In the environment there are biotic and abiotic factors that are both important. Abiotic factors include things like temperature, water, climate, oxygen, amount of sunlight, etc. These are important to living things, but are not in any way alive. However, biotic factors are all the populations in an ecosystem. To be deemed "alive" an organism must carry out certain life functions. These include respiration, nutrition, digestion, circulation, reproduction, excretion, growth, etc. Therefore, when examining an ecosystem, there is a connection between abiotic and biotic factors, however, the biotic factors are all the organisms capable of carrying out the life functions mentioned above. A living thing can be a bacteria, fungus, protist, plant or animal. And in terms of evolution, any living thing that survives in its environment, due to the adaptations it possesses, and then goes on to reproduce, is not only alive, but is also considered "fit".