Photosynthesis
• Carried out by autotrophs, this is the
principal means by which energy enters
the food chain
Photosynthesis
• The chemical equation for photosynthesis
is below
Photosynthesis uses the energy from sunlight to
convert water and carbon dioxide into sugar and
oxygen
• Chloroplasts are the
organelles in which
photosynthesis take
place.
• Within the chloroplasts
are chlorophyll A and
chlorophyll B, pigment
molecules that help
absorb light
When Chlorophylls Absorb Light
The absorption of light energy
by a chlorophyll causes an
electron to gain energy, or
“jump”
Sunlight
Chlorophyll
When Chlorophylls Absorb Light
Normally, an electron releases
this extra energy and returns
back to its “ground state”
Chlorophyll
When Chlorophylls Absorb Light
NADPH
Chlorophyll
But in organisms, special
molecules known as electron
acceptors can capture the
extra energy and carry it to
other molecules for use.
NADP+ is one such electron
acceptor that can capture a
pair of high energy electrons
(converting it to NADPH) and
shuttle them elsewhere for
use
Both chlorophyll A
and chlorophyll B
have specific
wavelengths in which
they can absorb light
Inside a Chloroplast
• Thylakoids are saclike photosynthetic membranes
• Proteins in the thylakoid membrane organize chlorophyll and
other pigments into photosystems
• Photosystems refer to the light collecting “unit” of a chloroplast
• The stroma is the space outside the thylakoid membrane
The Two Parts of
Photosynthesis
• Photosynthesis is divided into the light
dependent and light independent reactions
Light
Dependent
Light
Independent
The Two Parts of Photosynthesis
• The light dependent reactions use the energy from
light to create ATP and NADPH
Light Dependent Reactions
1. Sunlight strikes
photosystem 2 first,
causing an electron to
“jump” and gain energy
Sunlight
Photosystem-2
Light Dependent Reaction
Excited Electron
Electron
Transport Chain
Photosystem-1
2. This electron
then goes through
the electron
transport chain.
This chain slowly
lets the electron
down energetically
until it reaches
photosystem one.
Light Dependent Reactions
3. Sunlight strikes
photosystem 1 now,
causing the electron to
again “jump” and gain
energy
Sunlight
Photosystem-1
Light Dependent Reaction
NADPH
Chlorophyll
4. Except this time the
electron is captured by
NADP+ and taken for use in
the light independent reaction
Light Dependent Reaction
Excited Electron
Electron
Transport
Chain
5. When an
excited electron
goes through the
electron transport
chain, it causes
many hydrogen
atoms (yellow
circles) to go
across the
thylakoid
membrane
Light Dependent Reaction
6. The hydrogen
atoms then diffuse
through ATP
synthase and
produce ATP as
they pass through
ATP
Synthase
ATP
Light Independent Reaction
Primarily consists of the Calvin Cycle. This cycle uses the ATP and
NADPH from the light dependent reactions as energy sources to convert
carbon dioxide into sugar