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Review

Review. What are two main types of transport? What is the difference between simple diffusion and facilitated diffusion? What is a hypertonic, hypotonic and isotonic solution? Why do we use endocytosis / exocytosis ? What special structures do we use in endo / exocytosis ?.

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Review

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  1. Review • What are two main types of transport? • What is the difference between simple diffusion and facilitated diffusion? • What is a hypertonic, hypotonic and isotonic solution? • Why do we use endocytosis/exocytosis? • What special structures do we use in endo/exocytosis?

  2. Is a Bigger Cell Better? Sec C2.4 Unit C

  3. Objectives • calculate surface to volume ratios • relate these ratios to size, efficiency of diffusion, and structures in humans and plants

  4. Introduction • Cells are microscopic and carry out all life processes • What structure in the cell is important for transport of materials? • Cell membrane • Transport of materials must be kept at a maximum

  5. The Biggest Cells • Most cells are in the order of a few micrometers in diameter, and are visible only under the microscope • What are the largest cells in the human body? • Oocyte (egg cell) – is 1000 micrometers (1 mm) in diameter and is visible with the naked eye • Neural Cells – although only a few micrometers across, can be 1 metre long!! The pseudounipolar cell (in the spine), is only 135 micrometers across, but can be the height of a person in length!

  6. Why don’t huge cells exist?

  7. If cells were larger … • What happens to transport if the cell were larger and its volume increases? • More molecules needed to be transported • Distance to travel to the cell’s surface also increases • Must have a greater surface area to match need to transport • Need to look at surface area to volume ratio

  8. Calculating Surface Area to Volume Ratio • Need to find both total surface area and volume • Ex. Determine the surface area to volume ratio for cubes with following side lengths: • a) 1.0 cm • b) 2.5 cm • c) 4.0 cm • How do we find total surface area of a cube? Volume?

  9. Example cont… • Surface area of one side= s2 • Volume of cube = s3 • Total surface area? • A = 6s2 • Surface area to volume ratio A = 6s2 = 6 V s3 s Note: We can only use this expression for a cube where 6 sides are equal

  10. Example • Using the expression we derived for a cube, find the surface area to volume ratio for a cube with sides: • a) 1.0 cm • b) 2.5 cm • c) 4.0 cm Answers: a) 6.0 cm b) 2.4 cm c) 1.5 cm

  11. What does this mean? • Larger surface area to volume ratio means more efficient cell transport • Ie. higher surface area and smaller volume

  12. Practice • Calculate the surface area to volume ratio for a rectangular prism with: • Length l= 3.0 cm • Width w= 2.5 cm • Height h= 1.5 cm • Formula= 2lw+2lh+2wh lwh • Answer: 2.8

  13. The Size and Shape of Organisms • Surface area determines opportunity for transport • i.e. little surface area, transport very limited • In cells, bigger is not necessarily better • Cells are specialized though in terms of function • This determines their size and shape • If a cell needed to transport a lot of material (ex. A liver cell), what might their size be in relation to a cell which doesn’t need to transport very much?

  14. Maximizing Potential • Need to maximize surface area to volume ratio • Look at the two pictures; which plant has an easier time of transporting materials? Why? What might the larger plant do to increase its surface area?

  15. Internal Transport Systems • Systems developed to reduce dependence on diffusion and surface area • Animals: circulatory, digestive and respiratory systems • Plants: xylem and phloem

  16. Specialized Structures • These structures increase the overall surface area to volume ratio • Ex. Alveoli in lungs  small sacs to increase surface area for gas exchange • Ex. Small intestine villi and microvilli (projections) for absorption of nutrients

  17. Homework • P. 288 • questions: p 288 #2-6 • Read Sec C2.4 (p. 289-293) • Questions: p. 289 #1-2 • p. 293 #1-5

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