Vacuoles

Introduction 

A vacuole is a membrane-bound organelle found in plants and fungal cells, as well as some protist, mammal, and bacterial cells. Vacuoles are full of water that contains inorganic and organic compounds in solution, including enzymes, yet they may also contain solids that have been engulfed. Vacuoles are simply larger versions of membrane vesicles generated by the merging of several membrane vesicles.

Discovery of Vacuoles

In protozoa, scientist Spallanzani discovered star-shaped vacuoles for the first time in 1776. In the year 1841, Dujardin coined the term vacuoles. “Vacuole membrane” was renamed as “tonoplast” by scientist de Vries in the year 1885.

Types of Vacuoles

1.Gas vacuoles

Gas vesicles, commonly called gas vacuoles, are nano compartments that are permeable to gas and are found mainly in Cyanobacteria but also in several bacteria.

Bacteria use gas vesicles to adjust their buoyancy.The hydrophobic gas vesicle protein A (GvpA) forms the vesicle walls, which form a cylindrical hollow protein structure that fills with gas. Changes in the morphology of the gas vesicle are caused by small variations in the amino acid sequence; for example, GvpC is a bigger protein.

Gas vacuoles are found in :

• Blue-Green Algae
• Purple photosynthetic bacteria
• Green photosynthetic bacteria  
• Halophilic archaebacteria

2.Central Vacuoles

A big vacuole is found in plant cells. It is called central vacoule. It is filled with water and substances. In a plant cell, the central vacuole collects water and regulates turgor pressure. It also pulls the cell contents toward the cell surface, allowing plant cells to absorb extra light energy for photosynthesis, which helps them to make more food. Animal, protist, fungus and bacterial cells all have vacuoles, but only plant cells have huge central vacuoles.  The primary function of the central vacuole in plant cells is to retain salt, minerals, nutrients, proteins and pigments, as well as to aid plant growth and play a vital structural role.

3. Contractile Vacuole

Many free-living protists have contractile vacuoles, a specialised osmoregulatory organelle. The contractile vacuole is part of a bigger complex that also contains radial arms and a spongiome. The contractile vacuole contracts regularly to eliminate excess water and ions to regulate liquid flow into the cell. The contractile vacuole expands as it slowly takes in water, a process known as the diastole. When it reaches its limit, the central vacuole relaxes and contracts (systole) repeatedly to release water.

4. Food Vacuole

A “food vacuole” is a big sac inside a cell that provides food for cells. Vacuoles are utilised by some cells in mammals, plants, fungi, and microbes to store cellular fuel.

Others define “food vacuole” as a sort of digestive vacuole seen solely in protozoan microbes.

5. Sap Vacuole

Sap vacuoles are little sac-like structures found in cells that are filled with water and used for material storage (cell sap).

Within the cell, it creates an enclosed compartment that is filled with water, absorb inorganic and organic compounds (enzymes)

It stores food and a variety of nutrients that the cell requires to thrive, as well as waste materials that guard the cell against contamination.

Functions of Vacuoles

•     Isolating elements that could be damaging to the cell or pose a threat
•     Keeping waste products contained
•     Water storage in plant cells
•     Keeping the cell’s internal water pressure, or turgor, constant
•     Maintaining an internally acidic pH
•     It’s made up of tiny molecules
•     Unwanted chemicals are expelled from the cell
•     Because of the central vacuole pressure, plants can maintain structures like leaves and flowers
•     By growing in size, the germinating plants or their components (their leaves) can develop swiftly while consuming relatively little water
•     Protein bodies, which are modified vacuoles, retain stored proteins required for germination in seeds

Vacuoles in Plant and Animal cells

In cells, vacuoles are storage spheres. They can be present in both flora and fauna cells. However, vacuoles in plant cells are significantly larger. Vacuoles can preserve food or any other nutrients that a cell requires to live. Plant cells often have one or sometimes more than one vacuole, whereas animal cells, if any, have smaller vacuoles. Large vacuoles assist the plant in maintaining its shape and allowing it to retain water or food for later use. Because the storing function is less important in animal cells, the vacuoles are small.

Structure of Vacuoles

They don’t have a standard shape or size; instead, their structure fluctuates depending on the cell’s needs.

The vacuoles in immature and actively proliferating plant cells are quite tiny. These vacuoles are formed by the gradual fusing of vesicles produced from the Golgi body in immature dividing cells.

A vacuole is a sac filled with cell sap that is surrounded by a membrane termed the tonoplast or vacuolar membrane.

Conclusion

Vacuoles are membrane-bound sacs inside a cell’s cytoplasm that serve a variety of functions. Vacuoles are quite large in mature plant cells and play an important role in providing structural support as well as activities and a vast ocean of courses to choose from.

Without a vacuole, a cell will be unable to perform its normal duties and would ultimately die. In plants, the vacuole is responsible for water storage and structural maintenance.