Biology, Seventh Edition
Solomon • Berg • Martin
Chapter 34
Roots and Mineral
Nutrition
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Taproot system has
• One main root formed from the
radicle
• Multiple lateral roots extending
from the main root
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Fibrous root system has
• Multiple adventitious roots of the
same size (developing from the
end of the stem)
• Multiple lateral roots branching
off from the adventitious roots
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Taproot
system
Fibrous root
system
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
LM of a
lateral root
Lateral roots
originate at
the pericycle
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Primary roots have
• An epidermis
• Ground tissues
–Cortex and sometimes pith
• Vascular tissues
–Xylem and phloem
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Ranunculus root
Cortex
comprises the
bulk of
herbaceous
dicot roots; note
X-shaped xylem
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Closeup of the root’s stele
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Primary roots, cont.
• Each root tip is covered by a root
cap whose function is to
–Protect the delicate root apical
meristem
–Orient the root so that it grows
downward
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
LM of a
Quercus sp.
root tip
showing its
root cap.
The root
apical
meristem is
protected
by the root
cap
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Primary roots, cont.
• Epidermis protects the root
• Root hairs are short-lived
extensions of epidermal cells
–Increase surface area of root in
contact with soil
–Aid in absorption of water and
dissolved nutrient minerals
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Root hairs on a radish seedling
(length approx. 5 cm)
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Cortex consists of parenchyma
cells that often store starch
• Endodermis
–Is innermost layer of cortex
–Regulates movement of nutrient
minerals into root xylem
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Endodermal cells
• Have a Casparian strip around
their radial and transverse walls
–Strip is impermeable to water and
dissolved nutrient minerals.
• Have carrier proteins in their
plasma membranes
–Proteins actively transport nutrient
minerals
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Endodermis and nutrient mineral uptake
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Root’s stele, or vascular
cylinder, consists of
• Pericycle
• Xylem
• Phloem
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Pericycle gives rise to
• Lateral roots
• Lateral meristems
• Xylem conducts
• Water
• Dissolved nutrient minerals
• Phloem conducts
• Dissolved sugar
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Monocot roots
• Often consist of pith surrounded
by a ring of alternating bundles of
–Xylem
–Phloem
• Lack a vascular cambium and
therefore do not have secondary
growth
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
LM of a
cross
section of
a
monocot
root
(Smilax)
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Herbaceous dicot roots
• Xylem forms a solid core in the
centre of the root
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Pathway of water and nutrient
mineral ions
• Root hair/epidermis
• Cortex
• Endodermis
• Pericycle
• Root xylem
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Water and dissolved nutrient
minerals move through
epidermis and cortex along
• Either the apoplast (along
interconnected porous cell walls)
• Or the symplast (from one cell’s
cytoplasm to the next through
plasmodesmata)
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Pathways of water and dissolved
nutrient minerals in the root
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Roots of gymnosperms and
woody dicots develop
secondary tissues
• Production of these is result of
• Activity of two lateral meristems
• Vascular cambium
• Cork cambium
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CHAPTER 34 Roots and Mineral Nutrition
• Vascular cambium produces
• Secondary xylem (wood)
• Secondary phloem (inner bark)
• Cork cambium produces
• Periderm (outer bark)
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
The tissues in a
primary root
At onset of
secondary growth,
vascular cambium
extends out to
pericycle, forming
continuous, noncircular loop
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Vascular
cambium
produces
secondary xylem
to its inside and
secondary
phloem to its
outside
Ring of
vascular
cambium
gradually
becomes
circular
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Prop roots
• Develop either from branches or
from a vertical stem
• Grow downwards into the soil to
help support certain plants in an
upright position
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CHAPTER 34 Roots and Mineral Nutrition
• Buttress roots
• Have swollen bases or braces
• Support certain tropical rainforest
trees that have shallow root
systems
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Pneumatophores
• Aerial “breathing” roots
• May assist in getting oxygen to
submerged roots
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Some epiphytes
• Have roots modified to
photosynthesize
• Absorb moisture
• Or, if parasitic, penetrate host
tissues
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CHAPTER 34 Roots and Mineral Nutrition
• Corms and bulbs
• Often have contractile roots
–These grow into the soil and then
contract
–Corm or bulb is thereby pulled
deeper into the soil
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Mutualistic relationships
between roots and other
organisms
• Mycorrhizae
• Root nodules
• Root grafts
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Mycorrhizae
• Mutually beneficial associations
between
–Roots
–Soil fungi
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CHAPTER 34 Roots and Mineral Nutrition
LM of ectomycorrhizae
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CHAPTER 34 Roots and Mineral Nutrition
LM of endomycorrhizae
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Root nodules
• Swellings that develop on roots of
leguminous plants
• Swellings house millions of
rhizobia (nitrogen-fixing bacteria)
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Root graft
• Natural connection between roots
of trees belonging to the same or
different species
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Factors influencing soil
formation include
• Parent material
• Climate
• Organisms
• Passage of time
• Topography
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Most soils are formed from
parent material that is broken
into smaller and smaller
particles by weathering
processes
• Climate and organisms work
together in weathering rock
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Important in forming soil and in cycling
nutrient materials are organisms such as
•
•
•
•
•
•
•
Plants
Algae
Fungi
Worms
Insects
Spiders
Bacteria
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Topography affects soil
formation
• Steep slopes have little or no
soil on them
• Moderate slopes often have
deep soils
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Soil is composed of
• Inorganic minerals
• Organic matter
• Air
• Water
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Inorganic minerals provide plants
with
• Anchorage
• Essential nutrient minerals
• Organic matter
• Increases soil’s water-holding
capacity
• Releases essential nutrient minerals
into the soil as it decomposes
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CHAPTER 34 Roots and Mineral Nutrition
• Soil air provides oxygen for soil
organisms to use during aerobic
respiration
• Soil water provides water and
dissolved nutrient minerals to
plants and other organisms
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Cation exchange
• Cations are attracted and
reversibly bound to clay particles
• Clay particles have
predominantly negative charges
on their outer surfaces
• Roots secrete protons (H+)
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Cation exchange, cont.
• Protons are exchanged for other
positively charged mineral ions
• Mineral ions are freed into the
soil water to be absorbed by
roots
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Cation exchange
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
How acid
alters soil
chemistry
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Ten of the nineteen essential
elements plants require are
macronutrients
(required in quantity)
• Carbon
• Oxygen
• Potassium
• Magnesium
• Sulfur
•
•
•
•
•
Hydrogen
Nitrogen
Calcium
Phosphorus
Silicon
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Nine of the elements are
micronutrients
(required in trace amounts)
• Chlorine
• Iron
• Boron
• Manganese
• Sodium
•
•
•
•
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Zinc
Copper
Nickel
Molybdenum
Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Diversity of
life in fertile
soil
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Mineral depletion
• May occur in farmed soils
–Because natural pattern of nutrient
cycling is disrupted when crops are
not allowed to decompose into soil
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
• Soil erosion
• Removal of soil from land by
agents such as
–Water
–Wind
• Causes decrease in soil fertility
–Because essential nutrient minerals
and organic matter are removed
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Biology, Seventh Edition
CHAPTER 34 Roots and Mineral Nutrition
Copyright © 2005 Brooks/Cole — Thomson Learning