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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?


Is a bigger cell better

Is a Bigger Cell Better?

Sec C2.4

Unit C


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!


Why don t huge cells exist

Why don’t huge cells exist?


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

Vs3s

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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