The ability of living organism to detect and respond to changes in the environment is referred to as

1. Analyze the question The question asks for the term describing a living organism's ability to detect and respond to changes (stimuli) in its environment.

2. Explain the concept Living things share certain characteristics: nutrition, respiration, excretion, growth, reproduction, movement, and irritability (sensitivity). Irritability is the ability to detect a change in the environment (a stimulus) and respond to it. Examples include:

• Your hand withdrawing quickly from a hot object
• A plant shoot bending toward light
• The pupil of your eye narrowing in bright light

3. Go through the options

• A. Locomotion: This is movement of the whole organism from one place to another. It is a possible response, but it is not the ability to detect and respond.
• B. Irritability: This is the ability to detect and respond to stimuli. It matches the definition exactly.
• C. Growth: This is a permanent increase in size or mass. It has nothing to do with detecting changes.
• D. Taxis: This is the movement of a whole organism in response to a directional stimulus, such as a Euglena swimming toward light (phototaxis). It is only one type of response, not the general ability to detect and respond.

4. Answer The correct option is B. irritability.

5. Exam tip Link the word to its meaning: irritability = "irritated" by a stimulus, so you react. Taxis and locomotion are only the movement part of a response. When a question mentions detecting and responding, think irritability (also called sensitivity).