Why Do Stems Grow Upward?

Stems are an important part of the plant that can range from millimeters to hundreds of meters, depending upon the type of the plant. They have many functions like giving support to the plant, conducting water, and providing nutrients to different parts of the plant. Moreover, sugars made by the process of photosynthesis are also transported to the rest of the plants withthe help of the stems.

The stem is made up of three types of cells, which are:

  • Parenchyma cells: They help in the metabolic functions of the plant, such as photosynthesis.
  • Collenchyma cells: They provide structural support to the stem.
  • Sclerenchyma cells: They provide stiffness and strength to the stem.

The roots are grown downward as they collect all the nutrients and water for the plant’s growth and provide stability for the firmness of the plant on the ground. On the other hand,the stems grow in the direction of sunlight as they trap it for the process of photosynthesis. Photosynthesis is a chemical process where the plant uses the sunlight to convert carbon dioxide into simple sugars; in short, plants use the whole process to make their food.


The main hormone which is being produced in the plant for its growth is known as Auxins. They are produced and transported to the stem as soon as possible as they need to straighten out to absorb the sunlight. That is why more auxins are delivered to the underside than to the topside of the stem. This results in stem elongation and faster growth. PILS proteins are the main component for storing this hormone in different parts of the plant, which is an important job for growth and metabolism. Therefore, higher auxin levels at the right time and place produce a healthy and better yield plant.

sapling-plant-growing-seedlingThe strangest thing in nature is that the stem grows upward, which is against the force of gravity, and the roots grow downward. The main reason behind this is Geotropism or Gravitropism and Phototropism. Geo means earth, and tropism means the growth of the plant, which is triggered by any stimulant. So as we know, the roots grow downwards facing gravity, which is known as positive geotropism. The stem growing upwards vertically is called negative geotropism. Phototropism is caused by the response to the sunlight in the growth of the plant.

Both processes are caused by the unequal distribution of auxin in various parts of the plant that stimulate differential growth. So, when a stem is planted horizontally, there are more auxins on the bottom side that stimulate the stem to grow upwards against the force of gravity. And if a root is planted horizontally, the auxins are more on the bottom side, causing them to grow downwards, facing the force of gravity. With the help of phototropism, the auxins in the stem promote growth, and auxins in the roots inhibit it.