The carbon that plants need for photosynthesis comes from:

• A. carbon dioxide in the atmosphere
• B. proteins absorbed from the soil
• C. carbonates in the soil
• D. glucose stored in roots

Answer: (A)

Verified step by step guidance

1. Understand the process of photosynthesis: Photosynthesis is the process by which plants convert light energy into chemical energy, using carbon dioxide (CO₂) and water (H₂O) as raw materials to produce glucose (C₆H₁₂O₆) and oxygen (O₂).
2. Identify the source of carbon for photosynthesis: The carbon atoms in glucose (C₆H₁₂O₆) come from carbon dioxide (CO₂) in the atmosphere, which plants absorb through small openings in their leaves called stomata.
3. Eliminate incorrect options: Proteins absorbed from the soil are not a source of carbon for photosynthesis; they are used for other metabolic processes. Similarly, carbonates in the soil are not directly used in photosynthesis. Glucose stored in roots is a product of photosynthesis, not a raw material.
4. Focus on the correct option: Carbon dioxide (CO₂) in the atmosphere is the correct source of carbon for photosynthesis, as it provides the carbon atoms that are incorporated into glucose during the Calvin cycle.
5. Conclude the reasoning: Based on the understanding of photosynthesis and the elimination of incorrect options, the correct answer is that the carbon plants need for photosynthesis comes from carbon dioxide in the atmosphere.