3. Table of Content
Introduction
Calvin cycle
Carbon fixation
Reduction
Regeneration
Chemical equation for the Calvin cycle
Summary
4. Introduction
Photosynthesis consists of two parts
The first requires sunlight and the second does not
The light-independent reactions make-up the
second part of photosynthesis
You should note that the name "light-
independent reactions" is a little misleading
5. Cont…..
These reactions do not directly require light, but
they can't occur without the NADPH
and ATP produced in the light-dependent reactions
6. Calvin Cycle
The Calvin cycle is also called dark reactions or
light-independent reactions because it's the part
that doesn't need sunlight to happen
The Calvin cycle (also known as the Benson-Calvin
cycle) is the set of chemical reactions that take place
in chloroplasts during photosynthesis
7. Cont……
In the light-independent reactions, the plant uses
carbon dioxide (CO2) and the ATP and NADPH from
the light-dependent reactions to produce a sugar
called glucose(C6H12O6)
The Calvin cycle takes place within the stroma of
the chloroplast
This is where plants make sugar molecules that they
can use to make other essential component
All other organisms can use this sugar for energy
8.
9. Cont…..
There are three phases to the light-
independent reactions, collectively called the Calvin
cycle
• carbon fixation
• Reduction
• regeneration
10. Carbon fixation
A series of reactions outline the cycle:
The cycle begins when carbon dioxide (CO2) from
the atmosphere enters plant cells
An enzyme called rubisco catalyzes the first
reaction, where CO2 binds to a specific 5-carbon
molecule called ribulose-1,5-bisphosphate (RuBP).
11. Cont….
This reaction creates a 6-carbon molecule which
then splits into two 3-carbon molecules
This part of the cycle is a form of carbon fixation
This just means that inorganic carbon is converted
to organic molecules, like sugar.
12. Reduction
The high-energy products from the light reactions
are used in the next reaction
ATP and NADH donate electrons to the 3-carbon
molecules, which are converted to a 3-carbon sugar
called glyceraldehyde-3-phosphate (G3P)
Some of these G3P molecules leave the cycle to
form glucose molecules
These will be used by the plant during cellular
respiration
13. Cont…..
Three turns of the cycle are needed for one G3P
molecule to exit the cycle
Glucose is made of 6 carbons, so two G3P
molecules are needed to make one glucose
molecule.
After three turns of the cycle, this leaves five more
G3P molecules which are recycled
This allows the cycle to continue
14. Regeneration
ATP is used to convert the leftover G3P into the
molecules that can bind incoming carbon dioxide
and restart the cycle
15. Chemical equation for the Calvin
cycle
The overall chemical equation for the Calvin cycle is:
3 CO2 + 6 NADPH + 5 H2O + 9 ATP →
glyceraldehyde-3-phosphate (G3P) + 2 H+ + 6
NADP+ + 9 ADP + 8 Pi
(Pi = inorganic phosphate)
16. Summary
The reactions of the Calvin cycle add carbon
(from carbon dioxide in the atmosphere) to a
simple five-carbon molecule called RuBP
These reactions use chemical energy from NADPH
and ATP that were produced in the light reactions
The final product of the Calvin cycle is glucose