3.5.1 Photosynthesis
Light dependent reaction:
• Photosynthesis is a two stage reaction: light dependent reaction (LDR)
and the light independent reaction (LIR). Both occur in the chloroplast
but in different locations.
• The light dependent reaction occurs on the grana (thylakoid membrane).
• The light independent reaction occurs in the stroma.
• LDR is the first stage of photosynthesis and it requires light. Light energy
and water are used to create ATP and reduced NADP which are needed
for the light-independent stage.
Photoionisation:
• Light energy is absorbed by the chlorophyll
• This results in electrons becoming excited and raising up an energy level
to leave chlorophyll.
• The chlorophyll becomes positively charged.
• Some of the energy from the released electrons is used to make ATP and
reduced NADP in chemiosmosis.
Chemiosmosis:
• The electrons that gained energy and left the chlorophyll move along a
series of proteins embedded within the thylakoid membrane called
electron carriers.
• As they move along they release energy and some of the energy from
electrons is used to pump the protons across the chloroplast membranes
via active transport.
• An electrochemical gradient is created.
• The protons pass through the enzyme ATP synthase which produces ATP.
Photolysis:
• Light energy is absorbed by chlorophyll and splits water into oxygen,
protons and electrons.
Light dependent reaction:
• Photosynthesis is a two stage reaction: light dependent reaction (LDR)
and the light independent reaction (LIR). Both occur in the chloroplast
but in different locations.
• The light dependent reaction occurs on the grana (thylakoid membrane).
• The light independent reaction occurs in the stroma.
• LDR is the first stage of photosynthesis and it requires light. Light energy
and water are used to create ATP and reduced NADP which are needed
for the light-independent stage.
Photoionisation:
• Light energy is absorbed by the chlorophyll
• This results in electrons becoming excited and raising up an energy level
to leave chlorophyll.
• The chlorophyll becomes positively charged.
• Some of the energy from the released electrons is used to make ATP and
reduced NADP in chemiosmosis.
Chemiosmosis:
• The electrons that gained energy and left the chlorophyll move along a
series of proteins embedded within the thylakoid membrane called
electron carriers.
• As they move along they release energy and some of the energy from
electrons is used to pump the protons across the chloroplast membranes
via active transport.
• An electrochemical gradient is created.
• The protons pass through the enzyme ATP synthase which produces ATP.
Photolysis:
• Light energy is absorbed by chlorophyll and splits water into oxygen,
protons and electrons.
