Explain how the chemistry of water influences life processes: its polarity and hydrogen bonding give it cohesion, adhesion, a high specific heat, and its role as the universal solvent and a reactant (Virginia 2018 Biology SOL BIO.2.a).

What this topic is asking

Virginia Biology SOL standard BIO.2.a asks how the chemistry of water influences life processes. Water is the most abundant molecule in living things, and almost every reaction in a cell happens in it. The Biology EOC expects you to connect water's polarity and hydrogen bonding to its life-supporting properties: cohesion, adhesion, a high specific heat, and its role as the universal solvent. These properties are not trivia; they explain transport in plants, temperature regulation, and why water is the medium of life.

Polarity and hydrogen bonding

Because of this polarity, the positive hydrogen of one water molecule is attracted to the negative oxygen of another, forming a weak hydrogen bond. Individually these bonds are weak, but there are so many of them that together they give water its remarkable behavior. Almost every special property of water traces back to hydrogen bonding, so this is the idea to anchor your understanding on.

Cohesion and adhesion

In a plant, water evaporates from the leaves (transpiration) and the cohesive hydrogen bonds pull the whole column of water up from the roots, while adhesion to the walls of the xylem helps hold it in place. This is why cohesion and adhesion are exam favorites: they explain how tall plants move water without a pump.

High specific heat

Water has a high specific heat, meaning it takes a large amount of energy to change its temperature, because much of the energy goes into breaking hydrogen bonds rather than speeding up the molecules. As a result, water absorbs and releases heat slowly and resists temperature change. This stabilizes the temperature of cells, of organisms (which are mostly water), and of the planet: large bodies of water moderate the climate of nearby land, and sweating cools the body as water evaporates and carries heat away.

The universal solvent

Water is called the universal solvent because its polarity lets it dissolve a huge range of polar and charged (ionic) substances. The positive and negative ends of water surround and separate the particles of a solute, pulling them into solution. This matters because the chemistry of life happens in solution: nutrients, ions, and waste are transported dissolved in water, and most cellular reactions take place in a watery medium. Nonpolar substances such as oils do not dissolve in water, which is why cell membranes (made of lipids) form barriers.

Water as a reactant

Water is not only the medium; it is a participant. It is a reactant in photosynthesis, where it is split to provide electrons and hydrogen, and it is a product of cellular respiration. Reactions that break molecules apart by adding water are called hydrolysis, and reactions that join molecules by removing water are dehydration synthesis, both central to how cells build and break down macromolecules.

Try this

Q1. Explain why ice floats on liquid water, and why this matters for life in a pond. [2]

• Cue. In ice the hydrogen bonds hold the molecules in a spaced-out lattice, so ice is less dense than liquid water and floats; the ice layer insulates the water below, letting organisms survive the winter.

Q2. Why does water dissolve salt (an ionic compound) but not oil? [2]

• Cue. Water is polar, so its charged ends surround and separate the charged ions of salt; oil is nonpolar, so water is not attracted to it and it does not dissolve.