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Plant Structure and Function Ch. 35 http://www.uic.edu/classes/bios/bios100/labs/plantbod.gif Morphology of a Flowering Plant • Root system and shoot system are connected by vascular tissue that is continuous throughout plant Monocots vs. Dicots http://waynesword.palomar.edu/images/monocot3.gif http://www.biology4kids.com/misc/photos /dicotflower1.jpg http://www.biologie.uni-hamburg.de/bonline/library/onlinebio/monocot_flower.gif http://waynesword.palomar.edu/images/monocot3.gif Plant Cell Nucleus Chloroplast Cell Wall Roots • Functions – Anchor plant in the soil – Absorb water and minerals – Store food Root Structure Cortex Vascular cylinder Epidermis Key Root hair Dermal Zone of maturation Ground Vascular Zone of elongation Apical meristem Root cap 100 µm Zone of cell division Root Systems Taproot Fibrous root http://waynesword.palomar.edu/images/mangro3b.jpg http://waynesword.palomar.edu/images/mangro3b.jpg •Red mangrove growing in seawater •Adventitious prop roots support and securely anchor this shrub in the mud and loose sand of tidal waters. •Close-up view of prop roots •Numerous pores called lenticels which provide gas exchange and an additional source of oxygen for the submersed roots. Epidermis Cortex Vascular cylinder -xylem -phloem Developing lateral root Buttress roots. Aerial roots Storage roots. Prop root Modified Roots Stems • Functions – Support – Transport – Storage Monocot arrangement Dicot arrangement • Proximity of terminal bud inhibits growth of axillary buds (Apical dominance) http://www.answers.com/topic/redtip9845-jpg-1 Modified Stems Storage leaves Stem Roots Stolons—allow asexual reproduction Bulbs—store food Node Rhizome Root Tubers—store food Rhizomes—horizontal stem Leaves • Leaf structure – Shape – Size – Edges Mesophyll Leaf Structure Stomata Modified Leaves • Tendrils—allow plant to cling to support • Spines—reduces water loss Modified Leaves • Storage—modified for water storage (succulents) • Bracts—attracts pollinators Modified Leaves • Reproductive leaves— produce adventitious plantlets which fall off and take root Tissue Systems 1. Ground System •Parenchyma --cube-shaped, thin and flexible cell walls --function in photosynthesizing and storing organic products and wound healing •Collenchyma --elongated, thicker cell walls --cells grouped in strands or cylinders to support leaves and stems (parts that are still growing) •Sclerenchyma--cells have rigid, thick walls with lignin --at maturity, consists of dead cells --supports and strengthens plant Tissue Systems 2. Vascular System Xylem -Conducts water and minerals from roots to plant -composed of dead cells that form water-pipe system Phloem -Conducts food throughout plant -composed of living cells arranged into tubules Water-conducting Cells of Xylem WATER-CONDUCTING CELLS OF THE XYLEM Vessel Tracheids 100 µm 60 µm ma cells Pits Tracheids and vessels (colorized SEM) Vessel element Vessel elements with perforated end walls Tracheids Vessel elements with perforated end walls Sugar-conducting Cells of Phloem Tracheids SUGAR-CONDUCTING CELLS OF THE PHLOEM x of Sambucus, ed red) (LM) Sieve-tube members: longitudinal view (LM) Companion cell lls in pear (LM) Sieve-tube member Plasmodesma 25 µm Sieve plate Nucleus Cytoplasm Companion cell 30 µm 15 µm from ash tree) (LM) Sieve-tube members: longitudinal view Sieve plate with pores (LM) Sheath of sclerenchyma phloem xylem parenchyma Tissue Systems 3. Dermal Tissue System - Forms the outer covering of plants •Epidermis-outer layer of cells covered by waxy cuticle •Stomata-structures that regulate passage of gases into/out of plant Meristems: Primary Growth Growing region where cells actively divide Apical meristems- grow in length at tips of stems and roots Primary growth in stems Shoot apical meristems (in buds) Epidermis Cortex Primary phloem Primary xylem Vascular cambium Cork cambium Lateral meristems Pith Secondary growth in stems Periderm Cork cambium Pith Cortex Primary phloem Primary xylem Root apical meristems Secondary xylem Secondary phloem Vascular cambium Lateral meristems • Add thickness to woody plants, a process called secondary growth • Two lateral meristems – vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem – cork cambium replaces the epidermis with periderm, which is thicker and tougher Primary Growth in Roots Cortex Vascular cylinder Epidermis Key Root hair Dermal Zone of maturation Ground Vascular Zone of elongation Apical meristem Root cap 100 µm Zone of cell division Primary Growth in Shoots Apical meristem Leaf primordia Developing vascular strand Axillary bud meristems 0.25 mm •Secondary growth occurs in stems and roots of woody plants but rarely in leaves Vascular cambium •Produces secondary xylem and phloem Cork cambium •Produces tough, thick covering for stems and roots •Replaces epidermis Anatomy of a Tree Trunk • As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals • The outer layers, known as sapwood, still transport materials through the xylem Growth ring Vascular ray Heartwood Secondary xylem Sapwood Vascular cambium Secondary phloem Bark Layers of periderm Growth, morphogenesis, and differentiation produce the plant body • The three developmental processes of growth, morphogenesis, and cellular differentiation act in concert to transform the fertilized egg into a plant Growth: Cell Division and Cell Expansion • By increasing cell number, cell division in meristems increases the potential for growth • Cell expansion accounts for the actual increase in plant size The Plane and Symmetry of Cell Division • The plane (direction) and symmetry of cell division are immensely important in determining plant form • If the planes of division are parallel to the plane of the first division, a single file of cells is produced Division in same plane Single file of cells forms Plane of cell division Division in three planes Cube forms Nucleus Cell divisions in the same plane produce a single file of cells, whereas cell divisions in three planes give rise to a cube. The Plane and Symmetry of Cell Division • If the planes of division vary randomly, asymmetrical cell division occurs Developing guard cells Asymmetrical cell division Unspecialized epidermal cell Unspecialized Guard cell epidermal cell “mother cell” Unspecialized epidermal cell An asymmetrical cell division precedes the development of epidermal guard cells, the cells that border stomata (see Figure 35.17). The Plane and Symmetry of Cell Division • The plane in which a cell divides is determined during late interphase • Microtubules become concentrated into a ring called the preprophase band Preprophase bands of microtubules Nuclei Cell plates 10 µm Genetic Control of Flowering • Flower formation involves a phase change from vegetative growth to reproductive growth • It is triggered by a combination of environmental cues and internal signals • Transition from vegetative growth to flowering is associated with the switching-on of floral meristem identity genes • Plant biologists have identified several organ identity genes that regulate the development of floral pattern Pe Ca St Se Pe Se Normal Arabidopsis flower. Arabidopsis normally has four whorls of flower parts: sepals (Se), petals (Pe), stamens (St), and carpels (Ca). Pe Pe Se Abnormal Arabidopsis flower. This flower has an extra set of petals in place of stamens and an internal flower where normal plants have carpels. • The ABC model of flower formation identifies how floral organ identity genes direct the formation of the four types of floral organs Sepals Petals Stamens A B Carpels C B+C A+B gene gene activity activity A gene activity A schematic diagram of the ABC hypothesis C gene activity