5.1 Photosynthesis

Question 1

Specifically, where does the Light Dependant Reactions occur

Answer 1

Thylakoid membranes

Question 2

Describe and explain the processes of the Light Dependant Reaction

Answer 2

• Chlorophyll absorbs light energy and exites electrons within, leading to photoionisation of chlorophyll
• Exited electrons move out of the chlorophyll, and down the electron transport chain, releasing energy through a series of redox reactions
• Energy is used to pump protons from the stroma into the thylakoid space
• Electrons at the end of the electron transport chain reduce NADP to reduced NADP
• Protons diffuse through ATPsynthase
• Energy released is used to generate ATP
• ADP + Pi –> ATP
• Photoysis of water uses **light energy **to split water into protons, oxygen and electrons, and these electrons replace those lost in the chlorophyll

Question 3

Describe the photolysis of water

Answer 3

Light energy used to split water into oxygen, protons and electrons that replace those lost in chlorophyll

Question 4

Describe the photoionisation of chlorophyll

Answer 4

• Chlorophyll absorbs light energy
• Which exites electrons within
• Leading to electrons moving out of the chlorophll
• And down the electrons transport chain

Question 5

What is the role of NADP in the light dependant reactions

Answer 5

Accept electrons at end of electron transport chain, reducing it to reduced NADP

Question 6

Where specifically does the light independant reactions occur

Answer 6

Fluid stroma

Question 7

Describe and explain the processes of the light independant reactions

Answer 7

• CO2 combines with RuBP to form 2 molecules of GP
• Catalysed by the enzyme Rubisco
• GP is reduced into triose phosphate
• Using **energy from ATP **hydrolysis, and electrons provided by reduced NADP oxidised to NADP
• 2 molecules of triose phospate combine to regenerate RuBP
• So all RuBP is regenerated
• The remaining carbons are used to synthesise organic molecules (e.g hexose sugars)

Question 8

Describe and explain carbon fixation as part of the light independant reactions

Answer 8

• CO2 combines with RuBP to produce 2 molecules of GP
• Catalysed by Rubisco

Question 9

What is the role of ATP in the light independant reactions

Answer 9

Provide energy to reduce GP to triose phosphate when it is hydrolysed

Question 10

What is the role of reduced NADP in the light independant reactions

Answer 10

Oxidised to provide electrons for the reduction of GP into triose phosphate

Question 11

How much RuBP is regenerated in the light independant reactions

Answer 11

ALL RuBP is regenerated

Question 12

What are the limiting factors in relation to photosynthesis

Answer 12

• Carbon dioxide concentration
• Temperature
• Light intensity
• Water avaliability

Question 13

Why is light intensity a limiting factor for photosynthesis

Answer 13

It provides energy needed for the light dependant reaction

Question 14

Why is water avaliability a limiting factor in photosynthesis

Answer 14

Causes stomata to close, reducing carbon dioxide concentration

Question 15

In regards to photosynthesis and respiration, how can plant growth occur

Answer 15

• NPP - GPP - R
• Rate of photosynthesis must be greater than rate of respiration for growth to occur