Question

The pressure exerted by the protoplast due to the entry of water against the rigid cell wall is called (a) Osmotic potential (b) Pressure potential (c) Water potential (d) Matrix potential

Short answer

The correct answer is (b) Pressure potential.

Step-by-step solution

Understand the Terminology

The first step in solving this exercise is to understand the different terms given in the options. Osmotic potential refers to the potential of water molecules to move from a hypotonic solution to a hypertonic solution. Pressure potential is the pressure exerted against the cell wall due to the water content in a cell. Water potential is a measure of the potential energy in water and its drive to move from one place to another. Lastly, matrix potential is the ability of the soil to retain water against the force of gravity and plant uptake.

Match the Definition with the Right Term

The question asks for the term that refers specifically to the pressure exerted by the protoplast (the living content of a cell, excluding the cell wall) against the rigid cell wall due to the entry of water. This phenomenon describes the definition of pressure potential.

Key concepts

Protoplasts

Protoplasts are a fundamental concept in the study of plant physiology. They are essentially the living part of a plant cell that comprises everything within the cell membrane, excluding the cell wall. This includes the cytoplasm, the nucleus, and other cellular organelles.

Protoplasts play a critical role in understanding how cells interact with their environment, particularly in terms of osmosis and pressure. When water enters a plant cell, it fills the protoplast and creates internal pressure against the cell wall. This process is crucial for maintaining the cell’s shape and for the overall structural integrity of plants. Understanding protoplasts is essential when studying cellular responses to water movement, which has direct implications on plant turgor and growth. Furthermore, in laboratory settings, protoplasts can be isolated for genetic modification or fusion experiments, making them a powerful tool in plant molecular biology and biotechnology.

Cell Wall

The cell wall is a rigid layer that surrounds the cells of plants, fungi, bacteria, and some protists. In plants, it's chiefly composed of cellulose, hemicellulose, and lignin. It serves several functions:

• It gives the cell its shape and provides physical protection.
• Cell walls are responsible for the strength and rigidity of plant tissues.
• They help control the direction of growth by regulating cellular expansion and resisting internal hydrostatic pressure.

The relationship between the cell wall and the protoplast is dynamic; the cell wall maintains the structure, while the protoplast exerts a pressure against it – a concept we refer to as pressure potential. Understanding the cell wall’s characteristics is pivotal for comprehending how plants maintain turgidity and manage water transport.

Water Potential

Water potential is a term used to describe the energy state of water in a system. It is denoted by the symbol \( \Psi \) and is measured in units of pressure. Water potential is a comprehensive measure that takes into account several factors that influence the movement of water. These factors include osmotic potential, pressure potential, and gravity. The total water potential within a plant cell determines the direction and movement of water – it will always move from an area of higher water potential to an area of lower water potential.

For students to fully grasp the concept of water potential, it is vital to understand that aside from osmotic and pressure potential, there are other factors such as matric potential, which comes into play with the water content in soil. Due to its complexity, water potential is a critical concept in the study of plant physiology and understanding how water moves through the environment.

Osmotic Potential

Osmotic potential, also referred to as solute potential, is specifically the component of water potential that is attributable to solute concentration. In essence, it is the potential of water to move across a semi-permeable membrane due to the presence of solutes. Osmotic potential is always negative in a system because the addition of solutes to water lowers its potential energy.

The concept of osmotic potential is particularly important for understanding how water is absorbed and retained by cells and how it moves within plants. It also influences the turgor pressure, which is vital for plant cell functions such as opening and closing of stomata, and elongation of cells during growth. Students often encounter this concept when studying processes like osmosis and its effects on plant cells.