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BIOA01H3 (699)
Lecture 12


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Biological Sciences
Mary Olaveson

LECTURE TWELVE Plant life on the edge  Plants have adapted to a huge range of extreme habitats/environments/climates  Frost  Heat/drought  Perpetual inundation  Salty habitats  Toxic solids – heavy metals  Extreme nutrient limitation  Low light Perpetual inundation  An overabundance of fresh water can cause other things to become limiting for example carbon dioxide as carbon dioxide concentration decreases as well as oxygen. How to access these gases.  Limitations in a freshwater environment; [CO2] , and [O2]for photosynthesis is lower in water than in air  Light decreases as you go lower down in water  Nutrient levels are lower underwater, compared to in soil  In running water; the current can be very strong; plants need to adapt to this Types of aquatic plants  True hydrophytes ;submerged plants  Floating [inside the water] vs emergent leaves [in the open with a little water]  Free roots vs. no roots True hydrophytes [submerged plants]  Spend entire life cycle underwater: water is not a limiting resource  Dissected narrow leaves  Greatest number of adaptations:  Poorly developed xylem; no need for water carrying structures  Almost no mechanical strengthening; water supports the weight; no collenchyma or sclerenchyma  Maximum surface to volume ratio  The minimal O2 and CO2 can get in quickly  Thin cuticles, no stomata [since no gas exchange]  Running out of water is not a problem  Adapted intercellular air space  To keep them well positioned in waterReduced xylem [overabundance of water]:  Tissues bathed in H2O, little need for directed H2O transport  Only 2 xylem cells make up the tubing system within one plant  Little mechanical support  Buoyancy: H2O support  A collenchyma/sclerenchyma cap usually provides support in a terrestrial plant  Water plants have only one vascular bundle, found in the centre of the stalk; to decrease the wear and tear caused by potentially harsh currents Little resistance to currents  Narrow dissected leaves: little mechanical resistance, decreases war and tare inflected by the water  Central vascular bundle (Stem): withstands forces of water currents  Makes the entire stem more pliable, less likely to withstand great damage  Leaves are very thin/threadlike or net like; all of which decrease overall ressitance to currents  Fast diffusion of CO2 to chloroplasts: enabled by the narrow or dissected leaves  Increase surface to volume ratio by the shape/size of leaves  Allows CO2 to reach chloroplasts quickly and maximize photosynthetic output  Fast diffusion of CO2 to chloroplasts; due to fact that leaves are so thin; ex sometimes 1-2 cell layers thick; usually transparent; CO2 can diffuse from cell to cell, light can reach all cells quickly  Leaves have Thin and porous cuticle, no stomata increases how co2 can permeate [ Increases CO2 permeability] because co2 can make it through the leaf no need for stomata. Airspace in submerged tissues [LIGHT]  Plants need to ensure they get enough light; as they are usually anchored to the bottom of the lake  Leaves: reduced airspace, such that leaves remain submerged  Stems: air in lacunae [openings in the stem] to grow upwards towards light  Lacunae is actively filled by the plant by O2 or CO2; orients the entire plant to the water surface where light is optimal  Lacunae provide enough buoyancy and leaves have minimal buoyancy to still keep the plant in the water but they don’t have any airspaces to remain submerged Flowering in hydrophytes: above H2O  Even true hydrophytes will produce flowers that have reproductive structures sticking out in
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