Question

Assertion: The more the solute molecules in solution, the lower (more negative) is the solute potential of solution. Reason: For a solution at atmospheric pressure, water potential = solute potential.

Short answer

The statements are correct. The solute potential decreases with increasing solute concentration due to the restriction in water movement. At atmospheric pressure, the water potential equals the solute potential since the pressure potential is zero.

Step-by-step solution

Define Solute Potential

Solute potential, also known as osmotic potential, is the potential of water molecules to move from a region of lower solute concentration to higher solute concentration across a semi-permeable membrane. It is a negative quantity because the movement is against the concentration gradient.

Define Water Potential

Water potential is a measure of the potential energy in water, or the free energy of water per unit volume. In the atmosphere, it includes the gravitational potential energy, pressure potential energy, and solute potential energy.

Understand the Relationship

At atmospheric pressure, the water potential equals the solute potential, since the pressure potential is zero. Due to the presence of solute molecules, water movement is restricted, and therefore, the water potential decreases. Thus, the more the solute molecules in the solution, the lower (more negative) is the solute potential.

Key concepts

Water Potential

Water potential is a key concept in understanding how water moves through plants, soils, and other systems. It's essentially a measure of the free energy of water in a system, accounting for factors like gravity, pressure, and solute concentration.

Think of it as the 'potential' water has to do work, which in biological systems, means the potential to move from one place to another. Water moves from areas of higher water potential to areas of lower water potential. Pure water at atmospheric pressure, with no solutes or pressure applied, is considered to have a water potential of zero.

As solutes like salt or sugar are added to the water, they bind with water molecules, reducing the number of free water molecules available to do work. This process lowers the water potential of the solution, which is generally expressed as a negative value compared to pure water.

Osmotic Potential

Osmotic potential, sometimes called solute potential, is an aspect of water potential that specifically accounts for the presence of solutes. It's a measure of the tendency of water to move via osmosis across a semi-permeable membrane separating two solutions with different solute concentrations.

The more solute particles present in a solution, the lower (more negative) its osmotic potential. This is because the water's free energy decreases due to the effect of the solutes: they limit the movement of water molecules by creating a zone where water prefers to stay to balance the concentrations.

Biological membranes, like those found on cells, are semi-permeable, allowing water to pass through while typically blocking solutes. This property is crucial for processes like nutrient absorption and waste removal.

Concentration Gradient

The concentration gradient is a term we use to describe the spatial variation in the concentration of a substance, like a solute in a solvent. Imagine dropping a bit of ink into a glass of water. Initially, there's a high concentration of ink where it enters the water, which will slowly spread out.

In terms of solute potential, water moves from areas of low solute concentration (high water potential) to areas of high solute concentration (low water potential) in an effort to balance these differences in concentration. This movement of water is an attempt to reach equilibrium, where the concentration of the solute would be the same throughout.

Cells often maintain different solute concentrations inside and outside their membranes, creating concentration gradients that are vital for many biological processes, including the movement of substances into and out of the cell.

Semi-Permeable Membrane

A semi-permeable membrane is a barrier that selectively allows certain molecules or ions to pass through it while blocking others. In the context of osmosis and solute potential, it's the 'gatekeeper' that permits water to flow but retains most solute particles.

This membrane is fundamental to life, making it possible for cells to control their internal environments. For example, within our kidneys, semi-permeable membranes filter blood, allowing water and small molecules to pass into the urine while keeping blood cells and proteins in the bloodstream.

Understanding semi-permeable membranes helps us grasp how the body conserves water while filtering out waste, how plants absorb water from the soil, and how cells maintain proper pressure and balance.