<span>The answer is a certain required chemicals must be actively
transported. Blood brain barrier is a
selective membrane that separates blood circulating from the brain and the
fluid of extracellular in the central nervous system. This is also called a
filtering mechanism, the capillaries that carry blood to the brain and spinal
cord tissue blocking the path way of the certain substance.</span>
A. Migration (birds migraye to warmer climates during colder months)
The instrument that records and measures the seismic waves during an earthquake is a seismograph. It uses the vibration propagated by from the earthquake source's energy. It mainly uses a suspended pen that records the motion between itself and the paper film.
