Biological membranes - Osmosis

Question 1

define osmosis

Answer 1

the net movement of water from a region of higher water potential to a region of lower water potential (down a water potential gradient) across a partially permeable membrane

Question 2

define solute

Answer 2

the substance that dissolves in a liquid to form a solution

Question 3

define solvent

Answer 3

the liquid in which a solute dissolves

Question 4

define solution

Answer 4

the mixture formed when a solute has dissolved in a solvent

Question 5

define water potential

Answer 5

the tendency of water molecules to leave a solution

Question 6

what is water potential measured in

Answer 6

units of pressure (kPa)

Question 7

what is the water potential of pure water

Answer 7

0

Question 8

what is the effect of adding solutes on water potential

Answer 8

lowers the water potential (giving a negative value) as fewer water molecules are free the leave the solution

Question 9

when will osmosis stop

Answer 9

when water potential is equal on both sides of the membrane or when another force stops further movement of water e.g cell wall (this does not mean water stops moving just no NET movement)

Question 10

describe the movement of water in animal cells when placed in a lower water potential

Answer 10

water moves from a higher water potential inside the cell to a lower water potential outside the cell by osmosis through the partially permeable cell surface membrane

Question 11

what is the effect on animal cells placed in a lower water potential

Answer 11

reduction in cell volume
cell becomes crenated
cells in a tissue pull away from other cells
cytoplasm becomes more concentrated
enzymes require aqueous conditions therefore metabolic reactions disrupted
cells die if lots of water lost

Question 12

describe the movement of water in animal cells placed in a higher water potential

Answer 12

water moves from a higher water potential outside the cell to a lower water potential inside the cell by osmosis through the partially permeable cell surface membrane

Question 13

what is the effect on animal cells placed in a higher water potential

Answer 13

pressure inside the cell increases
plasma membrane is fragile and cannot withstand the pressure
no cell wall to prevent bursting
cells burst - lysis

Question 14

what is the name of lysis in red blood cells

Answer 14

haemolysis

Question 15

describe the movement of water in plant cells placed in lower water potential

Answer 15

water moves from a higher water potential inside the cell to a lower water potential outside the cell by osmosis through the partially permeable membrane

Question 16

describe the effect on plant cell placed in a lower water potential

Answer 16

volume of cytoplasm and vacuole decreases
contents of cell don’t push out on cell wall (flaccid)
plasma membrane eventually pulls away from cell wall in places (plasmolysed)
cell can die if membrane rips

Question 17

what fills the gaps in a plasmolysed cell

Answer 17

the sugar solution

Question 18

describe the movement of water in a plant cell placed in a higher water potential

Answer 18

water moves from a higher water potential outside the cell to a lower water potential inside the cell by osmosis through the partially permeable membrane

Question 19

what is the effect on a plant cell placed in a higher water potential

Answer 19

volume of cytoplasm and vacuole increases
contents push out on cell wall
cell wall pushes back on contents
cell is turgid

Question 20

what do some unicellular animals have to prevent bursting when placed in distilled water

Answer 20

contractile vacuoles

Question 21

what is the importance of turgor to a plant

Answer 21

supports the structure of the plant to prevent wilting