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OCR Biology > 2.5 BIOLOGICAL MEMBRANES > Flashcards

2.5 BIOLOGICAL MEMBRANES Flashcards

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1
Q

State the 3 roles of plasma membranes

A

1) partially permeable barriers between cells and environment/organelles and cytoplasm
2) site of chemical reactions
3) site cell communication/signalling

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2
Q

Why is the plasma membrane called “fluid-mosaic”?

A
  • Mosaic = proteins, glycoprotiens, glycolipids, cholesterol are scattered throughout the phospholipid bilayer
  • Fluid = membrane components are free to move
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3
Q

How does the plasma membrane have a role in cell signalling?

A
  • contains membrane-bound receptors for hormones and drugs to bind
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4
Q

Describe the phospholipid bilayer

A
  • hydrophobic, nonpolar tails on inside
  • hydrophilic, polar heads on outside
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5
Q

Role of glycoproteins and glycolipids?

A
  • maintain stability and facilitate cellular recognition
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6
Q

Which molecules CAN get through the partially permeable plasma membrane? (3)

A
  • Gases
  • Hydrophobic molecules (are uncharged/nonpolar/fat soluble)
  • Small polar molecules
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7
Q

Which molecules CANNOT get through the partially permeable plasma membrane? (2)

A
  • Large polar molecules
  • Ions (charged molecules)
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8
Q

Which two factors affect membrane structure and permeability?

A

Temperature and Solvents

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9
Q

How does high temperature affect the plasma membrane?

A
  • Increases kinetic energy, phospholipids move more, fluidity of membrane increases, membrane more permeable and structure breaks down
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10
Q

How do organic solvents (alcohol) affect the plasma membrane?

A
  • Alcohols will dissolve lipids and break the phospholipid bilayer
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11
Q

Describe simple diffusion

A
  • The passive net movement of particles form an area of higher concentration to an area of lower concentration, down a concentration gradient
  • Occurs as particles have kinetic energy, ATP not required
  • Stops when equilibrium is reached
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12
Q

Which particles use simple diffusion across plasma membranes?

A
  • Small, lipid soluble (nonpolar) molecules
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13
Q

Describe facilitated diffusion

A
  • The passive net movement of particles from an area of higher concentration to lower concentration across a partially permeable membrane using protein channels/carriers
  • no ATP required
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14
Q

Role of channel proteins?

A
  • for charged/polar molecules
  • fills with water so polar molecules/ions can dissolve in water and diffuse over
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15
Q

Role of carrier proteins?

A
  • for large molecules
  • when molecule binds the carrier protein opens and changes shape then releases molecule on other side
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16
Q

Which particles use facilitated diffusion via channel proteins across partially permeable plasma membranes?

A
  • water soluble ions (charged)
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17
Q

Which particles use facilitated diffusion via carrier proteins across partially permeable plasma membranes?

A
  • large molecules
18
Q

Describe active transport

A
  • the net movement of particles from an area of lower concentration to an area of higher concentration, against the concentration gradient using carrier proteins and ATP
19
Q

Describe the role of carrier proteins in active transport

A
  • carrier proteins act as a pump to move substances across membrane (e.g 3 Na+ into the cell for every 2 K+)
  • Uses hydrolysis of ATP into ADP and Pi to release energy for shape change
20
Q

State the steps of activate transport via carrier proteins

A

1) Molecule binds to receptor site on carrier protein
2) ATP binds to carrier protein and is hydrolysed into ADP and Pi
3) Carrier protein changes shape and releases molecule on other side

21
Q

Define endocytosis

A
  • Bulk transport of molecules into a cell using ATP
22
Q

Define exocytosis

A
  • Bulk transport of molecules out of a cell using ATP
23
Q

State the steps of endocytosis and the role of ATP

A

1) A segment of the plasma membrane surrounds and encloses a molecule
2) the particle enclosed in the vessel is absorbed into the cytoplasm of the cell
3) ATP is required to surround around the particles

24
Q

State the steps of exocytosis and the role of ATP

A

1) Vesicles containing particles move and fuse with the plasma membrane
2) Contents is released outside of the cell
3) ATP is required for motor protiens to move vesicle along the cytoskeleton

25
Q

State and explain the 5 factors affecting simple diffusion

A
  • Temperature (higher temp=faster rate)
  • Molecule size (smaller molecule=faster rate)
  • Concentration gradient (steeper gradient=faster rate)
  • Diffusion distance (thinner membrane=faster rate)
  • Surface area (larger surface area=more diffusion)
26
Q

Describe osmosis

A
  • The net movement of water molecules from an area of higher water potential to an area of lower water potential through a partially permeable, down a water potential gradient
27
Q

What is meant by low water potential (kPa)?

A
  • Low proportion of water molecules
  • High proportion of solutes
  • Low pressure
  • MORE NEGATIVE
28
Q

What is meant by high water potential (kPa)?

A
  • High proportion of water molecules
  • Low proportion of solutes
  • High pressure
  • LESS NEGATIVE (CLOSER TO ZERO)
29
Q

What is the water potential (kPa) of pure water?

A

0

30
Q

Define isotonic solution

A
  • When water potential of the solution and cell is equal
31
Q

Define hypotnic solution

A
  • When water potential of solution is more postive than the cell (most water molecules are in solution)
32
Q

Define hypertonic solution

A
  • When the water potential of a solution is more negative than the cell (most water molecules are in cell)
33
Q

Explain what happens when animal cells are placed in a hypotonic solution

A
  • Animal cells have no cell wall
  • Higher water potential in the solution compared to cells so water moves into the cell via osmosis
  • Animal cells swell/burst due to the high pressure
34
Q

Explain what happens when plant cells are placed in a hypotonic solution

A
  • Plant cells have cell wall
  • Higher water potential in solution compared to cell so water moves into cell vacuole via osmosis
  • Pressure exerted on cell wall causes turgidity and prevents bursting
35
Q

Explain what happens when animal/plant cells are placed in a hypertonic solution

A
  • Higher water potential in the cells so water moves out the cell via osmosis
  • Cells become shrivelled
36
Q

State the type of protein required for active transport across a membrane

A
  • Carrier protein
37
Q

Describe polar molecules

A
  • Partially charged
  • Are fat INSOLUBLE (cant dissolve in fatty acid tails)
  • Are hydrophillic (attracted to water molecules)
38
Q

Describe nonpolar molecules

A
  • Uncharged
  • Are fat SOLUBLE (can dissolve in the fatty acid tails)
  • Hydrophobic (not attracted to water molecules)
39
Q

State the term used to describe the permeability of phospholipid bilayer membranes

A
  • PARTIALLY permeable
40
Q

Describe the roles of the membrane inside the cell

A

1) Membranes in eukaryotes separate organelles from one another for two reasons - to isolate harmful substances and also to keep reactants in the organelle for more faster/efficient reactions
2) In animals, folds in membranes increase SA for exchange of material
3) Cell recognition/signalling**

41
Q

Describe the role of cholesterole

A
  • Binds to phospholipid fatty acid tails, increasing the packing of the membrane which reduces the fluidity of the memrane

OCR Biology (27 decks)

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