A rainbow is a meteorological phenomenon characterized by a spectrum of colors appearing in the sky due to sunlight refracting, reflecting, and dispersing in water droplets, creating a beautiful, multicolored arc.

Normal human vision involves light entering the eye, refracting through the cornea and lens, forming a focused image on the retina. Signals are sent to the brain via the optic nerve, enabling clear sight.

Vision defects include myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia. These conditions result from abnormalities in the eye’s shape or lens flexibility, affecting the ability to focus clearly.

Hormones are chemical messengers secreted by glands, regulating various physiological processes. Examples include insulin, estrogen, and adrenaline. They travel through the bloodstream, influencing growth, metabolism, and other bodily functions.

The human heart is a vital organ that pumps blood through the circulatory system. It consists of four chambers—two atria and two ventricles. Its rhythmic contractions maintain blood circulation and oxygenate tissues.

The human brain is a complex organ responsible for cognition, emotions, and control of bodily functions. It consists of billions of neurons interconnected through synapses, forming the basis of consciousness and intelligence.