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Biology need to knows⚠️ > Cell membranes & Transport > Flashcards

Cell membranes & Transport Flashcards

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1
Q

The cell membrane Is made up almost entirely of…

A

Proteins and phospholipids

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2
Q

Why are phospholipids important components of cell membranes?

A
  • Phospholipids can form bilayers
  • Inner layer has the hydrophilic heads pointing outwards
  • Outer layer as the hydrophobic tails pointing inwards
  • the phospholipid component of a membrane allows lipid-soluble molecules across but not water soluble molecules
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3
Q

What are extrinsic proteins?

A

They are on either side of the bilayer. They provide structural support and form recognition sites by identifying cells and receptor sites for hormone attachment

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4
Q

What are intrinsic proteins?

A

Extend across both layers of phospholipid bilayers. Some of these are carriers, transporting water soluble substances across and others allow active transport of ions across by forming channels

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5
Q

Who proposed the fluid mosaic model?

A

Singer and Nicolson (1972)

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6
Q

Why is the model called ‘fluid mosaic’?

A
  • the individual phospholipid molecules can move within a layer (fluid)
  • the proteins embedded in the model vary in shape, size and pattern (mosaic)
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7
Q

What does cholesterol in the membrane help with?

A

Stability, fluidity and rigidity

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8
Q

What is the function of glycoproteins?

A

Cell-cell recognition/communication

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9
Q

How does lipid soluble substances get across the membrane?

A
  • Small molecules e.g. oxygen and carbon dioxide dissolve in the phospholipid and diffuse across the membrane
  • the phospholipid layer is hydrophobic so lipid soluble molecules move through the cell membrane more easily than water soluble ones
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10
Q

How does water soluble substances get across the membrane?

A
  • glucose, polar molecules and ions cannot redily through the phospholipids and must pass through intrinsic protein molecules which form water filled channels across the membrane
  • as a result the cell surface membrane is selectively permeable to water and some solutes
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11
Q

Simple diffusion is an examle of what kind of transport

A

Passive transport

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12
Q

Define diffusion

A

The movement of molecules or ions from a region of high concentration to a region of low concentration down a concentration gradient until they are equally distributed

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13
Q

What is the rate of diffusion affected by?

A
  • the concentration gradient (the greater the difference in concentration of molecules in two areas the more molecules diffuse in a given time
  • the thickness if the exchange surface or distance of travel over which diffusion takes place (the thinner the membrane or the shorter the distance the more molecules diffuse in a given time)
  • the surface area of the membrane (the larger the area the more molecules have room to diffuse across in a given time
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14
Q

How can the rate of diffusion be Calculated?

A

Surface area x difference in concentration ÷ length of diffusion path

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15
Q

What other factors might affect the rate of diffusion?

A
  • the size of the diffusing molecule (smaller molecules have more kinetic energy so they diffuse faster than larger molecules)
  • the nature of the diffusing molecules (fat soluble/non-polar molecules diffuse faster than water soluble/ polar molecules
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16
Q

What is facilitated diffusion?

A
  • Ions and molecules such as glucose can not pass through the cell membrane because they are relatively insoluble in the phospholipid bilayer
  • facilitated diffusion is a special form of diffusion that allows movement of these molecules across a membrane
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17
Q

Where does facilitated diffusion occur on the membrane?

A

-Where there are transport protein molecules

Their number and availability limit the rate of facilitated diffusion

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18
Q

Is facilitated diffusion a passive process or does it require energy?

A

It is a passive process however it does require transoort proteins

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19
Q

What are channel proteins and what do they do?

A
  • channel protein are molecules with pores lined with polar groups
  • as the channels are hydrophilic ions, being water soluble, can pass through
  • the channels open and close according to the needs of the cell
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20
Q

What are carrier proteins and what do they do?

A
  • carrier proteins allow diffusion of large polar molecules such as sugars and amino acids across the membrane
  • a molecule attaches to its binding site on the carrier protein
  • the carrier protein changes shape and releases the molecule on the other side of the membrane
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21
Q

Why does the rate of uptake of amino acids plateau?

A

The protein carriers have become occupied and their number has become limiting

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22
Q

What is active Transport?

A

An energy requiring process in which ions and molecules are moved across membranes against a concentration gradient

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23
Q

Featured of active transport:

A
  • Ions and molecules are moved from a lower to a higher concentration gradient
  • the process requires energy from ATP (anything that affects respiration will affect active transport)
  • the process occurs through intrinsic carrier proteins spinning through membrane
  • the rate is limited by then number and availability of carrier proteins
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24
Q

Name some processes involving active transport

A
  • muscle contraction
  • nerve impulse transmission
  • reabsorbtion of glucose in the kidneys
  • mineral uptake into plant root hairs
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25
Q

How does active uptake of ions or molecules occur?

A

1) the molecule or ion combines with a specific carrier protein on the outside of the membrane
2) ATP transfers a phosphate group to the carrier protein on the inside of the membrane
3) the carrier protein changes shape and Carries the molecule or ion across the membrane to the inside of the cell
4) then molecule/ion is released into the cytoplasm
5) the phosphate ion is released from the carrier molecule back to the cytoplasm and recombines with ATP to form ADP
- The carrier protein returns to its original shape

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26
Q

The higher the concentration differences across a membrane…

A

The greater the rate of uptake

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27
Q

The graph shows that the rate of uptake is reduced with the addition of a respiratory inhibitor, what does it Suggest?

A

That the process requires ATP

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28
Q

Name a respiratory inhibitor and what it does

A

Cyanide is a respiratory inhibitor which will present aerobic respiration and the production of ATP in the mitochondria

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29
Q

What is co-transport?

A

A type of facilitated diffusion that brings molecules and ions into cells together on the same transport protein molecule

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30
Q

How does co-transport work?

A

1) A glucose molecule and two sodium ions outside the cell attach to a carrier protein in the cell membrane
2) the carrier protein changes shape and deposits the glucose molecule and the sodium ions inside the cell
3) the glucose molecule and sodium ions separately diffuse through the cell to the opposite membrane
4) the glucose passes into the blood by facilitated diffusion and sodium ions are carried by active active transport

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31
Q

Define osmosis

A

The movement of water molecules from an area of higher water potential to lower water potential across a water potential gradient

32
Q

What is water potential measured in?

A

Kilopascals (KPa)

33
Q

Pure water had a water potential of…

A

Zero

34
Q

What happens why solutes are added to pure water

A
  • tends to bring water molecules in
  • as the force pulls inwards it has a negative sign and so the addition of a solute to pure water lowers the water potential and gives it a negative value
35
Q

What happens to water molecules when there is a high concentration of solutes?

A

The more strongly water molecules are pulled in

the lower the water potential

36
Q

Where there is a high concentration of water molecules water molecules have a high potential…

A

Energy because they are free to move

37
Q

In a solution water molecules are weakly bound to the solute so…

A

They are free to move

the system has a lower potential energy

38
Q

What Is the pulling force that the water molecules are experiencing?

A

External water molecules, with higher potential energy will move down an energy gradient to the lower potential energy.
This is the pulling force they experience which is the osmotic pull inwards

39
Q

A more concentrated solution has…

A

Even fewer free water molecules

Consequently, the pull on water molecules is greater so the water potential is more negative

40
Q

What is solute potential?

A
  • The water potential is related only to the concentration of then solution and so it could be called (solute potential)
  • solute potential measures how easily water molecules move out of a solution
  • the more solute present the more tightly water molecules are held the lower the tendency of water molecules to move out
41
Q

What is pressure potential?

A
  • Water entering a plant cell by osmosis expands the vacuole and pushes the cytoplasm against the wall
  • the cell wall can only expand a little and so pressure outwards builds up resisting the entry of more water making the cell turgid
42
Q

Why does pressure potential have a positive sign?

A

As pressure potential is a push outwards it has a positive sign

43
Q

What are the two opposing forces in plant cells?

A

Pressure potential + solute potential

44
Q

What does pressure potential do to water?

A

A force which increases the tendency of water to move out

45
Q

Equation of water potential

A

Pressure potential + solute potential

46
Q

Describe the necessary conditions to be described as hypotonic

A

If the water potential of the external solution is less negative (higher) than the solution inside the cell it is hypotonic

47
Q

Where does water move with regard to the cell if it is hypotonic?

A

Water moves by osmosis into the cell

48
Q

State which condition is described: if the water potential of the external solution is more negative (lower) than the solution inside the cell

A

Hypersonic

49
Q

Where does the water move if it described as hypertonic?

A

Water flows by osmosis out of the cell

50
Q

The cell Is isotonic if?

A

The cell has the same water potential as the surrounding solution

51
Q

Described the movement of water in an isotonic solution

A

There will be no net movement of water

52
Q

What is plasmolysis?

A
  • plant cells in hypertonic solution lose water by osmosis.

- the vacuole shrinks and the cytoplasm draws away from the cell wall

53
Q

When plasmolysis is complete the cell is described as being?

A

Flaccid

54
Q

What happens when the cell is Flaccid?

A

Such cells cannot provide support so when a plant loses too much water and it’s cell become Flaccid and the plant wilts

55
Q

If the external concentration is high enough that the cell has lost just enough water that it’s membrane begins to be pulled away from the cell wall. What is this called?

A

Incipient plasmolysis

56
Q

At Incipient plasmolysis the water potential is…

A

Equal to the solute potential of the external solution

57
Q

What happens to a plant cell in a hypotonic solution?

A

-As water enters the cells the contents
expand and push out more on the cell wall increasing the pressure potential
- the pressure potential rises until it is equal and opposite to the pull inwards of the solute potential
- no more water can enter and there is no tendency for the cell to absorb water (it’s water potential is 0

58
Q

When the cell can take in no more water, it is described as?

A

Turgid

59
Q

Why is turgor important to plants?

A

It provides support, maintains their shape and holds them upright

60
Q

Relative water potential, pressure potential and solute potential when the cell is turgid

A

WP=0
PP=-SP

(cytoplasm pushed against cell wall)

61
Q

Relative water potential, pressure potential and solute potential when the cell is at Incipient plasmolysis

A

PP=0
WP=SP

(cytoplasm beginning to pull away from cell wall )

62
Q

Relative water potential, pressure potential and solute potential when the cell when it is plasmolysed

A

PP=0
WP=SP

(cytoplasm completely pulled away from cell wall)

63
Q

What does not have to be considered when looking at osmosis in animal cells?

A

Pressure potential

Animal cells do not contain cell walls

64
Q

Red blood cells are described as crenated when…

A

They are placed in concentrated salt solution water leaves the cells and they shrink

65
Q

Haemolysis occurs when…

A

Red blood cells are placed in distilled water, water enters by osmosis and without a cell wall they burst

66
Q

What are the two main ways that cells can transport material In bulk?

A

Endocytosis and exocytosis

67
Q

When does Endocytosis occur?

A

When material is engulfed by extensions of the plasma membrane and cytoplasm, surrounding it, making a vehicle

68
Q

Define exocytosis

A

The process by which substances may leave the cell, having been translated though the cytoplasm in a vehicle which fuses with the cell membrane
(digestive enzymes are often secreted in this way)

69
Q

What is phagocytosis?

A
  • The uptake of solid material that is too large to be taken in by diffusion or active transport
  • when granulocyres engulf bacteria a lysosome fuses with the vesicles formed and enzymes digest the cells. The products are absorbed into the cytoplasm
70
Q

Define pinocytosis

A

The uptake of liquid by the same mechanism, although the vesicles produced are similar

71
Q

Does exocytosis and pinocytosis require energy?

A

Yes

72
Q

What does Endocytosis do to the cell membrane?

A

Decreases its overall area

73
Q

What does exocytosis do to the cell membrane?

A

Increase its overall area

74
Q

What does Endocytosis and exocytosis do to the cell membrane.?

A

Changes its shape

75
Q

What propertybof the cell membrane is essential for Endocytosis and exocytosis?

A

It’s fluidity

Biology need to knows⚠️ (18 decks)

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