What is energy, and how is it used by living organisms?

 What is energy, and how is it used by living organisms?

Energy is the ability to do work or create some kind of change and exists in different forms, such as electrical, light, and heat energy. Living organisms require energy to perform a wide range of tasks, including heavy labor, exercise, thinking, and even during sleep. Energy is required for the synthesis and breakdown of molecules, the transport of molecules into and out of cells, the movement of the cell, ingesting and breaking down pathogenic bacteria and viruses, and exporting wastes and toxins.

Living cells obtain energy through bioenergetics, which is the concept of energy flow through living systems, such as cells. The cell's metabolism includes all of the chemical reactions that take place inside cells, including those that consume or generate energy. The cell's metabolism occurs through stepwise chemical reactions, some of which are spontaneous and release energy, whereas others require energy to proceed.

Living organisms are open systems, and energy is exchanged between them and their surroundings. Energy is subject to physical laws, such as the laws of thermodynamics that govern the transfer of energy in and among all systems in the universe. The first law of thermodynamics states that the total amount of energy in the universe is constant and conserved. The second law of thermodynamics explains that all energy transfers and transformations are never completely efficient and that some amount of energy is lost in a form that is unusable, such as heat energy. High entropy means high disorder and low energy.

Living cells have evolved to meet the challenge of obtaining, transforming, and using energy to do work. Chemical energy stored within organic molecules, such as sugars and fats, is transferred and transformed through a series of cellular chemical reactions into energy within molecules of ATP, which is easily accessible to do work. Examples of the types of work that cells need to do include building complex molecules, transporting materials, powering the motion of cilia or flagella, and contracting muscle fibers to create movement.