Cellular Transport

1
Cellular Transport

• Section 7.4

2
Cellular Transport

• How do substances move throughout the cell?
• Ever smelled cookies baking while you were in
  your bedroom?
• Two ways to transport substances
• Without energy Passive Transport
• With energy Active Transport

3
Diffusion is Passive

• Diffusion (AKA Passive Transport)- net mvmt of
  particles from an area where there are many to an
  area where there are fewer
• Animation
• The amount of substances in a given area is
  called concentration
• Substances diffuse from high to low
  concentrations
• Therefore, it doesnt require energy!
• Fig. 7.20
• What if the concentrations are the same?
• When there is continuous movement of the
  particles, but no overall change in concentration
  it is called Dynamic Equilibrium

4
Three Main Factors of Diffusion

• Concentration- high concentration, fast diffusion
• Temperature- high temp, faster movement
• Pressure- high pressure, particles are closer
  together and bounce into each other more often,
  faster diffusion
• CHEMISTRY!!!

5
Diffusion Across the Plasma Membrane

• Besides diffusing water across the cell, other
  ions and small molecules get diffused, too
• Facilitated Diffusion- uses transport proteins to
  move other ions and small molecules across the
  plasma membrane

6
Types of Transport Proteins Used in Diffusion

• Channel proteins open and close the P.M. to
  allow the substance to diffuse that are polar
• Carrier Proteins change shape as they diffuse to
  help move substances through the membrane
• Fig. 7.21
• Passive Transport
• Reading Check- How do Na ions get into a cell?

7
Applications of Diffusion

• Kidney dialysis
• Question
• Do substances need a stimulus to diffuse across a
  membrane?

8
Osmosis- Water You Doing?Diffusion of Water

• Water passes freely through the P.M. and doesnt
  need transport proteins
• The diffusion of water is called osmosis
• Regulating water in the cell helps maintain
  homeostasis
• How it works
• Solute/solvent which is which?
• Solute is the thing being dissolved, solvent does
  the dissolving
• Water is the solvent
• If there is a lot of water, the concentration of
  the cell is low its dilute
• Fig. 7.22
• Reading Check- Compare and contrast osmosis and
  diffusion

9
Types of Solutions- Egg Demo

• Isotonic Same concentration of water and solutes
  as its cytoplasm -Cells maintain normal shape
• Fig. 7.23
• Hypotonic if cell is in a solution that has a
  lower concentration of solute
• More water outside of cell than inside, so the
  water flows in because of osmosis and the cell
  swells
• Too much swelling can lead to a burst!
• Because plants of rigid cell walls, they dont
  burst in hypotonic solutions
• Grocers use this idea to keep veggies fresh by
  misting them
• Thats how pickles are made
• Fig. 7.24

10

• Hypertonic the concentration of the solute
  outside of the cell is higher than inside
• Cells shrivel because the water is leaving the
  cell (less pressure)
• In plants, it causes wilting
• Fig. 7.25
• Evaluate the benefits of sports drinks that
  contain electrolytes that athletes drink instead
  of water
• Is there any danger in consuming these drinks?
• Osmosis

11
Active Transport

• What if a substance has to move from an area of
  lower concentration to an area of higher?
• It requires energy and is called active transport
• Occurs in pumps- carrier proteins that help in
  transport
• Carrier Proteins
• Active Transport
• Fig. 7.26 Why does active transport require
  energy?

12
Na/K ATPase Pump- A type of Carrier Protein

• Found in PM of animal cells
• Maintains the level of sodium ions (Na) and
  potassium ions (K) inside and outside of the
  cell
• What is it used for?
• This protein pump is an enzyme to help with
  energy storing molecules
• Whats it transport?
• Three Na out of the cell, 2 K into the cell
• Why?
• The cell needs to get rid of Na and needs more
  K
• But, since theres lots of Na already on the
  outside of the cell and lots of K already on the
  inside of the cell, active transport has to be
  used

13
Na/K ATPase Pump

• Three Na bind to the transport protein to move
  out of the cell
• The transport protein requires ATP to change the
  shape of the protein
• After the protein changes shape, it releases the
  Na to the outside of cell
• In turn, the K on the outside of the cell bind
  to the protein
• The protein changes shape and releases the K on
  the inside of the cell

14
Transporting Large Particles

• Sometimes diffusion or transport proteins dont
  get the job done because the particles are too
  large
• Endocytosis is the process in which a cell
  surrounds the substance outside of the cell and
  engulfs it in the plasma membrane
• The membrane then pinches off and leaves the
  substance inside the cell
• Endocytosis
• Movie

15
Transporting Large Particles

• Exocytosis is the opposite of endocytosis
• Cells use it to expel wastes and secrete cell
  products, like hormones, that were manufactured
  inside the cell
• Both Endo and Exo require energy to maintain
  homeostasis in the cell
• Movie

16
Visualize It!

• Look at figure 7.29
• Make a Venn Diagram to compare and contrast the
  processes of endocytosis and exocytosis.

17
Questions to Ponder

• In what ways can materials move across a cell
  membrane?
• What is the difference between osmosis, diffusion
  and facilitated diffusion?
• Why are channel proteins needed?
• How do materials move against the concentration
  gradient?
• Pg. 208- Cutting Edge Biology