Question

One grape is placed in tap water and another grape is placed in salt water. The change in their mass is measured after a day. What is the controlled variable in this scenario?

Answer 1

When the grape is placed in sugar water, a hypertonic solution, water will move down the concentration gradient from high concentration (in the grape) to low concentration (the solution), causing it to shrink.

When the grape is placed in grape juice, an isotonic solution, water will not move across the semi-permeable membrane because water concentration is equal on both sides of it.

When the grape is placed in water, a hypotonic solution, water will move down the concentration gradient from high concentration (the water) to low concentration (in the grape), causing it to swell.

Answer 2

The explanation to the following scenario is discussed below -

• When a grape is kept in tap water, the water being a hypotonic solution, the water enters the grape due to osmotic pressure, and the grape gets swelled up. The concentration of water inside the grape is less than that to the outside.
• When a grape is kept in saltwater, the saltwater becomes a hypertonic solution for the grape. The water from the grape oozes out and the grape shrinks. The concentration of water inside the grape is more than that of the surrounding saltwater.
• Therefore, grape swells when kept in tap water, and shrinks when kept in saltwater.