How does water buffer a sudden drop in temperature?

Question

A property of water is that it is slow to heat and cool. According to my biology book, some energy from an increase in temperature would spent breaking hydrogen bonds, so that temperature does not rise too fast - helping a cell to maintain homeostasis.

As far as I can tell, this answer does not explain how a drop in temperature would be slowed down by water in a cell. How does water slow down heat loss? Is it just because it is difficult for the heat that is already inside the cell to leave?

Answer 1

From pure biophysical viewpoint the question

"Why does water buffer sudden temperature changes?" can be answered in the following way:

Water has relatively high specific heat capacity. This is the measure of the energy required to raise the temperature of one kilogram of a substance by one kelvin without a change of state occurring. "Relatively high" means that water can absorb more energy without noticeable (for the cell) increase in temperature.

Here are some heat capacity values from the above-linked Wikipedia article:

Animal (incl. human) tissue 3500 Jkg^-1
Water at 25 °C liquid 4181.3 Jkg^-1
Methanol liquid 2597 Jkg^-1
Ethanol liquid 2440 Jkg^-1
Paraffin wax solid 2500 Jkg^-1
Graphite solid 710 Jkg^-1

Water has relatively high thermal conductivity. This means that the absorbed heat is quickly distributed over the complete cell volume, leveling down the focal temperature increases in cell. Here are again some values for comparison:

Water 0.6 Wm^-1K^-1
Wood 0.2 Wm^-1K^-1
Paper 0.05 Wm^-1K^-1
Glycerol 0.3 Wm^-1K^-1

The follow-up questions:

"Why does water have relatively high heat capacity?" and "Why does water have relatively high thermal conductances?" are not within the scope of this site. However, here exactly comes your explanation with hydrogen bonds in play (from Wikipedia):

Hydrogen-containing polar molecules like ethanol, ammonia, and water have powerful, intermolecular hydrogen bonds when in their liquid phase. These bonds provide another place where heat may be stored as potential energy of vibration, even at comparatively low temperatures. Hydrogen bonds account for the fact that liquid water stores nearly the theoretical limit of 3 R per mole of atoms, even at relatively low temperatures (i.e. near the freezing point of water).