A chemical reaction within an organism is considered an open system. This is because an open system can exchange both matter and energy with its surroundings. In the context of living organisms, they interact continuously with their environment by taking in nutrients and expelling waste products.
For example, during the process of metabolism, organisms break down food to produce energy, which involves a series of chemical reactions. These reactions often require substances (like oxygen) from the external environment and release byproducts (such as carbon dioxide) back into it.
Moreover, organisms need to adapt to their external conditions, which is another characteristic of open systems. They can react to changes by altering their biochemical processes. This adaptability further highlights the open nature of biological systems when it comes to chemical reactions.