Chapter 34: Roots and Minerals

Roots-more extensive than shoot
ex. cornplant- 4 ft. tall, roots 8 ft. deep and 4 ft. across

  1. anchorage
  2. absorbing/absorbtion (water, minerals)
  3. storage ( surplus sugar stored in roots) (tap roots- carrots, beets, radished, turnips) (fibrous roots- sweet potatoes, yams

Tap roots- one main root, develops from embryonic root in seed (radicle)
tap root dies, surface roots form (lateral and shallow)
exception-Hickory tap roots do not die

Fibrous Root Systems
  1. embryonic root dies early on and is replaced by meristematic tissue at bottom of stem
  2. adventitious- roots that develop from stem tissue, not embryonic roots
  3. taproots- absorbs deep ground water
  4. fibrous- absorbs water on surface (rain)

Exterior Structure

root cap- protects meristem, replaced by mitosis(apical meristem)
  1. root cap cells- gravity detectors
  2. if root cap is cut, root cap eventually regenerates and directs roots in proper direction
Root hairs- extensions, short-lived, 1 cm(.5 inch)

Transport in xylem- one-way movement
  1. water moves horizontally into root
  2. meets xylem, moves vertically: PASSIVE
  3. pull from top, explained by tension/cohesion theory
  4. cohesion strong enough to pull water up 500 ft.
  5. cohesion due to water being a polar molecule

Root Pressure: ?push? on water, works in spring (moist soil)
  1. plant cells split ATD, use energy to pump ions to xylem
  2. water follows by osmosis
  3. have upward and increase water pressure in xylem
  4. forces water upwards: guttation

Sugar Movement: sugar is formed during dark reaction of photosynthesis

photosynthesis>>>glucose>>>fructose/sucrose(disaccharide)>>>loaded into phloem (sieve tube)>>> Sink(roots, meristems, flowers, fruits)

parenchymal in mesophyll (Source)

Pressure flow hypothesis:
  1. high pressure>>>low pressure
  2. linked cotransport: H+ gradient pulls in sugar
  3. also transports plant hormones, ATP, amino acid, ions(K+, Na+) and pathogens (ex. Tobacco mosaic virus

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