Vitamins are categorized as either fat-soluble or water-soluble. Vitamin C (ascorbic acid) and the B-complex vitamins are water-soluble, meaning they are not stored in the body to a significant extent and must be replenished regularly through the diet, unlike fat-soluble vitamins (A, D, E, and K).

In the solid state, atoms or molecules are held in fixed positions by strong intermolecular forces. Consequently, they lack the freedom to undergo translational or rotational motion and are restricted to vibrating about their equilibrium positions. This vibrational motion persists even at very low temperatures.

The human body is primarily composed of six major bio-elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Together, these six elements account for approximately 99% of the total body mass. These elements are essential for the formation of organic molecules such as proteins, carbohydrates, lipids, and nucleic acids, which form the structural and functional basis of life.

Bio-elements are chemical elements that are essential for the structure and function of living organisms. While there are 92 naturally occurring elements, only about 16 are commonly recognized as essential bio-elements. These include major elements like carbon, hydrogen, oxygen, and nitrogen, as well as various trace elements required for enzymatic and physiological processes.

Henna contains the pigment lawsone (2-hydroxy-1,4-naphthoquinone). This molecule binds to proteins and amino acids found in the keratin of skin and hair through a process known as Michael addition, resulting in the characteristic orange-red stain that persists as the keratinized cells are shed.

Cells possess complex machinery for the synthesis of essential biological macromolecules. DNA is synthesized during replication, RNA is produced through transcription, and proteins are assembled via translation, all of which are fundamental processes for cellular function and maintenance.

A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other, releasing a molecule of water (a dehydration synthesis reaction). This linkage is the fundamental covalent connection that joins amino acids together to form polypeptide chains, which subsequently fold into functional proteins.

Proteins are complex macromolecules composed of long chains of amino acids linked together by peptide bonds. There are twenty standard amino acids that serve as the building blocks for all proteins, and the specific sequence and folding of these amino acids determine the unique structure and biological function of each individual protein molecule.

Proteins and carbohydrates both provide approximately 4 kilocalories of energy per gram when metabolized by the human body. In contrast, lipids provide a higher energy density of approximately 9 kilocalories per gram, reflecting their role as efficient long-term energy storage molecules.

Carbon, oxygen, hydrogen, and nitrogen are the fundamental building blocks of life. They constitute the vast majority of the mass of biological macromolecules, including proteins, nucleic acids, carbohydrates, and lipids. Their unique chemical properties, such as the ability to form stable covalent bonds, make them essential for the structural and functional complexity required for cellular life.