Transport across cell membranes Flashcards

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1
Q

Give two ways in which pathogens can cause disease.

A
  1. (Releases) toxins;
  2. Kills cells / tissues.
  3. Accept any reference to cell / tissue damage
    Ignore infecting / invading cells
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2
Q

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.

A
  1. Water potential in (bacterial) cells higher (than in honey) / water
    potential in honey lower (than in bacterial cells);
    Q candidates must express themselves clearly
  2. Must be comparative e.g. high WP in cell and low WP in
    honey
  3. Water leaves bacteria / cells by osmosis;
  4. (Loss of water) stops (metabolic) reactions.
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3
Q

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.

A
  1. (Protein part of) LDL attaches to receptor

4. Goes through carrier / channel protein.

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4
Q

Explain how the monoclonal antibody would prevent the regulator protein from
working (lines 7−8).
………………………………………..

A

(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

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5
Q

Describe how the control group should have been treated.

A

Injection with salt solution

  1. Accept inject placebo in salt solution
  2. Otherwise treated the same.
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6
Q

The hydrostatic pressure falls from the arteriole end of the capillary to the venule
end of the capillary. Explain why.

A

Loss of water / loss of fluid / friction (against capillary lining)

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7
Q

(c) High blood pressure leads to an accumulation of tissue fluid. Explain how.

A

(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

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8
Q

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.

A

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).

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9
Q

Percentage of lipid in plasma

membrane by mass.

A
  1. Divide mass of each lipid by total mass of all lipids (in that type of cell);
  2. Multiply answer by 100.
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10
Q

Suggest one advantage of the different percentage of cholesterol in red blood cells
compared with cells lining the ileum.

A

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.

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11
Q

E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell
maintains a constant shape. Explain why.

A
  1. Cell unable to change shape;
  2. (Because) cell has a cell wall;
  3. (Wall is) rigid / made of peptidoglycan / murein.
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12
Q

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.
A
Calculations made (from raw data) / raw data would have recorded initial and final
masses.
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13
Q

Describe how you would use the student’s results in the table above to find the
water potential of the potato tissue.

A
  1. Plot a graph with concentration on the x-axis and percentage change in
    mass on the y-axis;
  2. Find concentration where curve crosses the x-axis / where percentage
    change is zero;
  3. Use (another) resource to find water potential of sucrose concentration
    (where curve crosses x-axis).
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14
Q

The structure of a plasma membrane is described as a fluid mosaic.
Explain why.
___________________________________________________________________

A

Fluid = molecules move around;
Mosaic = proteins floating among phospholipids/not just phospholipids/
other molecules in it/made of different sorts of molecules;

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15
Q

Give two functions of proteins in plasma membranes.

A
Any two from
Enzymes;
Antigens/cell recognition/cell markers;
Receptors;
Carriers;
Channels;
Any 2
Accept active transport and facilitated diffusion for 1 mark each
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16
Q

By what process did the calcium ions leave the cells after 10 minutes? Use evidence from the graph to support your answer.

A

Active transport;
Calcium ions move against a concentration gradient/calcium ion concentration
in solution is (much) higher than concentration inside cells;
2

17
Q

Describe two differences between active transport and facilitated diffusion.

A

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);

18
Q

Explain why molecules of oxygen and carbon dioxide are able to diffuse across membranes.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________.

A

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;

19
Q

Explain why ventilation increases the efficiency of gas exchange.

A

Brings more oxygen/removes carbon dioxide;
Maintains diffusion/concentration gradients;
Between alveoli and blood/capillaries;

20
Q

Many different substances enter and leave a cell by crossing the cell surface membrane. Describe how substances can cross a cell surface membrane. (5)

A

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
21
Q

Describe how the structure of a phospholipid molecule is different from the structure of a triglyceride molecule. (2)

A

Phosphilipid has a phosphate ion bonded to glycerol

- Phospholipid has two fatty acids bonded to glycerol

22
Q

Describe the structure of a cell membrane. (5)

A
  1. Double layer of phospholipid molecules;
  2. Detail of arrangement of phospholipids;
  3. Intrinsic proteins/protein molecules passing right through;
  4. Some with channels/pores;
  5. Extrinsic proteins/proteins only in one layer/on surface;
  6. Molecules can move in membrane/dynamic/membrane contains cholesterol;
  7. Glycocalyx/carbohydrates attached to lipids/proteins;
23
Q

Describe the part played by cell surface membranes in regulating the movement of substances into and out of cells. (6)

A
  1. Non-polar/lipid soluble molecules move through phospholipid layer/bilayer;
  2. Small molecules/water/gases move through phospholipid layer/bilayer;
  3. Ions/water soluble substances move through channels in proteins;
  4. Some proteins are gated;
  5. Reference to diffusion;
  6. Carriers identified as proteins;
  7. Carriers associated with facilitated diffusion;
  8. Carriers associated with active transport/transport wi
24
Q

Describe how proteins are arranged in a plasma membrane and the part they play in transporting substances into and out of cells. (6)

A

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;

25
Q

Describe the processes involved in the absorption of the products of starch digestion. (5)

A
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;