Energy Transfer In And Between Organisms: - Light Dependent Reaction

- Light Dependent Reaction -

Oxidation and Reduction 

Oxidation is when the substance gains oxygen or loses hydrogen. 

Reduction is when the substance loses oxygen or gains hydrogen.

Oxidation results in energy being given out, whearas reduction results in it being taken in. 

Making of a ATP

Photoionisation is a result of the chlorophyll molecule becoming ionised. 

The electrons leave the chlorophyll are taken up by a molecule electron carrier // the chlorophyll is oxidised // electron carrier is reduced. 

Electrons are passed along a series of oxidation-reduction chain reactions. // A transfer chain that is located in membrane of the thylakoids. 

With each carrier the energy level is lowered in the electron, the energy released is used to combine the inorganic phosphate and the ADP molecule to create ATP. 

Chemiosmotic theory

This explains the ATP production 

1.  Proton pumps // protein carrier are used to pump the protons (H+) from the stroma in the thylakoid membrane. 
2. Electrons released from photolysis drives the process as it produces protons // further increase of concentration in the thylakoid space.
3. A concentration gradient is maintained // higher concentration = in the thylakoid space, lower concentration = in the stroma 
4. Protons can only cross the thylakoid membrane through ATP synthesised channel proteins. 
5. The channels for small granules on the membrane surface = stalked granules. 
6. Protons pass through these ATP synthase channels they can cause changes to the structure of the enzyme // catalyse combination of ADP with inorganic phosphate to form ATP. 

Photolysis of water 

2H₂O → 4H+ + 4e⁻  + O² 

Protons are passed out of the thylakoid space through ATP synthase channels taken up by electron carrier = NADP.
On taking up the protons the NADP reduced // the reduced NADP = main product of the light dependent stage and enters the light independent reaction.

Reduced NADP is important because it is further potential source of chemical energy to the plant.
Oxygen is a by-product from the photolysis of water is either used in respiration or diffuses out of the stomata as waste product of photosynthesis.

Site of the light-dependent reaction: 

Chloroplasts are structurally adapted to their functions of capturing sunlight. 

Thylakoid membranes have a large surface area for attachment of chlorophyll, electron carriers and enzymes carry out light-dependent reaction. 

Network of proteins in grana holds the chlorophyll // precise to allows maximum absorption. 

Granal membranes have ATP synthase channels which catalyse the production of ATP // also selectively permeable which allows establishment of proton gradient. 

The chloroplast contain both DNA and ribosomes can quickly and manufacture some of the proteins involved in light-dependent reactions.