Photosynthesis
Why plants
don’t “eat”
What is Photosynthesis?
• Photo: Light
• Synthesis: Putting Together
• Photosynthesis: putting
together with light!
Why are plants green?
•Chlorophyll absorb light
•All but green
•Green is reflected back!
What are the two stages?
st
•1 :
Light-Dependent
Reactions
nd
• 2 : Light-Independent
Reactions
Where do Light-Dependent
Reactions Occur?
• In the
thylakoid
stacks of the
chloroplast
What happens during the
light-dependent reactions?
• Sunlight powers the production
of ATP
• Water is broken down into
oxygen
• What is a waste product here?
What are the steps of LightDependent Reactions?
• 3 steps:
–Photosystem II
–Photosystem I
–ATP Synthase
What happens during
Photosystem II?
• Chlorophyll absorbs sunlight
• Sunlight powers electrons to
leave H from H20 and move
through membrane
• H+ moves through
membrane
• If H leaves water, what is left?
What happens during
Photosystem I?
• Chlorophyll still
absorbs sunlight
• Electrons (e-) added
to NADP+ to make
NADPH
• NADPH moves to the
ATP Synthase
NADP+
NADPH
What happens during ATP
Synthase?
• H+ ions move back
through membrane
• Power ATP Synthase
to make ADP from
ATP
• Where have we
seen this before?
Where do Light-Independent
Reactions Occur?
• In the
stroma of
the
chloroplast
What happens during LightIndependent Reactions?
• ATP made
previously powers
making of Glucose
• CO2 is used to
make C6H12O6
(Glucose)
How many steps are there in
Light-Independent Reactions?
• ONE!
• The Calvin
Cycle
What happens during the
Calvin Cycle?
1. A 5-Carbon
molecule
attaches to a C
from CO2 to
become a 6Carbon molecule
2. Energy (ATP)
breaks the 6carbon into 2
3-carbon
molecules
3. 1 of the 3carbon
molecules
leaves the
cycle, the other
continues on.
4. Remaining 3carbon has
energy (ATP)
added to become
the 5-carbon
molecule we
started out with!
So how does that make a
Glucose?
• Glucose has 6
carbons…
• The 3-carbon
molecule that left,
after 2 cycles, comes
together to make
Glucose!
• 3C+3C=6C