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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
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?
objectives
Objectives
  • calculate surface to volume ratios
  • relate these ratios to size, efficiency of diffusion, and structures in humans and plants
introduction
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
the biggest cells
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!
if cells were larger
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
calculating surface area to volume ratio
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?
example cont
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

example
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

what does this mean
What does this mean?
  • Larger surface area to volume ratio means more efficient cell transport
    • Ie. higher surface area and smaller volume
practice
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
the size and shape of organisms
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?
maximizing potential
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?
internal transport systems
Internal Transport Systems
  • Systems developed to reduce dependence on diffusion and surface area
  • Animals: circulatory, digestive and respiratory systems
  • Plants: xylem and phloem
specialized structures
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
homework
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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