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Outline
I. Photosynthesis
A. Introduction
B. Reactions
II. Cellular Respiration
A. Introduction
B. Reactions
Photosynthesis
Photosynthesis
Method of converting sun energy into chemical
energy usable by cells
  Autotrophs: self feeders, organisms capable of
making their own food
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Light absorbing pigment molecules e.g. chlorophyll
Photoautotrophs: use sun energy e.g. plants
photosynthesis-makes organic compounds (glucose) from
light
Chemoautotrophs: use chemical energy e.g. bacteria
that use sulfide or methane chemosynthesis-makes
organic compounds from chemical energy contained in
sulfide or methane
Overall Reaction
 
Photosynthesis takes place in specialized
structures inside plant cells called chloroplasts
6CO2 + 12 H2O + light
energy → C6H12O6 + 6O2+ 6H2O
Carbohydrate made is glucose
Water is split as a source of electrons from hydrogen atoms
releasing O2 as a byproduct
Electrons increase potential energy when moved from water
to sugar therefore energy is required Light-dependent Reactions light energy is absorbed by chlorophyll molecules
this light energy excites electrons and boosts them to
higher energy levels.   are trapped by electron acceptor molecules that are
poised at the start of a neighboring transport system.   electrons “fall” to a lower energy state, releasing
energy that is harnessed to make ATP  
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Energy Shuttling
Light-dependent Reactions
ATP: cellular energy-nucleotide based molecule
with 3 phosphate groups bonded to it, when
removing the third phosphate group, lots of energy
liberated= superb molecule for shuttling
energy around within cells.
  Other energy shuttles-coenzymes
(nucleotide based molecules): move electrons
and protons around within the cell
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NADP+, NADPH
NAD+, NADP
FAD, FADH2
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Photosystem: light capturing unit, contains chlorophyll, the
light capturing pigment
Electron transport system: sequence of electron
carrier molecules that shuttle electrons, energy released to
make ATP
Electrons in chlorophyll must be replaced so that cycle may
continue-these electrons come from water molecules,
oxygen is liberated from the light reactions
End product: ATP and NADPH used to fuel the reactions of
the Calvin cycle (light independent or dark reactions)
Calvin Cycle (light independent or
“dark” reactions)
ATP and NADPH generated in light reactions used to
fuel the reactions that take CO2 apart, then
reassemble the carbons into glucose.
  Called carbon fixation: taking carbon from an
inorganic molecule (atmospheric CO2) and making an
organic molecule out of it (glucose)
  Simplified version of how carbon and
energy enter the food chain
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That wasn’t so bad…
Harvesting Chemical Energy
 
Take a look at the handout and answer the questions
about photosynthesis (page #1)
  Talk with your lab partner about the “big steps” of
photosynthesis.
  What is the end product of photosynthesis?
  Where does the Calvin Cycle obtain the carbon to
make glucose?
 
Cellular Respiration Overview
Cellular Respiration Overview
Transformation of chemical energy in food into
chemical energy cells can use: ATP
  These reactions proceed the same way in plants and
animals. Process is called cellular respiration
  Overall Reaction:
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C6H12O6 + 6O2 → 6CO2 + 6H2O
Plants and animals both use products of
photosynthesis (glucose) for metabolic fuel
  Heterotrophs: must take in energy from outside
sources, cannot make their own e.g. animals
  When we take in glucose (or other carbs), proteins,
and fats-these foods don’t come to us the
way our cells can use them
Breakdown of glucose begins in the cytoplasm: the
liquid matrix inside the cell
  At this point life diverges into two forms and two
pathways
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Anaerobic cellular respiration (aka fermentation)
Aerobic cellular respiration
C.R. Reactions
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Glycolysis
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Series of reactions which break the 6-carbon glucose
molecule down into two 3-carbon molecules called
pyruvate
Process is an ancient one-all organisms from simple
bacteria to humans perform it the same way
Yields 2 ATP molecules for every one glucose molecule
broken down
Yields 2 NADH per glucose molecule
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Anaerobic Cellular Respiration
 
Some organisms thrive in environments with little or no
oxygen
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No oxygen used= ‘an’aerobic
Results in no more ATP, final steps in these pathways
serve ONLY to regenerate NAD+ so it can return to pick up
more electrons and hydrogens in glycolysis.
End products such as ethanol and CO2 (single cell fungi (yeast)
in beer/bread) or lactic acid (muscle cells)
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Marshes, bogs, gut of animals, sewage treatment ponds
Aerobic Cellular Respiration  
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Oxygen required=aerobic
2 more sets of reactions which occur in a specialized
structure within the cell called the mitochondria
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1. Kreb’s Cycle
2. Electron Transport Chain
Kreb’s Cycle
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Completes the breakdown of glucose
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Takes the pyruvate (3-carbons) and breaks it down, the
carbon and oxygen atoms end up in CO2 and H2O
Hydrogens and electrons are stripped and loaded onto
NAD+ and FAD to produce NADH and FADH2
Production of only 2 more ATP but loads up
the coenzymes with H+ and electrons which move to
the 3rd stage
Electron Transport Chain
Electron carriers loaded with electrons and protons
from the Kreb’s cycle move to this chain-like a series
of steps (staircase).
  As electrons drop “down stairs”, energy released to
form a total of 32 ATP
  Oxygen waits at bottom of staircase, picks up
electrons and protons and in doing so becomes
water
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Energy Tally
 
36 ATP for aerobic vs. 2 ATP for anaerobic
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Glycolysis
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Kreb’s
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Electron Transport
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2 ATP
2 ATP
32 ATP
36 ATP
Anaerobic organisms can’t be too energetic but are
important for global recycling of carbon
Cellular respiration summary
1. Glycolysis ("splitting of sugar"): in the cytoplasm.
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pyruvate, 2 ATP (could go anaerobic)
2. Krebs Cycle: in mitochondria - strips away H+ and
stores them, CO2 and H2O are all that’s left of the
sugar
3. ETC – passing electrons down produces ATP from
ADP (32-36)
Total yield ~38 ATP
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