Why are plants important to human life?
You mean apart from their role in our nutrition and their impact on the air we breathe? Well for me it's about their diversity of form, their ingenuity and their beauty.
There is such a huge range in the form plants take from tiny plants that don't need to soil to huge plants that grow in water. The variety of form of their leaves alone is amazing. Just stand underneath a range of your local native trees and look so into the canopy. Simply amazing. We eat their shoots, their leaves, their roots, their flowers, their oils, their seeds and their fruits. We eat the animals they nourish too. We also use plants to die fabric, to make fabric. We use plants in industrial processes. The list goes on.
They are ingenious in how they exploit their environment. Some eat insects and have very clever although simple mechanisms to catch their prey. Some flower at night to attract night flying pollinators. Some live in water, some in very dry conditions. Whatever the soil type you will find plants that thrive in these conditions.
Then there's the beauty they contribute to our world. There colours are also diverse and exquisite. Some grow tall and cover buildings with beautiful green leaves and wonderful blooms. Some grow at ground level covering the earth we walk on with delicate flowers.
Who hasn't been delighted by a bunch of flowers or an amazing floral display? Who hasn't felt the restorative and healing power of being surrounded by plants in nature?
They sustain us and enrich our lives
Plants are the primary producers, that is they produce their own food by synthesizing it in the process of photosynthesis. Animals don't do that, thus depends on eating plant for energy and nutrients or eating other animals that eat plants. Hence all animals survive by eating plants directly or indirectly. Plants thus form the base of the food chain. Without plant life, animal life wouldn't be possible.
Plants also directly give off oxygen in the process of photosynthesis. Without oxygen, animals would not subsist. Animal system is structured to subsist on oxygen.
Plants are really important for the planet and for all living things. Plants absorb carbon dioxide and release oxygen from their leaves, which humans and other animals need to breathe. Living things need plants to live - they eat them and live in them.