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1.  Cell sizes.  To appreciate the differences in cell size, consider the following specific examples.  Escherichia coli, a typical bacterial cell, is cylindrical in shape, with a diameter of about 1 Ám and a length of about 2 Ám.  As a typical animal cell, consider a human liver cell, which is roughly spherical in shape and has a diameter of about 20 Ám.   And for a typical plant cell, consider the columnar palisade cells located just beneath the upper surface of many plants.  These are cylindrical in shape, with a diameter of about 20 Ám and a length of about 35 Ám.


(A) Calculate the approximate volume of each of these three cell types in cubic micrometers.  (Recall that V = pr2h for a cylinder and that V = 4pr3/3 for a sphere.)


(B) Approximately how many bacterial cells would fit in the internal volume of a human liver cell? 


(C) Approximately how many liver cells would fit inside a palisade cell?


2.  To get some feeling for the differences in size of various cellular structures, it is useful to compare the structures on a macroscopic scale.  Listed below is a variety of structures, with their approximate dimensions.  To compare their dimensions on a macroscopic scale, assume that each structure has been magnified a million-fold, using a scale such that 1 nm is represented by 1 mm. On this scale, a prokaryotic ribosome has a diameter of 25 mm, and is therefore the size of a large marble.  Convert each of the other dimensions to this macroscopic scale, and suggest a physical object that has approximately the same dimensions.


1.      Eukaryotic ribosome (Where proteins are made): 30 nm

2.      Mitochondrion (Where chemical energy is released):  1 x 2 Ám

3.      Chloroplast (Which traps light energy):  2 x 8 Ám

4.      Nucleus (Control center of the cell):  6 Ám in diameter

5.      Liver cell:  20 Ám in diameter

6.      Chicken egg:  4 x 6 cm

7.      Human being:  1.8 m tall


3.  On the same macroscopic scale as in question 2, what would be the dimensions of the following?


(A)    a typical cell membrane:  8 nm wide

(B)      the thickness of Glad wrap:  10 Ám


4.  What would be the dimensions E. coli and the palisade cell in question 1, if they were placed on the same macroscopic scale as the cell structures in question 2 (i.e., if they were magnified a million-fold)?


5.  How many cell membranes would have to be aligned side by side before the structure could be seen with the light microscope?  How many with the electron microscope? (Assume a typical membrane to be about 8 nm wide.)  (The limit of resolution for a light microscope is 200 nm and for an electron microscope 0.1-0.2 nm.)