What is Crenation?
Crenation is a term used in botany and zoology to describe an object’s shape, especially a leaf or shell, as being round-toothed or having a scalloped edge. In biology, crenation describes the formation of abnormal notched surfaces on cells as a result of water loss through osmosis.
When a cell is exposed to a hypertonic solution, water diffuses out of the cell by osmosis, causing the cytoplasm to decrease in volume. As a result, the cell shrinks and the cell membrane develops abnormal notchings, a process called crenation.
Crenation can also be used to describe a feature of red blood cells. In this case, the erythrocytes look as if they have projections extending from a smaller central area, like a spiked ball.
The crenations may be either large, irregular spicules of acanthocytes or smaller, more numerous, regularly irregular projections of echinocytes. Acanthocytes and echinocytes may arise from abnormalities of the cell membrane or from metabolic disorders.
Pickling cucumbers and salt-curing of meat are two practical applications of crenation. In pickling cucumbers, the cucumbers are soaked in a hypertonic solution of salt and vinegar, causing the cells to lose water and undergo crenation, resulting in a crunchy texture. In the salt-curing of meat, the meat is coated in salt, causing the cells to lose water and undergo crenation, which helps to preserve the meat.
In plant cells, the term plasmolysis is used to describe the shrinking of the cytoplasm from the cell wall in a hypertonic environment. In plasmolysis, the cell wall stays intact, but the cytoplasm shrinks, causing the cell to become flaccid
Definition of Crenation
In botany and zoology, crenation refers to the leaf-like scalloped edges of an object such as a leaf or a shell. In biology, crenation describes the formation of abnormal notched surfaces on cells as a result of water loss through osmosis.
Cells are usually in an isotonic solution inside the body, meaning that there is the same concentration of solute and water both inside and outside the cells. This equilibrium allows the cells to keep their shape, with water moving in and out at a constant rate and maintaining the same osmotic pressure across the semipermeable membrane.
However, when this equilibrium is disrupted by the presence of a higher concentration of solute in the solution, it creates a hypertonic environment, which causes the intracellular water to diffuse out. The cells start to shrivel and form abnormal spikes and notches on the cell membrane. This process is called crenation.
Example of Crenation
Red Blood Cell Crenation
Red blood cells are prone to undergoing crenation as either a response to ionic changes in the blood or abnormalities in the cell membrane, disrupting the cell’s ability to maintain an isotonic state.
There are two different types of crenated red blood cells: echinocytes and acanthocytes. Instead of the usual rounded biconcave shape, both these cells appear with a rounder form and spiny projections on the cell surface.
In echinocytes, the spines are short, uniform, and regularly spaced. Even though they possess adequate amounts of hemoglobin for survival, their occurrence suggests an underlying disease is present.
This type of crenation is usually reversible and can be caused by either ionic imbalances, such as the presence of high pH or high calcium concentrations, or by diseases such as uremia or pyruvate kinase deficiency, which results in cellular loss of potassium and water. It could also be a side effect of the consumption of certain drugs or chemotherapy agents.
The photograph below shows the presence of echinocytes amongst healthy red blood cells:
Acanthocytes possess spines on the cell membrane that manifest in uneven and abnormal distributions, numbers, and lengths.
The irregular morphology is caused by alterations in the membrane lipids as a result of diseases such as abetalipoproteinemia, which causes abnormal lipid concentrations within the blood as well as the inability to make certain lipoproteins vital for cell membranes.
Other diseases such as vitamin E deficiency, liver disease, or malabsorption may also have the same effect. This type of crenation is irreversible.
The morphology of acanthocytes is shown below:
Food Pickling
Food pickling is another example of crenation occurring in everyday life. Vegetables such as cucumbers are placed in acidic solutions to pickle, causing water to diffuse out and the characteristic shrinkage of the crenation process.
Crenation Versus Plasmolysis
While crenation occurs in animal cells, cells that have a cell wall cannot shrink and change shape when placed in a hypertonic solution. Plant and bacterial cells instead undergo plasmolysis. In plasmolysis, water leaves the cytoplasm, but the cell wall does not collapse.
Instead, the protoplasm shrinks, leaving gaps between the cell wall and the cell membrane. The cell loses turgor pressure and becomes flaccid. Continued loss of pressure can cause the collapse of the cell wall or cytorrhysis. Cells undergoing plasmolysis do not develop a spiky or scalloped shape.
Practical Applications of Crenation
Crenation is a useful technique for preserving food. Salt curing of meat causes crenation. Pickling of cucumbers is another practical use of crenation.
