THE PLANT BODY

Meristems Meristems n In flowering plants cells originate from regions of active cell division known as meristems. n The cells arising from meristems give rise to the many different cell types that make up a plant

Types of Meristems n Primary Meristems (also called Apical Meristems) result in primary growth - growth in length n Secondary Meristems result in secondary growth which in growth in width (increase in diameter)

Apical meristems n Also known as primary meristems n Found at the tips of all roots and stems n Contribute to the increase in length of the plant which is called primary growth n Give rise to the leaves, and non-woody stems and roots

Secondary Meristems n Some plants have additional meristems that result in increases in diameter which is secondary growth. Vascular cambiumVascular cambium cork cambiumcork cambium

Multicellular Organisms n In multicellular organisms, certain cells are specialized in structure and function n Tissues are specialized cells that perform specific functions n Plants composed of three basic tissues categories DermalDermal GroundGround VascularVascular

Dermal Tissue n Dermal tissues are the outermost layers in a plant n They protect the plant n Two types of dermal tissues EpidermisEpidermis PeridermPeriderm

Epidermis n Outermost layer In young plants and non-woody plants n Single layer of flatten cells n Cells secrete cutin which makes up the cuticle and prevents water loss Epidermal Cell Cuticle

Trichomes n Hairs (trichomes) may be present on the epidermis. n Sometime abundant enough so leaves look fuzzy n Trichomes may also be glandular Hair Gland

Guard Cells and Stomata n Pores known as stomata (singular stoma) occur on epidermis n Gases exchange occurs through stomata n 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 n In woody plants when the tree increases in diameter, the epidermis cracks and is replaced by periderm n The periderm consists: Cork cellsCork cells Cork cambiumCork cambium

Cork Cells n Outer bark on mature trees n Dead cells with walls containing suberin, a waterproofing fatty substance. n Prevents water loss from underlying tissues n Produced by cork cambium

Ground tissues n Major tissue of non-woody plant organs n Perform a variety of functions n The three types of ground tissue: Parenchyma Parenchyma Collenchyma Collenchyma Sclerenchyma Sclerenchyma

Parenchyma n Almost any shape or size n Loosely arranged with intercellular spaces n Many different functions: Photosynthetic cells in leaves and green stemsPhotosynthetic cells in leaves and green stems Storage cells in plant organs for starch, sugar, or waterStorage cells in plant organs for starch, sugar, or water

Parenchyma Cells Intercellular spaces

Parenchyma Cells

Collenchyma n Support tissue in young plant organs n Found in stems, leaves, and petals n Elongated cells with unevenly thickened primary cell walls with the walls thickest at the corners n Found tightly packed together just below the epidermis

Collenchyma Cells Longitudinal view Cross section showing uneven wall thickening

Sclerenchyma n Two cell types fibersfibers sclereids.sclereids. n Non-living at maturity n Thickened secondary walls

Fibers n Elongate cells n Function in support n Leaf and stem fibers from many plants used for cloth and rope.

Sclereids n Various shapes n Functions mechanical support andmechanical support and protectionprotection n 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 n Xylem - conducts water and minerals from the roots upward n Phloem - transports organic materials (sugars) synthesized by the plant

Xylem n Cells conducting water - non-living Tracheids - long thin cells with tapering walls and numerous pitsTracheids - long thin cells with tapering walls and numerous pits Vessel elements - short, wide, with horizontal end walls with large openingsVessel elements - short, wide, with horizontal end walls with large openings Both cells have secondary wallsBoth cells have secondary walls n Fibers - non-living - provide support n Parenchyma cells - metabolic activity

Tracheids and Vessels

Xylem Cells from Oak Wood

Primary and Secondary Xylem n Primary xylem develops from the apical meristem n Secondary xylem develops from the vascular cambium. n In trees secondary xylem is very extensive

Phloem n Cell Types in phloem Sieve Tube Members - transport sugarsSieve Tube Members - transport sugars Companion Cells - loading and unloadingCompanion Cells - loading and unloading Fibers - supportFibers - support Parenchyma - metabolic activityParenchyma - metabolic activity n Primary and Secondary phloem

Sieve Tube Member Living cells with only thin primary wallsLiving cells with only thin primary walls End walls have sieve plates (large pores with large plasmodesmata )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 memberSpecialized parenchyma cell develops alongside a sieve tube member Plasmodesmata connect it to sieve tube memberPlasmodesmata connect it to sieve tube member Loading and unloading sugars for transportLoading and unloading sugars for transport

Plant Tissues and Cells n Tissue TypeCell TypesFunction n Dermal Epidermisepidermal cells protection Peridermcork cells protection n Ground Parenchymaparenchyma cells storage, photosynthesis Collenchymacollenchyma cells support Sclerenchymasclereids, fibers support, protection

Plant Tissues and Cells Plant Tissues and Cells n Tissue TypeCell TypesFunction n Vascular Xylem tracheids water vessel elements conduction vessel elements conduction fibers support fibers support parenchyma metabolism parenchyma metabolism Phloem sieve tube transport member sugars companion cellsloading member sugars companion cellsloading fiberssupport fiberssupport parenchyma metabolism parenchyma metabolism

Plant Organs n Stems Support leavesSupport leaves Conduct water and sugarsConduct water and sugars n Roots Anchor the plantAnchor the plant Absorb water and mineralsAbsorb water and minerals n Leaves PhotosynthesisPhotosynthesis TranspirationTranspiration

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 n Study of tree rings has added many fields of study n Can tell us about past climates n Can be used to date from archeological sites artifacts n Tree ring research lab at the University of Arizona

Summary n Growth, replacement of cells, and asexual reproduction all depend on cell division n Tissues are groups of cells that perform a common function n Stems, roots and leaves are made up of three basic tissue types: dermal, ground, and vascular