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Plant Nutrition
Chapter 38
Plants
Shoots - above ground
Roots - below ground
dependent on each other.
Fig. 35.2
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Roots would starve without the sugar produced in the photosynthetic tissues of the shoot.
The shoot system depends on water and minerals absorbed from the soil by the roots.
• Shoots - stems and leaves.
• vegetative (leaf bearing) or
reproductive (flower bearing).
• Stem has nodes, leaves attached, and
internodes, segments between nodes.
• Growth of a young shoot is at its
terminal bud
• axillary bud - branch.
The presence of a terminal bud
inhibits the growth of axillary
buds, a phenomenon called
apical dominance.
Fig. 35.2
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
A plant is capable of indeterminate growth because it has perpetually
embryonic tissues called meristems in its regions of growth.
Indeterminate growth vs. Determinate growth
Apical meristems, elongation for
primary growth of
roots and shoots
Woody plants also
show secondary
growth, thickening of
roots and shoots due
to lateral meristems
• Modified shoots stolons, rhizomes, tubers, and bulbs, are often mistaken
for roots. Asexual reproduction.
•
Leaves are the main photosynthetic organs of most plants, but green stems are
also photosynthetic.
– leaves consist of a flattened blade, the petiole, which joins the leaf to a stem
node.
Monocots have parallel major veins length of the blade
Dicot have a multibranched network of major veins.
Roots anchor the plant in the soil, absorb minerals
and water, and store food.
Fig. 35.2
Copyright © 2002 Pearson Educati on, Inc., publishi ng as Benjami n Cummi ngs
Monocots have fibrous root systems.
Dicots have taproots.
• Most absorption of water and minerals in both
systems occurs near the root tips, where vast
numbers of tiny root hairs increase the surface
area enormously.
• Root hairs are extensions
of individual epidermal
cells on the root surface.
Fig. 35.3
Cop yright © 2002 P ear son Education, Inc., pub lis hing as B enjamin Cummings
Plants, photosynthetic autotrophs
transform inorganic compounds into organic ones.
A plant needs sunlight as its energy source for photosynthesis and
CO2 and inorganic ions, to synthesize organic molecules.
Roots, through
root hairs, absorb water and
minerals from the soil.
Carbon dioxide diffuses into
leaves from the surrounding
air through stomata.
Essential nutrients
If the absence of a particular mineral causes a
plant to become abnormal when compared to
controls grown in a complete medium, then
that element is essential.
Macronutrients - Elements required by plants in relatively large quantities
• There are 9 macronutrients : carbon, oxygen, hydrogen, nitrogen, sulfur,
phosphorus, potassium, calcium, and magnesium.
• Micronutrients - Elements that plants need in very small amounts
• The 8 micronutrients are iron, chlorine, copper, zinc, magnanese, molybdenum,
boron, and nickel.Most of these function as cofactors of enzymatic reactions.
• Loams,
equal amounts of sand, silt and clay.
Loamy soils provide a large surface area for retaining minerals and water
provide air spaces(oxygen) to the root for cellular respiration.
• Cation exchange The soil pH affects cation exchange and influences the
chemical form of all minerals.
• Even though an essential element may be abundant in the soil, plants may
be starving for that element because it is bound too tightly to clay or is in a
chemical form that the plant cannot absorb.
The atmospheres is nearly 80% nitrogen, but plants cannot use nitrogen in the form of N2.
It must first be converted to ammonium (NH4+) or nitrate (NO3-).
Nitrogen is lost from this local cycle when soil microbes called denitrifying bacteria
converts NO3- to N2 which diffuses to the atmosphere.
Other bacteria, nitrogen-fixing bacteria, restock nitrogenous minerals in the soil by
converting N2 to NH3 (ammonia), via nitrogen fixation.
A legume’s roots have swellings called nodules, composed of
plant cells that contain nitrogen-fixing bacteria of the genus
Rhizobium.
Inside the nodule, Rhizobium bacteria assume a form called
bacteriods, which are contained within vesicles formed by
the root cell.
Parasitic plants
extract nutrients from other plants
Carnivorous plants supplement
their mineral nutrition by
digesting animals
• Living in acid bogs and other habitats where soil
conditions are poor are plants that fortify themselves by
occasionally feeding on animals.