Eleni 3

15 flashcards · Biology · by Michael Katsikas

1. Define Osmosis

   Osmosis is the diffusion of water across a partially permeable membrane. (from dilute to concentrated)

2. Does osmosis require energy?

   No - Osmosis is s passive process

3. what is water potential ?

   The (partial) pressure exerted by water molecules as they collide with a membrane or container.

4. What are the units of water potential ?

   Pascal (Pa) or kPa (kilopascal) - Pascal is the S.I. unit for pressure.

5. What is the water potential of pure water ?

   0 kPa (at 25 degrees Celsius, and atmospheric pressure (100 kPa).

6. You have a beaker with two compartments filled with pure water, separated by a semipermeable membrane. If a solute (a substance that will dissolve in water - cannot pass through the pores of the membrane)) is added to pure water, the water potential will rise or lower ?

   It will lower. It will acquire negative values (we have to exert pressure to stop the water from the other side - pure water - of the membrane to equalize the concentration of water from the side that has the pure water). The more concentrated the solution, the lower (more negative) the water potential.

7. What happens when solutions of different concentrations are separated by a partially permeable membrane?

   Water molecules can move between solutions but the solutes cannot. There is a net movement of water from the solution with high water potential (less concentrated) to the solution with low water potential (more concentrated) until equilibrium is met.

8. What is hydrostatic pressure ?

   The increase in pressure due to a solutions intake of water by osmosis (as a result of an increased volume) is called hydrostatic pressure. (kPa)

9. What happens to the hydrostatic pressure when an animal cell is placed in a solution with higher water potential than the cytoplasm?

   Osmosis occurs which increases the hydrostatic pressure.

10. What term describes when hydrostatic pressure of an animal cell increases causing it to burst?

    The cell surface membrane cannot stretch much and therefore will burst, called CYTOLYSIS. This is a result of osmosis occurring and the hydrostatic pressure increasing.

11. What is the term that describes when an animal cell shrinks, and when does it occur?

    If an animal cell is placed in a solution with low water potential, it will lose water and cause the cell to shrink, called CRENATION.

12. How do plants control the water potential of the fluid around them?

    Plants cannot control the water potential of the fluid around them.

13. What part of the plant cell's structure can protect the cell against water potential changes?

    Cellulose cell wall

14. What happens to the plant cell when it is placed in a solution with a higher water potential?

    Water enters, increasing hydrostatic pressure, pushing against the cell wall and is normally called the turgor. The cell wall resists and is said to be turgid.

15. What happens to the plant cell when it is placed in a solution with a lower water potential?

    Water is lost, leading to a reduction in the volume of the cytoplasm, pulling the cell membrane away from the cell wall. The cell is PLASMOLYSED.