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○ All cells have primary cell wall, some cells have additional layers of cellulose that increase the strength of the cell wall called secondary cell wall ○ Primary wall is located outside of secondary wall because additional cellulose is produced at cell membrane ○ 3 plant tissues ■ Dermal ■ Ground ■ Vascular ● Dermal tissue ○ Function: protection ○ Epidermis is dermal tissue from the embryo apical meristem and is one cell layer thick ■ Similar to skin of multicellular animal ■ Epidermis covered by cuticle which waterproof plants surface ■ Gas exchange occurs through stomata which are epidermal openings that a pair of guard cells that regulate size of opening and controlling water loss and gas exchange ■ Trichomes: outgrowths of epidermal cells, hairlike ● Function: protect leaves from light intensity ■ Root hair which increase surface area for absorption of water and minerals ● Ground Tissue ○ Carries out storage of carbohydrates and water, photosynthesis, and support ○ 3 types of cells of ground tissue ■ Parenchyma: most abundant cell in primary tissue (spongy and palidade mesophyll) ● Primary cell walls, large vacuole, living at maturity ● Many chloroplast for photosynthesis ■ Collenchyma: living at maturity, irregular thickened primary walls ● Thickened cell walls provide flexible support for plant organs ■ Sclerenchyma: thick walls, secondary cells walls with ligden ● Ligden makes cell walls rigid ● Dead at maturity ● Strengthen tissue ● Give fruit a gritty texture
(Lec 1: Les 2) 3 ● Example: fibers ● Vascular tissue (Xylem) ●Vascular Tissue (Xylem) ○Similar to an animal’s circulatory system except in plants, they have separate transport systems for water and food molecules ○Xylem is vascular tissue specialized for conducting water and minerals ○In angiosperms, xylem is composed of conducting cells called vessels and tracheids. ○Both vessels and tracheids are dead at maturity ○Cells are elongated in shape and form hollow tubes ○Vessels are larger in diameter and stack end-to-end ○Tracheids are smaller in diameter and have tapered ends that overlaps ○Vessels conduct water more than efficiently than tracheids ○Both tracheids and vessels have liquefied secondary cell walls and also contribute to the support of the plant ○In addition to these conducting cells, xylem often has parenchyma cells for lateral transport and storage, and fibers for additional strengthening ○Secondary xylem produced by the vascular cambium forms wood ●Vascular Tissue (Phloem) ○