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Transcript
Biology Homeostasis and Cellular Transport Homeostasis • Literally means, “ inner balance” • Keeping internal conditions within healthy limits • It applies to things like body temperature and blood pressure Feedback Loops or Homeostatic Mechanisms Cellular Transport • Cellular transport describes how substances cross the cell membrane. • As you remember, the cell membrane controls what goes in and out of the cell. Phospholipids • The cell membrane is made mostly of phospholipids • They have a hydrophilic head and hydrophobic tail • Hydrophilic means water loving • Hydrophobic means water fearing Phospholipid Bilayer • The cell membrane is made of two layers of phospholipids • It also contains some proteins • The hydrophilic heads face the cytoplasm and extracellular fluid, while the tails face inward Types of Transport • Passive Transport – Substances cross the membrane without the use of energy (ATP is the most used energy molecule in the human body) • Active Transport – Substances cross the membrane through the use of energy, or ATP Passive Transport • Diffusion - The movement of substances from an area of high concentration to an area of low concentration Passive Transport Cont’d • Facilitated Diffusion – Diffusion that takes place using a membrane protein. • They can open and close when needed. Osmosis • The diffusion of water. Equilibrium • After diffusion or osmosis has taken place and there is an equal concentration of substances. Passive Transport Summary • Passive transport usually moves things: 1. That are small 2. From high to low concentration 3. That are lipid soluble 4. Without using ATP Active Transport • Movement of substances across the cell membrane that requires the use of ATP (energy). Types of Active Transport • Protein Pumps – A membrane protein and ATP are used to pump substances against their concentration gradient across into or out of the cell. • Example - Na/K ATP pump ://www.brookscole.com/chemistry_d/templates/student_resources/shared_resou rces/animations/ion_pump/ionpump.html Exocytosis and Endocytosis • Special vacuoles called vesicles, and ATP are used to add and remove substances from the cell. • http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535:: 535::/sites/dl/free/0072437316/120068/bio02.s wf::Endocytosis and Exocytosis Exocytosis • Substances in a vesicle are forced through the membrane using ATP and released in the fluid surrounding the cell. Endocytosis • Phagocytosis – “Cell eating,” cells use ATP and a vesicle to ingest solid molecules • Pinocytosis – “Cell drinking,” cells use ATP and a vesicle to ingest liquids Receptor Mediated Endocytosis • Cells ingest molecules using ATP after they bond to special receptor proteins on the cell’s surface. Active Transport Summary • Active transport can move things in a wide variety of ways, but certain situations must use active transport: 1. Moving large molecules 2. Moving from low to high concentration 3. Moving things that are not lipid soluble 4. All situations must use ATP Tonicity Cells will react differently when placed into solutions with varying concentrations of substances, an idea known as tonicity. Isotonic Solutions • Equal concentration of substances inside the cell and outside. • The size of the cell does not change. Hypertonic Solutions • Concentration of substances is greater outside the cell than inside. • The cell shrinks as a result. Hypotonic Solution • Concentration of substances is greater inside the cell than outside. • The cell swells as a result. • If the concentration is great enough, the cell will burst (aka lysis). Comparison of Human Blood Cells