1. CELL BOUNDARIES
CHAPTER 7

2. CELL MEMBRANE
CELL MEMBRANE (PLASMA MEMBRANE): REGULATES WHAT ENTERS AND LEAVES THE CELL AND ALSO PROVIDES PROTECTION AND SUPPORT.
It is a thin, flexible barrier
CELL MEMBRANE STRUCTURE:
Double layer known as a lipid bilayer
Gives cells its flexible nature while still controlling a barrier between the cell and its surroundings

3. CELL MEMBRANE

4. CELL MEMBRANE PARTS THE CELL MEMBRANE IS COMPOSED OF:
A PHOSPHOLIPID BILAYER
EMBEDDED PROTEINS
CAN FORM CHANNELS AND PUMPS FOR MOLECULAR TRANSPORT INTO AND OUT OF THE CELL
CARBOHYDRATE CHAINS
ATTACH TO THE PROTEINS AND ACT LIKE CHEMICAL IDENTIFICATION CARDS
CHOLESTEROL
THE CELL MEMBRANE IS KNOW AS “MOSAIC”
A MOSAIC IS A WORK OF ART MADE OF INDIVIDUAL TILES OR OTHER PIECES ASSEMBLED TO FORM A PICTURE OR DESIGN

5. PHOSPHOLIPID BILAYER
THE IMAGE IS SHOWING THE PARTS OF A PHOSPHOLIPID. NOTICE THE FLUID (WATER) NEVER TOUCHES THE TAILS OF THE PHOSPHOLIPID.

6. SINGLE PHOSPHOLIPID
NUMBER 1 IS THE HEAD: THE HEAD OF THE PHOSPHOLIPID IS HYDROPHILIC. HYDROPHILIC MEANS IT LIKES WATER.
NUMBER 2 ARE THE TAILS: THE TAILS ARE HYDROPHOBIC. HYDROPHOBIC MEANS THEY DO NOT LIKE WATER; THEREFOR, WATER WILL BE FOUND IN THIS SECTION OF THE CELL MEMBRANE.

7. CELL WALL
FOUND IN MANY ORGANISMS (PLANTS, ALGAE, FUNGI, AND MANY PROKARYOTES)
CELL WALLS LIE OUTSIDE CELL MEMBRANES, AND CONTAIN PORES TO ALLOW COMMUNICATION BETWEEN CELLS AND MOLECULES TO PASS THROUGH FROM CELL TO CELL.
MAIN FUNCTION:
IS TO PROVIDE SUPPORT AND PROTECTION FOR THE CELL

8. WHAT MAKES UP A CELL WALL?
MOST OF THE FIBERS IN A CELL WALL CONSIST OF CARBOHYDRATE AND PROTEIN FILAMENTS
THE FILAMENTS ARE PRODUCES INSIDE THE CELL AND THEN RELEASED THROUGH THE CELL MEMBRANE AND REBUILT OUTSIDE THE CELL MEMBRANE
PLANT CELL WALLS:
CONTAIN MOSTLY CELLULOSE (A TOUGH CARBOHYDRATE)

9. MEMBRANE’S MOST IMPORTANT FUNCTION
ONE OF THE MOST IMPORTANT FUNCTIONS OF A CELL MEMBRANE IS TO REGULATE THE MOVEMENT OF DISSOLVED MOLECULES FROM THE LIQUID ON ONE SIDE OF THE MEMBRANE TO THE LIQUID ON THE OTHER SIDE OF THE MEMBRANE

10. PASSIVE TRANSPORT cell uses no energy molecules move randomly
Molecules spread out from an area of high concentration to an area of low concentration.
(HighLow)
Three types:
Diffusion
Facilitative Diffusion – diffusion with the help of transport proteins
Osmosis – diffusion of water

11. DIFFUSION MEASURING CONCENTRATION:
CONCENTRATION OF A SOLUTION IS THE MASS OF SOLUTE IN A GIVEN VOLUME OF SOLUTION (M/V)
EX: IF YOU DISSOLVED 12 G OF SALT IN 3 L OF WATER WHAT WOULD THE CONCENTRATION BE?
12G /3L = 4G/L
EX: IF YOU DISSOLVED 12 G OF SALT IN 6 L OF WATER WHAT WOULD THE CONCENTRATION BE?
12G/6L=2G/L
THEREFORE THE CONCENTRATION OF THE FIRST SOLUTION IS TWICE AS CONCENTRATED AS THE SECOND SOLUTION

12. DIFFUSION IN A SOLUTION PARTICLES ARE CONSTANTLY MOVING DIFFUSION:
WHEN PARTICLES MOVE FROM AN AREA OF HIGH CONCENTRATION (4G/L) TO AN AREA OF LOW CONCENTRATION (2G/L)
MOLECULES TEND TO DO THIS NATURALLY, WITHOUT THE USE OF ENERGY, UNTIL THE CELL REACHES EQUILIBRIUM (SAME CONCENTRATION IN THE CELL
EVEN WHEN EQUILIBRIUM IS REACHED PARTICLES WILL CONTINUE TO MOVE ACROSS THE MEMBRANE IN BOTH DIRECTIONS

13. DIFFUSION

14. PERMEABILITY OF A MEMBRANE
PERMEABLE:
A CELL MEMBRANE IS PERMEABLE IF A SUBSTANCE IS ABLE TO DIFFUSE ACROSS THE MEMBRANE
IF A MOLECULE CANNOT GO THROUGH THE CELL MEMBRANE THEN IT IS SAID TO BE IMPERMEABLE
MOST MEMBRANES ARE SELECTIVELY PERMEABLE MEANING THAT SOME THINGS MAY GO ACROSS THE MEMBRANE AND OTHER MAY NOT

15. OSMOSIS
OSMOSIS:
DIFFUSION OF WATER THROUGH A SELECTIVELY PERMEABLE MEMBRANE, MOVING WATER FROM AN AREA OF HIGH CONCENTRATION TO AN AREA OF LOW CONCENTRATION
HOW IT WORKS:
WATER MOVES THROUGH A MEMBRANE THAT MOLECULES CANNOT GET THROUGH.
IF YOUHAVE A GLASS OF SUGAR WATER AND YOUR SUGER HAS A HIGHER CONCENTRATION ON ONE SIDE AND A LOWER CONCENTRATION OF THE OTHER SIDE THE WATER IS GOING TO MOVE FROM THE SIDE OF LOWER CONCENTRATION OF SUGAR TO THE SIDE OF HIGH CONCENTRATION OF SUGAR

16. OSMOSIS

17. RESULTS OF MEMBRANE TRANSPORT
ISOTONIC:
“SAME STRENGTH” (DYNAMIC EQUILIBRIUM)
THE CONCENTRATION OF THE SOLUTES IS THE SAME INSIDE AND OUTSIDE THE CELL
HYPERTONIC:
“ABOVE STRENGTH”
SOLUTION HAS A HIGHER SOLUTE CONCENTRATION THAN THE CELL, CAUSING WATER TO LEAVE THE CELL AND IT TO SHRIVLE (PLASMOLYSIS)
HYPOTONIC:
“BELOW STRENGTH”
SOLUTION HAS A LOWER SOLUTE CONCENTRATION THAN THE CELL, CAUSING WATER TO ENTER THE CELL AND IT TO SWELL (CYTOLYSIS)

20. OSMOTIC PRESSURE CAN BE DANGEROUS
FOR CELLS THAT DO NOT COME INTO NORMAL CONTACT WITH FRESH WATER OSMOSIS CAN CAUSE A CELL TO BECOME SWOLLEN WITH WATER AND EVENTUALLY BURST
LUCKILY ANIMAL CELLS DO NOT COME INTO CONTACT WITH FRESH WATER, MOST OF OUR CELLS ARE IN A LIQUID SUITABLE FOR THE CELL TO SURVIVE
ANIMAL CELLS ARE CONTAINED IN LIQUID SUCH AS BLOOD
PLANT CELLS ARE ALWAYS IN CONTACT WITH FRESH WATER, WHICH IS ANOTHER IMPORTANT REASON THEY CONTAIN A CELL WALL
THE CELL WALL KEEPS THE CELL FROM SWELLING AND EXPLODING

21. DEALING WITH OSMOSIC PRESSURE
Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure.
A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding.
Salt water fish pump salt out of their specialized gills so they do not dehydrate.
Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

22. FACILITATED DIFFUSION
Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane
Transport Proteins are specific – they “select” only certain molecules to cross the membrane
Transports larger or charged molecules

23. FACILITATEDDIFFUSION
High Concentration
Low Concentration
Cell Membrane
Glucose
molecules
Protein
channel
Transport Protein
Through a 
High
Low

24. ACTIVE TRANSPORT cell uses energy
actively moves molecules to where they are needed
Movement from an area of low concentration to an area of high concentration
(Low  High)
Three Types:
PROTEIN PUMPS
ENDOCYTOSIS
EXOCYTOSIS

25. ACTIVE TRANSPORT
Protein Pumps -transport proteins that require energy to do work
Energy is required due to the proteins changing shape.
Example: Sodium / Potassium Pumps are important in nerve responses.

26. ACTIVE TRANSPORT Endocytosis: taking bulky material into a cell
Uses energy
Cell membrane in-folds around food particle
“cell eating”
forms food vacuole & digests food
This is how white blood cells eat bacteria!

27. ACTIVE TRANSPORT PHAGOCYTOSIS “CELL EATING”
EXTENSIONS OF THE CYTOPLASM SURROUND A PARTICLE AND PACKAGE IT WITHIN A FOOD VACUOLE

28. PINOCYTOSIS “CELL DRINKING”
TAKING UP OF LIQUID IN THE SURROUNDING ENVIRONMENT BY TINY POCKETS FORMING ALONG THE MEMBRANE CREATING VACUOLES

29. ACTIVE TRANSPORT . Exocytosis: Forces material out of cell in bulk
membrane surrounding the material fuses with cell membrane
Cell changes shape – requires energy
EX: Hormones or wastes released from cell