Chemistry of Life: Atoms, Inorganic Compounds, and Mineral Salts

Atoms are the smallest building blocks of matter and combine to form molecules ranging from simple pairs to complex structures of hundreds of atoms.
Cells are the basic unit of life and are composed of both simple and complex molecules.
An element consists of identical atoms.
A compound is formed when two or more different elements combine (e.g., $2H$ and $1O$ forms a molecule of the compound water, $H_2O$ ).

Inorganic substances generally do not contain carbon, with the exception of $CO_2$ and carbonates.
They are typically small molecules composed of a few atoms, such as water and mineral salts.
Water ( $H_2O$ ): Essential for photosynthesis in plants and nutrition in animals; acts as a fluid medium for chemical reactions in both.

Sodium ( $Na$ ): Maintains water balance in plant cell sap (turgidity); regulates osmotic balance and kidney/nerve/muscle function in animals.
Potassium ( $K$ ): Facilitates the opening and closing of stomata in plants; involved in nerve impulse transmission in animals.
Calcium ( $Ca$ ): Component of the middle lamella in plant cell walls; used for building bones and teeth, muscle contraction, and nerve impulses in animals.
Phosphorus ( $P$ ): Component of cell membranes and $ATP$ ; promotes plant flowering and root development; used for animal bones and teeth.
Iron ( $Fe$ ): Required for chlorophyll synthesis in plants and as a part of the haemoglobin molecule in animals.
Iodine ( $I$ ): Not required by higher order plants; a constituent of the hormone thyroxin in animals. Deficiency leads to goitre (thyroid swelling).

Macro elements: Required in large quantities ( $Na$ , $K$ , $Ca$ , and $P$ ).
Micro elements: Required in small quantities ( $Fe$ and $I$ ).