1. TOPIC 1.4 – MEMBRANE TRANSPORT

2. 1.4 – A - Diffusion

3. IB BIO – 1.4
The hyprophilic heads within the cell membrane make it difficult for most molecules to pass through. This makes the membrane an effective barrier between the cell and the environment. 3
INTRO

4. IB BIO – 1.4
Diffusion is the passive movement of particles from areas of high to low concentration until an equilibrium is reached. This results from random collisions between the particles and requires no energy. 4
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Key Terms
Diffusion

5. IB BIO – 1.4
In this example, ink molecules collide and diffuse through the water over time. 5
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Key Terms
Diffusion

6. Small, Non-polar molecules Large, polar or ionic molecules
IB BIO – 1.4
Phospholipid bilayers are selectively permeable, which means that some molecules are able to pass through while others are not. This is mostly caused by the polarity of the hydrophilic heads. 6
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Small, Non-polar molecules
Large, polar or ionic molecules
Key Terms
Selective Permeability

7. Selective Permeability
IB BIO – 1.4
So, some molecules are able to diffuse freely through the phospholipid bilayer, while others are not. Specific examples are: 7
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Oxygen, carbon dioxide, and other small, nonpolar molecules; some water molecules
Glucose and other large, polar, water-soluble molecules; ions; water molecules
Key Terms
Selective Permeability

8. Only applies to molecules that are permeable to membrane.
IB BIO – 1.4
Simple diffusion occurs when particles pass through phospholipids and diffuse across the membrane without the aid of a protein. 8
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Key Terms
Simple Diffusion
Only applies to molecules that are permeable to membrane.

9. IB BIO – 1.4
Ions and other molecules that cannot pass the membrane through simple diffusion can do so through facilitated diffusion.
This involves the particles diffusing through channel proteins embedded in the membrane. These create a bridge in and out of the cell that bypasses the phospholipids. 9
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Key Terms
Facilitated
Diffusion

10. IB BIO – 1.4
The size and characteristics of channel pores in such proteins correspond to the particle that they help diffuse through the membrane. 10
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
A negatively-charged interior will only allow positive ions to pass
A positively-charged interior will only allow negative ions to pass
Key Terms
Facilitated
Diffusion

12. REVIEW Define diffusion. Outline the process of simple diffusion.
IB BIO – 1.4
Define diffusion.
Outline the process of simple diffusion.
Outline the process of facilitated diffusion
Compare and contrast the molecules that are transported through simple diffusion and facilitated diffusion. 12
REVIEW

13. 1.4 – B - Osmosis

14. IB BIO – 1.4
Osmosis is the passive movement of water across a semi- permeable membrane. Since water is able to move in/out of most cells free, molecules move towards areas of low concentration. 14
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Key Terms
Osmosis

15. IB BIO – 1.4 Hypotonic Hypertonic
The direction of osmosis depends on the solute conc. on both sides of the membrane. Water moves from hypo- to hypertonic areas. 15
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Hypertonic – area with higher solute concentration
Hypotonic – area with lower solute concentration
Hypotonic
Hypertonic
Cell is hypotonic
Environment is hypertonic
Water will move out of the cell.
Key Terms
Hypertonic
Hypotonic

16. IB BIO – 1.4
Water movement occurs until the solute concentrations are equal, which is the isotonic value. This causes changes in cell size. 16
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Key Terms
Isotonic

17. IB BIO – 1.4 Changes in Cell Size 17 Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Key Terms

18. IB BIO – 1.4
During medical procedures, it is important to bathe tissues in isotonic solutions so that cells aren’t damaged. Other solutions can potentially affect tissue cells in the following way: 18
Applications
A2: Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
Key Terms
Hypertonic solutions causes cells to shrink which damages the cell structure
Hypotonic solutions causes cells to grow, which results in them burstine

19. IB BIO – 1.4
Most tissue samples are stored in normal saline, which is a sodium chloride solution. It has the same osmolarity and so does not cause damage.
It can also be used to:
Rinse wounds
Moisten damaged areas before treatment
Form the basis of eye drops 19
Applications
A2: Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
Key Terms

20. REVIEW Define osmosis. Define hypotonic, isotonic and hypertonic.
IB BIO – 1.4
Define osmosis.
Define hypotonic, isotonic and hypertonic.
Outline the direction of water molecule movement during osmosis.
Discuss the importance of using isotonic solutions with tissue samples. 20
REVIEW

21. 1.4 – C – Active Transport

22. IB BIO – 1.4
Active transport is a form of transport that requires the use of energy in the form of ATP (passive transport requires none). It moves particles from low concentrations to high concentrations. 22
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
The three main types are:
Protein pumps
Endocytosis
Exocytosis
Key Terms
Active Transport

23. IB BIO – 1.4
Protein pumps are globular proteins embedded in the membrane that are able to ‘push’ molecules against their gradient. 23
Understandings
U1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Key Terms
Active Transport
Each pump is specialized to transport a certain molecule, which converts ATP to ADP in the process.

24. IB BIO – 1.4
Vesicles can be to used to transport materials within the cytoplasm of the cell without mixing their components.
They are small sacs of membrane that can change shape and move in and out of the cell. 24
Understandings
U2: The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
Key Terms
Vesicles

25. IB BIO – 1.4 25
Because of the membrane’s fluidity, it is able to bring materials into the cell by pinching into vesicles.
Understandings
U2: The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
This process of bringing materials into the cell is called endocytosis. It is an active process fueled by energy in the form of ATP.
Key Terms
Endocytosis

26. IB BIO – 1.4
There are three main types of endocytosis, each specialized for certain types of substances. 26
Understandings
U2: The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
Phagocytosis Large Cells & Particles
Pinocytosis Water & Liquids
Receptor-mediated Specific molecules
Key Terms
Endocytosis

27. IB BIO – 1.4
Exocytosis is the reverse process of endocytosis. The Golgi apparatus packages materials for excretion into vesicles.
Vesicles then travel to the membrane where they fuse to the phospholipid bilayer.
This releases the contents of vesicles into the environment. 27
Understandings
U2: The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
Key Terms
Exocytosis

28. IB BIO – 1.4
Because of the membrane’s fluidity, the membrane of the vesicle is able to fuse with the cell’s membrane. This increases the amount of cell membrane overall, which is vital for cell growth. 28
Understandings
U2: The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
Key Terms
Exocytosis

29. Endocytosis vs Exocytosis
IB BIO – 1.4
Endocytosis vs Exocytosis 29
Understandings
U2: The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
Key Terms

30. IB BIO – 1.4
Transport with vesicles allows cells to take in large particles (endocytosis), digest them, and then excrete waste (exocytosis) 30
Understandings
U2: The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
Key Terms
Vesicles

31. REVIEW Define active transport. Outline the function of protein pumps.
IB BIO – 1.4
Define active transport.
Outline the function of protein pumps.
Outline the process of endocytosis.
Outline the process of exocytosis
Discuss how vesicles can be used to transport materials within the cell. 31
REVIEW

32. 1.4 – D – Transport in Axons

33. IB BIO – 1.4
Neurons are a type of specialized cell that are adapted to carry signals over long distances throughout the body. They do so using various forms of transport along their axons. 33
INTRO

34. IB BIO – 1.4
In order to send signals, neurons depend on the flow of Na+ and K+ ions in and out of the axon. As the concentrations change, the signal is propagated. 34
Understandings
A1: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
Key Terms

35. Sodium-Potassium Pump
IB BIO – 1.4
Sodium-potassium pumps play a vital role in sending signals down an axon. They pump 3 Na+ ions out of and pump 2 K+ inwards. As a result, the charge inside the cell becomes relatively negative. 35
Understandings
A1: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
Key Terms
Sodium-Potassium Pump
When the charge becomes too positive, a signal is initiated which causes ion channels to open.

36. Sodium-Potassium Pump
IB BIO – 1.4
After the nerve signal has passed, the cell needs to ‘reset’ its internal potassium concentration. To do this, potassium channels open, specialized membrane proteins. Channel structure includes: 36
Understandings
A1: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
Four protein subunits
A narrow pore for K+ to pass through
Hydrophilic & hydrophobic regions which allow it to embed in the membrane
Key Terms
Sodium-Potassium Pump

37. Sodium-Potassium Pump
IB BIO – 1.4
Potassium-ion channels are voltage gated and only open when the concentration is high enough. When it drops, they close again. 37
Understandings
A1: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
Key Terms
Sodium-Potassium Pump

38. Axon Signal Propagation
IB BIO – 1.4
Axon Signal Propagation 38
REVIEW