Two Categories of Plant Tissues AP Biology Spring 2011

Simple Tissues Parenchyma: makes up most of the soft, moist primary growth of plants Thin walled, pliable cells are alive at maturity and retain the capacity to divide Participate in photosynthesis (mesophyll), storage, secretion, and wound healing

Simple Tissues Collenchyma: function to structurally strengthen the plant Ex. Strings in cellery Alive at maturity and are commonly arranged as strands or cylinders beneath the dermal tissue of stems The primary cell walls of collenchyma become thickened with cellulose and pectin at maturity

Simple Tissues Sclerenchyma: provide mechanical support and protection in mature plants The secondary cell walls are thick and often impregnated with lignin, which strengthens and waterproofs cell walls Form fibers such as in cloth, rope, and paper Sclereids type of fiber that forms strong coats around seeds as in a peach pit

Complex Tissues Vascular tissues function in the distribution of water, minerals, and sugars throughout the plant

Complex Tissues Xylem: consists of 2 kinds of cells, both dead at maturity, to conduct water and minerals absorbed from the soil Vessel members: short cells joined end to end to form a vessel with perforation plates at the ends of each member Tracheids: long cells with tapered, overlapping ends Both are waterproofed with lignin and can transport water upward and laterally in the plant

Complex Tissues Phloem: transports sugars and other solutes throughout the plant Contains living cells called sieve tube members that are connected end to end at the sieve plate to form sieve tubes Companion cells: type of parenchyma, located adjacent to the sieve tube members, function to load and unload sugars from the phloem

Complex Tissues Epidermis: dermal tissue system, a single layer of cells that covers all primary plant parts Cuticle: Waxy secretions from the epidermis, covers external surfaces of the plant to restrict water loss and resist microbial attack Stomata: specialized openings in the epidermis, regulate water and gaseous exchange with the air Periderm: replaces epidermis when roots and stems increase in diameter and become woody