Movement into and out of cells — practice questions

The potato cells contain cell sap with a certain solute concentration, hence a specific water potential. If the potato cylinder decreased in mass when placed in 0.4 M sucrose, it indicates that the 0.4 M sucrose solution has a lower water potential (is more concentrated/more negative) than the potato cell sap. Consequently, water moved by osmosis from the region of higher water potential (inside the potato cells) to the region of lower water potential (the surrounding sucrose solution) across the partially permeable cell membranes. This net loss of water caused the mass of the cylinder to decrease. The cells within this cylinder would be plasmolysed, meaning their protoplasts (cell membrane and contents) would have shrunk and pulled away from the rigid cell walls, making the tissue flaccid.

To calculate the percentage change in mass, we use the following formula:

Formula: Percentage Change = [ (Final Mass - Initial Mass) / Initial Mass ] × 100

Step 1: Identify the initial and final masses. Initial Mass = 2.50 g Final Mass = 2.35 g

Step 2: Substitute the values into the formula. Percentage Change = [ (2.35 g - 2.50 g) / 2.50 g ] × 100

Step 3: Calculate the change in mass. Change in Mass = 2.35 g - 2.50 g = -0.15 g

Step 4: Complete the calculation. Percentage Change = ( -0.15 g / 2.50 g ) × 100 Percentage Change = -0.06 × 100

Final Answer: Percentage Change = -6.0%

The negative sign indicates that the potato tissue lost mass, which means there was a net movement of water out of the cells via osmosis.