Water Movement Through Cell Membrane: 9 Facts You Should Know

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Cell homeostasis is maintained by the water movement through cell membrane that is semi-permeable in nature.

The cell membrane of any organism allows partial movement of particles across it. Water transportation takes place without spending energy. This article will discuss the water movement across the cell membrane in detail.

9 facts about water movement across the cell membrane:

  • Water transport across the cell membrane is an energy-independent process.
  • It is popularly known as osmosis.
  • It is a passive diffusion as it does not use energy.
  • Aquaporins facilitate water movement through it.
  • Water movement across the cell membrane maintains cell homeostasis.
  • The lipid composition of the cell membrane regulates the efficacy of the cell membrane with which it allows water movement.
  • Aquaporins restrict the movement of ions through it.
  • Cancer cells express more aquaporins on their surface.
  • Aquaporins increase membrane permeability to water.

How can water pass through the cell membrane?

Water (solvent) movement is observed from hypotonic to the hypertonic solution, i.e; from a region having low solute concentration to a region having high solute concentration. Across the semi-permeable membrane, only water can pass, and solute cannot move across the membrane.

To attain equilibrium in solute concentration, water moves from a region having a low concentration of solute to a region having a high solute concentration.

The biochemical composition of the cell membrane governs its potential to allow the movement of water through the cell membrane.

A high concentration of incorporated cholesterol restricts water movement, whereas a membrane with less cholesterol has a greater ability to transport water.

Aquaporins present on the cell membrane facilitate the transport of water through it. These are proteins incorporated in the cell membrane as channels. Aquaporins regulate the flow of water from the outside to the inside of the cell using a biological water channel.  

water movement through cell membrane
Diffusion across the plasma membrane from Wikimedia

These protein channels prevent the ions to move across the cell membrane and maintain an ion concentration gradient. Epithelial cells of the kidney are popularly known to have these protein water channels.

Four aquaporin channels are found in mammals and 10 in plants. Water moves across the cell membrane with the help of integral proteins, aquaporins.

Cancer cells express more aquaporins as compared to their homologous normal cells, which leads to an increase in oxidative stress.

Aquaporins increase membrane permeability to water and control their movement through gating, facilitating water uptake at lower temperatures and in bulk volume. Cell homeostasis is maintained by the transport of water across the cell membrane that is semi-permeable in nature.

Does the cell membrane store water?

No, the cell membrane cannot store water. A cell membrane is made up of phospholipid bilayers and the hydrophobic tail region of a phospholipid bilayer restricts the storage of water in the cell membrane.

Aquaporins are the channels through which water moves across the cell membrane.

Can water pass through the plant cell membrane?

Yes, water can pass through the plant cell membrane. The presence of cell walls in plants creates a difference in the efficiency with which water moves across the plant and animal cell membrane.

Only small molecules are allowed to pass through the rigid cell wall of plants. Water movement into the plant cell increases turgor pressure thereby limiting the rate and amount of further water entry.

Water potential is the movement of water into the cell and is quantified as a summation of pressure potential and solute potential. The pressure inside the cell is the pressure potential and the concentration of the solute inside the cell is the solute potential.

Water moves from the roots to the leaves of the plants and the plant transports solutes to the root of the plants generating a gradient. This gradient helps water to move into the roots through osmosis. Following osmosis, transpiration takes place which allows water to move up the xylem tubes and get evaporated out from the surface of the leaves.

When a plant cell is placed in distilled water it stiffens but retains its shape as water moves into the cell, however, a plant cell shrinks if it is placed in a concentrated salt solution as water diffuses out of the cell.

Can water pass through the fungi cell membrane?

Yes, water can pass through the fungi cell membrane using four types of aquaporins, viz; X intrinsic proteins, orthodox aquaporins, small basic intrinsic proteins (SIP) like aquaporins, and aquaglyceroporins.

Orthodox aquaporins are known to transport only water while aquaglyceroporins transport glycerol, urea, water, and arsenite.

Can water pass through the bacteria cell membrane?

Yes, water can pass through bacterial cell membranes easily as bacterial cell membranes usually do not contain cholesterol leading to unrestricted movement of water.

However, bacterial cell wall composition affects water permeability across it.

Give a practical application of osmosis.

After a deluge in West Kenya, NASA used the osmosis technique to develop a water purification system. It used forward osmosis to cleanse and purify wastewater.

The water was made safe for drinking by using a semi-permeable membrane that removed the impurities.

Conclusion

From this article, we can conclude that water moves across a cell membrane via passive diffusion which is alternatively known as osmosis. 

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