BIOL 103 Lecture 8

Breadth of photosynthetic microorganisms
cyanobacteria - prokaryotes that used to be called "blue-green algae"
photosynthetic bacteria - didn't discuss much
eukaryotic algae - microalgae (generally unicellular although can be colonial) and macroalgae (seaweeds and kelps)
the algae can also be broken into color groups: green, yellow-green, brown (seaweeds), red.
lichens are an odd mixture of algae or cyanobacteria with fungi
diatoms and dinoflagellates are algae
diatoms are encased in silicaeous shells
showed many pictures of lovely diatoms
dinoflagellates are the culprits of red tides that cause large fish kills
then some bizarre dino images
lichens are a mixture of algae or cyanobacteria and fungi living together in a symbiotic relationship
both types of organisms supply nutrients to the other
lichens (and cyanobacteria) can colonize bare rock surfaces
lichens are often the first organisms to colonize such areas and begin the process of soil formation
discussed possibility of lichens on the surface of Mars

Energetics
light energy is funneled through the light harvesting complexes to the photosynthetic reaction center
"capturing light energy" and converting it to electrical energy
a photon can excite an electron and move it to a higher energy level
this excited electron now contains potential energy
this energy can be harvested by using an electron transport chain
these chains are like waterfalls
excited electrons are at the top of the falls and drop down to lower levels sequentially
at each step, energy is released and can be captured
capturing this electrical energy converts it into chemical energy
mentioned high energy bonds like those in ATP as examples of chemical energy

Rough Z-scheme
showed the reaction center and an electron getting excited by a photon of light
Q2C: Where does this electron come from? from the splitting of water, thus releasing oxygen
this water splitting is the way that photosynthetic reactions and organisms produce oxygen
the excited electron then moves down the potential gradient of an electron transport chain
there is a second reaction center and the electron can be excited by a second photon
another electron transport chain follows
at each step electrical energy is converted into chemical energy
at the end of the second electron transport chain is the final electron acceptor - NADP+
the NADP+ becomes NADPH with this electron
NADPH is a reducing equivalent - a source of reducing power for reduction reactions
This reducing power is used to fix CO₂
these are the dark reactions of photosynthesis - reducing CO₂ to sugar (CH₂O

Nitrogen fixation
conversion of atmospheric N₂ to NH₃
this is a 6 electron reduction
it is a very expensive reaction using many ATP and NADPH
it is also an anaerobic process
Q2C: Why would an organism use substantial resources to run this reaction? if there is no fixed N around, it needs to make its own to survive
images of cyanobacteria with heterocysts
these structures limit oxygen concentrations in that cell, allowing for the anaerobic process of nitrogen fixation
showed other cyanobacterial images

Q2C: Who has eaten algae?
we all do in various food products
such things as alginate, agar, and agarose are from algal sources
these are used in many processed food products like salad dressings and ice creams
Spirulina is a cyanobacteria that many eat as a health food

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Biology 103 - Microbes and You Lecture 8 Outline Pond Scum

Biology 103 - Microbes and You
Lecture 8 Outline
Pond Scum