Photosynthesis- is the process that converts light energy into ___________________. This
chemical energy is usually a carbohydrate. Only photoautotrophs can do photosynthesis.
Heterotrophs must obtain their high organic nutrients from the environment.
6CO2 + 6H2O
___________>
C6H12O6 + 6O2
Glucose has more energy than carbon dioxide and water. The reaction is ____________ and will
require an energy input of ATP and NADPH2.
The equation describes the___________cycle
of photosynthesis and the chemical energy
needed to make the sugar.
In order to keep the reaction going, the cell
must regenerate _______________.
Regeneration of NADPH and ATP require light and intact chloroplasts with chlorophyll. This part
of photosynthesis is known as the light reaction. The
hydrogen needed to reduce NADP comes from the
splitting of water. In the overall purpose and products of
the light reaction is
1. ADP + P ____> ATP
2. NADP + H____> NADPHH____> 2H+ + 2e- + ½ O2
Chlorophyll is green and reflects green light
and absorbs ______________. Chlorophyll is
made from a tetrapyrole ring with Mg in the
middle and a hydrocarbon tail. These pigments
form photosystems found in the thylakoid
membrane. There are some other pigments in
photosystems which are yellow. These yellow
pigments (carotenoids and xanthophylls) allow
photosynthesis to occur in green light.
White light is mixture of different colors of light
with different wave lengths and frequencies.
When white light lands on a blue object, red
and green light is absorbed and blue is
reflected.
The absorption graph shows that the pigments absorb red and blue/violet light best. This is due to
the accessory pigments.
Chloroplasts have 3 membranes. The
outer 2 are
smooth and the inner one makes stacks of
_________
which is a granum. The chlorophyll and
other
pigments are found inside the thylakoid
membrane.
They have the ability to convert light
energy into
_____________ A stack of thylakoids is called a granum. The matrix that the grana are
embedded in is the stroma. It contains enzymes for _______________ synthesis. Below is a
diagram of the thylakoid and the location of chlorophyll. The chlorophyll molecules and accessory
pigments form photosystems (I & II). Each photosystem has a reaction center (p700& p680
respectively) Once photons are
absorbed by the pigments of the
photosystem, the electron
becomes excited and the
energy is passed on from
molecule to molecule until it
reaches the _____________.
The p680 and p700 has the
ability to pass the energized
electron on to the
________________________.
Also embedded in the thylakoid
membrane is a series of
proteins that have the ability to
be reduced an oxidized. Each
one has less reducing power
than the preceding one. Protein Q has the ability to receive an _________ electron from the
p680 reaction center. It then moves to PQ or plastoquinone. From there it move to a
cryptochrome complex which is a proton pump that when reduced has the ability to pump
___________ from the outside of the stroma to the inside of the thylakoid. From there it goes
plastocyanin. By this time the e- has lost much of its free energy and must be energized by
______________. The electron has now left the electron transport chain. Replacement
electrons for PS II come from the splitting of ________. A manganese complex associated with
PS II has the ability to split water to produce, H+, e-, and oxygen gas. The e- are shuttled to the
photosystem, H+ are used to lower the pH of the thylakoid, and the oxygen gas is released to the
atmosphere. As the electron transport chain runs, there is an accumulation of _____ on the
inside of the thylakoid. This is due to the splitting of water and the proton pump, PQ. As the H+
collect, the pH of the interior is _________ and there is a separation of charge across a
membrane. This can now do work.
On the thylakoid membrane, there are CF complexes which contain a channel (CF0) and a large
protein head (CF1). On the CF1 head, there is an enzyme ATP synthetase. This enzyme has the
ability to _______________ ADP--->ATP as 3 H+ pass through.
This is noncyclic photophosphorylation.
1. Water is split to make replacement e-, H+ and O2.
2. There are two photosystems involved.
3. NADP is reduced to NADPH.
Cyclic photophosphorylation is
considered to be a more ancient
biochemical pathway. It is found in
most photosynthetic bacteria and all
photosynthetic eukaryotes. It consists
of one photosystem (PSI) and a
simple _______________. At the end
of the electron transport chain, the
electron is returned to PS I. That
being the case, water is not split, nor
is NADP reduced. One part of the
electron carrier does pump H+ across
the thylakoid membrane to make ___.
Cyclic photophosphorylation does not
provide hydrogens for the reduction of
carbon dioxide to make a
carbohydrate. So therefore quite
often the hydrogens come from H2S.
In photosynthetic, eukaryotic cells, two
photosystems (II & I) work together to
form noncyclic photophosphorylation.
Overview light reaction
1. 18 ATP are made from 18ADP +
18P
2. Water is split. e- + H are used for
_______ , 6 O2 are released.
3. 12 NADPH are made.
Overview dark reaction
The carbohydrate is made in the
_________. It requires enzymes
every step.
1. 18ADP + 18P are made from
____ATP. Energy is _____________
2. NADPH is oxidized to make _____.
The hydrogens are transferred making
a carbohydrate.
3. 3 CO2 are used to make a triose G3P (glyceraldehyde 3-phosphate) or __________
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" _________ 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
monosaccharide with 2 phosphate groups
2. It will form an unstable _____________.
3. The intermediate will form 2 molecules
of phosphoglyceric acid.
4. PGA will be phosphorylated by ATP to form ____________.
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 _______. 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 __________.
This shows how 2 molecules of
G3P or PGAL are turned into a
molecule of glucose and how it
can be turned into
___________________.
While the glucose is needed for
_____________, 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 affect 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 ___________, an increase in light intensity will not increase the _____of photosynthesis.
2. Temperature- At first an increase in temperature results in an ___________ in the rate of
photosynthesis because the molecules are moving faster, but at a higher temperature the
reaction rate _____________________ because enzymes denature.
3. If a plant is given an increase in ___________, the
rate of photosynthesis decreases because of
phenomenon of photorespiration. The enzyme that puts
the CO2 onto ribulose biphosphate is ____________.
Sometimes rubisco can make a mistake and put oxygen
on to ribulose biphosphate. This happens when the
concentration of oxygen gas is ________than carbon
dioxide. This happens when the plant is water stressed
and the stomates are _______. Gas exchange takes
through pores on the bottom of the leaf called stomates.
Guard cells regulate stomates but as gas exchange occurs water leaves the stomates via
____________. When a plant becomes water stressed,
stomates close to conserve water, but this will stop
________________. 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
____________. 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 ______________. This Hatch-Slack pathway is able to deliver dwindling supplies
of CO2 when the stomates are closed. The enzyme (__________________) 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 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 ________________ 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 Hatch-Slack pathway
delivers the CO2. Plants that use C4
photosynthesis include
__________________________________.
Another variation of photosynthesis is
___________(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 ____________ for gas exchange.
The CO2 (like C4 photosynthesis) is fixed to
PEP by PEP _______________. 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 photosynthesis
(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 _______________________.