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. forms a boundary between inside and outside of the cell controls passage of materials in and out of cell (border patrol) cell membrane outside cell inside cell

cell membrane 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. protein cholesterol protein carbohydrate chain protein channel Functions 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. Some molecules can cross the membrane while others cannot. Which do you think will cross? What does selective mean? What does permeable mean? So, what does selectively permeable mean?

Cell membranes are composed of two phospholipid layers. –The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot. What is an everyday example of something that is semipermeable or selectively permeable? Why is selective permeability important?

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

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. osmosis diffusion 3.4 Diffusion and Osmosis

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

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

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

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

KEY CONCEPT Cells use energy to transport materials that cannot diffuse across a membrane. Like a chair lift moving you up the mountain using energy! 3.5 Active Transport, Endocytosis, and Exocytosis What is different from this picture than the picture in the previous slides?

Active transport requires energy input from a cell and enables a cell to move a substance against its concentration gradient. Passive transport requires no energy from the cell. Active transport is powered by chemical energy (ATP). 3.5 Active Transport, Endocytosis, and Exocytosis Cells use active transport to maintain homeostasis. Active transport occurs through transport protein pumps.

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. 3.5 Active Transport, Endocytosis, and Exocytosis Phagocytosis is a type of endocytosis; engulfs Large particles Vesicle

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

Think! 1.What might happen if vesicles in your neurons (nerve cells) are unable to fuse with the cell membrane? 2.How is endocytosis and exocytosis different from diffusion? 3.How are protein pumps different from protein channels? 4.Cholesterol is located between the fatty acid chains of the phospholipid layer. Do you think cholesterol is polar or nonpolar? Explain.