CELL MEMBRANE: a thin, flexible barrier which surrounds all cells. - regulates what enters & leaves cell - provides protection and support.- semi-permeable (allowing only certain molecules (like water) to pass freely through into or out of the cell)

Two processes to this movement: * Passive Transport * Active Transport

PASSIVE TRANSPORTTakes place without the support of cell energy. The most common form of passive transport is diffusion.

DIFFUSION: The movement of molecules (other than water) from a higher concentrated area to a lower concentrated area.Examples: gases such as oxygen and carbon dioxide, lipids, alcohol, some vitamins

Importance of Diffusion to Cells and Humans:

Cellular RespirationAlveoli of LungsCapillariesRed blood cellsTime-released medications

Rate of diffusion -depends on temperature and size of molecules.-molecules diffuse faster at higher temperatures then lower temperatures.-- small molecules diffuse faster than large molecules

OSMOSIS: The diffusion of pure water (and only water) from a higher concentrated area to a lower concentrated area.

                               

salt

Cell membrane

Importance of Osmosis on Cells and Humans:

- Cells remove water produced by cellular respiration- Large intestines cells transport water to the bloodstream- Kidney cells form urine

THE EFFECTS OF OSMOSIS ON CELLS

HYPERTONIC SOLUTION: the concentration of solutes is higher outside the cell than inside – cell loses water and shrinks.

Example: pouring salt onto a snail/slug.

                               

 

                    

 

HYPOTONIC SOLUTION: the concentration of solutes is lower outside the cell then inside the cell – cell gains water and swells (If the cell bursts, this is referred to as lysis or cytolysis)

Example: Putting 100% pure water into a patient’s IV bag would cause excess water to get into their cells. To keep cells from bursting, IV’s usually contain a salt or sugar solution.

ISOTONIC SOLUTION: the concentration of solutes are equal inside and outside of the cell – cell stays the same size

Example: Blood is isotonic to body cells. This means that the body cells will not shrink or burst when they come in contact with blood.

FACILITATED DIFFUSION: Protein Channels assist molecules such as glucose, amino acids, ions, etc. across the cell membrane WITHOUT the use of the cell’s ENERGY.

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

Importance of Facilitated Diffusion to Cells and Humans:Cells obtain food to carry out cellular respirationNeurons can communicateSmall intestines cells transport food to the blood streamMuscle cells contract

Active Transport• Molecules move from areas of low

concentration to areas of high concentration with the aid of ATP energy.

• Requires protein carriers called Pumps.

Importance of Active TransportGets rid of unwanted molecules such as sodium from urine in the kidneysMaintains internal conditions that are different from the environmentControls cellular pH levels

BULK MOVEMENT: large molecules, like proteins, are transported across the cell membrane. 2 processes:

* Exocytosis * Endocytosis

EXOCYTOSIS: wastes & cell products such as polysaccharides, hormones and mucous are packaged by the Golgi Apparatus and secreted out of the cell.

Tears

ENDOCYTOSIS: portion of the cell membrane surrounds a desirable molecule (such as food) outside of the cell and takes it in (Phagocytosis & Pinocytosis).

Phagocytosis• “Cellular Eating” – engulfing large

molecules, whole cells, bacteria • Ex. Macrophages ingesting bacteria or

worn out red blood cells.• Ex. Unicellular organisms engulfing

food particles.

Pinocytosis• “Cellular Drinking” – engulfing liquids

and small molecules dissolved in liquids; unspecific what enters.

• Ex. Intestinal cells, Kidney cells, Plant root cells