Water Relations Practice Questions

Correct answer: Osmotic potential

Water movement in plant cells occurs due to differences in osmotic potential across membranes. This governs processes like osmosis, plasmolysis, and turgor maintenance.

Correct answer: One with higher solute concentration than the cell

In a hypertonic solution (higher solute concentration than the cell), water moves out of the cell by osmosis. This causes the protoplast to shrink away from the cell wall, leading to plasmolysis.

Correct answer: Plasma membrane beginning to pull away from wall

Plasmolysis begins when the plasma membrane starts pulling away from the cell wall. This initial detachment marks the onset of water loss from the cell and is the first visible sign of plasmolysis.

Correct answer: Cellulose microfibrils in the wall

Cellulose microfibrils provide rigidity and tensile strength to the cell wall. They counteract the internal turgor pressure that builds up when water enters in a hypotonic solution, preventing the cell from bursting.

Correct answer: Pressure exerted by protoplast on cell wall

Turgor pressure is the outward pressure exerted by the cell contents against the cell wall. It helps maintain cell shape and rigidity.

Correct answer: Protoplast pressing firmly against the cell wall

In a fully turgid cell, water enters until maximum turgor pressure develops and the protoplast presses firmly against the cell wall. At this point, no further net water entry occurs.

Correct answer: Turgor pressure becomes zero

Incipient plasmolysis is the stage where turgor pressure just becomes zero. It marks the point of equilibrium between the cell and external solution.

Correct answer: Hypotonic solution

In a hypotonic solution, water enters the plasmolysed cell by osmosis. This restores turgidity and reverses plasmolysis.

Correct answer: Central vacuole

The central vacuole stores cell sap and regulates osmotic balance. It is crucial for generating and maintaining turgor pressure.

Correct answer: Drooping and wilting of shoots

Wilting occurs when plant cells lose turgor pressure due to water deficit. This causes leaves and stems to droop and become limp, as they lack the rigidity that turgor provides.

Correct answer: Supports cell shape and drives growth

Turgor pressure provides mechanical support to cells and drives cell enlargement during growth. It is essential for maintaining structural integrity and for the expansion of plant cells.

Correct answer: Onion epidermal peel cells

Onion epidermal cells have large central vacuoles and distinct cell walls, making plasmolysis (shrinking of the protoplast away from the wall) easily visible under a light microscope.

Correct answer: Pressure of the cell wall on the protoplast

Wall pressure (also called pressure potential) is exerted by the rigid cell wall against the expanding protoplast. It opposes and ultimately balances turgor pressure in a fully turgid cell, preventing further water entry.

Correct answer: No net movement of water occurs

A flaccid cell occurs when water movement reaches equilibrium. There is no turgor pressure, but plasmolysis has not yet started.

Correct answer: Plasmolysis is cellular; wilting is a tissue-level event

Plasmolysis is a cellular phenomenon involving individual cells losing water to a hypertonic medium. Wilting is a tissue-level effect caused by loss of turgor across many cells simultaneously.

Correct answer: Exosmosis (outward osmosis)

Exosmosis refers to the outward movement of water from a cell into a hypertonic external solution via osmosis. It occurs when the solute concentration outside the cell is higher than inside.

Correct answer: Availability of water in soil

Under natural conditions, soil water is usually available to plants. This prevents prolonged exposure to hypertonic environments.

Correct answer: Ambient light intensity

Plasmolysis depends on the osmotic gradient (external solute concentration), membrane permeability, and temperature. Ambient light intensity does not directly influence osmotic water movement across the membrane.

Correct answer: Opening and closing of stomata

Stomatal movement depends on changes in turgor pressure of guard cells. When guard cells become turgid, stomata open; when they lose turgor, stomata close. This regulates transpiration and gas exchange.

Correct answer: Maintain structural support and osmotic balance

Turgor pressure provides mechanical support to plant cells and tissues, while plasmolysis illustrates the osmotic behaviour of cells. Together, these phenomena underpin the regulation of water balance in plants.

Correct answer: Hypertonic solution

In a hypertonic solution, water moves out of the cell. This causes the protoplast to shrink away from the cell wall.

Correct answer: Exosmosis

Exosmosis is the movement of water out of the cell. It occurs when the cell is placed in a hypertonic solution.

Correct answer: Pressure of cytoplasm on cell wall

Turgor pressure is the pressure exerted by the cell contents against the cell wall. It helps maintain cell rigidity.

Correct answer: Cell wall pressure

Wall pressure is exerted by the cell wall against the expanding protoplast. It balances turgor pressure.

Correct answer: Turgor pressure is zero

Incipient plasmolysis is the stage where turgor pressure becomes zero. The cell begins to shrink from the wall.

Correct answer: No net movement of water

In a flaccid cell, there is no net movement of water. It occurs in isotonic conditions.

Correct answer: High solute concentration outside

A high solute concentration outside the cell draws water out. This causes plasmolysis.

Correct answer: Water potential gradient

Water moves along a water potential gradient. This drives water relations in plants.

Correct answer: Cell wall

The rigid cell wall resists excessive expansion. It prevents the cell from bursting.

Correct answer: Plant cells with large vacuole

Plant cells with large vacuoles show clear plasmolysis. The protoplast visibly shrinks away from the wall.

Correct answer: Equal solute concentration

In isotonic solutions, solute concentration is equal inside and outside. There is no net movement of water.

Correct answer: Cell turgidity

Water enters the cell in a hypotonic solution. This makes the cell turgid.

Correct answer: Shrinkage of protoplast

The protoplast begins to shrink away from the cell wall. This is the first sign of plasmolysis.

Correct answer: Continuous water supply

Plants usually have access to water. This prevents permanent loss of water and restores turgidity.

Correct answer: Maintaining cell rigidity

Turgor pressure maintains cell rigidity and supports plant structure. It is essential for plant stability.