Define Geotropism. Draw Labelled Diagram of Plant Showing the Geotropic Movements of Its Parts.

Introduction

Geotropism is a phenomenon that is commonly observed in plants, where the growth or movement of a part of a plant is influenced by gravity. The term "geotropism" is derived from the Greek word’s "geo" meaning earth and "tropism" meaning turning, and it describes the movement of a plant in response to the earth's gravitational pull.

Plants use geotropism to orient themselves in relation to the earth's surface. By responding to gravity, plants can ensure that their roots grow downwards into the soil, while their shoots grow upwards towards the sunlight. This allows them to access the nutrients and resources they need to survive and thrive.

The geotropic movements of plants are controlled by a variety of mechanisms, including the growth and development of cells, the distribution of hormones, and the perception of gravity by specialized structures within the plant. In this article, we will explore the science behind geotropism, including the various types of geotropism and the mechanisms that plants use to control their movements.

Types of Geotropism

There are two main types of geotropism: positive geotropism and negative geotropism.

Positive geotropism is the movement of a plant part towards the earth, or in the case of roots, downwards into the soil. This type of geotropism is commonly observed in the roots of plants, where it ensures that the roots grow towards the nutrients and water that are found in the soil.

Negative geotropism is the movement of a plant part away from the earth, or in the case of shoots, upwards towards the light. This type of geotropism is commonly observed in the shoots of plants, where it ensures that the leaves and stems grow towards the sunlight that they need for photosynthesis.

Mechanisms of Geotropism

The geotropic movements of plants are controlled by a variety of mechanisms that operate at the cellular and molecular levels. These mechanisms include the distribution of hormones, the growth and development of cells, and the perception of gravity by specialized structures within the plant.

One of the key hormones that is involved in geotropism is auxin. Auxin is a plant hormone that is produced in the shoot tips and is transported downwards through the plant. When auxin accumulates in the lower side of a plant part, it promotes cell elongation and growth, causing the part to bend towards the earth.

In the roots of plants, auxin accumulates on the lower side of the root, causing the cells on that side to elongate more than the cells on the upper side. This results in the root bending downwards into the soil.

In the shoots of plants, auxin accumulates on the upper side of the stem when the plant is oriented horizontally. This causes the cells on the upper side to elongate more than the cells on the lower side, resulting in the shoot bending upwards towards the light.

Another mechanism that is involved in geotropism is the redistribution of calcium ions within the plant. Calcium ions are essential for the growth and development of cells, and they play a key role in the perception of gravity by specialized structures within the plant.

When a plant is oriented horizontally, gravity causes the redistribution of calcium ions within the plant, with more calcium ions accumulating on the lower side of the plant part. This triggers a signalling cascade that ultimately leads to the accumulation of auxin on the lower side of the plant part, promoting cell elongation and growth and causing the part to bend towards the earth.

Perception of Gravity

The perception of gravity by plants is a complex process that involves specialized structures within the plant known as statocysts. Statocysts are specialized cells that contain dense, starch-filled organelles known as statoliths.

When a plant is oriented horizontally, the statoliths settle on the lower side of the cell, creating a gravitational signal that is sensed by the plant. This signal triggers a variety of responses within the plant, including changes in the distribution of hormones and the growth and development of cells.

The perception of gravity by plants is a critical component of geotropism, as it allows the plant to orient itself in relation to the earth's surface. By responding to gravity, plants can ensure that their roots grow downwards into the soil, while their shoots grow upwards towards the sunlight. This allows them to access the nutrients and resources they need to survive and thrive.

Geotropic Movements of Plants

The geotropic movements of plants can be observed in a variety of plant parts, including roots, stems, and leaves. These movements are controlled by a variety of mechanisms, including the distribution of hormones, the growth and development of cells, and the perception of gravity by specialized structures within the plant.

Roots

In the roots of plants, positive geotropism ensures that the roots grow downwards into the soil. When a seed germinates, the root begins to grow downwards towards the earth's surface, where it can access the nutrients and water that are found in the soil.

As the root grows, it bends towards the earth's surface, with the cells on the lower side of the root elongating more than the cells on the upper side. This results in the root bending downwards into the soil, where it can continue to grow and develop.

Stems

In the stems of plants, negative geotropism ensures that the shoots grow upwards towards the light. When a seed germinates, the shoot begins to grow upwards towards the surface of the soil, where it can access the sunlight that it needs for photosynthesis.

As the shoot grows, it bends upwards towards the sunlight, with the cells on the upper side of the stem elongating more than the cells on the lower side. This results in the shoot bending upwards towards the light, where it can continue to grow and develop.

Conclusion

Geotropism is a critical phenomenon that allows plants to orient themselves in relation to the earth's surface. By responding to gravity, plants can ensure that their roots grow downwards into the soil, while their shoots grow upwards towards the sunlight. This enables them to access the nutrients and resources they need to survive and thrive.