Vacuoles

Discovery and Functions of Vacuoles

Vacuoles are a kind of storage bubbles present in the plant cells. Such plants that have vacuoles may not appear healthy and need a lot of water. You can find them in animals as well as plant cells. Mostly found in plant cells, they are seen to have a larger size. 

Vacuoles can even store food products or a variety of different nutrients that a cell would require to live. These bubbles can even store waste material, so the remaining part of the cell gets safeguarded from contamination. With time, those waste products are discarded outside the cell. 

The size and shape of the vacuoles is simple. Vacuoles have a thin membrane that encloses them. This membrane stores fluid that can either be made up of waste product or nutrients. Plants can even use vacuoles in order to accumulate water.

These small sized water bags assist in supporting the plant. They are very closely linked to objects that are called vesicles. These objects are found in the entire cell region. 

In case of a plant cell, vacuoles are relatively bigger in size as compared to animal cells. In plants where the cell stops to grow further, you will find one very big vacuole in it. In some cases, vacuole can even occupy more than 50 percentage of the entire space of the cell. They hold food or water in them that can be required by the cell. In a way, they are similar to a backpack.
Vacuoles assist plants to maintain its structure. They have a very critical role to play in providing support to the cells of the plants. The volume of the cells of the plant is based on the amount of the materials present in the vacuoles. Vacuoles become light or bulky depending on the amount of water a plant has. 

A plant whose stems are drooping lacks water and has contracted vacuoles. Due to the cell walls such shrunken vacuoles still maintain the fundamental structure of the plant. When a plant locates a new water source, then the vacuoles again get filled up and due to this the plant again gains its original structure. 

There are several components of an animal cell. These are nucleolus, nucleus, ribosome, vesicle, coarse endoplasmic reticulum, Golgi apparatus, Cytoskeleton, smooth ER, mitochondria, vacuole, cytoplasm, lysosome and centrioles.

A vacuole is nothing but a membrane bound organelle. They look like a closed sac that is made up of membranes, composed of both organic and inorganic molecules. These molecules are called as enzymes. 

They have no specific size or shape. The content of the cell determines their shape. Vacuoles are not present in most of the eukaryotic cells. Their contents are different from the cytoplasm. They are categorized as ergastic by people. The solution that makes up a vacuole is known as cell sap.

The structure and working of a vacuole are dependent on the type of cell in which they are contained. Vacuoles are a very important part in fungus cells and plant as compared to animal cells.

How vacuoles got discovered?


Contractile vacuoles that were of star-shaped were first seen by scientist Spallanzani in protozoa in the year 1776. Dujardin named then as vacuoles in the year 1841. This term helped plant cells to easily differentiate its structure along with cell sap structure, from the remaining protoplasm. In the year 1885, scientist de Vries named “vacuoule membrane” as “tonoplast”.

Bacteria


Large sizes of vacuoles are generally found inside the three generations of filamentous sulfur bacteria namely, the Thioploca, the Beggiatoa and the Thiomargarita. The vacuoles in these cases occupy space from 40% to 98% of the entire space of the cell.
The vacuole has a high concentration of nitrate ions. They are thought as a storage organelle. Gas vacuoles are freely penetrable to gas. They are present inside a few species of Cyanobacteria. Such vacuoles enable the bacteria to get a firm control of its buoyancy.

Plants


Most of the plant cells that have got matured have only single large sized vacuole in them. It occupies more than thirty percentage of the entire volume of the cell. They can even occupy eighty percentage of the entire volume for specific types and conditions of cells. 

A vacuole in plant cells is basically enclosed by a covering membrane “tonoplast”. This membrane contains cell sap in it. Also named as the vacuolar membrane, a tonoplast is a kind of a cytoplasmic membrane that surrounds a vacuole. It separates the contents of the vacuole from the contents of the cytoplasm of the cell. 
 
Movement of protons between the vacuole and the cytosol stabilizes the pH of the cytoplasm. This makes the interior region of the vacuole acidic. This acidic pH creates a proton motive force that is used by the cell to displace nutrients inside and outside the vacuole. 

The low value of the vacuole pH enables degradative enzymes to work. Although vacuoles generally have a large size, they can be found in different sizes and numbers and vary with regards to the types of tissues and their development phases. 

Besides storage, the integral function of a central vacuole is the maintenance of turgor pressure at the walls of the cells. 


Proteins present in the tonoplast membrane monitor the water flow inside and outside the vacuole via an active transport. It pumps potassium ions inside and outside of the interior of vacuoles. 

Turgor pressure that has been exerted by a vacuole is important in assisting plants to be in a standing state. Central vacuole pushes the contents of the cytoplasm of the cell against tonoplast, so as to bring the chloroplasts nearer to light. Most of the plants accumulate chemicals inside the vacuole which then perform reaction with chemicals present in the cytosol. 

Fungi


Vacuoles present in the cells of fungi perform the same type of functions to the one performed in plants. There can be more than a single vacuole in every cell. In case of yeast cells, a vacuole has a dynamic shape that quickly modifies its morphology.
You can find it involved in several procedures that include the ion concentration, homeostasis of pH of cell, osmoregulation, storage of amino acids, polyphosphate as well as degradative procedure. 

Functions of a vacuole


The basic functions of a vacuole are to:

  • • Keep harmful molecules and substances separated from the remaining part of cells.

  • • Hold waste products.

  • • Hold liquid or fluid in plant cells.

  • • Keep the turgor or internal hydrostatic pressure constant in the cell.

  • • Maintain a constant interior acidic pH value in the cell.

  • • Hold small molecules.

  • • Eliminate all those things that a cell is not in the need of.

  • • Enable plants to efficiently hold themselves erect with hydrostatic pressure.

  • • Assist a plant in destroying and recycling disintegrated proteins that build up in the cells.

  • • Provide assistance in attacking bacteria and serve as a place for symbiotic bacteria.

  • • Keep the adequate pressure inside a plant cell, and assist in its growth.

  • Vacuoles are developed by the combination of several membrane vesicles. They play a significant role in autophagy. Vacuoles maintain a good balance between degradation and biogenesis of several cell structures and substances in certain types of organisms.

    They also assist in the recycling and lysis of proteins that have started to form inside the cell. Vacuoles are also involved in activities related to the destruction of invading bacteria. In case of protest, the vacuoles have got an additional functionality of accumulation of what has been absorbed by the organism. It assists in the digestionas well as waste management procedures for the cell.