Answer:
Organisms need to detect and respond to changes in their internal and external environment. This is because the conditions inside our body must be carefully controlled for it to function effectively and survive. The control systems that allow organisms to respond to changes are incredibly important.
All control systems include:
Cells called receptors, which detect stimuli (changes in the environment).
The coordination centre, such as the brain, spinal cord or pancreas, which receives and processes information from receptors around the body.
Effectors which bring about responses, and restore optimum levels, such as core body temperature and blood glucose levels. Effectors include muscles and glands, and so responses can include muscle contractions or hormone release