Which of the following statements about metabolism are true? 1) Catabolism is the process in which complex substances are broken down, yielding a net output of energy. 2) Metabolism is an integrated system in which many of the same reactions participate in degradative (catabolic) and biosynthetic (anabolic) pathways. 3) Anabolism involves the synthesis of polymeric biomolecules and complex lipids from monomers such as fatty acids and nucleotides. 4) All organisms require an external source of energy, such as glucose or sunlight, for metabolic energy.

Metabolism can be defined as all the chemical reactions inside a cell that are required to carry out cellular functions (e.g., reproduction, growth, development). The metabolic reactions can be divided into anabolic and catabolic reactions. Anabolic reactions refer to metabolic reactions that require energy in order to construct new molecules from smaller ones (i..e., biosynthesis). Anabolism comprises endergonic metabolic pathways which are fueled by the use of energy (e.g., cellular ATP). On the other hand, catabolic reactions refer to metabolic reactions where larger molecules are separated to form smaller ones. Catabolic reactions are exergonic because they do not require energy (for example, reactions involved in cellular respiration).