Bio102 Unit 2 Study Guide
Bio102 Unit 2 Study Guide Bio 102
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This 14 page Study Guide was uploaded by Amanda Merritt on Monday February 22, 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 52 views. For similar materials see Principles Biology II in Biology at University of Rhode Island.
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Date Created: 02/22/16
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
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