Unit 5- Cell Membrane & Cell Transport 5b- Cellular Transport

About Cell Membranes All cells have a cell membrane Functions: Maintains homeostasis Provides protection and support for the cell TEM picture of a real cell membrane. Animations of Active Transport & Passive Transport

What is the purpose of cellular transport? Homeostasis depends upon appropriate movement of materials across the cell membrane. Required materials must pass into the cells so they can be used. Ex. Oxygen and glucose for cellular respiration Waste materials must pass out of the cells as they are produced Ex. The CO2 produced as a waste product of cellular respiration

Membrane movement animation How? Each individual cell exists in a fluid environment, and the cytoplasm within the cell is a fluid environment. The presence of a liquid makes it possible for substances (such as nutrients, oxygen, and waste products) to move into and out of the cell. A cell membrane is semipermeable (selectively permeable). Materials can enter or exit through the cell membrane by passive transport or active transport. In solution, particles move constantly (more KE than a solid). They collide with one another and tend to spread out randomly. As a result, the particles tend to move from an area where they are more concentrated to an area where they are less concentrated

Passive Transport Cell uses no energy The movement of molecules occurs along a concentration gradient meaning molecules move from an area of high concentration to an area of low concentration 3 types of passive transport high low Weeee!!!

Simple Diffusion Animation Passive Transport: Diffusion: spreading out of molecules across a cell membrane until they are equally concentrated (equilibrium) *molecules never stop moving, just stay spread out* results from the random motion of molecules Occurs along a concentration gradient Molecules can diffuse across a membrane by dissolving in the phospholipid bilayer (ex O2, CO2) or by passing through pores in the membrane results from the random motion of molecules (driven by molecules’ kinetic energy) Equilibrium- Molecules do not stop moving, they are just moving equally in both directions

Passive Transport: 2. Osmosis: diffusion of water across a membrane Osmosis animation Passive Transport: 2. Osmosis: diffusion of water across a membrane Water moves from a high concentration of water to a low concentration of water Net direction of osmosis is determined by the relative solute concentrations on the two sides of the membrane. Aquaporin Depends on the % of H2O, not the amount Water moves through the bilayer as well as through channel proteins (aquaporins)

Solutions Solute- substance being dissolved Solvent- substance solute dissolves in Solution= solute+solvent

Passive Transport-Osmosis Hypotonic Solution: The solute concentration outside the cell is lower than the solute concentration inside the cell. (Low solute; High water) Hypo- below, low….less solute Hypotonic can be used to describe the cell or the environment….if the environment is hypotonic, the cell is hypertonic A cell placed in a hypotonic solution is gain water & get big and fat like a hippo Result: Water moves from the solution to inside the cell. Cell swells & may burst (cytolysis).Animation

Passive Transport-Osmosis Hypertonic Solution: The solute concentration outside the cell is higher than the solute concentration inside the cell. (High solute; Low water) Plasmolysis Hyper- above, more Plasmolysis- water rushes out, cell shrinks away from the rigid cell wall shrinks Result: Water moves out of the cell into the solution. Cell shrinks! Animation

Passive Transport-Osmosis Isotonic Solution: The solute concentrations outside the cell & inside the cell are equal. Iso- equal Result: No net movement. Water moves equally in both directions & the cell remains same size. (Dynamic Equilibrium)

Hypertonic, Hypotonic, Isotonic Solutions

In what type of solution are these cells? B C A Hypertonic Isotonic Hypotonic

How Cells Deal with Osmosis Paramecium (protist) removing excess water video Cells must compensate for the water that enters the cell in hypotonic environments & leaves the cell in hypertonic environments. Protists, like paramecia, have contractile vacuoles that collect & pump out excess water. Plants & bacteria have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called turgor pressure. Plasmolysis- in a hypertonic environment the cells shrink away from the cell walls & turgor pressure is lost.

How Cells Deal with Osmosis Animal cells are bathed in blood. Kidneys keep the blood isotonic by removing excess salt & water. Many multicellular organisms have outer surfaces that are waterproof to prevent water loss on land or water gain in freshwater. A small difference in solute concentration results in a very large osmotic pressure gradient across the cell membrane and the membranes of animals cells can’t withstand any appreciable pressure gradient. Water movement can eliminate differences, but it’s also a problem because it leads to a change in cell volume. Regulation of intracellular solute concentration is essential for control of cell volume.

Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Passive Transport: A B 3. Facilitated diffusion: diffusion of specific particles along a concentration gradient with the help of transport proteins Transport Proteins are specific – they “select” only certain molecules to cross the membrane Transports larger or charged molecules that cannot pass through the membrane on their own Glucose is an example of a molecule that passes into the cell through facilitated diffusion Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Carrier Protein http://bio.winona.edu/berg/Free.htm

Passive Transport: 3. Facilitated Diffusion Glucose molecules Cellular Transport From a- High High Concentration Channel Proteins animations Cell Membrane Low Concentration Protein channel Low Transport Protein Through a 

This is gonna be hard work!! Active Transport Requires the cell to use energy Molecules move against the concentration gradient – from an area of low concentration to an area of high concentration Active transport is used to: move large molecules concentrate molecules within the cell remove waste from the cell high low This is gonna be hard work!!

Types of Active Transport Sodium Potassium Pumps (Active Transport using proteins) 1. Protein Pumps (aka cell membrane pumps) –transport proteins that require energy to do work Example: Sodium / Potassium Pumps are used in nerve cells to transmit messages. Calcium, potassium, and sodium ions are examples of materials that must be forced across the cell membrane using active transport

Active Transport- Protein Pumps Sodium-Potassium Pump ATP supplies the energy that drives the pump

Types of Active Transport 2. Endocytosis: Cells take in large molecules by folding around them & forming a pouch Pouch then pinches off from the membrane & becomes an organelle called a vesicle This is how white blood cells ingest bacteria Some vesicles will fuse with lysosome so contents digested. Some will fuse with other organelles.

Types of Active Transport 3. Exocytosis: vesicles made by the cell fuse with the cell membrane, releasing their contents into the external environment Used to release large molecules, waste products, or toxins Used to release proteins after Golgi apparatus packages them into vesicles Endocytosis & Exocytosis animations

Endocytosis & Exocytosis