Life 103, week 4 notes
Life 103, week 4 notes Life 103
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This 6 page Class Notes was uploaded by Addy Carroll on Friday February 12, 2016. The Class Notes belongs to Life 103 at Colorado State University taught by Dr. Dale Lockwood and Dr. Tanya Dewey in Winter 2016. Since its upload, it has received 40 views. For similar materials see Biology of organisms-animals and plants in Biology at Colorado State University.
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Date Created: 02/12/16
Life 103 Notes *adapted from the lecture slides of Dr. Dale Lockwood* Land Plants: Mosses and Worts • Storming the beaches -In charophytes, a layer of a durable polymer called sporopollenin prevents exposed zygotes from dying out -The movement onto land by charophytes ancestors provided unfiltered sun, more plentiful CO2, nutrient-rich soil, and few herbivores or pathogens -Land presented challenges: a scarcity of water and lack of structural support • Four key traits appear in nearly all land plants but are absent in the charophytes -Alternation of generations (with multicellular, dependent embryos) -Walled spores produced in sporangia -Multicellular gametangia -Apical meristems ~Linear growth from root and shoot tips • Other traits that many land plants have include -Cuticle ~Provides protection and controls moisture loss -Secondary compounds ~Defense against herbivory and UV protection • Nonvascular plants -Bryophytes -Liverworts, phylum Hepatophytes -Hornworts, phylum Authocerophytes -Mosses, phylum Bryophytes • Vascular Plants -Seeded -Non seeded • Important points about Alternation of Generations (see textbook figure 29.3) -The gametophyte is haploid and produces haploid gametes by mitosis -Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis -The diploid embryo is pertained within the tissue of the female gametophyte -Nutrients are transferred from parent to embryo through placental transfer cells -Land plants are called embryophytes because of the dependency of the embryo on the parent • Multicellular Gametangia -Gametes are produced within organs called gametangia -Female gametangia, called archegonia, produce eggs and are the site of fertilization -Male gametangia, called antheridia, are the site of sperm production and release • Bryophyte sporophytes grow out of archegonia and are the smallest and simplest sporophytes of all extant plant groups • A sporophyte consists of a foot, a seta (stalk), and a sporangium, also called a capsule, which discharges spores through a peristome • Hornwort and moss sporophytes have stomata for gas exchange • Stomata are openings in the surface of the plant controlled by two cells -Control CO 2ain and H O2loss -All plants but liverworts have them • Hornworts -Likely as old as liverworts and mosses -About 100 known species • Ecology of mosses (see textbook figure 29.6 for life cycle) -Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat -Sphagnum is an important global reservoir of organic carbon -Peat bogs make up an estimated 70 years of industrial carbon ~Peat bogs are releasing carbon at an increasing rate -Peat is rich in carbon -Beginning source of coal deposits -More than 20% of homes in Ireland use peat bricks to heat the house -Peat is composed of many plants, but sphagnum moss is common in peat bogs • Tollund Man -People cutting peat in Denmark in 1950 thought they had discovered a recent murder victim - C dating showed that the man died in about 400 BCE -The acidity and anaerobic environment of the bog preserved the corpse ~Bones are dissolved but flesh remains -Evidence s that he was hung ~Evidence at burial indicates possibly a ritual sacrifice Ferns and Horsetails • Comparing the taxa -Bryophytes ~Height limited by lack of vascular tissues ~Flagellated sperm usually in moist environments ~Gametophytes are the dominant generation -Seedless Land Plants ~Vascular tissues allow for larger, taller plants ~Flagellated sperm and are usually restricted to moist environments ~Sporophytes are the dominant generation • Fern gametophytes -Hermaphroditic -A few millimeters in size • What it means to be vascular -Vascular tissue facilitates the transport of fluids (and hence nutrients) through the plant -Xylem conducts most of the water and minerals and includes dead cells called tracheids -Phloem consists of living cells and distributes sugars, amino acids, and other organic products -Water conducting cells are strengthened by lignin and provide structural support • Plant Parts -Roots are organs that anchor vascular plants ~They enable vascular plants to absorb water and nutrients from the soil -Leaves are organs that increase surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis ~Microphylls are leaves with a single vein ~Megaphylls are leaves with a highly branched vascular system *See textbook figure 29.12 • Roots -Not all underground structures are roots -True Roots ~Tap roots are large vertically growing roots Ex.) Carrots, radish, parsnips ~Tuberous roots are modified lateral roots for storage Ex.) Sweet potatoes, yams -Modified stems ~Corm ~Rhizomes ~Tuber -Bulbs • Sporophylls and Spore Variations -Sporophylls are modified leaves with sporangia -Sori are clusters of sporangia on the undersides of sporophylls -Strobili are cone-like structures formed from groups of sporophylls • Spores -Most seedless vascular plants are homosporous, producing one type of spore that develops into a bisexual (hermaphroditic) gametophyte -All seed plants and some seedless vascular plants are heterosporous -Heterosporous species produce megaspores that give rise to female gametophytes, and microspores that give rise to male gametophytes • Seedless Vascular Plants -Phylum lycophyta includes club mosses, spike mosses, and quill worts -Phylum Monilophyta includes ferns, horsetails, and whisk ferns and their relatives ~The previous name for the clade was Pterophyta • Ferns (see textbook figure 29.11 for life cycle) -Second largest plant phylum after the angiosperms -12,000 species -Relatively little economic impact ~Invasive species ~Limited food source ~Horticulture ~Toxic waste removal • Horsetails -Found on all continents except Asia and Australia -30 species in one genus today -Very diverse in the carboniferous forest ~30 meter high trees -Very limited economic importance Gymnosperms • Gymnosperm -Means “naked seed” • Seeds -A seed consists of an embryo and nutrients surrounded by a protective coat -Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems ~In other words, land plants no longer had to live close to the water in order to reproduce -Foundational for modern ecosystems -One important key to civilization • Seed Plants -In addition to having seeds, the following are common to all seed plants ~Reduced gametophytes ~Heterospory (see heterospory section below) ~Ovules (female gametophyte) ~Pollen (male gametophyte) -The gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte • Heterospory -The ancestors of seed plants were likely homosporous (homo=same), while seed plants are heterosporous (hetero=different) -Megasporangia produce megaspores that give rise to female gametophytes -Microsporangia produce microspores that give rise to male gametophytes • Ovules and Production of Eggs -An ovule consists of a megasporangium, megaspore, and one or more protective integuments (outside coating that is made up of sporophyte tissue) -Gymnosperm megaspores have one integument -Angiosperm megaspores usually have two integuments • Gymnosperm Female Anatomy -Megasporangium: diploid tissue where haploid microspores are formed (meiosis) -Megaspore: haploid cell that grows into the female gametophyte, including the egg nucleus • Gymnosperm Male Anatomy -Microsporangium: diploid tissue where haploid microspores are formed (meiosis) -Microspores: develop into male gametophyte -Pollen: contains the male gametophyte within the tough pollen wall ~Pollen grains have few cells, so they need protection from the environment by the pollen wall • Gymnosperm Fertilization (see textbook figure 30.3a) -The pollen is released into the air and it spreads for miles -The pollen grain reaches ovule and germinates -The pollen tube grows from the pollen grains and begins digesting through the Megasporangium -After digging its way through the megasporangium, the pollen tube reaches the egg nucleus, discharges sperm nucleus into the egg nucleus of female gametophyte • Pollen and Production of Sperm (see textbook figure 30.3b) -Microspores develop into pollen grains, which contain the male gametophytes -Pollination is the transfer of pollen to the part of a seed plant containing the ovules -Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals -If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule • The Evolutionary Advantage of Seeds (30.3c) -A seed develops from the whole ovule -A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat -Seeds provide some evolutionary advantages over spores ~They may remain dormant for days to years, until conditions are favorable for germination ~They may be transported long distances by wind or animals • The gymnosperms have “naked” seeds not enclosed by ovaries (fleshy fruit) and consist of four phyla: -Cycadophyta (cycads) -Gingkophyta (one living species: Ginkgo biloba) -Gnetophyta (three genera: Gnetum, Ephedra, Welwischia) -Coniferophyta (conifers, such as pine, fir, and redwood) • Phylum Cycadophyta -Individuals have large cones and palmlike leaves -These thrived during the Mesozoic, but relatively few species exist today -About 300 species alive today -Rare plant collectors are willing to steal these plants • Phylum Ginkgophyta -This phylum consists of a single living species, Ginkgo biloba -It has a high tolerance to air pollution and is a popular ornamental tree -Leaves remain little changed for 270 million years -Ginko biloba- Miracle cure? ~Used as culinary ingredient ~Many medicinal claims ~Recent large study -No benefit for memory ~In Alzheimer’s ~In Dementia
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