Transcript File
7-3 Cell Boundaries: Cell Membrane A lipid bi-layer that separates the inside of the cell from its environment Regulates what enters and leaves the cell Provides protection and support Most also contain proteins and carbohydrates Cell Wall Present in plants, fungi, algae, and many prokaryotes Lies outside the cell membrane Most have lots of pores and allow H2O, O2, CO2 to pass freely Main functions are support and protection Most made from fibers of carbs and protein Passive transport Cells must exchange molecules with their environment A cell membrane is semi permeable In passive transport the cell does not use energy to move substances across the membrane Some types of passive transport include Diffusion Osmosis Facilitated diffusion Diffusion: movement of particles from an area of high concentration to an area where they are less concentrated carbon dioxide, oxygen, and water can pass freely Equilibrium Once equilibrium is reached the molecules continue to move across the membrane but remain in balance H2Osmosis describes the movement of water only across a selectively permeable membrane The direction that water moves during osmosis depends on the concentration of solutes on either side of the membrane There is a net movement of H2O from high to low concentration SALT SUCKS!!!! Isotonic: solute concentrations are equal on either side of a membrane If there is no concentration gradient there is no movement of water across the membrane Hypertonic: solute concentrations outside are higher than inside the cell. When hypertonic, water moves to the outside of the cell and the cell shrivels up Hypotonic: (think hippo) solute concentrations inside are higher than outside the cell. When hypotonic, water moves inside the cell and it swells Facilitated diffusion uses carrier proteins to move larger molecules into the cell The orange dots may be glucose or other large molecules moving into the cell from an area of high to low concentration Active transport Cells sometimes must move materials in the opposite direction, against a concentration difference Requires energy Transport is carried out by transport proteins (pumps) found in the membrane Larger molecules can be transported across by endocytosis and exocytosis; can involve changes in shape of cell membrane ENDOCYTOSIS Process of taking material into the cell by means of infoldings (pockets) of the membrane Pocket breaks loose from the membrane and forms vacuole within cytoplasm Large molecules, food, cells can be taken up this way EXOCYTOSIS Cells release large amounts of material from the cell The membrane of the vacuole surrounding the material fuses with the cell membrane, forcing it out of the cell 2 examples of Endocytosis: Phagocytosis: (cell eating) extensions of cytoplasm surround a particle and package it within a food vacuole Cell then engulfs it Requires considerable amount of energy Pinocytosis: (cell drinking) cells take up liquid from surroundings Tiny pockets form along cell membrane, fill with liquid, pinch off to form vacuoles within cell Homeostasis: maintain internal balance Temperature and water need to stay constant so we can live If your body is too cold, what happens? If its too hot, what happens? When you don’t have enough water in your system? When you have too much water in your system? Birds, when cold, hunch down and adjust their feathers to have maximum insulation. Where is salt highly concentrated? What is salt going to do? What does it suck from? Explain how this whole process made the cell look the way it does.