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Structure &
Discovery of Cells
A. History Of Microscopes
• The microscope was developed in the 1600’s,
which helped scientists to discover cells.
1. Anton van Leeuwenhoeck
Was the first to try stacking several lenses together to view tiny
objects. He looked at pond water through his lenses. He
became the first scientist to describe living cells as seen through
a microscope.
2. Robert Hooke – used the microscope to examine thin slices
of cork. He called the tiny boxes he saw cells. He chose the name
"cells" because the chambers he saw reminded him of rooms in a
monastery which were called cells.
Cell Theory
The discoveries and observations that scientists
made using microscopes led to the development of
the cell theory.
The cell theory states…..
1. All living things are composed of cells
2. Cells are the smallest working unit of life
3. All cells come from pre-existing cells through cell division.
Types of Cells
All cells contain a cell boundary and DNA.
There are 2 Types of cells based on the nucleus
Prokaryotes & Eukaryotes
• Prokaryotic = “before nucleus”
• Prokaryotic cells lack a true nucleus and other
membrane bound organelles (internal
• Prokaryotes do contain DNA, usually
concentrated in a particular region of the cell. All
prokaryotes are microscopic and single celled.
• Eukaryotic = “true nucleus”
• Eukaryotic cells contain a true nucleus and
other membrane bound organelles.
• Eukaryotic organisms may be single celled or
multicellular. In multicellular organisms cells
become specialized.
Cell Boundaries
There are 2 types of cell boundaries.
1. Cell Membrane
2. Cell Wall
Cell Membrane
• Every prokaryotic and eukaryotic cell is surrounded by the
cell membrane. It helps to maintain homeostasis in the
cell by functioning as a protective barrier between the cell
and its environment.
• The cell membrane is selectively permeable which means
it allows only certain substances in and certain
substances out.
• A.K.A…… the plasma membrane.
The cell membrane is not a fixed sheet of molecules, but
rather it is a fluid structure composed of three biomolecule
groups, carbohydrates, lipids, and proteins.
Cell wall
Cell membrane
There are two types of lipids that make up the
cell membrane: phospholipids & cholesterol
Phospholipid Bilayer
• Phopholipids– Phospholipids contain one non-polar
end and one polar end. Each phospholipid contains 2
non-polar fatty acid tails and a polar head.
– The phospholipid bilayer consists of two layers of
phospholipid molecules that surround the cell. The nonpolar "tails" point toward each other and the polar heads
are on the outside forming a sandwich-like membrane.
• Cholesterol – Found in the cell membranes
of animal cells only to help stabilize them.
• Cholesterol is wedged between
the non-polar fatty acid tails of the
phospholipid bilayer.
Carbs & Proteins
• Carbohydrates serve as they are “ID tags”
to help identify cells
• Proteins are embedded in the phospholipid
bilayer. Their function is to act as channels
and pumps in order to transport specific
molecules or ions across the cell membrane.
• A- Phospholipid Bilayer
• B – Protein
• Protein Channel
• C – Glycoprotein
• D – Carbohydrate
• E. Cholesterol
• Cell membrane animation
Cell Wall
• Cell walls are the outer most boundary plants, fungi,
and bacteria. They are not found in animal cells.
• The primary function of the cell wall is to provide
structure and support. The cell wall does not regulate
what comes in and out of the cell.
• Cell walls of ……..
1. plants are composed of cellulose
2. fungi are composed of chitin
3. bacteria are composed of other polysaccharides