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The cell In It’s Environment • Function of the cell membrane? – To regulate what enters and leaves the cell. • Structure of the cell membrane – Double layer of lipids with carbohydrates and proteins scattered throughout. The Cell in Its Environment • The cell membrane is selectively permeable: – means some substances can pass through it while others cannot. Balloon The Cell in Its Environment • Three ways substances can move in and out of the cell 1. Diffusion - no energy required 2. Osmosis – no energy required 3. Active Transport – energy required Diffusion • Diffusion: • The movement of molecules from an area of higher concentration to an area of lower concentration. – Caused by molecules in motion. – Collisions cause molecules to spread out. http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf Air freshener Food dye in water Diffusion • Concentration gradient - Created when different concentrations are in contact with one another High Low Diffusion • Substances naturally move with the gradient High to low concentration is like going down hill – with the gradient. Diffusion – Example in living organisms – movement of oxygen from water into cells. Osmosis – A special type of diffusion • Osmosis is the diffusion of water molecules across a selectively permeable membrane – Water moves from high to low concentration What are three ways substances can pass across the cell membrane? Diffusion Osmosis Active transport Movement Across the Cell Membrane • Passive Transport • Moving materials across a cell membrane WITHOUT using energy Two examples of passive transport: • Diffusion • Osmosis Movement Across the Cell Membrane • Active Transport Movement of materials across a cell membrane which requires energy Active Transport • Sometimes molecules must move against the concentration gradient (from low to high or uphill) and this requires energy. http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__ mitosis_and_cytokinesis.html Methods of Active Transport • Two ways that the cell moves things by active transport. 1. Transport proteins 2. Engulfing Transport Proteins – Active Transport Transport proteins in the cell membrane act as channels through the membrane http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2 /animation__how_the_sodium_potassium_pump_ works.html http://www.youtub e.com/watch?v=S TzOiRqzzL4 Engulfing – Active Transport Engulfing: cell membrane surrounds and then engulfs a particle (amoeba and white blood cells). http://www.youtu be.com/watch?v =W6rnhiMxtKU http://www.youtube.com/watch?v=STz http://www.youtube.com/watch?v=s 0p1ztrbXPY&feature=related OiRqzzL4&feature=related Cell Size • Why are cells so small? – Small size makes it easier to move materials into and out of the center of the cell. – Makes all cell processes more efficient. Cell Size • How do cells maintain their small size? When a cell reaches a certain size it divides. We call this cell division MITOSIS. Let’s Review Explain the difference between osmosis and diffusion? • • Diffusion refers to the movement of molecules from high concentration to low concentration. Osmosis is diffusion of WATER across a selectively permeable membrane. Also from high concentration to low concentration. Let’s Review Do osmosis and diffusion require energy? • • No because they both are a form of Passive transport. Molecules or water (osmosis) move with the concentration gradient (downhill). Let’s Review Why does active transport require energy? • Because the cell is trying to move molecules against the concentration gradient – from low to high concentration Why are cells so small? • To allow materials to move in and out quickly making the cell more efficient. Let’s Review What happens to a cell when it reaches a certain size? • It divides to maintain its small efficient size What do we call this cell division? • Mitosis Diffusion http://www.youtube.com/watch?v=ULR79TiUj80 http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__ mitosis_and_cytokinesis.html http://www.stolaf.edu/people/giannini/flashanimat/transport/ diffusion.swf Osmosis and salt http://www.stolaf.edu/people/giannini/flasha nimat/transport/osmosis.swf