Plant Nutrition and Transport
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Plants require 16 essential elements
Section 23.1
All plants require several nutrients to stay healthy.
These plants have nutrient deficiencies.
Figure 23.2
(both): ©1991 Regents University of California Statewide IPM Project
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16 essential elements
Section 23.1
Essential elements are required for
metabolism, growth, and reproduction.
Figures 23.1, 23.2
(both): ©1991 Regents University of California Statewide IPM Project
Macronutrients | Form Taken Up by Plants | Percent Dry Weight | Selected Functions |
Carbon (C) | | 45 | Part of organic compounds |
Oxygen (O) | | 45 | Part of organic compounds |
Hydrogen (H) | | 6 | Part of organic compounds |
Nitrogen (N) | | 1.5 | Part of nucleic acids, amino acids, coenzymes, chlorophyll, ATP |
Potassium (K) | | 1.0 | Controls opening and closing of stomata, activates enzymes |
Calcium (Ca) | | 0.5 | Cell wall component, activates enzymes, second messenger in signal transduction, maintains membranes |
Magnesium (Mg) | | 0.2 | Part of chlorophyll, activates enzymes, participates in protein synthesis |
Phosphorus (P) | | 0.2 | Part of nucleic acids, sugar phosphates, ATP, coenzymes, phospholipids |
Sulfur (S) | | 0.1 | Part of cysteine and methionine (amino acids), coenzyme A |
Micronutrients | Form Taken Up by Plants | Percent�Dry Weight | Selected Functions |
Chlorine (CI) | | 0.01 | Water balance |
Iron (Fe) | | 0.01 | Chlorophyll synthesis, cofactor for enzymes, part of electron carriers |
Boron (B) | | 0.002 | Growth of pollen tubes, sugar transport, regulates certain enzymes |
Zinc (Zn) | | 0.002 | Hormone synthesis, activates enzymes, stabilizes ribosomes |
Manganese (Mn) | | 0.005 | Activates enzymes, electron transfer, photosynthesis |
Copper (Cu) | | 0.0006 | Part of plastid pigments, lignin synthesis, activates enzymes |
Molybdenum (Mo) | | 0.00001 | Nitrate reduction |
23-3
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Essential elements: macronutrients
Section 23.1
Macronutrients are required in large amounts. Carbon, oxygen, and hydrogen are the most abundant macronutrients.
Figures 23.1, 23.2
(both): ©1991 Regents University of California Statewide IPM Project
Macronutrients | Form Taken Up by Plants | Percent Dry Weight | Selected Functions |
Carbon (C) | | 45 | Part of organic compounds |
Oxygen (O) | | 45 | Part of organic compounds |
Hydrogen (H) | | 6 | Part of organic compounds |
Nitrogen (N) | | 1.5 | Part of nucleic acids, amino acids, coenzymes, chlorophyll, ATP |
Potassium (K) | | 1.0 | Controls opening and closing of stomata, activates enzymes |
Calcium (Ca) | | 0.5 | Cell wall component, activates enzymes, second messenger in signal transduction, maintains membranes |
Magnesium (Mg) | | 0.2 | Part of chlorophyll, activates enzymes, participates in protein synthesis |
Phosphorus (P) | | 0.2 | Part of nucleic acids, sugar phosphates, ATP, coenzymes, phospholipids |
Sulfur (S) | | 0.1 | Part of cysteine and methionine (amino acids), coenzyme A |
Micronutrients | Form Taken Up by Plants | Percent�Dry Weight | Selected Functions |
Chlorine (CI) | | 0.01 | Water balance |
Iron (Fe) | | 0.01 | Chlorophyll synthesis, cofactor for enzymes, part of electron carriers |
Boron (B) | | 0.002 | Growth of pollen tubes, sugar transport, regulates certain enzymes |
Zinc (Zn) | | 0.002 | Hormone synthesis, activates enzymes, stabilizes ribosomes |
Manganese (Mn) | | 0.005 | Activates enzymes, electron transfer, photosynthesis |
Copper (Cu) | | 0.0006 | Part of plastid pigments, lignin synthesis, activates enzymes |
Molybdenum (Mo) | | 0.00001 | Nitrate reduction |
23-4
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Essential elements: micronutrients
Section 23.1
Micronutrients are required in much smaller amounts.
Figures 23.1, 23.2
(both): ©1991 Regents University of California Statewide IPM Project
Macronutrients | Form Taken Up by Plants | Percent Dry Weight | Selected Functions |
Carbon (C) | | 45 | Part of organic compounds |
Oxygen (O) | | 45 | Part of organic compounds |
Hydrogen (H) | | 6 | Part of organic compounds |
Nitrogen (N) | | 1.5 | Part of nucleic acids, amino acids, coenzymes, chlorophyll, ATP |
Potassium (K) | | 1.0 | Controls opening and closing of stomata, activates enzymes |
Calcium (Ca) | | 0.5 | Cell wall component, activates enzymes, second messenger in signal transduction, maintains membranes |
Magnesium (Mg) | | 0.2 | Part of chlorophyll, activates enzymes, participates in protein synthesis |
Phosphorus (P) | | 0.2 | Part of nucleic acids, sugar phosphates, ATP, coenzymes, phospholipids |
Sulfur (S) | | 0.1 | Part of cysteine and methionine (amino acids), coenzyme A |
Micronutrients | Form Taken Up by Plants | Percent�Dry Weight | Selected Functions |
Chlorine (CI) | | 0.01 | Water balance |
Iron (Fe) | | 0.01 | Chlorophyll synthesis, cofactor for enzymes, part of electron carriers |
Boron (B) | | 0.002 | Growth of pollen tubes, sugar transport, regulates certain enzymes |
Zinc (Zn) | | 0.002 | Hormone synthesis, activates enzymes, stabilizes ribosomes |
Manganese (Mn) | | 0.005 | Activates enzymes, electron transfer, photosynthesis |
Copper (Cu) | | 0.0006 | Part of plastid pigments, lignin synthesis, activates enzymes |
Molybdenum (Mo) | | 0.00001 | Nitrate reduction |
23-5
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Soil
Section 23.1
Plant roots absorb nutrients from the soil.
Figure 23.3
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What is soil?
Section 23.1
Soil is a complex mixture of rock particles, organic matter, air, and water.
Figure 23.3
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Soil is home to many organisms
Section 23.1
Many organisms live in the soil, decomposing organic matter and releasing inorganic nutrients.
Figure 23.3
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Soil layers: litter
Section 23.1
Lying on the soil’s surface is litter, which consists of decomposing leaves and stems.
Figure 23.3
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Soil layers: humus
Section 23.1
As microbes decompose the litter, carbon dioxide is released into the atmosphere. The carbon that remains in the soil forms a layer of soil called humus.
Figure 23.3
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Soil layers: A horizon
Section 23.1
Most humus is in the topsoil (the A horizon). This layer of soil also supplies most of a plant’s water and nutrients.
Plant roots stabilize the topsoil, helping to prevent erosion.
Figure 23.3
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Soil layers: B horizon
Section 23.1
Below the topsoil is the B horizon, which has less organic matter. Roots extend into the B horizon.
Figure 23.3
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Soil layers: C horizon
Section 23.1
The C horizon mostly has weathered rocks.
Figure 23.3
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Soil layers: bedrock
Section 23.1
Below the C horizon is bedrock.
Figure 23.3
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Plants obtain nutrients from soil and air
Section 23.1
Symbiotic relationships with nitrogen-fixing bacteria help plants obtain useful forms of nitrogen.
Figure 23.4
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How plants obtain nutrients: nodules
Section 23.1
Some nitrogen-fixing bacteria live in growths called nodules on the roots of plants.
Figure 23.4
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How plants obtain nutrients: roots
Section 23.1
Plants take up other nutrients through their roots as well. These nutrients dissolve in the soil’s water and move into the plant as it absorbs water.
Figure 23.5
Nitrogen, potassium, calcium, etc. dissolved in water
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How plants obtain nutrients: gas exchange
Section 23.1
Figure 23.5
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Vascular tissue transports substances
Section 23.2
Vascular tissue forms the transportation system that connects plant parts.
Xylem and phloem function in different ways.
Figure 23.5
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Vascular tissue transport: xylem
Section 23.2
First, let’s look at how water and minerals are pulled up to leaves in xylem.
Figure 23.5
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Xylem transports water and minerals
Section 23.2
Xylem transport is explained by cohesion-tension theory. Cohesion is the tendency for water molecules to form hydrogen bonds with one another.
Figure 23.7
Transpiration: Water molecules evaporate from leaves.
Xylem transport: Water molecules are Pulled up stem.
Absorption: Water molecules are pulled into roots.
23-21
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Xylem and water transport: transpiration
Section 23.2
Because of cohesion, when water evaporates from the leaves, in a process called transpiration, it pulls adjacent molecules closer to the stomata.
Figure 23.7
Transpiration: Water molecules evaporate from leaves.
Xylem transport: Water molecules are Pulled up stem.
Absorption: Water molecules are pulled into roots.
23-22
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Xylem and water transport: diffusion
Section 23.2
As the concentration of water within the mesophyll decreases, water molecules diffuse out of nearby veins. Those molecules, in turn, pull neighboring water molecules up the xylem.
Figure 23.7
Transpiration: Water molecules evaporate from leaves.
Xylem transport: Water molecules are Pulled up stem.
Absorption: Water molecules are pulled into roots.
23-23
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Xylem transports water into tissues
Section 23.2
This movement of water molecules is repeated all the way down the xylem. Along the way, water molecules diffuse into “thirsty” tissues.
Figure 23.7
Transpiration: Water molecules evaporate from leaves.
Xylem transport: Water molecules are Pulled up stem.
Absorption: Water molecules are pulled into roots.
23-24
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Xylem and water transport: Casparian strip
Section 23.2
Water molecules are pulled in to roots. The Casparian strip is a waxy barrier that ensures all incoming material passes through cells.
Figure 23.6
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Xylem and water transport: stomata
Section 23.2
A waxy layer on leaves called the cuticle helps prevent water loss.
Also, pores in leaves called stomata close when the plant needs to conserve water.
Figure 23.8
Water: abundant|Stomata: open|Gas exchange: yes
Water: scarce|Stomata: closed|Gas exchange: no
(both): ©Ray Simons/Science Source
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Xylem and water transport: guard cells
Section 23.2
Guard cells determine whether a stoma is open or closed.
Figure 23.8
Water: abundant|Stomata: open|Gas exchange: yes
Water: scarce|Stomata: closed|Gas exchange: no
(both): ©Ray Simons/Science Source
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Phloem pushes sugars
Section 23.3
Now, let’s see how sugars are pushed to nonphotosynthetic cells in phloem.
Figure 23.5
23-28
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Phloem and sugar transport: sources
Section 23.3
The green leaves of this strawberry plant are sugar “sources” because they carry out photosynthesis.
Figure 23.10
Loading at the source
Solutes (sugars produced in photosynthesis) enter a sieve tube by active transport.
Water enters the sieve tube from the xylem by osmosis, increasing pressure in the sieve tube.
Phloem transport in sieve tube
Pressure pushes the solutes toward the sink.
Unloading at the sink
As the sink is reached, solutes are unloaded by facilitated diffusion or active transport into the sink cells.
Water moves out of the pholem to the xylem by osmosis, decreasing pressure in the sieve tube.
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Phloem and sugar transport: sinks
Section 23.3
Roots and fruits, which require sugar but do not carry out photosynthesis, are “sinks.”
Figure 23.10
Loading at the source
Solutes (sugars produced in photosynthesis) enter a sieve tube by active transport.
Water enters the sieve tube from the xylem by osmosis, increasing pressure in the sieve tube.
Phloem transport in sieve tube
Pressure pushes the solutes toward the sink.
Unloading at the sink
As the sink is reached, solutes are unloaded by facilitated diffusion or active transport into the sink cells.
Water moves out of the pholem to the xylem by osmosis, decreasing pressure in the sieve tube.
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Phloem and sugar transport: pressure flow
Section 23.3
According to pressure flow theory, phloem sap moves from high pressure at sources to low pressure at sinks. Water movement causes the pressure changes in the phloem tissue.
Figure 23.10
Loading at the source
Solutes (sugars produced in photosynthesis) enter a sieve tube by active transport.
Water enters the sieve tube from the xylem by osmosis, increasing pressure in the sieve tube.
Phloem transport in sieve tube
Pressure pushes the solutes toward the sink.
Unloading at the sink
As the sink is reached, solutes are unloaded by facilitated diffusion or active transport into the sink cells.
Water moves out of the pholem to the xylem by osmosis, decreasing pressure in the sieve tube.
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Phloem and sugar transport: pathway of sugar flow
Section 23.3
First, sugars are actively transported from photosynthetic cells to companion cells and then into the sieve tube.
Figure 23.10
Loading at the source
Solutes (sugars produced in photosynthesis) enter a sieve tube by active transport.
Water enters the sieve tube from the xylem by osmosis, increasing pressure in the sieve tube.
Phloem transport in sieve tube
Pressure pushes the solutes toward the sink.
Unloading at the sink
As the sink is reached, solutes are unloaded by facilitated diffusion or active transport into the sink cells.
Water moves out of the pholem to the xylem by osmosis, decreasing pressure in the sieve tube.
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23-32
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Phloem receives water from the xylem
Section 23.3
Then, water moves by osmosis from xylem into the sieve tube, increasing sieve tube pressure.
Figure 23.10
Loading at the source
Solutes (sugars produced in photosynthesis) enter a sieve tube by active transport.
Water enters the sieve tube from the xylem by osmosis, increasing pressure in the sieve tube.
Phloem transport in sieve tube
Pressure pushes the solutes toward the sink.
Unloading at the sink
As the sink is reached, solutes are unloaded by facilitated diffusion or active transport into the sink cells.
Water moves out of the pholem to the xylem by osmosis, decreasing pressure in the sieve tube.
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23-33
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Pressure pushes sugars towards the sink
Section 23.3
This pressure pushes the sugars toward the sink.
Figure 23.10
Loading at the source
Solutes (sugars produced in photosynthesis) enter a sieve tube by active transport.
Water enters the sieve tube from the xylem by osmosis, increasing pressure in the sieve tube.
Phloem transport in sieve tube
Pressure pushes the solutes toward the sink.
Unloading at the sink
As the sink is reached, solutes are unloaded by facilitated diffusion or active transport into the sink cells.
Water moves out of the pholem to the xylem by osmosis, decreasing pressure in the sieve tube.
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Sugars are deposited in the sink
Section 23.3
At the sink, transport proteins move sugars out of the sieve tube. Since the solute concentration in the phloem decreased, water leaves the sieve tube by osmosis.
Figure 23.10
Loading at the source
Solutes (sugars produced in photosynthesis) enter a sieve tube by active transport.
Water enters the sieve tube from the xylem by osmosis, increasing pressure in the sieve tube.
Phloem transport in sieve tube
Pressure pushes the solutes toward the sink.
Unloading at the sink
As the sink is reached, solutes are unloaded by facilitated diffusion or active transport into the sink cells.
Water moves out of the pholem to the xylem by osmosis, decreasing pressure in the sieve tube.
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Why fruits are sweet
Section 23.3
Transport of sugars from sources to sinks explains how non-photosynthetic cells obtain sugars (and why fruits are often sweet).
Figure 23.10
Loading at the source
Solutes (sugars produced in photosynthesis) enter a sieve tube by active transport.
Water enters the sieve tube from the xylem by osmosis, increasing pressure in the sieve tube.
Phloem transport in sieve tube
Pressure pushes the solutes toward the sink.
Unloading at the sink
As the sink is reached, solutes are unloaded by facilitated diffusion or active transport into the sink cells.
Water moves out of the pholem to the xylem by osmosis, decreasing pressure in the sieve tube.
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Xylem and phloem
This figure summarizes xylem and phloem transport.
Figure 23.14
23-37
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Phloem parasites
Section 23.4
Parasitic plants tap into the vascular tissue of other plants. Mistletoe roots push through the epidermis of this tree, connecting to its xylem and phloem.
Figure 23.11
©Mark Boulton/Alamy
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