Which element is listed as one of the three essential elements for plant growth obtained primarily through the roots?

• A. Nitrogen
• B. Phosphorus
• C. Calcium
• D. Carbon

Answer: (A)

The key idea is understanding how plants get essential nutrients and which ones come from the soil through the roots. Nitrogen is a major macronutrient that plants must have in relatively large amounts to grow—it's a building block of amino acids, proteins, and chlorophyll. Plants take nitrogen up from the soil mainly through the roots in the form of nitrate or ammonium ions, so it’s strongly tied to root uptake.

Carbon, by contrast, comes from the air and is fixed by the plant during photosynthesis, not obtained through roots from the soil. Calcium is essential too, but it’s considered a secondary macronutrient and is also absorbed via the roots; however, the trio most commonly highlighted for primary growth needs from soil includes nitrogen as one of the core elements.