4.3 Photosynthesis in Detail
KEY CONCEPT
Photosynthesis converts light energy is captured
and used to build sugars that store chemical
energy.
4.3 Photosynthesis in Detail
4.3 Photosynthesis in Detail
• The equation for the overall process is:
6CO2 + 6H2O  C6H12O6 + 6O2
granum (stack of thylakoids)
1
chloroplast
6H2O
thylakoid
6CO2
3
6O2
2
energy
stroma (fluid outside the thylakoids)
1 six-carbon sugar
4
C6H12O6
4.3 Photosynthesis in Detail
Photosynthesis in plants occurs in chloroplasts.
• Photosynthesis occurs in a series of stages in the
chloroplasts.
– grana (thylakoids)- photosystem II, photosystem I and
the electron transport chain.
– Stroma- Calvin Cycle
chloroplast
grana
(thylakoids)
stroma
4.3 Photosynthesis in Detail
The first stage of photosynthesis captures and transfers
energy.
• The light-dependent
reactions include groups
of molecules called
photosystems.
4.3 Photosynthesis in Detail
• Photosystem II captures and transfers energy.
1.chlorophyll absorbs
energy from sunlight
– energized electrons
enter electron
transport chain
2.water molecules are
split
– oxygen is released as
waste
3.hydrogen ions are
transported across
thylakoid membrane
4.3 Photosynthesis in Detail
• Photosystem I captures energy and produces energycarrying molecules.
4.chlorophyll absorbs
energy from sunlight
5.energized electrons are
used to make NADPH
– NADPH is transferred
to light-independent
reactions
4.3 Photosynthesis in Detail
• The light-dependent reactions produce ATP.
6.hydrogen ions flow through a channel in the thylakoid
membrane
7.ATP synthase attached to the channel makes ATP
4.3 Photosynthesis in Detail
4.3 Photosynthesis in Detail
The second stage of photosynthesis uses energy from
the first stage to make sugars.
• Light-independent
reactions occur in the
stroma and use
• CO2 molecules enter
the Calvin cycle
4.3 Photosynthesis in Detail
• The light-independent reactions make sugars.
– take place in stroma
– needs carbon dioxide from atmosphere
– use energy to build a sugar in a cycle of chemical
reactions
4.3 Photosynthesis in Detail
• A molecule of glucose is formed as it stores some of the
energy captured from sunlight.
1.carbon dioxide molecules enter the Calvin cycle
2.energy is added and carbon molecules are rearranged
3.a high-energy three-carbon molecule leaves the cycle
4.3 Photosynthesis in Detail
• A molecule of glucose is formed as it stores some of the
energy captured from sunlight.
4.two three-carbon molecules bond to form a sugar
– remaining molecules stay in the cycle
4.3 Photosynthesis in Detail
4.3 Photosynthesis in Detail