- Reproduction. There have been no reports of baby angels. Okay, angels could reproduce secretly or be some kind "worker bees" that don't reproduce.
- Organization: Well, we don't have any tissue samples from an angel.
- Metabolism: Angels can eat. But do they actually require food, or do they just eat out of courtesy?
- Homeostasis: We don't know if angels control their internal environment.
- Response to stimuli: Okay, angels do that.
- Growth: Angels haven't been observed to age or grow.
- Adaptation: Has not been observed.