Unit 7 Plants

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Unit 7 Plants

• Ch. 23 Roots, Stems, Leaves

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Seed Plant Structure

• 3 of the principal organs of seed plants are
  roots, stems, leaves
• The root system of a plant absorbs water
  dissolved nutrients

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Seed Plant Structure

• A stem has a support system for the plant body, a
  transport system that carries nutrients, a
  defense system that protects the plant against
  predators disease
• Leaves are the plants main photosynthetic
  systems

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Plant Tissue Systems

• Plants consist of 3 main tissue systems dermal
  tissue, vascular tissue, ground tissue

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Dermal Tissue

• The outer covering of a plant, that consists of a
  single layer of epidermal cells
• The outer surfaces are often covered with thick
  waxy layer to protect against water loss injury

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Vascular Tissue

• Contains several types of specialized cells
• Xylem consists of tracheids vessel elements
• Phloem consists of sieve tube elements
  companion cells

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Vascular Tissue - Xylem

• All seed plants have a type of xylem cell called
  a tracheid, cells that resist water pressure
• Vessel elements - wide cells that form hollow
  tubes, which water can move through freely

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Vascular Tissue - Phloem

• Sieve tube elements - main cells in phloem, form
  tubes through which materials, like sugars
  other foods, are carried in a watery stream
• Companion cells - phloem cells that surround
  sieve tube elements, help movement of substances
  in out of the phloem

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Ground Tissue

• Cells that lie between dermal vascular tissues
• Consists mainly of parenchyma - cells that are
  packed with chloroplasts are the site of most
  of a plants photosynthesis

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Ground Tissue

• Collenchyma - cells that have strong, flexible
  cell walls that help support larger plants (makes
  up strings of a stalk of celery)
• Sclerenchyma - rigid cell walls that make ground
  tissue tough strong

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Plant Growth Meristematic Tissue

• Meristems - clusters of tissue that are
  responsible for continuing growth throughout a
  plants lifetime
• Meristematic tissue - undifferentiated cells,
  they have not yet become specialized for specific
  functions, such as transport

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Plant Growth Meristematic Tissue

• Apical meristem - group of undifferentiated cells
  that divide to produce increased length of stems
  roots

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Plant Growth Meristematic Tissue

• Differentiation - cells develop into mature cells
  with specialized structures functions
• As cells differentiate, they produce each of the
  tissue systems of the plant dermal, ground,
  vascular tissue

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Types of Roots

• The 2 main types of roots are taproots, found
  mainly in dicots, fibrous roots, found mainly
  in monocots
• Taproot - primary root
• Ex.) carrots, dandelions, beets, etc.

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Types of Roots

• Fibrous roots - roots that branch to such an
  extent that no single root grows larger than the
  rest
• Ex.) grass

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Root Structure Growth

• A mature root has an outsider layer, the
  epidermis, a central cylinder of vascular
  tissue
• Between these 2 tissues, lies a large
  area of ground tissue

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Root Structure Growth

• Root hairs - tiny cellular projections that
  penetrate the spaces between soil particles
  produce a large surface area through which water
  can enter the plant

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Root Structure Growth

• Cortex - spongy layer of ground tissue just
  inside the epidermis
• Endodermis - another layer of cells that
  completely encloses the roots vascular subsystem
  in a region called the vascular cylinder

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Root Structure Growth

• Root cap - protects the root as it forces its way
  through the soil

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Root Functions

• Roots anchor a plant in the ground absorb water
  dissolved nutrients from the soil

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Stem Structure Function

• Stems have 3 important functions they produce
  leaves, branches, flowers they hold leaves up
  to the sunlight they transport substances
  between roots leaves

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Stem Structure Function

• Nodes - where leaves are attached
• Internode - regions between the nodes
• Buds - contain undeveloped tissue that can
  produce new stems leaves

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Monocot Dicot Stems

• In monocots, vascular bundles are scattered
  throughout the stem
• In dicots most gymnosperms, vascular bundles
  are arranged in a cylinder

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Monocot Dicot Stems

• Vascular bundles - contains xylem phloem tissue
• Pith - the parenchyma cells inside the ring of
  vascular tissue

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Primary Growth of Stems

• Primary growth - growth occurring only at the
  ends of a plant
• Its produced by cell divisions in the apical
  meristem, takes place in all seed plants

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Secondary Growth of Stems

• Secondary growth - method of growth where stems
  increase in width
• In conifers dicots, secondary growth takes
  place in lateral meristematic tissues called the
  vascular cambium cork cambium

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Secondary Growth of Stems

• Vascular cambium - produces vascular tissues
  increases the thickness of stems over time
• Cork cambium - produces the outer covering of
  stems

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Formation of Wood

• Heartwood - older xylem near the center of the
  stem that no longer conducts water
• Sapwood - surrounds heartwood, active in fluid
  transport

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Formation of Bark

• Bark - includes all of the tissues outside the
  vascular cambium, includes phloem, the cork
  cambium, cork

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Leaf Structure

• The structure of a leaf is optimized for
  absorbing light carrying out photosynthesis

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Leaf Structure

• Blades - flattened section, attached to the stem
  by a thin stalk - petiole

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Leaf Functions

• A leaf can be considered a system specialized for
  photosynthesis
• Subsystems of the leaf include tissues that bring
  gases, water, nutrients to the cells that carry
  out photosynthesis

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Leaf Functions

• Guard cells - specialized cells in the epidermis
  that control the opening closing of stomata
  (air spaces) by responding to changes in water
  pressure

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Leaf Functions

• Plants keep their stomata open just enough to
  allow photosynthesis to take place, but not so
  much that they lose an excessive amount of water

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Leaf Functions

• Transpiration - the loss of water through its
  leaves