Transcript Plants require certain chemical elements to complete their life cycle

Chapter 37
Plant Nutrition
• Concept 37.1: Plants require certain chemical
elements to complete their life cycle
• Plants derive most of their organic mass from the
CO2 of air
– But they also depend on soil nutrients such as water
and minerals
CO2, the source
of carbon for
Photosynthesis,
diffuses into
leaves from the
air through
stomata.
H2O
CO2
O2
Through
stomata, leaves
expel H2O and
O2.
O2
Minerals
Figure 37.2
Roots absorb
H2O and
minerals from
the soil.
CO2
H2O
Roots take in
O2 and expel
CO2. The plant
uses O2 for cellular
respiration but is
a net O2 producer.
Macronutrients and
Micronutrients
• More than 50 chemical elements
– Have been identified among the inorganic
substances in plants, but not all of these are
essential
• A chemical element is considered essential
– If it is required for a plant to complete a life
cycle
• Essential elements in plants
Table 37.1
• Nine of the essential elements are called
macronutrients
– Because plants require them in relatively large
amounts
• The remaining eight essential elements are
known as micronutrients
– Because plants need them in very small
amounts
• The most common deficiencies
– Are those of nitrogen, potassium, and
phosphorus
Healthy
Phosphate-deficient
Potassium-deficient
Nitrogen-deficient
Figure 37.4
• Concept 37.2: Soil quality is a major
determinant of plant distribution and
growth
• Along with climate
– The major factors determining whether particular
plants can grow well in a certain location are the
texture and composition of the soil
• Texture
– Is the soil’s general structure
• Composition
– Refers to the soil’s organic and inorganic chemical
components
• Acids derived from roots contribute to a
plant’s uptake of minerals
– When H+ displaces mineral cations from clay
particles
Soil particle
–
K+
–
Cu2+
–
–
K+
–
–
–
–
K+
–
Ca2+
Mg2+
H+
H2O + CO2
H2CO3
–
HCO3 +
H+
Root hair
(b) Cation exchange in soil. Hydrogen ions (H+) help make nutrients available by displacing
positively charged minerals (cations such as Ca2+) that were bound tightly to the surface
of negatively charged
soil particles. Plants contribute H+ by secreting it from root hairs
and also by cellular respiration, which releases CO2 into the soil solution, where it reacts
with H2O to form carbonic acid (H2CO3). Dissociation of this acid adds H+ to the soil
Figure 37.6b
solution
.
• Concept 37.3: Nitrogen is often the
mineral that has the greatest effect on
plant growth
• Plants require nitrogen as a component of
– Proteins, nucleic acids, chlorophyll, and
other important organic molecules
Soil Bacteria and Nitrogen
Availability
• Nitrogen-fixing bacteria convert atmospheric
N2 to nitrogenous minerals that plants can
absorb as a nitrogen source for organic
Atmosphere
synthesis
N
N
2
2
Atmosphere
Soil
N2
Nitrogen-fixing
bacteria
Denitrifying
bacteria
H+
Nitrate and
nitrogenous
organic
compounds
exported in
xylem to
shoot system
(From soil)
Soil
+
NH4
NH3
(ammonia)
–
+
NH4
(ammonium)
Nitrifying
bacteria
NO3
(nitrate)
Ammonifying
bacteria
Organic
material (humus)
Figure 37.9
Root
• Concept 37.4: Plant nutritional
adaptations often involve relationships
with other organisms
• Two types of relationships plants have with
other organisms are mutualistic
– Symbiotic nitrogen fixation
– Mycorrhizae
The Role of Bacteria in
Symbiotic Nitrogen Fixation
• Symbiotic relationships with nitrogen-fixing
bacteria
– Provide some plant species with a built-in
source of fixed nitrogen
• From an agricultural standpoint
– The most important and efficient symbioses
between plants and nitrogen-fixing bacteria
occur in the legume family (peas, beans, and
other similar plants)
• Along a legumes possessive roots are
swellings called nodules
– Composed of plant cells that have been
“infected” by nitrogen-fixing Rhizobium bacteria
Nodules
Roots
Figure 37.10a
(a) Pea plant root. The bumps on
this pea plant root are nodules
containing Rhizobium bacteria.
The bacteria fix nitrogen and
obtain photosynthetic products
supplied by the plant.
• Inside the nodule
– Rhizobium bacteria assume a form called
bacteroids, which are contained within vesicles
formed by the root cell
5 m
Bacteroids
within
vesicle
Figure 37.10b
(b) Bacteroids in a soybean root
nodule. In this TEM, a cell from
a root nodule of soybean is filled
with bacteroids in vesicles. The
cells on the left are uninfected.
• The bacteria of a nodule
– Obtain sugar from the plant and supply the
plant with fixed nitrogen
• Each legume
– Is associated with a particular strain of
Rhizobium
• Development of a soybean root nodule
1
Infection
thread
Roots emit chemical
signals that attract
Rhizobium bacteria.
The bacteria then emit
signals that stimulate
root hairs to elongate
and to form an
infection thread by an
invagination of the
plasma membrane.
Rhizobium
bacteria
Dividing cells
in root cortex
Bacteroid
Infected
root hair
Dividing cells in
pericycle
1
2
2 The bacteria penetrate
the cortex within the
Infection thread. Cells of
the cortex and pericycle
begin dividing, and
vesicles containing the
bacteria bud into cortical
cells from the branching
infection thread. This
process results in the
formation of bacteroids.
Developing
root nodule
3
3 Growth continues in the
affected regions of the
cortex and pericycle,
and these two masses
of dividing cells fuse,
forming the nodule.
4
4 The nodule develops
vascular tissue that
supplies nutrients to the
nodule and carries
nitrogenous compounds
into the vascular
cylinder for distribution
throughout the plant.
Figure 37.11
Bacteroid
Bacteroid
Nodule
vascular
tissue
Mycorrhizae and Plant Nutrition
• Mycorrhizae
– Are modified roots consisting of mutualistic
associations of fungi and roots
• The fungus
– Benefits from a steady supply of sugar donated by
the host plant
• In return, the fungus
– Increases the surface area of water uptake and
mineral absorption and supplies water and
minerals to the host plant
• Exploring unusual nutritional adaptations
in plants
EPIPHYTES
Staghorn fern, an epiphyte
PARASITIC PLANTS
Host’s phloem
Dodder
Haustoria
Mistletoe, a photosynthetic parasite
Dodder, a nonphotosynthetic
parasite
Indian pipe, a nonphotosynthetic parasite
CARNIVOROUS PLANTS
Venus’ flytrap
Figure 37.13
Pitcher plants
Sundews