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Biology > 4. TRANSPORT ACROSS MEMBRANES > Flashcards

4. TRANSPORT ACROSS MEMBRANES Flashcards

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1
Q

State the function of the cell-surface membrane

A

Separates two aqueous environments. Controls what goes into and out of the cell.

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2
Q

Describe the functions of membranes within cells

A

Membranes around organelles divide the cell into different compartments. They act as a barrier between organelles and the cytoplasm.

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3
Q

Define the term hydrophobic

A

Dissolves in organic solvents (does not dissolve in aqueous solutions)

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4
Q

Define the term hydrophilic

A

Dissolves in aqueous solutions

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5
Q

Explain why the cell-surface membrane is referred to as the fluid-mosaic model

A

Mosaic because they contain phospholipids and proteins, and fluid because the proteins move within the bilayer.

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6
Q

Describe the structure of the phospholipid bilayer

A

The hydrophillic head face outwards, and the hydrophobic tails face towards each other

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7
Q

Describe the function of cholesterol

A

Cholesterol affects the fluidity and increases the stability of the CSM.

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8
Q

Name the two types of proteins that exist within the CSM

A

Intrinsic and extrinsic

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9
Q

How would you recognise extrinsic proteins on a diagram of the CSM?

A

Extrinsic proteins are embedded in the outside of the bilayer

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10
Q

Describe the two functions of extrinsic proteins

A

Receptors and antigens

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11
Q

What are glycoproteins?

A

A protein with a carbohydrate group attached

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12
Q

What are glycolipids?

A

A lipid with a carbohydrate group attached

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13
Q

How would you recognise intrinsic proteins on a diagram of the CSM?

A

Intrinsic proteins are embedded within and span the CSM

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14
Q

Give two examples of intrinsic proteins

A

Carrier and channel proteins

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15
Q

How would you recognise a channel protein on a diagram of the CSM

A

It has a continuous pore all the way through

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16
Q

How do channel proteins transport substances?

A

They provide a hydrophilic passageway through the CSM

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17
Q

Why are channel proteins specific?

A

Because they are different sizes, charges and shapes, depending on the size and shape and charge of the ion or molecule

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18
Q

How would you recognise a carrier protein on a diagram of the CSM

A

It will be closed at one end

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19
Q

How do carrier proteins transport substances?

A

The molecule first binds with the carrier protein. This causes the carrier protein to change shape, transporting the molecule across the membrane. ​

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20
Q

Why are carrier proteins specific?

A

Each carrier protein is specific to one molecule or ion because it has a specific tertiary structure, which means it can bind to molecules with a specific shape and charge.​

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21
Q

Name the channel protein water moves through by osmosis

A

Aquaporins

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22
Q

Name the two types of diffusion

A

Simple diffusion and facilitated diffusion

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23
Q

Why is diffusion referred to as a passive process?

A

It does not require ATP

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24
Q

Define simple diffusion

A

Diffusion is the net movement of molecules or ions from an area of high concentration to an area of low concentration

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25
Q

How will lipid-soluble substances travel through the CSM?

A

Simple diffusion through the phospholipid bilayer

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26
Q

Define facilitated diffusion

A

Diffusion is the net movement of molecules or ions from an area of high concentration to an area of low concentration through channel or carrier proteins

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27
Q

Why can small polar molecules and ions not pass through the phospholipid bilayer by simple diffusion?

A

They are charged

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28
Q

How will small polar molecules and ions travel through the CSM?

A

Facilitated diffusion through channel proteins

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29
Q

Why can large molecules not travel through the phosphoilipid bilayer by simple diffusion?

A

They are too large

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30
Q

How will large molecules and ions travel through the CSM?

A

Facilitated diffusion through carrier proteins

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31
Q

State the factors that affect the rate of simple diffusion

A

Surface area, concentration gradient, temperature

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32
Q

State the factors that affect the rate of facilitated diffusion

A

Surface area, concentration gradient, temperature, number of channel / carrier proteins

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33
Q

Describe the effect of concentration gradient on rate of diffusion

A

The higher the concentration gradient, the faster the rate of diffusion

34
Q

Describe the effect of temperature on rate of diffusion

A

As temperature increases, rate of diffusion increases

35
Q

Describe the effect of surface area on rate of diffusion

A

The larger the surface area (e.g of the cell-surface membrane), the faster the rate of diffusion

36
Q

When is the rate of facilitated diffusion directly proportional to the concentration gradient?

A

If the number of channel / carrier proteins is not limiting

37
Q

How can you tell from a graph that the number of channel / carrier proteins has become a limiting factor of facilitated diffusion?

A

The line (rate of transport) starts to plateau

38
Q

Describe the other reason a graph would plateau

A

If it’s a graph of concentration, and equilibrium has been reached

39
Q

Define solute

A

The component in a solution that is dissolved in the solvent.

40
Q

Define solvent

A

A liquid that solutes are dissolved in.

41
Q

Define solution

A

A solute dissolved in a solution.

42
Q

Define water potential

A

The potential of water to move from one area to another

43
Q

Describe the effect of solute on water potential

A

As solute increases, water potential decreases / it becomes more negative.

44
Q

State what an isotonic solution is

A

Two solutions have the same water potential (same concentration)

45
Q

State what a hypotonic solution is

A

A solution has a lower concentration, and therefore a higher water potential

46
Q

State what a hypertonic solution is

A

A solution has a higher concentration, and therefore a lower water potential

47
Q

State the water potential of pure water

A

Zero

48
Q

Water will always move down a water potential gradient. What does this mean?

A

It moves from an area of higher water potential to an area of low water potential

49
Q

Describe what selectively permeable mean

A

Allows some substances through, but not others

50
Q

Define osmosis

A

The movement of water down a water potential gradient over a selectively permeable membrane

51
Q

Give 4 factors that affect the rate of osmosis

A

Water potential gradient, temperature, surface area, number of aquaporins

52
Q

Describe what can happen to an animal cell if too much water enters it by osmosis

A

The cell can swell and burst (lysis)

53
Q

Describe what can happen to an animal cell if too much water leaves it by osmosis

A

The cell can shrink and crenate

54
Q

Describe what can happen to a plant cell if too much water enters it by osmosis

A

It swells and becomes too turgid

55
Q

Describe what can happen to a plant cell if too much water leaves it by osmosis

A

It will shrink and become plasmolysed. The cell will completely pull away from the cell wall.

56
Q

Explain why animal cells placed in pure water bursts while a plant cell does not

A

Animal cell only have cell membranes, whereas plant cells have a cell wall made of cellulose which gives strength and support.

57
Q

State what turgid means

A

Swollen

58
Q

State what plasmolysed mean

A

When cells lose water in hypertonic solutions, the cytoplasm shrinks and the cell membrane pulls away from the cell wall.

59
Q

State how to find the point at which the water potential of the cell is equal to the water potential of the solution

A

The point where the curve intersects the x axis

60
Q

How are the cells of aquatic organisms adapted to their surroundings?

A

They contain solutes to make them isotonic with their surroundings

61
Q

Define active transport

A

The movement of molecules or ions from a region of a lower concentration to a region of higher concentration using ATP through carrier proteins.

62
Q

State why active transport is an active process

A

Because it requires energy in the form of ATP

63
Q

State one way in which active transport is similar to facilitated diffusion

A

It uses carrier proteins

64
Q

Describe the two main differences between active transport and facilitated diffusion

A

Active transport moves solutes from low to high concentration, whereas facilitated diffusion moves solutes from high to low concentration.
Active transport uses ATP as a form of energy source, whereas facilitated diffusion is a passive process.

65
Q

Give an example of a type of carrier protein

A

Co-transporters

66
Q

State the factors affecting the rate of active transport

A

The number of carrier proteins.
The rate of respiration in the cell and the availability of ATP. Temperature.

67
Q

Describe three ways you can recognise graphs of active transport

A

The rate of uptake will be faster, total uptake will be higher, the concentration on one side can fall to zero (shows uptake against a concentration gradient)

68
Q

Describe how glucose is absorbed in the ileum

A

Glucose enters the ileum epithelium with sodium ions by co-transport

69
Q

State the molecule that provides energy for active transport

A

ATP

70
Q

How are cells adapted to carry out active transport

A

They have a lot of mitochondria to produce more ATP

71
Q

By which method of molecular transport is glucose transported into the blood

A

Co-transport (into the ileum epithelial cells. Facilitated diffusion into the blood)

72
Q

What is the only active stage of the co-transport of glucose

A

Na+ are actively transported out of the epithelial cells and into the blood

73
Q

What is the purpose of actively transporting Na+ from the epithelial cells into the blood?

A

It reduces the concentration of Na+ in the epithelial cell so it is lower than the lumen

74
Q

What occurs because of the Na+ concentration gradient between the lumen and the epithelial cells?

A

Na+ and glucose are co-transported from the ileum lumen into the epithelial cell by facilitated diffusion down a concentration gradient

75
Q

In the co-transport of Na+ and glucose, which one travels down a concentration gradient, and which one travels up a concentration gradient?

A

Na+ travels down, and glucose travels up

76
Q

Describe the difference between villi and microvilli

A

Villi are projections of the epithelial tissue or an organ, whereas microvilli are projections of the cell membrane

77
Q

How does the presence of villi and microvilli in the ileum affect the rate of co-transport?

A

Villi and microvilli increase the rate of co-transport, because the surface area is increased

78
Q

What is the function of the colon (large intestine)?

A

To absorb water

79
Q

Name two conditions that affect the uptake of water by the colon

A

Diarrhea and constipation

80
Q

Diarrhea is treated by drinking a salt solution. These salts are absorbed by the colon cells. Describe the effect on the uptake of water by the colon.

A

The salts would decrease the water potential of the colon cells. More water would move by osmosis from the faeces into the colon cells, down a water potential gradient.

81
Q

Constipation is treated by drinking a salt solution. These salts remain in the lumen of the colon. Describe the effect on the uptake of water by the colon.

A

The salts would decrease the water potential of the faeces. More water would move by osmosis from the colon cells into the faeces, down a water potential gradient.

82
Q

What effect would this salt solution have on the faeces?

A

It would soften them.

Biology (26 decks)

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