Can the heat capacity of water be considered small or large? What is the biological significance of that characteristic?
From thermology it is called that the quantity of exchanged heat (Q) is equal to the mass (m) multiplied by the specific heat of the substance (c) multiplied by the changes of temperature (T), Q = m.c.ΔT., and that heat capacity is Q/T, as, m.c. Heat capacity, though, relates to a specific body, since it considers mass, whereas specific heat relates to the general substance. Thus it is more correct to refer to specific heat in this problem.
Water has a specific heat of 1 cal/g.oC which means that 1 oC per gram is altered in its temperature with the addition or subtraction of 1 cal of energy. This is a very elevated value (for example, the specific heat of ethanol is 0,58 cal/g oC, and mercury, a metal, has a specific heat of 0,033 cal/g. oC) making water an good thermal protector against variations of temperature. Even if sudden external temperature changes occur, the internal biological conditions are kept stable in organisms which contain enough water.
High specific heat is one of the most significant water properties.