Melvin Calvin received the Nobel Prize in Chemistry for his pioneering research on which specific aspect of photosynthesis in plants?

Introduction:
Photosynthesis is a complex process involving both light dependent and light independent reactions. While many scientists contributed to understanding photosynthesis, Melvin Calvin is especially famous for tracing the route of carbon atoms as they are incorporated into sugar molecules. This question asks you to identify the specific part of photosynthesis for which he received the Nobel Prize, distinguishing it from other plant physiology topics such as hormones or light reactions.

Given Data / Assumptions:
- The scientist mentioned is Melvin Calvin. - The context is a Nobel Prize in Chemistry related to plant processes. - Options include light reactions, plant hormones, carbon fixation and photons. - We assume standard historical and scientific accounts of his work.

Concept / Approach:
Melvin Calvin used radioactive carbon (carbon 14) tracers and chromatographic techniques to map the steps in which carbon dioxide is fixed into organic molecules in the stroma of chloroplasts. This series of reactions is now known as the Calvin cycle or Calvin Benson cycle. It represents the dark or light independent phase of photosynthesis, specifically the carbon fixation and reduction stages. He did not receive the Nobel Prize for discovering plant hormones, light reactions or the physical nature of photons, although these are important topics in plant science and physics. Therefore, the correct answer is his research on the pathway of carbon fixation.

Step-by-Step Solution:
Step 1: Recall that photosynthesis has two broad phases: light reactions (in thylakoid membranes) and carbon fixation or dark reactions (in the stroma). Step 2: Remember that the sequence of carbon fixation reactions that converts carbon dioxide into carbohydrate is known as the Calvin cycle. Step 3: Recognise that Melvin Calvin and his team used carbon 14 labelling to follow carbon atoms through this cycle. Step 4: Note that their work identified key intermediates such as 3 phosphoglycerate and ribulose bisphosphate, establishing the cyclic pathway. Step 5: Compare this with the study of plant hormones, which involved other scientists, and with light reactions and photons, which are more closely associated with photochemistry and physics. Step 6: Conclude that the Nobel Prize was specifically for his research on carbon fixation in the Calvin cycle.

Verification / Alternative check:
Historical records of the Nobel Prize in Chemistry list Melvin Calvin as a laureate for his research on the carbon dioxide assimilation in plants, which is another way of describing carbon fixation. Textbooks on photosynthesis often have a section called the Calvin cycle, named after him, and describe how carbon dioxide is incorporated into organic molecules. Discussions of light reactions focus on photosystems and electron transport chains, where other scientists made major contributions. This confirms that carbon fixation is the correct focus of his Nobel winning work.

Why Other Options Are Wrong:
The light reactions of photosynthesis: These involve chlorophyll, photosystems and ATP formation, but Melvin Calvin is mainly associated with the dark reactions and carbon fixation. The discovery and action of plant hormones: Plant hormones such as auxins and gibberellins were studied by other scientists, not primarily by Calvin. The physical nature of photons: This belongs to quantum physics and photochemistry; it was not the main subject of Calvin's plant based research.

Common Pitfalls:
Some students see the word photosynthesis and quickly choose light reactions or photons because they sound related to light. Others may vaguely remember that hormones are involved in plant growth and wrongly associate Calvin with them. To avoid mistakes, link Melvin Calvin directly with the term Calvin cycle, which is the carbon fixation pathway in the light independent reactions of photosynthesis.

Final Answer:
Melvin Calvin received the Nobel Prize for his work on The pathway of carbon fixation in the Calvin cycle during photosynthesis.