osmosis

Question 1

what is osmosis?

Answer 1

the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane, so equilibrium is reached either side

Question 2

what is water potential?

Answer 2

tendency of water molecules to move due to water pressure. when there is more solute, the more negative the water potential

Question 3

how do you produce a desired concentration of solution from a stock solution?

Answer 3

volume of stock solution = (required conc x final vol needed) / conc of stock
volume of water = final vol - vol of stock solution

Question 4

why is osmosis a passive process?

Answer 4

it does not require any metabolic energy

Question 5

why does the cytoplasm have a negative water potential?

Answer 5

it contains a number of solutes dissolved in water, these solutes contain glucose and mineral ions

Question 6

what happens to an animal cell when the Ψ of external > Ψ of cytoplasm?

Answer 6

movement of water into the cell causes hydrostatic pressure inside the cell to increase. the cell membrane is not strong enough to withstand the significant increase in hydrostatic pressure inside the cell so the cell membrane ruptures and bursts. this is called haemolysis in blood cells

Question 7

what happens to an animal cell when Ψ of internal > Ψ of external?

Answer 7

water will move out the cell by osmosis, causing it to shrink

Question 8

what happens to a plant cell when Ψ of external > Ψ of internal?

Answer 8

because the water potential outside the cell is greater than the inside, water enters the cell by osmosis.this causes the hydrostatic pressure inside the cell to increase, so the protoplast pushes outwards against the cell wall. as the cell wall is strong, it can withstand the pressure so the cell goes turgid

Question 9

what happens to a plant cell when Ψ of internal > Ψof external?

Answer 9

water moves out of the cell by osmosis which causes the protoplast to pull away from the cell wall. the plant cell becomes plasmolysed

Question 10

what is a protoplast?

Answer 10

consists of the cell membrane, cytoplasm and organelles found in the cytoplasm

Question 11

what prevents animal cells from shrinking or bursting?

Answer 11

the Ψof the liquid around the cells is tightly controlled