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… A = 6s2 = 6 V s3 s 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. Is Bigger Better? Read through the lab on page 290-291.
You need to come up with an hypothesis as well as make a data table (copy from textbook).