In the world of biology, cohesion is a fundamental concept that underpins numerous natural phenomena. This cohesive force is responsible for the sticking together of alike entities, and it plays a crucial role in various biological processes. From the cohesion of water molecules to the bonding of biomolecules, understanding this phenomenon is essential for comprehending the intricate workings of living organisms. In this article, we will delve into the definition of cohesion, explore its significance in biology, and examine its examples in different biological contexts.

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Understanding Cohesion in Biology

Cohesion, in the realm of biology, refers to the state of cohering or sticking together of alike entities. This sticking together is due to intermolecular forces that hold molecules or body parts in close proximity. These forces are particularly evident in water molecules, making water an exceptional example of cohesion.

The Cohesion of Water Molecules

Water, composed of dihydrogen monoxide (HOH) molecules, demonstrates the phenomenon of cohesion prominently. This polarity of water molecules creates a partially negative pole on the oxygen and a partially positive pole on the hydrogens, resulting in the molecules attracting one another.

The cohesive force in water is a weak or transient type of chemical bond known as an intermolecular hydrogen bond. This bond forms between the hydrogen of one HOH and the hydrogen of another HOH, leading to the formation of water drops as they cohere. Additionally, water also exhibits adhesion, which is the attraction between water molecules and dissimilar substances.

Importance of Cohesion in Biology

Cohesion holds paramount importance in various biological contexts. One significant example is its role in plant physiology. The cohesion and high surface tension of water significantly slow down water loss from plants through leaf stomata. Surface tension, which arises due to cohesion, enables certain insects like water striders to stay still above water or walk on its surface.

Furthermore, cohesion is not limited to physicochemical phenomena but also plays a crucial biological role in cell division. Sister chromatids cohere during cell division, ensuring proper segregation during anaphase. Protein complexes known as cohesins mediate this cohesion, helping keep sister chromatids connected until they reach the dividing cell’s equatorial region.

Examples of Cohesion in Biological Systems

  1. Cohesion of Water in Vascular Plants Cohesion and surface tension are essential factors enabling capillarity in vascular plants. This capillary action allows water to move upward through narrow tubes against gravity. Surface tension pulls water molecules inward from the surface, reducing surface area, and cohesion holds the water molecules together. Adhesion also helps water molecules bind to the walls of xylem tissues in plants, facilitating water ascent from roots to leaves.
  2. Cohesion in Plant Fusion In botany, cohesion refers to the fusion of plant parts. For instance, syncarpy involves the fusion of carpels in a pistil. The cohesion of plant structures contributes to their overall development and function.
  3. Cohesion in DNA Cohesion is not limited to macroscopic phenomena; it also operates at the molecular level. In cell division processes like mitosis and meiosis, sister chromatids cohere until they separate during anaphase. Cohesins, consisting of various protein complexes, are responsible for this cohesion of sister chromatids.


Cohesion is a fundamental concept in biology that explains the sticking together of alike entities. From the cohesion of water molecules, which has significant implications for plant physiology, to the cohesion of biomolecules during cell division, understanding this force enriches our knowledge of the intricate mechanisms in living organisms. Cohesion plays a crucial role in diverse biological processes, and its understanding is essential for comprehending the complexities of nature.


What is the difference between cohesion and adhesion?

Cohesion and adhesion are two distinct phenomena related to the attraction between molecules. Cohesion refers to the attraction between alike molecules, causing them to stick together. In contrast, adhesion involves the attraction between molecules of different substances, leading to the sticking of dissimilar materials. An example of cohesion is water molecules sticking together to form water droplets, while adhesion is demonstrated when water sticks to the surface of leaves or flowers.

Can cohesion be observed in plant parts?

Yes, cohesion can be observed in plant parts. In botany, cohesion refers to the process of alike molecules or body parts binding or staying close together. An example is the fusion of plant parts, as seen in syncarpy, where carpels in a pistil are united. Additionally, cohesion is crucial in the movement of water in plants through capillary action, which allows water to ascend through narrow tubes in the xylem.

How does surface tension relate to cohesion in water?

Surface tension and cohesion are interconnected phenomena in water. Cohesion is the attractive force between water molecules, causing them to stick together. Surface tension is a result of this cohesive force at the surface of water. The molecules at the surface experience a net inward pull due to the lack of molecules above them, resulting in a stronger cohesive force. This cohesive force creates a “skin” on the water’s surface, allowing certain insects like water striders to float on the surface and giving water droplets their spherical shape.

Why is cohesion important to plants and vascular systems?

Cohesion is vital to plants and their vascular systems, especially in the process of water transportation. Cohesion, along with surface tension and adhesion, enables capillary action, allowing water to move upward through narrow tubes against gravity. This mechanism plays a critical role in the transportation of water from the roots to various parts of the plant, including leaves and flowers. Cohesion’s ability to keep water molecules together helps in reducing water loss through transpiration and supports the overall health and function of plants.

How does cohesion play a role in cell division and DNA?

Cohesion is crucial in cell division, such as mitosis and meiosis, as it ensures the proper segregation of genetic material. Sister chromatids cohere until they reach the anaphase of cell division, where they separate and move to opposite poles of the cell. This cohesion of sister chromatids is facilitated by protein complexes called cohesins. Without cohesion, proper segregation of genetic material during cell division would not be guaranteed, leading to potential errors in the genetic makeup of daughter cells. Cohesion in DNA plays a significant role in maintaining genetic stability and ensuring the accurate transmission of genetic information from one generation to the next.


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