The cell is the basic unit of structure and organisation in living things.  All living things are made from and originate from cells.  Technological advances, such as the development of transmission and scanning electron microscopes which have much greater resolution and magnification than optical microscopes, have enabled scientists to better understand cell structure.

Eukaryotic cells, such as those found in animals, fungi and plants, contain membrane-bound organelles.  Organelles have distinctive structures and carry out specific functions.   

Prokaryotic cells, such as those found in bacteria, lack membrane-bound organelles, have smaller ribosomes and their ribosomal RNA differs to that found in eukaryotic cells. 

The cytoskeleton is made from microfilaments, intermediate filaments, and microtubules.  Microfilaments are involved in cellular movement. Intermediate filaments often have structural roles.  Microtubules form structures such as centrioles, eukaryotic flagella (also known as undulipodia), and cilia.

The chemical elements carbon, hydrogen and oxygen, along with nitrogen, phosphorus and sulfur, are found in many biological molecules. Some biological molecules are described as being monomers.  When many monomers of the same type join together, a polymer is formed. 

Water is of fundamental importance to living things.  Dipolar interactions between water molecules, which lead to the formation of hydrogen bonds, are responsible for many of the properties of water.  

The basic building block of a carbohydrate is a monosaccharide.  In disaccharides and polysaccharides, monosaccharides are held together by glycosidic bonds.  Carbohydrates often have storage (e.g. starch and glycogen) or structural (e.g. cellulose) functions.

The basic building block of a protein is an amino acid.  In dipeptides and polypeptides, amino acids are held together by peptide bonds.   Polypeptide chains often have highly complex structures which are held in place by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions.  Proteins have many different functions including exchange (e.g. carriers and channels), transport (e.g. haemoglobin), enzymes (e.g. amylase) and hormones (e.g. insulin). 

Enzymes are globular proteins whose mode of action is described by the induced fit model.  Enzymes show specificity and their activity is affected by pH, temperature, substrate concentration, enzyme concentration, and inhibitors. 

Enzymes catalyse biological reactions.  Types of enzymes include oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.

Lipids are diverse.  Triglycerides are formed when glycerol joins with three fatty acids by ester bonds.  They are energy storage molecules and also provide electrical and thermal insulation.  Phospholipids contain glycerol, two fatty acids and a phosphate group.  Cholesterol has four fused carbon-based rings.  Phospholipids and cholesterol are important components of plasma cell membranes.  Cholesterol is also used to make bile, vitamin D and steroidal hormones. 

The plasma cell membrane is described by the fluid mosaic model.  It is formed from phospholipids, cholesterol and proteins, as well as glycolipids and glycoproteins.  Cell membranes are partially permeable, permitting exchange of substances by diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis.