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The Cell
Landmarks in Cell Biology
The Cell Theory:
1. Cells are the basic unit of structure of all living things
2. Cells are the basic unit of function of all living things
3. ALL cells come from pre-existing cells
Microscopes have better allowed scientists to develop The Cell Theory.
Robert Hooke (1635-1703) – observed slices of cork through a magnifying
glass and observed box-like structures and called them cells.
The eyes of a fly from
Robert Hooke's
Micrographia (London:
1665)
In 1831, Robert Brown used the word
nucleus to describe the dark, central
globule. (The word nucleus is Latin for
little nut.)
Cheek Cells
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Exceptions to the Cell Theory :
1. Viruses - are they alive ?
According to the Cell Theory we have to say "no" because a virus is
not a cell. Viruses are made of two chemicals, protein & nucleic acid,
but have no membranes, nucleus, or protoplasm. They appear to be
alive when they reproduce after infecting a host cell.
2. Mitochondria & chloroplasts.
These cell organelles (small structures inside the cell) have their own
genetic material & reproduce independently from the rest of the cell.
3. Where did the first cell come from ?
According to statement #3 of the cell theory, all cells come from other
living cells. So how did the first cell ever appear ? It's the old
"chicken & egg" dilemma. We will investigate this question (& its
possible answer) in more detail during the Evolution Unit.
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Animal Cell
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Plant Cell
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Cell Structure and Organelles
Most cells possess the same organelles, however plant and animal cells
do differ a bit.
1. Cell Membrane
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Also known as Plasma Membrane
Surrounds the cell and controls what goes into and out of it
Selectively permeable (only allows certain materials in and out)
Double layered and composed of lipids and proteins
2. Cell Wall
• FOUND ONLY IN PLANTS
• Composed of cellulose
• Protects cell
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3. Cytoplasm
• Fluid like material that fills the space between the cell membrane
and the nucleus
• Contains all of the organelles
nucleolus
4. Nucleus
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Controls cellular metabolism and reproduction
Contains DNA and hereditary material
Surrounded by a nuclear membrane
nucleus
Contains the nucleolus
5. Nucleolus
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Produces and releases ribosomes into the cell
6. Ribosomes
• Site where proteins are synthesized from amino acids
• May be found in the cytoplasm or attached to the endoplasmic
reticulum
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7. Endoplasmic Reticulum
• System of fluid-filled canals
• Associated with transport of materials throughout the cell
8. Lysosomes
• Membrane bounded sacs that contain digestive enzymes
• Involved in the digestion of food in unicellular organisms
• Destroys damaged or old cell parts in multi-cellular organisms
9. Vacuoles
• Fluid filled sacs found in the cytoplasm
• Contain stored materials, such as food and wastes.
• Contractile Vacuole is used to pump excess water out of the cell.
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10.Mitochondria
• Powerhouse of the cell
• Site where respiration produces
energy for the cell
• Where ATP is produced for energy
• Contain their own DNA and can
duplicate themselves
11.Centrioles
• Found only in animal cells
• Located near the nucleus
• Have a part in cell division
12.Chloroplast
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Found only in plant cells
Contains green chlorophyll pigment
Have their own DNA and can replicate
Site of Photosynthesis
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13.Cilia and Flagella
• Organelles responsible for cell movement
•There are usually many cilia on the outside
of a cell and they are very small (Paramecium
have then
•There are not many flagella and they are
larger (Sperm have them)
Flagella
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14.Golgi Bodies
• The Golgi apparatus consists of stacks of sacs with
vesicles pinching off from the edges of the sacs.
• The function of the Golgi is to package materials for
export from the cell.
• Also called the Golgi Apparatus or Golgi Complex
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Amoeba
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Prokaryotic cells have no nucleus or
organelles enclosed within
membranes. Species in the domains
Archaea and Eubacteria have
prokaryotic cells.
Eukaryotic cells have a nucleus and
organelles that are surrounded by
membranes. Each organelle does a
specific cell function. All species in
the Eukaryota domain (protists, fungi,
plants, and animals) have eukaryotic
cells. Individual protists have only
one cell, while plants and animals
can have trillions of cells. Complex
creatures like humans have special
cells for special functions like carrying
oxygen around the body, digesting
food, or making bone.
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