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Cell Transport Essential Question: How do water and materials move in and out of cells? • Diffusion • Osmosis • Facilitated Diffusion • Active Transport Cell Membranes Essential Question: How do cell membranes work? Cell Membranes Function • To enclose the cell and regulate what enters and exits Structure • Lipid bilayer • Contains embedded proteins a) channels b) pumps c) markers/signals Cell Walls Function • To protect and support the cell Structure • Fibers of carbohydrate and protein – Ex: cellulose • Porous – Water, gases, nutrients, etc. pass through easily Cell Membrane vs. Cell Wall • Membranes are semi-permeable: some substances can pass through but others cannot – Small: water, O2, CO2 – Large: proteins, carbs – “Selectively permeable” B. Protein marker C. Extracellular fluid A. Carbohydrate chain D. Lipid bilayer E. Cytoplasm Cell Transport • Every living cell is surrounded by a liquid environment. • In a solution, particles are always moving. • Dissolved materials move across cell membranes in different ways. Concentration concentration: mass / volume • The amount of solute divided by the amount of solvent Diffusion • Movement of molecules from high to low concentration • Continues until equilibrium: concentration is the same throughout • Does not require energy • Ex: air freshener Animation Diffusion Osmosis • Diffusion of water through a selectively permeable membrane • Continues until equilibrium is reached • Does not require energy • **Occurs when solute does not pass through membrane • Ex: wrinkled fingers Animation Osmosis Osmosis in Living Cells Essential Question: How does osmosis affect your cells? Solutions Hypertonic: having a higher concentration of solute (“above strength”) Hypotonic: having a lower concentration of solute (“below strength”) Isotonic: having equal concentrations of solute (“same strength”) Water moves from hypotonic to hypertonic solutions! SALT SUCKS! Osmosis • Ex: celery in water; salt on a slug What happens when a living cell is placed into a solution? It depends on the solution! When a cell is placed in a solution… Isotonic • Concentration is the same as the cell • Zero net water movement Animal Cell Plant Cell When a cell is placed in a solution… Hypotonic • Concentration is lower than the cell • Net water movement into the cell Animal Cell Plant Cell When a cell is placed in a solution… Hypertonic • Concentration is higher than the cell • Net water movement out of the cell Animal Cell Plant Cell Osmotic Pressure • There is osmotic pressure on the hypertonic side of a membrane • This is because water flows in the direction of more solutes SALT SUCKS! So then why don’t cells burst? Animal cells – bathed in isotonic fluids Plants & bacteria – cell walls Facilitated Diffusion • Diffusion through protein channels • Used for large or charged particles that cannot pass through the membrane • High to low concentration • Does not require energy • Ex: glucose, K+ and Na+ Facilitated Diffusion Active Transport • Movement of particles from low to high concentration • Does require energy! Active Transport • Carried out by: 1) Protein “pumps” in membrane Ex: Ca+ 2) Endocytosis and exocytosis Ex: food and wastes • Endocytosis – Taking material into the cell by folding in the cell membrane and creating a vesicle • Exocytosis – Releasing material out of the cell by fusing a vesicle with the outer membrane Active Transport Active Transport Exocytosis
