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Transcript
The Cell and its Environment Finzer 2013 The Plasma Membrane - Gateway to the Cell Structure of the Cell Membrane • Homeostasis- “steady state” or balance • -cells constantly seek homeostasis • The Cell Membrane is responsible for maintaining the steady state within cells. • - Most cells live in some kind of fluid • -Single celled organisms- ponds, oceans, inside other bodies… • -Multicellular organisms- cells are surrounded by body fluid • - Cells have limits to changes they can survive • - Temperature • - Salt concentrations in the H2O • - Interstitial fluid- body fluid between cells Diffusion of Liquids • Diffusion- molecules move from an area of high concentration to an area of low concentration • - takes place in both solutions and air • - Gradual spreading out of molecules • - They spread out until they reach equilibrium • def . equilibrium- molecules evenly spread out Simple Diffusion • Requires NO energy • Molecules move from area of HIGH to LOW concentration DIFFUSION THROUGH MEMBRANES • Permeable- when membranes allow all substances to pass through • Selectively Permeable- when membranes allow some substances to pass through, & others not DIFFUSION Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY • CELL MEMBRANES ARE SELECTIVELY PERMEABLE! • Osmosis- diffusion of water through a selectively permeable membrane • (from high concentration to low concentration) Q? What decides what moves into the cell??? • A. Compare the solution outside the cell to the solution inside the cell. Diffusion of H2O Across A Membrane High H2O potential Low solute concentration Low H2O potential High solute concentration • Hypotonic- a solution having a lower concentration of solutes than the cell – water goes into the cell Cell in Hypotonic Solution 10% NaCL 90% H2O CELL 20% NaCL 80% H2O What is the direction of water movement? • Hypertonic- a solution having a higher concentration of solutes than the cell – water exits the cell Cell in Hypertonic Solution 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O What is the direction of water movement? • Isotonic- a solution having the same concentration of solutes as the cell – equal movement of water into and out of the cell Cell in Isotonic Solution 10% NaCL 90% H2O ENVIRONMENT CELL 10% NaCL 90% H2O NO NET MOVEMENT What is the direction of water movement? equilibrium The cell is at _______________. Isotonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) Hypotonic Solution CYTOLYSIS Hypertonic Solution PLASMOLYSIS Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic Rules for deciding what will happen to cells… • 1. look at the solute concentrations to set up the picture puzzle • 2. water moves first and fastest….so • 3. look at the water concentrations to decide what will happen to the cell …try some problems • Turgor Pressure- term used to describe water pressure within a cell, (usually plant cells) • -will continue to build up until equilibrium is reached • Plasmolysis- water diffuses out of a cell and turgor pressure is lost • - Plants “wilt” • - Cells shrink • Cytolysis- when cells burst because water pressure inside the cell is too great Cytolysis & Plasmolysis Cytolysis Plasmolysis hypotonic hypertonic hypertonic isotonic isotonic hypotonic What happens to fresh water organisms? • Contractile vacuoles- organelles that pump water out through the cell membrane • 2 WAYS SUBSTANCES ARE TRANSPORTED THROUGH MEMBRANES Three Forms of Transport Across the Membrane • PASSIVE TRANSPORT- the movement of substances through the cell membrane when NO ENERGY taken from the cell • Ex- diffusion……osmosis • -these both happen “naturally” • PT uses kinetic energy- the natural movement of molecules • Substances using PT: • -Water • -Carbon dioxide • -Oxygen • -Steroids • -Alcohol • -Glucose • Q ? Do these substances move into or out of the cell??? Proteins Are Critical to Membrane Function Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins. Facilitated Diffusion • Some Carrier proteins do not extend through the membrane. • They bond and drag molecules through the lipid bilayer and release them on the opposite side. • ACTIVE TRANSPORT- transporting substances across cell membranes USING ENERGY from the cell • Ex. Sodium (Na) & potassium (K) (the cell have high needs of these ions) • AC moves against natural diffusion----• - Plants have the ability to absorb Na & K when concentrations are higher inside the cell than outside the cell Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential • Endocytosis- taking into a cell – “cell eating” • Exocytosis- putting out of a cell • *Phagocytosis- taking in large solids • *Pinocytosis- taking in or putting out fluid drops - excrete or secrete – “cell drinking” • * Cell reaches around the particle to be taken in and forms a pouch-à vacuole Pinocytosis • Cell forms an invagination • Materials dissolve in water to be brought into cell • Called “Cell Drinking”