All life on Earth shares a fundamental chemical foundation, offering indirect evidence for evolution.

Despite their vast diversity, the cells of all living organisms rely on a few key groups of carbon-based compounds that function in similar ways. In this unit you will study:

• Carbohydrates: serve as respiratory substrates and contribute to structural components in plasma membranes and cell walls.
• Lipids: play multiple roles, including forming the bilayer of plasma membranes, acting as certain hormones, and serving as respiratory substrates.
• Proteins: are essential for cell structure and function, serving as enzymes, hormones, and components of the blood.
• Nucleic acids: encode the genetic instructions for protein synthesis. The universality of the genetic code among all living organisms, including viruses, further supports the theory of evolution.
• Water: is the most abundant component of cells, making it a crucial factor in the search for extraterrestrial life, as scientists prioritise the search for liquid water beyond Earth.
• Ions: play vital roles in biological processes, such as nerve impulse transmission, muscle contraction, and maintaining cellular balance.