Answer You don't really save the world. "Save a life, save the world," means you have saved the world for the person whose life you saved. Answer You can save someone's life who can go on to save the world. You never know, but the person whose life you saved can become a great scientist or leader who saves the world. Answer Saving a life isn't necessarily saving a person. You could save a plant's life to save the world. If all protists and plants were killed except for one small plant, the all animals on Earth would be in grave danger. If the last living plant is somehow also in danger, you'd nurture the plant, help it reproduce more plants, and bring the Plantae kingdom back to life, bringing more fresh oxygen back to Earth.