Class Test 2 Review

Hi all,
Some points to note and learn from.

• MCQ Qn 4:

Boiling destroys cell membranes therefore making it fully permeable.
Osmosis no longer takes place as the partially permeable membrane is no longer present. However, diffusion can still take place with or without a membrane.
Since the potato cells are placed in 15% salt solution for Ans A, there is a lower water potential in the solution than in the vacuoles of the potato cells. Thus, there will be net movement of water molecules down the water potential gradient by diffusion. Since there is no barrier, not only does water move out but the cell contents like proteins also diffuse out of the cell unlike that in Ans C with unboiled potato where the cell membranes are still intact resulting in the cells in Ans A weighing the lightest.

• MCQ Qn 6:

Diffusion and Osmosis are passive transport processes that do not require energy.
Only active transport requires energy. Energy comes from the process of respiration that requires Oxygen. Therefore, NO oxygen means No energy.

• MCQ Qn 7:

As Sucrose concentration increases, the water potential of the solution drops resulting in the water potential of the cell vacuoles being higher than the solution. Thus, there will be net movement of water molecules down the water potential gradient by exosmosis. Mass of the potato cells decrease gradually as shown by graph D.

• MCQ Qn 8:

The cell wall is fully permeable, so if the cell is placed in sugar solution, the sugar solution will fill the spaces in a plasmolysed cell.

Points to note for Structured Qn:

• Turgid, Flaccid and Plasmolysis are terms used only for PLANT cells.
• Instead, for a RBC, terms like haemolysis (bursting) and crenation (shrinkage) should be used.
  
• Terms such as Exosmosis and Endosmosis should be used when referring to living cells only. The term Osmosis should be used when referring to expts with non-living membranes such as visking tubings/dialysis tubings.
• When referring to osmosis, use the term water potential not water concentration as well as water potential gradient, not concentration gradient.
  
• State specifically the shape of the RBC.
• If there is equal water potential in both cell and solution, state that the water potential gradient is zero resulting in no net movement of water molecules, thus no osmosis.
• Use the template that is on this blog to help you phrase your answers!

Hope these tips help. Do learn from your mistakes and study hard for SA1!