Osmosis

Question 1

Define osmosis, what is the process?

Answer 1

Osmosis is the diffusion of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane

Question 2

What is water potential?

Answer 2

the pressure generated when water molecules hit the cell surface membrane
More water molecules=more pressure

Question 3

What is the symbol for water potential?

Answer 3

Psi

Question 4

What is water potential measured in?

Answer 4

Kilopascals (kPa)

Question 5

What has the highest water potential?

Answer 5

Pure (distilled) water (0kPa) as the highest pressure is being generated due to it only containing water

Question 6

What is the water potential like in cell cytoplasm?

Answer 6

It contains dissolved sugars and salts so the water potential is more negative than pure water

Question 7

What does a high water potential mean?

Answer 7

There is a large number of water molecules that are free to move

Question 8

Which direction does water move in osmosis?

Answer 8

From a lower concentration of solute molecules to a higher concentration of solute molecules
From a higher concentration of free molecules to a lower concentration of free water molecules
From a less negative water potential to a more negative water potential

Question 9

What does negative water potential mean?

Answer 9

The more water molecules, the less negative water potential. It gets further from 0 and more negative as there are less water molecules

Question 10

What happens to animal cells in pure water?

Answer 10

They will eventually burst through cytolysis (red blood cells are haemolysed)

Question 11

What happens to plant cells in pure water?

Answer 11

The swelling cytoplasm and vacuole will push against the cell wall which will stop the cell getting any larger and it becomes turgid

Question 12

What happens to animal cells in concentrated sugar/low water potential?

Answer 12

The cell contents shrink and the membrane wrinkles which creates bumps and wrinkles- this is called crenation

Question 13

What happens to plant cells in concentrated sugar/low water potential?

Answer 13

The cytoplasm and vacuole shrink (the cell becomes flaccid) and the plasma membrane pulls away from the cell wall (plasmolysis)

Question 14

What happens to an animal cell in a hypertonic solution?

Answer 14

Shrivelled

Question 15

What happens to an animal cell in an isotonic solution?

Answer 15

Normal

Question 16

Why happens to an animal cell in a hypotonic solution?

Answer 16

Lysed

Question 17

What happens to a plant cell in a hypertonic solution?

Answer 17

Plasmolysed

Question 18

What happens to a plant cell in an isotonic solution?

Answer 18

Flaccid

Question 19

What happens to a plant cell in a hypotonic solution?

Answer 19

Turgid

Question 20

What does hypertonic mean?

Answer 20

There is a higher amount of solutes in the water meaning a lower water potential. This means the cell shrinks due to the water diffusing down its concentration gradient from the higher water potential (inside cell) to the lower water potential (outside cell)

Question 21

What does isotonic mean?

Answer 21

Where the extracellular fluid has the same osmolality as the cell (the solution on the outside of the cell is equal to that on the inside of a cell). This means that although water is still diffusing through the membrane, it is doing so equally in both directions so there is no net flow of water, keeping the cell at its normal state

Question 22

What does hypotonic mean?

Answer 22

There is a smaller concentration of dissolved solutes and thus a higher water potential. This means that the extracellular fluid has a lower osmolality than the fluid inside of the cell (hypo means less than) so the net flow of water will be into the cell by osmosis from the higher water potential on the outside of the cell to the lower water potential on the inside of the cell. This effectively causes the cell to become swollen and can sometimes cause it to burst through osmotic lysis