Photosynthesis

An Overview of the Light Capturing Reaction of Photosynthesis

Prepared byJohn McCormick

August 21, 2009

The process of photosynthesis

The Basic Reaction

6CO2 + 6H2O C6H12O6 + 6O2

Sun

The Energy Source

Photons provide the energy necessary to drive photosynthesis

Photons:Are packets of energy

Have no massBehave as particles or wave

Electromagnetic Radiation

The smaller the wavelength the higher the energyλ Lamda is the symbol used for wavelengthf is the symbol for frequencyAs you move from left to right on the chart thewavelength gets longer and the frequency decreases

The structure of a Chloroplast

A Chloroplast:

• Is a double membrane organelle

•Chlorophyll is located in the thylakoids

•A stack of thylakoids is called a granum

•The light capturing reactions occurs in the thylakoids

There are two major forms of chlorophyll- Chlorophyll a

Chlorophyll b

Both molecules have a porphorin ring

Chlorophyll a and b both absorb lightEnergy from the visible end of the Electromagnetic spectrum

This is seen in an absorptionspectrum

The absorption spectrum shows:

Chlorophyll a and b absorb predominantly the red and blue wavelengths of light

Accessory pigments such as carotenoids absorb other wavelengths of light

When chlorophyll first absorbs a photon it becomes excited and:

Passes this electron e- to a primary

electron acceptor

This molecule then passes the electron down the electron transport chain

This results in the formation of ATP

This is seen here

A molecule of water is broken down to replace the electronsthat are lost in this process

H2O 2H+ + ½

Next, a photon of a different wavelength is absorbed by chlorophyll in Photosystem I and becomes excited.

This e- is passed to a primary electron acceptor.

The e- is then passed to

NADP+ an e- acceptor

NADP+ becomes reduced as a result

NADP+ has this structure

This is the entire Light Capturing reaction

Summary of the Light Capturing Reaction

ATP is generatedATP is generated

NADPH is producedNADPH is produced

Water is broken downWater is broken down

OO22 is generated is generated

Waiting on a Sunny Day provided by

To see animation of the entire process

http://www.cnr.vt.edu/DENDRO/forestbiology/photosynthesis.swf