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AQA A level Biology > 2.3 Transport across membranes > Flashcards

2.3 Transport across membranes Flashcards

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1
Q

What is the current model of the membrane called
And why is it called this

A

Fluid mosaic model
Fluid- bc the individual phospholipids can move relative to each other
Mosaic- bc the proteins vary in size and shape

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2
Q

What is the role of the cell surface membrane

A

It controls the movement of substances in and out of the cell

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3
Q

What is the name of the lipids in the membrane

A

Phospholipids

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4
Q

How are the phospholipids arranged in the membrane

A

As a bilayer

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5
Q

What are the characteristics of the phosphate head

A
  • Polar
  • Hydrophilic (attracted to water)
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6
Q

What are the characteristics of the fatty acids tails

A
  • Non-polar
  • Hydrophobic (repelled by water)
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7
Q

Function of phospholipids

A
  • Allow lipid-soluble substances to enter and leave the cell
  • Prevent water-soluble substances entering and leaving the cell
  • Make the membrane flexible and self-sealing
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8
Q

What is the role of extrinsic proteins

A
  • Give mechanical support to membrane
  • Act as cell receptors to molecules like hormones (if connected to glycolipids)
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9
Q

What are the 2 intrinsic proteins

A
  • Channel
  • Carrier
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10
Q

What are channel proteins

A

Water filled tubes which allow water soluble ions to diffuse across the membrane

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11
Q

What do carrier proteins do

A

They bind to ions or molecules (like glucose and amino acids) then change shape to move these across the membrane

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12
Q

What are the functions of the intrinsic proteins

A
  • Provide structural support
  • Transport water-soluble substances
  • Allow active transport to occur (carrier)
  • Form cell surface receptors
  • Help cells adhere together
  • Act as receptors
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13
Q

Function of cholesterol (3 things)

A
  • Reduce lateral movement of other molecules including phospholipids
  • Make the membrane less fluid at high temperatures
  • Prevent leakage of water and dissolved ions from the cell
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14
Q

Is cholesterol hydrophilic or hydrophobic

A

Hydrophobic

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15
Q

Why is cholesterol being hydrophobic a good thing

A

-It plays an important role in preventing loss of water and dissolved ions
- It also pulls the fatty acid tails together which limits their movement

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16
Q

What makes up a glycolipid

A

A carbohydrate covalently bonded with a lipid

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17
Q

Function of glycolipids

```

```

```

A
  • Act as recognition sites
  • Help maintain the stability of the membrane
  • Help cells to attach to one another and so form tissues
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18
Q

Function of glycoproteins

A
  • Act as recognition sites
  • Help cells to attach to one another and so form tissues
  • Allows cells to recognise one another
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19
Q

Define diffusion

A

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until an equilibrium is reached

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20
Q

How does facilitated diffusion differ from simple diffusion

A
  • F diffusion uses intrinsic proteins (both types)
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21
Q

What is transported during facilitated diffusion

A

Charged ions and polar molecules

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22
Q

How do the protein channels allow water soluble ions to pass through

A

They fomr water filled hydrophilic channels the stretch across the whole membrane

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23
Q

Are channel proteins selective

A

Yes

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24
Q

What happens if the particular ion isn’t present to a channel protein

A

It remains closed

25
Q

What happens to a carrier protein when a molecule binds to it

A

It changes shape so the molecule is released on the other side of the protein

26
Q

What 3 factors effect the rate of diffusion

A
  • concentration gradient
  • thickness of exchange surface
  • temperature
  • surface area
27
Q

Define osmosis

A

The passage of water from a region where it has a higher water potential to a region where is has lower water potential through a selectively permeable membrane

28
Q

What is the units that measure water potential

A

kPa

29
Q

What is the water potential of pure water

A

0 kPa

30
Q

The water potential of a solution must be …

A

negative

31
Q

What is meant by isotonic solution

A

The water potential of the external solution is the same as the cell

32
Q

What is meant by hypertonic solution

A

The water potential of the external solution is lower than the cell

33
Q

What is meant by hypotonic solution

A

The water potential of the external solution is higher than the cell

34
Q

What is the term used to describe a plant cell in a hypertonic solution, when water leaves the cell

A

Plasmolysed

35
Q

What is the term used to describe a plant cell in a hypotonic solution, when water enters the cell

A

Turgid

36
Q

What is the term used to describe an animal cell in a hypertonic solution, when water leaves the cell

A

Crenation

37
Q

What is the term used to describe an animal cell in a hypotonic solution, when water enters the cell

A

Cell lysis (bursts)

38
Q

Define active transport

A

The movement of molecules or ions into or out of a ell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins

38
Q

How does active transport differ from passive forms of transport

A
  • Energy is needed in the form ATP
  • Substances are moved against the concentration gradient
  • Carrier proteins molecules act as a pump are involved
  • It’s a very selective process
39
Q

Where does the molecule or ion being transported in active transport bind to

A

The receptor sites on the carrier protein

40
Q

Once ATP binds to the protein, what does it split into

A

ADP and a phosphate molecule

41
Q

What does the splitting of ATP into ADP and a phosphate molecule cause the protein to do

A

Change shape and open on the opposite side of the protein

42
Q

What happens to the protein when the phosphate molecule is released from the protein after active transport

A

The protein reverts back to it’s original shape

43
Q

When does ADP and the phosphate molecule recombine to form ATP

A

During respiration

44
Q

In the sodium potassium pump which ions are actively removed from the cell/organelle

A

The sodium ions

45
Q

In the sodium potassium pump which ions are actively taken in from the surroundings

A

The potassium ions

46
Q

State 1 similarity and 1 difference between facilitated diffusion and active transport

A

Similarity - Both use carrier proteins in the plasma membrane
Difference- Active transport requires energy (ATP) and occurs against the concentration gradient

47
Q

State 3 ways in which the rate of movement across membranes can be increased

A
  • By increasing the concentration gradient either side of it
  • By increasing the surface area
  • By increasing the density of protein channels (carrier proteins)
48
Q

Explain why the term co-transport is used to describe the transport of glucose into cells

A

Because glucose molecules and sodium ions move into the cell coupled together

49
Q

Is the movement of sodium ions out of the epithelial cell passive or active

A

Active

50
Q

Is the movement of sodium ions into the epithelial cells passive or active

A

Passive

51
Q

Is the movement of glucose molecules into the epithelial cells active or passive

A

Passive

52
Q

Name and describe five ways substances can move across the cell-surface membrane into a cell. (5 marks)

A
  • Simple diffusion of small/ non-polar molecules down a concentration gradient
  • Facilitated diffusion down a concentration gradient via protein carrier/ channel
  • Osmosis of water down a water potential gradient
  • Active transport against a concentration gradient via protein carrier using ATP
  • Co-transport of 2 different substances using a carrier protein
53
Q

Describe and explain two features you would expect to find in a cell
specialised for absorption. (2 marks)

A
  • Folded membrane so large surface area
  • Large number of co-transport/ carrier/ channel proteins so fast rate
  • Large number of mitochondria so make more ATP
  • Membrane- bound enzymes so maintains concentration gradient
54
Q

The movement of substances across cell membranes is affected by membrane structure. Describe how. (5 marks)

A
  • Phospholipid bilayer allows movement of non-polar/ lipid-soluble substances
  • Phospholipid bilayer prevents movement of polar/ lipid-soluble substances
  • Carrier proteins allow active transport
  • Channel/ carrier proteins allow faciliated diffusion
  • Shape of channel/ carrier determines which substances move
  • Number of channels/ carriers determines how much movement
  • Membrane surface area determines how much diffusion
  • Cholesterol affects fluidity
55
Q

Give two similarities in the movement of substances by diffusion and by
osmosis. (2 marks)

A
  • Movement down a gradient
  • Passive processes
56
Q

Compare and contrast the processes by which water and inorganic ions enter cells. ( 3 marks)

A
  • Both move down concentration gradient
  • Both move through channels in membrane
  • Ions can move against a concentration gradient by active transport
57
Q

Contrast the processes of facilitated diffusion and active transport. (3 marks)

A
  • Faciliated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins
  • Facilitated diffusion does not use ATP whereas active transport uses ATP
  • Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient

AQA A level Biology (33 decks)

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