Light-independent reaction
To be able to explain that:
• Energy from the light-independent
reaction is used to fix carbon dioxide.
1.
Write a balanced equation for photosynthesis
6CO2 + 6H2O  6O2 + C6H12O6
2. Give reasons why photosynthesis is important.
3.
4.
5.
Makes food, oxygen
In which cycle does photosynthesis feature?
carbon
What is the waste product of photosynthesis?
oxygen
What is the splitting of water called?
photolysis
6.
What is made during the light dependent reaction?
ATP, NADPH, oxygen
The Light-Independent Reactions
• The light-independent, or carbon-fixing
reactions, of photosynthesis take place in the
stroma of the chloroplasts
• CO2 readily diffuses into the chloroplast where it
is built up into sugars in another cyclic process
called the Calvin cyclt
Glossary
• Ribulose
biphosphate (RuBP)
• glycerate 3phosphate (GP)
• ribulose
bisphosphate
carboxylase
• 5 carbon sugar
• A 3 carbon
compound (an acid)
• An enzyme also
known as RuBISCO
• The fixation of Carbon Dioxide is light
independent.
• Carbon Dioxide combines with RuBP
CO2 

= 2 x glycerate 3 phosphate
RuBP
•CO2 is covalently bonded to
RuBP catalysed by the enzyme
RuBISCO
•The product is two molecules
of glycerate 3 phosphate
•This process is called fixation
• Energy and H+ ions are required to turn the
Glycerate 3 phosphate into the 3 carbon
sugar triose phosphate
• Energy is provided by ATP and the H+ ion is
provided by the NADPH from the light
dependant reaction
2NADPH
2ADP + Pi
2NADP
2ATP
CO2 

= 2 x glycerate 3 phosphate
RuBP
2 x Triose Phosphate
• Two triose phosphate molecules join together to form
one hexose sugar e.g. glucose
• Glucose may be immediately respired, stored as starch or
converted into other products
• The bulk of triose phosphate is converted into more
RuBP to enable the fixation of Carbon to continue
• This uses the rest of the ATP produced in the light
dependant reaction
2NADPH
2ADP + Pi
2NADP
2ATP
CO2 
2 x Triose Phosphate

= 2 x glycerate 3 phosphate
RuBP
ADP + Pi
ATP
Hexose sugar
• Plants can’t
ingest proteins
and fats
• Calvin cycle is
the starting point
for all the
substances a
plant needs
Product
synthesis
Hexose sugar
Eg Glucose,
Fructose
Glycerol from
Triose phosphate
Fatty acids
from glycerate
3 phosphate
Amino acids
synthesised
from glycerate
3 phosphate
Starch,
Cellulose,
Other
Carbohydrates
Lipids
Proteins
• 5 out of every 6
molecules of
triose phosphate
are used to
regenerate RuBP
Calvin cycle in summary
• CO2 combines with ribulose bisphosphate
• Glycerate phosphate is made
• Glycerate phosphate is converted into triose
phosphate
• Triose phosphate is converted into glucose
• RuBP is regenerated
Questions
1.
5.
Which compound is
carboxylated?
How is carbon dioxide fixed?
What does GP stand for?
Which compound is
regenerated?
What is ATP required for?
6.
What is NADPH required for?
2.
3.
4.
• RuBP
• Joined to RuBP
• Glycerate-3-phosphate
• RuBP
• Energy for reduction and
regeneration of RuBP
• Source of hydrogen for
reduction
What reaction converts GP into •
triose phosphate?
8. What kind of sugar is RuBP? •
9. Which enzyme is important in •
the Calvin Cycle?
10. How many carbon atoms in GP?•
•
11. Where does the Calvin Cycle
happen?
7.
reduction
pentose
Rubisco
3
stroma