CELL BIOLOGY The Early Discoveries

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CELL BIOLOGYThe Early Discoveries

• Robert Hooke English scientist, early
  microbiologist
• In 1665, he discovered that plants were composed
  of many individual units
• He called the units cells because they
  resembled the cells of a honeycomb

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Robert Brown (1830s) - Showed that cells contain
a central nucleus, and are filled with fluid

• Matthias Schleiden (1838)
• Showed that ALL plants are made of
• cells, and that cells are the basis for
• various functions of the plant

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Theodor Schwann (1839) -Showed that all animals
are made of cells, and that cells are the basis
for various functions
Rudolf Virchow (1858) -Showed that cells come
from other living cells
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CELL THEORY
1) All organisms are composed of cells, which are
the basic units of structure and function
2) All cells are produced from other cells
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Cell Characteristics
Cells can vary greatly in size, from bacteria to
ostrich eggs
Cell shapes are also extremely varied, from
spheres to rods to cubes
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Cell Functions
Individual cells take in and burn food for
energy, rid themselves of waste, exchange gases,
and make new living material.
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Examples of Cell Function

• Storage (Orange cells)
• Structure (Bone cells)
• Transport (Blood cells)
• Movement (Muscle cells)
• Energy Capture (Leaf cells)
• Communication (Nerve cells)

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The Cell and its Environment

• The Cell Membrane
• serves as a boundary between the cell and its
  environment
• holds the contents of the cell together
• acts as a gatekeeper for the cell (keeps some
  things out, lets others in)

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Properties of Cell Membranes
The cell membrane is 1) Semi-permeable 2)
Flexible and Strong
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Structure of the Cell Membrane

• Composed mostly of Phospholipid molecules
• Also is imbedded with large proteins
• Some proteins go all the way through the membrane

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Electron micrograph of the cell Membrane in
cross section
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The phospholipid bi-layer of a cell membrane
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Phospholipid layers
Proteins
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Crossing the Membrane
The cell membrane allows materials to pass into
and out of the cell in a variety of ways.
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1) Diffusion -movement of particles from an
area of high concentration to an area of low
concentration -will work until both
concentrations are equal. This is
called Dynamic Equilibrium
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Concentration Gradient
High Low
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Diffusion is responsible for most gases crossing
the membrane barrier.
What gases would need to cross into or out of a
cell?
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2) Osmosis -movement of water into and out of a
cell across the membrane.
-Osmotic Balance is similar to Dynamic
Equilibrium, but relates to water , not particles

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Passive Transport/Facilitated Diffusion
-For larger molecules and particles -Molecules/par
ticles do not enter between the phospholipids,
but through a special channel in a protein
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Specific sites on the membrane allow facilitated
diffusion Cross-membrane proteins make channels
for things to move in or out.
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Active Transport
-Cell uses energy to move particles against a
concentration gradient. -Things move from LOW
concentration to HIGH -Similar to Facilitated
Diffusion, but cell uses energy to go against a
concentration gradient.
Compare and Contrast Active Transport and
Facilitated Diffusion
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