2.5 Biological membranes

Question 1

membranes at surface of cells

Answer 1

• barrier between cell and env. ( diffusion, osmosis, active transport )
• allow recognition by other cells
• allow cell signalling

Question 2

fluid mosaic model

Answer 2

• describe arrangement of molecules in membrane
• phospholipid molecules form a continuous, bi layer
• ‘fluid’ bc phospholipids are constantly moving
• cholesterol binds to hydrophobic tails
• -> them pack more closely
• -> membrane less fluid, more rigid
• protein scatter like titles on mosaic
• glycoprotein has polysaccharide chain attached
• glycolipid has polysaccharide chain attached

Question 3

phospholipid bilayer

Answer 3

• hydrophilic head, attracts water face out either side to watery env.
• hydrophobic tails, repels water

Question 4

protein

Answer 4

• protein channels: small, charged particles
• carrier proteins: transport molecules, ions across membrane by active transport, facilitated diffusion
• receptor for cell signalling

Question 5

glycolipids and glycoproteins as receptor for messenger molecules

Answer 5

• stabilise membrane by H-bond w/ surrounding water molecules
• sites where drugs, hormones, antibodies bind
• are antigens

Question 6

affect of temp

Answer 6

temp < 0

• phospholipids dont move much, packed closely together and membrane rigid
• protein denature –> increase permeability
• ice crystals form and pierce membrane –> increase permeability

0 < temp < 45
- phospholipids can move around, arent packed as tightly together

temp > 45

• phospholipid starts to melt
• water inside cell expands, more pressure on membrance
• proteins denature
• -> cant control what enter/ leave
• -> increases permeability

Question 7

diffusion

Answer 7

• net movement of particles from high to low con , down a conc gradient

Question 8

osmosis

Answer 8

diffusion of water molecules across a semi-permeable membrane, down a water potential gradient

Question 9

facilitated diffusion: carrier proteins

Answer 9

move large molecules in/out, down conc gradient

Question 10

facilitated diffusion: channel proteins

Answer 10

form pores in membrane for charged particles to diffuse thr

Question 11

facilitated diffusion

Answer 11

-

Question 12

endocytosis

Answer 12

• cell surround a substance within a section of its membrane
• membrane pinches off to form a vesicle inside cell containing ingested substance
• ATP

Question 13

exocytosis

Answer 13

• vesicles containing substances pinch off from sacs of golgi body

Question 14

Centrosome

Answer 14

area of the cell cytoplasm where the centriole is

Question 15

facilitated diffusion

Answer 15

• movement of substance against concentration gradient
• across a membrane
• using ATP, protein carriers

Question 16

roles of membranes inside cell

Answer 16

• control what enters/ leaves organelle
• contain receptor to detect change in environment
• compartmentalization
• site for enzyme. electron carriers, components of metabolic pathway