Open this lesson by demonstrating the production of acidic carbon dioxide gas by activated yeast. Emerging ecologists then experiment with seashells to discover the effect of ocean acidification on shelled marine organisms. They measure changes in size and compare the relative strengths of shells after exposure to liquids of varying pH. You will appreciate detailed teacher's instructions for this lesson. Because there is no way to specifically measure shell strength, it is important to add weight a little at a time so that learners will at least be able to give a roundabout value. Have them measure the mass of the books or other objects for testing strength prior to placing them upon the shells.