Question

why did the branches of trees grow in upward direction​

Answer 1

All living beings are made up of cells. For every function specific set of cells are responsible. In case of growth of plant cell division causes trees to grow upwards; meristem is the place where cell division occurs. Meristems are located at the branch tip which are also known as apical meristem as a result trees grow in height. Where as the trunk diameter expands due to vascular cambium. Now for these cells to divide one of the major requirement is sunlight hence to receive sunlight the branches grow upwards.

Answer 2

Meristems are located at the branch tip which are also called as apical meristem as a result trees grow in height. ... Now for these cells to divide one of the major requirement is sunlight hence to receive sunlight the branches grow upwards. Weight is balanced by tree trunk and the roots intact to the soil spreading deep.