11.2 Light dependant reaction Flashcards
Two purposes of the reaction
- Pi+ADP to make ATP
- Split water into H+ ions and OH- ions (photolysis)
Describe the process of photoionisation
- Light is absorbed by chlorophyll
- Two electrons in the chlorophyll molecule are excited by light and are emitted from the chlorophyll molecule
Electron transport chain
Electrons pass along electron carriers (located in the thylakoid membrane) in a series of oxidation reduction reactions
Each electron carrier is at a lower energy level than the previous one so the electrons loose energy
Some of this energy is used to make ATP
Chemiosmotic theory
- Protons pumped from stroma into thylakoid space using proton pumps
- Energy to drive this comes from photolysis
- Photolysis also produces protons which further increases their concentration in the thylakoid space
4.This maintains a concentration gradient of protons between the thylakoid space and the stroma - Protons can only cross the thylakoid membrane into the stroma through ATP synthase channels
- As protons pass through these channels they cause changes to the structure of the enzyme which then catalyses the production of ATP from ADP and Pi
Photolysis
Electrons which are lost from the chlorophyll molecule are replaced from the water molecules that are split using light energy
Photolysis equation
2H2O —-> 4H+ + 4e- + O2
Reduction of NADP
Protons from the product of photolysis pass out of the thylakoid space through ATP synthase channels and are taken up by NADP which reduces NADP
How are chloroplasts adapted for the LD reaction
- Thylakoid membrane provides a large surface area for the attachment of chlorophyll enzymes and electron carriers
- Granal membranes have ATP synthase channels within them which catalyse the production of ATP
- Chloroplasts contain DNA and ribosomes so they can quickly manufacture proteins needed
- Network of proteins in the grant hold chlorophyll in a precise manner for maximum light absorption
