Osmosis in Animals & Plants | Biology for GCSE/IGCSE - Year 11 PDF Download

Osmosis in Plant Tissues

• When water moves into a plant cell, the vacuole enlarges, exerting pressure on the cell membrane against the cell wall
• The influx of water through osmosis results in the cell becoming sturdy and rigid
• This rigidity is vital for plants since it collectively provides support and fortitude, enabling the plant to stand upright with its leaves exposed to sunlight
• The cell wall's pressure regulates excessive water intake, preventing the cell from bursting
• Insufficient water intake causes the cells to lose their rigidity, resulting in wilting of the plant

Osmosis: Extended

• Osmosis entails the directional movement of water molecules from an area of higher water potential (a dilute solution) to one of lower water potential (a concentrated solution) through a partially permeable membrane.
• To avoid confusion between the concentration of water and the concentration of solute, we can describe a dilute solution as having a high water potential (illustrated on the right-hand side of the diagram below), while a concentrated solution has a low water potential (depicted on the left-hand side of the diagram below).

Osmosis in Animals & Plants: Extended

• Placing plant cells in a solution with a higher water potential than inside the cells, such as distilled water, results in the influx of water into the plant cells via osmosis.
• As water molecules enter the cells, they exert pressure against the cell membrane, which in turn pushes against the cell wall, causing the cells to become turgid.

• Placing plant cells in a concentrated solution, where the external water potential is lower than inside the cells, results in the outward movement of water molecules through osmosis. This causes the plant cells to become flaccid.
  • Flaccid plant cells can compromise the plant's structural support.
• Under a microscope, plasmolysis can be observed in the plant cells, indicating that the cell membrane has detached from the cell wall.

Animal cells in solutions of different concentrations

• Osmosis also impacts animal cells, leading to water loss or gain.
• Unlike plant cells, animal cells lack a rigid cell wall, making them more vulnerable to osmotic changes.
• Placing an animal cell in a hypertonic solution, with a lower water potential, causes water to exit the cell, resulting in crenation or cell shrinkage.
• Conversely, immersing an animal cell in a hypotonic solution, with a higher water potential, prompts water influx. Without a supportive cell wall, the cell membrane stretches until it reaches a breaking point, causing cell rupture.