Title: An annotated diagram explaining the different stages involved
in aerobic respiration including the role of oxygen in this process
Light dependent stage:
This stage takes place on the thylakoid membrane of the chloroplast. The
photosystems with photosynthetic pigments are embedded in this
membrane. The ATP and reduced NADP are made in this stage which is later
used for the Calvin cycle (light independent stage).
Light energy is used to break down water in a reaction called photolysis: this
then produces hydrogen ions, electrons, and oxygen in the thylakoid. The
oxygen is used in the plant for aerobic respiration, but most of it diffuses out
of the leaf through the stomata. The hydrogen ions are used during
chemiosmosis to produce a proton gradient so it can produce ATP during
photophosphorylation and to reduce NADP used in the light independent
stage. The electrons are used to replace those lost by oxidised chlorophyll.
Photophosphorylation:
When a photon (a particle of light) hits chlorophyll in the photosystem II
(PSII), the electrons inside PSII absorb the energy from the light and become
excited. The electrons are picked up by electron acceptors and pass along a
series of electron carriers (proteins) embedded in the thylakoid membrane.
Energy is released as the electrons pass along the chain. This energy pumps
protons across the thylakoid membrane into the thylakoid spaces. This
creates a proton gradient across the thylakoid membrane. The protons travel
down the gradient through channels with the ATP synthase enzymes that join
ADP and an inorganic phosphate to make ATP. This flow of protons down a
proton gradient is known as chemiosmosis. The kinetic energy from the
protons moving is converted into chemical energy in ATP molecules. These
ATP molecules are then used in the light independent stage of
photosynthesis. There are two types of photophosphorylation, cyclic and
non-cyclic.
Cyclic photophosphorylation uses only photosystem I, with chlorophyll a
(P700) present. When light hits PSI, the excited electrons pass to an electron
acceptor and back to the chlorophyll, a molecule they were lost from. Only a
small amount of ATP is made and there is no photolysis of water and no
reduced NADP is produced.
Non-cyclic photophosphorylation involves both photosystems I and II. Light
hits PSII and the pair of excited electrons pass along the electron carrier and
the energy released is used to make ATP. Light also strikes PSI and a pair of
electrons here are excited too. These electrons and the protons produced
, during photolysis of water to join to NADP and produce reduced NADP. The
electrons from the oxidised photosystem II replace the electrons lost from
photosystem I. Electrons lost by oxidised chlorophyll in PSII are replaced with
some from photolysed water. Protons from photolysed water take part in
chemiosmosis to make ATP.
Light independent stage:
This stage is also known as the Calvin Cycle and takes place in the stroma.
Light is not used during this stage. Products of the light dependent stage are
used, so the light independent stage will eventually stop if light becomes a
limiting factor.
Carbon dioxide is needed during the Calvin Cycle to provide carbon to
produce large organic molecules. Carbon dioxide from the atmosphere
diffuses into the open stomata in the leaf. It travels through the spongy
mesophyll layer and reaches the palisade mesophyll layer. It diffuses across
the cell wall and membrane into the stroma.
There are three main steps within the Calvin cycle:
1. Carbon fixation:
The carbon dioxide combines with ribulose biphosphate (RuBP)(5C).
The enzyme Rubisco (ribulose bisphosphate carboxylase) catalyses
this reaction.
RuBP is carboxylated. Produces two glycerate 3-phosphate (3C)
2. Reduction of GP
GP is phosphorylated and reduced to triose phosphate (TP) in a reaction
involving reduced NADP and ATP
3. RuBP is regenerated from TP in reactions that use ATP
ATP and five-sixths of the triose phosphate (TP) molecules are used
to regenerate ribulose bisphosphate (RuBP)
Title: Carry out an investigation involving the effect of light
intensity/carbon dioxide concentrations on rates of photosynthesis
in a plant.
Aim: To investigate the effect of light intensity and carbon dioxide
concentrations on the rate of photosynthesis
Risk assessment:
in aerobic respiration including the role of oxygen in this process
Light dependent stage:
This stage takes place on the thylakoid membrane of the chloroplast. The
photosystems with photosynthetic pigments are embedded in this
membrane. The ATP and reduced NADP are made in this stage which is later
used for the Calvin cycle (light independent stage).
Light energy is used to break down water in a reaction called photolysis: this
then produces hydrogen ions, electrons, and oxygen in the thylakoid. The
oxygen is used in the plant for aerobic respiration, but most of it diffuses out
of the leaf through the stomata. The hydrogen ions are used during
chemiosmosis to produce a proton gradient so it can produce ATP during
photophosphorylation and to reduce NADP used in the light independent
stage. The electrons are used to replace those lost by oxidised chlorophyll.
Photophosphorylation:
When a photon (a particle of light) hits chlorophyll in the photosystem II
(PSII), the electrons inside PSII absorb the energy from the light and become
excited. The electrons are picked up by electron acceptors and pass along a
series of electron carriers (proteins) embedded in the thylakoid membrane.
Energy is released as the electrons pass along the chain. This energy pumps
protons across the thylakoid membrane into the thylakoid spaces. This
creates a proton gradient across the thylakoid membrane. The protons travel
down the gradient through channels with the ATP synthase enzymes that join
ADP and an inorganic phosphate to make ATP. This flow of protons down a
proton gradient is known as chemiosmosis. The kinetic energy from the
protons moving is converted into chemical energy in ATP molecules. These
ATP molecules are then used in the light independent stage of
photosynthesis. There are two types of photophosphorylation, cyclic and
non-cyclic.
Cyclic photophosphorylation uses only photosystem I, with chlorophyll a
(P700) present. When light hits PSI, the excited electrons pass to an electron
acceptor and back to the chlorophyll, a molecule they were lost from. Only a
small amount of ATP is made and there is no photolysis of water and no
reduced NADP is produced.
Non-cyclic photophosphorylation involves both photosystems I and II. Light
hits PSII and the pair of excited electrons pass along the electron carrier and
the energy released is used to make ATP. Light also strikes PSI and a pair of
electrons here are excited too. These electrons and the protons produced
, during photolysis of water to join to NADP and produce reduced NADP. The
electrons from the oxidised photosystem II replace the electrons lost from
photosystem I. Electrons lost by oxidised chlorophyll in PSII are replaced with
some from photolysed water. Protons from photolysed water take part in
chemiosmosis to make ATP.
Light independent stage:
This stage is also known as the Calvin Cycle and takes place in the stroma.
Light is not used during this stage. Products of the light dependent stage are
used, so the light independent stage will eventually stop if light becomes a
limiting factor.
Carbon dioxide is needed during the Calvin Cycle to provide carbon to
produce large organic molecules. Carbon dioxide from the atmosphere
diffuses into the open stomata in the leaf. It travels through the spongy
mesophyll layer and reaches the palisade mesophyll layer. It diffuses across
the cell wall and membrane into the stroma.
There are three main steps within the Calvin cycle:
1. Carbon fixation:
The carbon dioxide combines with ribulose biphosphate (RuBP)(5C).
The enzyme Rubisco (ribulose bisphosphate carboxylase) catalyses
this reaction.
RuBP is carboxylated. Produces two glycerate 3-phosphate (3C)
2. Reduction of GP
GP is phosphorylated and reduced to triose phosphate (TP) in a reaction
involving reduced NADP and ATP
3. RuBP is regenerated from TP in reactions that use ATP
ATP and five-sixths of the triose phosphate (TP) molecules are used
to regenerate ribulose bisphosphate (RuBP)
Title: Carry out an investigation involving the effect of light
intensity/carbon dioxide concentrations on rates of photosynthesis
in a plant.
Aim: To investigate the effect of light intensity and carbon dioxide
concentrations on the rate of photosynthesis
Risk assessment:
