2.1.5 Biological Membranes

Question 1

roles of membranes

Answer 1

exchange of molecules
site for cell signalling - process where cells communicate with one another through the transmission of signals
site of chemical reactions
vesicle formation
compartmentalisation

Question 2

role of membranes: vesicle formation
within

Answer 2

vesicles from from membranes of golgi apparatus and rough endoplasmic reticulum

Question 3

role of membranes: site of chemical reactions
within

Answer 3

membranes inside organelles are the site of key chemical reactions
e.g. thylakoid membranes and inner mitochondrial membrane

Question 4

role of membranes: site of chemical reactions
surface

Answer 4

reactions occur at surface when hormones bind to receptors

Question 5

role of membranes: compartmentalisation
surface

Answer 5

allows conditions in cytoplasm to remain relatively constant

Question 6

role of membranes: compartmentalisation
within

Answer 6

ensures reaction conditions remain constant in organelles
e.g. pH in mitochondria so respiratory enzymes are not affected

Question 7

role of membranes: exchange of molecules
surface

Answer 7

specific transport proteins in the membrane

Question 8

role of membranes: exchange of moleucles
within

Answer 8

ensures certain molecules can enter/exit organelles
e.g. ATP can move out of mitochondria

Question 9

role of membranes: site for cell signalling

Answer 9

membranes have receptors which are specific to certain molecules - allows cell to cell communication

Question 10

phospholipid bilayer

Answer 10

2 layers of phospholipid molecules
polar phosphate head - form H bonds with water
hydrophobic fatty acid tails - face away from aqueous environment
can be saturated/unsaturated - determines fluidity of bilayer
hydrophillic phosphate heads - face towards aqueous environment
cholesterol interspersed between phospholipids
contains intrinsic and extrinsic proteins
glycoproteins + glycolipids stick out of bilayer

Question 11

why is the phospholipid bilayer called the fluid mosaic model

Answer 11

fluid: phospholipid molecules constantly moving relative to each other
mosaic: multiple proteins embedded within bilayer in a pattern

Question 12

effect of high temperatures on plasma membranes

Answer 12

phospholipids - more KE = move quicker/more frequently
increased number/sizes of gaps between phospholipids
bilayer becomes more fluid/melts
proteins denature (tertiary structure changes shape)

Question 13

arrangement and function of bilayer

Answer 13

hydrophobic tails pointing inwards
hydrophilic heads pointing out
provide barrier to large/polar molecules or ions

Question 14

arrangement and function of cholesterol

Answer 14

cholesterol molecules between phospholipids
regulates fluidity of the membrane
binds to hydrophobic tails
allows phospholipids to pack closer together
stabilises the membrane

Question 15

arrangement and function of glycoproteins/glycolipids

Answer 15

sticking out from surface of membrane
cell signalling, receptor sites, adhesion, act as surface antigens, stabilise cell shape

Question 16

how do membranes contribute to the process of cell signalling

Answer 16

signal molecule secreted
glycoproteins/glycolipids act as receptors
receptor is specific, shapes of receptor and signal are complementary
attachment of signal molecule causes change on cell surface

Question 17

function of channel proteins

Answer 17

allows ions,large, polar molecules to pass through membrane
complementary to a specific moleucle

Question 18

osmosis

Answer 18

net movement of water molecules across a partially permeable membrane down a water potential gradient
from an area with high water potential to an area with low water potential