Module 3: Cell Biology - Structure and Function

Your skin, the flowers outside, and the feathers on the bird flying past your window are all similar in that they are all composed of cells. The traditional cell theory states that all organisms are composed of cells, that cells are the basic units of structure and function, and that all cells come from other cells.

Cells are microscopic, which is important to the transfer of materials in and out of the cell. Cells contain structures that work together to maintain homeostasis. Organisms may be unicellular or multicellular, but all organisms must conduct similar life processes. Unlike multicellular organisms, which have specialized cells to perform these functions, single-celled organisms perform these functions alone.

Cellular processes such as photosynthesis and cellular respiration occur in different organelles and require materials to be transported into the cell. Movement of materials into the cell sometimes occurs spontaneously, and sometimes requires additional energy.