PHOTOSYNTHESIS
Photosynthesis is simply defined as “ formation of carbohydrates from CO2 and H2O by
illuminated green cells of plants, O2 and H2O by being the byproducts”. In other words,
capture of photons of light by green plant cells and conversion of their radiant energy into
chemical form of energy is called photosynthesis.
IMPORTANCE OF PHOTOSYNTHESIS
(i) Synthesis of organic food.
(ii) Non-photosynthetic or heterotrophic organisms depend upon for organic food. Plants
are, therefore called produces. Other are called consumers.
(iii) It converts radiant or solar energy into chemical energy.
(iv) Fossil fuels are products of photosynthetic activity of past plants.
(v) All plant products of photosynthetic activity of past plants.
(vi) It absorbs CO2 from atmosphere which tends to increase due to respiration of organisms
and combustion.
(vii) It evolves oxygen which is consumed in respiration and combustion of respiratory
substrate and formation of ozone in stratosphere for filtering out harmful radiations.
(viii) Productivity of crop depends upon rate of photosynthesis.
LANDMARKS IN PHOTOSYNTHESIS
1. STEPHAN HALES (1727) : Father of plant physiology pointed out that green plants require
sunlight to obtain nutrition from air.
2. JOSEPH PRIESTLY (1771): An English clergyman and chemist, showed that the plants purify
air which becomes foul by the burning of candles and respiration by mice.
3. INGENHOUSZ: A Dutch physician in 1779 demonstrated that light is necessary for
purification of air by plants.
4. JEAN SENEBIER (1782): He showed that the presence of noxious gas produced by animals
and by plants in darkness (CO2) stimulated production of “purified air” (O2) in light.
5. NICHOLAS THEODORE de SUSSURE (1804): He showed that the total weight of the organic
matter produced and oxygen evolved by the green plants in presence of sunlight was
greater than the weight of fixed air (CO2), consumed by them during this process. He
concluded that besides fixed air ( CO2), water must constitute the raw material for this
process.
6. PALLETIER AND CAVENTION (1818): They discovered and named green colour of leaf as
chlorophyll which could be separated from leaf by boiling in alcohol.
7. JULIUS ROBERT MAYER (1845): He observed that the green plants utilize light energy and 1
convert it into chemical energy of organic matter.
,PHOTOSYNTHESIS www.spiroacademy.com
8. JULIUS VON SACHS (1854): Showed that the process of photosynthesis takes place in
chloroplasts and results in the synthesis of starch. He also showed that chlorophyll is
confined to chloroplast.
9. GG STOCKS (1864): Obtained pure fraction of chlorophyll –a and b and detected the
presence of chlorophyll – c.
10. ENGELMANN (1888): Plotted the action spectrum of photosynthesis.
11. FF BLACKMAN (1905): Noted that photosynthesis is a two step process. A dark reaction also
occurs along with photochemical reaction. He also proposed the law of limiting factor.
12. WILLSTATTER AND STOLL (1913, 1918): Showed detailed account of chemical composition
and functioning of chlorophyll.
13. WARBERG (1920): Flash light experiment with chlorella as useful material for
photosynthesis experiments.
14. VAN NEIL (1931): Showed that the photosynthetic bacterial fixed CO2 in the presence of H2S.
He postulated that the plants evolve O2 by splitting H2O not CO2.
15. EMERSON AND ARNOLD (1932): Recognised light reaction consists of two distinct
photochemical process. They showed that about 2500 chlorophyll molecules are required to
fix one molecule of CO2 in photosynthesis.
16. ROBIN HILL (1937): Isolated chloroplast suspended in water in presence of suitable
hydrogen acceptor which evolve oxygen in presence of light. He demonstrated that the
source of O2 evolved during photosynthesis is water and not CO2.
17. RUBEN AND KAMEN(1941): Used radioactive oxygen O18 and proved that oxygen evolved
was part of water.
18. ARNON, ALLEN AND WHATLEY(1954): Demonstrated that fixation of CO 2 by chloroplast
using C14O2.
19. MELVIN CALVIN(1954): Traced the path of carbon in photosynthesis using unicellular algae
chorella. Melvin calvin gave C3-cycle and was awarded Nobel Prize in 1960 for the discovery
20. PARK AND BIGGINS(1961): Discovered quantosome 100 Angstrom thick and stated that it
contains about 230 chlorophyll molecules.
21. HATCH AND SLACK(1967): Discovered C4 pathway for fixation of CO2
22. HUBER, MICHEL AND DISSENHOFER (1985): Crystallised photosynthesis reaction centre of
bacterium Rhodobacter and got Nobel Prize in 1988.
RAW MATERIALS FOR PHOTOSYNTHESIS
In green plants including algae, photosynthesis takes place in chloroplasts of the cells.
During this process, solar energy is trapped and synthesis of carbohydrates takes place from
carbon dioxide and water. This sunlight, carbon dioxide, water, chloroplast are important
components necessary for plants to derive the process of photosynthesis.
2
, PHOTOSYNTHESIS www.spiroacademy.com
SUNLIGHT
Photosynthesis is a light dependent process. The literal meaning of world “Photosynthesis”
is “ the synthesis, with the help of light”. To drive photosynthesis in plants, sunlight provides
solar energy. Only 0.2% of the light energy, incident on earth is actually used by photo
autotrophs.
Light is the visible radiation which represents a very small portion of the total
electromagnetic spectrum of radiation, emitted by the sun. Visible light (approx. between
400nm to 700 nm) causes the physiological sensation of vision of man. Visible light is
actually a combination of several colours of different colours viz. Violet (400nm to 425 nm),
blue (425nm to 490nm), green (490 – 550 nm), yellow (550 -585 nm), organge (585 – 640
nm) and red (640 – 700 nm)
The most effective regions of visible light spectrum responsible for maximum
photosynthesis in plants are blue and red regions of which red light is most effective. On the
other hand, green light is least effective. Photosynthesis cannot take place beyond the
range of visible spectrum.
CARBON DIOXIDE
In land plants, carbon dioxide is obtained from the atmosphere through the stomata. Small
quantities of carbonates are also absorbed from soil through the roots. Hydrophytes get
their carbon dioxide supply from the aquatic environment as bicarbonates. The latter are
absorbed by hydrophytes through their general surface.
WATER
In the process of photosynthesis, the source of liberated oxygen in water. Photosynthetic
land plants absorb a large amount of water from the soil through the root hairs-present on
their roots. But relatively very small amount of this absorbed water is used in the process of
photosynthesis. Aquatic photosynthesis plants absorb water through their body surface.
As mentioned earlier, Van Niel (1931) hypothesized that the pototosynthetic organisms
require a source of hydrogen. He proposed that oxygenic photosynthesis is an oxidation
reduction reaction where hydrogen of water reacts with carbon dioxide to form organic
compounds
1937, Robin Hill demonstrated that in absence of carbon dioxide, isolated chloroplasts of
stellaria media produced oxygen when they were illuminated in presence of hydrogen
acceptor. Here ferricyanide is reduced to ferrocyanide by photolysis of water. This is Hill
reaction and can be represented as
3
Photosynthesis is simply defined as “ formation of carbohydrates from CO2 and H2O by
illuminated green cells of plants, O2 and H2O by being the byproducts”. In other words,
capture of photons of light by green plant cells and conversion of their radiant energy into
chemical form of energy is called photosynthesis.
IMPORTANCE OF PHOTOSYNTHESIS
(i) Synthesis of organic food.
(ii) Non-photosynthetic or heterotrophic organisms depend upon for organic food. Plants
are, therefore called produces. Other are called consumers.
(iii) It converts radiant or solar energy into chemical energy.
(iv) Fossil fuels are products of photosynthetic activity of past plants.
(v) All plant products of photosynthetic activity of past plants.
(vi) It absorbs CO2 from atmosphere which tends to increase due to respiration of organisms
and combustion.
(vii) It evolves oxygen which is consumed in respiration and combustion of respiratory
substrate and formation of ozone in stratosphere for filtering out harmful radiations.
(viii) Productivity of crop depends upon rate of photosynthesis.
LANDMARKS IN PHOTOSYNTHESIS
1. STEPHAN HALES (1727) : Father of plant physiology pointed out that green plants require
sunlight to obtain nutrition from air.
2. JOSEPH PRIESTLY (1771): An English clergyman and chemist, showed that the plants purify
air which becomes foul by the burning of candles and respiration by mice.
3. INGENHOUSZ: A Dutch physician in 1779 demonstrated that light is necessary for
purification of air by plants.
4. JEAN SENEBIER (1782): He showed that the presence of noxious gas produced by animals
and by plants in darkness (CO2) stimulated production of “purified air” (O2) in light.
5. NICHOLAS THEODORE de SUSSURE (1804): He showed that the total weight of the organic
matter produced and oxygen evolved by the green plants in presence of sunlight was
greater than the weight of fixed air (CO2), consumed by them during this process. He
concluded that besides fixed air ( CO2), water must constitute the raw material for this
process.
6. PALLETIER AND CAVENTION (1818): They discovered and named green colour of leaf as
chlorophyll which could be separated from leaf by boiling in alcohol.
7. JULIUS ROBERT MAYER (1845): He observed that the green plants utilize light energy and 1
convert it into chemical energy of organic matter.
,PHOTOSYNTHESIS www.spiroacademy.com
8. JULIUS VON SACHS (1854): Showed that the process of photosynthesis takes place in
chloroplasts and results in the synthesis of starch. He also showed that chlorophyll is
confined to chloroplast.
9. GG STOCKS (1864): Obtained pure fraction of chlorophyll –a and b and detected the
presence of chlorophyll – c.
10. ENGELMANN (1888): Plotted the action spectrum of photosynthesis.
11. FF BLACKMAN (1905): Noted that photosynthesis is a two step process. A dark reaction also
occurs along with photochemical reaction. He also proposed the law of limiting factor.
12. WILLSTATTER AND STOLL (1913, 1918): Showed detailed account of chemical composition
and functioning of chlorophyll.
13. WARBERG (1920): Flash light experiment with chlorella as useful material for
photosynthesis experiments.
14. VAN NEIL (1931): Showed that the photosynthetic bacterial fixed CO2 in the presence of H2S.
He postulated that the plants evolve O2 by splitting H2O not CO2.
15. EMERSON AND ARNOLD (1932): Recognised light reaction consists of two distinct
photochemical process. They showed that about 2500 chlorophyll molecules are required to
fix one molecule of CO2 in photosynthesis.
16. ROBIN HILL (1937): Isolated chloroplast suspended in water in presence of suitable
hydrogen acceptor which evolve oxygen in presence of light. He demonstrated that the
source of O2 evolved during photosynthesis is water and not CO2.
17. RUBEN AND KAMEN(1941): Used radioactive oxygen O18 and proved that oxygen evolved
was part of water.
18. ARNON, ALLEN AND WHATLEY(1954): Demonstrated that fixation of CO 2 by chloroplast
using C14O2.
19. MELVIN CALVIN(1954): Traced the path of carbon in photosynthesis using unicellular algae
chorella. Melvin calvin gave C3-cycle and was awarded Nobel Prize in 1960 for the discovery
20. PARK AND BIGGINS(1961): Discovered quantosome 100 Angstrom thick and stated that it
contains about 230 chlorophyll molecules.
21. HATCH AND SLACK(1967): Discovered C4 pathway for fixation of CO2
22. HUBER, MICHEL AND DISSENHOFER (1985): Crystallised photosynthesis reaction centre of
bacterium Rhodobacter and got Nobel Prize in 1988.
RAW MATERIALS FOR PHOTOSYNTHESIS
In green plants including algae, photosynthesis takes place in chloroplasts of the cells.
During this process, solar energy is trapped and synthesis of carbohydrates takes place from
carbon dioxide and water. This sunlight, carbon dioxide, water, chloroplast are important
components necessary for plants to derive the process of photosynthesis.
2
, PHOTOSYNTHESIS www.spiroacademy.com
SUNLIGHT
Photosynthesis is a light dependent process. The literal meaning of world “Photosynthesis”
is “ the synthesis, with the help of light”. To drive photosynthesis in plants, sunlight provides
solar energy. Only 0.2% of the light energy, incident on earth is actually used by photo
autotrophs.
Light is the visible radiation which represents a very small portion of the total
electromagnetic spectrum of radiation, emitted by the sun. Visible light (approx. between
400nm to 700 nm) causes the physiological sensation of vision of man. Visible light is
actually a combination of several colours of different colours viz. Violet (400nm to 425 nm),
blue (425nm to 490nm), green (490 – 550 nm), yellow (550 -585 nm), organge (585 – 640
nm) and red (640 – 700 nm)
The most effective regions of visible light spectrum responsible for maximum
photosynthesis in plants are blue and red regions of which red light is most effective. On the
other hand, green light is least effective. Photosynthesis cannot take place beyond the
range of visible spectrum.
CARBON DIOXIDE
In land plants, carbon dioxide is obtained from the atmosphere through the stomata. Small
quantities of carbonates are also absorbed from soil through the roots. Hydrophytes get
their carbon dioxide supply from the aquatic environment as bicarbonates. The latter are
absorbed by hydrophytes through their general surface.
WATER
In the process of photosynthesis, the source of liberated oxygen in water. Photosynthetic
land plants absorb a large amount of water from the soil through the root hairs-present on
their roots. But relatively very small amount of this absorbed water is used in the process of
photosynthesis. Aquatic photosynthesis plants absorb water through their body surface.
As mentioned earlier, Van Niel (1931) hypothesized that the pototosynthetic organisms
require a source of hydrogen. He proposed that oxygenic photosynthesis is an oxidation
reduction reaction where hydrogen of water reacts with carbon dioxide to form organic
compounds
1937, Robin Hill demonstrated that in absence of carbon dioxide, isolated chloroplasts of
stellaria media produced oxygen when they were illuminated in presence of hydrogen
acceptor. Here ferricyanide is reduced to ferrocyanide by photolysis of water. This is Hill
reaction and can be represented as
3
