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Transcript
Cells and Their Environment Chapter 4 p 74-84 What is a cell membrane? • The cell membrane protects the cell and helps move substances and messages in out of the cell. • Made of a phospholipid bilayer. • Plasma Membrane Video Homeostasis • A biological balance • Cells, tissues, organs, and organisms must maintain a balance. • Cells do so by controlling and regulating what gets into and out of the cell. Cell Membrane • Only small, nonpolar substances can cross the cell membrane. • How can polar substances move across the cell membrane?.... Through proteins in the lipid bilayer! • Construction of Cell Membrane Review Questions 1. Describe homeostasis? 2. What types of substances can pass through the cell membrane? 3. What would happen if the cell membrane were fully permeable to all substances? Transport • Passive • Active • Transport that does not require chemical energy to occur • example: diffusion, facilitated diffusion and osmosis • The movement of any substance across a cell membrane with the use of chemical energy – ie: Na+/K+ pump Passive Transport – SIMPLE DIFFUSION • Process by which molecules spread from an area of high concentration to an area of low concentration. • Concentration gradient: a difference in the concentration of a substance • Examples: – Oxygen diffusing into cells – Beaker of water with food coloring – Smell of perfume in a room ***Molecules are in constant motion Passive Transport - Diffusion • Molecules tend to “spread out” to reach equilibrium. Diffusion animations • http://www.northland.cc.mn.us/biology/Biol ogy1111/animations/transport1.html • http://highered.mcgrawhill.com/sites/0072495855/student_view0/c hapter2/animation__how_diffusion_works.h tml Passive Transport - Osmosis • Diffusion of water through a membrane from an area of high concentration to an area of low concentration. What determines the direction in which water molecules diffuse across a cell membrane? **the concentration of water and of solutes dissolved in the solution • http://www.stolaf.edu/people/giannini/flash animat/transport/osmosis.swf • http://www.tvdsb.on.ca/westmin/science/sbi 3a1/Cells/Osmosis.htm • http://highered.mcgrawhill.com/sites/0072495855/student_view0/c hapter2/animation__how_osmosis_works.ht ml • http://www.wiley.com/legacy/college/boyer /0470003790/animations/membrane_transp ort/membrane_transport.htm • http://www.youtube.com/watch?v=ls_mdB QVGJ4 Think about it… What happened if you eat salty foods? Grass wilts if you add too much fertilizer…WHY? Cells can be found in 1 of 3 solutions: 1. HypOtonic 2. Hypertonic 3. Isotonic HYPOTONIC • Concentration of solute molecules in the environment outside of the cell is lower than that in the cell. • Water moves in Red blood cell Hypertonic • Concentration of solute molecules outside the cell is greater than that in the cell • Water moves out Isotonic Concentration of solute molecules outside cell and inside are equal. **equilibrium Passive Transport – Facilitated Diffusion • Use of transport proteins to “help” move molecules across a membrane • Passive: energy Y or N? • Gradient: H to L • Example: glucose Passive Transport - Filtration • Type of Transport: Passive • Using pressure to push something through the cell membrane • Energy needed?? • Example…what organ in your body filters Active Transport • Movement of substances through a membrane from a low to high concentration with the use of energy. • ATP: energy form • Usually Low to high concentration – “Against a gradient” • Example: Na/K pump. Active Transport • http://www.brookscole.com/chemistry_d/te mplates/student_resources/shared_resources /animations/ion_pump/ionpump.html Some molecules are too large to pass thru membrane!!! Even with use of energy – Endocytosis…movement of substances into the cell by transport vesicles into the cell. – Exocytosis… movement of substances outside of the cell by transport vesicles into the cell Endocytosis Exocytosis http://www.coolschool.ca/lor/BI12/u nit4/U04L05.htm http://www.wiley.com/college/boyer/0470003790/animations/m embrane_transport/membrane_transport.htm http://www.teachersdomain.org/asset/tdc02_int_membr aneweb/