Metabolism

In the syllabus and the exam

Metabolism is used as an umbrella term that ties together most of the chemical-reaction content examined in the biomolecules and enzyme chapters, and candidates are expected to know it covers every reaction occurring inside living cells, controlled by enzymes, and split into two broad categories: catabolism, which breaks larger molecules down into smaller ones and usually releases energy (such as respiration breaking down glucose), and anabolism, which builds larger molecules from smaller ones and usually requires energy (such as protein synthesis from amino acids, or photosynthesis building glucose). Exam questions rarely test the word 'metabolism' in isolation but frequently expect candidates to classify a described reaction correctly as catabolic or anabolic, and to explain that because almost every metabolic reaction depends on a specific enzyme, factors that affect enzyme activity, such as temperature and pH, affect the whole rate of metabolism in an organism. A common error is treating metabolism as a synonym for respiration alone, when respiration is only one specific catabolic pathway within the much broader set of reactions that make up an organism's total metabolism. Candidates sometimes also confuse the direction of energy flow between anabolism and catabolism, particularly forgetting that building molecules (anabolism) generally consumes energy rather than releasing it. Because metabolism depends on enzyme activity throughout, candidates should be ready to explain why a fever, which raises body temperature only slightly above normal, can still speed up metabolic rate noticeably, whereas a much larger temperature rise eventually slows it down again as key enzymes begin to denature.

Example

Breaking down glucose to release energy and building large starch molecules from smaller glucose units are both part of a cell's metabolism, one releasing energy and the other requiring it.

Related terms

EnzymeCellular respiration

Source:SRC-DSKP-EN