Cell Theory

• What is life?

  Living things are distinguishable from non-living things.

  Attributes of living things: MRS GREN

  •Movement

  •Reproduction (including molecules)

  •Stimuli (responsiveness to stimulation (internal/external changes))

  •Growth (from within)

  •Respiration

  •Excrete wastes

  •Nutrition

  •Some non-living things tick some of these off- but not all (e.g. viruses).
• Living things are made of cells

  • A cell is the smallest and most basic form of life
  • Bacteria, Protist, Cell
  • Organism is the name for living things
• Unicellular vs Multicellular Organisms

  •Unicellular organisms are made up of only ONE cell. E.g. bacteria, phytoplankton (algae), protists (Amoeba), yeast.

  •Multicellular organisms are made up of more than one cell. E.g. animals, plants, fungi. They are much larger and more complex with many different type of cells.
• Other examples of Unicellular Cells

  E.Coli - Most are harmless, some can make you very sick

  Bakers Yeast - Converts sugars in dough into carbon dioxide and ethanol

  H.Pylori - Attacks the lining of the stomach, weakening it and resulting in the formation of ulcers 2/3 of the world’s population have H.Pylori in their stomach!
• Stem Cells 


  Unspecialised "blank" cell that can turn into other types of cells.
• Cells, DNA and Hereditary

  Cells contain DNA (deoxyribonucleic acid);

  •Found in chromosomes.

  •Make important molecules such as proteins.

  •Divide and produce new cells.

  Heredity – passing on genetic material from one generation to the next.
• Cytoplasm

  •All of the material within a cell, enclosed by the cell membrane, excluding the nucleus.

  •About 80% water.

  •Usually colourless.

  •Cytoplasm is made up of:

  •Cytosol, a gel-like substance.

  •The organelles.

  •Specialised subunit with a specific function.
• Structure and Function of Cell Membranes

  The cell membrane separates the cell from its surroundings and is found in all living cells. It controls the entry and exit of materials in and out of the cell, as well as having a range of other important roles in cell communication, cell adhesion, and the binding of hormones.
• Structure and function of cell membranes

  Cell membranes consist of:

  • two layers (bi-layer) of phospholipid molecules
  • two kinds of membrane proteins:
  • integral proteins which are permanently in the bilayer
  • peripheral proteins which tend to move temporarily and are not a permanent part of the membrane
  • cholesterol which is usually positioned between the phospholipids (in animal cells only)
  • glycoproteins which are membrane proteins with carbohydrate chains attached
  • glycolipids which are phospholipids with carbohydrate chains attached
• Cell Theory


  •The cell is the basic unit of structure and organisation in organisms.

  •New cells arise from pre-existing cells via the process of cell division.

  •Cells require and use energy.

  •Contain hereditary material (DNA) which is passed on to daughter cells.

  •Some organisms are unicellular whilst others are multicellular.