Problem 170 - Objective Biology for NEET

Question

Assertion: All solutions have lower water potential than pure water. Reason: All solutions have fewer free water molecule.

Step-by-Step Solution

Answer

Yes, the assertion and reason are correct. The assertion is true because the addition of solute to water decreases the number of free water molecules, thus, decreasing its potential. The reason is also true as the reduction in free water molecules is due to the presence of solute which leads to lower water potential.

Step 1: Understanding the Concept of Water Potential

Water potential is the measure of the potential energy of water in a system compared to pure water. In a solution of water and solute, the water potential will be less than that of pure water because solute particles collide with the water molecules and limit their freedom of movement, decreasing their potential energy.

Step 2: Relating Free Water Molecules to Water Potential

The freedom of movement or availability of free water molecules is inversely related to the concentration of solute in it. A high solute concentration means that there are less free water molecules, which leads to a lower water potential. Free water molecules are those that can diffuse and carry out osmosis.

Step 3: Confirming the Assertion and Reason

Therefore, the assertion is correct that all solutions have lower water potential than pure water because they have a reduced number of free water molecules due to the presence of the solute. The reasoning is also correct because it is indeed the reduction in free water molecules in a solution, due to the presence of solute, that leads to a lower water potential.

Key Concepts

Free Water Molecules

Free water molecules are those not bound or limited by solute particles in a solution. They retain the ability to move freely and engage in processes like diffusion and osmosis. In pure water, all water molecules are free, giving it the highest possible water potential. When solutes are added to water, they interact with water molecules and reduce their freedom. This is because solute particles occupy space and form hydrogen bonds with water molecules.

• Water molecules close to solute particles can no longer participate in osmosis.
• The decrease in free water molecules leads to a lower overall water potential.

A lower quantity of free water molecules means that the solution cannot perform osmosis as effectively as pure water.

Solute Concentration

The concentration of solutes in a solution plays a key role in determining its water potential. Solute concentration refers to the amount of solute that is dissolved in a given amount of solvent, often expressed in molarity. A higher solute concentration implies that more solute particles are present in the solution, which directly affects the water potential.

The Role of Solutes

In solutions, solutes disrupt the uniform distribution of free water molecules. Solute particles limit the movements of water molecules through interactions such as hydrophilic attractions, making fewer water molecules available to participate in cellular processes like osmosis.

• More solute leads to fewer free water molecules.
• Lower solute concentration means higher water potential.

If solute concentration increases, water potential decreases correspondingly. This is a fundamental concept in understanding how various solutions interact within biological systems.

Osmosis

Osmosis is a special kind of diffusion focusing on the movement of water molecules through a selectively permeable membrane. It occurs from a region of high water potential (more free water molecules) to a region of lower water potential (fewer free water molecules). This process is crucial for maintaining cell turgidity and homeostasis in living organisms.

The Movement of Water in Osmosis

Free water molecules drive the process of osmosis; when water potential is higher outside a cell than inside, water rushes into the cell, making it swell. Conversely, when water potential is higher inside, water exits the cell, potentially causing it to shrink.

• Water moves from areas of low solute concentration to high.
• Osmosis is vital for nutrient absorption and waste removal.

Understanding osmosis involves recognizing its reliance on water potential, which heavily depends on the concentration of solutes and availability of free water molecules.