The Cell Membrane and Cellular Transport PDF

THE CELL MEMBRANE AND CELLULAR TRANSPORT The Cell Membrane  The Cell Membrane is the structure found in both plant and animal cells that controls the movement of materials both into and out of the cell Functions of the Cell Membrane 1. Separates the contents of the cell from the...

THE CELL MEMBRANE AND CELLULAR TRANSPORT The Cell Membrane  The Cell Membrane is the structure found in both plant and animal cells that controls the movement of materials both into and out of the cell Functions of the Cell Membrane 1. Separates the contents of the cell from the outside environment 2. Serves as a barrier for which substances can enter and exit a cell 3. Recognizes chemical signals (messages) which will trigger the cell to react in a particular way Selective Permeability The cell membrane is considered selectively permeable, which means that some molecules can pass through, and some molecules cannot It maintains balance both inside and outside the cell Structure of the Cell Membrane Made up of a double layer of “phospholipids” A phospholipid is made of two parts: Phosphate Head- hydrophilic, or “water-loving” Lipid Tails- hydrophobic, or “water-fearing” (think oil, a substance that does not dissolve in water) Structure of the Cell Membrane The “water-loving” phosphate heads face the outside environment and the inside of the cell The “water-fearing” lipid tails face each other on the inside of the membrane Membrane Proteins Proteins are embedded within the membrane because most molecules cannot easily pass through the “water-fearing” lipid tails A protein channel enables molecules to pass through without interacting with the lipids Many types of these proteins exist Transport (Channel) Proteins Shaped like tubes and form a channel through the cell membrane Only allow certain molecules to pass through  Cell Transport Diffusion, Osmosis, and Active Transport  The cell absorbs substances needed for: covering energy consumption → sugars, fats cell construction →sugars, proteins cell activity regulation → proteins, hormones, enzymes conducting metabolic processes → water, ions, vitamins The cell excretes substances that: it doesn’t need or are harmful → carbon dioxide, urea are needed by other cells → enzymes, vitamins, hormones are necessary for protection →antibodies Passage of Materials through Cell Membranes Intake and release of substances are among the fundamental processes essential for cell existence. TYPES OF TRANSPORT: Passive Transport: Some molecules, like water, can move in and out of cells easily without using any energy. Active Transport: Other molecules cannot pass through the cell membrane as easily this process requires energy to move them.  Simple Diffusion Movement of molecules from an area of HIGH concentration to an area of LOW concentration These molecules pass directly through the lipid bilayer without the help of channels NO ENERGY is required! Example: Oxygen, Carbon Dioxide Facilitated Diffusion Movement of molecules down their concentration gradient with the help of transport proteins embedded within the cell membrane No energy is required! Example: Glucose Osmosis is a specific type of diffusion it is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. NO ENERGY is required Hypotonic Solution When the inside of a cell has a much higher salt (solute) concentration than the outside of a cell Water will diffuse into the cell to “dilute” the inside contents Result = Cell Swells and sometimes bursts (lyses) Hypotonic Solution  Hypertonic Solution When the outside of a cell has a much higher salt (solute) concentration than the inside of a cell Water will diffuse out of the cell to “dilute” it’s surroundings Result = Cell Shrivels (shrinks) Hypertonic Solution Isotonic Solution When the solute concentration outside the cell is equal to the solute concentration inside the cell No net movement of water occurs! Isotonic Solution Osmosis in Plant Cells Name that Solution! Hypertonic Isotonic Hypotonic Active Transport Movement of molecules through a cell membrane from an area of LOW concentration to an area of HIGH concentration Always requires ENERGY (ATP)! Always requires transport proteins embedded within the membrane to move molecules Types of Active Transport 1. Endocytosis- cells take in particles by engulfing them- cell membrane pinches in to form a vesicle Two Types: Phagocytosis Pinocytosis Vesicle Phagocytosis Cell “Eating” Movement of larger food particles across the membrane with the use of pseudopods Pinocytosis Cell “Drinking” Taking in of smaller dissolved ions or molecules Phagocytosis vs. Pinocytosis 2. Exocytosis Cell “Excreting” Cells get rid of particles by enclosing them in a vesicle (a membrane) and fusing that membrane with the cell membrane  Passive vs. Active Transport Passive Transport Active Transport Require Energy? NO Require Energy? YES Examples: Simple Examples: Protein pumps, Diffusion, Facilitated endocytosis (pinocytosis and Diffusion, Osmosis phagocytosis), exocytosis Uses: Water, Oxygen, Uses: Large and charged Carbon dioxide, Glucose particles! (Starch, Ions) It’s Like: Riding a bike It’s Like: Riding a bike uphill! downhill!