Apoplast

Apoplast

Every cell in the body is composed of living active structures which perform all the cellular activity and non-living structures which serve the purpose of protection, maintaining the shape and size of the cell, transport and many more. These non-living parts are collectively grouped under Apoplast. It primarily has the outer covering of the cell including the cell wall and spaces between the cells. In this article, we will briefly discuss the history of Apoplast, its constituents, and functions.

Definition and history

All the structures and gaps located in a cell outside the cell membrane are termed as Apoplast. The term was coined by Munch in the year 1930 to distinguish the living materials in the cell from dead matter. It mainly includes the outermost protective covering called the cell wall and the cellular gaps located outside the membrane. These intracellular gaps may be empty-spaced but they serve a major role in the transport of molecules across cells. All the living materials on the other hand including the cell membrane are referred to as Symplast. Although the apoplastic region is not alive, a cell cannot survive in the absence of the apoplastic structures.

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Functions and Uses

Protection

Cell wall is composed of tightly associated cells that are impenetrable and prevent the entry of harmful microbes and molecules inside the cell. The cell wall is also rigid which allows the cells to maintain their shape and size which is vital for their function. It acts as a shock absorber and protects the vital organs inside the cell from sudden impact thereby preventing the bursting of the cell.

Transport

The intracellular spaces or cell gaps are the regions of free transport where the exchange of ions, gasses, and other useful molecules can occur through diffusion. In plants especially, the apoplastic regions in the root cells absorb and transport water through the xylem to the leaves for the process of photosynthesis. Without this transport, processes like respiration and transpiration will also not occur.

Selective barrier

The rigidity of the cell wall and a definite shape allows certain small ions needed by the cell to pass through but prevents the entry of unwanted materials inside the cell thereby acting as a selective barrier along with the cell membrane.

Apoplastic colonization

Since most of the minerals and food particles pass through the apoplastic pathways, this region is highly prone to infections by microbes, particularly bacteria. These microbes receive moisture, nutrition, and protection once they cross the cellular barriers and enter the intracellular spaces. This colonization can be very harmful to the cells leading to tumor formation, inflammation, and even cell death.

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Frequently Asked Questions on Apoplast

The cell membrane is composed of proteins and lipids that are arranged continuously and it is generally considered an intermediate between living and dead cells. It does not perform metabolic activities but is involved in selective transport which is the characteristic of a living cell.

While the structures outside the cell membrane are apoplastic, the structures or cells inside the cell membrane are symplastic. Apoplastic cells do not perform metabolism and are dead cells while symplastic cells are involved in activities like respiration, food production, oxygen consumption, and many more.

Apoplast cells present in root hair cells are primarily involved in the transport of water and minerals although some nutrients may also be transported through them. Nutrients and food particles are primarily transported through the symplastic pathways.

Although primarily found in plants' roots for water transport, certain animal cells also have cell walls for rigidity and protection and intercellular spaces for transport which are a part of the Apoplast. Microorganisms like bacteria also have cell walls.