1. Unit 5- Cell Membrane & Cell Transport
5b- Cellular Transport

2. About Cell Membranes All cells have a cell membrane Functions:
Maintains homeostasis
Provides protection and support for the cell
TEM picture of a real cell membrane.
Animations of Active Transport & Passive Transport

3. What is the purpose of cellular transport?
Homeostasis depends upon appropriate movement of materials across the cell membrane.
Required materials must pass into the cells so they can be used.
Ex. Oxygen and glucose for cellular respiration
Waste materials must pass out of the cells as they are produced
Ex. The CO2 produced as a waste product of cellular respiration

4. Membrane movement animation
How?
Each individual cell exists in a fluid environment, and the cytoplasm within the cell is a fluid environment.
The presence of a liquid makes it possible for substances (such as nutrients, oxygen, and waste products) to move into and out of the cell.
A cell membrane is semipermeable (selectively permeable).
Materials can enter or exit through the cell membrane by passive transport or active transport.
In solution, particles move constantly (more KE than a solid). They collide with one another and tend to spread out randomly. As a result, the particles tend to move from an area where they are more concentrated to an area where they are less concentrated

5. Passive Transport Cell uses no energy
The movement of molecules occurs along a concentration gradient
meaning molecules move from an area of high concentration to an area of low concentration
3 types of passive transport
high
low
Weeee!!!

6. Simple Diffusion Animation
Passive Transport:
Diffusion: spreading out of molecules across a cell membrane until they are equally concentrated (equilibrium) *molecules never stop moving, just stay spread out*
results from the random motion of molecules
Occurs along a concentration gradient
Molecules can diffuse across a membrane by dissolving in the phospholipid bilayer (ex O2, CO2) or by passing through pores in the membrane
results from the random motion of molecules (driven by molecules’ kinetic energy)
Equilibrium- Molecules do not stop moving, they are just moving equally in both directions

7. Passive Transport: 2. Osmosis: diffusion of water across a membrane
Osmosis animation
Passive Transport:
2. Osmosis: diffusion of water across a membrane
Water moves from a high concentration of water to a low concentration of water
Net direction of osmosis is determined by the relative solute concentrations on the two sides of the membrane.
Aquaporin
Depends on the % of H2O, not the amount
Water moves through the bilayer as well as through channel proteins (aquaporins)

8. Solutions Solute- substance being dissolved
Solvent- substance solute dissolves in
Solution= solute+solvent

9. Passive Transport-Osmosis
Hypotonic Solution: The solute concentration outside the cell is lower than the solute concentration inside the cell. (Low solute; High water)
Hypo- below, low….less solute
Hypotonic can be used to describe the cell or the environment….if the environment is hypotonic, the cell is hypertonic
A cell placed in a hypotonic solution is gain water & get big and fat like a hippo
Result: Water moves from the solution to inside the cell. Cell swells & may burst (cytolysis).Animation

10. Passive Transport-Osmosis
Hypertonic Solution: The solute concentration outside the cell is higher than the solute concentration inside the cell. (High solute; Low water)
Plasmolysis
Hyper- above, more
Plasmolysis- water rushes out, cell shrinks away from the rigid cell wall
shrinks
Result: Water moves out of the cell into the solution Cell shrinks! Animation

11. Passive Transport-Osmosis
Isotonic Solution: The solute concentrations outside the cell & inside the cell are equal.
Iso- equal
Result: No net movement. Water moves equally in both directions & the cell remains same size. (Dynamic Equilibrium)

12. Hypertonic, Hypotonic, Isotonic Solutions

13. In what type of solution are these cells?B C A
Hypertonic
Isotonic
Hypotonic

14. How Cells Deal with Osmosis
Paramecium (protist) removing excess water video
Cells must compensate for the water that enters the cell in hypotonic environments & leaves the cell in hypertonic environments.
Protists, like paramecia, have contractile vacuoles that collect & pump out excess water.
Plants & bacteria have cell walls that prevent them from over-expanding.
In plants the pressure exerted on the cell
wall is called turgor pressure.
Plasmolysis- in a hypertonic environment the
cells shrink away from the cell walls &
turgor pressure is lost.

15. How Cells Deal with Osmosis
Animal cells are bathed in blood. Kidneys keep the blood isotonic by removing excess salt & water.
Many multicellular organisms have outer surfaces that are waterproof to prevent water loss on land or water gain in freshwater.
A small difference in solute concentration results in a very large osmotic pressure gradient across the cell membrane and the membranes of animals cells can’t withstand any appreciable pressure gradient. Water movement can eliminate differences, but it’s also a problem because it leads to a change in cell volume. Regulation of intracellular solute concentration is essential for control of cell volume.

16. Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer)
Passive Transport: A B
3. Facilitated diffusion: diffusion of specific particles along a concentration gradient with the help of transport proteins
Transport Proteins are specific – they “select” only certain molecules to cross the membrane
Transports larger or charged molecules that cannot pass through the membrane on their own
Glucose is an example of a molecule that passes into the cell through facilitated diffusion
Facilitated diffusion (Channel Protein)
Diffusion (Lipid Bilayer)
Carrier Protein

17. Passive Transport: 3. Facilitated Diffusion
Glucose
molecules
Cellular Transport From a-
High
High Concentration
Channel Proteins animations
Cell Membrane
Low Concentration
Protein
channel
Low
Transport Protein
Through a 

18. This is gonna be hard work!!
Active Transport
Requires the cell to use energy
Molecules move against the concentration gradient –
from an area of low concentration to an area of high concentration
Active transport is used to:
move large molecules
concentrate molecules within the cell
remove waste from the cell
high
low
This is gonna be hard work!!

19. Types of Active Transport
Sodium Potassium Pumps (Active Transport using proteins)
1. Protein Pumps (aka cell membrane pumps) –transport proteins that require energy to do work
Example: Sodium / Potassium Pumps are used in nerve cells to transmit messages.
Calcium, potassium, and sodium ions are examples of materials that must be forced across the cell membrane using active transport

20. Active Transport- Protein Pumps
Sodium-Potassium Pump
ATP supplies the energy that drives the pump

21. Types of Active Transport
2. Endocytosis:
Cells take in large molecules by folding around them & forming a pouch
Pouch then pinches off from the membrane & becomes an organelle called a vesicle
This is how white blood cells ingest bacteria
Some vesicles will fuse with lysosome so contents digested. Some will fuse with other organelles.

22. Types of Active Transport
3. Exocytosis:
vesicles made by the cell fuse with the cell membrane, releasing their contents into the external environment
Used to release large molecules, waste products, or toxins
Used to release proteins after Golgi apparatus packages them into vesicles
Endocytosis & Exocytosis animations

23. Endocytosis & Exocytosis