The vacuole contributes to turgor pressure by facilitating the osmotic inflow of water into the cell. While the reference states this inflow occurs across the plasma membrane, in plants specifically, the vacuole plays a vital role. Let's break it down:
Understanding Turgor Pressure
Turgor pressure is the force exerted within a cell that pushes the plasma membrane against the cell wall. It is crucial for:
- Plant rigidity: Turgor pressure keeps plant cells firm, providing structural support.
- Cell growth: It helps cells expand and elongate.
- Nutrient storage: Vacuoles can store nutrients and other compounds, contributing to the osmotic gradient.
The Vacuole's Role in Turgor Pressure
The vacuole, a large organelle found in plant cells, is a major player in establishing and maintaining turgor pressure. Here's how:
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Solute Accumulation: The vacuole accumulates a high concentration of solutes, such as ions, sugars, and organic acids. This creates a higher solute concentration inside the vacuole compared to the surrounding cytoplasm.
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Osmotic Gradient: The difference in solute concentration creates an osmotic gradient. Water moves from an area of low solute concentration (outside the cell or in the cytoplasm) to an area of high solute concentration (inside the vacuole) via osmosis.
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Water Influx: Water flows into the vacuole, increasing its volume.
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Pressure Exertion: As the vacuole expands with water, it pushes against the cytoplasm and ultimately the cell wall. This outward pressure is turgor pressure. The reference mentions that the turgor pressure pushes the plasma membrane against the cell wall, and this increased water within the vacuole directly contributes to that force.
Essentially, the vacuole acts as a storage reservoir for solutes, driving water into the cell and creating the necessary pressure for rigidity and other cellular functions. The inflow of water, as the reference suggests, is driven by osmotic gradients.
Example
Imagine a plant cell in a hypotonic environment (more water outside the cell). The vacuole's high solute concentration draws water in. The vacuole swells, pushing against the cell wall, making the cell turgid and the plant stem upright.
