1. Cell Biology: The Cell Membrane Lesson 2 – Transport Across the Cell Membrane ( Inquiry into Life pg. 69-80 )

2. Today’s Objectives  Analyze the structure and function of the cell membrane, including:  Describe passive transport processes  Explain factors that affect the rate of diffusion across a cell membrane  Predict the effects of hypertonic, isotonic, and hypotonic environments on osmosis in animal cells  Describe active transport processes  Compare specific transport processes  Explain why cells divide when they reach a particular surface area-to-volume ratio, including:  Differentiate between cells that have a high or low surface area- to-volume ratio  Demonstrate an understanding of the significance of surface area- to-volume ratio in cell size

3. Transport across Cell Membranes  4 main ways:  Passive Transport:  1) Diffusion  2) Osmosis  3) Facilitated Transport  Active Transport:  4) Active Transport

4. 1) Diffusion (passive transport)  Diffusion is the movement of a solute from an area of high concentration to an area of low concentration until evenly distributed  Solute is some solid particles or molecules suspended in air or liquid  Example: a foul odor in the corner of a room will spread out until it is evenly distributed  Example: cream in coffee will diffuse until concentrations are balanced

5. 1) Diffusion (passive transport)  Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion  Consider two containers of gas A and gas B separated by a partition; the molecules of both gases are in constant motion and make numerous collisions with the partition  If the partition is removed as in the illustration, the gases will mix because of the random velocities of their molecules  In time, a uniform mixture of A and B molecules will be produced in the container

6. 2) Osmosis (passive transport)  Osmosis is a special type of diffusion in which water moves from an area of high water concentration to an area of low water concentration across a membrane

7. 2) Osmosis (passive transport)  Pressure caused by the concentration gradient between two different solutions is called osmotic pressure  Hydrostatic pressure (gravity) offsets osmotic pressure  The solute cannot spread out because it is too big to pass through the membrane. Therefore, water moves across the membrane from [high water] to [low water].  Water moves through the protein-lined pores of the cell membrane

8. Water will move from side A to side B. Level on A will fall. Level on B will rise. Until gravity stops it = hydrostatic pressure)

9. 3) Facilitated Transport (passive transport)  In facilitated transport, solutes move across the membrane from an area of [high solute] to [low solute] with the help of a carrier protein  Example: molecules needed by the cell such as glucose enter through facilitated transport from the blood  Examples of solutes: gases, molecules

10. 4) Active Transport  In active transport, solutes move from an area of [low solute] to an area of [high solute] across a membrane with the aid of a carrier protein  Example of solute: ions  Since the movement is against the concentration gradient, energy is required (ATP)  Example: Sugar is removed from urine by active transport into the blood. Since there is already a lot of glucose in the blood, it is traveling against the concentration gradient  Example: Na/K Pump. Found in nerve and muscle cells. Carrier protein changes shape to fit Na and K

11. 4) Active Transport

12. Summary  Diffusion  Solute moves from [high solute] to [low solute]  No membrane required  No carrier protein required  No energy required  Osmosis  [high water] to [low water]  Membrane required  No carrier protein required  No energy required

13. Summary  Facilitated Transport  [high solute] to [low solute]  Membrane required  Carrier protein required  No energy required  Gas/molecule movement

14. Summary  Active Transport  [low solute] to [high solute]  Membrane required  Carrier protein required  Energy required (ATP)  Ion movement

17. Factors affecting Diffusion  Surface area vs. Volume

18. Cell Surface Area Volume S.A. : Volume Ratio LxWx6 LxWxH A 6 units 2 1 units 3 6:1 B 24 units 2 8 units 3 3:1 C 96 units 2 64 units 3 1.5:1 D 384 units 2 512 units 3 0.75:1 Nutrients (oxygen and glucose) enter a cell while wastes (carbon dioxide and urea) exit a cell across the cell membrane. The amount of cell membrane = surface area

19. Surface Area vs. Volume  Inside the cell, organelles use up nutrients and produce wastes  The larger the cell, the more nutrients needed and the more waste produced  The size of the cell (# of organelles) = volume  Small cells have a high SA : Volume ratio  They can supply the organelles with plenty of nutrients and remove wastes

20. Surface Area vs. Volume  Large cells have a low SA : Volume ratio because volume increases faster than surface area  If a cell gets too big, wastes will increase and nutrients able to enter the cell will decrease  Therefore, cells are limited in size: active cells must be smaller than less active cells because they need more nutrients and produce more waste  Some cells can increase their surface area without increasing volume by producing folds

21. Factors that will Increase Diffusion  A) Concentration Gradient  The difference in concentration between two areas  The greater the [] gradient, the faster the rate of diffusion  B) The size and shape of the molecules  C) Temperature  The higher the temperature, the faster the rate of diffusion  D) Type of Medium  Rate of diffusion is faster in air than in liquid  E) Movement of the Medium  Water or air currents increase the rate of diffusion  Example: stirring while adding cream to coffee

22. Endocytosis and Exocytosis  Endocytosis:  Process in which large materials enter a cell  Vesicles form as a way to transport molecules into a cell  Two types: phagocytosis and pinocytosis

23. Phagocytosis  A type of endocytosis in which whole cells, bacteria, or cell fragments are taken into the cell  Referred to as “cell eating”  Transports very large pieces

24. Pinocytosis  A type of endocytosis in which molecules such as proteins are taken into the cell  Referred to as “cell drinking”  Transports smaller “large” pieces and liquids

25. Exocytosis  A process by which products or wastes exit a cell  Reverse of endocytosis

26. Exocytosis

28. Hypertonic, Hypotonic, Isotonic Solutions  Use your textbook to find the following definitions:  Hypertonic solution:  Solution with a higher concentration of solute than its surroundings  If a cell is placed in a hypertonic solution, water will rush out of the cell in order to balance the concentration of solute causing the cell to shrivel  Hypotonic solution:  Solution with a lower concentration of solute than its surroundings  If a cell is placed in a hypotonic solution, water will rush into the cell in order to balance the concentration of solute causing the cell to swell and possibly burst  Isotonic solution:  Solution in which the osmotic concentration is the same as the solute concentration of its surroundings  If a cell is placed in a isotonic solution, water diffuses into and out of the cell at the same rate

29. Hypertonic, Hypotonic, Isotonic Solutions  Water will move from a hypotonic solution to a hypertonic solution  No net movement of water between isotonic solutions

30. Tonicity  Tonicity refers to concentration of solute in a solution  Below are the effects of tonicity on animal cells

31. RED BLOOD CELLS IN DIFFERENT SOLUTIONS

32. NORMAL RED BLOOD CELLS RBC PLACED IN A HYPERTONIC SOLUTION RBC PLACED IN A HYPOTONIC SOLUTION

33. Tonicity Experiment – Thistle Tube  Inside tube is hypertonic, outside tube is hypotonic  Water moves from [high water] (hypotonic) to [low water] (hypertonic)