Question

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

Short answer

The protozoan will burst because water enters the cell by osmosis, increasing pressure.

Step-by-step solution

Understand the Osmosis Concept

Osmosis is the movement of water molecules from a region of lower solute concentration to a region of higher solute concentration through a semipermeable membrane. It's important to understand that water will naturally move into or out of a cell to balance solute concentrations on either side of the cell membrane.

Identify the Protozoan's Environment Change

In this problem, a protozoan is moved from a high solute concentration environment (ocean) to a low solute concentration environment (fresh water). This switch introduces a difference in solute concentration across the protozoan's cell membrane.

Predict Water Movement Across the Membrane

Since the protozoan is now in fresh water, which has a lower solute concentration than the inside of its cells, water will flow into the cell through osmosis. Water naturally moves towards the region with higher solute concentration.

Explain the Outcome

As water continues to move into the cell, the protozoan's cell volume will increase. If too much water enters, the cell can swell to the point that it bursts, since the cell membrane cannot withstand the increased pressure indefinitely.

Key concepts

Protozoan

Protozoans are fascinating single-celled organisms which can be found in a variety of environments. They are considered eukaryotes, meaning they have a well-defined nucleus and complex cell structures. Protozoans are not plants, animals, or fungi, but they share some traits with these groups. They can move independently, often with the help of tiny hair-like structures called cilia or whip-like structures known as flagella.

These microscopic creatures often thrive in watery environments, such as oceans, ponds, and swamps. The ability to adapt to their environment is critical because their survival hinges on maintaining their internal balance. For protozoans, living in the ocean means they are usually adapted to a salty, high solute concentration environment.

Cell Membrane

The cell membrane, also known as the plasma membrane, is a crucial component of protozoan life. Imagine the cell membrane as a flexible, dynamic wall that surrounds the cell. Its primary function is to control what enters and exits the cell. This semipermeable nature allows some substances to pass while keeping others out.

The cell membrane is made up of a double layer of phospholipids with embedded proteins. These proteins act as guardians or channels, allowing selective passage of ions and nutrients. The membrane's structure ensures that essential processes, like nutrient uptake and waste expulsion, are carried out efficiently. However, when it comes to water movement, processes like osmosis rely heavily on this membrane's permeability.

Solute Concentration

Solute concentration refers to the amount of solutes - such as salts, sugars, and proteins - dissolved in a solution. In biological terms, it plays a significant role in processes such as osmosis. Understanding solute concentration is key to predicting water movement in cells.

A high solute concentration means that the solution has more dissolved substances compared to another region. For example, the ocean has high solute concentration due to its salt content. Conversely, fresh water is characterized by lower solute concentration. When a protozoan accustomed to oceanic conditions is introduced into fresh water, the difference in solute concentration becomes a vital factor in how the cell behaves. Water tends to move from regions of lower solute concentration (fresh water) into regions of higher solute concentration (inside the protozoan), potentially leading to cell swelling.

Fresh Water Environment

A fresh water environment is vastly different from a marine one in terms of solute concentration. Fresh water bodies such as lakes, rivers, and streams have relatively low amounts of dissolved salts and minerals compared to the ocean.

This environment poses unique challenges to organisms that are conditioned to higher solute concentrations. When a marine protozoan is exposed to fresh water, it faces the risk of imbalance. The osmotic pressure across the cell membrane changes dramatically as water enters the cell in an attempt to equilibrate the solute concentrations on both sides of the membrane.

If water continues to enter unchecked, it can lead to the cell absorbing too much and eventually bursting, as the cell membrane is unable to accommodate the excessive internal pressure indefinitely.