Question

what will happen if apical meristem is cut or damage

Answer 1

The plant has one apical dominant meristem on its trunk that helps the plant to grow vertically. If this dominant meristem is cut off or damaged, one or more lateral meristems will assume dominance, these meristems will start growing faster and the new growth will be lateral. Often several branches will exhibit this behavior after the removal of apical meristem, leading to a bushy growth. 

Answer 2

Apical meristem is responsible for lateral growth of the plant and the plant will stop growing in length if the apical meristem is damaged.