Biodiversity is the variety of life on Earth, including the different species of plants, animals, and microorganisms that inhabit various ecosystems. It is essential for the survival and well-being of both humans and the planet as a whole. While all the options mentioned in the question are important, the correct answer is option 'B' because human existence is directly dependent on biodiversity.

Importance of Biodiversity for Human Existence:

1. Ecosystem Services:
- Biodiversity provides numerous ecosystem services that are essential for human survival. These services include air and water purification, soil fertility, climate regulation, pollination, and pest control.
- For example, forests act as carbon sinks, absorbing greenhouse gases and mitigating climate change. Wetlands filter water, reducing the risk of floods and improving water quality for human use.

2. Food Security:
- Biodiversity contributes to food security by providing a wide variety of plants and animals that serve as a source of food for humans.
- Crop diversity is crucial for maintaining agricultural resilience and adapting to changing environmental conditions. It ensures a sustainable food supply and helps prevent crop failures due to pests, diseases, or climate change.

3. Medicinal Resources:
- Biodiversity is a rich source of medicinal resources. Many plants and animals have bioactive compounds that are used in the development of medicines.
- Around 70% of the world's population relies on traditional medicine, which is primarily based on natural products derived from biodiversity.

4. Economic Benefits:
- Biodiversity supports various economic sectors, including tourism, agriculture, fisheries, and pharmaceuticals.
- Natural landscapes, such as national parks and wildlife reserves, attract tourists and generate revenue. Biodiversity-rich areas are often popular destinations for eco-tourism.
- Biodiversity also provides raw materials for industries, such as timber, fibers, and biofuels.

5. Cultural and Aesthetic Value:
- Biodiversity is deeply interconnected with cultural and traditional practices of indigenous communities worldwide.
- Many cultures have strong spiritual and emotional connections to nature, and biodiversity plays a significant role in their rituals, ceremonies, and folklore.
- Additionally, biodiversity contributes to the aesthetic value of landscapes, providing enjoyment and inspiration for people.

In conclusion, biodiversity is crucial for human existence as it provides essential ecosystem services, ensures food security, offers medicinal resources, supports economic activities, and holds cultural and aesthetic value. Protecting and conserving biodiversity is not only important for the well-being of humans but also for the overall health and sustainability of the planet.