HOMEOSTASIS IN CELLS pp. 69-78

Why are cells so small? How does a cell maintain homeostasis?

CELL REVIEW Cell membrane Genetic material (DNA) Ribosomes: make proteins Cytoplasm: surrounds the cell’s organelles

CELL TYPES Prokaryotes: oldest living cells that lack membrane-bound organelles, are unicellular, and very small in size Eukaryotes: contain a membrane-bound nucleus and organelles and much bigger than prokaryotic cells

Prokaryotic Cell

Animal Cell

Plant Cell

HOMEOSTASIS Organisms have mechanisms that keep conditions within a specific range, despite changes in the environment Changes in the environment for a single cell can include changes in temperature, water, concentration of solutes in surrounding environment, and build up of wastes

Cell membrane Selectively permeable (semi-permeable): controls what comes into and out of the cell Made of phospholipids that form a lipid bilayer

Fluid mosaic model: cell membrane behaves more like a fluid than solid and the layers are always moving

The cell membrane has many different macromolecules imbedded within the phospholipids - Carbohydrates and lipids can be use for cell-to- cell communication or as cell markers - Peripheral proteins are attached to the surface of the cell membrane - Integral proteins are embedded in the bilayer and are often channel proteins. - Cholesterol makes the membrane more fluid and less rigid at colder temperatures

How does the cell membrane maintain homeostasis in a cell?