Growth, development and functioning of a living organism is due to

The correct answer is metabolism.

To understand why metabolism is the driving force behind the growth, development, and functioning of all living organisms, let us break down the concepts involved:

1. What is Metabolism?
Metabolism refers to the sum total of all chemical reactions occurring within a living cell or organism. These biochemical reactions are highly coordinated and are divided into two main categories:
• Anabolism (Constructive metabolism): The process of synthesizing complex molecules from simpler ones (e.g., photosynthesis, protein synthesis). This process requires an input of energy and directly leads to the growth of tissues and the development of the organism.
• Catabolism (Destructive metabolism): The process of breaking down complex organic molecules into simpler ones to release energy (e.g., cellular respiration). This energy is stored in the form of ATP (Adenosine Triphosphate) and is used to power various cellular functions.

2. Role in Growth and Development:
Growth involves an increase in cell size and number, which requires the synthesis of new cellular materials like proteins, lipids, and nucleic acids. Anabolic metabolic pathways construct these building blocks. Development involves differentiation and specialization of cells, which is also regulated by metabolic signals and pathways.

3. Role in Functioning:
For any living organism to perform essential functions (such as movement, response to stimuli, transport of molecules across membranes, and reproduction), a constant supply of energy is required. Catabolic pathways continuously break down nutrients to yield this energy.

Why other options are incorrect:
• An increase in Gibbs free energy: Processes that lead to an increase in Gibbs free energy are non-spontaneous and require energy input. Living systems work to keep their overall thermodynamic state stable and couple energy-releasing reactions with energy-consuming ones.
• A decrease in entropy: While living organisms maintain a highly ordered state (locally decreasing entropy), this is not the active biological mechanism itself but rather a consequence of metabolic processes that consume energy and release heat (which increases the overall entropy of the universe).
• Adaptation: Adaptation is an evolutionary process that allows species to survive and reproduce in their environment over generations, but it is not the direct physiological cause of daily growth and functioning in an individual organism.