Photosynthesis part deux:
The Calvin Cycle
Chapter 6-2 pages 117120
At right is Melvin Calvin
who worked all this out
Below is Calvin who
worked out Calvin Ball
Calvin Cycle
• From
photosynthesis we
get ATP and
NADPH
• Now we’ll use the
energy from that to
make biomolecules
• The energy from Niagra falls is
used to power turbines so we can
use electricity to do work
Carbon Fixation
• Carbon fixation is the
building of biomolecules
from CO2
• 3 steps of the Calvin
Cycle
1. CO2 diffuses into the stroma
from the surrounding
cytoplasm. RuBP is
combined with CO2. The
new 6 Carbon molecule
splits into 2 3 Carbon
molecules called PGA
Calvin Cycle
Step 2
2 PGAs converted to another 3 Carbon molecule PGAL,
in a two part process
1. PGA receives a Phosphate from ATP
2. NADPH gives its H+
The ADP, NADP+, and Phosphate are reused back in the photosynthesis reaction
• Confused, stare at this
picture, watch the lines
seem to move. Now get
back to work
Calvin Cycle
Step 3
Some of the PGAL
goes back to RuBP
so the Cycle can
continue
Other PGAL goes
elsewhere to make
Biomolecules
Balance sheet for Photosynthesis
• Calvin Cycle has to
turn 3 times to get a
PGAL
– That uses 9 ATPs and
6 NADPHs
• Now no glucose has
been made yet.
Cellular respiration is
where Glucose is
involved.
The Lakers appreciate
the Calvin Cycle, you
should to.
Alternative pathways
• C3 Plants only fix carbon
through the Calvin Cycle
– Most plants are this, trees
for example
• In hot climates plants lose
water through open
stomata so they need to
keep stomata closed
• But stomata are where
CO2 & O2 leave and enter
the cell
Alternative Pathways
• C4 pathway plants put
CO2 into 4 carbon
molecules
– Corn & Sugar Cane are
examples
• CAM pathway plants
have stomata open at
night and closed
during the day, the
opposite as normal
– includes Cactus &
Pineapple