The growth of trees upwards against the force of gravity is primarily attributed to a combination of biological mechanisms and physical processes. It is not based on levitation, as levitation refers to the process of objects floating or being suspended in the absence of external support.
The key factors enabling trees to grow upwards against gravity are:
Geotropism/Gravitropism: Trees possess a biological mechanism known as geotropism or gravitropism, which allows them to sense the direction of gravity and respond accordingly. The growth of the tree's roots is positively geotropic, meaning they grow downwards towards the center of the Earth, while the growth of the stem and branches is negatively geotropic, causing them to grow upwards against gravity.
Apical Dominance: Trees exhibit apical dominance, where the growth of the main shoot (apical bud) suppresses the growth of lateral branches below it. This phenomenon directs the tree's energy towards vertical growth, encouraging it to grow taller.
Cell Expansion and Division: Within the tree's stem and branches, specialized cells called meristems are responsible for cell division and elongation. Through controlled expansion and division of cells, new tissues are produced, allowing the tree to increase in height.
Transpiration and Water Movement: Transpiration, the process by which trees lose water through their leaves, creates a pressure gradient that helps water and nutrients move upwards from the roots to the upper parts of the tree. This mechanism, along with the cohesive properties of water, enables the transport of vital resources required for growth against gravity.
These combined mechanisms enable trees to grow vertically, defying the downward force of gravity. While levitation is not involved, the complex interplay of biological and physical processes allows trees to achieve their upward growth.