Option D is correct because the textbook explicitly states that 'Biodiversity is important for human existence' and 'All forms of life are so closely interlinked that disturbance in one gives rise to imbalance in the others.' The context further explains that if species of plants and animals become endangered, they cause environmental degradation that may threaten human existence. This interconnectedness means biodiversity conservation is essential for all organisms, not just animals or plants alone. The scientific role of biodiversity also mentions that 'each species' contributes to understanding life functions, reinforcing that all organisms matter.