UNIT 2: Photosynthesis

Question 1

photosynthesis

Answer 1

the process of using sunlight energy and chlorophyll to produce glucose from carbon dioxide and water.
occurs in the chloroplast

Question 2

light stage definition

Answer 2

requires the direct input of light and occurs in the thylakoid membranes

Question 3

dark stage definition

Answer 3

(light independent stage / calvin cycle)

does not require the direct input of light and occurs in the stroma.

Question 4

light stage

Answer 4

• sunlight photon strikes a cluster of chlorophyll molecules called a photosystem.
• the chlorophyll molecules transfer the energy to a reaction centre chlorophyll (RCC).
• the energy is absorbed by an electron which travels to a higher orbit as a result.
• the energised electron is released from the RCC and can take one of two paths:
  1. cyclic pathway (pathway 1)
  2. non-cyclic pathway (pathway 2)

Question 5

cyclic pathway (pathway 1)

Answer 5

• the energised electron is picked up by an electron acceptor.
• it is passed from electron acceptor to electron acceptor losing energy along the way.
• this energy is used to power the production of ATP from ADP and a phosphate.
• once the electron has been passed through it is taken back up by the RCC.
• the ATP is passed onto the next stage of photosynthesis - the dark stage.

Question 6

non-cyclic pathway (pathway 2)

Answer 6

• the energised electron is picked up by an electron acceptor.
• it is passed from electron acceptor to electron acceptor losing energy along the way.
• this energy is used to power the production of ATP from ADP and a phosphate.
• the photosystem is deficient in electrons and splits water into electrons, protons and oxygen gas.
• the electrons are taken up by the photosystem, the protons are stored in a proton pool within the chloroplast and the oxygen gas is either released into the atmosphere or used in respiration.
• the electrons that passed through the electron acceptors is now passed onto another photosystem.
• light strikes this second photosystem and the electrons are re-energised.
• the electrons are released and captured by NADP+ to become NADP-.
• protons are attracted towards and taken up by NADP- to become NADPH.
• NADPH and ATP are passed onto the next stage of photosynthesis - the dark stage.

Question 7

dark stage

Answer 7

• NADPH and ATP from the light stage are used to reduce (addition of protons and electrons) carbon dioxide in the stroma of the chloroplast.
• as a result, NADPH is converted back to NADP+ and ATP is converted back to ADP and a phosphate.

Question 8

Photolysis

Answer 8

The splitting of water by light