1. Which makes green tea faster: tea leaves or powder?

2. What will go cold faster: French fries or a baked potato? Why?

3. IN:
Oxygen
Nutrients
Water
The plasma membrane of a cell is the surface of exchange for materials between the inside and the outside of the cell.
OUT:
Carbon dioxide
Waste
Products (e.g. proteins)

4. Therefore, a larger volume requires more exchange across the membrane.
As the cell gets larger, it requires more resources to be imported and produces more products (and waste) to be exported.
Therefore, a larger volume requires more exchange across the membrane.

5. As the cell gets larger…

6. Diffusion Pathways
are shorter (and more efficient) in smaller cells with a larger surface are to volume ratio.

7. As the cell gets larger… …the surface area to volume ratio
actually gets
smaller…
…so the
exchange
processes
become less
efficient with
increasing size.

8. As the cell gets larger… …the surface area to volume ratio
actually gets
smaller…

12. Answer
Elephants do many different things with their big ears. One thing is that they can cool themselves down when they are hot. The blood flowing through the ears is close to the outside of the elephant body, and heat can be released as they flap them about.

13. Two Minute Essay
Explain the importance of surface area to volume ratio as a factor limiting cell size

14. Big Cell Exceptions
Epulopiscium is a giant species of bacteria. Read more about it here .
E. coli
100μm
Epulpoiscium, by AJ Cann on Flickr (CC)

15. Big Cell Exceptions
Caulerpa species of algae are one giant cell with many nuclei distributed throughout.

16. Structure/Function
Natural selection favours adaptations that give an advantage. Folded structures are everywhere in nature, maximising the surface area to volume ratio for exchange of materials.
Mammalian liver mitochondria:

17. C E L S
Surface are to volume ratio is a factor that limits the size of cells.
By dividing to make more, smaller cells, the efficiency of the exchange processes across the membranes (into and out of the cells) can be kept high.
Shorter diffusion paths.
More surfaces for reactions.
Removal of heat and waste D I V E
4-cell stage of a sea biscuit by Bruno Vellutini on Flickr (CC)

18. Magnification
The image we see through the light microscope has been magnified.
Objective lens
x eyepiece lens
Image from wikimedia commons:

20. Modern Microscopy
Image: d by USDA on Flickr (CC):

21. Modern Microscopy
As we develop more and more sophisticated and precise imaging tools, we can see more detail of the cells and molecules that make us.
Scanning electron microscopes deliver high-resolution, 3D surface images of structures, whereas transmission electron microscopes give us a view inside cells and organelles.
Image: d by USDA on Flickr (CC):

22. Emiliana huxleyi
photosynthetic plankton
Image from:

23. Transmission electron micrograph of HIV particles.
HIV-1. Transmission electron micrograph, via wikimedia commons:

24. Scanning electron micrograph of HIV particles budding on a human lymphocyte.
False-coloured scanning electron micrograph of HIV (green) budding on a lymphicoyte (blue) OR

25. Light Microscope
Elodea - Aquatic Plant
40X 400X

26. Transmission Electron Microscope (TEM)
Herpes Virus
Plant Root Cell

27. Scanning Electron Microscope (SEM)
Mosquito Head
200X 2000X

28. Scanning Electron Microscope (SEM)
Fly Eye

29. Scanning Electron Microscope (SEM)
Inside of Stomach
Surface of Tongue
Neuron

30. Scanning Electron Microscope (SEM)
Pollen
Yeast
Red Blood Cell, Platelet, and White Blood Cell

31. TEM vs. SEM
Viruses leaving a cell

32. 50μm
Human egg cell, from Gray’s Anatomy (1858).

33. 5μm
Human sperm cell, from Gray’s Anatomy (1858).

34. Scanning electron micrograph of human sperm and egg cells.
smallest human cell
largest human cell
5μm
Image from wikimedia commons

35. Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification.
What is the actual size of this specimen in micrometers (um)?
Actual size = measured length/magnification
60mm/5 = 12mm
12mm x 1000 um
=12,000 um
Magnification x 5
Measured Length = 60 mm

36. μm = micrometers Some units that I use & know X 1,000 ÷1,000 ÷1,000
abbr.
Metric equivalent
kilometer km
1,000m
1 x 103m
meter m 1m
centimeter cm
0.01m
1 x 10-2m
millimeter mm
0.001m
1 x 10-3m
micrometer μm m
1 x 10-6m
nanometer nm m
1 x 10-9m
X 1,000
÷1,000
÷1,000
÷1,000
μm = micrometers
We usually use this in discussion of cells. There are 1,000μm in one mm.
write this correctly

47. Practice

48. Practice

49. Practice
254X
8500X
320X
320,000X
.38x
380x
5.4x10-5

50. Practice
11μm
40 μm
175μm
200μm

51. LAB TIME
Measuring microscopic objects

52. Review notes from previous lesson
Questions???

53. Exam question #1...
1) A picture in your textbook indicates that it is magnified 5x, and when measured with a ruler is .25 cm in length. What is its actual length in micrometers (um)?
a) 5 um
b) um
c) um
d) um c

54. Exam question #2...
A red blood cell is 8 μm in diameter. If drawn 100 times larger than its actual size, what diameter will the drawing be in mm?
A mm
B mm
C. 8 mm
D mm B

55. Two Minute Essay
Explain the importance of surface area to volume ratio as a factor limiting cell size.
Free images from: Presentations ETC, University of Florida.

56. Markscheme
small cells have larger ratio (than larger cells) / ratio decreases as size increases;
surface area / membrane must be large enough to absorb nutrients / oxygen /
substances needed;
surface area / membrane must be large enough to excrete / pass out waste products;
need for materials is determined by (cell) volume;
cell size is limited (by SA / vol ratio) / cells divide when they reach a certain size;
reference to diffusion across / through membrane / surface area;

57. Emergent Properties
the whole is
more than the sum
of its parts