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AQA A Level Biology Paper 1 > Topic 2.2 - Transport into and out of Cells > Flashcards

Topic 2.2 - Transport into and out of Cells Flashcards

1
Q

What is a cell-surface membrane?

A

(Partially permeable) barrier between cell and its environment, controlling which substances enter and leave the cell

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2
Q

What is the functions of membranes around organelles?

A
  • Act as barriers between organelle and cytoplasm
  • Also control what comes in and out + partially permeable
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3
Q

Describe the phospholipids arrangement in a plasma membrane

A
  1. Bilayer
  2. Hydrophobic tails to inside
  3. Hydrophilic heads to outside
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4
Q

Describe how the plasma membrane acts as a barrier to water-souble substances

A

Centre of bilayer is hydrophobic, therefore the membrane doesn’t allow water-souble substances (like ions) through it

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5
Q

Name 3 functions of phospholipids in plasma membranes

A
  • Allow lipid-soluble substances to enter & leave the cell
  • Prevent water-soluble substances entering and leaving the cell
  • Makes membrane flexible
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6
Q

Cholesterol is present in all cell membranes expect _____ ____ ________

A

bacterial cell membranes

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7
Q

Where are cholesterol molecules found in cell membranes?

A

Between phospholipids

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8
Q

What is the role of cholesterol in cell membranes?

A

Controls the fluidity of the membrane

(provides stability e.g. helps to maintain shape of animal cells)

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9
Q

Describe how cholesterol gives cell membranes stability

A
  • Cholesterol molecules bind to hydrophobic tails of phospholipids = causes them to pack more closely together
  • Restricts movement of phospholipids
  • Makes membrane less fluid and more rigid
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10
Q

What model is used to describe the arrangement of molecules in membrane?

A

Fluid mosaic model

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11
Q

Why is the bilayer is ‘fluid’?

A

Because phospholipids are constantly moving

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12
Q

How are proteins arranged in the cell membrane?

A

They’re scattered through the bilayer (like tiles in mosaic)

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13
Q

What are extrinsic proteins?

A

Proteins which are partly embedded in bilayer so they stick out to the surface of the cell.

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14
Q

What are intrinsic proteins?

A

Proteins that span entire bilayer from one side to the other

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15
Q

What do channel proteins and carrier proteins allow?

A

Allow large molecules and ions to pass through membrane

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16
Q

What do receptor proteins on the cell-surface membrane do?

A

Detect chemicals such as hormones released from other cells

(chemicals signal to cell to respond in some way)

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17
Q

Describe how protein move may throughout the bilayer

A

Some proteins can move sideways through bilayer & others are fixed in position

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18
Q

What are glycoproteins?

A

Proteins that have a polysaccharide (carbohydrate) chain attached

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19
Q

What are glycolipids?

A

Lipids that have a polysaccharide (carbohydrate) chain attached

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20
Q

Increasing the temperature ____ membrane permeability

A

INCREASES

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21
Q

Describe and explain the membrane permeability when temperature are below 0 degrees.

A
  • Phospholipids don’t have much energy so can’t move much
    • So lipids are packed closely together & membrane is rigid
  • BUT channel proteins and carrier proteins deform which increases permeability of membrane
  • Ice crystals may form and pierce the membrane = makes highly permeable when it thaws
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22
Q

Describe and explain the membrane permeability for temperatures between 0 and 45°C.

A
  • Phospholipids can move around & aren’t packed as tightly together so the membrane is partially permeable
  • As temperature increases, phospholipids move more because they have more energy. This increases permeability of membrane
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23
Q

Describe the effect of high temperature on cell membranes

A
  • Phospholipids have more kinetic energy
  • Movement makes membranes more fluid and leaky
  • Increases no. of gaps between phospholipids
  • Glycoproteins/channel & carrier proteins denature

All increases permeability of membrane as substances can enter and leave that wouldn’t normally

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24
Q

Sketch a graph showing how increasing the temperature affects membrane permeability

A
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25
Q

Surrounding cells in an increasing concentration of solvent (e.g. acetone) will _______ membrane permeability

A

INCREASE

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26
Q

Why does surrounding cells in an increasing concentration of solvent (e.g. acetone) increase membrane permeability?

A

Because the solvent dissolves lipids in the cell membrane, causing it to lose its structure

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27
Q

What could you use to investigate how different conditions (e.g. temperature and solvent concentration) affects membrane permeability?

A

Beetroot → higher permeability of membrane = more pigment leaks out of cell

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28
Q

Define diffusion

A

Net movement of particles from an area of higher concentration to area of lower concentration

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29
Q

Is diffusion a passive or active process?

A

passive

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30
Q

Particles diffuse ___ a concentration gradient

A

DOWN

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31
Q

What type of particles can diffuse through cell membranes?

A

Small and non-polar particles

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32
Q

What are polar molecules?

A

Molecules that are partially positively or negatively charged on one side due to an uneven distribution of charge.

33
Q

Why are small particles able to diffuse through the cell membrane?

A

Because they can pass through spaces between phospholipids

34
Q

Why are non-polar particles able to diffuse through the cell membrane?

A

Because they can dissolve in the hydrophobic bilayer as being non-polar makes them soluble in lipids

35
Q

What is simple diffusion? (in membrane terms)

A

When molecules diffuse directly through cell membrane

36
Q

Why don’t large/charged particles diffuse through the phospholipid bilayer?

A

Because they would diffuse extremely slowly as they’re big/water soluble (& centre of bilayer is hydrophobic)

37
Q

Facilitated diffusion moves particles _____ a concentration gradient & is _____

A

DOWN … PASSIVE

38
Q

What do carrier proteins do?

A

Move large molecules across membranes and down their concentration gradient

39
Q

Describe how carrier proteins move large molecules across membranes

A
  1. Large molecule attaches to carrier protein
  2. Protein changes shape
  3. This releases the molecule on the opposite side of membrane
40
Q

What do channel proteins do?

A

Form pores in membrane for charged particles to diffuse through (down their concentration gradient)

41
Q

What is facilitated diffusion?

A

When large/charged particles diffuse through carrier proteins or channel proteins down a concentration gradient

42
Q

Name 3 factors that affect the rate of simple diffusion

A
  • Concentration gradient
    • (Higher it is = faster rate of diffusion)
  • Thickness of exchange surface
  • Surface area
43
Q

What are microvilli?

A

Projections formed by cell-surface membrane folding up on itself

44
Q

How do microvilli increase the rate of diffusion?

A
  1. Give cell a larger surface area
  2. Therefore more particles can be exchanged in same amount of time which increases rate of diffusion
45
Q

Name 2 factors that affect the rate of facilitated diffusion

A
  1. Concentration gradient
  2. Number of channel/carrier proteins
46
Q

Describe how the number of channel/carrier proteins affects the rate of facilitated diffusion

A
  • Once all proteins in membrane are in use, facilitated diffusion can’t happen any faster (even if concentration gradient is increased)
  • Therefore a greater no. of carrier/channel proteins leads to a faster rate of facilitated diffusion
47
Q

Why can water diffuse directly through the membrane even though it’s polar?

A

it’s relatively small

48
Q

Define osmosis

A

Diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential

49
Q

What is water potential?

A

Tendency of water molecules to diffuse out of or into a solution

50
Q

What has the highest water potential?

A

Pure water

51
Q

All solutions have ____ water potential than pure water

A

lower

52
Q

If 2 solutions have same water potential, they are said to be…

A

isotonic

53
Q

Name 3 factors that affect the rate of osmosis

A
  • Water potential gradient
    • (Higher water potential gradient = faster rate of osmosis)
  • Thickness of exchange surface
  • Surface area of exchange surface
54
Q

Describe what happens when a plant cell is placed in a very concentrated solution (i.e. how it becomes plasmolysed)

A
  1. Water moves out of cell by osmosis
  2. Cell has greater water potential
  3. Water moves down water potential gradient
55
Q

What technique do you use to make several solutions of different, known concentrations?

A

Serial dilution technique

56
Q

Describe how you can use serial dilutions to find the water potential of potato cells

A
  1. Use cork borer to cut potatoes into 5 indentically size chips (1 cm in diameter)
  2. Blot potato chips with paper towel
  3. Weigh mass of each potato chip on mass balance & record these values
  4. Place each potato chip into each sucrose solution
  5. Leave chips in solution for 20 minutes
  6. Remove chips and gently pat them dry with paper towel
  7. Weigh each chip again and record these masses
  8. Calculate % change in mass for each chip
  9. Use results to make calibration curve, showing % change in mass against sucrose solution
57
Q

Describe how you would find the water potential of potato cells from a calibration curve

A
  • Point at which curve crosses x-axis = point where water potential of sucrose solution = water potential of potato cells
  • Find concentration at this point & then look up water potential for that concentration of sucrose solution
58
Q

Define Active Transport

A

Movement of molecules/ions into or out of a cell from an area of lower concentration to an area of higher concentration using energy from ATP and carrier molecules

59
Q

Describe how carrier proteins move molecules in active transport

A
  1. Molecules/ions bind to receptors on carrier protein
  2. On inside of cell: ATP binds to carrier protein = causes it to split into ADP and phosphate molecule
    • Causes carrier protein molecule to change shape, releasing molecules/ions to other side of membrane
  3. Phosphate molecule is released from carrier protein & recombines with ADP to from ATP during respiration
    • Causes carrier protein to revert to its original shape
60
Q

Name 2 differences between active transport and facilitated diffusion

A
  1. Active transport = moves solutes from low to high concentration
  2. Active transport requires energy
61
Q

Describe how ATP enables active transport (as well as other biological processes)

A
  • Undergoes hydrolysis reaction = splits ADP and P¡ (inorganic phosphate)
  • This releases energy so solutes can be transported
62
Q

Co-transporters are type of ___ protein

A

carrier protein

63
Q

Describe how co-transporters enable molecules to move in active transport

A
  1. Bind 2 molecules at a time
  2. Concentration gradient of one of the molecules is used to move other molecule against its own concentration gradient
64
Q

Name 3 factors that affect the rate of active transport

A
  • Speed of individual carrier proteins
  • Number of carrier proteins
  • Rate of respiration in cell & availability of ATP
65
Q

Glucose is absorbed by _______ in mammalian ileum

A

Co-Transport

66
Q

Why is glucose absorbed from lumen (middle) of ileum by co-transport?

A

Because in the ileum (final part of small intestine), the concentration of glucose is too low for glucose to diffuse into blood

67
Q

Describe how glucose is absorbed from lumen (middle) of ileum by co-transport

A
  1. Sodium ions are actively transported out of ileum epithelial cells into blood by sodium-potassium pump (which requires ATP for active transport)
    1. This creates a concentration gradient as there is a higher concentration of sodium in the blood than in the epithelial cells
  2. This causes sodium ions to diffuse into epithelial cell by facilitated diffusion (down their concentration gradient) via sodium-glucose co-transporter proteins
  3. Glucose absorbed with Na+ ions against their concentration gradient
    • = concentration of glucose inside cell increases
  4. Glucose diffuses out of cell into blood, down its concentration gradient through protein channel by facilitated diffusion
68
Q

How many phosphate groups does an ATP molecule have?

A

3 phosphate groups

(Bonds between phosphate groups = unstable ∴ low activation energy = easily broken)

69
Q

Describe how ATP is synthesised to produce immediate source of energy

A
  1. Conversion of ATP to ADP = reversible reaction
  2. Therefore energy can be used to add an inorganic phosphate to ADP to form ATP
70
Q

Describe how ATP is used in metabolic processes

A

ATP provides energy needed to build macromolecules from their basic units (e.g. making starch from glucose)

71
Q

Describe how ATP is used in active transport

A

Provides energy to change shape of carrier proteins

72
Q

What is the function of a glycolipid?

A

Acts as a recognition site

73
Q

Describe what the terms hydrophobic and hydrophilic mean and explain why this property of membranes helps their structure (4)

A
  • Hydrophobic = water hating
  • Hydrophilic = water loving
  • Membrane is stable because heads always move towards the water
  • And tails always move away from the water, filling any gaps/holes that may form
74
Q

Name the roles of glycoproteins on the cell membrane (6)

A
  1. Acts as a receptor/binding site for hormones
  2. Can be used for recognition
  3. Cell adhesion
  4. Cell signalling
  5. Act as antigens
  6. Can act as a switch to trigger changes in membrane
  7. Attaches to water molecules
  8. Receptor to transfer proteins
75
Q

List some of the molecules that require channel proteins to cross the membrane and explain why (3)

A
  • Glucose – too large to pass across
  • Ions like sodium and potassium as they’re not lipid soluble
  • Any molecules moving against a concentration gradient that requires ATP for active transport
76
Q

Define Cell Signalling

A

Communication between cells using various signals, particularly hormones

77
Q

What is meant by recognition in plasma membranes?

A

Receptors can be used to target certain cells and to distinguish between self and non-self

78
Q

What is meant by receptors in plasma membranes?

A

A glycoprotein molecule on the surface of a cell that triggers a response to environmental changes, hormones and other cells

AQA A Level Biology Paper 1 (12 decks)

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