Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions. Living things include both the visible world of animals, plants, and fungi as well as the invisible world of bacteria and viruses. On a basic level, we can say that life is ordered. Organisms have an enormously complex organization. We're all familiar with the intricate systems of the basic unit of life, the cell. Life can also "work." Living creatures can ...

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

Living things include both the visible world of animals, plants, and fungi as well as the invisible world of bacteria and viruses. On a basic level, we can say that life is ordered. Organisms have an enormously complex organization. We're all familiar with the intricate systems of the basic unit of life, the cell. Life can also "work." Living creatures can take in energy from the environment. This energy, in the form of food, is transformed to maintain metabolic processes and for survival. Life grows and develops. This means more than just replicating or getting larger in size. Living organisms also have the ability to rebuild and repair themselves when injured. Life can reproduce. Think about the last time you accidentally stubbed your toe. Almost instantly, you moved back in pain. Finally, life can adapt and respond to the demands placed on it by the environment. There are three basic types of adaptations that can occur in higher organisms.

Reversible changes occur as a response to changes in the environment. Let's say you live near sea level and you travel to a mountainous area. You may begin to experience difficulty breathing and an increase in heart rate as a result of the change in altitude. These symptoms go away when you go back down to sea level. Body-related changes occur as a result of prolonged changes in the environment. Using there previous example, if you were to stay in the mountainous area for a long time, you would notice that your heart rate would begin to slow down and you would begin to breath normally. These changes are also reversible. Genotypic changes (caused by genetic mutation) take place within the genetic makeup of the organism and are not reversible. An example would be the development of resistance to pesticides by insects and spiders.

What does the word “reversible” in the passage mean?