Light Dependent Reaction Flashcards
(24 cards)
What stage is the light dependent reaction of the process photosynthesis?
The light dependent reaction stage is the first stage of photosynthesis
Label the chloroplast
Find labelled chloroplast image to compare to your version, mark and correct
Where does the light dependent reaction stage occur?
It occurs in the thylakoid membranes of the chloroplasts
What does the light dependent reaction need to occur?
Light
The light dependent reaction stage 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 photolysis of water?
It is the use of light energy to split 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+
What is the role of an electron carrier?
It accepts high energy electrons from chlorophyll and passes them along an electron transport chain in the thylakoid membrane
What happens as electrons move along the electron transport chain?
As they move along, they release energy through a series of redox reactions. Each carrier is at a lower energy level, and uses the lost energy to make ATP
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.
Why is the photolysis of water needed in the light dependent reaction?
To replace electrons lost by chlorophyll when it absorbs light and becomes photo ionised
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
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 catalyses 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
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 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
What are the final products of the light dependent reaction that is carried onto the light independent reaction?
ATP and reduced NADP
How are thylakoid membranes adapted for their role in the light dependent reaction?
They provide a large surface area for chlorophyll, electron carriers, and enzymes involved in the reactions like photosystem II
How are the granal membranes adapted for their role in the light dependent reaction?
They have ATP synthase within them which catalyse the production of ATP. They are also selectively permeable, which allows a proton gradient to be established
How are chloroplasts adapted for their role in the light dependent reaction?
They contain both DNA and ribosomes, allowing them to quickly and easily manufacture the proteins involved in the light dependent reaction
