Chemical Basis of Life, Atomic Structure, and Radioisotopes

Fundamentals of Elements, Compounds, and Elemental Deficiencies

  • Elements vs. Compounds:

    • An element is a pure substance consisting of a single type of atom.

    • A compound is a substance formed when two or more individual elements combine chemically (e.g., individual sodium and chloride elements combining to form sodium chloride, NaClNaCl).

    • Emergent Properties: Compounds exhibit new, unique physical and chemical properties that differ completely from the individual properties of their constituent elements.

  • Essential Elements of Life:

    • The four most abundant elements found across all living organisms are:

    • Carbon (CC)

    • Hydrogen (HH)

    • Oxygen (OO)

    • Nitrogen (NN)

    • Together, these four major elements account for approximately 96.3%96.3\% of human body mass.

    • Other remaining essential elements account for approximately 3.7%3.7\% of body mass.

  • Comparison of Elemental Abundance:

    • Carbon makes up 18%18\% of total human body mass.

    • In contrast, carbon exists only as a trace element in the Earth's crust and the atmosphere, illustrating the stark biochemical difference between living organisms and the surrounding environment.

  • Biological Impact of Elemental Deficiencies:

    • Living organisms require precise elemental proportions; an excess, lack, or imbalance of any essential element causes severe physiological dysfunctions.

    • Iodine Deficiency in Humans:

    • Role of Iodine: Essential element required for the biosynthesis of thyroid hormone.

    • Function of Thyroid Hormone: Regulates major metabolic processes in the human body.

    • Pathophysiological Mechanism: When the body lacks sufficient iodine, thyroid hormone production decreases. In response, the brain continuously transmits signaling messages to the thyroid gland instructing it to synthesize more hormone.

    • Clinical Manifestation: Constant physical overstimulation causes enlargement of the thyroid gland (goiter).

    • Nitrogen Deficiency in Plants:

    • Visual Symptom: Yellowing of leaves (chlorosis), particularly affecting older leaves, causing them to lean over.

    • Mechanism: When nitrogen is limited, the plant prioritizes new growth by actively mobilizing and transferring existing nitrogen reserves from older leaves to growing regions.