AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Nitrogen is essential for plants because it is used to synthesise proteins and other substances required for growth and development of the plant body.
The passage states that organisms need materials from outside to "grow, develop, synthesise protein and other substances." Nitrogen is the key element needed for protein synthesis in plants. For a 1-mark answer, simply state this function — one clear, direct line is sufficient. Examiners look for the keyword protein synthesis / growth.