Plant Physiology

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Leaves
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Leaf Structure

• Epidermal tissue system
• chloroplasts only in guard cells
• Ground tissue system
• mesophyll
• Vascular tissue system
• Leaf adaptations
• sun and shade leaves
• xerophytes

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Photosynthesis
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Start with the Big Picture

• Its all about energy
• potential vs kinetic energy
• Nearly all energy used on earth comes from the
  sun
• Nearly all energy used on earth ends up as heat
• Metabolism
• the way living things manage energy

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Laws of Thermodynamics

• Energy can neither be created nor destroyed but
  it can be converted from one form to another
• In any transfer of energy there is always loss
  of useful energy, usually as heat

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What makes chemical reactions happen?

• Chemical bonds have potential energy
• When the bonds are broken, the energy is released
• Cells transfer energy from one molecule to
  another, often as a proton (H) or electron (e-)
• Enzymes are proteins that speed up chemical
  reactions
• ATP has high-energy phosphate bonds
• ATP bonds come from glucose
• Glucose comes from...

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Metabolism summary

• Photosynthesis
• light reactions
• dark reactions
• Respiration
• glycolysis
• Krebs cycle
• electron transport
• fermentation

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Photosynthesis
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Movie
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Light Reactions of Photosynthesis

• Chlorophyll is a pigment in the thylakoid
  membrane
• It can absorb light energy
• The absorbed energy knocks an electron out of the
  chlorophyll molecule
• This electron is transported from one molecule to
  another
• The energy is used to make ATP
• The original electron is replaced with one from a
  molecule of water, releasing O2

Movie 1
Movie 2
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A good summary...
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Dark Reactions (Calvin cycle)

• Occurs in the stroma of the chloroplast
• CO2 diffuses into spongy mesophyll cells
• RUBISCO is the enzyme that fixes the CO2 into a
  carbon compound
• its the most abundant protein on earth
• a very complicated enzyme!

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Rubisco
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Calvin cycle
Movie
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The atmosphere contains oxygen because of
photosynthesis
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Oxygen causes a problem for RUBISCO

• RUBISCO binds O2 as well as CO2
• the substrates compete for the active site
• O2 results in no new sugar
• Some plants have evolved a way to avoid this
  wasteful reaction

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Some C4 plants
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lt
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lt
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ATP
lt
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lt
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Water molecules
lt
Waterbox
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Companion cells
Sieve cells
lt
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lt
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lt
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End of Show
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Dicot leaf surface
Monocot leaf surface
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Palisade parenchyma
Upper epidermis
Xylem
Phloem
Stoma
Spongy parenchyma
Lower epidermis
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Sun leaf and shade leaf sections
Genetic vs environmental differences in leaves
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Xerophytes are plants that grow in dry conditions
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What are the adaptations to dry conditions?
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Leaf cross section
Which tissue holds the water?
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Parallel venation (monocots)
Net or pinnate venation (dicots)
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Typical horizontal leaf
Typical vertical leaf
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