Organism: an individual living thing
Environment: the conditions that surround someone or something: the conditions and influences that affect the growth, health, progress, etc., of someone or something
Habitat: the place or type of place where a plant or animal naturally or normally lives or grows
Adaptation: a change in a plant or animal that makes it better able to live in a particular place or situation
Definitions from: http://www.learnersdictionary.com
What if photosynthesis stopped happening?
Image from: https://upload.wikimedia.org
Read this article from how Stuff Works to find out what would happen.