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A Level - Biology > 4: Transport across cell membranes > Flashcards

4: Transport across cell membranes Flashcards

1
Q

What is plasma membrane?

A

All membranes around and within all cells

All have the same basic structure

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2
Q

What does the cell-surface membrane do?

A

Allows different conditions in and out of the cell
Controls the movement of substances
Provides structural integrity

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3
Q

How are phospholipids essential for cell-surface membranes?

A

Hydrophillic heads point towards outside of the cell as attracted by water on both sides
Hydrophobic tails point to the center of the cell membrane, repelled by water

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4
Q

What does amphiphatic mean?

A

Contains both hydrophobic and hydrophillic components

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5
Q

Why is a membrane said to be a fluid mosaic?

A

Fluid: flows, moves, changes shape
Mosaic: different size, patterns, shapes

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6
Q

Why does the cell-surface membrane have pores?

A

Selectively permeable

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7
Q

What types of proteins exist in the cell-surface membrane?

A

Intrinsic/integral/transmembrane

Extrinsic/peripheral

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8
Q

What is an intrinsic protein?

A

Span the full bilayer from one side to the other
They interact with the lipophillic core and it embeds them there
Protein channels / Carrier proteins

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9
Q

What is a protein channel?

A

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

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10
Q

What is a carrier protein?

A

Binds to ions or molecules (glucose/amino acids)
Causes a change in conformational shape
Moves the molecule across the membrane

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11
Q

What are the function of proteins in the bilayer?

A

Structural support
Acts as channels transferring water-soluble substances
Allows active transport using carrier proteins
Cell-surface receptors for identifying cells
Helps cells adhere (join) together
Acts as receptors (hormones)

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12
Q

What is an extrinsic protein?

A

Surface of bilayer, never extends beyond

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13
Q

What are the functions of extrinsic proteins?

A

Mechanical support
Cell receptors with glycolipids
Cell receptors for hormones

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14
Q

Where is cholestrol found?

A

Within the bilayer

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15
Q

What does cholestrol do in the bilayer?

A

Provides strength to membrane
Reduce lateral movement of molecules
Make the membrane less fluid at high temp
Prevent leakage of water and dissolved ions

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16
Q

What is a glycolipid?

A

Carbohydrate covalently bonded to a lipid

Carb. extends outside the cell

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17
Q

What is the function of glycolipids?

A 
Recognition sites (ABO Blood)
Maintain stability of membrane
Helps cells to attach to each other
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18
Q

What is a glycoprotein?

A

Carbohydrate chains bonded to extrinsic protein

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19
Q

What are the functions of glycoproteins?

A

Recognition sites
Help cells attach to each other
Recognition (e.g lymphocytes recognise own cells)

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20
Q

When is transport across the bilayer not possible?

A

Molecules not lipophillic
Too large to pass through channels
Same charge as proteins
Polar (electrically charged) therefore cannot move through the non-polar hydrophobic tails

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21
Q

What are the functions of intracellular membranes?

A 
Divides cytoplasm from organelle contents
Entry and exit 
Internal transport mechanisms 
Enzyme isolation
Interface for reactions
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22
Q

How can a rate of entry graph differ with facilitated diffusion and diffusion?

A

Facilitated diffusion graph plateaus as the channel protein becomes saturated

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23
Q

What are similarities between how H2O and O2 diffuse?

A

Move down conc. gradient

Diffuses through phospholipid bilayer

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24
Q

Why does the rate of uptake increase in the presence of oxygen?

A

Active transport - using O2 creates ATP energy to cause the carrier proteins to change shape

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25
Q

Why does uptake of a substance increases as conc. does?

A

Diffusion is proportional to conc. gradient

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26
Q

What are the things that hold chromatids together?

A

Centromere

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27
Q

How many chromosomes found in nuclei in telophase and a sperm cell if there are 26 in prophase?

A

Prophase: 26
Telophase: 26
Sperm cell: 13

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28
Q

How much mass of DNA found in nuclei in telophase and a sperm cell if there is 60 in prophase?

A

Mass of DNA in Prophase: 60
Telophase: 30
Sperm cell: 15

29
Q

How does faulty DNA cause cancer?

A

Protein is faulty / not made
Cells with faulty DNA divide
Uncontrolled division

30
Q

A cancer drug that stops spindle fibers shortening would stop what stage?

A

Anaphase

31
Q

Explain diffusion

A

Net movement of molecules or ions from a region of higher to lower concentration until even distribution

32
Q

How does kinetic energy affect particles?

A

All particles are constantly in motion due to kinetic energy
Motion is random
Particles constantly bounce off each other as well as other objects

33
Q

What is required for facilitated diffusion?

A

Trans-membrane channels and carriers

34
Q

Is facilitated diffusion require energy?

A

No, it is passive

35
Q

How are protein channels selective?

A

Each opens in the presence of a specific ion

Ion binds with protein causing it to change shape and opens one side and close the other

36
Q

What causes the particles to move in facilitated diffusion?

A

Kinetic energy of the molecules

37
Q

Define osmosis

A

Passage of water from region of high to low water potential through a selectively permeable membrane

38
Q

What is water potential (Ψ)?

A

Pressure created by water molecules (kPa)

39
Q

What is water potential of pure water under standard conditions?

A

0

40
Q

What are “standard conditions” for Ψ?

A

25C and 100 kPa of pressure

41
Q

How does adding solute affect Ψ?

A

Lowers water potential

Therefore any solutions Ψ must be negative

42
Q

How is water potential affected as a solution becomes more concentrated?

A

As concentration increases the Ψ becomes more negative

43
Q

How could you find the Ψ of cells?

A

Place them in a series of solutions with different Ψ

Where there’s no net change of water, the Ψ must be equal to the solution

44
Q

Does osmosis require energy?

A

Only requires kinetic energy of the water molecules

45
Q

Why does a partially permeable membrane not allow solute molecules?

A

They are too big to fit through the pores

46
Q

What is an isotonic solution?

A

A solution where the Ψ is the same as the cell

47
Q

What is a hypertonic solution?

A

A solution where the Ψ is lower than that in the cell

Hyper - high SOLUTE

48
Q

What is a hypotonic solution?

A

A solution where the Ψ is higher than that in a cell

Hypo - low SOLUTE

49
Q

What are the principles of exchange to increase exchange?

A

High SA:V ratio
Thin layer
Selectively permeable
Movement of the external & internal environment

50
Q

How does a high SA:V ratio affect exchange?

A

Increases rate of exchange - as increased frequency of collision with exchange surface

51
Q

How does a thin layer affect exchange?

A

Short diffusion pathway length

Quicker transport through membranes

52
Q

What is villi?

A

1mm in length which is folded to increase SA

53
Q

What is microvilli?

A

600nm in length

Found on enterocyte border

54
Q

What is an enterocyte?

A

Cell of the intestinal lining

55
Q

What is the purpose of the circularity systems?

A

Maintains concentration gradients

56
Q

What occurs when cells are placed in a hypertonic solution?

A

Plant cells tissue flaccid & plasmolysis

Animal cells shrink (RBC crenation)

57
Q

What occurs when cells are placed in a hypotonic solution?

A

Animal cells burst (cytolysis) & RBC undergo haemolysis

Plant cells become turgid

58
Q

Define active transport

A

Movement of molecules/ions from low to high conc. using ATP and carrier proteins

59
Q

How does active transport affect net movement?

A

No equilibrium reached

60
Q

How selective is active transport?

A

Highly selective

61
Q

Explain the process of active transport

A

Molecule/ion binds to carrier protein
ATP attaches to protein and phosphorylation occurs and causes conformational change
Opens to opposite side of the membrane and molecule/ion released

62
Q

What is the phosphorylation?

A

ATP ADP + Phosphorus

63
Q

Explain the process of a sodium-potassium pump?

A

3 Na+ binds to binding site
Phosphorylation occurs (ATP -> ADP + P)
Conformational change in shape and Na+ released
2 K+ ions bind to protein and dephosphorylation causes change (P dissociates)
2 K+ ions released and process repeats

64
Q

What is direct/primary active transport?

A

Ions/molecules pumped against conc. gradient

65
Q

What is indirect/secondary active transport?

A

Conc. gradient generated by ion pump, then co-transport of ion with chemical

66
Q

What is co-transport?

A

A molecule is transported against conc. gradient with another substance down the conc. gradient

67
Q

Describe the co-transport in the enterocyte?

A

Direct active transport causes Na+ to go to blood and K+ ions to diffuse into cell (Na-K pump)
Indirect active transport (co-transport) glucose binds to Na+ which moves down conc. gradient
Facilitated diffusion of glucose from enterocyte to bloodstream

68
Q

What is the effect of an isotonic solution?

A

No affect on animal cells

Incipient plasmolysis in plant cells

69
Q

What is incipient plasmolysis?

A

When the protoplast is just about to pull away from cell wall

A Level - Biology (22 decks)

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