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CELL THEORY
NOTES
THE CELL THEORY
-Proposed by Schleiden, Schwann and Virchow
-Three parts of the theory:
1. All living things are made of one or more
cells.
2. Cells are the basic units of structure and
function in living things.
3. All cells come from other existing cells.
CELL SIZE
• Why are cells so small?
• Small cells have a large surface area to
volume ratio
• Allows the cell to get all the food and
nutrients it needs from its environment
– and get rid of the waste it doesn’t need.
– The larger the cell gets, the harder this
becomes
WHAT DO ALL CELLS HAVE
IN COMMON?
• Cell membrane
– Outer boundary of cell, controls what enters and
leaves the cell
• Cytoplasm (cell interior)
– Plasma substance that fills up the ‘space’ around
cell organelles
• Cytoskeleton (cell skeleton)
– Proteins that support cell organelles and keep cell
shape
• Ribosomes
– Found throughout all cells
– Sites of protein synthesis
PROKARYOTES
• Small, simple cells
• All are Bacteria
• No nucleus or other
internal organelles
– They DO contain a
chromosome (DNA)
• Move with cilia (hairs)
or with a flagella (tail)
• Single-celled
organisms
EUKARYOTES
• Evolved from prokaryotes
• Larger, more complex
cells
• Contain a nucleus and
many other organelles
• Some move using cilia,
flagella or pseudopodia
(false feet)
• May be part of a
unicellular or
multicellular organism
– Plants, animals, fungi,
protists