Chapter 5: Membrane

Fluid-Mosaic Model

The plasma membrane is a fluid, phospholipid bilayer in which proteins are fully or partially embedded

Unit Membrane Model

The membrane was thought to be fairly static, with proteins evenly distributed across its surface

Integral Proteins

Span the membrane. They have polar regions at both ends and non-polar regions in the middle

Peripheral Proteins

Are loosely bound to the surface of the membrane

Channel Proteins

They have a channel through which particular molecules can flow to pass through the membrane

Carrier Protein

Specifically combine with certain molecules to allow them to pass through one side to the other

Cell Recognition Proteins

These glycoproteins help the body determine or distinguish self from non-self

Receptor Proteins

These proteins bind specific molecules to bring about a specific cellular response

Enzymatic Proteins

Enzymes which are attached to the membrane and help carry out metabolic reactions

Cell Adhesion Molecules

These proteins help anchor cell together

Attachment to the Cytoskeleton

These proteins anchor the membrane to the cytoskeleton

Selectively permeable

Only allows certain substances in or out.


The movement of molecules down their concentration gradients. It does not require the input of energy. Processes which go against it require energy.

Size, charge, temperature, and pressure

What alters diffusion?


The diffusion of water across a membrane


Solute and water concentrations are the same as those in the cell


The solute concentration is less than in the cell. There is a net gain of water which can make it swell and burst


The solute concentration is lower than that in the cell. There is a net loss of water which makes it shrivel

Passive Transport

Molecules freely pass in and out of the cell. No energy is requied

Facilitated Transport

Specific molecules as assisted in/out of the cell. No energy is used

Active Transport

Specific molecules are pumped against their concentration gradient in/out of the cell


Export or secretion of large materials out of the cell


Import of large materials into the cell


Import of large, non-specific particles


Cell drinking. Liquids or small dissolved substances are taken in



Tight Junction

Allow cells to be tightly connected together and prevents material/fluid from slipping in between them. Found in intestines and bladder


Spot welds or rivets. Hold together cells under mechanical stress. Found in skin and uterus

Gap Junction

Contains membrane channels which allow for fast communication between cells. Found in cardiac cells and help coordinate contractions


These function like gap junctions, but they are found in plant cells