THE ROLE OF THE CELL MEMBRANE IN TRANSPORTSection 2.2Unit C

OBJECTIVESdefine and give examples for movement of matter through the cell membrane passive and active transport,

facilitated diffusion, osmosis, endocytosis and exocytosis

REVIEW Cell membrane/plasma membrane is a

phospholipid bilayerPhospholipids arranging so centre of

bilayer is hydrophobic (afraid of water) and outside is hydrophilic (loves water)

How are they arranged? Which way do each part of the phospholipid arrange itself?

Proteins are embedded or attached to the membrane

Fluid-mosaic model

DIFFUSION: INTRODUCTION Movement of particles from an area of high

concentration to an area of low concentration Moving towards equilibrium/sameness How can we increase the rate of diffusion

(i.e. how fast diffusion is occurring)? Add energy- ex. Stir or heat

Ex. Opening a bag of coffee releases aroma molecules

DIFFUSION IN CELLS Occurs across the cell membrane (water or

solutes) Difference between concentrations over the

cell membrane = concentration gradient Process called passive transport

No energy required for movement

PERMEABILITY OF MEMBRANES Cell membrane is called selectively

permeableAllows only certain particles pass (not all)Essential to maintain equilibrium and

function Semi-permeable passage of materials

determined by size, charge, and solubilityEx. Membranes used in water treatment

and desalinationWhat kinds of molecules might not get

through? Why not?

Concentration Gradient

Involves different

concentrations

In cells, concentrations separated

by membrane

Involves molecules/io

ns of different

types

Different molecules/ions move along

own concentration

gradients

Drives diffusion and osmosis

Fig C2.15 p. 277

DIFFUSION LAB Page 276 in your textbook Read through the lab. You will need to make a lab write-up. It must

include: Title The question (copy from book) Come up with a hypothesis List of materials Write the procedure in your own words Analyzing and Interpreting questions Forming a conclusion

REVIEW What is the process of diffusion? What is passive transport? What is concentration gradient?

OSMOSIS Diffusion of water across a semi-permeable

membrane Example of passive transport From area of higher concentration to lower

concentration of water

The movement of water can predicted by determining what the amount of solute is relative to the cell

A large amount of solute (high concentration) = low amount of water

A small amount of solute (low concentration) = high amount of water

Recall: water moves from high to low

PREDICTING MOVEMENT OF WATER

PREDICTING MOVEMENT OF WATER Compare solute solution (3 types)

1) hypertonic- higher concentration of solutes than that in the cellEx. Cell is in a salt solution: solution has less water than the cell

2) hypotonic- lower concentration of solutes than that in cellEx. Solution has more water than cell

3) isotonic- same concentration of solutes in solution as in cell Ex. Solution has same amount of water as the cell

What would be the net movement of water in a hypertonic solution? Hypotonic? Isotonic?

HYPERTONIC SOLUTION

HYPOTONIC SOLUTION

ISOTONIC

HOW OSMOSIS WORKS: AN ANIMATED TUTORIAL http://highered.mcgraw-hill.com/sites/007249

5855/student_view0/chapter2/animation__how_osmosis_works.html

OSMOSIS AND ANIMAL CELLS When cells lose water, they shrink

(plasmolysis) When cells gain water, they swell and may

even burst (cytolysis) When there is no net change in water, cells

remain in homeostasis, or a state of equilibrium (i.e. no change)

EXAMPLE: BLOOD CELLS http://highered.mcgraw-hill.com/sites/0073377988/student_view0/c

hapter3/hemolysis_and_crenation.html

EXAMPLE Identify each picture below as hypertonic,

hypotonic or isotonic (which one is experiencing plasmolysis, cytolysis, equilibrium?)

Isotonic(equilibrium)

Hypotonic(cytolysis)

Hypertonic(plasmolysis)

OSMOSIS IN PLANT CELLS Plant cells have a maximum amount of water that can

holdWhat makes it different than animal cells? What

different structure does it have? Movement of water into plant cell increases turgor

pressure Turgor pressure supports plant’s structure High turgor pressure

cells are turgid (firm) Low turgor pressure

cells are flaccid (soft, floppy)

EXAMPLE: PLASMOLYSIS IN ONION CELLS

Plasmolyse onion rouge (red onion plasmolysis) – note how the cell contents pulls in from the cell wall:

http://www.youtube.com/watch?v=gYbt7hhIxPo&feature=related&safety_mode=true&persist_safety_mode=1&safe=active

EXAMPLE: PLASMOLYSIS IN ELODEA PLANT http://www.youtube.com/watch?v=VK-_YHakvho&safet

y_mode=true&persist_safety_mode=1&safe=active

FACILITATED DIFFUSION For particles that are soluble with water

Why would they need a special way across the membrane?

Uses proteins for diffusion – still passive transportChannel proteins: pores for small

molecules to pass throughCarrier proteins: attach to larger

molecules, change shape and physically brings it inside the cell

http://www.youtube.com/watch?v=s0p1ztrbXPY&safety_mode=true&persist_safety_mode=1

ACTIVE TRANSPORT Movement against concentration gradient

What does this mean? Carrier proteins- act like a pump and use

energyLike swimming upstream

Energy from mitochondriaUses energy molecules called ATP

http://www.youtube.com/watch?v=STzOiRqzzL4&feature=related

ENDOCYTOSIS AND EXOCYTOSIS For very large molecules Cell uses vesicles

Sac surrounding large particleLike vacuoles, but smaller and

temporary

ENDOCYTOSIS Movement into the cell Steps:

1) vesicle forms around particle2) cell membrane pinches off3) vesicle now inside cell

EXOCYTOSIS Movement out of the cell

For waste particles or cell productsSteps:

1) vesicle surrounds particle in cell2) moves to membrane and fuses with it3) vesicle ruptures, releasing contents

ANIMATION http://www.youtube.com/watch?v=4gLtk8Yc1

Zc&feature=related

SUMMARY VIDEO http://www.youtube.com/watch?v=kfy92hdaA

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