OCR GCSE Biology Practice Exam 2026 – Comprehensive All-in-One Guide to Exam Success

Biodiversity refers to the variety of life in all its forms, including the different species of plants, animals, fungi, and microorganisms in a given area. This encompasses not only the number of species present but also the complex ecosystems they inhabit and the relationships they have with one another and their environment.

Option A captures this broad concept well, as it emphasizes the diversity of species themselves. Biodiversity is fundamentally about the richness and variety of life on Earth, which is vital for ecosystem resilience, providing essential services such as pollination, nutrient cycling, and habitat provision.

The other options each highlight important aspects of ecological science but do not encompass the full definition of biodiversity. The total number of organisms in an ecosystem relates to abundance but does not address the variety of species. Different habitats contribute to the complexity of ecosystems but do not define biodiversity itself. Genetic differences within a single species pertain to genetic biodiversity, which is a part of the overall biodiversity concept but does not encompass all levels of biological diversity such as species and ecosystem diversity. Therefore, the correct answer effectively conveys the essence of biodiversity as the variety of life and species.