Cells are the basic units of structure and function in organisms
All cells arise from existing cells
Development of the cell theory:
Hooke in 1663, observed cork (plant): named the cell
Brown observed and named nucleus
Schwann in 1800’s states: all animals are made of cells
Schleiden in 1800’s states: all plants are made of cells
Pasteur’s work with bacteria ~ 1860 disproved idea of spontaneous generation (living things from nonliving)
Virchow observes cells dividing and states all cells come from preexisting cells
A cell is the simplest structural and functional unit of life.
There are no smaller subdivisions of a cell or organism that,
in themselves, are alive.
An organism’s structure and all of its functions are ultimately
due to the activities of its cells.
Cells come only from preexisting cells, not from nonliving
matter. All life, therefore, traces its ancestry to the same
Because of this common ancestry, the cells of all species have
many fundamental similarities in their chemical composition
and metabolic mechanisms.
Importance of Cell Theory
Cells are small
Small cells are more efficient Surface area to volume ratio must remain high
Features Common to All Cells
Crossing the Membrane Cell Membrane Structure and Transport
Defines cell boundaries
Controls interactions with other cells
Controls passage of materials in and out of cell (contributes to homeostasis)
Fluid Mosaic Model of Membranes
Cell membranes are selectively permeable (semi-permeable)
Some solutes cross the membrane freely, some cross with assistance, and others do not cross at all.
The diffusion of water molecules through a selectively permeable membrane Osmosis will continue as long as there are more water molecules on one side of the membrane (“osmotic pressure”) Water will continue to diffuse until there are equal numbers of molecules inside and outside the cell (“osmotic balance”) Osmosis
60% H 2 O 90% H 2 O
Water will move out of to the left across the membrane until osmotic balance has been reached
100% H 2 O 80% H 2 O
90% H 2 O 90% H 2 O
75% H 2 O 90% H 2 O Water leaves the cell and it shrinks. This is called plasmolysis in plant cells