Table of Contents

1
Uptake and Movement of Water and Solutes

• Water enters the plant through osmosis, but the
  uptake of minerals requires transport proteins
• Why does water move into the root from the soil?
• Moves into due to water potential difference.

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Figure 36.1 The Pathways of Water and Solutes in
the Plant
3
Uptake and Movement of Water and Solutes

• The force exerted by the rigid cell wall as water
  enters is called the pressure potential, or
  turgor pressure.
• Water enters a plant cell until the pressure
  potential exactly balances the solute potential.
  The cell is then called turgid.
• Keeps plant cells firm and plants dont wilt.

4
Uptake and Movement of Water and Solutes

• Mineral ions generally require transport proteins
  in order to cross membranes.
• Can be passive or active.
• Proton pump helps get ions in by facilitated
  diffusion.

5
Transport of Water and Minerals in the Xylem

• In the xylem, water and minerals constitute the
  xylem sap.
• What causes the xylem sap to move upward?
• transpirationcohesiontension

6
Transport of Water and Minerals in the Xylem

• The transpirationcohesiontension mechanism
• The concentration of water vapor is higher inside
  the leaf than outside, so water diffuses out of
  the leaf through the stomata. This process is
  called transpiration.
• This creates a tension that draws water from the
  xylem.
• The removal of water from the veins, in turn,
  establishes tension on the entire volume of water
  in the xylem, so the column is drawn up from the
  roots.

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Figure 36.8 The TranspirationCohesionTension
Mechanism
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Transport of Water and Minerals in the Xylem

• Mineral ions in the xylem sap rise passively with
  the solution.
• Transpiration also contributes to the plants
  temperature regulation, cooling plants in hot
  environments.

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Transpiration and the Stomata

• Guard cells control the opening and closing of
  the stomata.
• Most plants open their stomata only when the
  light is intense enough to maintain
  photosynthesis.
• Stomata also close if too much water is being
  lost.

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Figure 36.11 Stomata (Part 1)
11
Transpiration and the Stomata

• Opening closing and of the stomata are regulated
  by controlling K concentrations in the guard
  cells.
• Light activates a proton pump gt K moves inside.
• Water moves inside to lower water potential.
• Guard cells open due to shape change.

12
Translocation of Substances in the Phloem

• Sugars, amino acids, some minerals, and other
  solutes are transported in phloem and move from
  sources to sinks.
• Transport often proceeds in both directions both
  up and down the stem simultaneously.

13
Translocation of Substances in the Phloem

• Sieve tube cells at the source have a greater
  sucrose concentration that surrounding cells, so
  water enters by osmosis. This causes greater
  pressure potential at the source, so that the sap
  moves by bulk flow towards the sink.
• At the sink, sucrose is unloaded by active
  transport, maintaining the solute and water
  potential gradients.
• This is called the pressure flow model.

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Figure 36.14 The Pressure Flow Model
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The Acquisition of Nutrients

• Plants are sessile organisms. Nutrients and
  energy must be brought to them in some way.
• A plant can extend itself by growing. The roots
  obtain most of the mineral nutrients needed.
• The essential elements for plants were identified
  by growing plants hydroponically, or without
  soil.

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Table 37.1 Mineral Elements Required by Plants
(Part 1)
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Table 37.1 Mineral Elements Required by Plants
(Part 2)
19
Soils and Plants

• Soils are complex mixtures of living and
  nonliving components, including bacteria, fungi,
  earthworms and other animals, particles of rock,
  clay, water, dissolved minerals, air spaces, and
  dead organic matter.
• The type of soil in a given area depends on the
  type of rock from which it forms and how it is
  broken down.
• Rocks are broken down by mechanical weathering,
  or physical breakdown and chemical weathering.

20
Soils and Plants

• The availability of nutrient ions is influenced
  by soil pH. pH 6.5 is optimal for most crops.
• In the process of liming, compounds such as
  calcium carbonate, calcium hydroxide, or
  magnesium carbonate are added to acidic soil to
  raise the pH.
• The pH of soil can be lowered by adding sulfur,
  which soil bacteria convert to sulfuric acid.

21
Nitrogen Fixation

• Most nitrogen fixation is done by bacteria.
• Cyanobacteria are the principle nitrogen fixers
  in aquatic ecosystems.
• Some nitrogen fixers live in close association
  with plant roots in a mutualistic relationship.
• Rhizobium fix nitrogen only in close association
  with the roots of legumes.
• These bacteria infect plant roots, causing the
  roots to develop nodules

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Figure 37.5 Root Nodules
23
Nitrogen Fixation

• Three things are required for fixation
• A strong reducing agent to transfer the hydrogen
  atoms to N2.
• Energy, supplied by ATP.
• The enzyme nitrogenase.
• Nitrogenase is strongly inhibited by O2.
• Many nitrogen fixers are anaerobes. But others,
  such as Rhizobium, are not.

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Nitrogen Fixation

• Another type of symbiosis in which plants depend
  on another organism for their nutrition is that
  of mycorrhizae, the root-fungus association.

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Nitrogen Fixation

• The nitrogen cycle includes the process of
  nitrogen fixation, nitrification, nitrate
  reduction, and denitrification.
• Soil bacteria called nitrifiers oxidize NH3 to
  nitrite (NO2) and nitrate ions (NO3) in a
  process called nitrification.

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Nitrogen Fixation

• Nitrate reduction is carried out by plants using
  their own enzymes, and reduces nitrate back to
  ammonia. The ammonia is used to produce amino
  acids.
• Animals can not reduce nitrate, and depend on
  plants for reduced nitrogen compounds.
• Bacteria called denitrifiers return the nitrogen
  from animal wastes and dead organisms back to N2
  gas in a process called denitrification.

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Figure 37.8 The Nitrogen Cycle
28
Carnivorous and Heterotrophic Plants

• Some plants that grow in acidic, nitrogen-poor
  environments trap and digest insects to help
  augment nitrogen and phosphorus supplies.
• These carnivorous plants include sundews, Venus
  flytraps, and pitcher plants.
• These plants have adaptations to capture small
  animals and digest the proteins.
• Carnivorous plants can survive without feeding on
  insects, but they grow much faster in their
  natural habitats when they succeed in capturing
  insects.

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Figure 37.9 Carnivorous Plants