OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What percentage of nitrogen is present in the atmosphere?

  1. 50%

  2. 78%

  3. 90%

  4. 99%

The correct answer is: 78%

The atmosphere is composed of a mixture of gases, with nitrogen being the most prevalent. Approximately 78% of the atmosphere is nitrogen, which plays a crucial role in various biological and environmental processes. This percentage indicates that nitrogen is critical for life, as it is a fundamental component of amino acids and nucleic acids, which are essential for the structure and function of proteins and genetic material in organisms. In contrast, the other percentages listed do not reflect the accurate composition of the atmosphere. For example, while oxygen makes up about 21% of the atmosphere, the remaining percentages attributed to other gases, such as argon and carbon dioxide, are much smaller. Therefore, knowing that nitrogen constitutes about 78% of the atmosphere is vital for understanding ecological and biological systems.

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