Cell Transport

Introduction

Water is an important component of cells. Cytoplasm contains varios gases and solutes which are transported from one cell to another. Exchange of these substances also take place between the cell and its environment. This movement of substances along with water in both plant and animal cells is termed as cellular transport.

Different modes of Cellular transport

• Diffusion:

  In this process, molecules of a solute move from a medium of higher concentration to that of a lower concentration. Movement continues until both the mediums become of same concentration. When the difference in concentration (diffusion gradient) is higher, movement of solutes or gases is faster. In plants, CO₂ intake from atmosphere and loss of water through leaves, take place by the process of diffusion.

• Osmosis:

  It is a special kind of diffusion process which involves a semi permeable membrane between the two mediums of different concentration. In this process,water molecules move from dilute solution to concentrated solution.In other words,Water molecules move from a medium of higher concentration of water molecules (dilute solution) to a lower concentration of water molecules (Concentrated solution).Osmotic movement depends on temperature, pressure and concentration of solute molecules.

  • Osmotic pressure:

  When a semi permeable membrane separates a solution from pure water, the water tends to move into the solution. The pressure of the solution required to stop the water from entering the solution is termed as osmotic pressure.

  • Reverse osmosis:

  If the pressure of the solution is increased more than the osmotic pressure, the water will move from the solution to the pure water (in reverse direction). This is called reverse osmosis.

  • Different types of solution and plant cells

  Isotonic solution: The solution has the same concentration of solute and water than that of inside the plant cell.

  Hypotonic solution: The solution has lower concentration of solute than that of inside the plant cell.

  Effect: Turgidity. Water enters into the cell and pressure increases on cell wall.

  Hypertonic solution: The solution has higher concentration of solute than that of inside the plant cell.

  Effect Plasmolysis. Water leaves the cell by osmosis. protoplasm shrinks and does not exert pressure on cell wall.

• Imbibition:

  It is a type of diffusion in which water moves along the diffusion gradient. Dry seeds soak water by this process. Rehydration of water loving (hydrophilic) colloids in cell wall tales place and seed swells.