Roots, Stems, and Leaves Ms. Moore 9/6/2012
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Transcript of Roots, Stems, and Leaves Ms. Moore 9/6/2012
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Roots, Stems, and Leaves
Ms. Moore9/6/2012
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• What part of the plant do we eat?
• Label the stems, roots, and leaves of each vegetable.
Small stem surrounded by leaves
Stem with eyes that grow into branches
Floral bud surrounded by leaves
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Principal Organs of Seed Plants• Roots– Absorb water– Anchor plants into ground– Hold plants upright through weather
• Stems– Support system– Transport system– Defense against predators and disease
• Leaves– Photosynthesis– Protect against water loss
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Tissue Systems• Dermal– Epidermal cells: surround outer covering of a plant– Waxy layer protects against water loss and injury (cuticle)
• Vascular– Xylem– Phloem
• Ground– Between dermal and vascular tissues
• Meristematic– Produces new cells by mitosis
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Dermal Tissue
• Single layer of closely packed cells• Covers and protects the plant; acts as “skin”• Thick waxy layer, known as cuticle
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Vascular Tissue
• Xylem– Tracheid– Vessel element
• Phloem– Sieve tube elements– Companion cells
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Ground Tissue• Parenchyma– Packed with chloroplasts;
site of photosynthesis
• Collenchyma– Celery “strings”; flexible
walls for support
• Sclerenchyma– Rigid; strength and support
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Meristematic Tissue
• Meristems: clusters of tissue responsible for continuing growth
• Meristematic tissue: undifferentialted cells produced by mitosis
• Apical meristem: group of cells near the end or top of plant that divide to produce increased length of stems and roots
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Mastery
• What are the three main organs of seed plants?
• List the three tissue systems of plants.
• What two cell types make up xylem? Phloem?
• What is the function of meristematic tissue in a plant?
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Types of Roots
• Taproots– Primary root grows long and thick– Mainly in dicots
• Fibrous roots– No single root grows larger than the rest– Mainly in monocots
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Structure and Growth• Root hair: water enters plant at
tiny projections
• Cortex: spongy layer of ground tissue
• Endodermis: encloses vascular subsystem
• Vascular cylinder: contains xylem and phloem
• Root cap: protects root as it grows through soil
• Casparian strip: waterproofs endodermis
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Uptake of NutrientsEssential Plant Nutrients
Nutrient Role in Plant Result of Deficiency
Nitrogen Proper leaf growth and color; synthesis of amino acids, proteins, nucleic acids, and chlorophyll
Stunted plant growth; pale yellow leaves
Phosphorus Synthesis of DNA; development of roots, stems, flowers, and seeds
Poor flowering; stunted growth
Potassium Synthesis of proteins and carbohydrates; development of roots, stems, and flowers; resistance to cold and disease
Weak stems and stunted roots; edges of leaves turn brown
Magnesium Synthesis of chlorophyll Thin stems; mottled, pale leaves
Calcium Cell growth and division; cell wall structure; cellular transport; enzyme action
Stunted growth; curled leaves
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Mastery
• Compare a taproot and a fibrous root.
• How are tissues distributed in a plant root?
• What are the two main functions of roots?
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Stem Structure and Function• Produce leaves, branches,
and flowers• Hold leaves up to sunlight• Transport substances
between roots and leaves
• Primary Growth: cell divisions in apical meristem• Secondary Growth: growth in lateral meristems in conifers and dicots
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Stem Structure
• Nodes: where leaves are attached• Internodes: region between two nodes• Buds: contain undeveloped tissue that can
produce new stems, leaves, flowers• Pith: parenchyma cells inside ring of vascular
tissue (outside cells = cortex) in stem
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Monocot vs. Dicot
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Growth
• Primary: apical meristem; all seed plants
• Secondary: lateral meristem; dicots– Vascular cambium: increases the thickness of
stems over time– Cork cambium: produces outer covering of stems
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Formation of Wood
• Heartwood: older xylem near center no longer conducts water; darker in color
• Sapwood: active in fluid transport; surrounds heartwood; lighter in color
• Bark: tissues outside the vascular cambium
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Mastery
• How do the functions of a stem relate to the roots and leaves of a plant?
• Describe how the arrangement of vascular bundles differs between monocot and dicot stems.
• What is primary and secondary growth?• How do heartwood and sapwood differ?
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Leaf Structure
• Structure is optimized for absorbing light and carrying out photosynthesis and gas exchange.– Blades: collect sunlight– Petiole: attachment
• Vascular tissues are connected directly to stem’s vascular tissues.
• Xylem and phloem tissues are gathered together into bundles that run from the stem into the petiole to the leaf blade.
• In the leaf blade, vascular bundles are surrounded by parenchyma and sclerenchyma cells.
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Leaf Function: Photosynthesis
• Photosynthesis: 6CO2 + 6H2O C6H12O6 + 6O2
• Mesophyll: specialized ground tissue where most photosynthesis occurs– Palisade mesophyll: closely packed cells that absorb light; located
under the epidermis– Spongy mesophyll: loose tissue with many air spaces (gas
exchange) • Stomata: porelike openings in the underside of the leaf that
allow CO2 and O2 to diffuse in and out of leaf• Guard cells: specialized cells in the epidermis that control
the opening and closing of stomata (due to changes in water pressure)
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• Why is photosynthesis important to all life?
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Leaf Function: Transpiration
• The surfaces of spongy mesophyll are kept moist so that gases can enter and leave the cells easily.
• Transpiration: the loss of water through the leaves
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Leaf Functions: Gas Exchange• Leaves take in CO2 and give off O2 during
photosynthesis. – Do leaves ever take in O2?
• Gas exchange takes place in the stomata.• Plants keep stomata open just long enough to
allow photosynthesis to occur. – Why don’t they keep stomata open at all times?– What cells regulate the opening and closing of
stomata?
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Mastery
• How is the structure of a leaf optimized for light absorption?
• What factors regulate the opening and closing of guard cells?
• Are stomata more likely to be open or closed on a hot day?
• Describe transport of water and nutrients in a leaf.
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Transport in Plants• Combination of root pressure, capillary action,
and transpiration (loss of water through leaves) provides enough force to move water through the xylem tissue.
Up next…Transpiration Lab!
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Water Transport
• How is water transported throughout the plant?
• Water molecules are attracted to one another by a force called cohesion; they are attracted to other molecules by adhesion.
• The tendency of water to rise in a thin tube (xylem) is called capillary action.– Water is attracted to the walls of the tube and they
are also attracted to one another.
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Nutrient Transport
• Phloem carries out the seasonal movement of sugars within a plant.
• Pressure-flow hypothesis: When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of fluid in that same direction. – Source: an area rich in nutrients– Sink: an area that needs nutrients
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Review
• Vocabulary
• Study Guide
• Any Questions?