Biological Membranes

Question 1

Examples of where we find biological membranes

Answer 1

Plasma membrane
Mitochondrion
Endoplasmic reticulum
Nucleolus

Question 2

Partially permeable

Answer 2

Only certain substances can pass through

Question 3

Components of plasma membrane (could be labelled diagram)

Answer 3

Phospholipid
Phospholipid bilayer
Channel protein
Carrier protein
Glycoprotein
Cholesterol within tails
Hydrophilic head
Hydrophobic tails
Intrinsic protein
Extrinsic protein

Question 4

What is the role of the plasma membrane

Answer 4

Separates cells components from external environment
Regulate transport of materials into and out of the cell
May contain enzymes
Has antigens for recognition of self cells
May release chemical signals to communicate between cells

Question 5

What is the role of membranes within cells

Answer 5

Separate organelle from cytoplasm
Provide surfaces for metabolic reactions
May contain enzymes that catalyse metabolic reactions
Membranes within cells can form vesicles to transport substances to different areas in the cell

Question 6

What substances can pass through the phospholipids in the bilayer

Answer 6

Small and non polar molecules eg O2, CO2
Water is polar but is so small it can also pass through
Large polar substances cannot pass through

Question 7

Plasma membrane described as what

Answer 7

Fluid mosaic model
Phospholipids free to move relative to each other
Proteins are embedded in bilayer varying in size and shape

Question 8

channel proteins

Answer 8

provide pores for molecules to move through to enter/exit the cell
allows charged/polar molecules eg. ions through.
shaped only to allow certain molecules to pass through
used for facilitated diffusion

Question 9

carrier proteins

Answer 9

shaped only to allow certain molecules to bind to them eg. large molecules such as glucose, amino acids
once the molecule has bound, carrier molecule changes shape to transfer it across the membrane
used for facilitated diffusion or active transport

Question 10

cholesterol

Answer 10

lipid
regulates fluidity of plasma membrane
found between fatty acid tails
low temps - maintain fluidity
high temps - reduces fluidity

Question 11

glycoproteins

Answer 11

carb chain attached to a protein
cell signalling, cell recognition (antigens) and binding cells together

Question 12

glycolipids

Answer 12

carb chain attached to a lipid
cell signalling and cell recognition

Question 13

factors affecting plasma membrane structure

Answer 13

1. temperature - as temps increase membrane gets more fluid and permeable. at very high temps proteins denature so membrane loses its structure and becomes more permeable. too low - can form ice crystals which pierce membrane making it highly permeable when it thaws.
2. cholesterol - more cholesterol the more fluid
3. solvents - some solvents dissolve the lipids in a cell membrane so the membrane loses its structure. less polar solvents may disrupt the membrane and increase permeability.

Question 14

how does saturation affect plasma membrane structure

Answer 14

more saturated fatty acids - membrane fluidity reduced at low temps as phospholipids can compress
more unsaturated - fluidity maintained at low temps. Don’t pack closely together

Question 15

simple diffusion

Answer 15

movement of a substance down its concentration gradient from a high to low concentration

Question 16

factors affecting rate of diffusion

Answer 16

1. temperature
2. surface area
3. concentration gradient
4. size of diffusing molecule - smaller=faster rate
5. diffusion distance - thinner=faster rate

Question 17

facilitated diffusion

Answer 17

movement of substances down their conc gradient from high to low conc using channel/carrier proteins
carrier- large molecules (inc ions + polar)
channel - small ions + polar

Question 18

active transport

Answer 18

movement of molecules from a region of lower conc to a region of higher conc against conc gradient.
so requires energy from ATP
uses carrier proteins that act as pumps

Question 19

role of ATP in active transport

Answer 19

molecule being transported binds to carrier protein
ATP binds to carrier protein
ATP is hydrolysed, releasing energy
the energy changes the shape of the carrier protein
molecule is transported across to other side of membrane

Question 20

factors affecting rate of active transport

Answer 20

1. number of carrier proteins present
2. ability to produce ATP - more ATP = faster rate of active transport

Question 21

bulk transport

Answer 21

moves substances that are too large eg. enzymes
endocytosis - bulk transport into cell
exocytosis - bulk transport out of cell

Question 22

endocytosis

Answer 22

1. substance to be taken in binds to a receptor on plasma membrane
2. plasma membrane folds in and surrounds substance
3. substance is brought into cell enclosed in a vesicle

Question 23

phagocytosis

Answer 23

bulk transport of solid matter into a cell

Question 24

exocytosis

Answer 24

1. substance to be transported is enclosed in a secretory vesicle
2. vesicle travels to plasma membrane
3. plasma membrane and vesicle fuse together and the contents of vesicle are secreted

Question 25

osmosis

Answer 25

net movement of water molecules down their water potential gradient across a partially permeable membrane