CO2 is the main raw material for making sugar. The amount of CO2 in the atmosphere is 0.04%. 1% of this CO2 is used in photosynthesis. Chemical reactions of water and CO2 occur in chloroplasts to produce sugars. The rate of photosynthesis increases when the amount of CO2 increases up to a certain limit. However, if the amount of CO2 is high, photosynthesis stops.

Oxygen is a by-product of photosynthesis. As the amount of oxygen in the atmosphere increases, the rate of photosynthesis decreases. If its amount is more, photosynthesis stops.

Sunlight participates in the formation of chlorophyll, opens the stomata and helps in making food. The rate of photosynthesis increases when the amount of light increases up to a certain limit. However, if the amount of light is high, photosynthesis stops. Photosynthesis can be maximized by increasing the light from 100 foot candles to 3000 foot candles. If the light is continuous, photosynthesis can reach its maximum level in 10-12 hours. Violet, blue, orange and red light are mostly used in photosynthesis. The rate of photosynthesis is higher in red and blue light. However, as a single light, red light has the highest rate of photosynthesis. Scientists Hoover and Gabrielsen (1948) proved that photosynthesis occurs more in red light and less in green light.

1. Light: Sunlight participates in the formation of chlorophyll, opens the stomata and helps in making food. The rate of photosynthesis increases when the amount of light increases up to a certain limit. However, if the amount of light is high, photosynthesis stops. Photosynthesis can be maximized by increasing the light from 100 foot candles to 3000 foot candles. If the light is continuous, photosynthesis can reach its maximum level in 10-12 hours. Violet, blue, orange and red light are mostly used in photosynthesis. The rate of photosynthesis is higher in red and blue light. However, as a single light, red light has the highest rate of photosynthesis. Scientists Hoover and Gabrielsen (1948) proved that photosynthesis occurs more in red light and less in green light.
2. Oxygen: Oxygen is a by-product of photosynthesis. As the amount of oxygen in the atmosphere increases, the rate of photosynthesis decreases. If its amount is more, photosynthesis stops.
3. Water: The raw material of photosynthesis is water. It increases the rate of chemical reactions. Water breaks down to produce O2 and NADPH+H+.
4. Carbon Dioxide: CO2 is the main raw material for making sugar. The amount of CO2 in the atmosphere is 0.04%. 1% of this CO2 is used in photosynthesis. Chemical reactions of water and CO2 occur in chloroplasts to produce sugars. The rate of photosynthesis increases when the amount of CO2 increases up to a certain limit. However, if the amount of CO2 is high, photosynthesis stops.
5. Temperature: A particular effector of photosynthesis is temperature. The optimum temperature for photosynthesis is 22-350C. At temperatures above 450C, photosynthesis in most plants ceases. For every 100C increase in temperature, the rate of photosynthesis increases about 2.2-2.6 times. Some bacteria and high-temperature blue-green algae can carry out photosynthesis at temperatures up to 700C.
6. Minerals: Magnesium and iron form chlorophyll. When these minerals are lacking, the production of chlorophyll decreases and the rate of photosynthesis also decreases.
7. Vitamins: Vitamins in algae and other plants keep photosynthesis going.
8. Chemicals: The presence of hydrogen sulphide, chloroform, methane, toxic gases etc. in the air disrupts or stops the photosynthesis process.

In 1941, Reuben, Camen and Randall of the University of California in the United States used radioactive oxygen (18O2) in photosynthesis to prove that the source of O2 released in the photosynthesis process is water. They observed the photosynthesis of Chlorella algae by identifying the radioactive isotope 18O2 in water. See the released oxygen has a radioactive isotope (H218O).
6CO2+12H218O→ C6H12O6+6H2O+618O2
Again, he observed the photosynthesis of Chlorella algae by labeling the oxygen of CO2 with the radioactive isotope 18O2. They found that sugar has a radioactive isotope of oxygen (C6H1218O6). Emitted oxygen does not contain radioactive isotopes.
6C18O2 +12H2O→ C6H1218O6+6H2O+6O2
It is clear from the experiments that water is the source of O2 released in the photosynthesis process.

British biochemist Robin Hill (1937) took chloroplasts, water (H2O) and hydrogen acceptors (2A) in a container. Then put the test in the light for some time. Observe that H2 and O2 are produced. Not using H2O produced no sugars, but using CO2 produced O2.
2H2O + 2A → 2AH2 + O2

Scientist Van Niel (1935) observed the photosynthesis of sulfur bacteria. Sulfur bacteria use hydrogen sulfide (H2S) instead of H2O in photosynthesis. That is, sulfur bacteria produce sugars using CO2 and H2S. O2 is not produced as H2O is not used.

In the early 20th century, scientists believed that carbon dioxide was the source of O2 released during photosynthesis. It has now been proved that water is the source of O2 released in the process of photosynthesis.
1. Van Niel test
Scientist Van Niel (1935) observed the photosynthesis of sulfur bacteria. Sulfur bacteria use hydrogen sulfide (H2S) instead of H2O in photosynthesis. That is, sulfur bacteria produce sugars using CO2 and H2S. O2 is not produced as H2O is not used.
2. Hill reaction
British biochemist Robin Hill (1937) took chloroplasts, water (H2O) and hydrogen acceptors (2A) in a container. Then put the test in the light for some time. Observe that H2 and O2 are produced. Not using H2O produced no sugars, but using CO2 produced O2.
2H2O + 2A → 2AH2 + O2
3. Ruben Kamen’s radioactive oxygen experiment
In 1941, Reuben, Camen and Randall of the University of California in the United States used radioactive oxygen (18O2) in photosynthesis to prove that the source of O2 released in the photosynthesis process is water. They observed the photosynthesis of Chlorella algae by identifying the radioactive isotope 18O2 in water. See the released oxygen has a radioactive isotope (H218O).
6CO2+12H218O→ C6H12O6+6H2O+618O2
Again, he observed the photosynthesis of Chlorella algae by labeling the oxygen of CO2 with the radioactive isotope 18O2. They found that sugar has a radioactive isotope of oxygen (C6H1218O6). Emitted oxygen does not contain radioactive isotopes.
6C18O2 +12H2O→ C6H1218O6+6H2O+6O2
It is clear from the experiments that water is the source of O2 released in the photosynthesis process.

In 1843, the scientist Liebig said, if a physiological process is controlled by more than one effector, the rate of the process will be controlled by the slowest effector. This is called Law of minimum. In 1905, F. F. Blackman expanded the Law of Minimum to determine the Law of Limiting Factor. He said, when a biochemical reaction is influenced by more than one effector, the rate of the reaction is determined by the effector of the lowest magnitude. This formula is called Law of Limiting Factor. The lesser factor is called Limiting Factor. The formula is called Blackman’s Law of Limiting Factor after him.
Explanation: According to the principle of limiting factors, each factor of photosynthesis has an optimum value. Another factor controls the rate of the process when the optimum value is exceeded.
30-350C is the optimum temperature for photosynthesis. As the temperature gradually increases from 00C, the rate of photosynthesis also increases and peaks at 30-350C. But when the temperature is raised above 350C, the rate of photosynthesis suddenly decreases rapidly. Another effector then controls the rate of photosynthesis.
Again, the optimum value of leaf CO2 utilization per hour for photosynthesis is 10 mg. As the level of CO2 utilization gradually increased from 1 mg, the rate of photosynthesis also increased and peaked at 10 mg. But when CO2 is increased above 10 mg, the rate of photosynthesis suddenly drops rapidly. Another effector then controls the rate of photosynthesis.
As can be seen from the diagram, according to the principle of Limiting Factor, if the rate of photosynthesis is controlled by several factors at the same time, the amount of any one effector indicates the steady state of photosynthesis.

The ratio of O2 released to CO2 taken in during photosynthesis is called the photosynthetic rate or PQ. When the amount of O2 released in photosynthesis is high, the rate of photosynthesis increases and when the amount of O2 released is low, the rate of photosynthesis decreases.