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9700 > cell membrane and transport > Flashcards

cell membrane and transport Flashcards

1
Q

two types of cell membrane

A

cell surface membrane and membrane around the organelles

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2
Q

cell membrane size

A

7nm thick

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3
Q

functions of cell membrane

A
  • Controls movement of substances in and out of the cell
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4
Q

the function of the phospholipid bilayer

A

Semi-permeable
The barrier to water-soluble substances
Allows passage of lipid-soluble substances

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5
Q

proteins and phospholipid form

A

hydrogen bond with water for stability

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6
Q

proteins and glycoproteins are used for

A

cell recognition

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7
Q

proteins function

A
  • transport proteins
  • enzymes
  • cytoskeleton
  • cell to cell adhesion
  • cell signalling
  • cell recognition
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8
Q

What makes up the biomembrane?

A
  • Phospholipids
  • Cholesterol
  • Proteins
  • Carbohydrates – in glycoproteins and glycolipids
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9
Q

another name for cell membrane

A

biomembrane

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10
Q

Fluid

A

phospholipids and protein molecules are able to move about and diffuse sideways within its monolayer

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11
Q

Mosaic

A

proteins scattered within the membrane

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12
Q

What can cross the phospholipid bilayer?

A
  • Oxygen
  • Carbon dioxide
  • Uncharged / non-polar molecules
  • Small molecules
  • Traces of water
  • Lipid soluble substances
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13
Q

hydrophilic head in phospholipid

A

made of glycerol attached to PO4 [hydrophilic due to the presence of phosphate group[polar]

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14
Q

hydrophobic tail in phospholipid

A

made of 2 fatty acid chains [nonpolar)

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15
Q

how do the hydrophobic tails and hydrophilic heads in phospholipid help in a cell membrane

A

This allows the phospholipids to form a membrane around the cell; 2 rows of phospholipids arranged with their hydrophilic heads in watery solution on either side of the membrane and middle hydrophobic tails forming a layer impervious to water.

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16
Q

individual phospholipid molecules can move in

A

the monolayer through diffusion

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17
Q

is the hydrophilic exterior head of a phospholipid polar or nonpolar

A

it’s polar

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18
Q

is the hydrophobic interior tail of a phospholipid polar or nonpolar

A

its non polar

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19
Q

Some phospholipid tails are unsaturated

A

with double bond

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20
Q

more unsaturated makes it more

A

fluid [unsaturated FA’s are bent [KINK]so they fit together more loosely]

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21
Q

The longer the fatty acid tail,

A

, lesser the fluidity

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22
Q

fluidity is affected by

A

1) length of a fatty acid tail
2) the number of unsaturated fatty acids
3) cholesterol
4) temperature

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23
Q

how does the length of a fatty acid affect fluidity?

A

shorter the tails, more the fluidity [longer tails will make more intermolecular interactions, thus less fluidity]

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24
Q

how does the number of unsaturated fatty acids affect fluidity?

A

more the number of unsaturated fatty acids, more the fluidity

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25
Q

how does the cholesterol affect fluidity?

A

maintains the fluidity of the cell membrane

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26
Q

how does the temperature affect fluidity?

A

as temperature increases, fluidity increases – cholesterol reduces the fluidity by increasing the intermolecular interactions
As temperature decreases, fluidity decreases – cholesterol increases the fluidity by disrupting the intermolecular interactions

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27
Q

cholesterol size

A

Relatively small molecule

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28
Q

cholesterol has

A

Have hydrophilic head and hydrophobic tails – fit in the membrane same like phospholipids [head facing towards the phospholipid head]

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29
Q

In animal cells cholesterol number in the cell surface membrane

A

is too high as phospholipids

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30
Q

In plant cells cholesterol number in the cell surface membrane

A

very less

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31
Q

In prokaryotes cholesterol number in the cell surface membrane

A

absent

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32
Q

Functions of cholesterol in cell membrane:

A
  • For maintaining mechanical stability
    prevents ions or polar molecules from passing through the membrane
    To maintain the fluidity of the cell membrane –
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33
Q

how does cholesterol help in maintaining mechanical stability

A

strengthens the membrane by getting in between the phospholipids and the membrane increasing or reducing fluidity

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33
Q

how does cholesterol prevent ions or polar molecules from passing through the membrane?

A

Hydrophobic regions of the cholesterol prevents ions or polar molecules from
passing through the membrane – very helpful in myelin sheath because
leakage of ions would slow down the nerve impulse

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33
Q

how does cholesterol help To maintain the fluidity of the cell membrane?

A

at low temperatures, kinetic energy is less, phospholipid tails tend to pack together, but cholesterol prevents this from happening thus maintaining the fluidity of the membrane
at high temperature : Kinetic energy is more, molecules move apart but cholesterol bring them closer and avoid more flexibility by interacting with hydrophobic group

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34
Q

Proteins also have hydrophobic and hydrophilic regions

A

[AMPHIPATHIC] due to the presence of hydrophobic and hydrophilic amino acids

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35
Q

transport proteins:

A

hydrophilic channels or pathways for ions and polar molecules; specific; 2 types – carrier proteins and channel proteins

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36
Q

Some membrane proteins are enzymes

A

e.g. cells lining the small intestine have digestive enzymes in the cell surface membrane

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37
Q

Cytoskeleton:

A

some proteins on the inner cell surface membrane are attached to cytoskeleton

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38
Q

Cell signalling

A

glycoprotein

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39
Q

Cell recognition

A

– glycoprotein and glycolipid

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40
Q

INTEGRAL / INTRINSIC PROTEINS

A
  • Found in phospholipid bilayer
  • Stuck inside not easily removed
  • Some extend across the bilayer called transmembrane proteins e.g. channel and carrier proteins that aid in transport
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41
Q

PERIPHERAL / EXTRINSIC PROTEINS

A

Found on the inner side and the outer side the membrane
Easily removed

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42
Q

Membrane proteins are called ‘peripheral’ if they are

A

temporarily attached to the membrane or ‘integral’ if they are permanently attached to the membrane.

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43
Q

Integral proteins are described as ‘intrinsic’ if they extend
across the

A

whole bilayer and ‘extrinsic’ if they are found only on one side of
the bilayer.

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44
Q

Channel and carrier proteins are two types of

A

integral transmembrane proteins,They are both embedded in the cell membrane
and span the entire membrane

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45
Q

glycolipids

A

= lipids + carbohydrate chain

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46
Q

glycoproteins

A

proteins + carbohydrate chain

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47
Q

functions of glycoproteins and glycolipids

A
  • receptor molecules
  • cell to cell recognition
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48
Q

receptor molecules

A

carbohydrate chains help the GP and GL to act as receptor molecules. Different
cells have different receptor molecules. e.g. signaling receptor in liver cell to detect glucagon
hormone

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49
Q

Cell-to-cell recognition:

A

some GL and GP act as cell markers or antigens. Carbohydrate chains bind
to complementary sites on other cells; useful in growth and development, immune response. Each
cells have different types antigens

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50
Q

Cell signaling

A

is the molecular mechanism by
which cells detect and respond to external?
stimuli, including communication between
cells.

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51
Q

Signaling

A

getting a message from one place to the other

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52
Q

Signalling pathways can be

A

electrical
[nervous system] or chemical [hormone
system in animals

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53
Q

Signalling molecules

A

neurotransmitters,
hormones

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54
Q

insulin is

A

a horomone

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55
Q

stimulus for a release of ligand which is an insulin hormone

A

high glucose level in blood;

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56
Q

Signalling molecules are small for

A

easy transport

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57
Q

transport system for hormones

A

blood

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58
Q

Receptors are protein molecules located in the

A

cell surface membrane

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59
Q

cell signalling process outside the cell

A
  • Stimulus causes cells to release a “ligand” / “signalling molecule”
  • Signalling molecule is transported to the target cells
  • ligand binds to the cell surface receptor on the target cells – complementary
    binding
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60
Q

INSIDE THE CELL -

A
  • Complementary binding – between receptor protein and ligand [specific]
  • Ligand changes the shape of the receptor protein – conformational change
  • Receptor spans the membrane and therefore the message is passed to the inside
    of the membrane
  • Change in shape of the receptor allows it to interact with the next component of
    the signalling pathway, G PROTEIN, so the message gets transmitted –
    transduction
    CELL SIGNALLING PROCESS
  • ‘G protein’ - acts as a switch that brings about the release of a ‘second
    messenger’
  • amplification of the original signal occurs with the help of secondary
    molecules by activation of different enzymes – known as the ‘signalling
    cascade’
  • Finally enzymes are produced which bring about the required change in cell
    metabolism [RESPONSE]
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61
Q

‘Transduction

A

occurs during cell signalling and is the process of converting a
signal from one method of transmission to the other

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62
Q

‘Second messenger

A

is a small soluble molecule which diffuses through the cell
relaying and amplifying the message

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63
Q

Signaling cascade

A

: the sequence of events triggered by the G protein

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64
Q

G protein named so

A

because the switch mechanism
involves binding to GTP [guanine
triphosphate] molecules

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65
Q

Some signaling molecules are

A

hydrophobic, e.g. steroid hormone
[oestrogen]. They can diffuse across the cell surface membrane directly
and bind to receptors in the cytoplasm or nucleus

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66
Q

4 other basic ways in which a receptor can alter the activity of the cell:

A
  1. Opening an ion channel and thereby changing the membrane
    potential
  2. Acting directly as a membrane-bound enzyme
  3. Acting as an intra cellular receptor when the initial signal passes
    straight through the cell surface membrane [e.g. oestrogen receptor
    is in the nucleus and directly controls gene expression when
    combined with oestrogen]
  4. Direct cell to cell contact is another mechanism of signaling e.g.
    lymphocyte detecting foreign antigens
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67
Q

Phospholipid bilayer is a very effective barrier, particularly against

A

ions and water soluble substances

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68
Q

5 different ways by which exchange of materials is achieved:

A

Diffusion
Facilitated diffusion
Osmosis
Active transport
Bulk transport

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68
Q

DIFFUSION

A

The net movement of molecules or ions from a region of higher concentration
to a region of lower concentration down a concentration gradient, as a result
of random movements of particles

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69
Q

diffusion movement is because of

A

the natural kinetic energy of the molecules or ions

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70
Q

Through diffusion, molecules or ions tend

A

to reach an equilibrium

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71
Q

some molecules/ions are able to pass through living cell membranes by
diffusion

A

example respiratory gases like oxygen and carbon dioxide
[uncharged, non-polar].

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72
Q

Water molecules are highly polar, but can diffuse

A

across the phospholipid bilayer because of its small size

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73
Q

Hydrophobic substances also can cross membranes because the

A

interior of membranes are also hydrophobic

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74
Q

Factors affecting rate of diffusion:

A
  1. Steepness of the concentration gradient:
  2. Temperature:
  3. The nature of the molecules or ions:
  4. The surface area across which diffusion is taking place:
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75
Q

how does the steepness of the concentration gradient affect the rate of diffusion

A

Steeper the concentration gradient, faster the rate of diffusion of that substance

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76
Q

how does the Temperature affect the rate of diffusion

A

Higher the temperature, more the kinetic energy, faster the diffusion

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77
Q

how does the the nature of the molecules or ions affect the rate of diffusion

A

 Larger molecules require more energy, so diffusion is slower.
 Non - polar molecules like glycerol, alcohol and steroid hormones, diffuse more
easily than polar ions as they are soluble in non-polar phospholipid tails

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78
Q

how does the surface area across which diffusion is taking place affect the rate of diffusion

A

 Greater the surface area, more the rate of diffusion. Surface area of cell membranes can be increased by folding – e.g. microvilli, cristae
 Larger the cell, smaller its surface area in relation to its volume [SA:V ratio decreases as the size of any 3D object increases]
 This is why cells need to be small [molecules need to cross quickly]

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79
Q

Surface area to volume ratio decreases as

A

cells get larger. Single celled organisms have relatively large SA:V ratio compared to large multicellular organisms

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80
Q

The larger the surface area to volume ratio,

A

the quicker the rate of diffusion takes place

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81
Q

No. Of cells In humans [multicellular]

A

100 trillion

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82
Q

No. Of cells In amoeba [unicellular]

A

1

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83
Q

SA to V ratio In humans [multicellular]

A

less

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84
Q

SA to V ratio In amoeba [unicellular]

A

More

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85
Q

Diffusion distance In humans [multicellular]

A

Large

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86
Q

Diffusion distance In amoeba [unicellular]

A

Less

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87
Q

Diffusion speed In humans [multicellular]

A

Slow

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88
Q

Diffusion speed In amoeba [unicellular]

A

Fast

89
Q

Hence, humans need

A

respiratory,circulatory and excretory systems to speed up the diffusion process.

90
Q

Amoeba does not need systems as

A

diffusion is facilitated

91
Q

Facilitated diffusion

A

diffusion [higher conc. To lower conc.] of a substance through a transport protein [channel protein or carrier protein] in a cell membrane; the protein provides hydrophilic areas that allow the molecule or ion to pass through the membrane, which would otherwise be less permeable to it

92
Q

2 TYPES OF TRANSPORT PROTEINS

A

Channel proteins and carrier proteins

93
Q

in facilitated diffusion

A

Larger polar molecules [glucose and amino acids] and ions [sodium and
chloride] require proteins molecules to pass through

94
Q

Most channel proteins are ‘gated’

A

means part of the protein inside the surface of the membrane can move to close or open the pore like a gate, which allows control of ion exchange

95
Q

Rate of facilitated diffusion depends on the

A

number of channel or carrier proteins and also whether the channel proteins are open or not

96
Q

Some carrier proteins called ‘pump’,

A

requires energy and are involved in active transport – movement of molecules against the concentration gradient using ATP

97
Q

The carrier pump is specific for a

A

particular type of molecule or ion, and also requires energy – provided by ATP

98
Q

sodium potassium pump

A

a membrane protein that moves sodium ions out and potassium ions into the cell using ATP

99
Q

CHANNEL PROTEINS

A
  • Fixed shape
  • Water-filled pores [e.g. aquaporins]
  • mostly remains open –sometimes ‘gated’
  • Mainly for Facilitated Diffusion
  • Not specific
    *For polar molecules and ions
    *integral Transmembrane proteins
    *Proteins with hydrophilic and hydrophobic regions
100
Q

CARRIER PROTEINS

A
  • Flips between two conformations
    *For both Active Transport and Facilitated Diffusion
    *Specific
    *For polar molecules and ions
    integral Transmembrane proteins
    *Proteins with hydrophilic and hydrophobic regions
101
Q

Factors affecting the rate of facilitated diffusion:

A
  • The number of carrier or channel proteins in the membrane
  • The concentration of molecules on each side of the membrane
  • Whether the channel proteins are open or not – ‘gated’
102
Q

OSMOSIS

A

The net diffusion of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane is called osmosis

103
Q

osmosis is a type of diffusion only happening in

A

water molecules

104
Q

Solution

A

= solute + solvent

105
Q

in a sugar soln

A

sugar is the solute; solvent is water

106
Q

WATER POTENTIAL

A

A measure of the tendency of water to move from one place to another; water moves from a solution with higher water potential to one with lower water potential; water potential is decreased by the addition of solute, and increased by the application of pressure; the symbol of water potential is ψ or ψw

107
Q

Water always moves down a

A

water potential gradient

108
Q

Water moves till the water potential is the

A

same throughout the system, i.e. until equilibrium is reached

109
Q

Water potential depends on 2 factors:

A
  1. the concentration of the solution
  2. how much pressure is applied to it: as pressure increases, water potential of a solution increases
110
Q

water potential can be measured in

A

pressure units called ‘kilopascals’ / kPa

111
Q

Water potential of pure water is

A

always higher than that of a solution[assuming there is no extra pressure applied to the solution]

112
Q

Water potential of pure water is always

A

‘0 kPa’

113
Q

Therefore, for solutions, since water potential is always less than pure water,

A

the water potential value is less than ‘0’ [- kPa]

114
Q

A solution with a water potential of -10 kPa

A

has a higher water potential than a solution with a water potential of -20 kPa

115
Q

Osmosis in animal cells

A
  • If the water potential of the surrounding solution is too high, the cells swell and burst
  • If the water potential of the surrounding solution is too low, the cell shrinks
  • This shows the importance of maintaining water in our body
116
Q
A

red cell bursts

117
Q
A

red cell remains normal

118
Q
A

red cell shrinks

119
Q

Outer covering of cell wall

A

very strong and rigid

120
Q

When kept in a solution with high water potential,

A

water molecule enters till they reach equilibrium; plant cell protoplasm expands, building pressure on the cell wall and the cells will become turgid, but don’t burst

121
Q

plant cells in soln with lower water potential

A

When kept in a solution with lower water potential, water leaves the cells by osmosis,
protoplast shrinks until it is exerting no pressure on the cell wall. It pulls away from the cell wall – gets plasmolysed

122
Q

incipient plasmolysis

A

A condition when protoplasm do not exert pressure on the cell wall

123
Q

Active transport

A

is the movement of molecules or ions through transport proteins across
a cell membrane, against their concentration gradient, using energy from ATP

124
Q

Certain ions like potassium and chloride are often

A

found to be 10 – 20 times more concentrated inside the cells than outside [i.e. a concentration gradient exists, with a lower conc. outside and a higher conc. inside the cell] Therefore for ions to enter, they have to move against the concentration gradient – ACTIVE TRANSPORT, Achieved by carrier proteins called pumps – each of which is specific for an ion or a particular type of molecule. The process requires energy – provided by ATP – through respiration inside the cell

125
Q

ATP helps to

A

change the shape of carrier proteins and also to transport molecules against a
concentration gradient across the membrane

126
Q

sodium-potassium (Na+ – K+) pump

A
  • Found in the cell surface membrane of all
    animal cells
  • Uses 30% of a cell’s energy [70% in nerve cell]
  • For each ATP molecule used, this protein
    pumps 3 sodium out of the cell and 2
    potassium into the cell
  • Both are positive ions, the net result is that
    inside the cell becomes more negative and
    than outside the cell – thus creating a
    potential difference
127
Q

example of active transport

A

sodium-potassium (Na+ – K+) pump

128
Q

Significance of active transport:

A
  1. reabsorption in kidney tubules
  2. absorption in the gut
  3. to load sucrose from photosynthesizing cells of leaves to the phloem tissue
  4. for root hairs to absorb inorganic ions from the soil
129
Q

exocytosis and endocytosis is used for

A

bulk transport

130
Q

Endocytosis – bulk transport

A

into the cell

131
Q

Exocytosis – bulk transport

A

out of the cell

132
Q

exo and endocytosis requires

A

energy – ACTIVE PROCESS

133
Q

ENDOCYTOSIS

A
  • engulf materials to form a vesicle or a vacuole
  • Requires energy
  • Happens in 2 forms:
    1) phagocytosis
    2)pinocytosis
134
Q

phagocytosis

A

e.g. engulfing of bacteria by WBC forming phagocytic vacuoles

135
Q

pinocytosis

A

bulk uptake of liquid

136
Q

micropinocytosis

A

small amount of water uptake forming very small vesicles

137
Q

EXOCYTOSIS

A
  • Reverse of endocytosis
  • Requires energy
  • Materials are removed from cells
    – e.g. secretion of digestive
    enzymes, secretory vesicles, in
    plants for making cell wall
138
Q
A

exocytosis

139
Q
A

endocytosis

140
Q

Osmosis can be made faster using

A

transport proteins, though membrane is enough for the process

141
Q

Cholesterol is in between the

A

phospholipid layers and not near the outer surface of phospholipids

142
Q

All water soluble molecules can travel only through the

A

transport proteins, whereas fat-soluble substances can directly cross the lipid bilayer

143
Q

Active processes requires

A

ATP [active transport, exocytosis and endocytosis

144
Q

Passive processes do not require

A

ATP [osmosis, diffusion, facilitated diffusion]

145
Q

Down the conc. gradient means from

A

higher concentration to lower concentration

146
Q

Up / against the conc. gradient means from

A

lower concentration to higher concentration

147
Q

Diffusion, facilitated diffusion and osmosis occurs by

A

random movement of molecules

148
Q

Exocytosis and endocytosis also depends on the

A

fluidity of the membrane

149
Q

Compared to diffusion, facilitated diffusion is faster due to the

A

presence of proteins

150
Q

Fluidity of the cell membrane is also important in

A

cytokinesis[cytoplasmic division during cell division]

151
Q
  • S.A =
A

length x height]

152
Q

Volume =

A

length x height x depth

153
Q

SA:V ratio =

A

total surface area / volume

154
Q

larger the surface area to volume ratio,

A

greater the diffusion

155
Q
A
156
Q
A
157
Q
A
158
Q
A
159
Q
A
160
Q
A
161
Q
A
162
Q
A
163
Q
A
164
Q
A
165
Q
A
166
Q
A
167
Q
A
168
Q

which process is the movement of molecules that are too large to diffuse in
through a csm?

A

endocytosis / exocytosis

169
Q

properties of glycolipids / glycoproteins

A
  1. act as receptor sites for hormones
  2. form hydrogen bonds w water
  3. recognise antibodies
170
Q

properties of phospholipids

A
  1. to allow cytokinesis to occur in mitotic cell division
  2. to allow entry and exit of water-soluble gases
  3. to allow phagocytosis of a bacterium into cells
171
Q

factors inversely prop to rate of diffusion

A
  1. size of diffusing molecule
  2. diffusion distance
172
Q

channel protein vs carrier protein

A

Channel proteins: water-filled pores that allow charged substances,
usually ions, to diffuse through the membrane. They have a fixed shape
and can be gated to control ion exchange. This does not use ATP and is
in facilitated diffusion.
Carrier proteins: can flip between two shapes, and is mainly in active
transport where it uses ATP to change shape and carry ions/molecules
up the concentration gradient. It is also involved in passive transport
(facilitated diffusion) down the concentration gradient without the use of
energy.
fat-soluble substances could pass through the phospholipids and
water-soluble would pass through a water filled pore (protein channel)
idk why but its thru a carrier protein
carrier proteins only transport solutes in an ezyme-substrate way, not
solvents

173
Q

virus invading a cell

A

binding to a protein receptor, followed by endocytosis

174
Q

what supports the view that a membrance protein is involved in active
transport?

A

it can only function if mitochondria are supplied with sufficient oxygen

175
Q

what is correct for the csm and membranes within cells?

A

both have sites for enzyme attachment

176
Q

as fluidity of csm decreases what process would be least changed?

A

active transport!
the number and position of transmembrane proteins involved in active
transport would be least changed

177
Q

even distribution of proteins w floresecent dyes in csm cool question

A

protein molecules in the outer layer of the csm and those which span the
bilayer can move freely between phospholipid molecules

178
Q

which part of phospholipid molecule makes up most of the thickness of a
csm

A

hydrocarbon chains!!

179
Q

why does rate of facilitated diffusion level off whereas rate of simple diffusion
does not

A

fd is limited by the number of protein channels in the membrane

180
Q

which molecules are involved in cell signalling?

A

only trans-membrane proteins
not glycos or surface proteins (idk it could be this too)

181
Q

role of g protein in cell signalling

A

to act as a switch releasing a second messenger

181
Q

vit c is water soluble so it shud go through carrier na cuz its a vitamin

A

it isnt
a charged molecule, molecules with charge and dissolved pass through
channel

182
Q

for sa: v ratio take the

A

greatest sa

183
Q

osmosis is only

A

solvent

184
Q

active transport does not occur withou

A

o2 (mitochondria are unable to
produce atp)

185
Q

diffusion can occur within an absence of

A

membranes

186
Q

prokaryotes have

A

proteins and phospholipids in their csm

187
Q

glycos + proteins help immune system

A

identify cells [antigen markers]

188
Q

high concentration of ions in the vacuole does not increase

A

the efficiency of
ion uptake

189
Q

endo/exo cytosis r not a result of

A

the random movement of molecules

190
Q

glucose can’t pass directly thru csm

A

it needs protein / carrier proteins

191
Q

oxygen passes freely through the membrane as it is

A

soluble in lipids

192
Q

glycoproteins form hydrogen bonds w water to stabilise

A

membrane

193
Q

phospholipd tails and cholestrol maintain

A

membrane fluidity

194
Q

facilitated diffusion is driven by the

A

ke of the molecukes which are diffusing +
it depends on number of protein channels also

195
Q

water can cross cell membrances by passing thru

A

channel proteins

196
Q

going out of cell / secretion =

A

exocytosis

197
Q

glycoproteins are most important for recognising

A

self / non-self antigens
[they would enable a hormone to recognise its target cell aw)

198
Q

membrane proteins have both

A

hydrophobic and hydrophilic regions

199
Q

fleshy leaves and fewer stomata

A

DO NOT REDUCE the water potential
gradient in xerophytes

200
Q

cholestrol can help increase

A

fluidity, but not decrease fluidity

201
Q

since ions r thru carrier proteins,

A

cystic fibrosis means the carrier protein is
faulty

202
Q

thinner side of cell

A

expands more

203
Q

in cold weather

A

ur tryna increase fluidity

204
Q

more cholestrol =

A

more fluidity

205
Q

active transport does not result in an

A

equilibirum (cuz lower to higher)

206
Q

some of the csm is lost when endocytosis occurs and

A

there is an increase in
the csm when exocytosis occurs

207
Q

during lysis, more water enters

A

s the cell than leaves in (NOT more water
enters the cell and none leaves it) - osmosis is the net movement of water

208
Q

channel proteins are not fixed

A

in position [ both the membrane and proteins
are fluid ]

209
Q

glycoproteins in the outer layer of the membrane

A

can move

210
Q

visking tubing can be used to represent

A

csm and tonoplast NOT CELL WALL
bcz cell wall is fully permeable instead of being partially permeable

211
Q

in those potato piece qs only

A

water moves

212
Q

no movement is not the same as

A

no net movement

213
Q

Why is it called the fluid mosaic model?

A

phospholipid (and protein) molecules, move about/ diffuse/AW ;
protein (molecules), scattered/AW ; A different proteins present

214
Q

Role in cell membrane of
Glycoproteins

A

receptors / receptor molecules;
for hormones / neurotransmitters / named hormone /
neurotransmitter (e.g. insulin, acetylcholine, noradrenaline);
idea of ( ) antigens / (cell surface) markers / cell
recognition / cell adhesion;
help to stabilise membrane structure / forms H bonds with watermolecules

215
Q

carrier proteins

A

allow named substance (e.g. glucose / amino acids) / polar substance
/ ion(s) / hydrophilic / water soluble substance (to pass through
membrane);
(ref) against concentration gradient / active transport;
energy / ATP (req for transport);
(and) facilitated diffusion / faster than simple diffusion (for ions
/ polar molecules);

216
Q

Cholesterol

A

maintains / regulates fluidity of membrane / prevents membrane
being too rigid or fluidfRluid / mechanical stability (qualified) /
prevent ions / polar / water soluble / named molecule, passing /
leaking through membrane;

217
Q

General points to write when asked “how is XYZ a cell signalling mechanism”

A

The “molecule” [given in qs] acts as a cell signalling molecule
It moves through the bloodstream/extracellular space /intracellular space
To reach the target cell which is the [given in qs]
It will bind to complementary, specific, receptors [on the cell membrane - depends on qs]
This will lead to response which is [given in qs]
AVP e.g. detail of change, such as activating G proteins / secondary messenger / enzyme cascade /chain of reactions

218
Q

Phospholipids

A
  1. can form a bilayer ;
  2. link between, hydrophobic core / AW, and barrier to water-soluble substances ; A polar/ ionic
  3. idea of, hydrophilic / phosphate, head, forming H bonds with water ; A facing, water / watery environment / aqueous environment / cytoplasm / cytosol
  4. ref. contribution to fluid nature of membrane ;
  5. further detail ; e.g. mainly saturated fatty acids, less fluid e.g. mainly unsaturated fatty acids, more fluid
  6. ref. to control over membrane protein orientation ; e.g. hydrophobic – hydrophobic interaction for ‘floating’ proteins
219
Q

Some cells take in bacteria by endocytosis. Explain how endocytosis occurs at the cell surface membrane.

A
  1. attachment (of bacteria) to receptor(s) ; AW
  2. ref. ability to attach to antibody (bound to antigen on bacterium)
  3. infolding / invagination / AW, of membrane ; A membrane engulfs A pseudopodia
  4. form (round bacterium)
  5. fusion / AW, of membrane ;
  6. formation of, vacuole / vesicle ;
220
Q

Functions of lysosome in endocytosis of bacteria

A

break down / digest / destroy, bacteria / pathogen(s) ;
break down / digest / destroy, (worn out / defective / AW), organelles / named organelle (in animal cell) ; A autophagy
catalyses / speed up, hydrolysis ;
any two named substrates ; e.g. (any named) polysaccharides / proteins / (phospho)lipids / (named) nucleic acids
idea that recycle / reuse, biological molecules within cell ;
(macrophage / phagocyte) cut up to present antigen

221
Q

The surface area to volume ratio decreases as animals increase in size.
Use this fact to suggest why multicellular animals require transport systems

A

dea that diffusion (via, body surface / to cells), cannot satisfy needs / too slow ;OR transport system delivers materials to cells more quickly ; (A) efficient supply of, nutrients / oxygen, to all cells
long(er) distances (to reach some, cells / tissues) ;
takes, materials / AW, close to cells ;

222
Q

How does phospholipid molecule make it suitable for its function.

A

Hydrophilic phosphate head and hydrophobic fatty acid tail
Forms a bilayer with head outside and tail inside
Head faces aqueous environment and tail faces each other to form hydrophobic core
Forms H-bonds with water
Stabilises membrane
Fatty acid may be saturated/unsaturated
Unsaturated makes membrane fluid
Barrier to polar substance

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