Water and Mineral Salts in Living Organisms
Water: The Essence of Life
Properties of Water
Water, the most abundant molecule in living matter, comprises 20% to 85% of an organism’s mass, decreasing with age. A water molecule consists of two hydrogen atoms and one oxygen atom, covalently bonded at a 104.5° angle. Although electrically neutral, the atoms have different electronegativity values, giving water its polar character. This polarity allows water molecules to form hydrogen bonds with each other.
- Dielectric Constant: The force with which water opposes the electrostatic attraction between positive and negative ions.
- Low Degree of Ionization: Liquid water contains a small number of ionized molecules.
- High Cohesion Force: The force of attraction that binds water molecules together.
- High Surface Tension: The force on the surface of water that allows it to behave as an elastic and tense surface.
- High Adhesion Force: The force of attraction that binds water molecules to the walls of small ducts, allowing it to rise against gravity.
- High Specific Heat: The temperature required to raise the temperature of water by 1°C, due to the tendency to form hydrogen bonds.
- High Heat of Vaporization: The heat absorbed in the transformation from liquid to gas.
- Density Decrease Below 4°C: Water’s density decreases below 4°C.
Functions of Water
The functions of water are intimately connected to its properties. The most important functions include:
- Transport vehicle and solvent for nutrients and waste products.
- Facilitates metabolic reactions.
- Regulates body temperature.
- Provides flexibility and elasticity to tissues, acting as a lubricant and shock absorber.
- Maintains internal temperature.
- Acts as a solvent.
- Allows for life under frozen surfaces.
- Participates in various chemical reactions.
- Distributes substances.
Mineral Salts
Mineral salts are inorganic molecules present in all living things. They can be dissolved or precipitated and may be associated with organic molecules.
Dissolved Salts
Soluble in water, dissolved salts regulate osmotic phenomena, pH balance, and enzyme activity. They also generate and maintain electrical potential, body salinity, and stabilize colloidal dispersions. Examples include anions like chloride (Cl–), phosphates, and nitrates (NO3–); and cations like sodium (Na+), calcium (Ca2+).
Precipitated Salts
Found in a solid state and insoluble in water, precipitated salts form protective structures like skeletons. Crystals in organisms are abundant in silicates, carbonates (CaCO3), and phosphates (Ca3(PO4)2).
Osmosis and Osmoregulation
Osmosis
Osmosis is a physical phenomenon related to the behavior of water across a semipermeable membrane. The membrane allows the passage of solvent (water) but not solutes. This involves simple diffusion without energy expenditure. Osmosis is crucial for the cellular physiology of living beings.
A semipermeable membrane has pores of molecular size, allowing small molecules like water to pass through but not larger molecules like sugar.
Osmoregulation
Osmoregulation is the active regulation of the osmotic pressure of the body’s internal environment to maintain homeostasis. This prevents the internal state from becoming too diluted or concentrated. Osmotic pressure measures the tendency of water to move between solutions through osmosis.
Osmoregulation, primarily performed by the kidneys and heart, regulates water balance within the human body. Metabolic reactions require a precise balance of water and dissolved solutes. Osmosis occurs between two solutions separated by a membrane with differing solute concentrations. There is a net movement of water from the hypotonic solution to the hypertonic solution until solute concentrations equalize.