PPllaanntt SSttrruuccttuurree GGrroowwtthh aanndd DDeevveellooppmmeenntt Chapter 35 Three Basic Plant Organs • Roots • Anchors a vascular plant • Absorbs Minerals & Water • Stores nutrients • Stems • Alternating system of nodes and internodes • Axillary buds • Terminal Bud • Apical Dominance • Leaves • Main photosynthetic organ • Blade & Petiole • Monocot & Dicot vein patterns differ Three Tissue Systems • Dermal Tissue • Outer protective covering • Epidermis in non-woody plants • Periderm replaces epidermis in woody plants • Vascular Tissue • Plumbing • Transports materials (water & nutrients)between roots and shoots • Xylem: conveys water from roots to shoots • Phloem: conveys organic nutrients from where they are made to where they are needed • Ground Tissue • The rest (everything that isn’t Dermal or Vascular Tissues) • Pith is internal to the vascular tissue • Cortex is external to the vascular tissue • Ground tissue is often specialized in storage, photosynthesis and supportPPllaanntt SSttrruuccttuurree GGrroowwtthh aanndd DDeevveellooppmmeenntt Chapter 35 Common Types of Plant Cells • Parenchyma Cells • Thin & flexible primary walls • Most lack secondary walls • Protoplast has a large central vacuole • “typical” plant cells – not very specialized • Perform most metabolic functions including photosynthesis • Generally retain the ability to differentiate into other types of plant cells • Alive at functional maturity • Collenchyma Cells • Grouped in strands or cylinders • Useful for supporting the young parts of the plant • Unevenly thick primary cell walls and no secondary cell walls • They are flexible • Alive at functional maturity • Scerenchyma Cells • Also function in support • Thick secondary walls strengthened with lignin • Very specialized for support • Dead at functional maturity: the “skeleton” remains after the cell dies • Sclereids • Shorter than fibers and irregular in shape • These impart hardness to nut shells, seed coats, and give pear fruit the characteristic gritty texture • Fibers • Usually arranged in threads • Long slender and tapered • Often used for commercial purposes (for rope or cloth, for example) Water Conducting Cells of the Xylem • Tracheids • Dead at functional maturity • Found in xylem of all vascular plants • Long thin cells with tapered ends • Water moves from cell to cell through pits • Vessel Elements • Dead at functional maturity • Generally wider, shorter and thinner walled than tracheids • Aligned end to end, forming pipes called “vessels” • Ends have perforations for water to flow throughPPllaanntt SSttrruuccttuurree GGrroowwtthh aanndd DDeevveellooppmmeenntt Chapter 35 Sugar Conducting Cells of the Phloem • Alive at functional maturity • Sieve Cells • in seedless vascular plants and gymnosperms • Sieve Tube Members • in angiosperms • Members make up Sieve Tube • Lack organelles such as nucleus, ribosomes and vacuoles • Ends of the cells have sieve plates with pores that allow fluid to flow • Sieve Tube Members have generally have fully functional cells associated with them called “Companion cells” • Nucleus and ribosomes serve both cells Plant Growth: Meristems • Primary Growth • produces the primary plant body • Secondary Growth • thickens the plant • generally occurs only in woody plants Root Primary Growth • Primary Growth of Roots • The tip of the root is covered with a “root cap” • Protects the tissue below called apical meristem • Root cap also produces a slime that helps the root push through the soil • Growth occurs just behind the root tip • Three Zones • Zone of Cell Division • Zone of Elongation • Zone of Maturation • Lateral roots originate from the pericycle • the outmost layer of the vascular cylinder Primary Growth of Shoots • Shoot apical meristem is not covered by a cap • Rapidly dividing cells in the terminal bud • Leaf primordia & axillary buds develop below • Form shoots later in lifePPllaanntt SSttrruuccttuurree GGrroowwtthh aanndd DDeevveellooppmmeenntt Chapter 35 Secondary Growth • Growth in thickness • Produced by lateral meristems • Occurs in Woody plants • Simultaneous with Primary Growth • But in different areas • Process is similar in Roots and Stems Secondary Plant Body • Tissues Produced by • Vascular Cambium • Adds secondary xylem (wood) • Adds secondary phloem • Cork Cambium • Adds a tough, thick covering • Mainly cork cells Vascular Cambium • One cell layer thick • A cylinder of meristematic cells • Produces • Xylem on the inside • Becomes “wood” • Phloem on the outside • Usually less phloem than xylem Secondary Xylem: Wood • Older layers of xylem no longer transport water and minerals (xylem sap) • This xylem is called “heartwood” • Outer layers still transport sap • This xylem is called “sapwood” Secondary Phloem • Only the youngest phloem carries phloem sap (sugar) • This phloem is closest to the vascular cambium • Older phloem is sloughed off as the diameter of the root or stem expandsPPllaanntt SSttrruuccttuurree GGrroowwtthh aanndd DDeevveellooppmmeenntt Chapter 35 Cork Cambium • Produces two tissue types • phelloderm to the inside • Cork cells to the outside • Cork cells make a waxy substance • called suberin • Functions as a protective barrier • Cork Cambium and all these two tissues it prodcues are cumulatively called “periderm” • Periderm replaces epidermis • Periderm is air- and water- tight Bark • Cork cambium does not continue to divide • No increase in circumference • It splits as the stem or root expands • Then loses its meristematic activity • A new cork cambium forms to the inside • Older layers of periderm are sloughed off • This is what we generally call “bark” • Bark is actually all the tissues external to the vascular cambium Vocabulary These are some terms that I expect you to know from this chapter. Please DO NOT assume that these are the only terms you should know. I selected the terms listed here because they have a considerable probability of appearing on one of my exams. • Root •