Plant Form and Function

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Plant Form and Function
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How are Plants Bodies Organized?

• Plants have complex organ system
• Remember groups of cells make tissues, groups of
  tissues make organs, groups of organs make organ
  systems.

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Groups and combinations of various cell types
form 3 types of tissue

• Ground tissue
• Vascular tissue
• Dermal tissue

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Ground tissue

• Composed of 3 basic cell types
• Collencyma
• Parencyma
• Schlerenchyma

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Ground tissue (GT)

• Parenchyma are most common
• Nonwoody roots, stems and leaves are made up
  primarily of GT.
• The GT composition depends upon need. E.g. large
  amounts of collencyma cells will give structure
  yet allow for flexibility while sclerencyma are
  found when structure requires for rigidity.

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Parencyma

• Parenchyma loosely packed, cube-shaped or
  elongated cells that contain a large central
  vacuole and have thin flexible cell walls. They
  are involved in many metabolic functions
  including photosynthesis, storage of water and
  nutrients, and healing.

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Collenchyma

• Collenchyma Cell walls are thicker than those
  of parenchyma cells and the cells are irregular
  in shape. They provide structure and are
  usually grouped in strands. Also provide support
  for areas of the plant that are still
  lengthening. (Celery is composed of many
  collenchyma cells.

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Sclerenchyma

• Sclerenchyma Have thick, even, rigid cell
  walls. They support and strengthen the plant in
  areas where growth is no longer occurring. This
  type of cell dies at maturity, providing a
  support framework.

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Dermal tissue

• Forms the outside covering of plants.
• In young plants it consists of the epidermis
  (outer layer composed of parenchyma cells).
• Outer layer is covered by the cuticle (prevents
  water loss).
• Some epidermal cells extend to form root hairs
  for increased water absorption.
• Stomata regulate gases exchange and water loss.
• In woody stems and roots the epidermis is
  replaced by dead cork cells.

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Vascular Tissue

• Surrounded by GT and functions in transport and
  supports.
• Xylem transports water and provides structural
  support.
• In angiosperms the xylem has 2 major components
  (both dead at maturity)
• Phloem conducts organic compounds and some
  mineral nutrients.

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Components of xylem

• Tracheids thick-walled sclerenchyma cell with
  tapering ends that moves water from one end to
  the other by means of pits (thin porous areas of
  the cell wall).
• Vessel elements are sclerenchyma cells that
  have either large holes in the top and bottom
  walls or no end walls at all. These elements are
  then stacked to form long tubes called vessels.
  Water moves more easily through vessels than
  tracheids. Angiosperms only!

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Components of Phloem

• Sieve tube member (lacks a nucleus) the
  conducting parenchyma cell of angiosperm phloem.
• Are stacked to form long sieve tubes.
• Lying next to the sieve tube cells are
  specialized parenchyma cells called companion
  cells (assists in transport).
• Phloem also contains sclerenchyma called fibers
  (like hemp, flax and jute fibers).

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Tissues group together to form organs

• Roots
• Stems
• Leaves

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Organs group together to form systems

• Shoot system (leaves and stems)
• Root system

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Primary vs. Secondary Growth
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Plant Growth

• Plant growth originates mainly in meristems,
  regions where cells continuously divide.
• Most plants grow in length through apical
  meristems located at the tips of stems and roots.
  
• Gymnosperms and most dicots also have lateral
  meristems, which allow stems and roots to
  increase in diameter.

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Apical Meristems
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Plant Growth, continued

• There are two types of lateral meristems
• The vascular cambium, located between the xylem
  and phloem, produces additional vascular tissue.
• The cork cambium, located outside the phloem,
  produces cork. Cork replaces the epidermis in
  woody stems and roots.

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Roots

• Purposes
• Achorage
• Absorption
• Storage

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Anchorage

• The primary root (the 1st root to develop)
  anchors the seed.
• Further expansion of this root allows for
  stability both for the plant and the soil.
• Types Fibrous or tap root system

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Absorption

• The epidermis of the root is very permeable to
  water.
• Root hairs expand surface area and incrase the
  roots ability to absorb water and minerals.
• Stuctures of importance include Epidermis,
  cortex, endodermis, casparian strip, pericycle as
  part of the vascular cylinder.

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Storage
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Structure of Roots
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Dicot and Monocot Root Structures
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• Primary Growth in Roots, continued
• Vascular tissue in roots matures into the
  innermost core of the root.
• The outermost layer or layers of the central
  vascular system is the pericycle. Lateral roots
  are formed by the division of pericycle cells.

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• Secondary Growth in Roots
• Dicot and gymnosperm roots often experience
  secondary growth. Secondary growth begins when a
  pericycle and other cells form a vascular cambium
  between primary xylem and primary phloem.
• The vascular cambium produces secondary xylem
  toward the inside of the root and secondary
  phloem toward the outside.