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?
- Photoionisation of chlorophyll
- Photolysis of water
- 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 process by which the movement of hydrogen ions across a biological membrane generates ATP
What is the step by step process of chemiosmosis?
1.Electros go through a series of redox reactions as they are passed along electron carriers
- As the electrons move along they release energy which pumps H+ ions across the chloroplast membranes
- This results in a high concentration of H+ ions in the thylakoid lumen compared to the stroma
- This creates an electrochemical gradient which leads to H+ ions passing through ATP synthase by facilitated diffusion
- This movement causes ATP synthase enzyme to change shape which drives the phosphorylation of ADP into ATP
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 and funnelled down into photosystem II which activates the photosynthetic pigment. This activations leads to the photoionisation of chlorophyll and the photolysis of water.
In the photolysis of water, water molecules are split into protons, electrons and oxygen molecules. The electrons are passed along the electron transfer chain, the protons are used in chemiosmosis and the oxygen is considered a “waste product”.
In the photoionisation of chlorophyll, electrons absorb light energy and become excited. This raises them up an energy level and they leave chlorophyll, making chlorophyll ionised.
The excited electrons move along the electron transfer chain, releasing energy. This energy pumps hydrogen ions across the chloroplast membranes by active transport. Due to the photoionisation of chlorophyll and photolysis of water, a high concentration of protons is built up in the thylakoid lumen.
The high concentration of protons creates an electrochemical gradient. The protein ATP synthase allows the diffusion of protons across the chloroplast membranes. With this movement ATP synthase changes shape which catalyses the phosphorylation of ADP + and inorganic phosphate into 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)
Complete diagram on Freeform of light dependent reaction
Complete diagram on Freeform of light dependent reaction
