Transcript PhotosynthesisCalving CycleON

PhotosynthesisThe Basis for Life on Earth
Part II
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 make glucose
This is the Calvin cycle. The various compounds only show the
carbon skeleton, leaving the hydrogen and oxygen atoms off. The
next slide after that includes the names of the molecules used in the
cycle.
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).
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
In the Calvin cycle, CO2 is combined with
A) a protein called rubisco
B) ribulose biphosphate Ru-Bp
C) phosphoenol phosphate (PEP)
D) pyruvate
B
CO2 is combined with ribulose biphosphate which is
a monosaccharide or carbohydrate.
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.
Which of the following does not occur during the
Calvin cycle?
A) carbon fixation
B) oxidation of NADPH
C) release of oxygen
D) regeneration of the CO2 acceptor
E) consumption of ATP
C
The release of oxygen occurs when the protein
complex associated with photosystem II breaks
down water.
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.
What must be added to the carbon skeleton in
order for a plant to synthesize amino acids?
A) hydrocarbons B) oxygen C) phospate groups
D) amine groups E) organic acids
D
Amine groups must be added to a carbon skeleton
in order for a plant to make amino acids
Environmental factors affects the rate of photosynthesis.
1. Light intensity- At first an increase in the light intensity results in a
corresponding increase in the rate of photosynthesis as the photosystems 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.
Which of the following is true for photorespiration
to occur?
A) Stomata are opened.
B) There is an increase in absporption of amine
groups.
C) There is an increase in the amount of oxygen
present.
D) There is an decrease in the amount phosphates
present
C
Photorespiration occurs when there is an increase
in oxygen and decrease in carbon dioxide. This
usually occurs when the stomata are closed.
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 CO2
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 these mesophyll and
spongy mesophyll. The chloroplast
are different.
The chloroplasts in the mesophyll have well defined thylakoids and
specialize in the light reaction and the Hatch-Slack pathway. The
thylakoids in the bundle-sheath 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 HatchSlack 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.
C4 photosynthesis (light reaction, Hatch-Slack, Calvin cycle) is called
this because the first product made has 4 carbons.
In what respect are the photosynthetic
adaptations of C4 plants and CAM plants similar?
A) In both cases, only photosystem I is used.
B) Both types of plants make sugar without the
Calvin cycle.
C) In both cases, an enzyme other than rubisco
carries out the first step in carbon fixation.
D) Both types of plants make most of their sugar in
the dark.
E) Neither C4 plants nor CAM plants have
thylakoids.
C
In both cases, an enzyme other than rubisco
carries out the first step in carbon fixation.