Transition to Land & Life Cycles. Background. Plants from Algae 8/28/2011. What does it mean to be a plant? Lecture 1

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1 Transition to Land & Life Cycles What does it mean to be a plant? Lecture 1 Background Descendants of charophytan green algae Photosynthesis Modular growth (mitosis & apices) Sexual Reproduction in Eukaryotes Three basic life cycles Plants from Algae 1

2 Chlorophytes never made it to land Charophytes did Volvox -Colonial chlorophyte -Hollow sphere of a single layer of ,000 cells -A few cells are specialized for reproduction 2

3 Charophytes Charales (300 species) -Macroscopic -Plant-like plasmodesmata -Sister clade to land plants Choleocaetales (30 species) -Microscopic -Plant-like mitosis -Next closest plant relatives Charophytes (Cont.) Bryophytes Bryophytes are the closest living descendants of the first land plants. -Called nontracheophytes because they lack tracheids (specialized transport cells) Simple, but highly adapted to diverse terrestrial environments. 3

4 Photosynthesis Complete and balanced equation: 3CO 2 + 6H 2 O Light C 3 H 6 O 3 + 3O 2 + 3H 2 O Occurs in two stages: Light & Dark Reactions 4

5 Primary Photosynthetic Pigments Pigments absorb light Chlorophyll makes leaves green, absorbs light in the visible spectrum. Reflects green light Therefore appears green Primary Pigments Chlorophyll a All photosynthetic eukaryotes & cyanobacteria Chlorophyll b Plants, green algae, & euglenoid algae Accessory pigment (not directly involved in photosynthetic energy transduction) Broadens the range of light for photosynthesis Chlorophyll c Takes place of chlorophyll b in some algae 5

6 Chlorophyll a CHO Chlorophyll b Two other pigments Carotenoids (anti-oxidants protecting chlorophyll) Red, orange, or yellow lipid-soluble pigments Found in chloroplasts & cyanobacteria Hydrophobic Two groups Carotenes & Xanthophylls Carotenoids break down giving rise to.? 6

7 Phycobilins Found in cyanobacteria & chloroplasts of red algae Water soluble 7

8 Modular Growth Indeterminate growth Grow through entire life Add new body parts Repeated addition of same basic units Above ground Bud-stem-leaf units Below ground New lateral roots Primary Growth Plants increase in length by primary growth. Meristems Group of young, undifferentiated cells Give rise to new cells Apical meristem Increase in length Shoot apical meristem Root apical meristem Cell division results in two cell populations Remain undifferentiated meristematic cells Rapidly dividing new growth descendent cells 8

9 Eukaryotic Reproduction Life Cycles 2 Sexual Reproduction Alternation between meiosis & fertilization Meiosis = Reduction from 2n n. Fertilization = n + n = 2n Meiosis 9

10 Steps in meiosis Prophase I: Chromosomes come together, pairs coil, become shorter. Metaphase I: Move to metaphase plate. Anaphase I: Paired chromosomes move to opposite poles. Metaphase II: Chromosomes lined up at the equatorial plane. Anaphase II: Centromeres separate, move toward opposite poles of spindles. Telophase II: Completed migration. Four new haploid nuclei are formed. Meiosis differs from Mitosis in 3 ways. 1. Two nuclear divisions in meiosis. In both DNA only replicated once. 2. Nuclei produced in meiosis is haploid (1/2 the number of chromosome). 3. Meiosis results in different gene combinations. 10

11 Inheritance Allele Alternative form of a gene. Occupy same site on homologous chromosomes (locus). Gregor Mendel 11

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13 Plant Life Cycles Lecture III Three types 1. Gametic meiosis 2. Zygotic meiosis 3. Sporic meiosis Life Cycles Gametic life cycle Animal kingdom (some protists & algae) The gamete is the only haploid cell produced. 2n multicelled meiosis fertilization mitosis 1n 2n gamete zygote 2n multicelled 13

14 Zygotic life cycle Fungi Kingdom The zygote is the only diploid cell produced mitosis fertilization meiosis mitosis 1n 1n 2n 1n multicelled gamete zygote spore 1n 14

15 Allomyces arbusculus Rhizopus stolonifer, Zygomycete Ascomycetes 15

16 Basidiomycota Sporic life cycle Plant Kingdom Alternation of generations (plants, many algae) Gametophyte = haploid, gamete-producing generation. Sporophyte = diploid, spore-producing generation. 2n sporophyte meiosis mitosis mitosis fertilization 1n 1n 1n spore gametophyte gamete mitosis 2n zygote 16

17 Bryophytes Pterophytes Gymnosperms 17

18 Angiosperms 18