The boiling point of water is c. 100 degrees
Answer:
it is poisonous or harmful to the human body
Biologically thinking, I would say viruses.
Viruses are Inert organisms, they are not influenced by temperature on the opposite of other organisms like humans or bacteria (there are some exceptions in bacteria)
Temperature influences proteins, it could change their conformation and their activity, especially for enzymes.
Temperature decreases the energy flow, due to the decrease of thermal agitation of small molecules like ions in cells.
Viruses don't need active enzymes to live, it just needs host cells, which will be easier on cold days because of the decrease of immune system activity
On cold days you can see an emergence of viruses infections like flu or cold.
I believe that the food web is more stable
I don't have enough information but it could be natural selection or mutations.