Water is the most abundant substance in the human body, making up approximately 60% of body mass.
Water is important to the human body as it plays a role in regulating body temperature, lubricating and cushioning joints and maintaining blood pressure (blood plasma is composed mostly of water), just to name a few.
Diffusion: the net movement of a substance from a region of higher concentration to a region of lower concentration.
Water will move from where there is more water (high concentration) to where there is less water (low concentration)
The movement of water across the cell membrane, down its concentration gradient is called osmosis.
Osmosis is a passive transport method, as it does not require the cell to use ATP.
Water can cross the cell membrane through small protein channels called aquaporins.
The rate at which diffusion occurs will increase if:
- Temperature increases
- The concentration gradient increases
- The molecule is small in size
Tonicity describes how an extracellular solution (a solution outside the cell) can change a cell's volume by affecting osmosis.
Solutions are made of solvents and solutes. The solute is what is dissolved in the solvent.
Hypotonic Solution: A solution with less solute and therefore more water compared to the cell. In this situation, water will follow its concentration gradient and enter the cell.
Hypertonic Solution: A solution with more solute and therefore less water compared to the cell. Because the cell has a relatively higher water concentration, water will leave the cell.
Isotonic Solution: A solution with an equal solute and water concentration compared to the cell. There will be no net movement of water into or out of the cell, although water will still move in and out.
