Levels of Organization

Unicellular Organisms

• Prokaryotic unicellular - no nucleus; one cell
• Eukaryotic unicellular - one cell with a nucleus
• Neither has cell differentiation

Multicellular

• made of many eukaryotic cells
• each type of cell has a different function

Cell Differentiation

• fertilized egg becomes different types of cells - blood, nerve, skin, bone, etc.
• each cell type has same DNA but uses different parts of the DNA instructions
• cells become specialized in structure & function during differentiation

Stem Cells

• unspecialized
• in animals
• found in embryos
• in bone marrow & muscle

Meristems

• groups of unspecialized cells
• in plants
• root tips and stem tips

Tissues

• group of similar cells working together
• animals - muscle (skeletal, heart), connective (bone, blood) , nervous (brain, spinal cord), epithelial (skin, lining of stomach)
• plants - dermal (outer); vascular (stem, roots); ground (roots, leaves)

Organs

• groups of different tissues that work together
• perform a special job(s)

Organ Systems

• group of different organs working together
• perform series of jobs
• animals - digestive, nervous, etc.
• plants - shoot (leaves, stem, flowers); root (roots, rhizomes, tubers)

Organisms

• group of different organ systems working together in multicellular organisms
• each system depends on the others