What is an example of something that exist in natural systems?

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Explanation:

Examples of natural systems include: real number system, solar system, and planetary atmosphere circulation systems.

Natural physical systems include the solar system and an animal's digestive system. Human-made physical systems include mechanical systems, optical systems, electrical systems, and combinations of these. The names of these systems come from the type of energy they use.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products