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Ch 10-Roots and Plant Nutrition
Roots play a variety of roles in plants
-roots anchor plants and absorb water and minerals
-some roots are useful as human food
-roots are important sites of hormone production
-the roots of some plants help support stems
-human use of roots
Roots anchor plants and absorb water and minerals
When seeds germinate, the first plant
organ to emerge is the root.
As the plant develops, the primary root
is replaced by a more extensive,
branched root system.
Some roots are useful as human food
http://www.foodofy.com/wpcontent/uploads/2015/06/sweetpotato-2.jpg
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https://www.morningagclips.com/swee
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http://www.turniprecipes.co.uk/types-of-turnip/
Roots play a variety of roles in plants
Roots are important sites of hormone production
The roots of some plants help support stems
Buttress roots
These roots aid tropical plants
growing in thin soils.
Aerial roots
Rope-like roots from tree
branches which anchor in the soil.
Prop roots in corn
Human uses of roots
Spruce roots are used by
Native Americans in the
construction of traditional
birch bark canoes.
Thirty-five percent of the world’s
sugar comes from the roots
of sugar beets (Beta vulgaris).
In pre-modern Europe, human-shaped
roots of the mandrake plant, Mandragora
officinarum, were thought to indicate
special powers, and extracts used as a
pain reliever and anesthetic.
Plants produce specialized roots
Pneumatophores
The pneumatophores grow upward Into the
air and absorb oxygen through lenticels.
Contractile roots
Common in dandelions.
Epiphytic plants that grow nonparasitically on other
plants have specialized roots.
Ex: The “flower pot plant”
Dischidia rafflesiana
There are two major types of root system:
1) Fibrous root system
Annual grasses generally have fibrous root systems.
2) Tap root system.
Carrots and radishes have tap roots.
Adventitious roots develop from the shoot system.
Adventitious roots in tomato
Prop roots in corn
Root structure
-External root structure
The branch roots and main root axis are covered with an epidermis.
Branch roots or lateral roots
The branch roots decrease in age from the soil surface to
the root tip. (youngest branches at the root tip)
(youngest branches at the root tip)
Numerous root hairs
At the root tip is the root apical meristem, RAM
This is the region of meristematic cells which divide rapidly and
increase the number of cells in the main portion of the root.
Root cap
The root cap protects the RAM
The cells in the root cap are generated by the RAM
Mucigel
The tips of the root are embedded in mucigel.
Mucigel is a gluey polysaccharide produced by the Golgi
of the root tip epidermal cells.
Internal view of the roots
The last few millimeters of a root tip consists of 4 major
zones:
1)Root cap
2)The root meristem, a zone of cell division
3) The elongation zone
4) The zone of maturation
Root apical meristem gives rise to 3 precursor tissues:
During tissue specialization, procambium gives rise to the mature vascular tissues.
Protoderm develops into the epidermis of young roots
Ground meristem produces tissue known as the cortex
Monocot Root
Eudicot Root
endodermis
pericycle
pith
cortex
cortex
phloem
xylem
Cortex
-air spaces provide oxygen to diffuse through roots
Vascular cylinder
Endodermis – cells of the innermost cortex layer that forma waterproof barrier
between the cortex and vascular cylinder
Water and minerals that have entered roots via cell walls cannot cross the endodermis to the vascular tissue
(xylem and phloem).
Casparian strip
Endodermal cell walls of dicots have a strip of water repellent
material, suberin, that forms the Casparian strip on the top,
bottom,and side walls.
Walls facing inward and outward do not.
Water from the cortex can move through the cell
walls without suberin.
Dissolved minerals can enter the cytoplasm of
endodermal cells if their cell membranes contain
the appropriate transporter protein.
The primary vascular system includes:
-a surrounding cylinder of tissue known as the
pericycle
The pericycle produces branch roots.
Branch roots start to form while embedded in the root tissue.
The branch roots push through the cortex to the surface.
In plants with woody roots, cell division in the pericycle
contributes to the formation of vascular cambium to
generate secondary xylem and phloem.
Epidermal Root Hairs
Root hairs may reach
1.3 cm, but most root
hairs are only about
10 um in diameter.
Epidermal Root Hairs
As root hairs develop,their cell membranes become embedded
with proteins that selectively transport materials from
the environment into the root hair cytoplasm.
ATP is hydrolyzed to drive the uptake process
through an electrochemical gradient.
As the protons move back into the cell through the
transporter protein, a mineral ion is carried with it.
Root xylem obtains minerals and water in 2 different ways:
Symplastic transport-
Apoplastic transport-
Study outline for Chapter 10-Roots and Plant Nutrition
List the 4 major roles of roots in the plant.
Name some examples of roots that are useful for human food.
Define the following terms and label the figures below.
-buttress roots
-aerial roots
-prop roots
-pneumatophores
-contractile roots
roots that support stems
specialized roots
Explain how the following root examples are used by humans.
-spruce roots
-sugar beets (Beta vulgaris)
-mandrake (Mandragora officinarium)
Draw and label the two major types of root systems. Give an example for each type of root system.
Define the following terms of root external structure and label the figure below.
-branch roots/lateral roots
-epidermis
-root hairs
-root apical meristem (RAM)
-root cap
-mucigel
Study outline for Chapter 10-Roots and Plant Nutrition
The root apical meristem (RAM) gives rise to 3 precursor tissues in the root.
Fill in precursor tissues and tissue systems.
Precursor tissues
Tissue systems in root
What are the main differences between a eudicot root and a monocot root?
Label the figure below with following terms and give the function of each term.
-epidermis
-cortex
-endodermis
-pericycle
-xylem
-phloem
Label the figure below with the following terms: root hair, epidermis, cortex, endodermis, Casparian strip, pericycle,
xylem, phloem, plasmodesmata, air space, apoplastic route, symplastic route and transport protein.
Explain the difference between symplastic transport and apoplastic transport of minerals and water in the root.