The Plasma Membrane

Plasma Membrane

The outer layer of a cell is semi-permeable.

Semi-permeable means that only certain molecules can pass through it.

Plasma Membrane

Has two layers of lipid molecules -Phospholipid bilayer

Polar heads point to the outside (Phosphate head)

Non-polar (straight) tails form the inside of the membrane

Fluid Mosaic Membrane

Its called a fluid mosaic membrane because it is a mosaic of different kinds of molecules. These include: lipids protein carbohydrate chains

The 3 Ways a Cell regulates what comes into a cell: Simple Diffusion – some materials move into and

out of the cell without using energy.

Carrier Facilitated Diffusion – movement into the cell through a protein in the plasma membrane

Active Transport – use energy in the form of ATP to move other molecules into and out of the cell

Comparison of Active Transport and Passive Transport (continued)

Most solutes can cross the membrane only if there is a carrier protein or a channel protein to transfer them.

Passive transport, in the same direction as a concentration gradient, occurs spontaneously, whereas transport against a concentration gradient (active transport) requires an input of energy. Only carrier proteins can carry out active transport, but both carrier proteins and channel proteins can carry out passive transport

Diffusion In a solution, molecules move

constantly.

They collide with each other and tend to spread out randomly.

The molecules tend to move from an area where they are more concentrated to an area where they are less concentrated, a process known as diffusion.

Diffusion Diffusion "goes from the

higher concentration side to the lower concentration side".

There is no energy input to cause diffusion;

It simply occurs due to the random motion of the substance moving across the plasma membrane.

Diffusion

Even after the solution has reached equilibrium, individual molecules continue to move rapidly across the membrane in both directions.

Osmosis

Diffusion of water through a semi-permeable membrane.

Not all substances can cross cell membranes.

If something can cross the cell membrane then the membrane is permeable.

The cell membrane is described as being selectively permeable.

Cell membranes are selectively permeable, which means that some substances can pass across them and others cannot.

Osmosis

Osmosis – the diffusion of water through a selectively permeable membrane.

Carrier Facilitated Diffusion Facilitated Diffusion – movement of specific

molecules across cell membranes through protein channels

Active Transport Active Transport - when material moves from an area

of lower concentration to an area of greater concentration

Active transport requires the cell to spend energy, usually in the form of ATP.

Review Questions

1. The ____ of a phospholipids is polar, and the long _______ are non-polar.

2. What does the term “selectively permeable” mean in regards to a cell membrane.

3. What are the three major ways of taking in or of regulating the passage of materials into and out of the cell?

4. True or False, Osmosis of water is a form of diffusion.

Warm-Up – Label the diagram with as much detail as possible.

Phospholipid Phosphate Head

Hydrophilic Fatty Acid Tails

Hydrophobic