Which one of the following statements is correct?

Which one of the following statements is correct?

In photosynthesis by green plants, carbon dioxide is used for making carbohydrate.
During photosynthesis, plants use oxygen for making carbohydrate.
The carbohydrate generated by plants comes from soil.
The carbohydrate generated by plants comes from urea.
This question was previously asked in
UPSC CAPF – 2018
Photosynthesis is the process by which green plants convert light energy into chemical energy in the form of organic compounds (carbohydrates). The inputs for photosynthesis are carbon dioxide (CO₂) and water (H₂O), and the outputs are glucose (a carbohydrate, C₆H₁₂O₆) and oxygen (O₂). The overall chemical equation is approximately 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂. This equation shows that carbon dioxide is directly incorporated into the carbohydrate molecule. Plants absorb CO₂ from the atmosphere through their stomata.
Let’s evaluate the other options:
B) Oxygen is produced as a byproduct during photosynthesis, not used to make carbohydrate.
C) While water and minerals essential for plant growth come from the soil, the carbon atoms that form the backbone of the carbohydrate molecule come from atmospheric carbon dioxide.
D) Urea is a nitrogenous compound used as a fertilizer to provide nitrogen for plant growth. Nitrogen is essential for synthesizing proteins and nucleic acids, but the carbon backbone of carbohydrates comes from CO₂.
Therefore, the correct statement is that carbon dioxide is used for making carbohydrate in photosynthesis.
In photosynthesis, plants use carbon dioxide and water, with the help of light energy and chlorophyll, to synthesize carbohydrates and release oxygen. Carbon dioxide is the source of carbon atoms in the carbohydrate.
Photosynthesis occurs in two main stages: the light-dependent reactions (where light energy is converted into chemical energy in the form of ATP and NADPH, and water is split) and the light-independent reactions (Calvin cycle), where the chemical energy is used to fix carbon dioxide and synthesize glucose.
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