The preferred temperature of living organisms varies tremendously.
Warm-blooded mammals prefer a fixed temperature, whereas cold-blooded
animals readily live at different temperatures. Some bacteria, termed ther-
mophiles, prefer very high temperatures such as those found at hot springs
at locations such as Yellowstone National Park in the USA. By gaining
the ability to live at relatively high temperatures, these organisms have gained
an ecological advantage over other organisms that otherwise might com-
pete for the same nutrients. The coloration of these organisms arises due
to their incorporation of pigmentation that is used in the capture of light
through a process called photosynthesis (Chapter 20).
Volume, mass, and number
The quantity of a physical system can be characterized by its volume or
by the amount. The volume is a measure of the space occupied and is
measured in liters. The volume is not a fixed quantity of an object. For
example, puffer fish expand greatly in volume as a defense mechanism
when they sense danger. These fish possess a special sac inside their bodies
that can be filled with water rapidly, and the combination of a large body,
their tough outer body, and the presence of toxins makes them difficult
prey. The mass is a measure of the quantity of matter an object contains.
The unit of mass is the kilogram, although gram or milligram are also com-
monly used in biochemistry. Remember that the weight is a useful measure
only at a fixed gravitational-field strength. Astronauts in space experience
microgravity and have a very small weight while their mass remains the
same. In addition to the mass, it is useful to know the number of atoms
(or molecules) present in the object. The common unit is the mole, which
equals unity for 6.022136 × 1023 molecules, with the conversion constant
between number and moles being termed Avogadro’s constant. The molar
mass is the mass per mole of a substance, with the unit Dalton, Da, being
equal to 1 g/mol. The molar mass is commonly used for biological objects
such as proteins. For example, myoglobin, the protein that serves as the
oxygen store and carrier in muscle, has a molar mass of about 15 kDa.
Properties of gases
The ideal gas laws
Scientists, starting in the seventeenth century, discovered that for gases
the properties of pressure, P, temperature, T, volume, V, and amount, n,
are all quantitatively related to each other though the ideal gas law. When
a gas in a chamber is compressed by a piston the volume decreases but
the pressure is found to increase. If you heat a gas in a closed container,
the pressure in the container increases. Also, as you increase the amount
6 CHAPTER 1 BASIC THERMODYNAMIC AND BIOCHEMICAL CONCEPTS
