Plant Organs

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Plant Organs

• Roots Stems

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I. Roots

• A. F(x)s grow underground
• 1. Absorb water nutrients from soil
• 2. Anchor plant in the soil
• 3. Make hormones important for growth
• development

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I. Roots

• B. Structure
• 1. Root cap
• F(x) protects apical meristem

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I. Roots

• B. Structure
• 2. Root hairs
• F(x)
• increase surface area for absorption

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I. Roots

• B. Structure
• 3. Casparian Strip
• F(x)
• channel water
• dissolved nutrients into vascular tissue
• allow movement only into roots

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I. Roots

• C. Types of Roots
• 1. Taproots
• a. Large main root that can store food
• b. F(x) absorption,
• anchoring
• E.g.

beet
carrot
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C. Types of Roots

• 2. Fibrous roots
• a. Numerous small roots
• b. Grow near surface
• c. F(x) absorption,
• anchoring
• c. E.g. grass

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C. Types of Roots

• 3. Prop or
• Adventitious roots
• a. Grow down to soil from stem,
• above ground
• b. F(x)s support,
  absorption
• c. E.g. corn,
• banyon tree

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C. Types of Roots

• 4. Aerial Roots
• a. Grow without soil,
• in air
• b. F(x) absorb water from moist air
• c. E.g. orchids in tropical
  rainforest

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II. Stems

• A. F(x)s
• 1. Hold leaves up to sunlight
• 2. Transport water nutrients from roots to
  leaves
• 3. Food storage in some plants

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II. Stems

• B. Stem Structures
• 1. Node place where
• one or more leaves are
• attached
• Note At the point of attachment of each leaf,
• there is a lateral bud with
• an apical meristem
• capable of developing
• into a new shoot

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II. Stems

• B. Stem Structures
• 2. Internode
• part of stem
• between nodes

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II. Stems

• C. Specialized stems
• 1. Rhizome horizontal underground stem
• 2. Tuber
• Underground stem w/ buds
• Food storage
• E.g. potato, parsnip

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II. Stems

• C. Specialized stems
• Bulb
• large bud w/ layers
• Food storage
• Many edible
• E.g. onion, garlic

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II. Stems

• C. Specialized stems
• 4. Corm
• Upright, thickened underground stem
• Food storage
• Not usually edible
• E.g. shamrock plant (Oxalis)

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II. Stems

• C. Specialized stems
• 5. Some plants almost
• all stem,
• no leaves
• E.g. cactus

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II. Stems

• D. Stem growth
• 1. Growth in Length only at tips of stems
  where new primary growth occurs via apical
  meristems
• 2. Growth in Circumference
• width via
• lateral meristems

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II. Stems

• E. Primary Growth in Stems
• 1. Vascular tissue arranged in
• vascular bundles
• 2. Dicots bundles in a ring around
  outside edge
• 3. Monocots bundles scattered throughout
  stem

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II. Stems
Dicot stem CS
Vascular bundles
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II. Stems

• E. Primary Growth in Stems
• 4. Pith center of the stem
• 5. Cortex ground tissue btwn.
• Vascular Bundles epidermis

Vascular bundle
monocot
dicot
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II. Stems

• F. Secondary Growth in Stems
• Which get wider year after year,
• monocots or dicots?
• DICOTS!
• Most monocots have no secondary growth.
• 1. ?stem width in dicots due to cell in
• vascular cambium

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II. Stems

• 2. Vascular Cambium arises in vascular bundle
  btwn. xylem phloem
• 3. Cylinder formed by cambium,
• then secondary xylem inside,
• then secondary phloem on outside of cylinder

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II. Stems

• G. Woody Stems
• 1. Heartwood
• 2. Sapwood
• 3. Bark
• DRAW THIS!

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II. Stems

• G. Woody Stems
• 1. Heartwood
• Dark color
• Center of tree trunk
• Dead xylem , no longer transports water
• F(x)
• support

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II. Stems

• G. Woody Stems
• 2. Sapwood
• Lighter in color
• Nearer to outside of tree trunk
• F(x) transport (live xylem)
• Note In a large diameter tree, heartwood gets
  wider, sapwood stays relatively same width

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II. Stems

• G. Woody Stems
• 3. Bark
• F(x) protection
• Made of cork, cork cambium phloem

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II. Stems

• H. Stem F(x)s
• 1. Phloem moves sugars
• a. Translocation sugars moved from
  source (photosynthesis in leaves)
• to sink (where they are stored)
• b. Products of Photosynthesis can move
• in ____?___ direction
• ANY

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II. Stems

• H. Stem F(x)s
• 1. Phloem moves sugars
• c. Pressure Flow Hypothesis
• i. Sugars PUMPED into sieve tubes
• _at_ the source
• ii. Turgor pressure increase due to water
  entering sieve tubes by osmosis

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II. Stems

• H. Stem F(x)s
• 2. Xylem moves water nutrients
• a. Cohesion-Tension Theory
• combination of 3 processes
• i. Transpiration
• ii. Cohesion
• iii. Adhesion

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Transpiration

• In leaves, release of excess water to atmosphere
• Creates negative pressure in xylem
• Replacement water pulled from xylem
• Water enters roots to replace lost water

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Cohesion

• Water molecules stick to each other pull each
  other up narrow xylem tubes
• Water is a polar molecule, therefore
• Water molecules attract each other!

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Adhesion

• Water molecules strongly attracted
• to xylem wall

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II. Stems

• b. Final words on water movement in plants
• i. Varies with time of day
• ii. Midday stomata open, rapid movement
• iii. Night stomata closed movement stops
• Exception cacti stomata open _at_ night
• Why?
• to minimize water loss