Tag Archives: chemistry

Week 1: Introduction to Unit 3 Biology


Image Source – A polysaccharide cellulose molecule

There is a great diversity of living organisms on earth, but the closer you look at them, the more similar they become. The Cell Theory states that:

  1. All organisms are composed of cells and the products of cells
  2. All cells come from pre-existing cells
  3. The cell is the smallest living organisational unit

You should remember that there are two basic types of cells – prokaryotic and eukaryotic. Also recall some of the basic components of cells (including the plasma membrane, cytoplasm and nucleus) and the differences between plant and animal cells (cell wall, chloroplasts and large vacuole). In Unit 3 Biology we look closer at the structure and function of cellular organelles and the molecular composition of cells. Inorganic molecules (water, carbon dioxide, oxygen and nitrogen) are important substances for cellular function. Organic compounds include carbohydrates, lipids, proteins and nucleic acids. We will study these biochemicals in more detail this term. This site, Organic Chemistry, provides an excellent summary of biochemistry, including diagrams of the various molecules and bonds between atoms.


What do bread and ginger beer have in common?

They are both made with yeast (Saccharomyces cerevisiae) - a living organism that produces ethyl alcohol and carbon dioxide when allowed to grow in suitable conditions. This is an example of anaerobic respiration, or fermentation, which produces a small amount of energy (ATP) compared to aerobic respiration. An animation of the process of ATP production during fermentation is here.

In bread making, the carbon dioxide gas is captured in a gluten matrix produced by working the flour together with water into a dough. When the dough is baked, the yeast is killed, the small amount of alcohol evaporates and the carbon dioxide produces a light, fluffy loaf of bread. More about the science of bread making here.

When making beer, sugar is added to ‘feed’ the yeast and carbon dioxide bubbles are produced, along with a small amount of alcohol (less than 0.5% in the bottle we will produce). The lemon juice and ginger added to homemade ginger beer is for taste.