<span>Lipids insulate against the cold.
Fat is our natural coat produced by the over eating process. Not really sure, but it comes to mind that the layer under the skin can be the main reason for it as it prevents and keep our inner parts warm. Also the high blood flow that it demands can help by over circulating it.</span>
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 think its ADP because it breaks off the third phosphate.
It differs due to the life cycle of each tree, and the very specific way the trees go.
