Answer: Response to the environment.
Step-by-step explanation:
Living organisms respond to their environment, and this response to stimuli is an important characteristic of life, because it helps the organism to stay in balance. Anything that causes a living organism to react is called a stimulus, which can be external or internal.
The effectors produce an appropriate response to the stimulus in order to maintain homeostasis within the organism.
Ultraviolet light can damage the DNA in cells, causing mutations. So, once the skin is exposed to sunlight, the organism tries to cover all the cells with melanin, which block UV rays.