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Relationship between photosynthesis and cellular respiration…
Relationship between
photosynthesis
and cellular respiration
Definitions
Photosynthesis
A process that uses solar energy to reduce carbon dioxide to carbohydrate.
Cellular respiration
A process that uses energy from carbohydrate, fatty acid, or amino acid breakdown to produce ATP.
Equations
Photosynthesis
6CO2 + 12 H2O ----> C6H12O6 + 6H2O + 6O2
Water
is split and oxygen is released.
Carbon dioxide
is required and
oxygen
is released.
Cellular respiration
C6H12O6 + 6O2 ----> 6O2 + 6H2O
Oxygen is combined with hydrogen and
water
is formed.
Oxygen
is required and
carbon dioxide
is released.
Processes
Photosynthesis
Light reactions
Solar energy ----> Chemical energy (ATP, NADPH) + O2
Flow of electrons
Photosystem II
absorbs
solar energy
and passes the energy between pigments until it is concentrated into a reaction center. The electrons in the reaction center become so energized that they escape and move to electron acceptors.
Photosystem I
absorbs solar energy and the energized electrons leave it's reaction center to be moved to electron acceptors.
Those electrons are passed to
NADP+
molecules, which accepts two electrons and a hydrogen ion (H+) and reduces to
NADPH
.
The energized electrons are then sent down an
electron transport chain (ETC)
where they are passed between a series of membrane-bound carriers. Hydrogen ions (H+) capture the energy released in the ETC and flow down their gradient through
ATP synthase
complexes, producing
ATP
(later to be used in the Calvin cycle)
.
ATP Production
Water is oxidized and two hydrogen ions (H+) remain in the
thylakoid space
.
The electrons move down the electron transport chain (ETC) through redox reactions, releasing energy, which is then used to pump hydrogen ions (H+) from the
stroma
, which is within the
chloroplasts
.
Citric acid cycle
reactions
Chemical energy (ATP, NADPH) ----> Chemical energy (carbohydrate)
Flow of carbon dioxide molecules
Carbon dioxide fixation
A molecule of dioxide attaches to a 5-carbon molecule called ribulose-1.5-biphosphate (RuBP) resulting in a 6-carbon molecule that splits into two 3-carbon molecules.
Reduction of carbon dioxide
The 3-carbon molecules are called 3-phosphoglycerate (3PG) and are reduced to glyceraldehyde (G3P).
Regeneration of RuBP
For every 3 turns of the citric acid cycle, 5 molecules of G3P are used to reform 3 molecules of RuBP.
Cellular respiration
Glycolysis
The only phase of cellular respiration that is an anaerobic reaction (meaning it does not require oxygen) and takes place outside of the mitochondria in the
cytoplasm
.
The breakdown of glucose to two 3-carbon (C3)
pyruvate
molecules.
Oxidation occurs here and NADH is formed, providing enough energy to gain two
ATP
.
Preparatory reaction
Takes place in the
matrix
of the
mitochondria
.
The breakdown of pyruvate to a 2-carbon (C2) acetyl group and a 1-carbon CO2 molecule.
Occurs twice per
glucose
molecule because glycolysis ends with two pyruvate molecules.
Citric acid cycle
Takes place in the matrix of the mitochondria, as well.
Each 2-carbon acetyl group combines with a 4-carbon molecule, resulting in two 6-carbon citrate molecules.
NAD+
reduces to
NADH
and
FAD
reduces to
FADH2
as the citrate bonds are broken and oxidation occurs. CO2 is released and ATP is produced.
Occurs twice as two acetyl groups enter the cycle per glucose molecule.
Electron transport chain
Electrons given up by the NADH and FADH2 are passed down the electron transport chain until it is received by oxygen at the end of the chain where it combines with hydrogen ions (H+) and becomes water.
Takes place in the cristae of the mitochondria.
ATP synthase
, an enzyme, synthesizes ATP from ADP + P.