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A level Biology > membranes > Flashcards

membranes Flashcards

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1
Q

which parts of a phospholipid molecule is hydrophilic / hydrophobic ?

A

head is hydrophilic

tail is hydrophobic

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2
Q

what is the phospholipid bilayer ?

A

double layer of phospholipid molecules, with heads facing outwards

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3
Q

which type of cell membrane is cholesterol present in ?

A

all of them except bacterial cell membranes

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4
Q

what does cholesterol do to the membrane and how ?

A

Fits between phospholipid molecules and binds to the hydrophobic tails, causing them to pack closer.
This makes membrane less fluid, more rigid.

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5
Q

how do proteins allow substances to pass through membrane?

A
  • form channels which allows small / charged particles through
  • carrier proteins transport molecules / ions across membranes by active transport / facilitated diffusion
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6
Q

what are the four functions glyco lipids/proteins linked with the membrane :

A
  • stabilize membrane by forming H-bonds with surrounding water molecules
  • sites where drugs/hormones/antibodies bind
  • act as receptors for cell signalling
  • act as antigens
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7
Q

describe how cells communicate

A
  • cell releases a messenger molecule (e.g. hormone)
  • molecule travels (e.g. in blood)
  • messenger molecule binds to receptor on cell membrane
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8
Q

what are membrane - bound receptors ?

A

proteins in cell membrane that act as receptors for messenger molecules

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9
Q

what special structure feature do receptor proteins have?

A

specific shape, which only messenger molecules with complementary shape can bind to

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10
Q

what is a target cell ?

A

a cell that responds to a particular messenger molecule

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11
Q

Describe membrane permeability at low temp > 0

A
  • pack close, so membrane is rigid
  • channel / carrier proteins deform, increasing permeability
  • ice crystals may piece membrane (increase permeability)
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12
Q

Describe membrane permeability at mid temp 0 - 45

A
  • phospholipid have more energy, move more, not as tightly packed
  • membrane is partially permeable
  • increase in temp increases permeability
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13
Q

Describe membrane permeability at high temp < 45

A
  • bilayer breaks down, membrane becomes more permeable

- channel / carrier proteins deform (increase permeability)

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14
Q

Describe the effect of a solvent on membrane permeability

A
  • increases permeability due to the solvent dissolving lipids in membrane, so it loses structure
  • increase in concentration will increase permeability
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15
Q

define diffusion

A

the net movement of particles from an area of high concentration to an area of low concentration

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16
Q

what does it mean that diffusion is a passive process ?

A

requires no energy

17
Q

what are the four factors of rate of diffusion ?

A

temp / conc gradient / thickness of exchange surface / surface area

18
Q

what color is phenolphthalein in alkaline conditions ?

A

pink

19
Q

what color is phenolphthalein in acid conditions ?

A

colourlless

20
Q

what is facilitated diffusion ?

A

diffusion of larger molecules / ions / polar molecules through carrier / channel proteins in the membrane

21
Q

how do carrier proteins carry out facilitated diffusion ?

A
  • large molecule attaches to carrier protein
  • protein changes shape
  • molecule released on other side
22
Q

how do channel proteins carry out facilitated diffusion ?

A
  • form pores in membrane for charged particles to diffuse through
    (there are diff channel proteins for diff charged particles)
23
Q

what is used in active transport ?

A

carrier proteins

24
Q

what is endocytosis ?

A

cell surrounds substance with section of plasma membrane and pinches off to form a vesicle inside cell, this uses ATP for energy

25
Q

describe exocytosis

A
  • vesicle buds off from Golgi body
  • vesicle moves to plasma membrane
  • vesicle fuses with membrane
  • contents are released outside of cell
    (uses ATP)
26
Q

define osmosis

A

diffusion of water molecules across a partially permeable membrane down a water potential gradient

27
Q

what has the highest water potential ?

A

pure water

28
Q

define hypotonic solution

A

higher water potential

29
Q

define isotonic solution

A

same water potential

30
Q

define hypertonic solution

A

lower water potential

31
Q

describe plant cell in hypotonic solution

A
  • water moves into cell
  • vacuole swells
  • vacuole / cytoplasm push against wall
  • cell becomes turgid
32
Q

describe plant cell in hypertonic solution

A
  • water moves out of cell
  • cell becomes flaccid
  • cytoplasm / membrane pull away from cell wall
  • called plasmolysis
33
Q

why is membrane described as mosaic ?

A

arranged w/ lots of different components

A level Biology (26 decks)

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