Hooke: identified and named cells, used cork Leeuwenhoek: made better lenses for microscopes; observed greater detail Schleiden: proposed plants are made up of cells Schwann: all living things are made up of cells Virchow: all cells come from pre-existing cells

Cell City Analogy In a far away city called Grant City, the main export and production product is the steel widget. Everyone in the town has something to do with steel widget making and the entire town is designed to build and export widgets. The town hall has the instructions for widget making, widgets come in all shapes and sizes and any citizen of Grant can get the instructions and begin making their own widgets. Widgets are generally produced in small shops around the city, these small shops can be built by the carpenter's union (whose headquarters are in town hall). After the widget is constructed, they are placed on special carts which can deliver the widget anywhere in the city. In order for a widget to be exported, the carts take the widget to the postal office, where the widgets are packaged and labeled for export. Sometimes widgets don't turn out right, and the "rejects" are sent to the scrap yard where they are broken down for parts or destroyed altogether. The town powers the widget shops and carts from a hydraulic dam that is in the city. The entire city is enclosed by a large wooden fence, only the postal trucks (and citizens with proper passports) are allowed outside the city.

KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment. Acts like a fence.

Cell membranes are composed of two phospholipid layers Phospholipids have 3 parts: Charged phosphate group Glycerol Two fatty acid chains Label the head Label the tail Which part is attracted to water?

Cell membranes are composed of two phospholipid layers. The cell membrane has two major functions. boundary controls passage cell membrane outside cell forms a boundary between inside and outside of the cell controls passage of materials in and out of cell (border patrol) inside cell

Cell membranes are composed of two phospholipid layers. The cell membrane is made of a phospholipid bilayer. There are other molecules embedded in the membrane. Functions Cholesterol: Proteins: Carbohydrates: cell membrane protein cholesterol carbohydrate chain protein channel Cholesterol: Strengthens Proteins: Gates, cytoskeleton, differ for each cell membrane Carbohydrates: ID tags

Cell membranes are composed of two phospholipid layers. The fluid mosaic model describes the membrane. Fluid: Cell membrane moves, not rigid Does not flip, though, outside stays out, inside stays in Mosaic: variety of molecules similar to tiles with different textures and patterns

Cell membranes are composed of two phospholipid layers. The cell membrane is selectively permeable. What does selective mean? What does permeable mean? So, what does selectively permeable mean?

Chemical signals are transmitted across the cell membrane. Receptors bind with ligands and change shape. There are two types of receptors. intracellular receptor Examples: Aldosterone in kidneys

Chemical signals are transmitted across the cell membrane. Receptors bind with ligands and change shape. There are two types of receptors. intracellular receptor membrane receptor Examples: red blood cells carrying carbon dioxide

3.4 Diffusion and Osmosis KEY CONCEPT Materials move across membranes because of concentration differences.

3.4 Diffusion and Osmosis Passive transport does not require energy input from a cell. Molecules can move across the cell membrane through passive transport. There are two types of passive transport. diffusion osmosis

3.4 Diffusion and Osmosis High Low Diffusion and osmosis are types of passive transport. Molecules diffuse down a concentration gradient. Where will the ball roll? Does it take energy? High Low

3.4 Diffusion and Osmosis Diffusion and osmosis are types of passive transport. Osmosis is the diffusion of water molecules across a semipermeable membrane. Which direction will the water molecules move?

3.4 Diffusion and Osmosis There are three types of solutions. Isotonic: Iso means equal so… Hypertonic: Hyper = above so… Hypotonic: Hypo = below so… Isotonic: Iso means equal; outside and inside of cell have same concentration Hypertonic: Hyper = above, more dissolved outside of cell, or more water inside cell; water Exits the cell Hypotonic: Hypo = below, less dissolved outside of cell, less water in cell; water goes into cell

3.4 Diffusion and Osmosis Some molecules can only diffuse through transport proteins. Some molecules cannot easily diffuse across the cell membrane. Facilitated diffusion is diffusion through transport proteins. Move with concentration gradient! No energy required

3.5 Active Transport, Endocytosis, and Exocytosis KEY CONCEPT Cells use energy to transport materials that cannot diffuse across a membrane. What is different from this picture than the picture in the previous slides?

3.5 Active Transport, Endocytosis, and Exocytosis Active transport requires energy input from a cell and enables a cell to move a substance against its concentration gradient. Active transport is powered by chemical energy (ATP). Active transport occurs through transport protein pumps. Cells use active transport to maintain homeostasis.

3.5 Active Transport, Endocytosis, and Exocytosis A cell can import and export large materials or large amounts of material in vesicles during the processes of endocytosis and exocytosis. Cells use energy to transport material in vesicles. Endocytosis is the process of taking material into the cell. Phagocytosis is a type of endocytosis; engulfs Large particles Vesicle

3.5 Active Transport, Endocytosis, and Exocytosis Exocytosis is the process of expelling material from the cell. Vesicle