� - Types of plant cells o Parenchyma cells-most...

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Types of plant cells o Parenchyma cells—most common cells; primary cell walls, smallest cell wall, evenly thick o Collenchymas Cells—uneven thickness, flexible support o Sclerenchyma cells—very thick walls, contain cellulose and ligin, inflexible support, inside primary wall Transport—Vascular system comprised of xylem and phloem o Water conducting cells of xylem: vessels and tracheids (type of sclerenchyma) Thick walls to support water, Sugar conducting cells of phloem: sieve tubes and companion cells. Sieve tube cells alive, but lack nucleus; companion cells are adjacent and control sieve tube cells o Water travels through ground up and through stomata, exit accompanied by gas exchange o Phloem transport is versatile In spring, leaves are not big enough for photosynthesis but need energy to open up. Sugar moves from roots to leaves. o Plant cell-to-cell transport: symplastic (inside cell from cell to cell) and apoplastic (outside cells through cell walls) o Sugar loaded at sources, unloaded at sinks—Uses ATP Sink: root, flower, emerging leaf Source: leaf o Much of plant support comes from turgor (water) pressure Xylem only goes up Vascular bundle in the center or roots Ring of cells around vascular bundle: Casparian strip of endodermis keeps water from entering the xylem from purely apoplastic route Bad tings for the plant can enter apoplastically and get transported throughout the plant, but what gets into the vascular bundle is regulated. o Water movement Phloem (pushes), Xylem (pulls) Guard cell openings regulated by turgor Potassium moves into guard cells, then water follows Water moves through xylem Transpiration: biological evaporation (water leaving through stomata) Adhesion/coesion: Water molecules attracted to each other by hydrogen bonds How high a plant can support chain of water limits plant height o Xylem is tough, contains ligin. More ligin means less useful as biofuel. Can’t remove ligin because then no more transportation of water. Plants that can produce extra xylem for more water transport—Woody plants, otherwise herbaceous; o Secondary growth—vascular meristem (cambium) forums between xylem and phloem cells, new xylem on inside keeps forming, new phloem on outside keeps growing Primary meristem—in shoot and in root, Seconary meristem (if able) between xylem and phloem
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Additional cells for bark and to fill in circumference More water transport, more support/rigidity, more leaves Cell division of bark cells to fill cracks as the tree gets wider o Energy Cellulose + enzymes->fermentable sugars->etanol Requires removal of ligin Plants response to environment o Light Respond to direction of light Seedling germination light dependant Blue, red, far-red o Plants respond to touch o Chemicals Caterpillar saliva—can induce secretion of chemicals Release chemicals to signal other organisms Attract parasites to kill predators
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This note was uploaded on 04/09/2008 for the course BIO 311D taught by Professor Reichler during the Spring '08 term at University of Texas.

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� - Types of plant cells o Parenchyma cells-most...

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