BIO 9 Plants - 2009 BIO153: Lecture 9 Plants (I) February...

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1 2009 BIO153: Lecture 9 Plants (I) February 9, 2009 Plants are a clade composed of the green algae or Chlorophyta (which are classified in cotemporary taxonomies as protists) and the land plants. Our current thinking is that green algae themselves are a grade (the Charales are the sister taxon of the land plants); the land plants (the non-vascular plants; the seedless vascular plants; the gymnosperms and angiosperms) are a clade , and the land plants + the green algae are a clade. Green algae vary a great deal in their structure (some are unicellular; some colonial, some multicellular etc.), but in many ways they are similar to land plants: they have: chloroplasts with double membranes chlorophyll a & b cellulose in the cell wall The first fossils of green algae are from ~700 million years ago, and a corresponding rise in O 2 levels is observed in the geological record. (My favourite green alga: Chlamydomonas nivalis , which causes watermelon snow!)
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2 Green algae are ecologically important today because of their contribution to global photosynthesis. Also: green algae in symbiosis with fungi form lichen some live as endosymbionts in protists Charales (stoneworts) are green algae that are the sister taxon of the land plants features of growth & reproduction more complex than most green algae multicellular individuals are haploid, but gametes can fuse and form a diploid zygote diploid zygote undergoes immediate meiosis to restore haploidy; divides to form a haploid gametophyte (TYPE I life cycle; see below). Land Plants: 1 st truly terrestrial organisms (land plants originated about 470 million years ago) are a clade (suggests that the transition to land happened once) form the foundation of terrestrial food webs (major terrestrial autotroph) allowed for the terrestrial invasion (i.e. colonization of land) by fungi and animals Features of land plants in general, all are autotrophs (with a few exceptions -- a few species have developed a purely parasitic lifestyle and no longer make their own food) they exhibit an enormous range of size :~ 1mm ~100m most are sessile (a few aquatic plants such as Lemma (duckweed) are planktonic - float or drift in water) Plants may be extremely long-lived: some individuals of the creosote bush ( Larrea spp.) may be greater than 14,000 years old (longer than recorded human history)!
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3 The story of land plants is the story of adaptation to life out of water What are the benefits of life on land? unimpeded access to CO 2 , sunlight compared to living in the water: no absorption of light by the medium; no reflection at surface; no turbidity thus, much higher rates of photosynthesis are possible! However, there are
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This note was uploaded on 04/25/2010 for the course BIOLOGY BIO153 taught by Professor Cordon during the Fall '10 term at University of Toronto.

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BIO 9 Plants - 2009 BIO153: Lecture 9 Plants (I) February...

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