1. Overview of photosynthesis/ respiration
The light dependent reaction
The light-dependent reaction in such detail as to show that: •
chlorophyll absorbs light, leading to photoionisation of chlorophyll
• some of the energy from electrons released during photoionisation
is conserved in the production of ATP and reduced NADP
• the production of ATP involves electron transfer associated with
the transfer of electrons down the electron transfer chain and
passage of protons across chloroplast membranes and is catalysed
by ATP synthase embedded in these membranes (chemiosomotic
theory)
• photolysis of water produces protons, electrons and oxygen.
Light hits the photosystem
This energy causes the electrons to be excited and photosystem 2 loses
an electron
Photolyzed water then produces hydrogen ion further increases their
concentration inside the thylakoid space to maintain a
concentration gradient and an electron which acts as an electron donor
The electron flow of the original one through electron carriers that was
lost generates energy which allows hydrogen ions to move against their
concentration gradient from….
The hydrogen ions then want to move to the higher concentration gradient
in the stroma from the thylakoid membrane pumped from the stroma
using protein carriers in the thylakoid membrane to maintain a
concentration gradient so they travel through ATP synthase channel
(they form small granules on the membrane surface - stalked
granules) proteins as H+ is a polar molecule - bilayer is
impermeable to
As the H+ pass through the ATP synthase channels, they cause
changes to the enzyme which catalyses ATP synthesis. This
stimulates the production of ATP from ADP and pi
The hydrogen ions along with the electron contribute to the reaction that
converts NADP to reduced NADP
The two purposes of the LDR:
To add Pi to ADP making ATP
, To split water into H+ ions and OH- ions through photolysis as it is caused by
light
Exam question
Describe what happens during photoionisation in the light dependent
reaction
1. Chlorophyll absorbs light OR Light excites/moves electrons in chlorophyll;
2. Electron/s are lost OR (Chlorophyll) becomes positively charged;
The light independent reaction
The light-independent reaction uses reduced NADP from the
lightdependent reaction to form a simple sugar. The hydrolysis of
ATP, also from the light-dependent reaction, provides the additional
energy for this reaction. The light-independent reaction in such
detail as to show that: • carbon dioxide reacts with ribulose
bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate
(GP). This reaction is catalysed by the enzyme rubisco
• ATP and reduced NADP from the light-dependent reaction are used
to reduce GP to triose phosphate
• some of the triose phosphate is used to regenerate RuBP in the
Calvin cycle
• some of the triose phosphate is converted to useful organic
substances.
C02 from the atmosphere diffuses into the leaf through the stomata and
dissolves in the water around the walls of the mesophyll cells
It then diffuses through the cell - surface membrane, cytoplasm and
chloroplast membranes into the stroma of the chloroplast
RuBP (5 carbon molecule) (ribulose bisphosphate) reacts with C02
catalysed by the enzyme Rubisco (ribulose bisphosphate carboxylase) into
a carbon 6 molecule
This breaks down immediately as it is unstable into glycerate-3-phosphate
(2 3 carbon molecules)
Ammino acids and fatty acids can be produced immediately from the
glycerate 3 phosphate
The 2GP is converted to triose phosphate using ATP hydrolysis and
reduced NADP
NADP is then re-formed and goes back to the LDR
Some of the triose phosphate is converted into hexose sugars
Most is used to regenerate ribulose bisphosphate using ATP from the LDR
The light dependent reaction
The light-dependent reaction in such detail as to show that: •
chlorophyll absorbs light, leading to photoionisation of chlorophyll
• some of the energy from electrons released during photoionisation
is conserved in the production of ATP and reduced NADP
• the production of ATP involves electron transfer associated with
the transfer of electrons down the electron transfer chain and
passage of protons across chloroplast membranes and is catalysed
by ATP synthase embedded in these membranes (chemiosomotic
theory)
• photolysis of water produces protons, electrons and oxygen.
Light hits the photosystem
This energy causes the electrons to be excited and photosystem 2 loses
an electron
Photolyzed water then produces hydrogen ion further increases their
concentration inside the thylakoid space to maintain a
concentration gradient and an electron which acts as an electron donor
The electron flow of the original one through electron carriers that was
lost generates energy which allows hydrogen ions to move against their
concentration gradient from….
The hydrogen ions then want to move to the higher concentration gradient
in the stroma from the thylakoid membrane pumped from the stroma
using protein carriers in the thylakoid membrane to maintain a
concentration gradient so they travel through ATP synthase channel
(they form small granules on the membrane surface - stalked
granules) proteins as H+ is a polar molecule - bilayer is
impermeable to
As the H+ pass through the ATP synthase channels, they cause
changes to the enzyme which catalyses ATP synthesis. This
stimulates the production of ATP from ADP and pi
The hydrogen ions along with the electron contribute to the reaction that
converts NADP to reduced NADP
The two purposes of the LDR:
To add Pi to ADP making ATP
, To split water into H+ ions and OH- ions through photolysis as it is caused by
light
Exam question
Describe what happens during photoionisation in the light dependent
reaction
1. Chlorophyll absorbs light OR Light excites/moves electrons in chlorophyll;
2. Electron/s are lost OR (Chlorophyll) becomes positively charged;
The light independent reaction
The light-independent reaction uses reduced NADP from the
lightdependent reaction to form a simple sugar. The hydrolysis of
ATP, also from the light-dependent reaction, provides the additional
energy for this reaction. The light-independent reaction in such
detail as to show that: • carbon dioxide reacts with ribulose
bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate
(GP). This reaction is catalysed by the enzyme rubisco
• ATP and reduced NADP from the light-dependent reaction are used
to reduce GP to triose phosphate
• some of the triose phosphate is used to regenerate RuBP in the
Calvin cycle
• some of the triose phosphate is converted to useful organic
substances.
C02 from the atmosphere diffuses into the leaf through the stomata and
dissolves in the water around the walls of the mesophyll cells
It then diffuses through the cell - surface membrane, cytoplasm and
chloroplast membranes into the stroma of the chloroplast
RuBP (5 carbon molecule) (ribulose bisphosphate) reacts with C02
catalysed by the enzyme Rubisco (ribulose bisphosphate carboxylase) into
a carbon 6 molecule
This breaks down immediately as it is unstable into glycerate-3-phosphate
(2 3 carbon molecules)
Ammino acids and fatty acids can be produced immediately from the
glycerate 3 phosphate
The 2GP is converted to triose phosphate using ATP hydrolysis and
reduced NADP
NADP is then re-formed and goes back to the LDR
Some of the triose phosphate is converted into hexose sugars
Most is used to regenerate ribulose bisphosphate using ATP from the LDR
