Cell Membrane. Structure and Function. Cell Membrane. Solute vs. Solvent. About Cell Membranes. Cellular Transport Notes 9/22/13

Transcription

1 Cell Membrane Cell Membrane Structure and Function Cellular Transport Notes About Cell Membranes 1. All cells have a cell membrane 2.Functions: a.controls what enters and exits the cell to maintain an internal balance called homeostasis b.provides protection and support for the cell About Cell Membranes (continued) 3. Structure of cell membrane TEM picture of a real cell membrane. Solute vs. Solvent Lipid Bilayer - 2 layers of phospholipids a.phosphate head is polar (water loving) b.fatty acid tails non- polar (water fearing) c. Proteins embedded in membrane Phospholipid Solute (salt) Lipid Bilayer Solvent (water) 1

2 Passive Transport Diffusion No energy required McGraw Hill Animation Movement of molecules from an area of high concentration to an area of low concentration (with the concentration gradient). Wee!!! Three types Diffusion movement of solute Osmosis movement of water Facilitated Diffusion movement of solute through a protein channel. high low Concentration gradient Diffusion: the concentration gradient Diffusion Diffusion 2

3 Diffusion in Organisms Osmosis Osmosis in Plants Osmosis in Plants Normal plant cell Normal Red Onion Cells What happened to the cytoplasm and cell membrane? Plant Cell in Salty Environment Osmosis in Elodea Leaves Normal Cell Salt Water Plant cell shrivels In salt water 3

4 Osmosis in Animal Cells Osmosis Tonicity Demos Pruney Fingers Phospholipids only let small molecules pass through How can the larger ones get in the cell? Proteins in the Cell Membrane Proteins allow only certain molecules pass by based on their shape. Facilitated Diffusion Animation 4

5 Diffusion or Facilitated Diffusion? Carbohydrates in the cell membrane Cell to Cell Communicat Active Transport Active Transport Movement of molecules from an area of low concentration to an area of high concentration (against the concentration gradient). Energy required This is gonna be hard work!! Always uses protein channels high low Movement of Molecules Across the Cell Membrane Which type of transport? 5

6 Which type of transport? Which type of transport? Active Transport Which type of transport? Which type of transport? Will the cell shrivel, swell, or stay the same? Why do plant cells have 1 large vacuole instead of several small vacuoles like animal cells? 6

7 Requirements for Maintaining Homeostasis Homeostasis is the body s balancing act An organism must be able to sense changes in the external and internal environments It must be able to respond to those changes with appropriate adjustments Homeostasis in Plants Homeostasis in Blood Clotting Cell Size As the cell size decreases the surface area to volume ratio increases. If the cell grows larger and the surface area to volume ratio gets too small: substances won t be able to enter the cell fast enough to fuel the reactions waste products will start to accumulate within the cell as they will be produced faster than they can be excreted. 7

8 Why Cells Aren t Big? Why Cells Aren t Big? All organisms need to exchange substances such as food, waste, gases and heat with their surroundings. The rate of exchange of substances therefore depends on the organism's surface area that is in contact with the surroundings. These substances must diffuse between the organism and the surroundings. The requirements for materials depends on the volume of the organism, so the ability to meet the requirements depends on the surface area : volume ratio. As organisms get bigger their volume and surface area both get bigger, but volume increases much more than surface area. Why Cells Aren t Big? So as organisms get bigger their surface area/volume ratio gets smaller. It becomes more difficult for them to exchange materials with their surroundings. Maximum size (single cell) 100 µm. In anything larger than this materials simply cannot diffuse fast enough to support the reactions needed for life. Why are cells so small? Why Cell s Aren t Big Investigation So how do organisms larger than 100 µm exists? All organisms larger than 100 µm are multi-cellular, which means that their bodies are composed of many small cells, rather than one big cell. Each cell in a multi-cellular organism is no bigger than about 30 µm, and so can exchange materials quickly and independently. Humans have about 1014 cells. Which has greater surface area? 8

9 Summary Summary Why does the small intestine have many finger-like projections called villi? Why do human lungs contain millions of small sacs called alveoli to extract oxygen from the air we breathe? Why aren t there just a few large cells to collect oxygen? Get a piece of graph paper from the extra copies bin. Summary Why are kidney s made of many small units called nephrons? Create a graph, plotting the surface area against the volume of each cube. Draw a line connecting the points and label axes and units. Cubes 1cm3 2 cm3 3 cm3 4 cm3 5 cm3 9