transport across membrane Flashcards
1
Q
cell surface membrane
A
- 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)
2
Q
responses to water
A
- 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)
3
Q
protein of membrane
A
- partially/fully embedded in the lipid bilayer
- superficially attached on either surface of the lipid bilayer
4
Q
simple diffusion
A
- 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
5
Q
facilitated diffusion
A
- 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
6
Q
osmosis
A
- 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
7
Q
active transport
A
- 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)
8
Q
bulk transport
A
- 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