The work of enzymes in living system is (a) oxygen transfer (b) to provide immunity (c) to catalyse biochemical reactions (d) to provide energy

Biochemical reactions are the chemical processes that take place within living organisms. These reactions are essential for sustaining life, as they include processes such as digesting food, producing energy, and replicating DNA. Enzymes play a critical role in these reactions by lowering the activation energy required, which in turn speeds up the reaction without being consumed themselves.

Take the process of digestion as an example. It involves multiple biochemical reactions to break down complex food molecules into simpler forms that the body can absorb and utilize. Protease enzymes break down proteins, amylases help in the digestion of carbohydrates, and lipases are responsible for breaking down fats. Without enzymes, these reactions would occur much too slowly to be compatible with life.

Biological catalysts, primarily enzymes, are substances that increase the rate of a reaction without undergoing any permanent chemical change themselves. Like a key fits into a lock, enzymes have active sites specifically shaped to bind to a substrate, which is the molecule upon which the enzyme acts.

This binding forms an enzyme-substrate complex that facilitates the conversion of substrates into products. Enzymes are highly specific; each one is tailored to accelerate only one type or a few types of reactions. This specificity ensures that metabolic pathways within cells are precisely regulated and that reactions occur at the right time and place.

Cells require energy to perform various functions, and they produce this energy through biochemical reactions involving enzymes. The primary way cells generate energy is through a process called cellular respiration, where glucose and other nutrients are broken down.

There are three main stages of cellular respiration: glycolysis, the Krebs cycle, and oxidative phosphorylation. In glycolysis, enzymes break down glucose into pyruvate, yielding a small amount of ATP, the energy currency of the cell. The Krebs cycle then processes the pyruvate to produce electron carriers, which are used in the final stage, oxidative phosphorylation. This stage, powered by the enzyme-driven electron transport chain, generates the majority of the cell's ATP. Through these enzyme-catalyzed steps, cells can efficiently convert the energy stored in nutrients into a usable form.