This document discusses cell boundaries and membrane transport. It begins by defining cell boundaries as the cell membrane and cell wall. The cell membrane is a thin, flexible barrier that regulates what moves in and out of the cell through passive and active transport. The cell wall provides additional structure and protection for some cell types. The cell membrane is made of a phospholipid bilayer with embedded proteins. Materials move across the membrane through diffusion, osmosis, and protein-mediated transport processes. Osmosis allows water to move across the membrane down its concentration gradient. Active transport requires energy and pumps molecules against their concentration gradient with protein transporters. Cells maintain equilibrium through these passive and active transport mechanisms.

2. Cell Boundaries
Chapter 6

3. What are boundaries?
 We have borders
surrounding
countries
 We have boundaries
on a playing field
 Why are borders
important?

4. What are the borders of a
cell?
 Cell membrane
 Thin, flexible barrier
 Cell wall
 Plant, algae, fungi, prokaryotes
 Strong supporting layer

5. Cell Membrane
 What does it do for cell?
 Controls what goes in and out
 Regulates molecules moving from one liquid side of the
cell to the other liquid side of the cell
 Protects
 Supports

6. Cell Membrane
 Lipid bilayer
 What are lipids?
 What does bi- mean?
 What’s a layer?
 A cell membrane is made of two
layers of lipid molecules

7. Cell membrane
 Phospholipids bilayer
 Made of a negatively charged
phosphate “head”
 PO43-
 Attracts water because the phosphate is charged
(-)
 Water is a polar , slightly positive ends and
slightly negative ends
 Attached to the phosphate
group are 2 fatty acid chains
 Hydrophobic= don’t like water
 So the inside of the cell
membrane doesn’t let water in
but the outside allows cells to be
dissolved in aqueous
environments

9. Other things in the
membrane…
 Proteins embedded
in lipid bilayer
 Carbohydrates
attached to proteins
 So many different
molecules in
membrane, we call it
a “mosaic” of
different molecules

11. Proteins
 Proteins help things
get across
membrane
 Kinda like a pump

12. Carbohydrates…
 Chemical
identification cards
 “ID” card of cell
 Helps individual cells
id each other

14. Cell Walls
 Outside cell membrane
(does NOT replace
membrane!!!)
 Plants, algae, fungi,
prokaryotes
 Have pores to allow
things in
 Function: SUPPORT
and PROTECT

16. Cell walls made of…
 Protein and carbs
 Plant cell walls made
up of CELLULOSE
 This is a tough
carbohydrate
 Wood and paper

17. The Cell Membrane
 A biological membrane
 Cells exist in liquid environments
 Things need to get in and out of cell
 Different ways to do this….

18. Concentration (conc.)
 Solution
 Mix of 2 or more substances
 Solutes
 Substance dissolved in solution
 Concentration
 Molarity (M) is # of Moles of a substance per liter of solution
 6.02 x 1023 “small things” (molecules, atoms, ions, electrons, ions, etc)
 Moles is a unit for measuring EXTREMELY small things
 is mass of SOLUTE in a given volume of solution (g/L)
 What is the concentration of 12 grams of salt dissolved in 3
liters of water?
 12g/3L= 4g/L

19. Diffusion
 Particles constantly move
 Collide randomly
 Spread out randomly
 Diffusion is moving from area of HIGH conc. to
area of LOW conc.
 This is what we call the CONCENTRATION
GRADIENT

21. Equilibrium
 When the conc. Of a
system is the same
throughout
 (same conc. on both
sides)

22. What happens when we
reach equilibrium?
 Particles continue moving across membrane but in
both directions!
***No more changes in concentration

23. If things can cross a
membrane we call the
membrane PERMEABLE
If things canNOT cross a
membrane we call the
membrane IMPERMEABLE

24. Biological membranes
are…
 SEMI-PERMEABLE
 A.K.A.
 Selectively permeable
 Cell membranes are picky

25. What’s this have to do
with cells?
 Cell have liquid inside and are found in liquid
environment
 We have substances (solutes) inside and
outside cell
 Unequal concentrations means we get
DIFFUSION!!!
 B/c diffusion depends on random particle
movements, substances diffuse across
membranes without requiring the cell to use
energy

26. What diffuses across the
membrane???
 Small, uncharged
(non-polar) molecules
 Examples:
 Carbon dioxide
 Oxygen

27. Cells are always trying to Maintain Equilibrium by…
3 ways…
 PASSIVE Transport  ACTIVE Transport
 2 types  1 type
 Requires NO energy  REQUIRES Energy
 Goes with Conc. Gradient  Goes Against Conc. Gradient
 types:  ACTIVE TRANSPORT
 SIMPLE DIFFUSION-  Involves “transporter”
 No protein required membrane protein and
 Small, uncharged particles ENERGY (ATP)
 FACILITATED DIFFUSION-
 CHANNEL or CARRIER proteins
 Trans-membrane protein channel
 Protein with a specific shape; open-close
mechanism
 Ex. Osmosis and ligand-gated channels

28. Osmosis
 Water (H2O) can pass easily through most
biological membranes
 Def:
 Diffusion of Water through a semi-permeable
membrane
 Small molecules of water can sometimes diffuse
across easily (no protein needed)
 AQUAPORIN:
 What does “aqua” mean???
 Protein in cell membrane that allows water through (speeds up
diffusion of water across the membrane)
 Type of Facilitated diffusion (more on this later)

29. How Osmosis works…
 We have water molecules and some other molecules, let’s
say sugar
 If we have more water on one side of the membrane (HIGH
conc. of H2O), then the water will diffuse across…
 Membrane will let water thru but not sugar
 Water can move back and forth (not sugar)

30. Water moves from areas of
HIGH conc. To areas of LOW
conc.
 Water moves across till equilibrium is reached
 Isotonic:
 when conc. Of both solutions is equal
 Hypertonic: “above strength”
 When we begin with more sugar in water
 More concentrated sugar solution on side A
 Hypotonic: “below strength”
 When we end with less sugar
 Dilute sugar solution on side A

33. Osmotic Pressure
 Central vacuole fills with water and exerts and
out ward pressure on cell membrane and cell
wall
 Cell wall does NOT allow cell to expand past a
certain size
Osmoregulation
 Osmoregulation
 means by which cells keep the
concentration of cell cytoplasm or blood
at a suitable concentration.

34. Problems in Plant Cell

35. Osmotic Pressure
 Pressure exerted by osmosis on the
HYPERTONIC side of a semi-permeable
membrane
 Think about blowing up a balloon…
 Can cause serious problems for cell
 Cell is full of sugar, salts, proteins, molecules
 Inside of cell is Hypertonic
 Osmotic pressure should make fresh water go…?
 In or Out?
 In
 Cell will become inflated/swollen
 Too much cell will burst like a balloon

36. Why don’t all our cells
burst?
 What are our cells (animal) contained in?
 Fresh water?
 No…..blood or other fluids, which are ISOTONIC
 The conc. Of sugars, salts, proteins and molecules in these
fluids is the same as the conc. in the cell
 Bacteria and plant cells
 They DO come in contact with fresh water…what do
they have PROTECTING them?
 CELL WALL
 Prevent cells from expanding even when there’s a lot of
osmotic pressure
 But, cell walls are prone to injuries when there is too much
osmotic pressure

37.  Which is a RBC in isotonic solution?
 RBC in hypertonic solution?
 RBC in hypotonic solution?

40. How do big molecules
diffuse across a membrane
so quickly if the membrane
is selectively permeable?

41. Problems for diffusion…
 Things too large (like Glucose!)
 Charged molecules and Polar molecules
 Positive/negative
 Opposites attract but likes do not…
 These all present serious problems for things
getting across membranes…

42. Facilitated Diffusion
 What does facilitate mean?
 Proteins are the extra help
 “escorts” across the membrane
 We call these membrane proteins…
 Protein channels
 Carrier proteins
 LIGAND receptor proteins

43. Facilitated Diffusion
•takes place through proteins, or assemblies of proteins, embedded in
the plasma membrane
Protein channels
Carrier proteins
LIGAND receptor proteins

44. Facilitated Diffusion
(continued)
 FAST
 SPECIFIC
 Still diffusion
so we only see
it from high
concentration
to low
 Does NOT
require energy

46. What about when we want to
go against the
concentration?
(From low concentration to
high?)

47. What do we need???
ENERGY!!!!

48. ACTIVE transport
 Process that moves molecules against the concentration gradient
 Requires ENERGY
 A protein pumps small molecules and ions across a cell membrane against
the conc. Gradient
 Direct and Indirect Active transport (see animation)
 Forms of molecular transport proteins are used to pump small molecules
and ions across membrane even against the conc. grad.
 Direct: every 3 Na+ ions pumped across for every 2 K+ ions
 Indirect: Build up of ions on one side opens up another channel to shuttle in other
molecules (Na+/Glucose channel)
 Electrochemical gradient
 membrane potential (cell membrane is negative)
 Na+ opens build up on the outside of the cell…draws water out of the cell so it doesn’t
swell or burst!
 To pump large molecules and clumps…
 2 other processes:
 Exocytosis: exo-means….cyto- means…..-sis means….
 Endocytosis: endo-means….cyto- means…..-sis means….
 They can change shape of membrane

49. Build up of Na+ ions on one side of membrane from Na+/K+ pump
Now Na+ will flow thru another channel that allows one glucose in
too!
Pretty convenient!

50. Endocytosis
 When cells need to take in large material
 Process of taking material into the cell by
process of infolding, or pockets, of the
cell membrane
 Pocket breaks loose from cell membrane
and forms a vacuole or vesicle inside the
cell
 Two Types…
 Phagocytosis
 Pinocytosis

52. Two types of endocytosis:
1. Phagocytosis
 “cell eating”
 Extensions of cytoplasm surround the particle
and package it within a food vesicle
 Cell then engulfs the package
 Amoebas
2. Pinocytosis
 “cell drinking”
 When cell needs to take up liquid
 Tiny pockets in cell membrane form
 Fill with liquid or many smaller molecules
 Then pinch off to form vesicles inside of cell

55. Exocytosis
 Exo- means…
 Cyto means…
 Sis means…
 When cell releases large amounts of material
 Excretes stuff
 Membrane of vacuole surrounding particle
inside cell fuses with the cell membrane
 The contents in vacuole are then forced out of
the cell
 We see this in removal of water by contractile
vacuoles

58. Cells are always trying to Maintain Equilibrium by…
3 ways…
 PASSIVE Transport  ACTIVE Transport
 2 types  1 type
 Requires NO energy  REQUIRES Energy
 Goes with Conc. Gradient  Goes Against Conc. Gradient
 types:  ACTIVE TRANSPORT
 SIMPLE DIFFUSION-  Involves “transporter”
 No protein required membrane protein and
 Small, uncharged particles ENERGY (ATP)
 FACILITATED DIFFUSION-
 CHANNEL or CARRIER proteins
 Trans-membrane protein channel
 Protein with a specific shape; open-close
mechanism
 Ex. Osmosis and ligand-gated channels

59. MEMBRANE MAMBO!!!

60. Membrane Mambo
 10 minutes to plan
 2 teams/Cells
 Nucleus for each team
 Each member must be assigned a molecular role (must be labeled)
 Membrane protein(s)
 Molecule A (ex. Glucose)
 Molecule B (ex. Na+)
 Molecule C (ex. Water)
 Remember molecules are ALWAYS moving!!!
 MUST act out the following types of membrane transport:
 Simple Diffusion
 Osmosis
 Facilitated diffusion (channel, carrier and ligand)
 Active transport (direct and indirect)
 Be prepared to determine the concentration on either side of the membrane
 Your “Nucleus” must turn in a paper with every ones name and roles
 Summary of how each scenario will be acted out