The Plasma/Cell

Membrane

Objective

Recognize the importance of semi-permeable membranes in regulating diffusion and maintaining homeostasis.

The Cell Membrane

The “cell membrane” is also known as “the plasma membrane.”

To survive, ALL living things must maintain a balance regardless of internal and external conditions.

http://www.nature.com/scitable/content/ne0000/ne0000/ne0000/ne0000/14704938/SelectiveTransport_ksm_2_1.jpg

The plasma membrane is the boundary between the cell and its environment.

– It allows a steady supply of glucose, amino acids, and lipids to enter the cell no matter what the external (outside) conditions are.

–Remove excess amounts of nutrients when levels are too high.

–Allow wastes and other products to leave the cell

Homeostasis

The plasma membrane helps maintain homeostasis, which is the process of maintaining the cells internal (inside) environment

http://www.anselm.edu/homepage/jpitocch/genbio/homeostasis.JPG

Selective Permeability

The cell membrane is selectively permeable.

– Is a process used to maintain homeostasis in which the plasma membrane allows some molecules in the cell while keeping others out.

http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2010/2010%20Exam%20Reviews/Exam%201%20Review/osmotic_pressure.jpg

“Selective” “Permeable”

Selective – able to regulate which particles enter and leave (it’s choosey)

Permeable – allows particles to pass through

*another way to say selectively permeable is “semi-permeable”

Why is the orange membrane considered semi-permeable?

What particles can’t get through the pores (holes) in the membrane?

http://upload.wikimedia.org/wikipedia/commons/thumb/2/2a/Semipermeable_membrane.png/250px-Semipermeable_membrane.png

Structure of the Membrane

The plasma membrane is composed of TWO layers of phospholipids back to back

The phospholipid bilayer is made up of:

–A Hydrophilic head that is attracted to water

–A Hydrophobic tail that is NOT attracted to water (scared of water).

The cell’s environment is mostly water. It is the most abundant material inside a cell as well.

“Fluid” Mosaic Model

The plasma membrane is described as being a flexible boundary of a cell. The phospholipids move within the membrane.

Other Components: Cholesterol

Cholesterol plays an important role of preventing the fatty acid chains of the phospholipids from sticking together.

http://www.cytochemistry.net/cell-biology/cholesterol.jpg

Other Components:

Transport Proteins

Allow substances or water materials to move across through plasma membrane.

http://www.one-school.net/Malaysia/UniversityandCollege/SPM/revisioncard/biology/movementacrossmembrane/images/facilitateddiffusion.png

Other Components:

Receptor Proteins

The surface of the membrane bind to chemical messengers to allow certain substances to pass through the plasma membrane.

http://fwcdscience.wikispaces.com/file/view/transduction.gif/43381569/transduction.gif

Passive Transport versus

Active Transport

NO energy required Energy REQUIRED