Light Dependent Reaction Flashcards
What stage is the light dependent reaction of the process photosynthesis?
The light dependent reaction stage is the first stage of photosynthesis
Where does the light dependent reaction stage occur?
It occurs in the chloroplast of the plant cell, on the thylakoid membranes or the grana
What does the light dependent reaction need to occur?
Light
What does the light dependent reaction use light energy for?
The light energy splits water into hydrogen ions, oxygen and electrons
The light dependent reaction stage is is split into four key stages, what are these stages in order?
- Photolysis of water
- Photoionisation of chlorophyll
- Chemiosmosis
- Production of ATP + reduced NADP
What is the name of the process that involves light energy splitting water during the light dependent reaction of photosynthesis? Describe what happens during this process:
The process is called photolysis. It involves light energy being absorbed by chlorophyll and splitting water into oxygen, H+ ions (protons) and electrons
What is the photolysis of water?
It is the light energy being absorbed by chlorophyll and splitting water into oxygen, H+ ions and electrons (e-)
What is the word equation that shows the process of photolysis?
H2O ~> 1/2 O2 + 2e- + 2H+
After water molecules are split, what molecules do they form? What is each molecule’s function after being formed?
H+ ions (proton) are formed. They are picked up by NADP to form NADPH, to be used in the light independent reaction.
Electrons (e-) are formed. They are passed along a chain of electron carrier proteins, which release energy needed in this stage.
Oxygen is formed. Oxygen is useless in photosynthesis, but can be used for respiration or be diffused out the lead through the stomata.
What is the photoionisation of chlorophyll?
The photoionisation of chlorophyll makes chlorophyll become ionised by light
What is the process of the photoionisation of chlorophyll?
- The chlorophyll absorbs the light energy and the energy is picked up by the electrons
- The electrons becomes excited and raise up in energy levels, which causes them to leave the chlorophyll molecule
- The moment the electrons leave the chlorophyll molecule, the chlorophyll molecules become ionised
After the photoionisation of chlorophyll, what happens to the released electrons?
Some of the released electrons have their energy taken and used to make ATP and reduced NADP in chemiosmosis
What is chemiosmosis?
The movement of ions across a partially permeable membrane, from an area of a high concentration to an area of low concentration
What is the step by step process of chemiosmosis?
- The electrons that left the chlorophyll move along a series of proteins embedded within the membrane
- As the electrons move along they release energy and some of the energy is used to pump the protons across chloroplast membranes
- A high concentration of protons is created in the thylakoid lumen, due to the photolysis of water and chemiosmosis. This results in there being more protons in the thylakoid lumen than the chloroplast stroma
- This difference creates an electrochemical gradient. This leads to facilitated diffusion occurring
- The protons can only diffuse through the ATP synthase, which cause a change in shape with the protein. The change in shape provides energy for the catalyst of an ATP
- Lastly some of the protons that have moved back down the electrochemical gradient are picked up by the coenzyme NADP to become reduced NADP
How is the reduced NADP created in the light dependent reaction?
Once the hydrogen ions have diffused through ATP synthase into the chloroplast stroma, they are then picked up by the coenzyme NADP to form reduced NADP
