7.3 From Cell To Organism I. Diversity in Cells A. Prokaryotic Cells 1. Always unicellular 2. Limited in size 3. Lack nucleus & membrane bound organelles 4. Vary in cell wall composition & ability to move a. many have a flagella b. flagella – long thread-like structure that rotate quickly to move an organism c. pili – short, thick outgrowths that allow attachment to surfaces or other cells

B. Eukaryotic Cells 1. Vary in size 2. Can be unicellular or multicellular 3. Examples – plant & animal cells a. Both have same organelles b. Plant cells also have chloroplasts, a large central vacuole, & a cell wall 4. Can become specialized in function a. examples – muscle cells, nerve cells, skin cells, etc.

II. Levels of Organization A. Tissues 1. A distinct group of cells that have similar structures & functions a. ex- muscle tissue B. Organs 1. A specialized structure with a specific function made up of many different tissues a. ex – the heart - made up of muscle, nerve, & other tissues C. Organ System 1. Various organs that carry out a major body function a. ex- circulatory system – carries blood throughout the body

III. body types A. More than half the biomass on Earth is composed of unicellular organisms B. Cell Groups 1. Colonial organisms a. cells that live as a connected group but do not depend on each other for survival i. ex.- coral reefs C.. Multicellularity 1. Only occurs in eukaryotes 2. Includes some protists, most fungi, & all plants & animals 3. Begin as only one cell & divide 4. Undergo differentiation – the process by which specialized functions are created