Roots

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Roots
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Roots

• Originally deemed the part of the plant that grew
  underground, but with the evolution of aerial
  roots (ones that grow above ground) and aerating
  roots (ones that grow upward especially above
  water), the definition has changed.

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Roots

• The better definition of a root is the part of
  the plant body that bears no leaves and therefore
  has no nodes (places where branches come up).

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Root Functions

• The major functions of roots are
• Anchor the plant
• 2) Absorb water and inorganic nutrients

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Root Functions

• Roots also can act as storage organs for the
  plant
• They also enter into a symbiotic relationship
  with fungi and/or bacteria in the soil in order
  to obtain nutrients easier.

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Root Morphology

• The tip of each root has a conical covering of
  tissue known as the root cap.
• Underneath the root cap lies the apical meristem,
  which is the root region undergoing mitosis in
  order to grow and push the root through the soil.

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Root Morphology

• The outer surface of the root is known as the
  epidermis.
• The epidermis produces outgrowths known as root
  hairs that increase the surface area for
  absorption.
• Root hairs typically only live a few days before
  they are replaced by new ones.

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Root Morphology

• Under the epidermis lies the cortex whose primary
  role is starch storage.
• The innermost layer of the cortex is the
  endodermis (containing Casparian Strips) which
  acts as a barrier to nutrients, preventing them
  from passively entering the vascular tissue.
• This allows the plant to accumulate lots of
  minerals in its roots.

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Root Morphology

• Inside the endodermis lies the vascular tissue.
• This is where water and nutrients start their
  journey up the plant.
• It is also an area of sugar movement or storage
  depending on the environmental conditions.

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Dicot Roots
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Monocot Roots
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Root Growth

• Roots will grow in the direction of the correct
  oxygen, moisture and nutrient levels for plant
  growth.
• Primary growth is elongation whereas secondary
  growth is an increase in diameter.

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Root Systems

• There are two main types of root systems
• 1) Taproot system where there is a large primary
  root with lots of smaller, secondary roots
  emerging from it. It is found mostly in dicots
  where starch storage is key.

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Root Systems

• 2) Fibrous System where there is no primary root
  and all roots are similar in size. They jut out
  in all directions. Found commonly in monocots.
  The main function is anchorage.

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Monocot and Dicot Roots
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Roots (below ground)

• The first structure to appear when a seed
  germinates and is called the radicle in the
  embryo.
• The function of the root system is to absorb
  water and nutrients from the soil for the growing
  plant, as well as providing a stable anchor.

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• Water is absorbed by a process called OSMOSIS
  (Note Root cells are usually hypertonic to soil,
  so water will enter the cells passively by
  osmosis.)
• The walls of root cells are very thin and have a
  large surface area.
• The depth of the root depends on the moisture
  content of the soil.

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General Structure

• Each root has a meristemic area near its tip to
  allow for growth.
•  At the tip of each root is a cluster of cells
  forming the root cap these cells produce a
  mucus-like substance which lubricates the
  movement of the root through the soil.
• Root hairs increase surface area of the epidermis
  increasing absorption of nutrients and water.

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Some definitions

• Xylem a series of pipes running through the
  roots, stems and leaves carrying water through
  plant
• Phloem carries food and dissolved materials
  through plant
• Vascular Cylinder central portion of a root
  that contains the xylem and phloem

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Monocot Roots

• fibrous roots (many branched roots of equal size)
• Examples grasses, grains, corn
• Cross Section
• - separate strands of xylem and phloem alternate
  around a pith-like region

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Monocot root
epidermis
Vascular Cylinder
cortex
xylem
phloem
pith/parenchyma
endodermis
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Note the xylem and phloem in these differently
stained monocot roots.
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Dicot Roots

• tap roots (1 large main root and smaller lateral
  roots)
• Examples carrots, beets, beans, dandelions, most
  trees
• Cross Section
• xylem is irregular and a solid strand
• phloem is arranged in separate strands

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Dicot root
Vascular Cylinder
epidermis
cortex
phloem
xylem
NO pith/parenchyma
endodermis
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Note the xylem and phloem in these differently
stained dicot roots.
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More Definitions

• Epidermis - provides protection and regulates
  water movement
• - epidermal cells can elongate and form root
  hairs which increase the surface area for water
  absorption

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• Cortex - the innermost layer of cortex cells is
  called the endodermis
• - the endodermal cells are coated with a waxy
  layer called the casparian strip (this prevents
  water from moving in the spaces between the
  endodermal cells)

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Lab Activity

• Look at monocot and dicot root slides using the
  microscope.
• Describe how to tell the difference between
  monocot and dicot roots.

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Home Fun?

• Read 558-563
• Describe
• a) cortex
• b) endodermis
• c) Casparian strip
• d) vascular cylinder 
• e) pith/parenchyma
• Do P. 5634