31.3
Tonicity in Plants
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Q1: What happens to plant cells in a hypotonic environment?
In hypotonic environments, solute concentration outside the cell is lower than inside, causing water to enter via osmosis. The plasma membrane pushes against the plant cell wall, creating turgor pressure. This pressure stiffens the plant, allowing it to remain upright and preventing the cell from bursting.
Q2: How does plasmolysis occur in plant cells?
Plasmolysis occurs in hypertonic environments where extracellular solute concentration is higher than inside the cell. Water leaves the cell through osmosis, causing vacuoles to shrink and the plasma membrane to detach from the cell wall. The cytoplasm constricts, and the plant loses turgor pressure, resulting in wilting.
Q3: Why doesn't a plant cell burst in hypotonic conditions?
The rigid cell wall prevents plant cells from bursting by limiting plasma membrane expansion. Although water influx creates turgor pressure that pushes the membrane outward, the cell wall's structural integrity constrains this expansion. This protection allows cells to become turgid without lysing, maintaining plant rigidity.
Q4: What is the difference between hypertonic and hypotonic environments for plants?
In hypotonic environments, water enters cells, creating turgor pressure and plant stiffness. In hypertonic environments, water leaves cells, causing plasmolysis and wilting. Isotonic environments have equal solute concentrations inside and outside, resulting in no net water movement and flaccid, drooping plants.
Q5: How do plants in dry environments prevent water loss?
Plants in dry environments store water in vacuoles, limit stomatal opening, and develop thick, waxy cuticles to reduce water loss. Some species living in salty environments store salt in roots, which creates osmotic gradients that draw water from surrounding soil. These adaptations help maintain osmotic balance in extreme conditions.
Q6: What is turgor pressure and why is it important for plants?
Turgor pressure is the force generated when water influx causes the plasma membrane to push against the cell wall in hypotonic conditions. This pressure keeps non-woody plants upright and maintains their structural rigidity. When plants lose turgor pressure in hypertonic environments, they wilt and droop.
Q7: What happens to plant cells in isotonic environments?
In isotonic environments, solute concentrations are equal inside and outside the cell, resulting in no net water movement. Cells become flaccid without turgor pressure support, and the plant begins to droop. Unlike hypotonic conditions, the plasma membrane does not press against the cell wall.