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Name: __________________
Cells and cell organelles – size matters?
Eukaryotes have their genetic material enclosed within a definite membrane bound nucleus
and their cytoplasm contains a variety of organelles. In contrast, prokaryotes such as bacteria
lack a membrane bound nucleus and do not have many organelles that can be seen in the
typical plant and/or animal cell. Viruses typically consist of an external coat of protein which
encloses the genetic material, either DNA or RNA.
This activity is designed to assist you to become aware of the relative scale of various types
of cells, organelles and viruses.
Materials
2 large sheets of plain paper; a ruler; a pencil
Measurements
1 meter (m) = 1000 millimeters (mm)
1 millimeter = 1000 micrometers (m)
1 micrometer = 1000 nanometers (nm)
PART A: SCALE DRAWINGS
Q1. Complete the following using exponents.
1 meter = 103 millimeters
1 meter = ….. micrometers
1 meter = ….. nanometers
How small is a micrometer (m)? If 100 pages made a book with a thickness of about 6 mm,
then every page is about 0.06 mm or 60 m.
Scale drawings of cells and some organelles
1. On a sheet of paper draw a line 1 centimeter long in one corner. This will be your
scale bar that represents 1 micrometer (m).
2. Using this scale of 1 cm to 1 m, draw a series of circles on the sheet of paper to
represent the average size of various cells identified in Table 1. (Animal cells are
generally between 10 to 30 m and plant cells between 10 to 100 m.)
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Table 1: Average size of some cell types
Cell Type
Average diameter
(m)
7
25
50
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1
Eukaryote human red blood cell
human white blood cell
cortical plant cell
Prokaryote Bacillus bacterium
Staphylococcus bacterium
Q2. Given that these examples are typical, compare the relative sizes of bacterial cells with
cells from eukaryotes?
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3. Now add line diagrams to depict the plant cell wall and several cell organelles, using
the dimensions below (you may need to refer to your textbook to check the shape of
the organelle).
Chloroplast
5 m long
Mitochondrion
1.5 x 0.5 m
Nucleus
6 m diameter
Primary cell wall
1 m thick
4. Using the same scale of 1 cm to 1 m, try to add the following viruses to your sheet:
Smallpox virus
0.25 m (250 nm)
Influenza virus
0.10 m (100 nm)
Foot-and-mouth virus
0.01 m (10 nm)
PART B: OTHER STRUCTURES IN CELLS
1. On a second sheet of paper draw a line 100 mm (10 cm) long in one corner. This will
be your scale bar and will represent a length of 100 nm. Using this scale of 1 mm to 1
nm (0.1 m), draw circles to denote the viruses listed above.
2. On this sheet of paper draw simple outline diagrams to show the structures of cells
listed in Table 2.
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Table 2 Some average measurements for selected components of eukaryotic cells
Structure
plasma membrane
lysosome vesicle
ribosome
DNA molecule
Typical measurement (nm)
7 nm thick
200 nm diameter
25 nm diameter
2 nm wide
Q3. Many scientists support the hypothesis that mitochondria and chloroplasts were once
free-living bacterial cells that now live inside other cells. Does the size of these organelles
provide support for this hypothesis?
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Q4. With a scale of 1 mm to 1 nm, what measurement would be needed to show the average
diameter of a human white-blood cell? _________________________________
Q5. The largest known bacterium, Epiloposcium fishelsoni, lives in the intestines of the
brown sturgeon fish and was identified in the 1990s. Because of its size it was first not
recognized as bacterial in nature but was thought to be a unicellular protest. These bacteria
grow to a length of more than 0.5 mm and are related to bacteria in the genus Clostriduim.
a.
Express this length in m:
0.5 mm = ……. m
and in nm:
0.5 mm = ……. nm
b.
Assume that this bacterium is circular in outline. Make a scale drawing of one
bacterial cell and, inside this cell, insert a human red blood cell. Would you predict that this
bacterium lives inside cells of the fish intestines or in the intestinal cavity? Explain.
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