Which Swiss botanist contributed to the chemical understanding of photosynthesis and showed that plants absorb nutrients selectively?

• A. Antoine Lavoisier
• B. Louis Pasteur
• C. Cagniard de la Tour
• D. Nicolas-Theodore de Saussure

Answer: (D)

The key idea is linking chemistry to how plants grow and take up nutrients. Nicolas-Theodore de Saussure showed that the matter a plant adds as it grows mainly comes from carbon dioxide in the air and water absorbed from the soil, with light driving the conversion into organic matter. This established the chemical basis of photosynthesis and demonstrated that plants use carbon from CO2 and hydrogen from water, not just minerals from the soil. He also showed that plants absorb mineral nutrients from the soil in selective ways, taking up certain elements in specific quantities needed for growth. That combination—clarifying the chemical inputs for photosynthesis and illustrating selective nutrient uptake—is why he is the correct figure. The other scientists contributed to related areas of chemistry or biology, but not in this integrated explanation of both photosynthesis chemistry and selective nutrient absorption.