The Cell Membrane & Transport

The Cell Membrane• Functions:– Structural support & protection– Helps maintain HOMEOSTASIS– Selective barrier –SEMIPERMEABLE

• Water, food, oxygen, waste and nutrients are transported through the cell membrane.

Structure• Lipid Bilayer = Double

layer of phospholipids• Each Phospholipid has:– 2 non-polar tails:

Hydrophobic (Repels water, Water FEARING)

– 1 polar head: Hydrophilic (Attracted to water, Water LOVING)

• Proteins, carbohydrates, and cholesterol are also in the membrane

Homeostasis• The maintenance of stable internal conditions

within the cell or organism. • The body’s ability to maintain equilibrium

BALANCE

• Conditions within and around organisms are constantly changing (temperature, water, oxygen), so our cells need a way to adjust to the changing conditions.

Semipermeable• Some substances can pass across it and others can not• Also called “Selectively Permeable” • Large molecules such as proteins and sugars don’t pass

freely and must be transported into the cell

Passive Transport

Allows some particles to move in or out of cell without the use of energy.

•Using Diffusion

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlDiffusion-

– particles spread from high concentration to low concentration until equilibrium is reached

– movement of Solutes (sugar, salt, minerals) – No energy required

Concentration Gradient- difference in concentration between two areas across

from each other.Molecules will move with the gradient from a high concentration to a lower

concentration .“Rolling down a hill doesn’t require

energy”

Solutions

• Solute is the material that is being dissolved (sugar)

• Solvent is doing the dissolving (water)

Types of Diffusion

• Simple—unassisted diffusion of small particles or lipid-soluble molecules

• Osmosis—unassisted diffusion of water

• Facilitated diffusion—diffusion with the help of carrier proteins

• Osmosis:– diffusion of water from an area of high to low water

concentration – Occurs continuously (all the time) in the cell– No energy required

•HYPERTONIC solution: 1. Solute concentration outside the cell is higher (less water)2. Water diffuses out of the cell 3. Cell will shrink

Plant cell-cell membrane pulls away from the cell wall (wilts)

•HYPOTONIC solution:1. Solute concentration greater inside the cell (less water)2. Water moves into the cell3. Cell will swell & burst (Lysis)

Plant cell-pressure on cell wall increases- (Turgor)

•ISOTONIC solution: 1.Concentration of solutes is the same

inside & outside the cell

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

• Facilitated Diffusion – transport proteins embedded in cell membrane

“carries” the substance across the membrane.– Substances like glucose, amino acids, and ions use

these – No energy required

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

Cell in Isotonic Solution

CELL

10% NaCL90% H2O

10% NaCL

90% H2O

What is the direction of water movement?The cell is at __________.

ENVIRONMENT

NO NET MOVEMENT

Equilibrium

Cell in Hypotonic Solution

CELL

10% NaCL90% H2O

20% NaCL

80% H2O

(More H20 outside of cell than inside)What is the direction of water movement?

Cell in Hypertonic Solution

CELL

15% NaCl85% H2O

5% NaCl95% H2O

(More H20 inside than outside)What is the direction of water movement?

ENVIRONMENT

Active Transport• Movement of substances from a lower

concentration to a higher concentration • Energy is needed – ATP (adenosine triphosphate) is the source of the energy.

• Transport goes AGAINST concentration gradient (going up a hill requires energy)

• Carrier Proteins (Transport Proteins)– Endocytosis– Exocytosis

• Carrier Proteins (Transport Proteins)– Use ATP to pump molecules into or out of the cell– Low concentration to high concentration

• Endocytosis – Cell membrane folds inward surrounding the material

to transport it INTO the cell– Once inside the cell it’s transported to a lysosome

Two Types of Endocytosis

Phagocytosis • “Cell Eating”• Engulfs large materials like

bacteria

Pinocytosis• “Cell Drinking”• Engulfs extracellular fluid,

including sugar and proteins

• Exocytosis – Materials, like waste, are surrounded by a vesicle and

transported to the cell membrane– Vesicle fuses with the cell membrane and releases its

contents OUTSIDE the cell