1. Please get out a sheet of paper for notes.

2. Differentiation, Stem Cells, and Multicellular Organization

3. Multicellular Organization Cells work together and communicate in groups that form increasingly larger and more complex structures. Levels of organization (simplest to most complex): 1) Cell 2) Tissue 3) Organ 4) Organ System 5) Organism

4. Cell Differentiation The process by which unspecialized cells develop into specialized cells. Every cell has a full set of identical DNA. Cells differentiate and use only specific genes (like a cookbook). Once unspecialized cells specialize, they give rise to more specialized cells.

5. Stem Cells Stem cells are undifferentiated cells. Adult stem cells are found among specialized cells of organs and tissues (e.g. bone marrow). Embryonic stem cells are cells from embryos. If the differentiation of stem cells can be manipulated there are many medical possibilities.

6. Stem cells are unique body cells. Stem cells have the ability to –divide and renew themselves –remain undifferentiated in form –develop into a variety of specialized cell types

7. Outer cells differentiate to form skin and the nervous system. Middle cell layer forms bones, muscles, kidneys. Inner cell layer forms internal organs such as pancreas, lungs, and intestinal lining.

8. First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules. Stem cells come from adults and embryos. –Adult stem cells can be hard to isolate and grow. –The use of adult stem cells may prevent transplant rejection. –The use of embryonic stem cells raises ethical issues –Embryonic stem cells are pluripotent and can be grown indefinitely in culture.