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Transport in Plants . or Why do they need so much durn water?. To answer this we need a Quick Review of Photosynthesis. The source of all metabolic energy on earth (this is why plants are way cooler than animals!). What does photosynthesis do?. PS is a 2-step process FIRST STEP:

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transport in plants

Transport in Plants

orWhy do they need so much durn water?

to answer this we need a quick review of photosynthesis

To answer this we need a Quick Review of Photosynthesis

The source of all metabolic energy on earth

(this is why plants are way cooler than animals!)

what does photosynthesis do
What does photosynthesis do?
  • PS is a 2-step process
  • FIRST STEP:
    • turns light energy into chemical energy
    • (your book calls these the “light-dependent reactions”)
  • SECOND STEP:
    • uses that chemical energy to “fix” atmospheric carbon into sugar
    • (your book calls these the “light-independent reactions, or the “Calvin Cycle”)
slide4
Where does photosynthesis take place?
  • In chloroplasts
  • In higher plants these are located primarily in leaf cells
a closer look at thylakoids
A closer look at thylakoids
  • These are internal membranes in the chloroplast
  • They create an “inner thylakoid space” similar to the inter membrane space in mitochondria
chlorophyll
Chlorophyll
  • The main energy receiving molecule in chloroplasts
  • Light can easily excite its electrons
  • Electron excitation makes chlorophyll become a good electron donor (i.e. a reducer in a red/ox reaction)
  • These energetic electrons can now enter an electron transport system similar to that in mitochondria
slide7
Other pigments contribute to light absorption:
    • Carotenes (absorb in the blue: appear orange-yellow)
    • Xanthophylls (absorb in the blue-green: appear reddish)
  • These pigments pass their energy to chlorophyll
all higher land plants have the same photosynthetic pigments
All higher land plants have the same photosynthetic pigments
  • The things we call “algae” have different photosynthetic pigments
    • Red
    • Brown
    • “Blue-green”
    • Green
  • Some unicellular marine algae can change their photosynthetic pigments rather quickly (why?)
ok that was step 1 of photosynthesis
OK, that was step #1 of photosynthesis
  • The second step uses the energy (ATP and NADPH) created in step one to fix atmospheric carbon in a process called the “Light-independent reactions” or “Calvin Cycle”
  • This occurs in the stroma of the chloroplast
  • CO2 is “sucked” out of the air by enzymatically attaching it to a 5C sugar called ribulose bisphosphate (RuBP)
  • The enzyme that does this is called RuBP Carboxylase, aka RuBisCO (the most abundant protein in the world)
  • The product is… what would you guess? (5+1=?)
  • … Two 3C sugars called phosphoglycerate
  • Six turns of the CC ultimately produce one glucose molecule for export
  • These glucoses are the basis for ALL metabolic life on earth
so plants get all their carbon from the atmosphere
So plants get ALL their carbon from the atmosphere
  • That means their cells must be in contact with the atmosphere
  • That means their cells (which are full of water) lose water through evaporation
  • This is more or less important for different plants:
    • Aquatic plants – no problem
    • Plants in Oneonta – usually no problem
    • Plants in very dry places – BIG problem!
stomates
Stomates

Comprised of two opposing “guard cells”

how do plants solve this co 2 h 2 0 conflict
How do plants solve this CO2/H20 conflict?
  • There are two main ways:
    • Morphoplogical
    • Biochemical
morphological adaptations to dry conditions xerophytes
Morphological adaptations to dry conditions (xerophytes)
  • Strategies:
    • Avoid dry weather
      • Only grow/flower etc. when it is wet (be dormant the rest of the time)
    • Get more water
      • Have really extensive root systems
      • Be a really good water extracter (actually a biochemical solution)
    • Lose less water from leaves
      • Several strategies for this
what are the major environmental factors that cause the loss of water from leaves
What are the major environmental factors that cause the loss of water from leaves?
  • Humidity
  • Temperature
    • Lower temperatures = lower humidity
  • Wind
  • Which of these can plants alter?
ways to cut down on transpiration
Ways to cut down on transpiration
  • Have a low surface/area ratio
    • Thicker – water is further from the surface
  • Reduce the size of leaves (sometimes to “spines”)
    • Stems are perpendicular to the sun - cooler
  • Have a waxy cuticle
    • Some xerophytes have 10X the wax on their surface
  • Have fewer stomates
    • Good and bad as a solution to this problem
  • Curl leaves
    • Stomates are more plentiful on the bottoms of leaves - maintains higher local humidity
  • Have “sunken” stomates
    • Creates a “still” area – maintains a higher local humidity
  • Have hairy leaves
    • Same…
here s another glitch
Here’s another glitch...
  • PS evolved when there was tons of CO2 and very little O2 in the atmosphere
  • The modern atmosphere is 21% O2, .035% CO2
  • RuBisCO sometimes “accidentally” fixes O2 instead of CO2 (called “photorespiration”)
  • Very, very energy inefficient
  • Worse where it is hot and dry
  • “Tropical grasses” have evolved a “pre-fixation” strategy which minimizes photorespiration
  • The first product is a 4C compound, so the process is called “C4 photosynthesis”