The Cell Membrane and Passive Transport

1. The Cell Membrane and Passive Transport

2. passive transport always worksdowna concentration gradient (from high to low concentration the rate of passive transport is determined by particle size, lipid solubility, distance to travel, and the slope of the concentration gradient does not require the input of energy, useful in biological systems i.e. in the lungs, alveoli increase the surface area and capillaries are one cell thick as an adaptation to facilitate diffusion of O2 and CO2. Passive Transport

3. diffusion is defined as“the movement of particles from an area where they are more highly concentrated to an area where they are less concentrated” as a result of the random motion of the particles Simple Diffusion

5. the cell membrane isselectively or semi-permeable tightly-packedphospholipidsallowsmallpolar(i.e. H2O, O2, CO2) molecules andshort chain nonpolarfatty acidsto pass freely but preventionsand large molecules(i.e. amino acids, carbohydrates, nucleic acids, and large lipids) from passing the fatty acid portion imbeddedproteinsfacilitate the passage of small molecules unable to cross phospholipid bilayer Cell Membrane

7. http://www.youtube.com/watch?v=ULR79TiUj80

8. recognitionproteins (glycoproteins) (antigens = “antibody generators”) have carbohydrates attached and provide a cell with a unique identity form the basis of the immune system for the recognition of potential pathogens • transport proteins move larger molecules in or out of the cell • some act as gatekeepers, opening and closing channels through the cell membrane (i.e. Na+/K+ pump allows neurons to fire) • others carry materials across the cell membrane • receptor proteins act as sites for hormones to attach to communicate chemical messages (i.e. insulin stimulates the opening of pores to allow sugar molecules in) • cholesterol maintains the fluidity of the cell membrane, protein filaments anchor the cell membrane to the cytoplasm

9. specializedtransmembraneproteins act ascarrierorchannelproteins for the diffusion of large or fat-insoluble molecules transport is stillpassiveas it will only go down a concentration gradient e.g. glucose attaches to abinding siteon achannel proteinon one side of the membrane the shape of the protein changes in order to allow glucose to diffuse to the other side of the membrane  protein changes back to its original shape, ready to accept another glucose molecule Facilitated Diffusion http://www.youtube.com/watch?v=I4123hUU8xo&feature=related

11. Summary

13. osmosis is the “diffusion of water across a semi-permeable membrane” results in anetdiffusion of water from one side of amembrane to another osmotic conditionsdescribe the relative concentration of solutes in the medium around a cell that will determine the direction of water movement (in or out of the cell) Osmosis

14. hypertonic solutions have a higher (hyper = above) solute concentration (= lower water concentration) outside the cell resulting in a net movement of water out of the cell Hypertonic Solutions

16. If an animal cell such as red blood cell is placed into a hypertonic solution, water molecules is transported out from the red blood cells by osmosis (as shown in the diagram above). • The red blood cells will shrink due to the lost of water from the cell and probably die. • The red blood cells are said to undergo crenation .

17. hypotonic solutions have a lower (hypo = under) solute concentration (= higher water concentration) outside the cell resulting in a net movement of water in to the cell Hypotonic Solutions

19. If an animal cell such as red blood cell is placed into a hypotonic solution, water molecules is transported into the red blood cells by osmosis (as shown in the diagram above). • The red blood cells will inflate and finally burst because the thin membrane cannot withstand the high pressure inside the cell. • The red blood cells are said to undergo hemolysis

20. isotonic solutions have the same (iso = same) solute concentration outside the cell resulting in no net movement of water in or out of the cell Isotonic Solutions

22. If an animal cell such as red blood cell is placed into a isotonic solution, amount of water molecules is transported into the red blood cells by osmosis is equal to the amount of water molecules transported out from the cell (as shown in the diagram above). • Therefore the amount of water in the cell remain unchanged. • The red blood cells maintain their shape.

23. Summary: Osmosis http://www.youtube.com/watch?v=MUcP_sZ1eCk

24. osmosis is of great importance for freshwater organisms (living in a hypotonic solution) as they have evolved adaptations for expelling water (i.e. contractile vacuoles in Paramecium). Kidneys are an adaptation to hypertonic environments (i.e. land) as they adjusting the water level in urine)  Osmosis Lab: Solute Concentration of Potatoes Osmosis and Adaptations