Roots, Stems and Leaves

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Roots, Stems and Leaves

• Chapter 23 Biology II

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Structure of Seed Plants

• Roots
• Stems
• Leaves

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Roots

• Branching networks in the soil
• Absorb water
• Dissolve nutrients from moist soil
• Anchor plants in the ground
• Hold plants upright

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Stems

• Supports the plant body
• Transports nutrients within the plant
• Tall stems hold leaves up to the sun, up to 100 m
  tall
• Vascular tissues within supply the plant with
  water and nutrients

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Stem Variations
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Leaves

• Principal organs for photosynthesis
• Broad, flat surface increases SA for sunlight
  absorption
• Adjustable pores conserve water and allow for the
  exchange of gases

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Leaves
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Meristematic Tissue

• The only plant tissue that produces new cells by
  mitosis
• All the cells of a plant originate in meristems
  and look alike

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Meristematic Tissue

• Eventually divide into the 3 main tissues of a
  plant
• Found at the end, or tip of each growing stem and
  root apical meristem

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Apical Meristems
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Tissue Systems

• Dermal
• Vascular
• Ground

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Dermal Tissue

• The outer covering of a plant
• Called epidermal cells in non-woody plants
• Covered with a thick, waxy cuticle that protects
  against water loss and injury

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Dermal Tissue

• Trichomes tiny cellular projections which help
  protect the leaf and give it a fuzzy appearance
• Roots root hair cells
• Leaves underside guard cells

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Vascular Tissue

• Transports water and nutrients throughout the
  plant
• Xylem water-conducting tissue
• Phloem food-conducting tissue

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Xylem

• Tracheids long, narrow cells with walls
  impermeable to water
• Have openings that connect neighboring cells to
  one another
• Mature and die their cytoplasm disintegrates

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Xylem

• Vessel Elements found in angiosperms wider than
  tracheids
• Arranged end to end, on top of each other, like a
  stack of tin cans
• When the cell dies the cell walls at the end die,
  making one long tube

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Phloem

• Sieve Tube Elements cells arranged end to end to
  form sieve tubes
• The end walls have many holes in them
• As the mature, they lose most nuclei and
  organelles the space becomes a pipeline for
  sugar and other foods to be carried

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Phloem

• Companion Cells surround sieve tube elements
• Keep their nuclei and other organelles throughout
  their lifetime
• Support the phloem cells
• Aid in the movement of substances in and out of
  the phloem stream

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Ground Tissue

• The cells between dermal and vascular tissues

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Ground Tissue Parenchyma

• Ground-tissue cell with a thin cell wall and a
  large central vacuole
• Site of the most of a plants photosynthesis

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Ground Tissue Collenchyma

• Ground-tissue cell with a strong, flexible cell
  wall
• Helps support larger plants

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Ground Tissue Sclerenchyma

• Ground-tissue cell with an extremely thick, rigid
  cell wall
• Makes ground tissue tough and strong

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Types of Roots Taproots

• Found mainly in dicots
• Primary root grows long and thick
• Secondary roots remain small
• Long taproots Oak trees, hickory trees,
• Short taproots carrots, dandelions, beets, etc.

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Types of Roots Fibrous Roots

• Found mainly in monocots
• Branch to such an extent that no single root
  grows larger than the rest
• Helps prevent topsoil from being washed away by
  heavy rain

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Root Structure and Growth
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Root Root Hairs

• Tiny projections from the outer surface, or
  epidermis, of a root

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Root Cortex

• Spongy layer of ground tissue just inside the
  epidermis of a root

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Root Endodermis

• Layer of cells that completely encloses vascular
  cambium

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Root Vascular Cylinder/Cambium

• Central region of a root that includes the
  vascular tissue-xylem and phloem

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Root Root Cap

• Tough structure that protects a root as it forces
  its way through the soil