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Transcript
CELL TRANSPORT The ABSORPTION and CIRCULATION of materials into a cell. Regents Biology OBJECTIVES Upon completion of this unit students will be able to: 1. Define the key terms associated with the processes of the cell membrane. 2. State the difference between diffusion and osmosis. 3. Explain the differences between passive transport and active transport. 4. List and briefly describe the various types of active and passive transport. 5. State the difference between EXOcytosis and ENDOcytosis. 6. State the difference between pinocytosis and phagocytosis. 7. Identify and differentiate isotonic, hypotonic, and hypertonic solutions. KEY TERMS Active Transport Cell Membrane Diffusion Endocytosis *Equilibrium Exocytosis *Fluid-Mosaic Model Hypertonic Solution Hypotonic Solution Isotonic Solution *Kinetic Energy Osmosis * NOT IN GLOSSARY, SO USE INDEX OF TEXTBOOK OR DICTIONARY.COM Passive Transport Phagocytosis Pinocytosis Solute Solution Solvent INTRODUCTION: CELL TRANSPORT • Vital materials, such as OXYGEN AND DIGESTED FOODS that allow a living organism to survive must REACH ALL CELLS OF THE ORGANISM. Also, the waste materials must be carried away and released into the environment. • The life function of TRANSPORT is responsible for this movement and is defined as THE LIFE FUNCTION BY WHICH ORGANISMS ABSORB AND DISTRIBUTE MATERIALS NECESSARY TO MAINTAIN LIFE • We will talk about both absorption and circulation as separate processes. A. ABSORPTION • Absorption is THE 1ST STAGE OF TRANSPORT; CELLS TAKE DISSOLVED MATERIALS THROUGH THE CELL MEMBRANE TO THE INTERIOR I. THE CELL MEMBRANE • The key organelle involved with cell transport is the CELL MEMBRANE • The function of the cell membrane is to CONTROL what enters and leaves the cell. Because not all substances can easily go into and out of the cell, the cell membrane is said to be SELECTIVELY PERMEABLE. REMEMBER: The cell membrane is a LIPID bilayer with floating PROTEINS (“floating icebergs of protein in a fatty sea”) •The model on the previous page is used to describe the structure of the cell membrane and is called the FLUID-MOSAIC MODEL. Fluid because the lipid bilayer continually moves around and is never motionless. Mosaic because that is how it appears; a mosaic is A PIECE OF ART THAT IS MADE UP OF LOTS OF LITTLE PIECES PUT TOGETHER •Factors that affect the movement of materials into and out of a cell include: 1. SIZE OF THE MOLECULES 2. ELECTRICAL PROPERTIES OF MOLECULES 3. TYPE OF CELL I. PASSIVE TRANSPORT 1. Diffusion • No cellular energy is expended in this absorption process. • Diffusion is a natural process by which molecules move from and area of HIGH CONCENTRATION to an area of LOW CONCENTRATION • Diffusion occurs because THE MOLECULES ARE IN CONSTANT RANDOM MOTION and only if THERE IS A CONCENTRATION GRADIENT (DIFFERENCE IN CONCENTRATION) • As a result of diffusion, THE MOLECULES EVENTUALLY BECOME EVENLY DISTRIBUTED THROUGHOUT THE AVAILABLE SPACE EQUILIBRIUM IS WHERE THE MOLECULES ARE STILL IN MOTION, BUT THERE ARE EQUAL AMOUNTS OF MOLECULES MOVING OUT OF A GIVEN AREA AS ARE MOVING INTO THE AREA BEFORE AFTER Look at all the students in one corner. This is a HIGH CONCENTRATION. Where there are no students, it is a LOW CONCENTRATION. A few minutes later, after the students were milling around, look what happened. They all spread out. There really isn’t a high or low concentration at all, but rather an equal amount, or EQUILIBRIUM of students in every part of the room. 2. Osmosis • Osmosis is the THE DIFFUSION OF WATER MOLECULES INTO OR OUT OF A CELL THROUGH THE CELL MEMBRANE • It is also a form of PASSIVE transport because it DOES NOT REQUIRE ENERGY • Whether there is a net movement if water into or out of a cell depends on THE CONCENTRATION GRADIENT; WHETHER THERE IS A HIGHER CONC’N OF WATER ON ONE SIDE OF THE CELL MEMBRANE THAN THE OTHER REMEMBER: All osmosis is diffusion BUT not all diffusion is osmosis 1.ISOTONIC SOLUTION: CONC’N GRADIENT IS ZERO; NO NET GAIN OR LOSS OF WATER BY THE CELL 2.HYPOTONIC SOLUTION: CONC’N OF H20 IS LOWER INSIDE OF THE CELL; NET MOVEMENT OF H20 INTO THE CELL; ANIMAL CELLS WILL SWELL AND BURST WHILE PLANT CELLS WILL SWELL AND HAVE INCREASED TURGOR PRESSURE 3. HYPERTONIC SOLUTION:CONC’N OF H20 IS HIGHER INSIDE OF THE CELL; NET MOVEMENT OF H20 OUT OF THE CELL; ANIMAL CELLS WILL SHRINK WHILE IN PLANT CELLS THE CYTOPLASM WILL SHRINK (PLASMOLYSIS) B. OTHER TYPES OF ABSORPTION I. Active Transport •PROBLEM: Some needed substances are needed in HIGHER concentration inside the cell. •This means that after equilibrium is reached, these substances must move AGAINST their CONCENTRATION GRADIENT and move from an area of LOW concentration to HIGH concentration SOLUTION: Pumps Active Transport • HOMEOSTASIS makes it possible for a cell to maintain a stable internal environment that is chemically different from its surroundings. • The plasma membrane is be involved in active transport through the use of PROTEIN RECEPTORS Active and Passive Transport have often been compared to rolling a ball up and down a hill: It requires no energy or ATP to roll a ball down a hill. It happens naturally just like diffusion. However, pushing the ball up the hill, against the gradient, requires the input of energy/ATP. Selectively permeable membrane C. GETTING THE BIG STUFF IN AND OUT A. MOVEMENT OUT EXOCYTOSIS • Exocytosis involves THE MOVEMENT OF LARGE MATERIALS OUT OF THE CELL B. MOVEMENT IN ENDOCYTOSIS • Endocytosis involves THE MOVEMENT OF LARGE MATERIALS INTO A CELL • There are 2 types of endocytosis, and they both require energy so they are also forms of ACTIVE TRANSPORT 1. PINOCYTOSIS = CELL DRINKING • This involves the absorption of SMALL molecules that still too big to diffuse through the cell membrane 2. PHAGOCYTOSIS = CELL EATING • This involves the absorption of molecules much TOO BIG to diffuse through the cell membrane and structures called PSEUDOPODS • The term “ENGULF” is commonly used when describing phagocytosis An Ameba engulfing a Paramecium. SUMMARY: Methods of Transport Across a Cell Membrane CELL TRANSPORT REVIEW 1. T is the life process that involves the A and C materials throughout a cell or organism. 2. P of transport does NOT require E or . 3. D of passive transport. 4. D H and O are forms is the movement of molecules from an area of concentration to L concentration. 5. O is the diffusion of W 6. A . transport DOES require E or . 7. Two types of E or “cell drinking” and P “cell eating”. include P or