M2, C5 Plasma Membranes

Question 1

what is compartmentalisation

Answer 1

the formation of separate membrane-bound areas in a cell

Question 2

define plasma membrane

Answer 2

the cell surface membrane that separates the cell from its external envrionment

Question 3

what are membranes formed from

Answer 3

a phospholipid bilayer
hydrophilic phosphate heads form the inner and outer surface of a membrane
fatty acid tails are sandwiched inside to form the hydrophobic core

Question 4

where do cells normally exist

Answer 4

aqueous environments

Question 5

why are phospholipid bilayers suited for aqueous environments

Answer 5

the outer surfaces of the hydrophilic phosphate heads can interact with water

Question 6

what is the fluid-mosaic model

Answer 6

shows how proteins occupy various positions in the membrane
phospholipids are free to move within the layer relative to each other
this gives the membrane flexibility

Question 7

what are the components in a cell membrane

Answer 7

glycoprotein
glycolipid
cholesterol
hydrophilic heads of phospholipid molecules
Channel proteins
Carrier Proteins
hydrophobic tails of phospholipid molecules

Question 8

what are the 2 types of membrane proteins

Answer 8

intrinsic and extrinsic

Question 9

what are intrinsic proteins

Answer 9

transmembrane proteins that are embedded in both layers of the membrane
have amino acids and hydrophobic R groups on the external surfaces which interact with the hydrophobic core keeping them in place

Question 10

what are channel proteins

Answer 10

channel proteins - provide a hydrophilic channel to allow passive movement of polar molecules and ions down a concentration gradient. this is held in place by the interactions between the hydrophobic core and the R groups on the outside of proteins

they are intrinsic

Question 11

what are glycoproteins

Answer 11

Proteins with carbohydrates attached

they play a role in cell adhesion (when cells join together) and act as receptors for chemical signals

Question 12

what are glycolipids

Answer 12

phospholipids with carbohydrates attached

antigens so the immune system recognises it as self or non-self

Question 13

what is cell signalling

Answer 13

involves glycoproteins
when the chemical binds to the receptor on the glycoprotein, it elicits a response from the cell which can set off a cascade of events

Question 14

what are extrinsic proteins

Answer 14

Extrinsic proteins: these are proteins which are found on the surface of the plasma membrane. They usually function as enzymes and catalyse chemical reactions inside the cell.

Question 15

why is cholesterol in the plasma membrane

Answer 15

It is found between individual phospholipids preventing them from packing to closely together preventing the structure from crystallizing, as a result it regulates the fluidity and rigidity of the PLBL

Question 16

what needs to happen for a chemical reaction to take place

Answer 16

all the organelles need to be in specific positions

Question 17

what happens to phospholipids as temperature increases

Answer 17

they gain kinetic energy meaning they move more
the membrane becomes more fluid because it loses its structure
Carrier and Channel proteins denature and lose their shape increasing the permeability of the PLBL

Question 18

what does the loss of structure in cell membranes mean

Answer 18

they become more permeable meaning particles can more easily cross it

Question 19

what happens to carrier and channel proteins as temp increases

Answer 19

denature

increases membrane permeability further

Question 20

why is water essential for the formation of the phospholipid bilayer

Answer 20

Because the non-polar tails of the phospholipids are orientated away from water which forms a bilayer with the hydrophobic core
the charged phosphate heads interact with water which keeps it intact

Question 21

what are carrier proteins

Answer 21

carrier proteins - passive and active transport into cells. this often involves the proteins changing shape

they are intrinsic

Question 22

how do organic solvents affect membranes

Answer 22

they dissolve membranes which disrupts cells= an increase in permeability

Question 23

give a common example of an organic solvent

Answer 23

alcohol

Question 24

why is alcohol in anti-septic wipes

Answer 24

the alcohols dissolve the membranes of bacteria in a wound, killing them and reducing the risk of infection

Question 25

why are pure or very strong alcohol solutions dangerous

Answer 25

they are toxic they destroy cells the molecules can enter the membranes and disrupt the membrane because they lie between phospholipids

Question 26

what happens when a membrane is disrupted

Answer 26

it becomes more fluid and more permeable

Question 27

give an example of a cell that needs intact cell membranes to function

Answer 27

nerve cells if neuronal membranes are disrupted then nerve impulses are no longer transmitted as normal, hence why people behave differently when they drink alcohol

Question 28

suggest an experiment to investigate how temperature affects membrane permeability

Answer 28

1. get 5 small pieces of beetroot, all equal sizes 2. thoroughly wash under water 3. place in 100ml of distilled water in a water bath 4. increase the water bath by 10 degrees 5. samples of water taken 5 mins after the water bath has increased by 10 degrees 6. measure the absorbance of each sample using a colorimeter with a blue filter 7. repeat 3 times the results show that absorbance rapidly increases after 50 degrees hence suggesting that the membrane is disrupted between 40 and 50 degrees

Question 29

what microscope would you see a detailed plasma membrane

Answer 29

electron microscope - you would see the double line which is 7-10 nm thick (a light microscope you would see a single line)

Question 30

how can polar and non-polar molecules pass through the membrane

Answer 30

Polar molecules require proteins to enable them to pass through the membrane Non-polar molecules can diffuse directly through the phospholipid bilayer

Question 31

define diffusion

Answer 31

the net movement of particles from a region of higher concentration to a region of lower concentration

Question 32

when does diffusion continue to

Answer 32

until there is a concentration equilibrium between the 2 areas

Question 33

why does diffusion happen

Answer 33

particles in a gas or liquid have kinetic energy | this movement is random and unequal

Question 34

what slows down the overall movement in diffusion

Answer 34

particles are constantly colliding with each other this means diffusion over short distances are faster

Question 35

what factors affect the rate of diffusion

Answer 35

temp - increases kinetic energy concentration difference - overall movement will be larger diffusion distance

Question 36

what is simple diffusion

Answer 36

diffusion when there is no barrier/ membrane

Question 37

why are membranes described as partially permeable

Answer 37

polar molecules diffuse through a membrane at a slow rate | small polar molecules pass through more easily

Question 38

what is the rate at which molecules or ions diffuse across membranes is affected by

Answer 38

surface area | thickness

Question 39

what is facilitated diffusion

Answer 39

diffusion across a membrane through protein channels

Question 40

what are membranes with protein channels known as

Answer 40

selectively permeable

Question 41

what is the rate of facilitated diffusion dependent on

Answer 41

``` temperature concentration gradient membrane surface area thickness number of channel proteins present ```

Question 42

what is active transport

Answer 42

the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration

Question 43

what is needed for active transport

Answer 43

metabolic energy is supplied by ATP

Question 44

what do carrier proteins act as in active transport

Answer 44

pumps

Question 45

give the process of how an ion is transported into a cell via a carrier protien

Answer 45

1. the molecule binds to receptors in the channel of the carrier protein on the ourside of the cell 2. ATP binds to the carrier protein inside the cell and is hydrolysed into ADP and phosphate 3. The binding of the phosphate molecule to the carrier protein causes the protein the change shape which opens up to the inside of the cell 4. molecule is released to the inside of the cell 5. phosphate molecule is released from the carrier protein and recombines with ADP to form ATP 6. Carrier protein returns to its original shape

Question 46

why is active transport into the cell selective

Answer 46

because specific substances are transported by specific carrier proteins

Question 47

what is bulk transport

Answer 47

form of active transport large molecules and whole cells are too large to move through channel or carrier proteins so are moved into and out of cell by bulk transport

Question 48

what are two types of bulk transport

Answer 48

endocytosis - bulk transport into cells exocytosis - bulk transport out of cells

Question 49

what are the two types of endocytosis

Answer 49

phagocytosis - for solids pinocytosis - for liquids

Question 50

give the process for endocytosis

Answer 50

1. cell surface membrane invaginates when it comes into contact with material 2. the membrane enfolds the material 3. the membrane fuses which forms a vesicle 4. vesicle pinches off and moves into cytoplasm to transfer material

Question 51

what are the basic steps for exocytosis

Answer 51

its the opposite of endocytosis vesicles formed by the Golgi apparatus move towards and fuse with the cell surface membrane the contents of the vesicle are then released outside of the cell

Question 52

why is ATP needed for bulk transport

Answer 52

the move vesicles along the cytoskeleton change the shape of the cell to engulf materials fusion of cell membranes as vesicles form or as they meet the cell surface membrane

Question 53

what is a solute

Answer 53

a substance dissolved in a solvent forming a solution

Question 54

what is water potential

Answer 54

the pressure exerted by water molecules as they collide with a membrane or container it's measured in pascals symbol is the greek letter psi

Question 55

define pure water

Answer 55

has a water potential of 0kPa which is the highest possible value for water potential

Question 56

what happens when solutions with different concentrations/ different water potentials are separated by a partially permeable membrane

Answer 56

the water molecules can move between the solutions but solutes usually can't there is a net movement of water from the solution with high water potential to the solution with lower water potential

Question 57

is a solution more or less concentrated if the water potential is high

Answer 57

less

Question 58

what is hydrostatic pressure

Answer 58

the diffusion of water into a solution leads to an increase in volume of this solution if the solution is in a closed system, pressure increases

Question 59

what are the units of hydrostatic pressure

Answer 59

kPa

Question 60

what happens if an animal cell is placed in a solution with a higher water potential than that of the cytoplasms

Answer 60

water will move into the cell by osmosis, increasing hydrostatic pressure inside the cell

Question 61

what is cytolysis

Answer 61

when the cell-surface membrane of an animal cell can't stretch enough to withstand the hydrostatic pressure so breaks and the cell will burst

Question 62

what happens if an animal cell is placed in a solution that has a lower water potential than the cytoplasm

Answer 62

it will lose water to the solution by osmosis down the water potential gradient causes a reduction in the cell volume and the cell-surface membrane 'puckers' (crenation)

Question 63

how is cytolysis or crenation prevented

Answer 63

animals have control mechanisms to make sure their cells are continuously surrounded by aqueous solutions with an equal water potential (isotonic)

Question 64

what is the aqueous solution in blood

Answer 64

blood plasma

Question 65

in a red blood cell, what happens if it is in a high water potential solution

Answer 65

water enters cell it swells and bursts haemoglobin is released

Question 66

in a red blood cell what happens if it is a low water potential solution

Answer 66

water leaves cell haemoglobin is more concentrated so the cell appears darker cell shrinks and shrivels

Question 67

in a red blood cell what happens if it is an equal water potential solution

Answer 67

water constantly enters and leaves at equal rates | red blood cell is normal

Question 68

where are solutes stored in a plant cell

Answer 68

dissolved in the vacuole

Question 69

what differs plants and animals in terms of osmosis

Answer 69

plants are unable to control water potential of fluid around them eg. roots are usually surrounded by almost pure water

Question 70

what happens when water enters a plant cell by osmosis

Answer 70

hydrostatic pressure increases membrane is pushed against the rigid cell wall the pressure against the cell wall is called turgor as turgor increases it resists entry of further water and the cell is said to be turgid

Question 71

what is turgor pressure

Answer 71

pressure against the cell wall

Question 72

what is a cell called when it stops the entry of water into it

Answer 72

turgid

Question 73

what happens when plant cells are placed in a solution with a lower water potential

Answer 73

water is lost from the cells by osmosis | there is a reduction in the volume of the cytoplasm

Question 74

what does it mean when a cell is said to be plasmolysed

Answer 74

when water is lost from the cell through osmosis if this doesn't stop then volume of cytoplasm keeps reducing which pulls the cell-surface membrane away from the cell wall

Question 75

how can you investigate osmosis in plant cells

Answer 75

place pieces of potato or onion into sugar or salt solutions with different concentrations/different water potentials water will move into or out of cells depending on water potential of the plant tissue as the plant tissue gains or loses water it will increase or decrease in mass and size

Question 76

how can you investigate osmosis in animal cells

Answer 76

eggs are used boil the egg, remove the shell and there is a single membrane bound structure place the eggs in different concentrations of sugar syrup overtime osmosis takes place and there will have been a net movement of water into or out of the eggs

Question 77

how thick is the plasma membrane

Answer 77

7-10nm