diffusion across membranes Flashcards
what is the definition of diffusion
net movement of molecules from an area of high concentration to an area of low concentration
what is the definition of facilitated diffusion
movement of molecules from an area of high concentration to an area of low concentration across a partially permeable membrane via a carrier or channel protein
what energy is used for passive processes
Kinetic energy
Does a substance need to be stirred for particles to move on their own with kinetic energy
No, kinetic energy moves the molecules.
What is the term given when molecules have moved down a concentration gradient and are now evenly dispersed
Equilibrium, no net diffusion
what molecules will be able to pass the membrane by simple diffusion
Oxygen, Carbon dioxide as they are very small.
Why can fat soluble molecules diffuse through the membrane
Because they dissolve in the lipid bilayer
What proteins do water molecules use to diffuse across the lipid bilayer
Aquaporins- allow the polar water molecules to pass through the membrane
how are conc gradients maintained across a plasma membrane
- give an example
Molecules will constantly enter cells and pass into organelles to be used up in metabolic reactions.
Keeping concentration high in the cell and low in the organelle- keeps more molecules entering the cell and the organelle.
CO2 diffusing into the palisade mesophyll cells and then diffusing into the chloroplast for photosynthesis
what are the factors affecting simple diffusion
Temp- increase/decrease changes movement of molecules with kinetic energy.
diff. distance- longer diffusion distances= slower rate of diffusion.
surface area- more diffusion can take place across a large surface area
size- smaller ions diffuse more rapidly than large molecules.
conc gradient
why can polar or charged molecules not pass through the lipid bilayer
Because they are unable to interact with the hydrophobic tails of the bilayer
what protein allows glucose to pass the lipid bilayer
Transmembrane carrier protein
how do carrier proteins work
they open on one side allowing molecule to enter, they then close and open on the other side, allowing the molecule to pass the membrane
