SUMMARY QUESTIONS Flashcards
State the overall function of the cell-surface membrane
To control the movement of substances in and out the cell
State which end of the phospholipid molecules lies towards the inside of the cell-surface membrane
Hydrophobic tail
State through which molecules in the CSM each of the following are likely to pass in order to get in or out of a cell
A: a molecule that is soluble in lipids
B: a mineral ion
A: phospholipid
B: protein (carrier or channel)
From your knowledge of the CSM, suggest 2 properties that a drug should possess if its to enter a cell rapidly
- lipid-soluble
- small in size
- have no electrical charge (or if it does = charge should be opposite to that on the protein channel)
State factors that affect the rate of diffusion
- concentration gradient
- surface area over which diffusion takes place
- thickness of exchange surface
- temperature
Contrast facilitated diffusion and diffusion
Facilitated diffusion only occurs at channels on the membranes where there are special protein carrier molecules
Explain why facilitated diffusion is a passive process
- there is no ATP from respiration use din the process
- the only energy is the in-built (kinetic) energy of the molecules themselves
Glucose molecules are transported into cells through the pores in the proteins that span the phospholipid bilayer. Explain why they don’t pass easily through the phospholipid bilayer
- Only lipid-soluble substances diffuse across
- water-soluble soluble substances like glucose diffuse only very slowly
List 2 changes to the structure of CSMs that would increase the rate at which glucose is transported into a cell
- increase its surface area with microvilli
- more proteins with pores that span the phospholipid bilayer
- (note that thickness of CSM membrane doesn’t vary to any degree)
Oxygen is required by cells for respiration. This diffuses into the blood through the epithelial layers of the alveoli and blood capillaries. Calculate by how much each of the following changes would increase or decrease the rate of diffusion of oxygen:
A - the SA of the alveoli is doubled
B - the SA of the alveoli is halved and the oxygen concentration gradient is doubled
C - the oxygen concentration gradient is halved and the total thickness of the epithelial layers is doubled
D - The oxygen concentration of the blood is halved and the carbon dioxide concentration of the alveoli is doubled
A - x2
B - no change
C - 1/4
D - x2 (the CO2 concentration is irrelevant)
Explain what is meant by a selectively permeable membrane
A membrane that is permeable to water molecules (and a few other small molecules) but not to larger molecules
Under standard conditions of pressure and temperature, what is the water potential of pure water
0
Four cells have the following water potentials:
Cell A = -200 kPa
Cell B = -250 kPa
Cell C = -100 kPa
Cell D = -150 kPa
Determine the order in which the cells have to be placed for water to pass from one cell to the next if they are arranged in a line
C, D, A, B
Explain why an animal cell placed in pure water bursts while a plant cell placed in pure water doesn’t
- Both cells have a lower water potential than pure water and so water enters them by mitosis
- the animal cell is surrounded only by a thin CSM and so it swells until it bursts
- the plant cell is surrounded by a rigid cellulose cell wall
- Assuming the cell is turgid, water cannot enter as the cellulose cell wall prevents the cell expanding and hence it bursting
Plant cells that have a water potential of -600 kPa are placed in solutions of different water potentials. Determine in each of the following cases whether, after 10 mins, the cells would be turgid, plasmolysed or at incipient plasmolysis
A - Solution A = -400 kPa
B - Solution B = -600 kPa
C - solution C = -900 kPa
D - Solution D = pure water
A = turgid
B = incipient plasmolysis
C = plasmolysed
D = turgid
