Some key ideas for biophysics from basic physics and chemistry

Section 1.5 of Biological Physics by Nelson lists

1.5.1 Molecules are small

He describes how in 1773, Benjamin Franklin estimated the linear size of a single molecule from observing that one teaspoon of oil covered half an acre of pond!

1.5.2 Molecules are particular spatial arrangements of atoms

1.5.3 Molecules have well-defined internal energies

1.5.4 Low-density gases obey a universal law

Boltzmann's constant is universal, i.e., it does not depend on the chemical or structural details of the system being described.

At room temperature

k_B T = 4.1 pN nm (most important formula in this book!)

I tend to think k_B T = 25 meV since this is a useful scale in solid state physics.
But, Nelson deliberately writes it terms of a force scale (picoNewton) and length scale (nanometer) that is relevant to the physics of cells.