7-3 Cell Boundaries Objectives: What are the main functions of the cell membrane and the cell wall? What happens during diffusion? What is osmosis?

Introduction Among the most important parts of a cell are its borders Separate the cell from its surroundings Cell membrane: all cells are surrounded by a thin, flexible barrier Cell wall: a strong supporting layer around the membrane

Cell Membrane Function Regulates what enters and leaves the cell Provides protection and support Almost all cell membranes are made of a double-layered sheet Lipid bilayer: 2 layers of lipids Flexible structure and strong barrier

Cell Membrane Cont’d Many kinds of molecules in cell membranes Most have protein molecules and carbohydrates (etc.)

Cell Walls Outside the cell membrane Most are porous to allow water, oxygen, carbon dioxide, and certain other substances to pass through easily

Cell Walls Cont’d Function Made Provide support and protection Mostly of cellulose Fibers of carbohydrate and protein Main part of wood and paper Inside the cell and then released at the surface of the cell membrane

Diffusion Through Cell Boundaries One of the most important functions of the cell membrane is to regulate the movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side Demo

Measuring Concentration Cytoplasm is a solution of many different substances in water Solution: a mixture of 2 or more substances Solutes: substances dissolved in the solution Concentration: the mass of solute in a given volume of solution More solutes in a volume=greater concentration

Diffusion Diffusion: Particles tend to move from an area of high concentration to an area of less concentration Does not need cell energy Equilibrium: when the concentration of the solute is the same throughout Particles will continue to move until equilibrium is reached Particles are in constant motion Activity

BLUE TICKET QUESTION What conditions are present when equilibrium is reached in a solution?

BLUE TICKET ANSWER Equilibrium is reached when the concentration of the solute is the same throughout the solution

Osmosis Some substances are too large or too strongly charged to cross the lipid bilayer Permeable: a substance that is able to diffuse across a membrane Impermeable: substances cannot pass across Selectively permeable: some substances can pass across and others cannot Osmosis: the diffusion of water through a selectively permeable membrane

How Osmosis Works Isotonic: “same strength Hypertonic: “above strength” Hypotonic: “below strength Osmosis Activity

Osmotic Pressure If cells are surrounded by fresh water, they will swell and burst Plants and bacteria are surrounded by a cell wall which prevents bursting Blood is isotonic so cells will not burst

Blue Ticket Question What structures protect plant and bacterial cells from potential damage resulting from osmotic pressure?

Blue Ticket Answer Cell walls

Facilitated Diffusion Cell membranes have protein channels that make it easy for certain molecules to cross the membrane Facilitated diffusion: help the diffusion of glucose across the membrane

Facilitated Diffusion Cont’d 100s of different protein channels have been found that allow particular substances to cross different membranes Fast and specific

Facilitated Diffusion Cont’d Will only happen if there is a higher concentration of the particular molecules on 1 side than on the other side Does not use the cell’s energy https://www.youtube.com/watch?v=faXBWOETTb4 Lab

Active Transport https://www.youtube.com/watch?v=STzOiRqzzL4 Active transport: move materials against a concentration difference Requires energy Usually moves ions with transport proteins Endocytosis and exocytosis move larger molecules and clumps of materials https://www.youtube.com/watch?v=STzOiRqzzL4

Molecular Transport A considerable portion of the energy used by cells in their daily activities is devoted to providing the energy for active transport

Endocytosis and Exocytosis Endocytosis: taking material into the cell by means of infolding of the cell membrane https://www.youtube.com/watch?v=pvOz4V699gk

Endocytosis and Exocytosis Cont’d Exocytosis: the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell https://www.youtube.com/watch?v=U9pvm_4-bHg

7-3 Exit Ticket Answer the following questions. Use complete sentences. You may NOT use your book. You MAY use your notes. This is a quiz grade. What are the main functions of the cell membrane and the cell wall? What happens during diffusion? What is osmosis?