Question

The two main components which determine water potential are (a) Solute potential (b) Pressure potential (c) Matric potential (d) Both (a) and (b)

Short answer

The correct answer is (d) Both (a) and (b).

Step-by-step solution

Understand Solute Potential

Solute potential, also termed as osmotic potential, is the potential of water molecules to move from an area of lower solute concentration to an area of higher solute concentration.

Understand Pressure Potential

Pressure potential refers to the physical pressure on a solution. It increases water potential as it increases since it facilitates water movement.

Understand Matric Potential

Matric potential is related to the capacity of water to adhere to surfaces of any solid materials present (e.g., cell walls). However, it's not a primary factor determining water potential in a cell or system.

Conclude From the Definitions

Based on our understanding about solute potential, pressure potential and matric potential, it's clear that both solute potential (osmotic potential) and pressure potential are the main determinants of water potential, not the matric potential.

Key concepts

Solute Potential

Solute potential, also known as osmotic potential, plays a key role in determining the direction in which water will move. This potential arises due to the presence of solutes dissolved in water, and it is a crucial component in the movement of water through plant cells.
In simple terms, solute potential is the tendency of water to move from regions with fewer solutes to regions with more solutes. When solute concentration increases, the potential becomes more negative, making it less likely for water to move into that solution. This happens because water wants to dilute the concentrated solution.

• If you add sugar to water, for instance, the solute potential becomes more negative, indicating a stronger pull on water molecules.
• Plant cells tend to draw water through the membrane if the inside of the cell has a higher concentration of solutes compared to the outside.

This concept is significant in understanding how water is absorbed by plant roots and how it travels throughout the plant.

Pressure Potential

Pressure potential, often referred to as turgor pressure in plants, relates to the physical pressure on water in a system. It's comparable to the pressure exerted in a water pipe that helps push water through it.
This potential is critical for maintaining plant rigidity; excessive water loss would result in plants wilting. Pressure potential aids in ensuring that water moves from regions of higher pressure to regions of lower pressure.

• Think of a balloon filled with water; the more water inside, the greater the pressure, making it easier for water to exit if the balloon is pinched.
• In plants, healthy turgor pressure keeps stems upright and leaves expanded, aiding in photosynthesis and growth.

Pressure potential interacts with solute potential to determine the water potential that finally dictates the movement of water in plant cells.

Matric Potential

Matric potential is associated with the adhesion of water molecules to surfaces, particularly in soil or plant cell walls. Imagine water soaking into a sponge – matric potential is what describes the pull exerted by the sponge to hold onto the water.
This potential predominantly influences how water is retained in soils and is less significant in aquatic plant tissues or systems where the volume of water is large compared to cell wall surfaces.

• Matric potential helps explain why some soils retain water better than others. Sandy soils have low matric potential and thus poor water retention.
• Clayey soils, on the other hand, have high matric potential, providing a stronger grip on water molecules.

Despite its importance in soil-water interactions, matric potential isn’t a major contributor to the water dynamics within plant cells, especially compared to solute and pressure potentials.