Topic 2 - Transport across cell membranes Flashcards
Name and describe 5 ways substances can move across the cell-surface membrane into a cell.
- water -> diffuses by osmosis, high WP to low WP
- small/non-polar molecules -> simple diffusion down conc gradient
- facilitated diffusion -> down conc gradient using protein carrier/channel
- AT -> against conc gradient via a protein carrier using ATP
- co-transport -> 2 diff substances using a protein carrier
Function of ATP hydrolase
-hydrolyses ATP auto ADP+Pi
-releasing energy stored in phospho-hydride bond
Movement of Na+ out of the cell allows absorption of glucose into the cell lining the ileum. How?
- Because this forms an Na+ conc gradient,
- so Na+ can diffuse back into the cell lining the ileum bringing glucose with it using co-transport
Describe and explain two features you’d expect to find in a cell specialised for absorption.
- high no. mitochondria
-> release ATP can be used for AT - more protein channels
-> so faster rate of absorption
The movement of substances across cell membranes is affected by membrane structure. Describe how.
- phospholipid bilayer -> only lipid-soluble, small, non-polar molecules can pass through
-> prevents lipid insoluble, large, polar substances passing - carrier proteins allow AT
-channel/carrier proteins allow facilitated diffusion + co-transport
-membrane SA determines how much diffusion
Rate of uptake of monosaccharides between concentrations
- Monosaccharides taken up by facilitated diffusion
- Rate of uptake proportional to external conc of monosaccharides
- when plateaus if conc still inc then all channel proteins in use
How is a graph of mono glycerine uptake evidence for them being lipid soluble.
- rate of uptake does not level off so diffusion always occurring
- lipid-soluble molecules can dissolve straight through membrane
Method for osmosis potato practical - consider controlled varibles
- Weigh potato cubes before buying and weigh them every 10 minutes
- dry cubes by blotting with paper towel
- control temp by…
Why is it important in an osmosis-temp related practical measuring pigments (eg. beetroot) to put the same volume of water in each test tube.
- changes in water volume alters conc of pigment
- allows results from diff temps to be compared
Suggest how inc temperature may cause release od red pigment from beetroot.
- Damage to membrane -> membrane proteins denatured
- inc fluidity of phospholipid bilayer -> more dye released
Suggest and explain two ways a cell-surface membrane of cells in an area where nutrients are needed to be transported rapidly may be adapted.
- Extra protein channels -> for facilitated diffusion
- folded membrane -> larger surface area
Suggest how a carrier protein transports one sodium ion into the cell in exchange for one H+ out of the cell.
- Cotransport
- using ATP hydrolysis
- Na+ and H+ bind to protein
- protein changes shape allowing the ions to move across the membrane
Explain how high absorption of salt from the diet can result in higher conc salt in blood plasma and therefore build-up of tissue fluid.
- inc salt means lower WP of tissue fluid
- less water returns to capillary by osmosis at venule end
Compare and contrast the processes by which water and inorganic ions enter cells
- both move down conc gradient (when ions facilitated diffusion)
- both move through protein channels in membranes
- ions can move against concrete gradient if AT used
Contrast processes of facilitated diffusion and AT.
FD
- channel/carrier proteins
- no ATP
- down conc grad
AT
- carrier proteins only
- use ATP
- against conc grad
Uptake of chloride ions on a graph with vs without respiration inhibitor
With inhibitor
- slower initial uptake means only diffusion
- if levels off -> same conc inside + outside cells
Without inhibitor
- faster initial uptake -> diffusion and AT
- no level off -> uptake against gradient
WHY?
ATP released in respiration for AT
