Transport across cell membranes Flashcards
Give two ways in which pathogens can cause disease.
- (Releases) toxins;
- Kills cells / tissues.
- Accept any reference to cell / tissue damage
Ignore infecting / invading cells
Putting bee honey on a cut kills bacteria. Honey contains a high concentration of
sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills
bacteria.
- Water potential in (bacterial) cells higher (than in honey) / water
potential in honey lower (than in bacterial cells);
Q candidates must express themselves clearly - Must be comparative e.g. high WP in cell and low WP in
honey - Water leaves bacteria / cells by osmosis;
- (Loss of water) stops (metabolic) reactions.
LDL enters the liver cells (lines 3−4).
Using your knowledge of the structure of the cell-surface membrane, suggest how
LDL enters the cell.
- (Protein part of) LDL attaches to receptor
4. Goes through carrier / channel protein.
Explain how the monoclonal antibody would prevent the regulator protein from
working (lines 7−8).
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(c) Any two from:
1. (Monoclonal antibody) has a specific tertiary structure / variable region /
is complementary to regulator protein
Do not award MP1 if reference to active site.
2. Binds to / forms complex with (regulator protein)
“It” refers to monoclonal antibody in MP1 and MP2
3. (So regulator protein) would not fit / bind to the receptor / is not
complementary to receptor
Describe how the control group should have been treated.
Injection with salt solution
- Accept inject placebo in salt solution
- Otherwise treated the same.
The hydrostatic pressure falls from the arteriole end of the capillary to the venule
end of the capillary. Explain why.
Loss of water / loss of fluid / friction (against capillary lining)
(c) High blood pressure leads to an accumulation of tissue fluid. Explain how.
(c) 1. High blood pressure = high hydrostatic pressure;
2. Increases outward pressure from (arterial) end of capillary / reduces
inward pressure at (venule) end of capillary;
3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.
Allow lymph system not able to drain tissues fast enough
The water potential of the blood plasma is more negative at the venule end of the
capillary than at the arteriole end of the capillary. Explain why.
d) 1. Water has left the capillary;
2. Proteins (in blood) too large to leave capillary;
3. Increasing / giving higher concentration of blood proteins (and thus wp).
Percentage of lipid in plasma
membrane by mass.
- Divide mass of each lipid by total mass of all lipids (in that type of cell);
- Multiply answer by 100.
Suggest one advantage of the different percentage of cholesterol in red blood cells
compared with cells lining the ileum.
Red blood cells free in blood / not supported by other cells so cholesterol helps
to maintain shape;
Allow converse for cell from ileum – cell supported by others
in endothelium so cholesterol has less effect on maintaining
shape.
E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell
maintains a constant shape. Explain why.
- Cell unable to change shape;
- (Because) cell has a cell wall;
- (Wall is) rigid / made of peptidoglycan / murein.
Q6.A group of students carried out an investigation to find the water potential of potato tissue.
The students were each given a potato and 50 cm3
of a 1.0 mol dm−3 solution of sucrose.
• They used the 1.0 mol dm−3 solution of sucrose to make a series of different
concentrations.
• They cut and weighed discs of potato tissue and left them in the sucrose solutions
for a set time.
• They then removed the discs of potato tissue and reweighed them.
The table below shows how one student presented his processed results.
Concentration of sucrose solution / mol dm−3 / Percentage change in mass of potato tissue 0.15 +4.7 0.20 +4.1 0.25 +3.0 0.30 +1.9 0.35 −0.9 0.40 −3.8 (a) Explain why the data in the table above are described as processed results.
Calculations made (from raw data) / raw data would have recorded initial and final masses.
Describe how you would use the student’s results in the table above to find the
water potential of the potato tissue.
- Plot a graph with concentration on the x-axis and percentage change in
mass on the y-axis; - Find concentration where curve crosses the x-axis / where percentage
change is zero; - Use (another) resource to find water potential of sucrose concentration
(where curve crosses x-axis).
The structure of a plasma membrane is described as a fluid mosaic.
Explain why.
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Fluid = molecules move around;
Mosaic = proteins floating among phospholipids/not just phospholipids/
other molecules in it/made of different sorts of molecules;
Give two functions of proteins in plasma membranes.
Any two from Enzymes; Antigens/cell recognition/cell markers; Receptors; Carriers; Channels; Any 2 Accept active transport and facilitated diffusion for 1 mark each
By what process did the calcium ions leave the cells after 10 minutes? Use evidence from the graph to support your answer.
Active transport;
Calcium ions move against a concentration gradient/calcium ion concentration
in solution is (much) higher than concentration inside cells;
2
Describe two differences between active transport and facilitated diffusion.
Active transport against / facilitated down with concentration gradient;
Accept answers in terms of water potentials
Active transport uses ATP/energy, /facilitated doesn’t;
Reject along/across gradient
Active uses carrier (proteins), / facilitated (often) uses channel (proteins);
Explain why molecules of oxygen and carbon dioxide are able to diffuse across membranes.
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Lipid/fatty acid part of membrane is non-polar/hydrophobic;
Accept lipid/fatty acid bilayer
Oxygen and carbon dioxide small/ non-polar (molecules);
Oxygen/carbon dioxide can diffuse through/dissolve in/
get between molecules in this layer;
Down a concentration gradient;
Explain why ventilation increases the efficiency of gas exchange.
Brings more oxygen/removes carbon dioxide;
Maintains diffusion/concentration gradients;
Between alveoli and blood/capillaries;
Many different substances enter and leave a cell by crossing the cell surface membrane. Describe how substances can cross a cell surface membrane. (5)
By diffusion - substances move DOWN a concentration gradient
- Simple diffusion - through bilayer is small and/or non-polar
- Facilitated diffusion - substances diffuse though transport proteins
- By osmosis - movement of water only down a concentration gradient
- By active transport - ATP used in transporting substances against concentration gradient
- Co-transport of glucose and amino acids using Na+ ions
- Endocytosis and exocytosis - bulk transport of substances into/out of a cell
Describe how the structure of a phospholipid molecule is different from the structure of a triglyceride molecule. (2)
Phosphilipid has a phosphate ion bonded to glycerol
- Phospholipid has two fatty acids bonded to glycerol
Describe the structure of a cell membrane. (5)
- Double layer of phospholipid molecules;
- Detail of arrangement of phospholipids;
- Intrinsic proteins/protein molecules passing right through;
- Some with channels/pores;
- Extrinsic proteins/proteins only in one layer/on surface;
- Molecules can move in membrane/dynamic/membrane contains cholesterol;
- Glycocalyx/carbohydrates attached to lipids/proteins;
Describe the part played by cell surface membranes in regulating the movement of substances into and out of cells. (6)
- Non-polar/lipid soluble molecules move through phospholipid layer/bilayer;
- Small molecules/water/gases move through phospholipid layer/bilayer;
- Ions/water soluble substances move through channels in proteins;
- Some proteins are gated;
- Reference to diffusion;
- Carriers identified as proteins;
- Carriers associated with facilitated diffusion;
- Carriers associated with active transport/transport wi
Describe how proteins are arranged in a plasma membrane and the part they play in transporting substances into and out of cells. (6)
1 Some proteins pass right through membrane;
2 Some proteins associated with one layer;
3 Involved in facilitated diffusion;
4 Involved in active transport;
5 Proteins act as carriers;
6 Carrier changes shape / position;
7 Proteins form channels / pores;
8 Protein allows passage of water soluble molecules / charged particles / correct named example;
Describe the processes involved in the absorption of the products of starch digestion. (5)
Glucose moves in with sodium (into epithelial cell); Via (carrier / channel) protein / symport; Sodium removed (from epithelial cell) by active transport / sodium- potassium pump; Into blood; Maintaining low concentration of sodium (in epithelial cell) / maintaining sodium concentration gradient (between lumen and epithelial cell); Glucose moves into blood; By (facilitated) diffusion;