1.3 & 1.4 Cellular
Membranes

• What do you know?
• What questions do you have?
Read & Consider 1.3.1 – 1.3.3

Cells are surrounded by water inside and out. Membrane behavior is dictated by interactions with water.
• Polar
• Nonpolar

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The diagram should include:
 Phospholipid bilayer
 Cholesterol
 Glycoproteins
 Integral proteins
 Peripheral proteins


Watch – History of Cell Membrane up to Gorter and
Grendel’s 1925 discovery
“ Insights into cell membranes via dish detergent ”
 Davson and Danielli’s “Fat Sandwich Model” – accepted until 1972
 Singer and Nicolson’s “Fluid Mosaic Model” – accepted today

• What do you know?
• What questions do you have?
• Compare and contrast diffusion and osmosis.
Read & Consider 1.4.1-1.4.2

Diffusion: passive movement of particles from a region of high concentration to a region of low concentration.

Osmosis: passive movement of water molecules from a region of lower solute concentration to a region of higher concentration.
Isite.lps.org

Simple Diffusion –there is no expenditure of energy in moving the molecules across the membrane.
Facilitated Diffusion – larger molecules move passively through the membrane via channel proteins.
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Molecules moving from low to high concentration must be actively moved.
Video

A transport mechanism for the movement of large quantities.
 Exocytosis: vesicle membrane fuses with the plasma membrane.
 Endocytosis: a vesicle is formed by the in folding of the plasma membrane.
Material Transport

o Phospholipid molecules can change places in the horizontal plane (creates fluidity). o Molecule exchange in the vertical plane DOES
NOT occur (maintains integrity).
Video

Inner Life of a Cell
2007 – the President and Fellows of Harvard College

Tissue or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis. Complete the exploration phase for the lab with the following aim:
To determine the osmolarity of an unknown substance by bathing samples in hypotonic and hypertonic solutions.