Cell Membrane: Structure and Function

In or Out?

1. What are some things that can pass through a window screen?

2. What are some things that cannot pass through a window screen? Why is it important to keep these things from moving through the screen?

3. The cell is surrounded by a cell membrane, which regulates what enters and leaves the cell. Why is it important to regulate what moves into and out of a cell?

Interest Grabber

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

Section 7-3

Figure 7-12 The Structure of the Cell Membrane

Cell Membrane

Function = controls what enters the cell and what leaves the cell

Made of a lipid bilayer Has proteins Has some carbohydrates, which

help with identification Is fluid (fluid mosaic model)

Diffusion

Def. of diffusion = Spreading of molecules in a given space.

What happens? -Substances move from an area

where there is more of them to an area where there is less of them

Diffusion

Def. of permeable = membrane that lets substances pass through it

Cell membrane is selectively permeable, which means that it lets some things in but does not let other things in

Substances keep moving till there is about equal amounts of them on both sides of the membrane

HighConcentration

LowConcentration

CellMembrane

Glucosemolecules

Proteinchannel

Section 7-3

Diffusion

Factors that Affect Diffusion

Amounts of substances involved

Temperature

Pressure

Stirring -speeds up the rate of diffusion

Diffusion

Diffusion Video

Osmosis Def. of osmosis = movement of

water from greater to lesser

Figure 8.11 Osmosis

Figure 8.12 The water balance of living cells

Osmosis

Water goes into a cell causing it to swell up and burst = plasmoptysis

Water leaves the cell causing it to shrink = plasmolysis

*Know the difference between plasmoptysis and plasmolysis!*

Osmosis

Some one-celled organisms have a contractile vacuole that pumps water out of a cell

In plants, as water goes into the cell, it builds up pressure that pushes against cell wall. This is called turgor pressure.

Contractile Vacuole

Osmosis

Osmosis Video

Passive Transport

NO ENERGY NEEDED!

Is the movement of small molecules in and out of a cell

Molecules go from greater to lesser (=with concentration gradient)

Examples: amino acids, fatty acids, glycerol, simple sugars (glucose)

Passive Transport

Passive Transport

Passive Transport Video

Active Transport

ENERGY NEEDED!

Molecules go from lesser to greater (=against concentration gradient)

This is when large molecules are pulled through the cell membrane by the use of ENERGY

Do not fully know how it works

Molecule tobe carried

Moleculebeing carried

Energy

Section 7-3

Figure 7-19 Active Transport

Active Transport

Active Transport Video

Endocytosis and Exocytosis

Def. of endocytosis = process by which cells take in large molecules from the outside

-ex. pinocytosis and phagocytosis

• Def. of exocytosis = process by which cells get rid of large molecules in the cell

Pinocytosis

Pinocytes are pockets on the cell membrane.

Large molecules fall into the pockets and get turned into food vacuoles inside the cell

Pinocytosis

Phagocytosis: Engulfing

This is when large molecules are surrounded and pulled into the cell

Examples: amoeba, white blood cells called phagocytes

This is the same method used by white blood cells to trap bacteria in our blood

Phagocytosis: Engulfing

Endocytosis and Exocytosis Video

Endocytosis and Exocytosis