Cell Structure and Function!
All about cells! Why do we spend an entire month
on just cells?
1) What is the smallest living part that still
counts as being “alive?”
2) Can we keep dividing us into smaller and
smaller parts, or do we reach a point where
what is left is no longer living?
Those two questions make up this next unit, and
the answer is: The smallest living unit of an
organism is the cell.
What keeps these organisms alive?
 Trees
 Mice
 Algae
 Bacteria
 Tigers
 You
Cells are crucially important but why?
 The smallest living unit within any organism
is a cell.
 Cells make up ALL living things, whether an
organism consists of one or many different
cells.
 Cells are dynamic… what does this mean?
 They have intricate parts. Each part plays a
specific role and has a specific function within
the cell.
INSERT PICTURES OF UNICELLULAR
DIATOMS – unicellular algae with hard silica cell
walls-come in many shapes and sizes
Discovery of the Cell
 Cell theory
 The contributions of several scientists lead to
the following theory.
The cell theory states:
1) All living things are made up of cells.
2) Cells are the basic units of structure and
function in living things.
3) New cells are produced from existing cells.
Who discovered what?
An Englishman by the name of Robert Hooke
used an early compound microscope to look at
non-living slice of cork. Notices that the cork is
made up of thousands of tiny empty chambers –
he called these “cells” (we now know that cells are
not empty)
Around the same time a Dutch scientist named
Anton van Leeuwenhoek examined pond water
and other things, including human saliva. He drew
the organisms he saw in the mouth – this was what
we now call bacteria
In 1838 a German botanist (plant guy) Matthias
Schleiden concluded that all plants are made up of
cells.
The next year a German biologist Theodor
Schwann stated that all animals were made of
cells.
In 1855 a German physician Rudolf Virchow
concluded that new cells could only be produced
from the division of existing cells.
How did they do this? With microscopes then as
technology became more sophisticated we could
see more and only confirmed the findings that
those five scientists found out with a simple
compound microscope.
Light microscopes: a typical light microscope
allows light to pass through a specimen and uses
two lenses to form an image.
 The first lenses magnifies it by 10, the second
magnifies it even more.
 This microscope is what you have already
used in the pond water lab and duckweed lab!
 Limits to Light microscope:
o Because it is light, the light waves are
diffracted (scattered) as they pass
through matter.
o Can only produce clear images to a
magnification of about 1000x.
o Cells are nearly transparent making it
difficult to see the structures within in
because they do not reflect light back.
Cell Stains
 Using chemical stains or dyes can solve the
problem of cells being transparent.
 Some of the stains are so specific that they
reveal only compounds or structures within
the cell.
 Fluorescent dyes can be attached to specific
molecules allowing the viewer to identify the
locations of these molecules and watch them
move throughout the cell.
Electron Microscopes
 Can see quite a bit smaller then the light
microscope because it uses a beam of
electrons, not light. The electrons are focused
by magnetic fields.
 Two types of electron microscopes:
o Transmission (TEM)
o Scanning (SEM)
Transmission Electron Microscope (TEM)
 Used to explore cell structures and large
protein molecules
 Beams of electrons can only pass through thin
samples, therefore, cells and tissues must be
cut first into ultra thin slices before examined.
 Produce flat, two-dimensional images.
Scanning Electron Microscope (SEM)
 Pencil-like beam of electrons is scanned over
the surface of a specimen.
 Specimens do not have to be cut into thin
slices to be seen.
 Produces three-dimensional of the specimen’s
surface.
 Limits of electron microscopy:
o Specimens must be placed in a vacuum to
be studied because electrons are easily
scattered by air molecules and go
everywhere!
o Researchers chemically preserve samples
first and then carefully dehydrate them
before looking at them. Electron
microscopy can only be used on nonliving
cells and tissues.