1. 2.4 Membranes
2.4.1
Draw a diagram to show the fluid mosaic model of a biological membrane. (1)
The diagram should show the phospholipid bilayer, cholesterol, glycoproteins and integral and peripheral proteins.
Use the term plasma membrane not cell surface membrane for the membrane surrounding the cytoplasm.
Integral proteins are embedded in the phospholipid of the membrane whereas peripheral proteins are attached to its surface.

2. 2.4 Membranes
2.4.2
Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes. (3)
Hydrophobic – ‘afraid of water’
Hydrophilic – ‘loves water’

3. 2.4 Membranes

4. 2.4 Membranes

5. 2.4 Membranes

6. 2.4 Membranes Fibers of the extracellular matrix
Carbohydrate (of glycoprotein)
Glycoprotein
Microfilaments of cytoskeleton
Phospholipid
Cholesterol
Proteins
Plasma membrane
Glycolipid
Cytoplasm

7. 2.4 Membranes

8. 2.4 Membranes 2.4.3 List the functions of membrane proteins including
hormone binding sites – Insulin on liver
Immobilized enzymes – epithelial villi cells
Cell adhesion – Tight junctions
channels for passive transport – facilitated diffusion channels
pumps for active transport.

10. Concept Check
Membranes organize cell activities. The proteins imbedded in the membranes are essential to their function. These membrane proteins have properties that allow them to “float” in the membrane. Which of the following describe those properties?
The surface region of the protein in the interior of the membrane is mostly hydrophobic.
The surface region of the protein in the interior of the membrane is mostly hydrophillic.
The surface region exposed to the outer environment is hydrophobic.
The surface region exposed to the interior environment is hydrophobic.

11. Answer
Membranes organize cell activities. The proteins imbedded in the membranes are essential to their function. These membrane proteins have properties that allow them to “float” in the membrane. Which of the following describe those properties?
The surface region of the protein in the interior of the membrane is mostly hydrophobic.

12. 2.4 Membranes 2.4.4 Define diffusion (1)
Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration (down a concentration gradient), until there is an equal distribution.
Define osmosis
Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration (high water concentration) to a region of higher solute concentration (low water concentration).

13. 2.4 Membranes
2.4.5
Explain passive transport across membranes in terms of diffusion. (3)
Requires no energy
Moves from down the concentration gradient
Some molecules pass through the membrane
Some molecules use channels for facilitated diffusion

14. Passive transport is diffusion across a membrane
In passive transport, substances diffuse through membranes without work by the cell
Spreading from areas of high concentration to areas of low concentration
Equilibrium
Membrane
Molecules of dye
Figure 5.14A
Figure 5.14B

15. Passive Transport

16. Small nonpolar molecules such as O2 and CO2
Diffuse easily across the phospholipid bilayer of a membrane

17. Transport proteins may facilitate diffusion across membranes
Many kinds of molecules
Do not diffuse freely across membranes
For these molecules, transport proteins
Provide passage across membranes through a process called facilitated diffusion
Solute molecule
Transport protein
Figure 5.15

18. Osmosis is the diffusion of water across a membrane
In osmosis
Water travels from a solution of lower solute concentration to one of higher solute concentration
Lower concentration of solute
Higher concentration of solute
Equal concentration of solute
H2O
Solute molecule
Selectively permeable membrane
Water molecule
Solute molecule with
cluster of water molecules
Net flow of water
Figure 5.16

19. Osmosis

20. Concept Check
This diagram represents osmosis of water across a semipermeable membrane. The U-tube on the right shows the results of the osmosis. What could you do to level the solutions in the two sides of the right hand U-tube?
Add more water to the left hand side.
Add more water to the right hand side.
Add more solute to the left hand side.
Add more solute to the right hand side.

21. Answer
This diagram represents osmosis of water across a semipermeable membrane. The U-tube on the right shows the results of the osmosis. What could you do to level the solutions in the two sides of the right hand U-tube?
Add more solute to the left hand side.

22. 2.4 Membranes

23. 2.4 Membranes
2.4.6
Explain the role of protein pumps and ATP in active transport across membranes. (3)
Requires energy, in the form of ATP, or adenosine triphosphate
Molecules are ‘pumped’ across the membrane UP the concentration gradient
Pumps fit specific molecules
The pump changes shape when ATP activates it, this moves the molecule across the membrane

24. Active Transport

25. Active Transport

26. 2.4 Membranes
2.4.7
Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane. (3)
2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis. (2)

28. 2.4 Membranes
Endocytosis – the mass movement INTO the cell by the membrane ‘pinching’ into a vacuole
Exocytosis – the mass movement OUT of the cell by the fusion of a vacuole and the membrane
This is possible because the of the fluid properties of the membrane (able to break and reform easily, phospholipids not attached just attracted)

29. Exocytosis

30. Endocytosis
endo- and exo-
-cytosis

31. Endocytosis can occur in three ways
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
Pseudopodium of amoeba
Food being ingested
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
Material bound to receptor proteins
PIT
Cytoplasm
Plasma membrane
TEM 54,000
TEM 96,500 
LM 230
Figure 5.19C

32. CONNECTION Faulty membranes can overload the blood with cholesterol
Harmful levels of cholesterol
Can accumulate in the blood if membranes lack cholesterol receptors
LDL particle
Protein
Phospholipid outer layer
Cytoplasm
Receptor protein
Plasma membrane
Vesicle
Cholesterol
Figure 5.20

33. Endocytosis and Exocytosis