Photosynthesis
Solar Energy (Sunlight)
- form of energy known as electromagnetic energy (Radiation)
- travels in rhythmic waves (analogous to a rock dropped in a pond)
Electromagnetic spectrum
- Entire Range of Radiation
- The segment most important to life is Visible Light - (400nm ---------------------700nm)
- The theory of light as waves explains most of its properties, but it behaves as though it consists of discrete particles which are known as photons
- Each photon has a fixed quantity of energy (the shorter the wavelength , the greater the energy)
- A photon of violet light packs about twice as much energy as a photon of Red light
When light meets matter
- As light meets matter, it may be Reflected, Transmitted, or Absorbed
- Substances that absorb light are called pigments
- Different pigments absorb light of different wavelengths
- When a molecule absorbs a photon of light, one of the molecules electrons is elevated to a higher energy level to an Excited State which is very UNSTABLE
Types of Pigments in Chloroplasts
- Chlorophyll a
- Chlorophyll b
- Carotenoids
- clustered in the thylakoid membrane in assemblies of a few hundred pigment molecules
Assembly Complex
- Of the many chlorophyll a molecules in each assembly, only one can trigger the light reactions by donating its excited electron to the 1° electron acceptor
- This chlorophyll a molecule is known as the Reaction Center
- The other chlorophyll a, chlorophyll b, and carotenoid molecules function collectively as a light gathering antenna that passes the energy from molecule to molecule until it reaches the Reaction Center
Photosystem
The antenna complex, its reaction center, and the primary electron acceptor are collectively known as a photosystem
Two Types:
1) Photosystem I
2) Photosystem II
The antenna complex, its reaction center, and the primary electron acceptor are collectively known as a photosystem
Two Types:
1) Photosystem I
2) Photosystem II
Photosystem I
- Reaction center is a specialized chlorophyll a molecule known as P700
- It is called P700 because the pigment absorbs a wavelength of light at 700 nm the best (far red part of the spectrum)
Photosystem II
- The reaction center is a specialized chlorophyll a molecule known as P680
- Absorbs light at 680 nm the best (also in the red part of the spectrum)
P700 verses P680
- P700 and P680 are identical chlorophyll a molecules…..so why does one absorb light at 700 nm the best while the other absorbs light at 680 nm the best?
- P700 and P680 are no different in structure than any of the other chlorophyll a molecules that make up the antenna complex…..why do these 2 molecules serve as the reaction centers?