transport across membrane

Question 1

cell surface membrane

Answer 1

• made almost entirely of protein and phospholipids
• phospholipid molecule has
• a head: composed of a glycerol to which is attached to a phosphate group (hydrophilic, forms hydrogen bonds with water)
• 2 fatty acid tails (hydrophobic, comprises of 2, long, fatty acid residues consisting of hydrocarbon chains)

Question 2

responses to water

Answer 2

• when phospholipid is added to water, the molecules float with their hydrophilic “heads” in contact with the water molecules and their fatty acid tails exposed and away from the water
• phospholipid molecules arrange these;ves as a phospholipid bilayer with fatty acid tails (hydrophobic) facing each other (within the cell membrane)

Question 3

protein of membrane

Answer 3

• partially/fully embedded in the lipid bilayer

- superficially attached on either surface of the lipid bilayer

Question 4

simple diffusion

Answer 4

• form of passive transport
• from regions of higher concentrations to regions of lower concentrations
• molecules of non-polar substances (e.g. glycerol, fatty acids
• phospholipid bilayer fully permeable to non-polar, but forms a barrier to ions, large and polar substances
• transient pores in phospholipid permits small and uncharged substances (gases) to pass through

Question 5

facilitated diffusion

Answer 5

• diffusion through cell membranes using specific protein channel/carriers from regions of higher concentration to lower concentration
• polar molecules (e.g. water in high concentration)
• channel/carrier proteins are large enough for a specific substances to pass through (inions, large and polar substances)
  e. g. sodium ions, amino acids

Question 6

osmosis

Answer 6

• net movement of water molecules from a region of a higher to lower water potential through a selectively permeable membrane
• equilibrium is reached when the water potential is the same in both regions

Question 7

active transport

Answer 7

• the process in which energy in the form of ATP is used to move substances across a membrane against a concentration gradient (lower to higher)
• occurs against concentration gradient
• requires energy in the form of ATP
• active uptake is a highly selective process, only substances needed are taken up
• involves a “protein pump’ at membrane (membranes are specific to particular substances)
• cell surface membrane of root hair cells use active transport to absorb mineral salts needed
• cell surface membrane of intestinal epithelial cell to absorb nutrients (e.g. glucose and amino acids from intestine)

Question 8

bulk transport

Answer 8

• occurs by movement of vesicles of matter (solids or liquids) across the cell surface membrane
• ATP is required
• exocytosis: process bu which cells export products such as enzymes by means of vesicles
• endocytosis: substances imported into cells
  2 types of endocytosis
  1. phagocytosis: wholesale import of solid matter
  2. pinocytosisL bulk import of fluids