Why can ATP be called a key source of energy in metabolic reactions? What processes do ATP spend?

ATP is the main substance that provides energy processes in the cell: it accumulates energy in the process of energy exchange and releases in the process of plastic metabolism.
This energy is spent in the process of plastic exchange for the synthesis of organic substances specific to each organism. Part of the energy in the process of metabolism is constantly lost in the form of heat, so organisms need a constant influx of energy from the environment.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.