[matt-attack]

We can survive without a constant stream of incoming raw materials. I wouldn’t think that makes us any less alive. Nor are we a parasite on the food.

[sigmoid10]

You could make a distinction here in that we only need raw materials, we don't need another organism to reproduce. Mosquitos can also easily consume raw materials in the form of nectar to survive, but they need to take blood from other animals if they want to reproduce. If you go along this chain of thought, you can come up with arbitrary definitions.

[AbortedLaunch]

We need mitochondria.

[stevenjgarner]

We need 20 different amino acids to build all our proteins. We can synthesize 11 of them (non-essential amino acids), but we must obtain the other 9 Essential Amino Acids fully formed from the food we eat.