Answer:
immune system
An immune system of a humans body is something that affects the processes of the human body. It is how there is some form of resistance in the human body. When some things get compromised in regard to health, hygiene and activities, that leads to resistance issues in the human body.
Answer:
freeze and sink over and over until the entire lake was frozen.
Explanation:
This would eliminate many aquatic organisms and produce a system with far fewer life forms in lakes which freeze periodically.