Metabolic reactions take place

The correct answer is both a and b.

Metabolism refers to the sum total of all chemical reactions that occur within a living organism to maintain life. These biochemical processes are catalyzed by enzymes and can occur in two distinct environments:
1. In Vivo: This term translates to "within the living." It refers to metabolic reactions occurring naturally inside a living cell, tissue, or organism. An example is cellular respiration taking place inside human cells.
2. In Vitro: This term translates to "in glass." It refers to biological processes or chemical reactions occurring outside a living organism in a controlled laboratory environment, such as in a test tube or petri dish. Enzyme-catalyzed reactions can be replicated in laboratory setups without the presence of intact living cells.

Since metabolic reactions can occur both naturally inside living systems (in vivo) and experimentally in laboratory setups (in vitro), they take place in both environments.