Biology 1060 Unit 3 Week 5 Notes
Biology 1060 Unit 3 Week 5 Notes Bio 1060
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This 6 page Class Notes was uploaded by Margaret Notetaker on Sunday April 10, 2016. The Class Notes belongs to Bio 1060 at Saint Louis University taught by Dr. Thole in Spring 2016. Since its upload, it has received 13 views. For similar materials see General Biology II in Biology at Saint Louis University.
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Date Created: 04/10/16
Margaret S General Biology (Bio 1060) Week 5 Lecture Notes Unit 3: Plants 4-‐4-‐16 What Adaptations Were Important for Life on Land? • Seeds, which allow for reproduction without water • Roots, which pull water from the s • Xylem (sclerenchyma cells) is a sort of “skeleton” for land plants so they can stay upright on lan o Bryophytes are tiny because they don’t have thi • Pollen is important for fertilization, and allows plants to use wind to their advantage • The wax cuticle is used to keep water in and to keep the inside of the plant wet; overall it conserves water Bryophytes: Liverworts, Mosses, Hornworts are a Paraphyletic Group • Algae have cell walls • Bryophytes are nonvascular • They use spores instead of seeds (similar to fungi) o Spores are always haploid and divide mitotically to make new organisms • Bryophytes are SMALL (water diffuses through their tissues) • Bryophytes don’t need soil for water uptake • Bryophytes do not have true leaves • Bryophytes form: fuzzy haploid gametophytes (which produce gametes) and sporophytes (diploid stalks that yield spores) o Sporophytes are bigger than gametophytes o Sporophytes stay attached to gametophytes o Gametophyte is dominant to the sporophyte, because the sporophyte cannot live on its own • Bryophytes are the result of the first step onto land • Gametophytes are much more visible • Sporophytes are fused gametes, and they divide mitotically to produce new organisms with gametophytes Moss Life Cycle: Haplodiplontic • Moss are dependent on water for dispersing sperm • this is the haplodiplontic life cycle • In mosses, only the sporophyte is diploid; the egg is retained while sperm are released in response to rain • Sporophyte contains tissue called sporangium, specifically where meiosis occurs Lycophytes and Ferns-‐Still Rely on Water For Fertilization (Don’t Use Seeds) • True vascular plants • Lycophytes, ferns, gymnosperms, angiosperms, and even bryophytes are all land plants, but bryophytes are not vascular • Rhinie cherts preserve fossils of early vascular plants (400 mya) • Rhynia plants: o Still no true roots o Stems have true vascular tissue in middle o Cuticle o Stomata (CO2 in, O2 out) o No true leaves yet o Sporangia for spores to be produced • Earliest lycophyte fossils: o Leaflike arrangements though not true leaves • Lycophytes: leaves and roots are seedless, vascular plants; they are the early land plants, with single veins, and they reproduce with spores o 1 living group called isoetes, which contain vascular cambium o In the Jurassic period, giant now-‐extinct lycophyte trees evolved seedlike structures • Ferns and horsetails are also seedless vascular plants o Ferns are leafy, they are found in the understory of the rainforest and are common houseplants • Fern life cycle: o The adult sporophyte is independent of the gametophyte o The only dominant sporophyte eventually becomes large and independent with the development of vascular tissues o Gametophytes are too small to be seen o The sporophyte and leaf are the only diploid structures in the life cycle o The egg is retained, and the sperm are released in moisture o Sporangia are on the underside of fern leaves, where meiosis occurs to produce spores • All plants up until now have needed water to reproduce 4-‐6-‐16 Seed Plants Finally Eliminate Water Dependency for Fertilization • Seed plants have vascular tissue, seeds, and pollen • Consist of angiosperms and gymnosperms • Seeds are embryos, and they also have a holding for food (for angiosperms, this is called the endosperm), as well as an outer seed coat (integument) • Gymnosperms have no endosperm, so they don’t undergo double fertilization • The presence of pollen in both types of seed plants eliminates the need for water o Pollen is a male gamete (sperm) that is dispersed by air Gymnosperms • Gymnosperms have “naked seeds” (their seeds are not contained within fruit) • 4 groups of gymnosperms are still alive • No flowers • Gymnosperms develop on a “scale” (piece of a cone) o The lower part of the tree is male cones o Upper part of the tree is female cones • Gymnosperm life cycle: sporophyte dominant • Sporangia: site of meiosis, produces both male/female gametophytes from spores o Pollen: male o Ovule: female • Gametophytic phase is completely reduced to pollen and egg • Fertilization occurs on the cone scale • 4 Types of Gymnosperms: o Cycads: look like palm trees but with cone structures (about 300 species) o Ginkgo: only 1 species, seeds form fleshy structure that looks like fruit but isn’t o Conifers: most diverse group, typical Evergreen trees, live in dry/cold places o Gnetophytes: very weird, look like angiosperms but aren’t Angiosperms • Angiosperms changed the planet about 140 mya • Specific to angiosperms: flowers, double fertilization, fruit from ripened ovaries of flowers • Angiosperms were so successful that they came to quickly outnumber everything else • Amborella, water lilies, star anise, and magnolids are very ancient angiosperms • Angiosperms can be split into two groups: monocots and eudicots • The most diversity in angiosperms is between monocots and eudicots Monocots • 1 embryonic seed leaf • No vascular cambium (never produce wood), scattered vascular bundles • Parallel venation (grass, wheat, rice, corn, and barley all have parallel veins) • Floral organs occur in multiples of 3 (3, 6, 9 petals, as well as actual flowers occur in triplets) Eudicots • Most diverse group of angiosperms • True dicots are eudicots, sisters to monocots, but amborella, water lilies, star anise, and magnolids are all dicots • Eudicots have 2 embryonic stem leaves • Vascular cambium (can have wood), vascular bundles are in rings • Net-‐like venation • Floral organs in multiples of 4 or 5 Life Cycle of Angiosperms • Different because it includes double fertilization and female gametophyte is enclosed in sporophyte tissue (which becomes fruit) • Dormancy of seeds is key to life cycle Plant Evolutionary Trends • As plants have evolved, sporophyte generation became dominant and gametophyte generation is reduced • Moving from water to land, starting with green algae o In the aquatic environment: the plant is completely submerged and desiccation is not an issue o Algae and mosses have a small and simple body with no need for specialized vascular system o Cell densities are similar to water densities o To move to land, plants needed to prevent water loss, transport H2O and nutrients, and to support the body • Prevention of water loss o Cuticle (waxy layer prevents diffusion to some degree) o Stomata (2 guard cells form pores in leaves) • Water transport and upright growth o Vascular system is made of elongated hollow cells joined together (xylem) o First group to develop vascular system is lycophytes (bryophytes do not have this) o Evolutionary sequence of water-‐conducting cells o Simple water conducting cells are in bryophytes, they have no lignin, and they are the beginning of the vascular tissue o First vascular systems: lycophytes have these, lignin is present, primary and secondary cell walls o Tracheids: narrow cells organized like pipes, solid secondary cell wall of lignin (lycophytes, ferns, gymnosperms) o Vessel elements: (gnetophores and angiosperms), wider, ends have gaps, lignin o Water-‐conducting cells are dead at maturity o The absence of cytoplasm increases the efficiency of water transport • How do plants reproduce in dry areas? o The oldest lineages (lycophytes, ferns) need water for fertilization (use swimming gametes) o Limits plant size to have limited access to water o Limits where/when plants can reproduce o Pollen is a major innovation for dry areas • There is an evolutionary shift from gametophyte dominated generations to sporophytic dominated generations • There is an evolutionary shift from sporophytic dependency on gametophyte to sporophytic independence 4-‐8-‐16: Test Day
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