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Cells must maintain a steady internal environment despite changes outside the cell. Known as homeostasis, this steady state allows the plant cell to adapt to external changes and help the plant to survive. Plant cells use different functions to maintain homeostasis: osmosis, diffusion and active transport.
Osmosis and Diffusion
Plant cells must maintain an even balance of water inside the cell as outside. They do this by pulling molecules across their cell wall and cell membrane. Inside the cell, the large vacuole holds water until needed. The movement of molecules naturally from areas of high concentration to those with lower concentration. This process of passive transport of any molecule is known as diffusion, but if occurring with water molecules, is referred to as osmosis.
A cell in a solution with more water on the outside of the cell than inside (hypertonic) will pull water into the cell. Plant cells might bulge in such a solution but not burst due to their rigid cell walls.
Isotonic solutions move nothing across the membrane of the cell since molecule concentrations on both sides of the plant cell are equal, and hypotonic solutions push water or other molecules outside of the cell. Hypotonic solutions result in wilting plants with the cell membrane shrinking inside the cell wall.
Active transport acts in the opposite direction of passive transport. Like pushing a rock uphill, active transport requires energy in the form of ATP produced in the cell.
Plant root cells maintain a homeostasis of nutrients drawn from the soil via the roots through active transport. Because a higher concentration of nutrients exists inside the root cells than in the surrounding soil, the plant cell must use ATP energy to pull more nutrients from the soil. Without ATP, nutrients from inside the plant cells would move out of the cells and into the soil through diffusion.
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