Photosynthesis: Capturing and Converting Energy

1
Photosynthesis Capturing and Converting Energy

• In the process of photosynthesis, plants convert
  the energy of sunlight into the energy in
  chemical bonds of sugars and starches
  (carbohydrates).
• carbon dioxide water glucose
  oxygen
• 6CO2 6H2O C6H12O6
  6O2
• 
  sunlight

2
Photosynthesis

• Photosynthesis involves two sets of reactions
  the light-dependent light-independent reactions
• The light-dependent reactions
• 1. Light absorption
• Photosynthesis takes place in the chloroplast.
• The chloroplast contain saclike photosynthetic
  membranes that have chlorophyll and other
  pigment molecules. This membrane is called the
  thylakoid.

3
Photosynthesis Capturing and Converting Energy
4
(No Transcript)
5
Photosynthesis Capturing and Converting Energy

• Chlorophyll and the pigment molecules are
  used in whats called a photosystem.
• Green plants contain two photosystems (II I)
• Photosynthesis starts when light is absorbed by
  one of the pigment molecules in photosystem II.
• This energy is passed among pigment molecules
  until it reaches the reaction center.
• High energy electrons are released from here.

6
Photosynthesis Capturing and Converting Energy
7
Photosynthesis Capturing and Converting Energy
8
Photosynthesis Capturing and Converting Energy

• 2. Electron transport
• After release from the reaction center, the
  high-energy electrons are moved by a series of
  electron carriers in the photosynthetic membrane.
  
• This process is called electron transport.

9
Photosynthesis Capturing and Converting Energy

• At the end of this process, the high-energy
  electrons are passed to the electron carrier
  NADP, converting it to NADPH.
• This compound will be used later in the
  light-independent reactions.

10
(No Transcript)
11
Photosynthesis Capturing and Converting Energy

• 3. Oxygen production
• The high-energy electrons removed from the
  chlorophyll and used in electron transport
  (mentioned above), are replaced by electrons
  from a water molecule.
• To get the electrons the water molecule is split
  thereby leaving a molecule of oxygen gas
  which is released into the air.

12
Photosynthesis Capturing and Converting Energy

• 4. ATP Formation
• The splitting of water molecules to replace the
  electrons results in the build up of hydrogen
  ions on the inside of the membrane.
• This results in the photosynthetic membrane
  being positively charged on the inside and
  negatively charged on the outside.

13
Photosynthesis Capturing and Converting Energy

• This difference in charge is an energy source
• that is used to make ATP from ADP.
• ATP (adenosine triphosphate) is the compound
  that stores energy in cells

14
Photosynthesis Capturing and Converting Energy
15
Adenosine Triphosphate (ATP)
16
ATP
17
Photosynthesis Capturing and Converting Energy

• Summary
• The light reaction uses sunlight and water to
• produce oxygen and two energy-storing
• compounds, NADPH and ATP.

18
Investigating Photosynthesis

• Early researchers wondered where the mass of a
  plant comes from as it grows.
• In the 17th century Jan van Helmont, based on
  his experiment, concluded that most of the mass
  a plant gains comes from water.
• Van Helmont's experiment accounts for the
  hydrate or water portion of the carbohydrate
  produced by photosynthesis.

19
Investigating Photosynthesis

• But, where does the carbon portion of the
  carbohydrate come from?