Osmosis

Question 1

Define osmosis

Answer 1

The movement of water down a water potential gradient, from a higher water potential to a lower water potential, across a selectively permeable membrane

Question 2

Define Solvent, Solute and Solution.

Answer 2

• solvent liquid that can dissolve other substances
• solute substance that is dissolved in a solvent
• solution a solvent with solute dissolved in it

Question 3

Under standard conditions what is the water potential of pure water?

Answer 3

0kPa

Question 4

Define Hypotonic, Hypertonic and Isotonic

Answer 4

• Hypotonic a solution that has a higher water potential that the one you are comparing it with
• hypertonic a solution with a lower water potential than the one you are comparing it with
• isotonic a solution with the same water potential as the one you are comparing it with

Question 5

Describe what happens in an animal cell when the extracellular solution is higher/less negative, lower/more negative and the same

Answer 5

-higher/less negative water moves into the cell via osmosis down its water potential gradient. The cell swells and may eventually burst
-lower/more negative water moves out of the cell via osmosis down its water potential gradient and the cell shrinks
-the same no net movement of water. The cell will not change in shape nor size

Question 6

Describe what happens in plant cells when the extracellular solution is higher/less negative, lower/more negative and the same

Answer 6

-higher/less negative water moves into the cell via osmosis down its water potential gradient. The cell swells but does not burst. This is the best condition for a plant cell as it is turgid
-lower/more negative water moves out of the cell via osmosis down it’s water potential gradient. The protoplast pulls away from the cell wall and the cell is plasmolysed.
-the same no net movement of water, the protoplast neither pulls away from the cell wall nor pushes against it

Question 7

Describe the process of co-transport in epithelial cells in the ileum

Answer 7

1. Na+ ions are pumped out of the cell by active transport by the Na+K+ pump into the blood
2. This lowers the concentration gradient of Na+ ions in the cell and maintains a concentration gradient for Na+ ions to enter the cell from the lumen
3. Na+ ions and glucose are transported into the cell, via the sodium glucose co-transporter, moving down the Na+ ion concentration gradient
4. Glucose diffuses out of the cell, into the blood via facilitated diffusion.

Question 8

Describe Endocytosis and Exocytosis

Answer 8

-endocytosis takes substances into the cell
-exocytosis takes substances out of the cell