Download PhotosynthesisCalvin Cycle

Overview light reaction
1. 18 ATP are made from 18ADP +
18P
2. Water is split. e- + H are used for
#3. 6 O2 are released.
3. 12 NADPH are made.
Overview dark reaction
The carbohydrate is made in the
stroma. It requires enzymes every
step.
1. 18ADP + 18P are made from 18
ATP. Energy is released
2. NADPH is oxidized to make NADP.
The hydrogens are tranferred making
a carbohydrate.
3. 3 CO2 are used to make a triose G3P (glyceraldehyde 3-phosphate) or PGAL
phosphoglyceraldehyde. 2 of these are
used to make glucose.
The Calvin cycle will make one extra
PGAL. PGAL is a triose. It takes 2
PGALs to make glucose, the hexose. So
therefore the Calvin cycle needs to be
"turned" twice in order to make a molecule
of glucose. (Actually 6 times).
Steps of the Calvin Cycle
1. Carbon dioxide combines with ribulose
biphosphate. Ru-Bp is a pentose
monosacharide with 2 phosphate groups
2.It will form an unstable intermediate.
3. The intermediate will form 2 molecules
of phosphoglyceric acid.
4. PGA will be phosphorylated by ATP to
form DPGA
5.DPGA is reduced by NADPH to form the triose, PGAL. A phosphate group is removed in this
reaction.
6. In the last step, 5 molecules of glyceral aldehyde phosphate (G3P) or PGAL are needed to
remake 3 molecules of Ru-BP. 3 ATP are needed to make this happen. 1 G3P is left over. PGAL
is a triose. In order to make glucose, the Calvin cycle must be turned twice.
This shows how 2 molecules of
G3P or PGAL are turned into a
molecule of glucose and how it
can be turned into starch.
While the glucose is needed for energy,
there is a second reason why the Calvin
cycle evolved; to provide a carbon skeleton
so that other organic molecules or
structures can be made.
Environmental
factors affects the
rate of
photosynthesis.
1. Light intensityAt first an
increase in the
light intensity
results in a
corresponding
increase in the rate of photosynthesis as the photo-systems are activated. As the photosystems
become saturated, an increase in light intensity will not increase the rate of photosynthesis.
2. Temperature- At first an increase in temperature results in an increase in the rate of
photosynthesis because the molecules are moving faster, but at a higher temperature the
reaction rate decreases because enzymes denature.
3. If a plant is given an increase in oxygen, the rate of
photosynthesis decreases because of phenomenon of
photorespiration. The enzyme that puts the CO2 onto
ribulose biphosphate is rubisco. Sometimes rubisco
can make a mistake and put oxygen on to ribulose
biphosphate. This happens when the concentration of
oxygen gas is greater than carbon dioxide. This happens
when the plant is water stressed and the stomates are
closed. Gas exchange takes through pores on the
bottom of the leaf called stomates. Guard cells
regulates stomates but as gas exchange occurs water leaves the stomates via transpiration.
When a plant becomes water stressed, stomates close
to conserve water. water, but this will stop gas exchange.
This will increase the O2 and decrease CO2.
Photorespiration begins. C3 photosynthesis is a plant
that does the Calvin cycle and the light reaction. There
are plants that modify C3 photosynthesis by adding an
additional pathway-
The leaf of a C3 plant (normal leaf). Chloroplasts are located in the palisade and spongy
mesophyll. There are no chloroplasts in the bundle sheath cells. C4 photosynthesis includes the
light reaction, the Calvin cycle and the Hatch-Slack pathway. These C4 plants also have a
different anatomy. This Hatch-Slack pathway is able to deliver dwindling supplies of CO 2 when
the stomates are closed. The enzyme (PEP carboxylase) that fixes the CO2, combines it with a
three carbon compound, phosphoenol pyruvate (PEP) to form a four carbon compound. This
enzyme does not make a mistake like rubisco. The name of this enzyme is PEP carboxylase.
The leaf of a C4 plant. There are no palisade
mesophyll cells. Instead there is a layer of
mesophyll around the the bundle sheath cells.
Chloroplasts are located in the mesophyll and
spongy mesophyll. The chloroplasts are
different. The chloroplasts found in the
mesophyll have well defined thylakoids and
specialize in the light reaction and the HatchSlack pathway. The thylakoids in the bundlesheath chloroplast do not have defined
thylakoids, are larger and store starch. This
indicates the light reaction is not prevalent, and
they do specialize in the Calvin cycle after the
Hatch-Slack pathway delivers the CO2. Plants
that use C4 photosynthesis include corn, sugar
cane, and sorhum.
Another variation of photosynthesis is CAM
(crassulacean acid metabolism). These CAM
plants include succulent plants and pineapples.
Because of the intense heat and arid
conditions, these plants only open up the
stomates at night for gas exchange. Plants that
use C4 photosynthesis include corn, sugar
cane, and sorhum.
The CO2 (like C4 photosynthesis) is fixed to
PEP by PEP carboxylase. It is then converted
to an organic acid and stored until the day. During day stomates are closed and the cell releases
the CO2 from the organic acid and the Calvin cycle occurs. C3 photosynthessis(light reaction and
Calvin cycle) is called this because the first stable product has 3 carbons. C 4 photosynthesis
(light reaction, Hatch-Slack, Calvin cycle) is called this because the first product made has 4
carbons.