The correct option is Julius von Sachs.
Explanation
The historical understanding of photosynthesis evolved through specific experiments establishing the role of light, pigments, and the synthesis of organic compounds in plants.
Scientist-wise Analysis:
- Julius von Sachs (Correct): In 1854, Julius von Sachs provided evidence that glucose is produced when plants grow and is usually stored as starch. He further established that the green substance in plants (chlorophyll) is located in special bodies (chloroplasts) within plant cells, identifying these as the sites of glucose synthesis.
- Joseph Priestley (Incorrect): In 1770, Priestley conducted the bell jar experiments, revealing the essential role of air in the growth of green plants. He demonstrated that plants restore the air depleted by burning candles or breathing animals.
- C.B. van Niel (Incorrect): A microbiologist who, based on studies of purple and green bacteria, demonstrated that photosynthesis is a light-dependent reaction where hydrogen from a suitable oxidizable compound reduces carbon dioxide to carbohydrates.
- T.W. Engelmann (Incorrect): He described the first action spectrum of photosynthesis. Using a prism to split light into spectral components and illuminating the green alga Cladophora, he observed that bacteria accumulated mainly in the regions of blue and red light.
Key Takeaway: Julius von Sachs is credited with proving that the green parts of plants produce glucose, which is subsequently stored as starch.