Transport across cell menbranes Flashcards
explain the phospholipid bilayer in cell membranes
hydrophilic phosphate heads (attracted to water) face outwards
hydrophobic fatty acid tails (repel water) face inwards
whats the structure of a cell membrane, name 5
-phospholipid bilayer
-channel proteins
-carrier proteins
-glycolipids
-cholesterol
whats the function of the phospholipid bilayer?
allows movement of non-polar/small molecules down a concentration gradient
restrict movement of large/polar molecules
what’s the function of channel proteins?
allows the movement of water soluble molecules, polar molecules and ions down a concentration gradient (facilitated diffusion)
transports polar molecules through its pores
different channel proteins transport specific molecules
what’s the function of carrier proteins?
allow movement of molecules down a concentration gradient using ATP (down a concentration gradient)
transports large molecules, the protein changes shape when a molecule attaches
how is the phospholipid bilayer adapted to its function?
-maintains a different environment on each side of the cell
-cholesterol increases stability
-surface proteins used in cell recognition (act as antigens)
what is the role of cholesterol?
makes the membrane more stable and less flexible
what are the factors affecting rate of simple diffusion?
surface area, concentration gradient, thickness of the surface (diffusion distance)
define simple diffusion across a cell membrane
net movement of small non-polar molecules across a selectively permeable membrane, down a concentration gradient
what are the factors affecting rate of active transport?
pH/temp (tertiary structure of the protein) speed of the carrier protein, number of carrier proteins, rate of respiration (ATP production)
how are sodium ions and glucose absorbed by cells lining the ileum
1) sodium ions are actively transported out the epithelial cells lining the ileum into the blood by a sodium potassium pump (creates a conc gradient higher in lumen)
2) sodium ions and glucose move into the epithelial cell from the lumen by facilitated diffusion via a co-transporter protein
3) creates a conc gradient of glucose (higher in the cell)
4) glucose moves out of the cell into the blood via facilitated diffusion through a protein channel.
how are the sodium ions transported out the epithelial cells lining the ileum into the blood?
active transport via a co transport protein using a sodium potassium pump.
what is water potential?
the likelihood of water molecules to diffuse in or out of a solution.
what has the highest water potential?
pure water
what lowers water potential?
adding solutes
