1. The Diversity of Cellular Life

2. Unicellular Organisms 1. An organism that consists of a single cell is called a unicellular organism. Unicellular organisms carry out all the essential functions of life that larger organisms do.

3. Multicellular Organisims 2. Organisms that are made up of many cells are called multicellular organisms. 3. Cells throughout a multicellular organism can develop in different ways to perform different tasks. This process is called cell specialization.

4. Levels of Organization 4. The levels of organization in a multicellular organism are individual cells, tissues, organs, and organ systems. a. Individual cells are the first level. b. Similar cells are grouped into units called tissues. 1. A tissue is a group of cells that perform a particular function. c. Groups of tissues that work together form an organ. d. A group of organs that work together to perform a specific function is called an organ system.

5. 5. Cells of certain tissues will have different structures than cells of another type of tissue. a. This is called cell differentiation. b. This allows cells to have structures specific for its function. Example: Structure: Cells of muscles have more mitochondria than nervous cells. Function: Muscle cells must use more energy to contract than nervous cells need to carry impulses.