Osmosis

What is osmosis?

• The net movement of water down a potential gradient through a semi-permeable membrane

What the unit for water potential and why?

• Pascals(Pa) / Kilopascals (kPa)

• this is because water potential is the pressure which is exerted by water molecules onto membranes or surfaces

What is the highest water potential?

• 0 pascals

What is the water potential of pure water?

• 0 Pascals

What happens to the water potential a solution becomes more concentrated?

• It becomes negative

What are the 3 types of solutions around cells?

• Hypertonic

• Isotonic

• Hypotonic

What is a hypertonic solution and what does it mean for the movement of water?

• It is a solution which has a high concentration of solutes such as glucose in the solution compared to the concentration inside of the cell

• This means that water will move out of the cell down the water potential gradient via osmosis

What is an isotonic solution and what does it mean for of movement of water?

• The concentration of solutes is the same inside of the cell as the solution outside

• This means that there is no difference in water potential and therefore no water moves in or out of the cell via osmosis

What is a hypotonic solution and what does it mean in terms of movement of water?

• It is a solution which has a lower concentration of solutes in the solution than inside of the cell

• This means that water will move into the cell down the water potential gradient via osmosis

How do animal cells behave in a hypertonic solution and why?

• This causes the cell to lose water and become shrivelled (or undergone crenation)

  • Due to there being a higher water potential inside of the cell than outside, which means that water will move down the water potential gradient out of the cell via osmosis.

How do animal cells behave when in a isotonic solution and why?

• This means that the cell does not change shape

  • Due to there being no water potential gradient, it means that water will move into the cell and out of the cell at the same rate which means that there will be no net movement of water in or out of the cell via osmosis.

How do animal cells behave when in an hypotonic solution and why?

• Because there is an increase in water potential in the cell, the cell will eventually reach its threshold where it cant hold any more water and will burst (or undergone lysis)

  • Due to there being a higher water potential in the solution than in the cell, that means that water will move into the cell down the concentration gradient via osmosis

How do plant cells behave in a hypertonic solution and why?

• They undergo Plasmolysis - this means that the plasma membrane will detach from the cell wall and the plasma membrane will deform.

  • This is due to there being a higher water potential inside of the cell than outside, which means that water will move down the water potential gradient out of the cell via osmosis.

• However, the general shape of the cell is maintained

  - This is due to the cell wall being made of cellulose which helps in providing structure to the cell to retain its shape and not deform as well

How do plant cells behave when in a isotonic solution and why?

• The plant stays the same - this means that it stays the same shape and so does the plasma membrane

  • This is due to there being no water potential gradient, it means that water will move into the cell and out of the cell at the same rate which means that there will be no net movement of water in or out of the cell via osmosis.

How do plant cells behave in a hypotonic solution and why?

• The plant cell will become turgid and the plasma membrane will push against the cell wall

  • This due to there being a higher water potential in the solution than in the cell, that means that water will move into the cell down the water potential gradient via osmosis

• However, the structure of the cell maintained and will not burst

  • This is due to the cell wall acting as a protective layer, due to its cellulose which helps in providing structure and stopping it from bursting and so its shape is maintained