Humans and plants depend on each other to survive because their organ systems help complete each other’s needs. For example, the respiratory system of humans takes in oxygen and releases carbon dioxide. Plants, through their leaf and photosynthesis system, take in carbon dioxide and release oxygen, which humans need to breathe. Also, the digestive system of humans needs food, and plants provide fruits, vegetables, and grains that humans eat for energy and nutrients. In return, humans help plants grow by taking care of them, planting more trees, and spreading seeds. The circulatory system in humans carries the oxygen that plants produce to every cell in the body. Plants also need nutrients from the soil, which can be helped by humans through farming and composting.In short: Humans and plants rely on each other in a cycle — humans need oxygen and food from plants, and plants need carbon dioxide and care from humans to grow and stay healthy.