Cell Theory, Cell Size, Tissues

Cell Theory:
A. All living things are composed of cells.
B. Cells are the smallest living units and the basic organizational unit.
C. All cells arise from pre-existing cells.

II. Size of Cells:
A. Cells vary in size; generally smaller cells are more common.
  1. Advantage: Higher surface area to volume ratio for efficient metabolism.
  2. Metabolic processes and exchanges are limited by surface area.

III. Levels of Organization in Multicellular Organisms:
A. Cells—first level of organization.
  1. Numerous cell types: adipose, epithelial, blood cells, etc.
B. Tissues—groups of similar cells performing specific functions (4 main types in animals).
  1. Epithelial tissue (protection, absorption).
  2. Connective tissue (support, protection).
  3. Nervous tissue (impulse conduction).
  4. Muscle tissue (movement).
C. Organs—composed of various tissues working together.
  1. Example: Heart (muscle + nervous tissues).
D. Organ Systems—groups of organs performing a function (e.g., cardiovascular system).
  1. 12 major organ systems in humans.

IV. Organisms:
A. Cells classified by nucleus presence:
  1. Prokaryotes (no nucleus, circular DNA).
  2. Eukaryotes (nucleus contains DNA, single or multicellular).