Lesson 3- Light Dependant Reactions : Photolysis and Photophodphorylation Flashcards
What happens to the light energy when it enters the chloroplast
Absorbed by the photosynthetic pigments in the photo systems and converted to chemical energy
What happens when the light energy is absorbed by PSI and PSII
Energy from light raises 2 electrons in each chlorophyll molecule t is higher energy level. The chlorophyll molecules are now in an excited state
What is photosionisation
When light causes electrons to become excited and leave chlorophyll
What charge will chlorophyll molecules have after they have been ‘excited’ by light absorption
Positive (they have been oxidised as they have lost electrons)
What happens to excited electrons ?
They leave the excited PSII and pass along the electron transport chain via electron carrier molecules in a series of redox reactions, losing energy in the process. They move towards PSI
What is produced from the photolysis of water
4 hydrogen ions, 1 molecule of oxygen, 4 electrons
What do the electrons produced by photolysis of water do?
Replace the electrons that have left PSII
Why does photolysis only occur in PSII?
Because only PSII have the enzymes
What are 2 products of the light- dependant stage of photosynthesis
Reduced NAD and ATP
What happens in photo-phosphorylation
Process by with ATP is produced
ADP + Pi → ATP
What is Chemiosmosis?
Chemiosmosis is the movement of chemicals (protons) down their concentration gradient, the energy released from this can be used by ATP synthase to synthesise ATP
What is photoionisation ?
Photoionisation describes the process of using light energy to excite electrons in chlorophyll enough so that they can leave the molecule. It leaves the chlorophyll as a positively charged ion.
What happens to the chlorophyll as electrons leave
Becomes oxidised
What happens to the electron carrier as it gains electrons
Becomes reduced
What is Photolysis?
The energy from light is used to split water into protons (4 H+ ions), 4 electrons and oxygen. Only PSII can split water as it has the correct enzyme complex.