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

Living organisms require nitrogen primarily to synthesize proteins, which are essential macromolecules involved in numerous biological processes. Proteins are composed of amino acids, and nitrogen is a crucial element in the amino acids' structure. Since proteins play a vital role in the formation and function of cells, tissues, and organs, nitrogen is indispensable for growth, repair, and overall maintenance of living organisms. While carbon dioxide is part of photosynthesis in plants, it does not involve nitrogen in its production. Similarly, the process of cellular respiration, which helps organisms release energy from stored nutrients, primarily involves carbohydrates and does not rely on nitrogen. Lastly, waste product removal is a function of various metabolic processes that may include nitrogen-containing compounds but does not highlight the necessity of nitrogen in a fundamental way. Thus, the role of nitrogen in protein synthesis is the most significant reason for its importance to living organisms.