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Transcript
Cellular Transport The plasma membrane is responsible for helping to maintain homeostasis in the cell because it controls what enters and exits the cell. The membrane is made of a doublelayered sheet called a phospholipid bilayer. The head of a phospholipid is polar and is called hydrophilic (water-loving). It points to the cytoplasm and external environment. The two tails are nonpolar point toward each other in the center of the membrane and are called hydrophobic (water-fearing). Embedded in the phospholipids layers are membrane proteins and cholesterol molecules. Some membrane proteins help certain molecules pass across the cell membrane, while others serve as means of communication between cells. Proteins Are Critical to Membrane Function copyright cmassengale 7 The cell membrane has a liquid quality to it. This along with the scattered proteins causes it to sometimes be referred to as a “fluid mosaic”. Cholesterol molecules help strengthen the cell membrane and help to keep its fluid property. Passive Transport = NO Energy Required Passive transport is the passage of particles/molecules across the plasma membrane without the use of energy. This is movement with the concentration gradient from high to low. Simple diffusion, facilitated diffusion, and osmosis are the 3 types of passive transport. * Floating with the tide- no energy required Concentration gradient Concentration gradient means there is a difference in concentration of a substance across a space or a membrane. Equilibrium is the opposite of a gradient. The concentration is equal on both sides. 1. DIFFUSION Diffusion is the net movement of particles from an area of high concentration to low concentration. Small molecules like Oxygen and hydrogen use simple diffusion to get into the cell. This means they travel directly across the phospolipids. Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to 14 LOW) 2. OSMOSIS Osmosis is the diffusion of water molecules across a selectively permeable membrane. Osmosis is powered by the unequal distribution of particles called a concentration gradient. The difference in concentration causes water to move across the membrane. 3 TYPES OF SOLUTIONS There are 3 different types of solutions that the cell comes in contact with. Hypertonic, hypotonic, and isotonic solutions all affect the cell differently. A. Isotonic solutions have the same concentration of solute as the solution on the inside of the cell. The water concentration is equal inside and outside the cell. The water will move in and out of the cell at an equal rate. This causes no change in shape of the cell. B. Hypotonic solutions have a lower concentration of solute than the solution inside the cell. This means the water concentration is greater OUTSIDE the cell. This causes water to move into the cell and the cell will swell. Hypo = Gonna Blow Hypotonic solutions cause plants to stand up and become rigid and stiff. The central vacuole fills up and presses against the cell wall causing turgor pressure. They do not burst because of the cell wall. Animal cells will rupture and die if in hypotonic solutions too long. Rupture of the cell is called cytolysis. C. Hypertonic solutions have a higher concentration of solute than the solution inside the cell. Therefore, the water concentration is greater INSIDE the cell. This causes water to move out of the cell and the cell to shrink. Shrinking of the cells is called plasmolysis. Hypertonic solutions cause plants to wilt. Both hypertonic and hypotonic solutions can kill cells. 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 _______________. copyright cmassengale 22 Cell in Hypotonic Solution 10% NaCL 90% H2O CELL 20% NaCL 80% H2O What is the direction of water movement? copyright cmassengale 23 Cell in Hypertonic Solution 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O What is the direction of water movement? copyright cmassengale 24 Osmosis in Red Blood Cells Isotonic Hypotonic copyright cmassengale Hypertonic 25 hypotonic hypertonic isotonic hypertonic isotonic hypotonic copyright cmassengale 26 Passive transport also uses membrane proteins to move particles in and out of the cell. Channel proteins and carrier proteins are used for transport. Channel proteins are hollow and particles move through them with the concentration gradient. 3. FACILITATED DIFFUSION Facilitated diffusion uses carrier proteins that opens and closes to either side of the cell membrane. These also move with the concentration ACTIVE TRANSPORT=USES ENERGY Active transport is the passage of particles across the membrane against the concentration gradient, from low to high. This type of transport requires energy. There are 3 examples of active transport. Sodium-potassium pump, endocytosis, and exocytosis. * swimming against the tide = energy required Three Forms of Transport Across the Membrane copyright cmassengale 31 Active transport is done by carrier proteins. They bind with a substance outside the cell and then energy causes the protein to release the substance inside the cell against the concentration gradient. 1. Sodium-Potassium Pump Inside the cell there are a large number of negatively charged proteins and other organic compounds that cannot escape from the cell. A large number of + ions like to collect around them. These ions cause water to draw into the cell which unless checked can cause the cell to burst. The Sodium-Potassium (Na+-K+) pump is a mechanism to prevent this. The pump transports 3 Na+ ions out of the cell and in exchange takes 2 K+ ions into the cell. This automatically activates when the cell begins to swell. Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; copyright cmassengale travels through the transport protein35 2. Endocytosis- uses vesicles to move material into the cell When a cell needs to take IN large particles it uses the process of endocytosis. The cell surrounds and encloses the material in a portion of its membrane. This forms a vesicle that floats in the cytoplasm like a bubble. Materials INTO cell = En 3. Exocytosis- uses vesicles to move materials out of the cell. When a cell is ready to release the materials as waste the “bubble” attaches itself to the plasma membrane. It then opens to the outside of the cell and releases its contents. This is called exocytosis. Materials EXIT the cell = EX