Question

Assume that you place a freshwater plant into a saltwater solution and examine it under a microscope. What happens to the plant cells? What if you placed a saltwater plant in pure water? Explain. Draw pictures to illustrate your explanations.

Short answer

When a freshwater plant cell is placed in a saltwater solution, water moves out of the cell due to osmosis, causing the cell to shrink (plasmolysis). This results in a loss of turgor pressure and may lead to wilting and cell death. On the other hand, when a saltwater plant cell is placed in pure water, water moves into the cell, causing it to expand and become turgid. If too much water enters, the cell membrane may rupture, causing cell lysis.

Step-by-step solution

Understand Osmosis

Osmosis is the process wherein water molecules move from an area of higher concentration to lower concentration through a semipermeable membrane. In the case of plant cells, the semipermeable membrane is the cell membrane which allows water to move in and out of the cell.

Freshwater plant in saltwater solution

When a freshwater plant cell is placed in a saltwater solution, the concentration of water is higher inside the cell than in the surrounding environment. Due to osmosis, water will start moving out of the cell, causing it to shrink. This shrinking of the cell is called plasmolysis. The cell will lose its turgor pressure and may lead to the plant cells wilting and eventually dying, if not removed from the saltwater solution. To illustrate this, draw a plant cell before placing it in saltwater with a distinct vacuole and cytoplasm. Then, draw the cell after being in saltwater with the cytoplasm shrinking and the cell membrane detaching from the cell wall.

Saltwater plant in pure water

When a saltwater plant cell is placed in pure water, the concentration of water is lower inside the cell than in the surrounding environment. Due to osmosis, water will start moving into the cell. This causes the cell to expand and the vacuole to increase in size. The cell will become more turgid, which is normal for healthy plant cells for maintaining their structure. However, if too much water enters the cell, it could lead to the rupture of the cell membrane and cause cell lysis, or the breaking down of the cell. To illustrate this, draw a saltwater plant cell before placing it in pure water with a smaller vacuole and turgid cytoplasm. Then, draw the cell after being in pure water with an increased vacuole size and an increased turgidity, or the cell membrane ruptured due to cell lysis, if too much water entered. In conclusion, placing a freshwater plant in a saltwater solution will cause its cells to lose water and shrink due to plasmolysis, while placing a saltwater plant in pure water will cause its cells to take in water and either become turgid or rupture due to cell lysis. Illustrations of these changes can help visualize the effects of osmosis on plant cells in different water environments.