In the context of the Calvin cycle and overall photosynthesis, where does most of a plant’s biomass ultimately come from?

• A. Energy from sunlight, which is directly converted into plant tissue mass
• B. Mineral nutrients absorbed from soil, such as nitrogen and phosphorus, which are converted into carbohydrates
• C. Carbon atoms fixed from atmospheric $C_0{O}_2$ into sugars during the Calvin cycle
• D. Water taken up by roots, whose hydrogen and oxygen make up most of the dry mass of the plant

Answer: (C)

Verified step by step guidance

1. Understand that plant biomass primarily consists of organic molecules like carbohydrates, proteins, and lipids, which are built from carbon-containing compounds.
2. Recognize that during photosynthesis, plants convert light energy into chemical energy, but the energy itself does not directly become biomass; instead, it powers the synthesis of organic molecules.
3. Recall that the Calvin cycle is the stage of photosynthesis where carbon dioxide (CO\_2) from the atmosphere is fixed into organic molecules, specifically sugars, which form the backbone of plant biomass.
4. Note that mineral nutrients like nitrogen and phosphorus are essential for plant growth but do not contribute the majority of the carbon atoms in biomass; they are incorporated into other molecules such as proteins and nucleic acids.
5. Conclude that the majority of a plant's biomass comes from carbon atoms fixed from atmospheric CO\_2 during the Calvin cycle, as these carbon atoms are the primary building blocks of the plant's organic matter.