Biological membranes

Question 1

Partially permeable-

Answer 1

-membranes don’t let all types of molecules pass through

Question 2

Role of plasma membrane

Answer 2

-separates cell components from outside environment
-regulates transport of materials in and out the cell
-contains enzymes involved in metabolic pathways
-has antigens so recognised as self
-release chemical for cell signalling
-receptors for signals
-site chemical reactions

Question 3

Role of membranes within cells(3 examples)

Answer 3

-cristae give mitochondria large SA for respiration
-thylakoid membrane house chlorophyll (photosystems) for photosynthesis
-digestive enzymes on epithelial cells in small intestine to break down sugars

Question 4

Fluid mosaic model

Answer 4

-phospholipid bilayer with proteins floating in it creating mosaic pattern
-lipid molecules change places and some proteins move so is fluid
-pores which act as channels allowing polar molecules dissolved in water through
-carrier proteins, change shape and carry specific molecules across membrane
-cholesterol regulates fluidity, maintains mechanical stability and resists effects of temp. changes

Question 5

Facilitated diffusion

Answer 5

-movement of molecules from high to low conc. across a partially permeable membrane via protein channels/carriers
-polar molecules diffuse through water filled channels

Question 6

Diffusion across membrane

Answer 6

-small molecules eg. O2, CO2 diffuse through bilayer
-fat soluble molecules eg. steroid hormones diffuse through as dissolve in bilayer
-water soluble molecules pass through protein channel

Question 7

How conc gradient maintained

Answer 7

-oxygen diffuses into cytoplasm and used in respiration
-CO2 diffuses into chloroplasts and used for photosynthesis

Question 8

Factors effecting rate diffusion

Answer 8

-temperature, as temp increases, diffusion increases due to having more kinetic energy
-diffusion distance
-SA- larger SA, quicker diffusion
-Size of diffusing molecule- smaller molecules diffuse quicker
-Concentration gradient- steeper gradient, faster diffusion

Question 9

Osmosis

Answer 9

-passage of water molecules down conc gradient across a partially permeable membrane

Question 10

Water potential

Answer 10

-pure water has highest WP (0kPa)
-when solute added, WP decreases
-water will move from high WP to low WP
-very low WP = -500kPa

Question 11

Water potential of plant cells

Answer 11

Pure water
-water moves into cell
-cell wall prevents bursting, but membrane pushed against the wall
-cell is turgid
Conc sugar solution
-water moves out of cells
-cell membrane pulls away from wall
-cell is plasmolysed
-tissue with plasmolysed cells is flaccid

Question 12

Water potential of animal cells

Answer 12

Pure water
-water move into cell
-cell bursts (cytolysed)
Conc sugar solution
-water moves out of cells
-cell shrinks and becomes crenated

Question 13

Active transport

Answer 13

-movement of substances against the conc gradient, across membrane, requiring ATP
-hydrolysis of ATP into ADP + Pi
-eg. root hair cells use active transport to accumulate more mineral ions from soil

Question 14

Carrier proteins

Answer 14

-specific regions that combine reversibly with ions
-they also have region to bind ATP for hydrolysis
-this energy helps carrier t undergo conformational change, carrying ion from one side to the other

Question 15

Bulk transport (Na, K pump)

Answer 15

-3 Na+ bind to specific site
-ATP binds to protein at specific site
-ATP hydrolysed to ADP + Pi
-2K+ bind to specific site
-energy released enables change of shape allowing 3 Na+ out and 2K+ into cell

Question 16

Endocytosis

Answer 16

-how large particles brought into cell
-segment of plasma membrane surrounds and encloses particle and brings into cell in a vesicle
eg. phagocytosis
-phagocyte approaches bacteria
-cell extends to surround it
-bacteria now enclosed within phagocytic vesicle

Question 17

Exocytosis

Answer 17

-how large molecules leave cells
-vesicle fuses with membrane
eg. vesicles containing neurotransmitter in pre-synaptic bulb

1. vesicle containing substance moves towards cell membrane
2. cell surface membrane and vesicle fuse
3. fused site opens , releasing contents

Question 18

Affect of decreasing temp on membrane

Answer 18

-saturated fatty acids become compressed
-proportions of saturated and unsaturated fatty acids determine fluidity when cold
-cholesterol prevents phospholipids from packing too close together, preventing reduction in fluidity

Question 19

Affect of increasing temp on membrane

Answer 19

-phospholipids have more kinetic energy, increasing fluidity
-permeability increases
-affects the way proteins embedded in memebrane are positioned, altering RoR
-increase in fluidity could affect folding of membrane during phagocytosis or change ability of cell signalling
-cholesterol buffers to an extent

Question 20

Effect temp on beetroot investigation

Answer 20

-heat beetroot tissue
-this disrupts membrane causing pigment to leak
-amount of leakage is proportional to damage of membrane
-measure using colorimeter