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Unit 2: Cells
Mr. Nagel
Meade High School
• What did the following scientists contribute
to our knowledge about CELLS?
– Hooke
– von Leeuwenhoek
– Schleiden
– Schwann
– Virchow
IB Syllabus Statements
• 2.1.1
– Outline the cell theory.
• 2.1.2
– Discuss the evidence for the cell theory.
• 2.1.3
– State that unicellular organisms carry out all the
functions of life.
• 2.1.6
– Explain the importance of the surface area to
volume ratio as a factor limiting cell size.
Cell Theory
Cell Theory
• Robert Hooke (1665)
– Cork cells (30x)
• Anton von Leeuwenhoek (same time)
– Unicellular organisms (300x)
• Schleiden (plants) and Schwann (animals) (1839)
– Animal and plant cells
• Rudolph Virchow (1855)
– Determines cells only come from other cells
• Sum of conclusions lead to Cell Theory
Cell Theory
• Cell Theory:
– Cells are the fundamental unit of life.
– All living things are composed of cells.
– Cells can only come from pre-existing cells.
• Unicellular organisms carry out all life
• What is the difference between a Law,
Theory, and Fact?
• Why is this only a Theory?
Cell Structure
• Balloons and improvised tape measures:
– Surface Area vs. Volume
• Measure the circumference of your balloon
at three varying sizes.
– Calculate:
• Volume
• Surface Area
• SA/V ratio
Cell Structure
• What do you notice about the SA:V ratio
as the balloon (model cell) expands?
• Why would it be important for a cell to
have a much greater surface area than
IB Syllabus Statements
• 2.1.6
– Explain the importance of the surface area to
volume ratio as a factor limiting cell size.
• 2.1.4
– Compare the relative sizes of molecules, cell
membrane thickness, viruses, bacteria,
organelles and cells, using the appropriate SI
• 2.1.5
– Calculate the linear magnification of drawings and
the actual size of specimens in images of known
Cell SA:V Ratio
Hierarchy of Biology
• Organize the following from smallest to
– Tissue, atom, organism, organelle, organ,
population, cell, community, ecosystem,
organ system, molecule
• Provide an example of each!
Cell Stats
• Biggest Cell
– Giraffe nerve (2m)
• Smallest Cell
– Bacteria (0.2µm)
Early microscopes were similar to the
ones used in today’s classrooms
(Light microscopes)
-Visible light passes through the
specimen and then through the
glass lens which magnifies the
• Several things are important in the world
of microscopes:
– Resolution – ability to clearly see between
• Limits of Resolution: π*r2 (area of light)
– Magnification – just how LOW can we go?
• Light microscopes are limited to 0.2 µm (2000x)
(size of a small bacterium) and are effective at about 1000
times the size of the specimen.
Light microscopes can NOT see organelles.
• Electron microscopes have magnets to focus an electron
beam. The wavelength of the electron beam is far
shorter than that of light, and the resulting image
resolution is far greater (about 0.5 nm).
– Scanning electron microscopes (SEM)
• Exterior (spray with fine metallic mist) – 50,000x
• Electrons project onto photographic plate
– Transmissions electron microscopes (TEM)
• Interior (thin slices) – 2,000,000x
Light Microscopy
Electron Microscopy
Size and Scale
Size and Scale
Calculating Magnification
• When drawing cells and cell ultrastructures…
– Include a scale bar: |---| = 1µm
– Include magnification: x250
• To find magnification:
– M = Measured size of diagram / Actual Size of object
– M = objective lens * eyepiece lens
• In the next slide:
– Find the magnification. (Hint: Think of map scales)
– State the size of one of the beads.
Calculating Magnification
• 4 cm / 200 µm = 4 x 10-2 m / 200 x 10-6 m
– =0.02 x 104 = 200x
• Create a “double bubble map” comparing
and contrasting Prokaryotic cells with
Eukaryotic cells.
• Be as thorough as possible… a complete
map will be an excellent reference!