Thermal Properties and Biological Functions of Water

Applications and Skills

Comparison of Water and Methane Thermal Properties

Water and methane are small molecules with similar covalent structures, yet their physical properties differ significantly due to water's polarity.

Since water is polar, it has stronger intermolecular attraction (hydrogen bonds) and therefore has a much greater specific heat capacity, latent heat of vaporization, melting point, and boiling point.

Water as a Coolant in Sweat

• Water is essential to living organisms.
• Water has a high latent heat of vaporization, which means it takes a lot of heat to evaporate water from a liquid to a vapor.
• This is very important as a cooling mechanism for living organisms. As humans sweat, the water droplets absorb heat from the blood flowing under our skin, causing the water to evaporate and our blood to cool down. This will, in turn, cool our whole body down.
• This cooling is controlled by negative feedback through receptors in the hypothalamus.
• If the body is overheated, receptors in the hypothalamus sense this and stimulate the sweat glands to secrete sweat.
• Some reptiles, such as crocodiles, cool by opening their mouths (gaping). Dogs also pant, which causes water to evaporate from their upper respiratory tract.

Transport of Substances in Blood

Blood transports many different substances to different parts of the body using a variety of methods based on their solubility in water.

• Water is critical both as a solvent in which many of the body's solutes dissolve.
• Due to its polarity, water is a great solvent for other polar molecules and ions. This is vital because it allows water to act as a transport medium (blood and cytoplasm) for important molecules in biological organisms.
• Sodium Chloride (NaCl) is an ionic compound that is very soluble in water. Na⁺ and Cl^- ions dissolve and are carried in the blood plasma.
• Glucose is polar and is soluble in water; it is therefore transported in the plasma.
• Amino acids have both a negative and a positive charge, but their "R" groups vary; therefore, they can be hydrophilic or hydrophobic. They are all soluble enough to be carried in the plasma.
• Fats are non-polar and therefore insoluble in water. They are transported in a single-layer sphere of phospholipids called a lipoprotein complex. The hydrophilic heads face outwards towards the water in the plasma, and the tails face inwards towards the fats. Proteins are also embedded in the phospholipid layer.
• Finally, cholesterol, which is mostly hydrophobic because it is a lipid, is also transported inside the lipoprotein complex with the small hydrophilic end facing the phospholipid heads.