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biology - core concepts > cell membranes and transport > Flashcards

cell membranes and transport Flashcards

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1
Q

define hydrophobic

A

a molecule that is repelled by water molecules

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2
Q

define hydrophilic

A

a molecule that is attracted to water molecules

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3
Q

define diffusion

A

the passive movement of a molecule or ion down a concentration gradient from a region of higher concentration to a region of lower concentration

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4
Q

define facilitated diffusion

A

the passive transfer of molecules or ions down a concentration gradient, by a protein channel or carrier molecules in the membrane

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5
Q

define co transport

A

a passive process that brings molecules and ions into cells together on the same protein transport molecules
e.g sodium and glucose

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6
Q

define active transport

A

transport of ions and molecules against the concentration gradient
uses energy from the hydrolysis of ATP, made by the cell in respiration
requires an intrinsic carrier protein

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7
Q

define exocytosis

A

the process by which substances may leave the cell in bulk, having been transported through the cytoplasm in a vesicle, which fuses with the cell membrane

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8
Q

define endocytosis

A

the process by which substances may enter the cell in bulk

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9
Q

define osmosis

A

the passive movement of water, from an area of higher water potential to an area of lower water potential across a selectively permeable membrane

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10
Q

define hypertonic

A

a solution with a lower water potential than its surrounding (due to more solute being present)

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11
Q

define hypotonic

A

a solution with a higher water potential than its surroundings (due to less solute being present)

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12
Q

define isotonic

A

a solution with the same water potential as its surrounding

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13
Q

define solute potential

A

due to the solutes in the vacuole and cytoplasm, it is the lowering of water potential due to the presence of solute molecules

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14
Q

define pressure potential

A

the pressure exerted by the cell contents of the cell wall, a force which increases the tendency of water to move out

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15
Q

why is the fluid mosaic model used to describe a phospholipid bilayer?

A
  • phospholipid molecules can move around and are quite flexible, making them have fluidity
  • randomly distributed protein molecules may vary in shape and size forming a mosaic pattern
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16
Q

explain how phospholipid molecules interact with water that is both in the cytoplasm and outside the cell

A

the hydrophilic heads forms hydrogen bonds with the water molecules on the outside of the cell membrane
hydrophobic tails - repel water

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17
Q

what is a glycoprotein?

A

proteins which have carbohydrate groups attached to the polypeptide chain

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18
Q

state two functions of membrane glycoproteins

A
  • antigens, allowing self replication
  • act as receptors
  • hold cells together
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19
Q

what is the permeability of cell membrane affected by?

A
  • temperature
  • organic solvents e.g ethanol
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20
Q

how is permeability affected by temperature?

A

the molecules moving through the membrane will have more kinetic energy and will diffuse more quickly
phospholipids gain kinetic energy

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21
Q

how is permeability affected by organic solvents?

A

ethanol dissolves the phospholipids and may denature the proteins, resulting in gaps or holes within the cell membrane
the membrane becomes more porous

acetone has a similar effect

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22
Q

what is osmosis?

A
  • the diffusion of water, from a higher water potential to an area of lower water potential across a selectively permeable membrane
  • it is a passive process so does not require ATP
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23
Q

what is water potential?

A

the tendancy for water to leave a solution or cell by osmosis

24
Q

what is water potential measured in?

A

kPa

25
Q

what is the water potential of pure water?

A

0kPa

26
Q

what are the methods of transport across the membrane?

A
  • diffusion
  • facilitated diffusion
  • co-transport
  • active transport
  • bulk transport
  • osmosis
27
Q

how do lipid soluble substances transport across the membrane?

A

small uncharged molecules (such as oxygen and carbon dioxide) dissolve in the hydrophobic tails and diffuse across the cell membrane

non polar substances can also dissolve in phospholipids and diffuse through cell membrane

28
Q

how do water soluble substances transport across the membrane?

A

polar molecules (such as glucose and amino acids) and charged ions (Na+) cannot diffuse through the phospholipids
they pass through intrinsic protein molecules

29
Q

what is diffusion?

A

passive movement of a molecule or ion down a concentration gradient, from a region of higher concentration to a region of lower concentration

30
Q

what are the factors affecting rate of diffusion?

A
  • concentration gradient
  • thickness of the surface
  • the surface area of the membrane
  • the size of the diffusing molecules
  • the nature of diffusing molecules
  • temperature
31
Q

what are the two types of facilitated diffusion?

A

gated protein channel
co-transport

32
Q

what is co-transport?

A
  • a type of facilitated diffusion that brings molecules and ions into cells together on the same protein transport molecule.
  • co-transport is a passive process
33
Q

what is facilitated diffusion?

A

the passive transfer of polar molecules or charged ions down a concentration gradient, across a membrane, by channel or carrier proteins in the membrane

34
Q

what is the rate of facilitated diffusion affected by?

A
  • number of channel/carrier proteins present in the membrane
  • the steepness of the concentration gradient
35
Q

what are the two types of protein molecules?

A
  1. channel proteins
  2. carrier proteins
36
Q

describe channel proteins

A
  • proteins molecules with water-filled hydrophilic pores
  • ions, being water soluble, can pass through because the pores are hydrophilic
  • each channel is specific for one type of ion
  • channels open and close depending on the ion needs for the channel
37
Q

describe carrier proteins

A
  • allows diffusion of larger polar molecules such as glucose and amino acids
  • a polar molecules attaches to a binding site on the carrier protein. this causes the protein to change shape releasing the molecule through the other side of the membrane
38
Q

what is gated protein channels?

A

can be opened and closed to allow ions through
e.g sodium ion gated channels that open during initiation of nerve impulse

39
Q

what are the steps to co-transport?

A
  1. there is a concentration gradient for sodium ions to move into the cell
  2. sodium ions and glucose bind to the carrier proteins
  3. the carrier protein changes shape, and the sodium ions and glucose are transported to the other side of the membrane
  4. this process can move glucose against its concentration gradient without the use of ATP - this is known as secondary active transport
40
Q

what are the steps to the active transport?

A
  1. the molecules or ion binds to the carrier proteins on the outside of the cell membrane
  2. ATP transfers a phosphate group to the carrier protein
  3. the carrier protein changes shape and carrier the ion or molecule across the membrane
  4. the molecule or ion is released into the cytoplasm of the cell
  5. the carrier protein returns to its original shape
41
Q

describe active transport

A
  • against the concentration gradient
  • uses energy from the hydrolysis of ATP, made by the cell in respiration
  • if respiration is inhibited, active transport is too
  • requires an intrinsic carrier protein as in facilitated diffusion, because transport is against the concentration gradient the process requires energy and the carrier acts as a pump
  • only charged particles can be actively transported
42
Q

what are the two methods of bulk transport?

A
  • endocytosis
  • exocytosis
43
Q

describe exocytosis

A

SECRETION
- the process by which substances may leave the cell having been transported through the cytoplasm in a vesicle, which fused with the cell membrane
- a vesicle is produced in the cytoplasm
- the vesicle moves to the plasma membrane, fuses with it and secretes its contents to the outside of the cell

44
Q

what are the two types of endocytosis?

A
  • phagocytosis
  • pinocytosis
45
Q

what is phagocytosis?

A

the uptake of solids
e.g white blood cells engulf bacteria

46
Q

what is pinocytosis?

A

the uptake of liquids
e.g lipid droplets

47
Q

describe endocytosis

A

UPTAKE
- cell membrane folds into particles
- the folding closes off the link to the outside of the cell
- the particle is fully trapped inside the cell in a vesicle or vacuole

48
Q

what is the equation of water potential?

A

water potential = pressure potential + solute potential

49
Q

why do not plant cells burst?

A

even though the cell cytoplasm and vacuole are full of water (turgid), the cell wall cannot stretch (inelastic) so this prevents the cell from overfilling

50
Q

what will happen to a plant cell when placed in a hypertonic solution?

A

water will move out of the cell into the surrounding solution by osmosis
the vacuole shrinks and the cytoplasm and cell membrane will withdraw from the cell wall
this causes the plant cell to become plasmolysed

51
Q

what is the incipient plasmolysis?

A
  • the point at which the cell membrane is just about to come away from the cell wall
  • where 50% of the cells in a sample are plasmolysed
52
Q

at incipient plasmolysis, what would pressure potential be?

A

0 kPa

53
Q

what is the equation for water potential at incipient plasmolysis?

A

water potential = solute potential

54
Q

explain why animal cells burst in a hypotonic solution

A
  • water moves into the cell by osmosis
  • from an area of high water potential to an area of lower water potential
  • the cell cytoplasm swells and the cell bursts
55
Q

explain why animal cells crenate in a hypertonic solution

A
  • water leaves the cell by osmosis
  • from an area of higher water potential to an area of lower water potential
  • the cell cytoplasm shrinks and the cell crenates

biology - core concepts (6 decks)

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