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Plant structure, growth, & development ~ 35
1. Plants have a hierarchical organization consisting of organs,
tissues, and cells• 3 basic organs
– Roots, stems, leaves• Shoot System
– Stems• Raises or separates leaves to expose to sunlight
– Leaves • Main photosynthetic organ
• Root System– Anchors a vascular plant in the soil– Absorbs minerals & H2O– Stores carbohydrates
Dermal, Vascular, and Ground tissues = Tissue System
• Tissue system connects all of the plants organs• Dermal Tissue System– Epidermis, cuticle, periderm– Outer protective covering
• Vascular Tissue System– Xylem, phloem, stele– Long distance transport of materials btwn root & shoot systems
• Ground Tissue System– Pith, cortex– Specialized cells for storage, photosynthesis and support
Differentiated Cell Types
Differentiated Plant Cells
• Parenchyma Cells– Typical plant cell w/ lg central vac– Metabolic functions, synthesizing, & storing
organic products
• Collenchyma cells– Flexible Support & strength w/o restraining
growth (young parts of plant shoot), grouped in strands
• Sclerenchyma Cells– Support & hardness– Much more rigid than Collenchyma lignin in cell
walls• Water Conducting cells of xylem– Support; harden as die at maturity– Hardening of tracheids & vessel elements tubes
to transport water; migrate btwn cells thru pits• Sugar Conducting cells of Phloem– Transport sugars throughout; alive at maturity– Chains of cells = sieve-tube elements & sieve
plates facilitate flow of sugars throughout plant
2. Meristems generate cells for primary & secondary growth
• Intermediate Growth– Growth occurs throughout
life of plant– Meristems
• Apical– Primary Growth– Roots to extend in soil– Shoots expose to sunlight– Tips of roots, buds & shoots
• Lateral– Secondary Growth– Growth in thickness– Vascular cambium, Cork
cambium
• Determinate Growth– Leaves, thorns, flowers stop
growing after reach certain size
3. Primary Growth Lengthens Roots & Shoots
• Primary growth of roots• Growth occurs behind root
cap in three overlapping zones
1. Cell Division2. Elongation3. Differentiation/Maturation
• Primary growth of shoots• Apical meristem– Dome shaped mass of dividing cells
at the shoot tip– Shoot elongation due to
lengthening of cells below shoot tip
• Leaf primordia– Development of leaves
• Tissue Organization of Stems
• Tissue Organization of Leaves– Epidermis
• Upper & lower• Pores = stomata• Gas exchange• Prevent loss of water• Guard cells regulate
opening/closing of stomata– Mesophyll
• Ground tissue (middle tissue)• Layers of parenchyma cells
– Vascular Tissue• Xylem & phloem reinforcing
shape of leaf = Vein• Bundle sheath cells protect
Vein
4. Secondary Growth Increases the Diameter of Stems and Roots in Woody
Plants• Secondary growth (thickness produced from
lateral meristems) occurs in stems and roots of woody plants, rarely in leaves
• Tissues produced by vascular cambium & cork cambium– V.Cambium adds secondary xylem (= wood) and
phloem• Inc vascular flow and support for shoots
– C.Cambium tough, thick covering of wax protect the stem from water loss, insects, bacteria, fungi
• Growth rings– Layers of sec. xylem accum– Tracheids, vessels, fibers– Walls of sec xylem heavily lignified= hardness & strength of wood
• Gymnosperms– Tracheids only
• Angiosperms– Tracheids & vessel elements
• Temperate regions– Early wood (spring; lrg cells) & late wood (summer; sml cells)– V.Cambium inactive in winter– Forms seasonal rings
5. Growth, Morphogenesis, and Cell Differentiation Produce the Plant Body• Growth – inc in size by cell division• Morphogenesis = creation of plant shape– Tissue, organ, organism its shape & position of cell
types– Development of specific patterns = Pattern Formation
• Cell fate– Lineage-based determined early in development– Position-based cell’s final position in an emerging organ
determines what kind of cell it will become
• Differentiation = cells with same genes become different from one another – Gene expression; Hox genes in animals = MADS-box in
plants for transcription factors
Organ identity genes
• Meristem identity genes– Vegetative growth flowering (floral meristems)
• Organ identity genes– Regulate development of floral pattern
• ABC Hypothesis– 3 classes of genes direct the formation of 4 types of
floral organs via gene activation for expression• A sepals & petals• B petals & stamens• C stamens & carpels