Biol. Unit 4, Chapters 2 & 3 - Photosynthesis and Respiration

Summary of photosynthesis and respiration, chapters 2 & 3, respectively, of unit 4.

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  • Created on: 24-11-12 10:51
Preview of Biol. Unit 4, Chapters 2 & 3 - Photosynthesis and Respiration

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Ajay Rai
Photosynthesis:
Light dependent:
Photolysis ­ energy from excited electrons in chlorophyll a is used to split H2O molecules to
protons, electrons and oxygen.
Water protons + electrons + oxygen
2H2O 4H+ + 4e- + O2
Photophosphorylation ­ energy containing electrons pass along a series of electron carriers in
thylakoid membranes. These carries form an electron transport chain. (Look at ETC in
respiration).
ADP + Pi + [energy from excited electrons] ATP
Reduced NADP production ­ electrons cannot directly react with CO2. The excited electrons in
chlorophyll a are transferred to NADP, forming reduced NADP. This requires energy. With each
electron NADP takes, it also accepts a proton and therefore has a neutral charge.
NADP + protons + electrons reduced NADP
NADP + H+ + e- reduced NADP
Light independent ­ CO2 combines with RuBP, the reaction being catalysed by rubisco. This
forms an intermediate 6C molecule which immediately splits into two 3C molecules called
glycerate3phosphate. ATP and electrons from reduced NADP (both from light dependent) is
used to reduce G3P to triose phosphate. 5/6 TP is used to regenerate RuBP. 1/6 is used to make
a hexose sugar. So the Calvin cycle needs to turn 6 times to make 1 hexose sugar.
Photosynthesis & Respiration

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Ajay Rai
Respiration:
Glycolysis 2 ATP molecules add two phosphate groups to the glucose molecule, producing a
phosphorylated 6C sugar. This is then broken down to 2 triose phosphate molecules, a 3C sugar.
These are then converted to pyruvate, an oxidation reaction as electrons are removed from TP
and transferred to NAD, a coenzyme, producing reduced NAD.
Link reaction ­ pyruvate leaves cytoplasm, entering mitochondria. NAD oxidises pyruvate to a
2C acetate molecule and CO2.…read more

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Ajay Rai
The lactic acid produced when pushing muscles to the limit is toxic, and needs to be removed
from respiring cells and broken down. It diffuses into the blood plasma and carried away in
solution. The liver cells absorb it and metabolise it. For this to happen however, oxygen is
needed. So anaerobic respiration does not mean `without oxygen' ­ the moment when oxygen is
needed is simply delayed in its occurrence.…read more

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