TRANSPORT

1. TRANSPORT

2. I. Cell Membranes • A. Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave cells • B. Some substances can cross the cell membrane without any input of energy by the cell • C. The movement of such substances across the membrane is known as passive transport

3. D. To stay alive, a cell must exchange materials such as food, water, & wastes with its environmentE. These materials must cross the cell or plasma membrane

4. The Cell Membrane

5. Overview • Cell membrane separates living cell from nonliving surroundings • thin barrier = 8nm thick • Controls traffic in & out of the cell • selectively permeable • allows some substances to cross more easily than others • hydrophobic vs hydrophilic • Made of phospholipids, proteins & other macromolecules

6. Phospholipids Phosphate • Fatty acid tails • hydrophobic • Phosphate group head • hydrophilic • Arranged as a bilayer Fatty acid Aaaah, one of thosestructure–function examples

7. More than lipids… • In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer It’s like a fluid…It’s like a mosaic… It’s the Fluid Mosaic Model!

8. Membrane Proteins • Proteins determine membrane’s specific functions • cell membrane & organelle membranes each have unique collections of proteins • Membrane proteins: • peripheral proteins • loosely bound to surface of membrane • cell surface identity marker (antigens) • integral proteins • penetrate lipid bilayer, usually across whole membrane • transmembrane protein • transport proteins • channels, permeases (pumps)

9. Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Enzymeactivity Cell surfacereceptor Cell adhesion Cell surface identity marker Attachment to thecytoskeleton

11. F. Small molecules like water, oxygen, & carbon dioxide can move in and out freely

12. G. Large molecules like proteins & carbohydrates cannot move easily across the plasma membraneH. The Cell Membrane is semipermeable or selectively permeable only allowing certain molecules to pass through

13. II. Diffusion • A. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration

14. Diffusion • 2nd Law of Thermodynamicsgoverns biological systems • universe tends towards disorder (entropy) • Diffusion • movement from highlow concentration

15. Diffusion • Move from HIGH to LOW concentration • “passive transport” • no energy needed movement of water diffusion osmosis

16. B. Small molecules can pass through the cell membrane by a process called diffusionC. Diffusion across a membrane is a type of passive transport because it does not require energy

17. Diffusion across cell membrane • Cell membrane is the boundary between inside & outside… • separates cell from its environment NO! Can it be an impenetrable boundary? OUT waste ammonia salts CO2 H2O products IN food carbohydrates sugars, proteins amino acids lipids salts, O2,H2O OUT IN cell needs materials in & products or waste out

18. inside cell outside cell Diffusion through phospholipid bilayer • What molecules can get through directly? • fats & other lipids • What molecules can NOT get through directly? • polar molecules • H2O • ions • salts, ammonia • large molecules • starches, proteins lipid salt NH3 sugar aa H2O

19. D. This difference in the concentration of molecules across a membrane is called a concentration gradientE. Diffusion is driven by the kinetic energy of the molecules1. Kinetic energy keeps molecules in constant motion causing the molecules to move randomly away from each other in a liquid or a gas

20. F. The rate of diffusion depends on temperature, size of the molecules, & type of molecules diffusing1. Molecules diffuse faster at higher temperatures than at lower temperatures2. Smaller molecules diffuse faster than larger molecules

21. G. Most short-distance transport of materials into & out of cells occurs by diffusionH. Solutions have two parts --- the solute which is being dissolved in the solvent1. Water serves as the main solvent in living things

22. I. Diffusion always occurs down a concentration gradient (water moves from an area where it is more concentrated to an area where it is less concentrated)1. Diffusion continues until the concentration of the molecules is the same on both sides of a membrane

23. 2. When a concentration gradient no longer exists, equilibrium has been reached but molecules will continue to move equally back & forth across a membrane

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25. The Special Case of WaterMovement of water across the cell membrane

26. III. Osmosis • A. The diffusion of water across a semipermeable membrane is called osmosis • B. Diffusion occurs from an area of high water concentration (less solute) to an area of lower water concentration (more solute)

27. C. Movement of water is down its concentration gradient & doesn’t require extra energyD. Cytoplasm is mostly water containing dissolved solutesE. Concentrated solutions have many solute molecules & fewer water molecules

28. Osmosis is diffusion of water • Water is very important to life, so we talk about water separately • Diffusion of water from high concentration of water to low concentration of water • across a semi-permeable membrane

29. F. Water moves from areas of low solute concentration to areas of high solute concentrationG. Water molecules will cross membranes until the concentrations of water & solutes is equal on both sides of the membrane; called equilibriumH. At equilibrium, molecules continue to move across membranes evenly so there is no net movement

30. hypotonic hypertonic Concentration of water • Direction of osmosis is determined by comparing total solute concentrations • Hypertonic - more solute, less water • Hypotonic - less solute, more water • Isotonic - equal solute, equal water water net movement of water

31. I. Hypertonic Solution • 1. Solute concentration outside the cell is higher (less water outside the cell compared to inside) • 2. Water diffuses out of the cell until equilibrium is reached • 3. Cells will shrink & die if too much water is lost • 4. Plant cells become flaccid (wilt); called plasmolysis

33. Managing water balance • Hypertonic • a cell in salt water • example: shellfish • problem: lose water & die • solution: take up water or pump out salt • plant cells • plasmolysis= wilt saltwater

34. J. Hypotonic Solution • 1. Solute concentration greater inside the cell (less water inside the cell) • 2. Water moves into the cell until equilibrium is reached • 3. Animal cells swell & burst (lyse) if they take in too much water • 4. Cytolysis is the bursting of cells

35. 5. Plant cells become turgid due to water pressing outward against cell wall 6. Turgor pressure in plant cells helps them keep their shape 7. Plant cells do best in hypotonic solutions

37. Managing water balance • Hypotonic • a cell in fresh water • example: Paramecium • problem: gains water, swells & can burst • water continually enters Paramecium cell • solution: contractile vacuole • pumps water out of cell • ATP • plant cells • turgid ATP freshwater

38. Water regulation • Contractile vacuole in Paramecium ATP

39. K. Isotonic Solutions • 1. Concentration of solutes same inside & outside the cell • 2. Water moves into & out of cell at an equal rate so there is no net movement of water3. Animal cells do best in isotonic solutions

41. Managing water balance • Isotonic • animal cell immersed in mild salt solution • example:blood cells in blood plasma • problem: none • no net movement of water • flows across membrane equally, in both directions • volume of cell is stable balanced

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44. IV. How Cells Deal With Osmosis • A. The cells of animals on land are usually in isotonic environment (equilibrium)

45. B. Freshwater organisms live in hypotonic environments so water constantly moves into their cells • C. Unicellular freshwater organisms use energy to pump out excess water by contractile vacuoles

47. D. Plant cell walls prevent plant cells from bursting in hypotonic environments • E. Some marine organisms can pump out excess salt

48. Managing water balance • Cell survival depends on balancing water uptake & loss freshwater balanced saltwater

49. V. Facilitated Diffusion • A. Faster than simple diffusion • B. Considered passive transport because extra energy not used • C. Occurs down a concentration gradient

50. D. Involves carrier proteins embedded in a cell’s membrane to help move across certain solutes such as glucose • E. Carrier molecules change shape when solute attaches to them • F. Change in carrier protein shape helps move solute across the membrane