1.3 Cell Membrane + Transport (osmosis) Flashcards
what is osmosis?
the diffusion of water from a region of high water potential to low water potential across a selectively permeable membrane
what are special membrane channel proteins that transport water called?
Aquaporins
what are dissolved substances called?
solutes
what does water potential measure ?
measures the concentration of free water molecules
what is water potential?
the tendency of water molecules to diffuse from one solution to another
what process does water diffuse by?
osmosis
what is water potential measured in?
kilopascals (kPa)
what is the water potential of pure water ?
0 kPa
what are three types of osmosis?
hypertonic
hypotonic
isotonic
hypertonic
solute conc is greater inside the cell than outside - cell loses water
hypotonic
solute conc is less than that inside the cell - cell gains water
isotonic
external and internal solute potential are the same
what happens to plant cell placed in pure water ?
cell swells and becomes turgid
vacuole is filled with water
why does the cell not burst in hypotonic solutions ?
due to the strength of the cell wall
what happens if the plant is placed in a hypotonic solution?
water enters by osmosis
causes the cell to swell and become firm
plant cells becomes TURGID
what happens when plant cell is placed in hypertonic solution?
water moves out of the cell by osmosis
causes the membrane to pull away from cell wall
causes vacuole to shrink and become FLACCID
PLASMOLYSED
what is said to happen to the cell in hypertonic solutions?
cell becomes plasmolysed
animal cell in hypotonic solution?
no cell wall causing cell to burst and become lysed
animal cell in a hypertonic solution?
water leaves by osmosis cell appears wrinkled crenated
what is the role of cell wall?
cell wall does not stretch
generates pressure potential
what is solute potential at incipient plasmolysis?
solute potential = water potential
what is point of incipient plasmolysis?
plasmolysis has just taken place
half cells plasmolysed half not
what is a sodium potassium pump ?
uses protein pump to move Na+ and K+ in and out cells
use of proton pump?
an active transport protein
uses ATP to transport hydrogen ions out of the cell
explain why there is no decrease in mass at any of the sucrose concentrations?
loss of mass is not linked to water movement
