1. What are the major biomolecules that make up the cell membrane?
(1) phospholipids
(2) proteins
2. How are phospholipids and proteins arranged?
Phospholipids are arranged in a bilayer. The hydrophilic heads of the phospholipid molecules face the aqueous(water base) environment inside and outside the cell.
The proteins are interspersed among the phospholipids in a mosaic pattern.
3. What is a phospholipid molecule?
It has a hydrophilic head: phosphate group and glycerol, which is polar (therefore it is hydrophilic).
It has a hydrophobic tail: 2 fatty acid, non-polar (therefore it is hydrophobic)
4. In the fluid mosaic model, what is the meaning of ‘fluidity’?
It means that the phospholipid molecules can move laterally on the cell membrane.
5. In the fluid mosaic model, what is the meaning of ‘mosaic’?
It means that the proteins are interspersed among the phospholipid molecules.
6. On the cell membrane, what kinds of protein molecules are there?
(1) channel protein (transmembrane protein)
(2) carrier protein
(3) antigen
(4) receptors
(5) enzymes
7. What are the function of the channel proteins on the cell membrane?
Allow the passage of certain ions (e.g. water molecules) to pass through. Do not need energy.
8. What are the functions of the carrier protein on the cell membrane?
Through active transport (i.e. require energy), transport certain substances through the cell membrane.
e.g. glucose, amino acid, certain ions.
9. What is the function of the antigens (glycoprotein) on the cell membrane?
For recognition
10. What is the function of the receptors on the cell membrane?
They are responsible for receiving chemical messages (e.g. hormones or neurotransmitters)
11. Generally speaking, what are the functions of proteins on the cell membrane?
(1) to allow certain ions and small, polar molecules to pass through
(2) through carrier protein, transport certain substances through the cell membrane
(3) cell recognition
(4) receive chemical messages from outside
(5) catalyse chemical reactions
(6) support the cell
12. What is the features of the cell membrane?
(1) differentially permeable
(2) elastic
13. What can directly pass through the phospholipid bilayer?
(1) lipid soluble materials (e.g. fatty acids, glycerol, vitamin A, vitamin D)
(2) small and non-polar substances (e.g oxygen, carbon dioxide)
14. What substances cannot pass through the cell membrane?
(1) molecules that are larger than the pores that appears among the phospholipid membrane or larger than the protein channels.
(2) shape of molecules that are not compatible with the carrier proteins.
15. What materials cannot directly pass through the phospholipid bilayer and need to pass through the channel protein (no need for energy) or carrier protein (need energy)?
Channel protein: water, certain ions
Carrier protein: monosaccharides, amino acids, vitamin C, certain ions, nucleotides.
Note: some ions can pass through the channel proteins and can also pass through with the help of carrier proteins (the carrier proteins can therefore regulate the concentration of these ions inside and outside the cell)
16. What is the importance of the cell membrane being elastic?
For changing shape or fusing of membrane in order to facilitate activities like phagocytosis and cell division.
17. What are the molecules that can increase the strength of the cell membrane, preventing it from easily being damaged?
(1) protein
(2) cholesterol
18. What are the 4 methods for substances to pass through the cell membrane? Which of them requires energy?
(1) diffusion
(2) osmosis
(3) active transport
(4) phagocytosis
Active transport and phagocytosis require energy.
19. What is the definition of diffusion?
It is the net movement of particles from a region of higher concentration to a region of lower concentration (i.e. down a concentration gradient) until the particles becomes evenly distributed.
20. What are the factors affecting the rate of diffusion? How do they affect diffusion?
(1) concentration gradient(the steeper concentration gradient, the faster the rate) (no diffusion gradient, no diffusion!)
(2) temperature (the higher the temperature, the faster the movement of molecules and the faster the rate)
(3) size of molecules (the smaller, the faster the rate)
(4) distance (the shorter, the faster the rate)
(5) surface area (the larger, the faster the rate)
21. What molecules in the body pass through the cell membrane solely by diffusion?
Oxygen and carbon dioxide
22. What is the definition of osmosis?
The net movement of water molecules across a differentially permeable membrane from a region of higher water potential to a region of lower water potential.
23. What is the relationship between the water potential and the concentration of the solution?
The higher the concentration of solution, the lower the water potential.
The lower the concentration of solution (to the extreme end, i.e. distilled water), the higher the water potential (i.e. the water potential of distilled water is the highest).
24. What is the difference between diffusion and osmosis?
Osmosis only involves water molecules, diffusion involves all molecules (including water molecules)
Molecules must pass through a differentially permeable membrane in osmosis. Diffusion does not require a differentially permeable membrane.
25. What materials can dialysis tubing (usually) allow to pass through?
Water molecules and glucose molecules
Sucrose cannot pass through! So in demonstration experiment with dialysis tubing to show osmosis, sucrose is used and not glucose.
26. What is the meaning of ‘hypotonic solution’? If animal and plants cells are placed in this solution, what is the consequence?
Solutions that have higher water potential than the water potential of the cytoplasm of the cell.
Therefore in hypotonic solution, there is a net movement of water into the cell,
animal cells will swell and eventually burst.
Plant cells will swell a little but will not burst since there is a cell wall.
27. What is ‘isotonic solution’? If animal and plants cells are placed in this solution, what is the consequence?
Solutions that have water potential the same as the water potential of the cytoplasm of the cell.
Therefore in isotonic solution, there will be no net movement of water into or out of the cell.
28. What is ‘hypertonic solution’? If animal and plants cells are placed in this solution, what is the consequence?
Solutions that have water potential lower than the water potential of the cytoplasm of the cell.
Therefore in hypertonic solutions, there will be a net movement of water out of the cell (lose water).
Animal cells will shrink.
In plants cells, the vacuole will shrink, and plasmolysis will occur.
29. What is the mechanism of active transport?
(1) substances that fit the shape of the carrier protein binds to the protein. (i.e. if the shape does not fit, the substance cannot pass through)
(2) carrier protein change shape with the use of ATP (energy)
(3) The substance is released on the other side of the cell membrane.
30. What is the importance of active transport?
(1) allow quicker absorption of useful materials (because active transport can be done along the concentration gradient)
(2) allow absorption of minerals from the soil against the concentration gradient (Since the water potential must be higher than the root cells in order for water molecules to be able to pass into the root by osmosis, that means the mineral concentration in the soil must be lower than that inside the root cells.)
31. What is the process of phagocytosis?
(1) A pit is formed at the cell membrane or pseudopodium extends to form a leg like structure.
(2) The particle is engulfed.
(3) The particle is enclosed in a small vacuole
(4) the particle is transported into the cell
(5) The cell release enzymes to digest the particle.
32. What is the importance of phagocytosis?
(1) obtain food( e.g. amoeba)
(2) engulf and kill harmful bacteria (e.g. phagocytes)