Transcript Photosynthesis

Photosynthesis
Stored Energy
What is Photosynthesis?
 plants convert the energy of sunlight into
the energy in the chemical bonds of
carbohydrates – sugars and starches.
Requirements for
Photosynthesis
 Carbon Dioxide - CO2
 Water - H2O
 Energy – In the form of sunlight
3 Main Stages
 1. Energy is captured from sunlight.
 2. Light energy is converted to chemical
energy (ATP & NADPH)
 3. ATP and NADPH power the synthesis
of organic molecules, using carbon from
carbon dioxide.
Where does
Photosynthesis occur?
 Inside plant cells – specifically
chloroplasts
1. DNA
2. Ribosomes
3. & 6. Outer
Membrane
4. Grana
5. Stroma
7. Starch Grain
Chloroplast
 Thylakoid – flattened,
membrane bound
sac
 Grana – stacks of
thylakoids
 Stroma – fluid matrix
Light Energy
(Energy is captured by sunlight)
Electromagnetic Spectrum
 Radiant Energy –
energy that is
transmitted in waves
that can travel
through a vacuum.
 Electromagnetic
spectrum – complete
range of radiant
energy.
PHOTONS!
 Tiny packets of radiant energy
When Photons strike a
surface…..
 1 – reflected
 2 – absorbed
 3 – transmitted
• Green plants are
green because they absorb all
of the colors of the visible
spectrum except the green
color (aka the green
wavelengths).
Pigments
 Molecules containing
atoms that enable
it to absorb light.
Types of Pigments
 Chlorophyll – the
primary lightabsorbing agent for
photosynthesis
 Carotenoids – yellow
& orange pigments
 Phycoerythrin – red
and blue
Photosytems- molecule clusters
of pigments found in the thylakoid
membranes
 Photosytem I
boost
electrons by
absorbing
light with a
wavelength of
700 nm
 Photosystem II
– boosts
electrons by
absorbing light
with a slightly
shorter
wavelength
than 680 nm
Stage 2
Light energy is converted to
chemical energy… a.k.a.
Light – Dependent
Reactions
Electron Carriers
 Excited electrons – high energy
 Special carriers – electron carriers
 Electron transport chain
NADP+ - accepts and holds 2 high energy
electrons along with a hydrogen ion (H +)
 NADP+ + H + = NADPH
Light-Dependent Reaction
 4 Basic Processes




Light absorption
Electron transport
O2 production
ATP formation
Light-Dependent Reaction
cont.
 1. Photons of radiant energy strike PSII
 Energy is passes to the chlorophyll molecule
 Excited electron (e-) is boosted to….
 2. A thylakoid membrane protein where…
the e- is passed along a series of electron
carriers called …
 the electron transport chain
 3. At the end of the ETC, an ATP is
released into the stroma
 4. PS I gets the e- from PS II. It gets
boosted to….
 5. Thylakoid membrane protein where…
 The e- is passed to the ETC…
 6. The ETC passes the e- to the electron
carrier NADP+ and is converted to
NADPH
 7. As e- move from chlorophyll to NADP+,
more H+ ions are pumped across the
membrane
 8. The inside of the thylakoid membrane
builds up with + charge
 9. Outside the thylakoid is – charged.
 10. H+ ions cannot exit without help. They
use ATP synthase.
 11. Protein channel rotates.
 12. As it rotates, ADP binds
with a phosphate to make
ATP
Why doesn’t the
chlorophyll run out of e ?
 Enzymes on the
inner side of the
thylakoids break up
water molecules
into 2 electrons,
H + ions , and 1
oxygen atom!
Light-Dependent Reaction
 Uses
 Water
 ADP
 NADP+
 Produces
 Oxygen
 ATP
 NADPH
The Calvin Cycle –
sometimes called Light
Independent Reactions
 Plants use the energy that ATP and
NADPH contain to build high-energy
compounds that can be stored for a long
time. Uses ATP and NADPH from the
light dependent reactions to produce
high-energy sugars.
Steps to the Calvin Cycle
 6 CO2 molecules enter the cycle from the
atmosphere
 These combine with 6, 5 - carbon
molecules to make 12, 3 - carbon
molecules
 The 12 are converted into higher-energy
forms (Energy from ATP & NADPH)
Calvin Cycle cont.
 2 of the 12, 3 – carbon molecules are
removed from the cycle to make sugars,
lipids, amino acids or other compounds
 The remaining 10, 3 – carbon molecules
are converted back to 6, 5 – carbon
molecules.