Overview:
Metabolism refers to all the chemical reactions that occur within an organism. It is a fundamental process responsible for maintaining life and involves various reactions that convert molecules into different forms. In this response, we will discuss the true statements about metabolism and explain each statement in detail.

A. All chemical conversions that occur in living organisms are chemical reactions:
- This statement is true. Chemical conversions in living organisms involve the rearrangement of atoms and bonds to form new molecules. These conversions are known as chemical reactions, which can be classified into different types such as synthesis, decomposition, and exchange reactions. Examples of chemical reactions in living organisms include the breakdown of glucose during cellular respiration or the synthesis of proteins during protein synthesis.

B. The sum total of all the chemical reactions occurring in our body is metabolism:
- This statement is true. Metabolism encompasses all the chemical reactions that occur within an organism. It includes processes involved in the breakdown of complex molecules (catabolism) to release energy and simpler compounds, as well as the synthesis of complex molecules (anabolism) using energy. Metabolism is responsible for vital functions such as energy production, growth, repair, and maintenance of the body.

C. Metabolic reactions can be demonstrated outside the body in cell-free systems:
- This statement is true. Metabolic reactions can be studied and demonstrated outside the body using cell-free systems. These systems typically involve the use of purified enzymes, cofactors, and substrates to recreate specific metabolic pathways in a controlled environment. By studying these cell-free systems, scientists can gain insight into the mechanisms and regulation of metabolic reactions. These experiments help to understand metabolic pathways, identify key enzymes, and develop new drugs or therapies.

Summary:
All the statements A, B, and C are true regarding metabolism. Chemical conversions in living organisms are indeed chemical reactions. Metabolism refers to the sum total of all the chemical reactions occurring in our body, including catabolic and anabolic processes. Additionally, metabolic reactions can be demonstrated outside the body in cell-free systems, which allow for controlled studies and deeper understanding of metabolic pathways.

D is correct .