The process in which complex substances are broken down into simpler ones is referred to as

Step 1: Analyze the question The question asks for the term describing the breakdown of complex substances into simpler ones.

Step 2: Explain the concepts

• Anabolism: building up of complex substances from simpler ones (e.g. photosynthesis, protein synthesis). It requires energy.
• Catabolism: breaking down of complex substances into simpler ones (e.g. respiration, digestion). It usually releases energy.
• Metabolism: the sum of all chemical reactions in an organism, both anabolism and catabolism.
• Tropism: growth movement of a plant in response to a stimulus (e.g. phototropism, geotropism).

Step 3: Apply to the question

• A is the opposite of what is asked (building up).
• C is too general because it includes both building up and breaking down.
• D has nothing to do with chemical breakdown.
• B matches exactly: breakdown of complex substances into simpler ones.

Answer: B. Catabolism

Exam tip: Think "Catabolism = Cut down" and "Anabolism = Assemble". Also remember that metabolism = anabolism + catabolism.