Problem 100 - Chemistry and Chemical Reactivity

Question

A protozoan (single-celled animal) that normally lives in the ocean is placed in freshwater. Will it shrivel or burst? Explain briefly.

Step-by-Step Solution

Answer

The protozoan will burst due to water moving in by osmosis.

Step 1: Understanding the Problem

The problem involves a protozoan being moved from the ocean, which is a saltwater environment, to freshwater. We need to determine what effect this change in the environment has on the protozoan.

Step 2: Identify the Salt Concentration Difference

The ocean has a high salt concentration compared to freshwater. This means that the protozoan is usually in a hypertonic environment where the concentration of solutes is higher outside than inside the cell.

Step 3: Predict the Direction of Water Movement

When placed in freshwater, the outside environment becomes hypotonic compared to the inside of the protozoan, meaning the concentration of solutes is higher inside the protozoan and lower outside.

Step 4: Apply the Concept of Osmosis

Osmosis will cause water to move into the protozoan to balance the solute concentration. In a hypotonic environment, water moves from an area of low solute concentration to high solute concentration, entering the protozoan.

Step 5: Determine the Effect on the Protozoan

As more water moves into the protozoan, it swells due to increased internal pressure. In the absence of mechanisms to regulate this influx, the protozoan may burst due to the excessive pressure.

Key Concepts

Hypertonic and Hypotonic Solutions

The terms "hypertonic" and "hypotonic" describe the solute concentration in a solution relative to another solution.
An ocean environment is hypertonic for ocean-dwelling protozoans, where the salt or solute concentration outside their cells is higher than inside. In contrast, freshwater environments are hypotonic to these cells.

• In a hypertonic solution, water tends to move out of the cell, potentially leading to plasmolysis or shrinking of the cell.
• In a hypotonic solution, water moves into the cell, risking swelling or bursting if the cell can't manage the water flow efficiently.

Understanding these conditions helps explain how cells maintain equilibrium with their environment. Cell membranes play a crucial role in regulating this, but sudden shifts can overwhelm cell mechanisms, as in the case of osmosis.

Cellular Water Movement

Water movement across cell membranes is essential for maintaining cellular functions. This process, called osmosis, is the diffusion of water through a semi-permeable membrane where water moves to achieve balance between solute concentrations.
In biological systems, water moves from areas of low solute concentration to areas of high solute concentration. Some key points about cellular water movement:

• Osmotic pressure drives water movement and is influenced by the solute concentration inside and outside of the cell.
• Cellular membranes control this movement using specialized channels called aquaporins.
• Excessive osmotic pressure can damage cell integrity if not properly managed.

When a protozoan from a hypertonic ocean is placed into hypotonic freshwater, water rushes into the cell, highlighting the critical role of osmosis in cellular survival.

Protozoan Cells in Different Environments

Protozoan cells exhibit fascinating adaptations, but environmental changes can challenge their survival. In their natural ocean habitat, protozoans are accustomed to high salt concentrations. However, moving to freshwater disrupts their balance. When a protozoan is suddenly placed in freshwater:

• The freshwater environment is hypotonic compared to their internal structure, leading to rapid water influx.
• Without adaptations to expel the excess water or manage osmotic pressure, protozoans can swell and burst.
• Some protozoans possess contractile vacuoles that help expel excess water, but not all have efficient mechanisms.

Adaptations in protozoan cells are crucial for their immediate response to environmental changes, highlighting the importance of evolutionary mechanisms that allow survival in varying conditions. These cellular adjustments are vital in dealing with diverse habitats.