Photosynthesis Reactions Long Answers

Question 1

What occurs in the light dependent reactions (step by step)

Answer 1

• a chlorophyll in each photosystem rises to a higher energy level and becomes excited
• electrons leave the excited chlorophyll molecule
• electrons pass along a transport chain in a series of oxidations and reductions. Electrons lose energy in these reactions.
• The energy is used in two ways: to synthesize ATP (from electrons released from photosystem 2) and to reduce NADP (from the electrons released from photosystem 1)
• electrons must be replaced so the process can continue
• the electrons of photosystem are replenished by accepting the electrons from the electron transport chain originating from photosystem 2
• water splits unto oxygen, hydrogen and electrons-which replenish the electrons in photosystem 2 and allow the process to continue

Question 2

Steps of the Calvin cycle:

Answer 2

• a carbon dioxide reacts with a 5 carbon sugar called RuBP, reaction is catalysed by an enzyme known as rubisco which permanently fixes CO2 into organic molecules
• an unstable 6 carbon compound is formed
• two 3-carbon molecules of glycerate-3-phosphate are formed
• glycerate-3-phosphate is reduced by NADPH, the reaction is driven by ATP
• two 3-carbon sugars called triose phosphate are formed
• some triose phosphates will be converted to carbohydrates and other organic compounds. The majority regenerates RuBP using ATP