3.5.2.1 LDR photosynthesis

Question 1

EQ - describe how in the LDR light energy generates ATP

Answer 1

1. light energy excites electrons in chlorophyll
2. electrons pass down electron transport chain
3. electrons reduce carriers
4. energy passed to carriers
5. energy used by proton pump to generate a proton / electrochemical gradient allowing chemiosmosis
6. ATP generated from ADP and Pi (phosphorylation)

Question 2

Full stages of light dependent reaction

Answer 2

1. light is absorbed by the pigments in photosystem II and funnelled down towards the reaction centre
2. the electrons of chlorophyll a in the reaction centre become excited to a higher energy level (photoionisation)
3. the high energy electrons are passed along a chain of electron carriers - reducing and oxidising the electron carriers
4. a proton pump is. powered allowing the protons to be pumped across the membrane into the thylakoid space (this along with photolysis creates an electrochemical gradient and allows ATP to be made - chemiosmosis)
5. Light is absorbed by the pigments in photosystem I and funnelled down towards the reaction centre causing electrons be emitted from photosystem I’s chlorophyll a to an electron carrier
6. The electrons from photosystem II replace the lost electrons from PSI
7. Water undergoes photolysis splitting into electrons, protons and oxygen - the electrons replace the lost electrons from PSII, the protons contribute to the electrochemical gradient and the oxygen is lost as waste
8. The electrons are removed from the chain by the final electron acceptor NADP, which also accepts protons moving through the ATP synthase forming reduced NADP

Question 3

What are photosystems, what do they contain & where are they found?

Answer 3

• protein complexes
• containing accessory proteins and reaction centre (chlorophyll a)
• found in the thylakoid membrane of the chloroplast

Question 4

Function of photosystems

Answer 4

• to absorb light and transfer energy and electrons

- ensures maximum light harvesting by funnelling light to chlorophyll a in the reaction centre

Question 5

Which photons are most effective in photosynthesis and why?

Answer 5

• red and blue

- green and yellow light wavelengths are reflected

Question 6

What is photoionisation?

Answer 6

• the light energy excites electrons, giving them energy causing them to be released
• release of electrons causes the atom to become positively charged

Question 7

What is photolysis?

Answer 7

splitting of a molecule using light energy

Question 8

What is phosphorylation?

Answer 8

adding phosphate to a molecule using light

Question 9

What is reduction?

Answer 9

when a molecule or atom has gained electrons and may have gained hydrogen or lost oxygen