Bioelements, Water, and Mineral Salts: Chemistry of Life

Bioelements: Chemical Basis of Life

Bioelements are the chemical elements that constitute living matter. They are classified based on their abundance:

Classification of Bioelements

• Primary Bioelements

  These make up the vast majority of living matter. They include Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), and Sulfur (S) – often abbreviated as CHONPS.

• Secondary Bioelements

  These include Sodium (Na+), Potassium (K+), Calcium (Ca2+), Magnesium (Mg2+), and Chlorine (Cl-). Although present in smaller proportions than primary bioelements, they are essential for life. In aqueous environments within living organisms, they are always found in their ionized forms.

• Trace Elements (Oligoelements)

  These are required in very small amounts. They can be:

  • Indispensable: Found in all living things.
  • Variable: Only needed by certain organisms.

Biomolecules: The Molecules of Life

Biomolecules are formed by the combination of bioelements. These molecules constitute living matter and are sometimes called 'immediate principles' because they can often be extracted from biological material using simple physical methods like evaporation, distillation, or dissolution.

Types of Biomolecules

There are two main categories:

• Inorganic Biomolecules: Primarily Water and Mineral Salts.
• Organic Biomolecules: Include Carbohydrates, Lipids, Proteins, and Nucleic Acids.

Water: The Essential Solvent

Biological Importance of Water

Water is the most abundant component in living organisms. The proportion of water varies among different species and changes with the age of the individual. Within organisms, water is found both inside cells (intracellularly) and outside cells (extracellularly), such as in blood, lymph, or plant sap. For unicellular and aquatic organisms, water also serves as their external environment. It acts as a crucial solvent, participates in numerous chemical reactions (either as a reactant or a product), and is indispensable for maintaining the structure and stability of many biological molecules.

Structure of Water

A water molecule (H₂O) consists of one oxygen (O) atom covalently bonded to two hydrogen (H) atoms. Oxygen is highly electronegative, meaning it attracts the shared electrons more strongly. This creates a partial negative charge (δ-) near the oxygen atom and partial positive charges (δ+) near the hydrogen atoms, making water a polar molecule. Due to this polarity, electrostatic attractions form between the partial positive charge of a hydrogen atom on one water molecule and the partial negative charge of the oxygen atom on a neighboring molecule. These attractions are known as hydrogen bonds.

Key Functions of Water

1. Volume and Turgidity: Water provides volume to cells, contributing to turgor pressure in plant cells and participating in the hydrostatic skeletons of some animals.
2. High Surface Tension: The cohesive forces between water molecules result in high surface tension, allowing some small organisms to move across its surface without sinking.
3. Cohesion and Adhesion: High cohesion (attraction between water molecules) and adhesion (attraction between water and other surfaces) enable water to move upwards against gravity in narrow tubes, such as xylem vessels in plants (capillary action).
4. High Solvent Capacity: As a polar molecule, water readily dissolves other polar substances and ionic compounds by forming hydrogen bonds or interacting with ions. This creates aqueous solutions where ions become surrounded by water molecules (solvated ions). Substances that do not dissolve well in water, such as oils, are termed hydrophobic.
5. Thermoregulation: Water has a high specific heat capacity, meaning it can absorb or release a large amount of heat with minimal change in its own temperature. This property helps organisms regulate their internal temperature and protects them from abrupt environmental temperature fluctuations, thus maintaining homeostasis.

Mineral Salts in Living Organisms

Mineral salts are inorganic compounds that readily ionize (dissociate into ions) when dissolved in water.

Forms of Mineral Salts

In living beings, mineral salts exist in two main forms:

• Precipitated: Found in solid, undissolved states, often forming structural components like bones and shells.
• Dissolved: Found as ions in aqueous solutions (intracellular and extracellular fluids), where they perform various functions, including maintaining osmotic balance and acting as enzyme cofactors.