Category: Biology Second Paper

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.

The German word Chranz means wreath. A garland-like ring of mesophyll cells containing tiny chloroplasts around the leaf bundle sheath is called Crange anatomy. In 1974, scientist Laetsch called this concentric ring of bundle sheaths as Chranz anatomy. Chranz anatomy is a particularly significant feature of C4 plants. It helps plants in photosynthesis in the presence of low CO2.

Starch is produced in the chloroplast during photosynthesis. Starch is first converted to glucose and then to sucrose. Sucrose is transported throughout the plant body. After being transported to different parts of the plant body, it is used in metabolism and stored for the future. During the day when glucose is high, water loss results in insoluble sediment. During the night, insoluble carbohydrates are converted to soluble glucose. Excess glucose is converted to white matter under the action of amylase enzyme. Chloride accumulates in plant roots, stems, leaves, flowers, fruits and seeds. It is useful in making amino acids, proteins, fats etc.

Crassulacean acid metabolism is abbreviated as CAM. CAM metabolism is a special feature of succulent plants. In 1804, De Saussure first observed that ficus bengalensis has more organic acids at night and less organic acids during the day. This occurs in many succulents of the Crassulaceae and Cactaceae families. Bryophyllum, Annanus, Orchid, Cractus, Crassula, Sedum etc. show decrease-increase in acid content. In the leaves of these plants, organic acid and pH decrease during the day and organic acid and pH increase at night. So at night the stomata are open and photosynthesis takes place. The increase in the amount of organic acids at night is called dark acidification and the decrease in the amount of organic acids at night is called light deacidification. The steps in the CAM process are similar to the C4 cycle.

1. Photosynthesis occurs at high temperatures (30-450C) in C4 plants. Hence they are functional at high temperatures.
2. Phospho-enol pyruvic acid is the most efficient CO2 acceptor in C4 plants.
3. Food production and transport is high due to the cranial anatomy of leaves.
4. Even if the concentration of CO2 is low, the trajectory of R can continue.
5. In C4 plants, respiration and photorespiration are low, so CO2 emission is high.
6. The C4 pathway remains active even though the stomata of frost plants are partially closed.
7. C4 plants carry some important adaptive traits. Due to these characteristics they can survive in tropical and arid regions.

1. Optimum temperature for C4 plants is 32-450C for photosynthesis.
2. C4 plants are capable of photosynthesis in the presence of small amounts of CO2.
3. C4 plant carbon-fixing enzymes are more efficient.
4. C4 plant carbon molecules readily participate in various metabolic processes.
5. No or very little photorespiration occurs in C4 plants.
6. C4 plants have chloroplasts around the bundlesheath so sugars can be transported easily.
7. Inhibition of photosynthesis in C4 plants is not obtained even when the oxygen content in the air is greater than 20%.

sugarcane, bhutra, china, kaun, oat, sorghum, millet, crab grass, guinea grass, dhaincha, reed etc.

1. They originate from tropical countries.
2. C4 plants are able to adapt to high temperatures.
3. Temperatures of 30-450C are favorable for their survival.
4. Their leaves have cranial anatomy.
5. They have a layer of mesophyll cells surrounding the bundle sheath of the leaf.
6. Calvin-Basham cycle and Hatch-Slack cycle occur in their mesophyll cells.
7. Their CO2 oxidation rate is high.
8. The photosynthesis rate of these plants is high.
9. Their respiration and photorespiration are less.
10. Their chloroplasts are of two types. Granular and non-granular chloroplasts.
11. Their photosynthesis is best when atmospheric CO2 concentration is 0.10-10 ppm.
12. As the photosynthesis rate of plants is very high, their compensation point is zero (0).
13. As both the C3 and C4 cycles are active in these plants, the CO2 assimilating enzymes are RuBisCO and PEPcase.
14. Oxaloacetic acid (OAA) is the first stable compound produced in the photosynthetic process of this plant.
15. Their photosynthetic rate continues under intense sunlight, stress and high temperatures.
16. They are highly adaptable and grow well in saline soils.
17. They reduce water loss and can be adapted to arid regions. That is, frosty features can be observed.
18. Bundlesheath cells and mesophyll cells contain many plasmodesmata.
19. Ribulose bisphosphate carboxylase enzyme activity is absent in mesophyll cells of C4 plants.
20. Bundlesheath chloroplasts contain many starch grains, but mesephyll chloroplasts do not contain starch grains.
21. Rubisco enzyme is present only in bundlesheath cells. No mesophyll cells.