Week 2 — The Chemistry of Life

Why this matters

A nursing student reading blood test results and a gardener watching water climb from roots to leaves both rely on this chemistry.

In plain language

Every living thing is made of tiny pieces called atoms (the smallest units of the substances around you), and four kinds of atom build about 96% of your body. This week you meet the three kinds of chemical bonds (the ways atoms stick to each other) and see why water, one of the simplest molecules, behaves in ways that make life possible, from floating ice to cooling sweat. You will learn to read pH (a number that tells you how acidic or basic a liquid is) and see why a small change in that number, from 7 down to 4, means 1,000 times more acid. You will also see how your body uses a buffer (a system that pushes back against a change in acidity) to keep your blood steady. These ideas are the chemistry under every later week of biology.

• Already covered: Week 1, The Science of Biology, gave you the characteristics of life, the levels of organization from atom to biosphere, and the controlled experiment, including the drops on a penny.
• This week: atoms, elements, and molecules; the three bonds; water's polarity and its properties; the pH scale; and buffers.
• How they connect: Week 1's ladder of organization starts with atoms and molecules, and this week zooms in on those bottom rungs; the penny result from Week 1 finally gets its explanation.
• Where we're going next: Week 3, Biological Macromolecules, uses these bonds and this water to build the large molecules of life: carbohydrates, lipids, proteins, and nucleic acids.

Focus

Why does life depend on water, and how much does one pH step change?

By the end of this module, you should be able to:

• [ ] tell an atom from a molecule and name a bond by its verb
• [ ] trace a property of water back to hydrogen bonds
• [ ] compare two pH values by counting steps, then raising ten
• [ ] explain what a buffer does and does not do

To-do

Plan your week

1. Read Chapter 2 (about 45 minutes), then the lecture and slides.
2. Work the tutorial (60–90 minutes) and practice set (20 minutes).
3. Do the Biology Lab & Inquiry (two hours), the discussion, and the assignment.
4. Take the quiz.

This week's checkpoint: say how many times more hydrogen ions pH 4 has than pH 7, by counting steps.

You've got this

Ask your instructor early if you get stuck.

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