Light Dependent Reaction Flashcards
(20 cards)
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
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 leaf through the stomata.
What is the photoionisation of chlorophyll?
The photoionisation of chlorophyll makes chlorophyll become ionised (lose an electron) 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
How is ATP produced in the light dependent reaction?
Electrons release energy as they pass along the electron transfer chain. This energy pumps hydrogen ions across the chloroplast membranes through active transport. A high concentration is created in the thylakoid lumen and a electrochemical gradient is created. This causes facilitated diffusion to occur through ATP synthase. This movement of hydrogen ions causes ATP synthase to change shape and catalyse the production of ATP.
Outline the light dependent reaction from start to finish.
1.
Light energy is absorbed by chlorophyll (in photosystem II) which causes water to split. The water molecule is split into hydrogen ions, oxygen and electrons. The hydrogen ions move into chemiosmosis. The oxygen atoms are released as “waste products” and the electrons are passed onto the electron transfer chain with electrons produced from the photoionisation of chlorophyll.
Light energy is absorbed by chlorophyll, which is picked up by electrons. These electrons become excited and raise up a energy level, causing them to leave the chlorophyll molecule. This ionises the chlorophyll molecule.
The excited electrons move along the electron transfer chain, releasing some energy. This energy pumps across the hydrogen ions across the chloroplast membranes through active transport. Due to the photoionisation of water and chemiosmosis, a high concentration of protons in the thylakoid lumen is created.
This high conc of protons create an electrochemical gradient. Due to the increase in the thylakoid lumen instead of the stroma facilitated diffusion occurs. The ATP synthase protein allows the protons to diffuse through. With the movement of the hdyrogen, the ATP synthase changes shapes which catalyses the production of ATP
What is the primary pigment?
What are the two accessory pigments?
Chlorophyll A
Chlorophyll B
Carotenoids (carotene)
What does decarboxylation?
The removal of a carbon dioxide from a molecule
What is the metabolic pathway?
A series of small reactions controlled by enzymes (like photosynthesis)
What is the wavelength of photosystem I?
What is the wavelength of photosystem II?
Photosystem I: Wavelength of 700nm
Photosystem II: Wavelength of 680nm
