Photosynthesis: Capturing and Converting Energy In the process of photosynthesis, plants convert the energy of sunlight into the energy in chemical bonds

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

PhotosynthesisPhotosynthesis involves two sets of reactions: the light-dependent & light-independent reactionsThe light-dependent reactions1. 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.



• Chlorophyll and the pigment molecules are used in what’s 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.




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.


• 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.


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.


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.


• This difference in charge is an energy sourcethat is used to make ATP from ADP.

• ATP (adenosine triphosphate) is the compound that stores energy in cells


Adenosine Triphosphate (ATP)

ATP


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

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.

Investigating PhotosynthesisBut, where does the carbon portion of the carbohydrate come from?

Documents

Photosynthesis: Capturing and Converting Energy In the process of photosynthesis, plants convert the energy of sunlight into the energy in chemical bonds