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AQA A-Level Biology A > Pack 3 - Transport Across Membranes > Flashcards

Pack 3 - Transport Across Membranes Flashcards

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1
Q

What are the 2 functions of the cell surface membrane?

A

Control passage of molecules in and out of cells/organelles

Forms boundaries between organelles and the cytoplasm

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2
Q

What are the 5 main components of a plasma membrane?

A 
Phospholpids
Proteins
Cholesterol
Glycoproteins
Glycolipids
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3
Q

What is the difference between an intrinsic and and extrinsic protein?

A

Extrinsic - sits on the outside or is slightly embedded

Intrinsic - runs through the whole membrane

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4
Q

What are the four molecules that make up a phospholipid?

A

Phosphate group
Glycerol
2 fatty acids

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5
Q

What are the bonds in the phospholipid called?

A

Ester bonds

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6
Q

Which end of a phospholipid is δ+?

A

Head (phosphate group)

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7
Q

How do phospholipids line up when they form a membrane?

A

o o
|| ||
|| ||
o o

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8
Q

What are the 6 functions of proteins within the plasma membrane?

A

Structural support

Help cells attach to each other

Channel proteins for water-soluble substances in facilitated diffusion

Carrier proteins for facilitated diffusion

Carrier proteins for active transport

Cell-surface receptors for
•eg. hormones
•cell recognition eg glucagon receptors in the liver (eg. hepatitis)

( )

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9
Q

What are the 4 functions of cholesterol?

A

Add strength to the membrane

Reduce movement of other molecules

Make the membrane less fluid at high temperatures

Prevent leakage of water and dissolved ions (through perforations)

0°oO0°o0

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10
Q

What are the 3 functions of glycoproteins?

A

Recognition sites - cell surface receptors for specific chemicals eg. neurotransmitters and hormones

Help cells attach to each other forming tissues

Allow cells to recognise each other eg. lymphocytes can recognise any organism’s own cells

Y
( )

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11
Q

What are the 3 functions of glycolipids?

A

Act as recognition sites - cell surface receptors for specific chemicals eg. ABO blood system

Help stability of the membrane

Help cells attach to each other forming tissues

Y
o
||

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12
Q

Explain the name fluid-mosaic model

A

Fluid
Molecules can move relative to each other

The membrane is flexible and constantly changing shape

Mosaic
Like the tiles in a mosaic, the proteins embedded in the phospholipid vary in size, shape and pattern

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13
Q

Why can’t most substances pass through the plasma membrane?

A

Not lipid soluble eg. water
Too large eg. glucose
Polar eg. Na+

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14
Q

List some properties of substances that can pass directly through the plasma membrane

A

Lipid-soluble eg. steroid hormones
Small molecules eg. O2
Non-polar molecules eg. CO2

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15
Q

Define passive (in exchange of substances)?

A

Does not require metabolic energy

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16
Q

Define active (in exchange of substances)?

A

Requires metabolic energy in the form of ATP

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17
Q

Define diffusion

A

The net movement of molecules or ions
From a region where they are highly concentrated to a region where they are less concentrated
Until evenly distributed

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18
Q

Is diffusion active or passive and why?

A

Passive as molecules move using their own kinetic energy therefore it does not require metabolic energy in the form of ATP

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19
Q

Why is meant by net flow?

A

The overall flow. Molecules of all substances will move in both directions.

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20
Q

When will net flow in diffusion stop?

A

When dynamic equilibrium is reached (there being equal concentrations on both sides)

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21
Q

What 6 factors affect the rate of diffusion?

A

1 Temperature

2 Difference in concentration gradient

3 Distance over which diffusion occurs

4 Area over which diffusion takes place

5 Nature of any structure across which diffusion occurs

6 Size of the diffusing molecule

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22
Q

How will temperature affect the rate of diffusion?

A

An increase in temperature will increase the kinetic energy of molecules and will therefore increase the rate of diffusion

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23
Q

How does a larger/steeper concentration gradient affect the rate of diffusion?

A

It will be faster

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24
Q

If the exchange surface for diffusion is relatively thick, what will happen to the diffusion rate?

A

The greater the distance, the slower the rate of diffusion

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25
Q

As the area over which diffusion takes place what will happen to the diffusion rate?

A

The greater the surface area over which diffusion takes place, the faster the diffusion rate

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26
Q

Why should a lipid-soluble molecule be able to get through a selectively permeable membrane more quickly?

A

Cell surface membranes are made primarily of lipids which allow lipids to pass through the membrane, between the phospholipids

27
Q

Why should a small molecule be able to enter a cell faster than a large one?

A

Small molecules can pass through pores more easily than larger molecules

28
Q

What is Fick’s law?

A

surface area × conc. distance
Diffusion rate ∝_____________________________

                                diffusion path length

Big × big
Small = Big

29
Q

Why does facilitated diffusion require?

A

Transport or channel proteins

30
Q

Give 4 properties of channel proteins and their use

A

Form water-filled hydrophilic channels across the membrane

Allow specific water soluble ions to pass through

Selective - only open in presence of a specific ion

The binding of specific ions changes the shape of the protein allowing the ions to pass

31
Q

Give 4 properties of carrier proteins and their use

A

Span the plasma membrane

A molecule eg. glucose (with a specific, complementary shape) binds to the carrier proteins

This causes the protein to change shape

The molecule is released on the opposite side of the membrane

32
Q

How would increased number of protein channels/carrier proteins in the same area of membrane affect the rate of diffusion?

A

It would increase as more can be passed through the membrane at one time

33
Q

Define osmosis

A

The passage of water
Where it has a higher water potential to a region where it has a lower water potential
Through a selectively-permeable membrane

34
Q

Is osmosis a specialised form of diffusion?

A

Yes

35
Q

What is a solute?

A

Something that dissolves in a solvent to form a solution

36
Q

What is the water potential of pure water?

A

0

37
Q

Which would water move from and to?

  • 300kPa
  • 200kPa
A

-200 to -300 as there is a higher water potential in -200

38
Q

Which is more concentrated?

  • 300kPa
  • 200kPa
A

-300 as it has a lower water potential (further from pure water)

39
Q

What will happen if you place RBCs in pure water?

A 
They will lyse
Cell Ψ < H20 Ψ
Net flow of water into the cell
By osmosis
To even the Ψs
Which will keep filling the cells until they burst
40
Q

What happens if you place RBCs in strong NaCl solution?

A 
They will shrivel
NaCl Ψ < Cell Ψ
Net flow of water out of the cell
By osmosis
To even the Ψs
Which will shrivel the cells
41
Q

What happens if you place plant cells in pure water?

A 
They will become turgid but not lyse
Due to strong cellulose cell wall
Cell Ψ < H20 Ψ
Net flow of water into the cell
By osmosis
To even the Ψs
Protoplast swells until pressing against the cell wall
Cell wall is rigid and cannot expand more
Therefore resists entry of more water
42
Q

What happens if you place plant cells in strong NaCl solution?

A 
They will become plasmolysed
NaCl Ψ < Cell Ψ
Net flow of water out of the cell/protoplast
By osmosis
To even the Ψs
Causing cell to become plasmolysed
43
Q

Define plasmolysis

A

When the protoplast shrivels due to a loss of water from the cell

44
Q

Describe incipient plasmolysis

A

When the corners of the vacuole are pulling away from the membrane

(The first sign of plasmolysis hence incipient [slight])

45
Q

Define hypertonic (solution)

A

When the solute concentration is greater outside the cell than inside the cell

46
Q

Define hypotonic (solution)

A

When the solute concentration is greater inside the cell than outside the cell

47
Q

Define isotonic (solution)

A

When the solute concentration is the same outside of the cell as inside the cell

48
Q

Which way will the water flow?

-500kPa -1100kPa

A

-500kPa -> -1100kPa

49
Q

Define active transport

A

Movement of molecules/ions into or out of a cell
From a region of lower concentration to a region of higher concentration
Using metabolic energy and carrier molecules (protein pump/carrier protein)

50
Q

Give an example of active transport in the human body

A

The sodium - potassium pump

51
Q

Explain the sodium - potassium pump

A

1) Na+ ions bind to specific receptor sites on the carrier protein
2) ATP binds to the protein and splits into ADP and a phosphate molecule
3) Energy is released the phosphate molecule remains bound to the carrier
4) The carrier protein changes shape. Na+ is released on the opposite side of the membrane
5) K+ ions now bind to their receptor sites. This causes the carrier protein to change shape again
6) K+ and phosphate are released on the original side of the membrane leaving the carrier protein ready to pick up more Na+

52
Q

What are the similarities between active transport and facilitated diffusion?

A

Both use protein carriers

Specifically binding sites for the molecules or ions being transported are present

53
Q

What are the differences between active transport and facilitated diffusion?

A

FD AT
High -> Low Low -> High

No metabolic energy needed ATP needed

54
Q

How do microvilli help to maximise absorption in the small intestine?

A

They increase the surface area

55
Q

What is starch broken down into in the small intestine?

A

Amylase Maltase

Starch -> Maltose -> a Glucose

56
Q

What are proteins broken down into

A 
Amino acids
(Using protease or trypsin)
57
Q

After a meal, will the concentration of molecules/ions be higher or lower in the lumen of the ileum than in the blood?

A

Higher in lumen

58
Q

What role does the circulatory system play in maintaining the concentration gradient between the lumen and the blood?

A

Carries away products of digestion

59
Q

Over time what will happen to the relative concentrations of glucose etc. in the lumen of the ileum and the blood?

A

Will reach equilibrium/lower in ileum

60
Q

Explain co transport across the wall of the ileum

A

1) Na+ ions are pumped out of the cell into the blood by the sodium potassium pump. This requires energy from ATP and is therefore active transport
2) This maintains a concentration gradient of sodium ions from the blood (high) to the cells/lumen (low)?
3) Sodium ions diffuse into the cell along their concentration gradient through the carrier protein. For this to happen glucose also has to bind to the protein and is therefore brought in with the sodium ions.
4) Glucose molecules pass into the blood plasma by diffusion using another type of carrier protein.

61
Q

In co transport across the wall of the ileum, is glucose moving into the cell down its concentration gradient or against it?

A

Down

62
Q

In co transport across the wall of the ileum, what’s effectively causes the movement of glucose into the cell?

A

Facilitated diffusion

63
Q

What usually happens at the start of movement of ions and molecules in and out of cells?

A

Active transport / ATP usage

AQA A-Level Biology A (5 decks)

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