Cell Energy:
Photosynthesis
Where Does Energy Come
From?
 Autotrophs: Use light energy from
the sun to produce food necessary
to give them energy.
 Heterotrophs: Can’t use the energy
of the sun, these organisms need to
obtain energy from foods they
consume.
Energy
 Energy comes in many forms: Light,
Heat, Electricity.
 One source of chemical energy that
living things use is adenosine
triphosphate (ATP).
ATP: Adenosine Triphosphate
 Consists of:
 Adenosine
 A 5-Carbon sugar called Ribose
 3 Phosphate groups (the key to its ability to store
and release energy).
 Energy storage and release
 Cells have the ability to store energy in small
amounts (3-5 seconds)
 ADP (energy source like ATP but with one less
phosphate group) must add a phosphate group so
the cell can store energy,
 Energy will be released from that ATP when that
same phosphate group is removed.
 ATP powers many reactions this way (active
transport, protein synthesis, muscle contraction)
Photosynthesis
 The process which plants use to
convert the energy of sunlight into
carbohydrates (sugars and starches)
they can use as an energy source.
Scientist of Photosynthesis
 Van Helmont- Experimented to see if
plants grew by taking materials out of
soil.
 He concluded that water was responsible for
the majority of plant growth.
 He had it ½ right, he didn’t realized that the
carbon dioxide in the air was used with the
water and sunlight to produce energy.
Scientist of Photosynthesis
 Priestly- Experimenting with a fig plant
and a candle under a jar, discovers that
plants release a chemical (we now know
is Oxygen) that allows the candle to burn.
 Ingenhousz-Discovers that plants
produce oxygen when in light but, not in
the dark.
Photosynthesis
 The photosynthesis reaction:
 6CO2+H2O --> C6H12O6+6O2 (With light
present).
 The photosynthesis reaction requires: Light,
Water, and Carbon Dioxide.
 The light used for photosynthesis to occur, is
captured by a green pigment (chlorophyll)
stored in the chloroplast.
 Plants also contain other pigments (red, orange,
yellow, etc.) that absorb light from another part of the
spectrum that chlorophyll does not absorb.
Photosynthesis
 Inside the Chloroplast:
 Chloroplast Envelope- Made of an inside and
outside membrane surrounds the chloroplast.
 Thylakoids- Saclike photosynthetic membrane
(location of Light Reaction).
 Granum- Stack of thylakoids
 Photosystems- Proteins in the thylakoids organize
chlorophyll and other pigments into clusters known
as photosystems, this is the light collecting unit of
the chloroplast.
 Stroma- Space outside of the thylakoids (location of
Dark Reaction).
Photosynthesis
 Light Reaction:
 The first step of photosynthesis.
 Requires Light.
 Takes place in the Thylakoids.
 Uses sunlight to produce Oxygen and
convert ADP & NADP into ATP and
NADPH.
 Requires water (H2O).
Photosynthesis

The steps of a Light Reaction
1. Pigments begin to absorb light, which is used to break
up water molecules into H+ and O (which is released
into the air).
2. Energy from electrons in the electron transport chain is
used to transport H+ from the stroma into the thylakoid.
3. Energy from light is used to reenergize electron. NADP
picks up these electron along with H+ at the outer
surface of the thylakoid to become NADPH.
4. As electrons pass from chlorophyll to NADP, more H+
ions are passed across the membrane, after a while
the inside becomes (+) and the outside becomes (-)
this difference in charge provides the energy
necessary to make ATP.
5. H+ use a protein called ATP synthase to help it pass
through the membrane, as H+ passes the membrane it
rotates the protein, As it is rotating it binds ADP and a
phosphate group together producing ATP.
Photosynthesis
 Dark Reaction:
 Also known as the Calvin Cycle, it is the
second step in photosynthesis.
 Takes place in the Stroma.
 Uses the energy from the ATP and NADPH
produced by the light reaction to make high
energy sugars.
 Doesn’t require light.
 Requires CO2.
Photosynthesis

The steps of a Dark Reaction:
1. 6 carbon dioxide molecules enter the reaction in
the stroma, they combine with 6 (5 carbon)
molecules to make 12 (3 carbon) molecules.
2. Energy from ATP and high-energy electrons from
NADPH are used to convert the 12 (3 carbon )
molecules into high-energy forms.
3. 2 of the 12 (3 carbon ) molecules are removed
from the cycle, the plant cell uses these molecules
to produce; sugars, lipids, amino acids, and
other molecules needed for plant metabolism and
growth.
4. The remaining 10 (3 carbon) molecules are
converted back to 6 (5 carbon) molecules like the
cycle started with, they will be used to start the
cycle over again.
Photosynthesis