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Uploaded byDr. Harwinder Kaur
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Angiosperm anatomy.ppt

Meristems are regions of active cell division that give rise to the different cell types in plants. There are two types of meristems - primary meristems result in growth in length through cell division while secondary meristems result in growth in width. Plants are composed of three main tissue types - dermal tissues which form the outer layers, ground tissues which make up the internal structure, and vascular tissues which transport water and nutrients. These tissues are made up of specialized cell types that carry out functions like protection, photosynthesis, storage, and transport.

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THE PLANT BODY
Meristems  In flowering plants cells originate from regions of active cell division known as meristems.  The cells arising from meristems give rise to the many different cell types that make up a plant
Types of Meristems  Primary Meristems (also called Apical Meristems) result in primary growth - growth in length  Secondary Meristems result in secondary growth which in growth in width (increase in diameter)
Apical meristems  Also known as primary meristems  Found at the tips of all roots and stems  Contribute to the increase in length of the plant which is called primary growth  Give rise to the leaves, and non-woody stems and roots
Secondary Meristems  Some plants have additional meristems that result in increases in diameter which is secondary growth. • Vascular cambium • cork cambium
Multicellular Organisms  In multicellular organisms, certain cells are specialized in structure and function  Tissues are specialized cells that perform specific functions  Plants composed of three basic tissues categories • Dermal • Ground • Vascular
Dermal Tissue  Dermal tissues are the outermost layers in a plant  They protect the plant  Two types of dermal tissues • Epidermis • Periderm
Epidermis  Outermost layer In young plants and non-woody plants  Single layer of flatten cells  Cells secrete cutin which makes up the cuticle and prevents water loss Epidermal Cell Cuticle
Trichomes  Hairs (trichomes) may be present on the epidermis.  Sometime abundant enough so leaves look fuzzy  Trichomes may also be glandular Hair Gland
Guard Cells and Stomata  Pores known as stomata (singular stoma) occur on epidermis  Gases exchange occurs through stomata  A pair of sausage-shaped cells, guard cells, regulate the opening and closing of the stomata
Guard Cells and Stoma Guard Cell Stoma (opening)
Periderm  In woody plants when the tree increases in diameter, the epidermis cracks and is replaced by periderm  The periderm consists: • Cork cells • Cork cambium
Cork Cells  Outer bark on mature trees  Dead cells with walls containing suberin, a waterproofing fatty substance.  Prevents water loss from underlying tissues  Produced by cork cambium
Ground tissues  Major tissue of non-woody plant organs  Perform a variety of functions  The three types of ground tissue: • Parenchyma • Collenchyma • Sclerenchyma
Parenchyma  Almost any shape or size  Loosely arranged with intercellular spaces  Many different functions: • Photosynthetic cells in leaves and green stems • Storage cells in plant organs for starch, sugar, or water
Parenchyma Cells Intercellular spaces
Parenchyma Cells
Collenchyma  Support tissue in young plant organs  Found in stems, leaves, and petals  Elongated cells with unevenly thickened primary cell walls with the walls thickest at the corners  Found tightly packed together just below the epidermis
Collenchyma Cells Longitudinal view Cross section showing uneven wall thickening
Sclerenchyma  Two cell types • fibers • sclereids.  Non-living at maturity  Thickened secondary walls
Fibers  Elongate cells  Function in support  Leaf and stem fibers from many plants used for cloth and rope.
Sclereids  Various shapes  Functions • mechanical support and • protection  Account for the hardness in nut shells and the grit of pear fruit
Sclerenchyma X-section of fiber showing thick secondary wall Fiber Sclereid x-section showing thick secondary wall Sclereids
Sclereids
Vascular tissues  Xylem - conducts water and minerals from the roots upward  Phloem - transports organic materials (sugars) synthesized by the plant
Xylem  Cells conducting water - non-living • Tracheids - long thin cells with tapering walls and numerous pits • Vessel elements - short, wide, with horizontal end walls with large openings • Both cells have secondary walls  Fibers - non-living - provide support  Parenchyma cells - metabolic activity
Tracheids and Vessels
Xylem Cells from Oak Wood
Primary and Secondary Xylem  Primary xylem develops from the apical meristem  Secondary xylem develops from the vascular cambium.  In trees secondary xylem is very extensive
Phloem  Cell Types in phloem • Sieve Tube Members - transport sugars • Companion Cells - loading and unloading • Fibers - support • Parenchyma - metabolic activity  Primary and Secondary phloem
Sieve Tube Member • Living cells with only thin primary walls • End walls have sieve plates (large pores with large plasmodesmata) End wall with sieve plate
Companion cells • Specialized parenchyma cell develops alongside a sieve tube member • Plasmodesmata connect it to sieve tube member • Loading and unloading sugars for transport
Plant Tissues and Cells  Tissue Type Cell Types Function  Dermal Epidermis epidermal cells protection Periderm cork cells protection  Ground Parenchyma parenchyma cells storage, photosynthesis Collenchyma collenchyma cells support Sclerenchyma sclereids, fibers support, protection
Plant Tissues and Cells  Tissue Type Cell Types Function  Vascular Xylem tracheids water vessel elements conduction fibers support parenchyma metabolism Phloem sieve tube transport member sugars companion cells loading fibers support parenchyma metabolism
Plant Organs  Stems • Support leaves • Conduct water and sugars  Roots • Anchor the plant • Absorb water and minerals  Leaves • Photosynthesis • Transpiration
Herbaceous Dicot Stem X P Epidermis Cortex (parenchyma cells) Pith (parenchyma cells) Vascular bundle Cross-section
Monocot Stem Epidermis Ground Tissue Vascular bundle Scattered Vascular Bundles
Roots Stele Epidermis Xylem Cortex Phloem Endodermis root hair
Leaf X P Epidermis Veins Spongy mesophyll (parenchyma) Palisade Mesophyll (parenchyma)
Leaf from Ligustrum
Secondary Growth in Dicots
5 Year Old Woody Dicot Stem One annual ring Periderm (cork) Cortex Secondary phloem Vascular Cambium 5 Years of Secondary Xylem
Three Year Old Tree
Dendrochronology  Study of tree rings has added many fields of study  Can tell us about past climates  Can be used to date from archeological sites artifacts  Tree ring research lab at the University of Arizona http://www.ltrr.arizona.edu/
Summary  Growth, replacement of cells, and asexual reproduction all depend on cell division  Tissues are groups of cells that perform a common function  Stems, roots and leaves are made up of three basic tissue types: dermal, ground, and vascular