1. Photosynthesis as an energy In eukaryotic photosynthetic cells, chloroplasts are
the sites of photosynthesis.
fixing mechanism 1. Light-dependent reactions - take place in
the membrane system of thylakoids.
1.) PHOTOSYNTHESIS Thylakoids are flattened fluid-
filled sacs, which form stacks
called grana at intervals.
Introduction to photosynthesis
Chlorophylls, carotenoids and
Photosynthesis is a metabolic process by which electron acceptors are located on
light energy is trapped and converted to this membrane system of
chemical energy, which is stored in chemical thylakoids
bonds of carbohydrates, fats, oils, and proteins 2. Calvin cycle – takes place in the stroma of
the chloroplast.
All life on Earth depends on photosynthesis either Stroma is a gel like structure
directly or indirectly. Stroma contains soluble enzymes
Photosynthesis occurs in plants, algae and certain and other chemicals
prokaryotes.
Global importance of photosynthesis:
Photosynthetic pigments
1. All life on earth depends on photosynthesis,
directly or indirectly Introduction to photosynthetic pigments
2. Fulfill both carbon and energy requirements
of organisms Photosynthetic pigments are substances which
3. Provide O2 for respiration of aerobic absorb visible light.
organisms Different pigments absorb different wavelengths of
4. Maintain O2 and CO2 balance in the light
atmosphere In a leaf we see green colour, because
5. Production of fossil fuel chlorophylls absorb violet, blue and red
6. Maintenance of global temperature light and therefore, they transmit and
reflect green colour.
During photosynthesis CO2 is reduced by the H of In chloroplast, there are two types of chloroplast
H2O and simple sugars are made using light pigments:
energy. (H2O is split into H+ ions and electrons 1. Chlorophylls (Chlorophyll a, Chlorophyll b)
which are transferred from water to CO2 reducing it 2. carotenoids (Carotenes, xanthophylls)
to sugars) Chlorophyll a
Process of photosynthesis consists of two main This the key light capturing pigment
stages, and they are integrated: They participate directly in the light reaction
1. Light-dependent reaction of photosynthesis.
2. Calvin cycle According to the action spectrum,
There are two types of photosynthetic mechanisms chlorophyll a is more effective for blue and
(pathways) based on the number of C atoms of the red light.
first stable product of the CO2 fixation: Chlorophyll b and carotenoids (carotenes and
1. C3 Mechanism – No of C atom of the first xanthophylls)
stable compound is three (PGA) They are effective in absorption of specific
2. C4 Mechanism – No of C atom of the first range wavelengths of light corresponding to
stable compound is four (OAA- different colours.
oxaloacetate) Other important function of some carotenoids
is photoprotection.
Photoprotection is absorption and
dissipation of excessive light energy.
If not, excessive light may cause damage to
the chlorophylls or interact with oxygen
and form reactive oxidative molecules
which are dangerous to the cell.
, The excited electrons will pass through several
Spectra relating to photosynthesis and
electron carriers until they reach the final electron
photosynthetic pigments
acceptor
1. ABSORPTION SPECTRUM:
An absorption spectrum is a graph of the relative
amounts of light absorbed at different Here, the chlorophyll a is oxidized, and electron
wavelengths by a pigment acceptor is reduced.
Photosystems
Chlorophyll molecules, other organic molecules
and proteins are organized into complexes in the
thylakoid membrane of chloroplasts. They are
called photosystems.
A photosystem contains:
i. A reaction centre complex - The reaction
centre complex contains organized
2. ACTION SPECTRUM proteins holding a pair of chlorophyll a
An action spectrum is a graph showing the molecules and a primary electron
effectiveness of different wave lengths of light in acceptor
stimulating the photosynthesis. (Rate of ii. Light harvesting complex – light
photosynthesis Vs wavelength) harvesting complexes contain various
photosynthetic pigments
There are two types of photosystems found in the
thylakoid membrane.
a) Photosystem I (PS I) –
The chlorophyll a molecule in the reaction
centre of PS I is known as P700 since they
absorb light at 700nm wavelength
effectively.
According to the above two spectra: b) Photosystem II (PS II) –
i.
Photosynthetic pigments absorb light of The chlorophyll a molecule in the reaction
wavelengths corresponding to red and blue light centre of PS II is known as P680 since
ii. Blue and red light in the visual spectrum of they absorb light at 680nm wavelength
sunlight is mainly used in photosynthesis effectively.
iii. The light energy for photosynthesis is absorbed
by photosynthetic pigments
Excitation of photosynthetic pigments by light
When a chlorophyll a molecule absorbs a photon, it
becomes excited.
The energy from the photon will be absorbed by the
chlorophyll a molecule and it will boost the
electrons of the chlorophyll a molecule to a higher
energy level.
The excited electrons which are carrying a higher
amount of energy will be accepted by a primary
electron acceptor.
Thereafter the chlorophyll a molecules will become
positively charged.
As the excited state is unstable, it will return to their
lower energy state.
1. Photosynthesis as an energy In eukaryotic photosynthetic cells, chloroplasts are
the sites of photosynthesis.
fixing mechanism 1. Light-dependent reactions - take place in
the membrane system of thylakoids.
1.) PHOTOSYNTHESIS Thylakoids are flattened fluid-
filled sacs, which form stacks
called grana at intervals.
Introduction to photosynthesis
Chlorophylls, carotenoids and
Photosynthesis is a metabolic process by which electron acceptors are located on
light energy is trapped and converted to this membrane system of
chemical energy, which is stored in chemical thylakoids
bonds of carbohydrates, fats, oils, and proteins 2. Calvin cycle – takes place in the stroma of
the chloroplast.
All life on Earth depends on photosynthesis either Stroma is a gel like structure
directly or indirectly. Stroma contains soluble enzymes
Photosynthesis occurs in plants, algae and certain and other chemicals
prokaryotes.
Global importance of photosynthesis:
Photosynthetic pigments
1. All life on earth depends on photosynthesis,
directly or indirectly Introduction to photosynthetic pigments
2. Fulfill both carbon and energy requirements
of organisms Photosynthetic pigments are substances which
3. Provide O2 for respiration of aerobic absorb visible light.
organisms Different pigments absorb different wavelengths of
4. Maintain O2 and CO2 balance in the light
atmosphere In a leaf we see green colour, because
5. Production of fossil fuel chlorophylls absorb violet, blue and red
6. Maintenance of global temperature light and therefore, they transmit and
reflect green colour.
During photosynthesis CO2 is reduced by the H of In chloroplast, there are two types of chloroplast
H2O and simple sugars are made using light pigments:
energy. (H2O is split into H+ ions and electrons 1. Chlorophylls (Chlorophyll a, Chlorophyll b)
which are transferred from water to CO2 reducing it 2. carotenoids (Carotenes, xanthophylls)
to sugars) Chlorophyll a
Process of photosynthesis consists of two main This the key light capturing pigment
stages, and they are integrated: They participate directly in the light reaction
1. Light-dependent reaction of photosynthesis.
2. Calvin cycle According to the action spectrum,
There are two types of photosynthetic mechanisms chlorophyll a is more effective for blue and
(pathways) based on the number of C atoms of the red light.
first stable product of the CO2 fixation: Chlorophyll b and carotenoids (carotenes and
1. C3 Mechanism – No of C atom of the first xanthophylls)
stable compound is three (PGA) They are effective in absorption of specific
2. C4 Mechanism – No of C atom of the first range wavelengths of light corresponding to
stable compound is four (OAA- different colours.
oxaloacetate) Other important function of some carotenoids
is photoprotection.
Photoprotection is absorption and
dissipation of excessive light energy.
If not, excessive light may cause damage to
the chlorophylls or interact with oxygen
and form reactive oxidative molecules
which are dangerous to the cell.
, The excited electrons will pass through several
Spectra relating to photosynthesis and
electron carriers until they reach the final electron
photosynthetic pigments
acceptor
1. ABSORPTION SPECTRUM:
An absorption spectrum is a graph of the relative
amounts of light absorbed at different Here, the chlorophyll a is oxidized, and electron
wavelengths by a pigment acceptor is reduced.
Photosystems
Chlorophyll molecules, other organic molecules
and proteins are organized into complexes in the
thylakoid membrane of chloroplasts. They are
called photosystems.
A photosystem contains:
i. A reaction centre complex - The reaction
centre complex contains organized
2. ACTION SPECTRUM proteins holding a pair of chlorophyll a
An action spectrum is a graph showing the molecules and a primary electron
effectiveness of different wave lengths of light in acceptor
stimulating the photosynthesis. (Rate of ii. Light harvesting complex – light
photosynthesis Vs wavelength) harvesting complexes contain various
photosynthetic pigments
There are two types of photosystems found in the
thylakoid membrane.
a) Photosystem I (PS I) –
The chlorophyll a molecule in the reaction
centre of PS I is known as P700 since they
absorb light at 700nm wavelength
effectively.
According to the above two spectra: b) Photosystem II (PS II) –
i.
Photosynthetic pigments absorb light of The chlorophyll a molecule in the reaction
wavelengths corresponding to red and blue light centre of PS II is known as P680 since
ii. Blue and red light in the visual spectrum of they absorb light at 680nm wavelength
sunlight is mainly used in photosynthesis effectively.
iii. The light energy for photosynthesis is absorbed
by photosynthetic pigments
Excitation of photosynthetic pigments by light
When a chlorophyll a molecule absorbs a photon, it
becomes excited.
The energy from the photon will be absorbed by the
chlorophyll a molecule and it will boost the
electrons of the chlorophyll a molecule to a higher
energy level.
The excited electrons which are carrying a higher
amount of energy will be accepted by a primary
electron acceptor.
Thereafter the chlorophyll a molecules will become
positively charged.
As the excited state is unstable, it will return to their
lower energy state.
