One of the oldest forms of life on Earth are Plants. They have been part of life much before the arrival of human beings on the planet. Man has depended on the plants for his survival from times immemorial so much so that plants have become an integral part of human beings. Whether human beings or animals would be able to live on in the absence of plants is beyond doubt.
There are about 30000 to 50000 species of plants on earth of which humans must have used about 7000 so far for food. The contributions of plants to people are varied. The first and foremost role of plants in our lives is they produce oxygen which is the lifeline to all human beings and animals. The stomata present in the leaves breathe in carbon dioxide available in the atmosphere and making use of light and water, release oxygen in the process of photosynthesis. Next comes the food chain. Plants provide the food required to different species and are the first in the food chain. They are available in abundance on earth providing food directly to people (those vegetarians who eat plants) or in indirectly (those who eat animal food which in turn depend on plants for their survival). Another major contribution to mankind is they regulate atmosphere, climate, soils and the water. They maintain the balance in ecosystem. Soil erosion would be a disaster making it impossible to grow food and support life. The shrubs and grasses hold the top soil in place thereby preventing its erosion from natural causes. They also serve as windbreaks, noise controllers, glare reducing buffers and also settling chambers for particulate pollution in the air. Another vital role is production of nitrogen in legumes which enriches the soil. So cutting and felling of plants is not advisable. Plants also provide the energy for millions of households in the form of wood and charcoal. Fuel is essential for people both for cooking purposes and keeping themselves warm in deterring climatic conditions. People can't survive without food and fuel. Even before the advent of science man used products or parts of plants to get relief for his pains and bodily problems. The growth of science and technology has helped in making tremendous strides in the medical field where life-saving medicines have been developed from plants from by isolating plant proteins. Plants also provide the raw material for producing clothing, farming tools etc... Cotton, synthetic fibers such as rayon all come from plants. Products like paper, wood, paints and by-products like turpentine, mulch, decorative barks, resins and dyes are all taken either from plants or plant extracts. Shelter, fencing, roofing materials and other building materials are all from the plants.
The disappearance of plants from the earth would be disastrous to both people and also animals. Actually it would be worse than any other natural calamity or even manmade nuclear threat. Bigger animals are dependent on smaller animals which in turn have plants for their food. People may find solutions or make other arrangements to problems arising from the non availability of plants, but the required quantity of food and oxygen both for human and animal consumption would be impossible to replace. So there wouldn't be any people or even animals without plants. An earth without plants means a planet without animals and people. To protest for ourselves we have to protest for plants!