Membranes

Question 1

5 roles of membranes within the cell or on the surface

Answer 1

within: 1. compartmentalize organelles
2. isolates harmful enzymes in lysosomes
surface: 1. recognition by other cells (immune system)
2. partially permeable so control what enters and leaves the cell.
both: can form vesicles to transport substances

Question 2

define and explain compartmentalization

Answer 2

the division of organelles within a cell which allows for specific microenvironments within the cell so each organelle has the optimum conditions to perform at its best ability.

Question 3

define partially permeable

Answer 3

permeable to only some molecules but not others

Question 4

define cell signaling

Answer 4

the way cells are able to interact with their environment and other cells, to either detect nutrients or to be involved in communication.

Question 5

define phospholipid bilayer

Answer 5

a thin polar molecule made of two layers of lipid molecules which acts as a partially permeable membrane.

Question 6

what is the fluid mosaic model of membrane structure

Answer 6

it describes the structure of an animals plasma
membrane. The fluid refers to the flexibility of the model and the mosaic to how the components are put together in lots of small pieces.

Question 7

define cell adhesion

Answer 7

the process where neighboring cells attach through specialized molecules on their surface.

Question 8

how does cholesterol affect the fluidity and stability of membranes?

Answer 8

fluidity: the presence of cholesterol regulates fluidity as it prevents ordered packaging of lipids increasing the fluidity of motion.
stability: without it cells will burst open as their membranes break. Their hydrophobic regions help to prevent ions or polar molecules inadvertently passing through the membrane.

Question 9

How does cell signaling work?

Answer 9

1. cells release a molecule e.g hormone
2. signaling molecules bind to specific receptor molecules on plasma membrane of target cells
3. signaling molecules have a complementary shape to the membrane receptor
4. response in the cell

Question 10

types of cell signaling

Answer 10

local signaling- cells close by, paracrine secretion
local signaling- nerve impulses across synapse
distance secretion- endocrine secretion, hormones into the blood
distance secretion- neurosecretion, hormones into the blood

Question 11

what is the effect of a high temp on cell membranes

Answer 11

high temp increases fluidity- fatty acid tails become less rigid and allow more movement of proteins and other molecules in the membrane the membrane becomes more permeable. Integral and peripheral proteins can be damaged.

Question 12

what is the effect of a low temp on membrane structure

Answer 12

stiffens the membrane- fatty acid tails move less and become more rigid decreasing fluidity and permeability potentially restricting entry of important molecules

Question 13

what is the effect of a low temp on membrane structure

Answer 13

stiffens the membrane- fatty acid tails move less and become more rigid decreasing fluidity and permeability potentially restricting entry of important molecules e.g. oxygen

Question 14

why is water as essential solvent in membranes

Answer 14

the non polar tails in the phospholipids are orientated away from the water forming a bilayer with a hydrophobic core, the charged polar heads interact wit the water keeping the bilayer intact.

Question 15

what is the effect of solvent concentration on permeability of cell membranes

Answer 15

organic solvents are less polar than water so will dissolve membranes disrupting cells - why antiseptic wipes use alcohols as it dissolves the membrane on the bacteria killing them and reducing the risk of infection.

Question 16

describe how to investigate the effect of temperature on membrane permeability

Answer 16

1. have 5 different test tubes labelled with 5 different temperatures (20,35,45,60,80)
2. place 5 beetroot discs in 15cm3 of distilled water in each test tube
3. place 5 test tubes in the water bath
4. when the thermometer reaches each temperature take the same test tube out of the water bath
5. place the test tube in a cold water cooling beaker
6. ue a pipette to transfer each solution to a cuvette
7. use a colorimeter to measure the absorbance for each temperature.

Question 17

define cytosis and the types

Answer 17

movement quantity of large molecules which requires ATP
Exocytosis: bulk transport of substances out of the cell
Endocytosis: bulk transport of substances into the cell
Pinocytosis: to take in or get rid of liquid materials
Phagocytosis: to take in or get rid of solid materials

Question 18

define active transport

Answer 18

the movement of molecules or ions across a membrane in the opposite direction of the concentration gradient which requires ATP and uses intrinsic carrier proteins as pumps (sopi pump)

Question 19

define facilitated diffusion

Answer 19

this is passive and doesn’t require ATP - movement of molecules from a region of high to low concentration uses both carrier and channel proteins

Question 20

define simple diffusion

Answer 20

movement of molecules from a region of high to low conc down a conc gradient

Question 21

define osmosis

Answer 21

osmosis the movement of water molecules from an area of high water potential to an area of lower water potential across a partially permeable membrane - water moves through the bilayer through protein channels called AQUAPRORINS

Question 22

difference between a channel and carrier protein

Answer 22

channel- allows solutes to diffuse through pore
carrier- solutes bind on one side and are released on the other side of the membrane.
carrier proteins a lot slower

Question 23

factors affecting the rate of diffusion

Answer 23

distance
temperature
concentration gradient
surface area

Question 24

why is ATP required in active transport

Answer 24

ATP requires the energy needed for solutes to move against their concentration gradient

Question 25

how do substances move across a membrane by simple diffusion.

Answer 25

substances move down a concentration gradient between the tails in the phospholipid bilayer.

Question 26

what types of molecules can move across a membrane by simple diffusion?

Answer 26

gases, small molecule and lipid based molecules

Question 27

how do substances move across a membrane by facilitated diffusion

Answer 27

substances can either be carried, bind to a carrier protein on one side of the membrane and released on the other, or diffuse through the pore of channel proteins. Carrier proteins have a specific shape to only allow certain molecules to bind and channel proteins are specific to one type of ion.

Question 28

how do substances move across a membrane by active transport

Answer 28

active transport gets the energy required from the hydrolysis of ATP and use carrier proteins that are specific to the ion and ‘pump’ them across the membrane

Question 29

how do molecules move out of the cell by exocytosis (e.g. secretion)

Answer 29

secretory vesicle travels towards the cell surface membrane with the molecules being transported trapped inside. the secretory vesicle fuses with the cell membrane and the molecules are transported out of the gap within the cell surface membrane.

Question 30

how do molecules move out of the cell by endocytosis (e.g. pinocytosis)

Answer 30

a pinocytic vesicle forms from the cell surface membrane containing the liquid from outside the cell and the vesicle enters with the liquid inside of it.

Question 31

which transport mechanisms require ATP

Answer 31

active transport

cytosis

Question 32

why is it easier for oxygen to diffuse across a membrane than a water molecule

Answer 32

an oxygen molecule can diffuse through by simple diffusion through the phospholipids as its a small molecule however water also diffuses by simple diffusion but in small amounts due to the fact that it is polar- large amounts of water would require aquaporin

Question 33

why can steroid hormones easily diffuse across a membrane by simple diffusion

Answer 33

because they are fat soluble so are able to pass though the membrane

Question 34

why are ions only able to cross the membrane through a protein channel

Answer 34

the ions are charged so would be repelled by the hydrophobic core of the phospholipid bilayer rather than be able to dissolve so have to be transported by ion channels for diffusion

Question 35

how would you investigate the effect of how diffusion is affected by surface area

Answer 35

cells can be represented by agar cubes of different sizes. If dyed pink the rate of diffusion is visible. place each different sized cubes of agar into the same volume of water and time the time taken for the water to diffuse in and for the pink colour to disappear

Question 36

what would you expect to see when investigating the effect of surface area on the rate of diffusion

Answer 36

the large surface area of the agar cube the longer the time would be for the pink colour to disappear- so the rate of diffusion is slower. This is because as the surface area increases so does the volume so there is a higher ratio of surface area: volume so it would take longer to diffuse into the cell

Question 37

how would you investigate the effect of how diffusion is affected by temperature

Answer 37

have 4 different temperatures e.g. 30, 40, 50, 60 and then in each different temperature water bath place a boiling tube with hydrochloric acid and an agar cube and time the time taken for the colour of the dyed agar to disappear for each of the temperatures.

Question 38

what would you expect to see when investigating the effect of temperature on the rate of diffusion

Answer 38

the lower the temperature the longer it would take for the colour of the dyed agar to disappear this is because the partials have a greater kinetic energy so there is more chance for successful collisions, so therefore there is a greater rate of diffusion

Question 39

what is the importance of the structure of ATP in active transport

Answer 39

the ATP molecule binds to the carrier protein inside the cell, this causes a change in shape of the tertiary structure of the protein, a phosphate group remains but the ADH will unattach. The phosphate group will later unattach after separate ions are released into the cell.

Question 40

glycoprotein

Answer 40

protein with carbohydrate group attached to peptide chain - involved in cell signaling and recognition act as receptors or antigens. Cell adhesion - binding together and attaches to water to stabilize membranes

Question 41

phospholipid

Answer 41

phosphate head attached to 2 fatty acid tails - form partially permeable barrier

Question 42

cholesterol

Answer 42

lipid with hydrophobic end and hydrophilic end - regulates fluidity of membrane

Question 43

glycolipid

Answer 43

lipid with cholesterol attached to glycosidic bond - cell markers or antigens recognized as the body as self or non self also attaches to water to stabalise the membrane

Question 44

channel protein

Answer 44

form hydrophobic channel through membrane so polar molecules or ions can get through

Question 45

carrier protein

Answer 45

involved in active or passive transport - for active the shape often changes

Question 46

extrinsic protein

Answer 46

on one side of bilayer only

Question 47

intrinsic protein

Answer 47

through both layers of bilayer