Transcript More than you ever wanted to know about photosynthesis (part 2)

More than you ever wanted to know
about photosynthesis (part 2)
Light Independent Reactions
Calvin Cycle and the formation of
Glucose
Melvin Calvin
• Nobel Prize winner
1961
• Discovered the cycle
by which glucose is
produced in plants,
now know as the
Calvin Cycle
Simple Explanation
• Carbon dioxide
enters the cycle
• Energy from ATP and
NADPH produced
from photosystem II
and ATP synthase is
used to join carbon
molecules together
• Glucose is formed
Step 1
• 6 molecules of a 5carbon sugar called
ribulose biphosphate
(RuBP) combine with
6 molecules of CO2
to form 12 molecules
of a 3-carbon
compound called
phosphoglycerate
(PGA)
Step 2
• Energy from 12 ATP and
12 NADPH produced
from light reactions is
used to convert the 12
PGA into 12 high
energy molecules
called
phosphoglyceraldehyde
(PGAL)
Step 3
• Two PGAL molecules
leave the cycle to form
a glucose molecule
(6 carbon sugar)
Step 4
• 6 ATP provide the energy
needed to convert the 10
remaining PGAL molecules
into 6 RuBP molecules
• The cycle begins again…
C4 Plants
• Certain tropical plants have an additional
pathway to transport CO2 into the Calvin cycle.
• 4-carbon compounds are created in specialized
leaf cells which is transported to cells where
photosynthesis occurs
• The 4-carbon compound is broken down into CO2
and is available for photosynthesis in addition to
the CO2 that enters the leaves through stomata
• This CO2 pump increases the rate of
photosynthesis
CAM Plants
• Cassulacean Acid Metabolism
• Plants that live in hot dry climates can not
keep their stomata open during the heat of
the day.
• They open their stomata at night and store
CO2 as organic acids in vacuoles
• The acids release the CO2 the next day inside
of the plant so photosynthesis can occur while
the stomata are closed