National League for Nursing (NLN PAX) Practice Exam

A drop of dilute ammonium hydroxide (NH4OH) is placed on one side of a slide containing a large number of swimming paramecium. Under this condition, which of these behaviors of the paramecia will be observed?

1. They will swim towards the ammonium hydroxide

2. They will swim in circles

3. They will eventually all swim away from the ammonium hydroxide

4. They will stop swimming altogether

The correct answer is: They will eventually all swim away from the ammonium hydroxide

The behavior observed in paramecia when a drop of dilute ammonium hydroxide is placed on a slide is that they will eventually all swim away from the ammonium hydroxide. Paramecia are sensitive to changes in their environment, particularly to the presence of chemicals that may be harmful or toxic. Ammonium hydroxide, even in dilute form, can be perceived as a negative stimulus due to its basicity and potential lethality. When paramecia encounter a high concentration of a chemical that is harmful, they demonstrate a behavior known as negative chemotaxis. This means they will actively move away from the source of the irritant or harmful substance. The presence of ammonium hydroxide creates a gradient, and the paramecia will likely initiate a vigorous swimming response to escape the area, leading them to swim away from the chemical. In other contexts, paramecia may swim toward certain nutrients or favorable environments, which is known as positive chemotaxis. However, in this scenario, the presence of ammonium hydroxide triggers a defensive response rather than an attraction, emphasizing the organism's ability to sense and react to potentially harmful stimuli.