1. Movement of materials Across
CELLULAR TRANSPORT
Movement of materials Across
the Cell Membrane
In and Out of cells
&
Within the Cell

2. Movement Through the Membrane
Cell Membrane C. Active Transport
Structure and Function Protein Pumps
B. Passive Transport Endocytosis
Diffusion Exocytosis
Osmosis
1. How Osmosis Works
Osmotic Pressure
Facilitated Diffusion

3. The Structure of the Cell Membrane
“Fluid Mosaic”
Phospholipid Bilayer and Embedded Proteins
Outside
of cell
Cell
membrane
Proteins
Protein
channel
Lipid bilayer
Carbohydrate
chains
Inside
of cell
(cytoplasm)

4. The Plasma Cell Membrane
The Cell Membrane
Regulates what enters and leaves the cell
Takes in food, water, gases
Eliminates wastes
Provides protection and Support
Lipid bilayer gives cells tough, flexible structure that forms strong barrier between cell and its surroundings

5. Cell (plasma) membrane
Cells need an inside & an outside…
separate cell from its environment
cell membrane is the boundary IN
food
- sugars
- proteins
- fats
salts O2
H2O
OUT
waste
- ammonia
- salts
- CO2
- H2O
products
- proteins
cell needs materials in & products or waste out

6. Semi-permeable membrane
Cell membrane controls what gets in or out
Need to allow some materials — but not all — to pass through the membrane
semi-permeable
only some material can get in or out
So what needs to get across the membrane?
sugar
lipids aa O2
H2O
salt
waste

7. Lipids of cell membrane
Membrane is made of special kind of lipid
phospholipids
“split personality”
Membrane is a double layer
phospholipid bilayer
“attracted to water”
phosphate
inside cell
outside cell
lipid
“repelled by water”

8. A Phospholipid is …
A pair of lipid “tails” and a phosphate (head) attached to a glycerol backbone.
Phosphate (“water loving”) heads face towards regions where there’s water
Fatty acid (“water fearing”) tails turn away from regions of water
The chemical nature of phospholipids explains why they orient themselves the way they do in a membrane

9. The Phospholipid Membrane “appears” like a Solid line, but is really a
Fluid mosaic of phospholipids with various kinds of embedded Proteins

10. Primary Functions of Membrane Proteins
Transport - proteins that span the membrane provide channels for moving select substances into and out of cells.
Cell Recognition – proteins with short chains of sugars attached act as identification markers specifically recognized by other cells.
Cell Receptors – proteins with specific shapes that serve as binding sites chemical messengers.
Enzymatic Activity – proteins embedded in membrane to catalyze chemical reactions

11. What’s needed for successful transport?
Membrane must be……
Thin (substances can easily move through)
Moist (substances must first be dissolved in water before they can be transported)
In contact with a transport medium (body fluids, blood or watery environment)
All three conditions must be met in order for the movement of materials across cell membranes

12. Cell Transport can be… PASSIVE
Movement due to random molecular motion of atoms
NO energy is needed!
Molecules move Down Concentration Gradient
molecule moves from area of higher concentration to area where its less concentrated
Equilibrium is reached when molecules are equally distributed OR …
Molecules continue to move equally in both directions across membrane
ACTIVE
REQUIRES ENERGY (ATP)!
Protein Pumps - Move substances AGAINST CONCENTRATION GRADIENT
Membrane Movement
Endocytosis
Exocytosis

13. What’s a Concentration Gradient?
High concentration
Concentration
Molecules per unit of volume
Greater number of molecules/volume= greater concentration
Gradient compares the difference in the concentration of that molecule at two different locations
Molecules move away from
Areas of higher concentration
To areas of lower concentration
“Down a Concentration
Gradient”
Lower
concentration

14. Diffusion Move from HIGH to LOW concentration diffusion of water
passive transport
no energy needed
diffusion of water
diffusion
osmosis

15. Passive Transport
Diffusion – movement of particles from an area of high concentration to an area of lower concentration (NO ATP)
High
concentration
Particles move
Equally In both directions
Membrane
Low Concentration
Net movement
Equilibrium Reached

16. Molecules move from high to low
Diffusion
move from HIGH to LOW concentration
Movement from high concentration of that substance to low concentration of that substance.

17. Simple Diffusion Verses Facilitated Diffusion
Simple Diffusion – particles move randomly between phospholipids spaces
Small molecules:
Oxygen (O2), carbon dioxide (CO2), water(H2O),
Lipids
Facilitated diffusion- particles move through specific Protein Channels
Large Molecules:
Glucose
Amino Acids
Some Hormones

18. Protein channels Proteins act as doors in the membrane
channels to move specific molecules through cell membrane
HIGH
Donuts!
Each transport protein is specific as to the substances that it will translocate (move).
For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer.
Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane.
These channel proteins allow fast transport.
For example, water channel proteins, aquaprorins, facilitate massive amounts of diffusion.
LOW

19. Facilitated Diffusion
Move from HIGH to LOW through a channel
sugar
sugar
sugar
sugar
inside cell
sugar
sugar
LOW
Which way will sugar move?
HIGH
outside cell
sugar
sugar
sugar
sugar
sugar
sugar
sugar

20. Facilitated Diffusion: Specific and Fast
Facilitated Diffusion: another example of Passive Transport
Section 7-3
No Energy Needed
Glucose
molecules
Particles still moving DOWN a
CONCENTRATION GRADIENT!!
High
Concentration
Cell
Membrane
Some larger,
Important particles
Move through
Specific Protein
Channels
Protein
channel
Low
Concentration
Facilitated Diffusion: Specific and Fast
Go to Section:

21. Types of Diffusion Move from HIGH to LOW concentration
directly through membrane
simple diffusion
no energy needed
help through a protein channel
facilitated diffusion (with help)
HIGH
LOW

22. Osmosis Movement of Water Across Cell Membrane

23. Osmosis Water is very important, so we talk about water separately
diffusion of water from HIGH concentration of water to LOW concentration of water
across a semi-permeable membrane

24. Passive Transport con’t
Osmosis:
Diffusion of water across a selectively permeable membrane
Continues until the number of water molecules are equal on both sides of a membrane ( equilibrium)
No energy needed; water molecules randomly move from where there’s more water (hypotonic) to where there’s less water (hypertonic)

25. The concentration of the solution outside the cell determines the Net movement of water (osmosis)
1.Hypotonic = Dilute
[water] : [solute]
2. Isotonic:
Concentrations Equal
inside and outside the
cell
3. Hypertonic:
HYPOTONIC
ISOTONIC
HYPERTONIC
Less water
Outside
The cell
More water
Outside
The cell
Water is
Equal to
Inside cell
Net movement
Into cell
Equilibrium
Net movement
Out of cell

26. Higher Concentration of Water Lower Concentration of Water
OSMOSIS: Need to know relative amounts of water on both sides of a cell membrane to determine the direction of net movement of water
Figure 7-17 Osmosis
Section 7-3
Higher Concentration
of Water
Water molecules
Cell
membrane
Lower Concentration
of Water
Sugar molecules
Sugar is dissolved in the water; it’s considered a Solute.
However, we are Only interested in the relative amount of water during osmosis
Go to Section:

27. Keeping water balance
Cell survival depends on balancing water uptake & water loss
HYPERTONIC
HYPOTONIC
ISOTONIC
freshwater
balanced
saltwater

28. Keeping right amount of water in cell1
Keeping right amount of water in cell
Freshwater
a cell in fresh water
high concentration of water around cell
cell gains water
example: Paramecium
problem: cells gain water, swell & can burst
water continually enters Paramecium cell
solution: contractile vacuole
pumps water out of cell
KABOOM!
freshwater
No problem, here

29. Controlling water
Contractile vacuole in Paramecium

30. Keeping right amount of water in cell3
Keeping right amount of water in cell
Balanced conditions
no difference in concentration of water between cell & environment
cell in equilibrium
example: blood
problem: none
water flows across membrane equally, in both directions
volume of cell doesn’t change
That’s better!
balanced
I could be better…

31. Keeping right amount of water in cell2
Keeping right amount of water in cell
Saltwater
a cell in salt water
low concentration of water around cell
cell loses water
example: shellfish
problem: cell loses water
in plants: plasmolysis
in animals: shrinking cell
solution: take up water
I’m shrinking, I’m shrinking!
saltwater
I will survive!

32. Effects of Osmosis on Animal Cells
Red Blood Cells in 3 different solutions
RBC loses water
Cells “shrink”
Cells take-in excess water
Swell and can burst
Cells are in
Equilibrium

33. Effects of Osmosis on Plant Cells
Water moves into plant cells, but
Cell wall prevents bursting
Water leaves plant cells, called
Plasmolysis

34. Active transport
Cells may need molecules to move against concentration “hill”
need to pump “uphill”
from LOW to HIGH using energy
protein pump
requires energy
ATP
Plants have nitrate & phosphate pumps in their roots.
Why?
Nitrate for amino acids
Phosphate for DNA & membranes
Not coincidentally these are the main constituents of fertilizer.
ATP

35. Active Transport
Moving particles AGAINST the concentration gradient REQUIRES ENERGY !
Particles are PUMPED through Protein Channels

36. Transport summary simple diffusion facilitated diffusion
ATP
active transport

37. Active Transport via Membrane Movement
When membrane MOVE, work is done
And ATP (energy) NEEDED
1. Endocytosis: A portion of the cell membrane takes in substances and forms a pouch (vesicle). The membrane pinches off to form an endocytic vesicle in side the cell.

38. Types of Endocytosis undissolved molecules
Pinocytosis
“cell drinking“
Undissolved molecules too large to enter through the cell membrane or protein channels, may enter this way

39. Phagocytosis: Cell Eating
Membrane forms PSEUDOPODS or "false feet".
Engulfing large particles with pseudopods
Bacteria, viruses
Dead, damaged cells
Small, one-celled organisms
Vesicle forms
Fuses with lysosome
Digested
Once digested, materials are used, recycled or expelled
Ameba
White blood cell
Engulf large particles/bacteria
viruses/ dead cells and debris

40. Exocytosis: bulk movement out of the cell
Wastes products
(toxic) And substances
Produced by Cells
(proteins, hormones) are carried by vesicles and exported

41. EXOCYTOSIS: When materials are EXpelled from the cell

42. Examples of Transport Digested food molecules transported
Across intestinal cells into blood
Lungs and blood exchange Gases
Kidneys Filter Blood (Active & Passive )
Intestinal Villi