When muscles contract in any organism, it means muscle fibers are generating tension with the help of motor neurons. ATP is the source of energy that allows this to take place. Voluntary muscle contraction is controlled by the central nervous system. The brain sends signals, through the nervous system to the motor neuron that innervates several muscle fibers. In the case of some reflexes, the signal to contract can originate in the spinal cord through a feedback loop with the grey matter. Involuntary muscles such as the heart or smooth muscles in the gut and vascular system contract as a result of non-conscious brain activity or stimuli proceeding in the body to the muscle itself. The organism will respire more as much more energy will be needed, in the form of ATP.
ATP is also used in Active transport. This is the movement of a substance against its concentration energy (from low to high concentration). In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. Active transport is a good example of a process for which cells require energy: adenosine triphosphate (ATP). Examples of active transport include the uptake of glucose in the intestines in humans and the uptake of mineral ions into root hair cells of