutrient depletion” in the soil immediately surrounding them o Why continued root growth is vital Mechanisms of Nutrient Uptake Membrane proteins allow specific ions to cross the membrane BEcause root hairs have such a large SA, the contain a large number of membrane proteins that bring nutrients into the cytosol of root cells Proteins often work with a proton pump Establishing a Proton Gradient Plants harvest diffused nutrients and concentrate them in their tissues Proton pumps leads to a strong excess of protons on the exterior of the plasma membrane relative to the interior In the case of root cells o Differential results in a strong pH gradient favoring the movement of protons back into the cell o Outside of membrane becomes positively charged relative to the outside o “Voltage” across membrane Voltage is a form of potential energy o The charges that are separated by the membrane creates a membrane potential Difference in electrical charge across a cell membrane Using a Proton Gradient to Import Cations Electrical gradient established by proton pumps, which favors the entry of positive ions, is strong enough to overcome the pH gradient, which opposes the entry of these cations Potassium o Required as a cofactor of over 40 enzymes o Key role in bringing water into cells via osmosis o Maintaining normal turgor pressure Using A Proton Gradient To Import Anions Anions enter through a membrane transport proteins: cotransporters o Transports two solutes at once Electrochemical gradient set up by proton pumps makes it possible?
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