The cellular level of anatomical organizationAnatomy and Physiology

Brief history of cell theory

Cell membrane structure

Transport into /out of cell

Transport within the cell

Important organelles

Cell Theory:

1. All living things are made of one or more cells

2. Cells are the basic units of structure and function in organisms

3. All cells arise from existing cells

Development of the cell theory:

Robert Hooke in 1663, observed cork (plant): named the cell

Robert Brown observed and named nucleus

Theodor Schwann in 1800’s states: all animals are made of cells

Development of the Cell Theory

Matthias Schleiden in 1800’s states: all plants are made of cells

Louis Pasteur’s work with bacteria ~ 1860 disproved idea of spontaneous generation (living things from nonliving)

Rudolf 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.

Importance of Cell Theory

Importance of Cell Theory

Cells come only from preexisting cells, not from nonliving matter. All life, therefore, traces its ancestry to the same original cells.

Because of this common ancestry, the cells of all species have many

fundamental similarities in their chemical composition, and metabolic and

physiological mechanisms.

Why Cells are Small

Small cells are more efficient

Surface area to volume ratio must remain high for materials to easily reach all parts of the cell

Cell Membrane Structure and Transport

Cell Membrane• Defines cell boundaries

• Controls interactions with other cells

• Controls passage of materials in and out of cell (contributes to homeostasis)

• Fluid-Mosaic model

Fluid Mosaic Model of Membranes

Membrane Proteins

Membrane Fluidity

Membrane Permeability• 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 membraneOsmosis 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% H2O 90% H2O

Water will move out of to the left across the membrane until osmotic balance has been reached

100% H2O

80% H2O

90% H2O

90% H2O

75% H2O

90% H2O

Water leaves the cell and it shrinks. This is called plasmolysis in plant cells

Facilitated Diffusion

Involves carrier or channel proteins to transport substances that otherwise could not pass the phospholipid bilayer (because of their polarity or charge, like ions)

Active Transport and ATP Powered Pumps

Animal cells contain membrane vesicles called lysosomes, filled with enzymes that can degrade proteins, lipids, nucleic acids, and other biomolecules. These enzymes are most effective at acid pH, and it can be experimentally shown that the pH inside lysosomes is about 5.0, whereas the pH of the cell cytoplasm is close to 7.0. The diagram (at right) illustrates one lysosome inside a cell.

Endocytosis

Exocytosis