Light Dependent Reaction

Question 1

What stage is the light dependent reaction of the process photosynthesis?

Answer 1

The light dependent reaction stage is the first stage of photosynthesis

Question 2

Where does the light dependent reaction stage occur?

Answer 2

It occurs in the chloroplast of the plant cell, on the thylakoid membranes or the grana

Question 3

What does the light dependent reaction need to occur?

Answer 3

Light

Question 4

What does the light dependent reaction use light energy for?

Answer 4

The light energy and water are used to create ATP and reduced NADP which are needed for the light independent stage

Question 5

What is the name of the process light energy is involved in during the light dependent reaction of photosynthesis? Describe what happens during this process

Answer 5

The process is called photolysis. It involves light energy being absorbed by chlorophyll and splitting water into oxygen, H+ ions (protons) and OH- ions

Question 6

The light dependent reaction stage is is split into four key stages, what are these stages?

Answer 6

1. Photoionisation of chlorophyll
2. Production of ATP + reduced NADP
3. Chemiomosis
4. Photolysis of water

Question 7

What is the photolysis of water?

Answer 7

It is the light energy being absorbed by chlorophyll and splitting water into oxygen, H+ ions and electrons (e-)

Question 8

What is the word equation that shows the process of photolysis?

Answer 8

H2O ~> 1/2 O2 + 2e- + 2H+

Question 9

After water molecules are split, what molecules do they form? What is each molecule’s function after being formed?

Answer 9

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.

Question 10

What is the photoionisation of chlorophyll?

Answer 10

The photoionisation of chlorophyll makes chlorophyll become ionised by light

Question 11

What is the process of the photoionisation of chlorophyll?

Answer 11

1. The chlorophyll absorbs the light energy and the energy is picked up by the electrons
2. The electrons becomes excited and raise up in energy levels, which causes them to leave the chlorophyll molecule
3. The moment the electrons leave the chlorophyll molecule, the chlorophyll molecules become ionised

Question 12

After the photoionisation of chlorophyll, what happens to the released electrons?

Answer 12

Some of the released electrons have their energy taken and used to make ATP and reduced NADP in chemiosmosis

Question 13

What is chemiosmosis?

Answer 13

The process by which the movement of hydrogen ions across a biological membrane generates ATP

Question 14

What is the step by step process of chemiosmosis? (roughly:)

Answer 14

1. The electrons that left the chlorophyll move along a series of proteins embedded within the membrane
2. As the electrons move along they release energy and some of the energy is used to pump the protons across chloroplast membranes
3. 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
4. This difference creates an electrochemical gradient. This leads to facilitated diffusion occurring
5. 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 ADP and an inorganic phosphate
6. Lastly some of the protons that have moved back down the electrochemical gradient are picked up by the coenzyme NADP to become reduced NADP