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Lecture 12

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Biological Sciences
Bebhinn Treanor

Lecture 12—Plant Life on the Edge  Adaptations huge range of habitats  Poorly developed xylem since water is not a limiting reasource  Arctic (extreme cold weathers)  (almost) no mechanical strengthening  Desert (hot and dry)  Supported by body of water  Bogs (nutrient poor)  Maximum surface-to-volume ratio  Little oxygen and carbon dioxide in water can easily enter the plant & get quick access to LIFE ON THE EDGE CONDITIONS photosynthetic parenchyma  Frost  Thin cuticle, no stomates since water is not limited  Heat/drought  Adapted intercellular air space  Perpetual inundation  Overabundance of freshwater  Type of limitation which is most common to southern Ontario  Salty habitats  Toxic soils (heavy metals)  Extreme nutrient limitations  Low light INTRODUCTION TO AQUATIC PLANTS: THE FRESHWATER ENVIRONMENT  Water is never limiting, but the overabundance of freshwater may limit other things, such as carbon dioxide for photosynthesis (concentration is much lower than in the air);; same as oxygen  Light decreases as you go deeper in water  Nutrient level is also lower in water than nutrients associated with soil  Water current may be so strong in creeks and river that they have to adjust so that the plants do not get torn apart  True Hydrophytes: Reduced xylem  Tissues bathed in water, little need for directed water transport  No need for vast vascular system since water is abundant (only 2 xylem cells make up tubing system for water lilies) TYPES OF AQUATIC PLANTS A) True Hydrophytes (submerged plants)  All of the plants organ is associated with water (no contact with atmosphere) B) Floating vs. emergent leaves C) Free roots vs. no roots  Little mechanical support TYPE A OF AQUATIC PLANTS: TRUE HYDROPHYTES  Since water keeps them upright  Greatest # of adaptations: spend whole life in waterdissected, narrow leaves 1 | P a g e  Typically hydrophytes have one vascular system placed in middle (no need wasting  Exception to aquatic plants: male flowers open underneath the water and release resources) individual pollen that are organized in pollen boats (have leaf like structures) make their way of up surface of water, and they arrange themselves on top of these leaves so that the pollen is sticking up and not in contact with water  Female flower makes sure it grows so that its above surface and produce a dip male pollen goes toward female flowers via gravity  little resistance to currents  Narrow/dissected leaves: little mechanical resistance  Central vascular bundle (stem): withstands forces of water currents  By placing vascular system in middle, their little wear & tear via air currents (less prone to be torn apart in strong current)  Typical leaves are thin or strongly directed (or large leaves may have windows) reduce water resistance to currents and decrease wear & tear via currents  Fast diffusion of carbon dioxide to chloroplast  Narrow and/or dissected leaves (leaves with windows)  Thin leaves (sometimes 1-2 cell layer thick)  Increase surface-to-area ratio, so plants can take up carbon dioxide efficiently maximize photosynthetic output  Thin and porous leaves  might be totally absent  No stomates  carbon dioxide goes through whole surface  Example: leaf may be 2 layers thick TYPES OF AQUATIC PLANTS A) True Hydrophytes (submerged plants) B) Floating vs. emergent leaves C) Free roots vs. no roots FLOATING LEAVES  Typically primitively lobed  Airspace in submerged tissues  Leaves: reduced air space leaves remain submerged  Example: water chestnut  Stems: air in lacunae to grow towards light  Essential for plants to get light most hydrophyte
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