The Plasma/Cell The Plasma/Cell MembraneMembrane

ObjectiveObjective

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

The Cell MembraneThe Cell Membrane

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

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

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

The plasma membrane is the The plasma membrane is the boundary between the cell and its boundary between the cell and its environment. environment. – It allows a steady supply of glucose, It allows a steady supply of glucose,

amino acids, and lipids to enter the cell amino acids, and lipids to enter the cell no matter what the external (outside) no matter what the external (outside) conditions are.conditions are.

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

– Allow wastes and other products to Allow wastes and other products to leave the cellleave the cell

HomeostasisHomeostasis The plasma The plasma

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

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

Selective PermeabilitySelective Permeability

The cell membrane is The cell membrane is selectively selectively permeable.permeable.– Is a process used to Is a process used to

maintain homeostasis maintain homeostasis in which the plasma in which the plasma membrane allows membrane allows somesome molecules in the molecules in the cell while keeping cell while keeping others out.others out. http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/

2010/2010%20Exam%20Reviews/Exam%201%20Review/osmotic_pressure.jpg

““Selective” “Permeable”Selective” “Permeable”

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

Permeable – allows particles to pass Permeable – allows particles to pass throughthrough

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

Why is the orange Why is the orange membrane membrane considered semi-considered semi-permeable?permeable?

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

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

Structure of the MembraneStructure of the Membrane

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

The phospholipid The phospholipid bilayer is made up bilayer is made up of:of:– A Hydrophilic head A Hydrophilic head

that is attracted to that is attracted to waterwater

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

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

““Fluid” Mosaic ModelFluid” Mosaic Model

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

Other Components: CholesterolOther Components: Cholesterol

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

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

Other Components: Other Components: Transport ProteinsTransport Proteins

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

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

Other Components: Other Components: Receptor ProteinsReceptor Proteins

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

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

Passive Transport versus Passive Transport versus Active TransportActive Transport

NO energy required Energy REQUIRED