Final answer:
Primary growth is the type of plant growth where the length of shoots and roots increases through cell division at the apical meristems.
Step-by-step explanation:
The type of growth in which the roots and shoots of plants increase in length due to the activity of their apical meristems is known as primary growth. The apical meristem is located at the tips of the stems and roots, and is comprised of undifferentiated cells that divide mitotically. These cells give rise to all the specialized tissues of the plant. Primary growth allows the plant to extend its shoots and roots to access additional resources such as light for the shoot and water and minerals for the roots.