BIOLOGICAL DIVERSITY CHAPTER 30 GREEN PLANTS text ISBN 978 0 07 353222 6 pg 588 613 30 1 Defining Plants o green algae and land plants shared a common ancestor o plants are autotrophic o fungi were important to the colonization of land by plants increased plants nutrient uptake from the ground Land plants evolved from freshwater algae o hard life conditions on land o green algae had two major clades chlorophytes charophytes o unlike charophytes land plants have multicellular haploid and diploid stages diploid embryos over time trend has been for embryo protection and smaller haploid stage in the life cycle Land plants have adapted to terrestrial life o cuticle waxy covering secreted to the exposed surfaces to keep water inside of the plant limits gas exchange required for respiration and photosynthesis tiny mouth shaped openings responsible for gas diffusion into and out of the o stomata plant o tracheids specialized cells that organize the transport of water and minerals land plants can either have them or not have them tracheophytes have specialized cells xylem phloem xylem and phloem have strands of tissue in the stems roots and leaves water transport food transport o all land plants have haploid and diploid generations evolutionary shift between towards a dominant diploid generation allows for increased genetic variability in land plants o land plants have haplodiplontc life cycles undergo mitosis after both gamete fusion and meiosis results in multicellular haploid individual and a multicellular diploid individual The haplodiplontic cycle produces alternation of generations o land plants produce gametes by mitosis in a multicellular haploid individual diploid generation sporophyte alternates with the haploid generation gametophyte o diploid sporophyte produces haploid spores by meiosis meiosis takes place in the sporangia where diploid spore mother cells sporocytes undergo meiosis each produces four haploid spores spores are the first cells of the gametophyte generation o spores divide by mitosis and produce a multicellular haploid gametophyte source of the gametes when gametes fuse they create a zygote that is diploid and the first cell of the next sporophyte generation zygote grows into a diploid sporophyte by mitosis and produces sporangia meiosis ultimately occurs The relative size of haploid and diploid generations vary o haploid generation consumes a larger portion of the life cycle in mosses and ferns than it does in gymnosperms and angiosperms 30 2 Chlorophytes and Charophytes Green Algae Charophytes are the closest relatives to land plants clade of streptophytes also some green algae o charophytes closely related to land plants haplontic life cycles evolution of a diplontic embryo and haplodiplontic life cycle occurred after the move onto land 30 3 Bryophytes Dominant Gametophyte Generation o bryophytes are the closest living descendants of the first land plants lack tracheid specialized transport cells mycorrhizal associations nontracheophytes tight symbiotic relationship between plants and fungi Bryophytes are unspecialized but successful in many environments enhanced water uptake o most bryophytes are small o have conducting cells instead of tracheids for water and nutrients o liverworts mosses and hornworts o gametophytes are photosynthetic and more conspicuous than sporophytes o require water to reproduce sexually o usually found in moist places Liverworts are an ancient phylum o contain air chambers with upright branching rows of photosynthetic cells each with a pore at the top to facilitate gas exchange unlike a stoma cannot close o reproduction similar to mosses asexual reproduction occurs when lens shaped pieces of tissue that are released from the gametophyte grow to form new gametophytes Mosses have rhizoids and water conducting tissue o gametophyte consists of small and leaf like structures o anchored into the ground by rhizoids consists of cells that absorb water but not nearly the amount of water taken in by a root rhizoid is not a root o moss leaf like structures have little in common with leaves of vascular plants Hornworts developed stomata lack vascular strands and stomata all cells are haploid o among the earliest land plants but the earliest fossil spores date from Cretaceous period when angiosperms were emerging o hornwort sporophytes resemble tiny green broom handles rise from even smaller gametophytes less than 2 cm o sporophyte has stomata for gas exchange is photosynthetic and usually has a single large chloroplast 30 4 Tracheophyte Plants Roots Stems and Leaves o Cooksonia is the first known vascular plant appeared 420 mya Vascular tissue allows for distribution of nutrients o vascular tissues efficient water and food conducting systems consist of strands of cylindrical or elongated cells that form a network throughout a plant extends from near the tips of the roots through the stems and to the leaves two types of vascular tissue xylem phloem conducts water and dissolved minerals up from the roots conducts sucrose and hormones throughout the plant vascular tissues increases the height and size of tracheophytes develops in the sporophyte not gametophyte o cuticle and stomata are also characteristics of tracheophytes Tracheophytes include seven extant phyla grouped into three clades o three clades of vascular plants exist today lycophytes club mosses pterophytes ferns seed plants Stems evolved prior to roots o fossils of early vascular plants show stems but no roots or leaves stunted the growth of plants Roots provide structural support and transport capability o true roots are only found in the tracheophytes o roots have a dual function transport support o roots have evolved at least two separate times Leaves evolved more than once o leaves increase surface area of the sporophyte enhances photosynthesis Seeds are another innovation in some phyla predators o most seeds provide food for the growing plant o lycophytes and pterophytes do not have seeds o highly resistant structures well suited to protecting a plant embryo from drought and from 30 5 Lycophytes Dominant Sporophyte Generation and Vascular Tissue earliest vascular plants lacked seeds lycophytes are the sister group to all vascular plants sporophyte stage is dominant stage o sporophytes have leafy stems that are seldom more than 30 cm long 30 6 Pterophytes Ferns and Their Relatives Whisk ferns lost their roots and leaves secondarily o sporophytic generation consists of evenly
View Full Document
Unlocking...