Photosynthesis
Photosynthesis is a reaction in which light energy is used to produce glucose in plants. The
process requires water and carbon dioxide, with the products being glucose and oxygen.
There are two stages of photosynthesis, these are the light dependent stage and the light
independent stage. The rate of photosynthesis is determined by carbon dioxide
concentration, light intensity and temperature.
Chloroplasts are the site of photosynthesis and are adapted to photosynthesis in the
following ways:
- Contains stacks of thylakoid membranes called grana which provides a large surface
area for the attachment of chlorophyll, electrons and enzymes.
- A network of proteins in the grana hold the chlorophyll in a very specific manner to
absorb the maximum amount of light.
- The granal membrane has ATP synthase channels embedded allowing ATP to be
synthesised as well as being selectively permeable allowing the establishment of a
proton gradient.
- Chloroplasts contain DNA and ribosomes allowing them to synthesise proteins
needed in the light dependent reaction.
, Light dependent reaction:
- Occurs in the thylakoid
- Requires photosynthetic pigments e.g. chlorophyll a, chlorophyll b or carotenoids
- Light strikes a chlorophyll molecule and electrons within it are excited to higher
energy level, they leave the chlorophyll molecule and are accepted by an electron
carrier. This process is called photoionisation. The chlorophyll molecule has lost
electrons so it has been oxidised. The electron carrier has gained electrons so has
been reduced.
- The electrons are passed along a series of electron carriers in the thylakoid
membrane in a series of oxidation- reduction reactions. Each new carrier is at a
slightly lower energy level than the previous one so the electrons lose energy at
each stage.
- Some of this energy is used to combine an inorganic phosphate molecule with an
ADP molecule to make ATP. The mechanism by which this happens is called the
chemiosmotic theory.
- The chlorophyll molecule is now short of electrons which must be replaced.
Photolysis of water occurs, providing the electrons to replace those lost by
chlorophyll molecule.
- The protons from the split water and the electrons from the electron carrier join to
form a hydrogen atom and reduce the electron carrier called NADP to form ‘reduced
NADP’
- Oxygen leftover from the photolysis of water diffuses out of the leaf.
- ATP and reduced NADP produced from the light dependent reaction are then used
in the light independent reaction.
Chemiosmosis
Photosynthesis is a reaction in which light energy is used to produce glucose in plants. The
process requires water and carbon dioxide, with the products being glucose and oxygen.
There are two stages of photosynthesis, these are the light dependent stage and the light
independent stage. The rate of photosynthesis is determined by carbon dioxide
concentration, light intensity and temperature.
Chloroplasts are the site of photosynthesis and are adapted to photosynthesis in the
following ways:
- Contains stacks of thylakoid membranes called grana which provides a large surface
area for the attachment of chlorophyll, electrons and enzymes.
- A network of proteins in the grana hold the chlorophyll in a very specific manner to
absorb the maximum amount of light.
- The granal membrane has ATP synthase channels embedded allowing ATP to be
synthesised as well as being selectively permeable allowing the establishment of a
proton gradient.
- Chloroplasts contain DNA and ribosomes allowing them to synthesise proteins
needed in the light dependent reaction.
, Light dependent reaction:
- Occurs in the thylakoid
- Requires photosynthetic pigments e.g. chlorophyll a, chlorophyll b or carotenoids
- Light strikes a chlorophyll molecule and electrons within it are excited to higher
energy level, they leave the chlorophyll molecule and are accepted by an electron
carrier. This process is called photoionisation. The chlorophyll molecule has lost
electrons so it has been oxidised. The electron carrier has gained electrons so has
been reduced.
- The electrons are passed along a series of electron carriers in the thylakoid
membrane in a series of oxidation- reduction reactions. Each new carrier is at a
slightly lower energy level than the previous one so the electrons lose energy at
each stage.
- Some of this energy is used to combine an inorganic phosphate molecule with an
ADP molecule to make ATP. The mechanism by which this happens is called the
chemiosmotic theory.
- The chlorophyll molecule is now short of electrons which must be replaced.
Photolysis of water occurs, providing the electrons to replace those lost by
chlorophyll molecule.
- The protons from the split water and the electrons from the electron carrier join to
form a hydrogen atom and reduce the electron carrier called NADP to form ‘reduced
NADP’
- Oxygen leftover from the photolysis of water diffuses out of the leaf.
- ATP and reduced NADP produced from the light dependent reaction are then used
in the light independent reaction.
Chemiosmosis
