2.1.5: plasma membrane

Question 1

what is a partially permeable membrane?

Answer 1

• allows certain molecules to enter and exit a cell
• involved in cell signalling

Question 2

what is intracellular signalling?

Answer 2

communication between one part of a cell and a different part of the same cell (within the a singular cell)

Question 3

what is intercellular signalling?

Answer 3

communication between two different cells

Question 4

what does compartmentalisation do?

Answer 4

to separate organelles from each other so reactions don’t interfere

Question 5

what is a example of membranes being a site of chemical reactions?

Answer 5

there are many proteins embedded in the thylakoid membranes and similar enzymes also embedded in mitochondrion

Question 6

what is the model of a plasma membrane and why?

Answer 6

fluid (it is flexible) mosaic (studded with proteins in a random pattern) model

Question 7

what are the components that make up plasma membranes?

Answer 7

• phospholipids
• glycolipids
• cholesterol
• channel proteins
• carrier proteins
• glycoproteins
• various extrinsic proteins

Question 8

what is the structure of the phospholipid bilayer?

Answer 8

two layers of phospholipid molecules with their hydrophilic heads facing outwards and their hydrophobic tails facing inwards

Question 9

what is the structure and function of the glycolipids?

Answer 9

• a lipid with attached carbohydrate (sugar) chains
• recognised by the cells of the immune systems as self or non-self and to maintain the stability of the cell membrane and to facilitate cellular respiration

Question 10

what is the structure of cholesterol?

Answer 10

• a lipid with a hydrophilic end and a hydrophobic end
• regulates the fluidity of membranes and adds stability to membranes without making them too rigid

Question 11

what is an intrinsic protein?

Answer 11

proteins that are embedded within the membrane

Question 12

what is an extrinsic protein?

Answer 12

proteins that are loosely bound to the membrane from the outside

Question 13

what is the shape and function of a channel protein?

Answer 13

• tubular shaped
  -allows the passive movement of polar molecules and ions down a concentration gradient, acting like a pore

Question 14

what is the structure and function of a carrier protein?

Answer 14

• each type has one more specific binding site for its solute
• important role in both passive transport and active transport into cells

Question 15

what is the structure and function of glycoproteins?

Answer 15

• a protein with sugar molecules attached
• play a role in a cell adhesion and as a receptor for chemical signals

Question 16

what is the structure and function of various extrinsic proteins?

Answer 16

• primary, secondary, tertiary and quaternary protein structure
• required for transport

Question 17

what type of signals do cells use to communicate?

Answer 17

chemical signals

Question 18

how do cells detect a target cells?

Answer 18

they have complementary receptors

Question 19

how is the method by which a molecule passes a membrane dependant on?

Answer 19

• size
• whether it’s charged or polar
• whether it needs to move down or against a concentration gradient

Question 20

what is passive transport?

Answer 20

molecules are moving down a concentration due to their own kinetic energy - no extra energy in the form of atp is needed

Question 21

what is active transport?

Answer 21

extra energy in the form of atp is needed to move molecules against the concentration gradient

Question 22

what is diffusion?

Answer 22

the net movement of particles from a region of high concentration to a low concentration, down a concentration gradient, until equilibrium is reached

Question 23

what are the 6 factors that affect the rate of diffusion?

Answer 23

• properties of diffusing molecules (non-polar and smaller diffuse faster)
• concentration gradient (bigger difference = faster diffusion)
• temperature (higher temperature = more kinetic energy = faster diffusion)
• surface area to volume ratio (larger sa = faster diffusion)
• thickness of membrane (shorter diffusion = faster diffusion)
• number of channel/carrier proteins (more proteins = faster diffusion)

Question 24

what are the 2 types of diffusion?

Answer 24

simple and facilitated diffusion

Question 25

what are the types of molecule that can diffuse through a plasma membrane via simple diffusion?

Answer 25

- large and small non-polar molecules - small, polar molecules can pass

Question 26

what are the types of molecule that can diffuse through a plasma membrane via facilitated diffusion?

Answer 26

charged ions and larger, polar molecules (repelled by core)

Question 27

what is primary active transport?

Answer 27

involves the movement of ions/molecules against their concentration gradient with the direct use of atp to power the process

Question 28

what is secondary diffusion?

Answer 28

when a concentration gradient established by a transmembrane pump is used to move another molecule into the cell against a concentration gradient

Question 29

what is bulk transport?

Answer 29

another form of active transport that transports large molecules (enzymes, hormones etc) that are too large to move through channel and carrier proteins

Question 30

what is endocytosis?

Answer 30

- bulk transport into cells - the cell surface membrane bends inwards when it comes in contact with the material to be transported - the membrane enfolds the material until a vesicle is formed - moves into the cytoplasm to transfer the material further processing within the cells

Question 31

what are the 2 types of endocytosis?

Answer 31

- phagocytosis (solids) - pinocytosis (liquids)

Question 32

what is an example endocytosis?

Answer 32

vesicles containing bacteria are moved towards lysosomes, where bacteria is digested by enzymes

Question 33

what is exocytosis?

Answer 33

the reverse of endocytosis. vesicles, usually formed by the golgi apparatus, move towards and fuse with the cell surface membrane, releasing the contents outside of the cell

Question 34

what is osmois?

Answer 34

the movement of water molecules, across a partially permeable membrane, from a high concentration to a low concentration

Question 35

what is the water potential of pure water at standard temperature and pressure?

Answer 35

zero

Question 36

what is water potential?

Answer 36

the pressure exerted by water molecules on a membrane or a container

Question 37

what does it mean if a solution has a high or low water potential?

Answer 37

- high = has a low concentration of solute and higher concentration of water - low = has a high concentration of solute and a lower concentration of water

Question 38

how does adding solutes affect water potential?

Answer 38

lowers the water potential, so it makes the water potential more negative

Question 39

how does temperature affect membrane structure and permeability?

Answer 39

- temperature increased = phospholipids have more kinetic energy - more fluid and loses structure - if continued increase = membrane will break down completely - increases the permeability of the membrane - carrier and channel proteins will denature

Question 40

how does solvent affect membrane structure and permeability?

Answer 40

- many organic solvents are less polar then water (like alcohols) - will dissolve membranes, disrupting cells - non-polar alcohol molecules can enter the cell membranes and the presence disrupts the membrane = more fluid = more permeable

Question 41

what is the method for investigating the effect of ethanol concentration on membrane permeability?

Answer 41

- take 5 test tubes and label each on with a different ethanol concentrations - trim 5 beetroot cylinders to 30 mm, rinsing each one and then patting it dry - label the cuvette tray with the ethanol concentrations - swirl the tubes once and remove the cylinders - pour the remaining liquid into the cuvette for the corresponding concentration and fill an extra cuvette with distilled water - use the colorimeter with a green filter to measure the absorbance of each concentration and plot a graph of ethanol concentration against absorbance

Question 42

what is the variables for when investigating the effect of ethanol concentration on permeability?

Answer 42

- independent = concentration of ethanol - dependent = absorbance of the beetroot solution - control = size of disks, volume of ethanol, thickness of disk, amount of time in test tubes, same filter colour

Question 43

what is the method for determining the water potential by measuring changes in mass?

Answer 43

- label 6 boiling tubes with different concentrations of salt solution and place 30cm of distilled water in one tube and 30cm of the appropriate salt solution in the others - make 5 potato cylinders that are 50mm long and divide a piece of filter paper into 6 sections for each potato and blot the cylinders dry - record the mass and put them in the test tubes - leave for 45 minutes then take them out and blot them dry again - reweigh the cylinders and calculate the percentage change in mass ((change in mass /original mass) x100)