Vacuoles of plant cells are known to attain a large size. These vacuoles can cover up to 95% of the cell space. Generally, these vacuoles acquire 80% of the cell space.
Vacuole is an important organelle present in the cells of plants, animals, protists, fungi and bacteria. Apart from water, vacuoles also contains different kinds of organic/inorganic molecules, solid materials and enzymes. Vacuoles are kind of large-sized vesicles. Multiple membrane vesicles come together to form vacuoles; which is why they are larger than other cell organelles. Vacuoles play an important role in the smooth functioning of various processes of plant and protist cells. The role played by vacuoles in animal and bacterial cells is not as significant as that in plant and protist cells.
Functions of Vacuole
Vacuole is considered as the 'storage bin' of cells. Along with nucleus, vacuole is one of the important organelles of cells. The different functions performed by vacuole are listed below.
- The waste products generated in cells are accumulated in vacuoles. Thus, vacuoles protect other organelles of the cell from harmful effects of wastes.
- Maintaining the right pH level is one of the important functions of vacuoles. The vacuoles help in maintaining an acidic internal pH in cells. Apart from maintaining the cell pH, vacuoles also maintain the turgor and hydrostatic pressure.
- The toxins produced in cells have the potential to harm/disturb the health of cells. Vacuoles do the crucial job of isolating them from the rest of the cell components.
- Vacuoles play an important role in the process of autophagy - a process in which degradation of cell components takes place. Autophagy is a catabolic process in which components that are no longer needed by the cell undergo degradation. During the process of autophagy, vacuoles maintain a balance between biogenesis and degradation of substances in cells.
- Vacuoles are known to protect cells from certain bacteria. Destroying the bacteria that attack cells is an important function performed by vacuoles.
- The food vacuoles found in amoeba perform the important job of digestion.
The role played by vacuoles in animal cells is not as important as in plant cells. The functions that vacuoles perform in different types of cells are listed below.
Contractile Vacuole Function
Generally, contractile vacuoles are found in freshwater organisms. Metazoans like hydra and sponges possess the contractile vacuoles. These vacuoles expand and contract on a regular basis. The water which enters the cells of freshwater organisms through food and osmosis is removed by contractile vacuoles.
Function of Vacuoles in Plant Cells
Vacuoles of plant cells are larger than those found in animal cells. The central vacuole present in plant cells is one of the important cell organelles. The central vacuole, surrounded by tonoplast, offers support to cells which constitute leaves and other soft parts of plants. The solutes present in vacuoles are known to absorb water. As water enters the vacuoles, cells become inflated; it allows the soft parts of plants (for example, leaves) to retain their shape and turgidity. Thus, maintaining the cell in a proper shape is the main function of vacuoles.
The role that vacuoles play in fungal cells is much similar to that in plant cells. The number of vacuoles present in fungal cells can be greater than one. These vacuoles play an important role in processes like homeostasis of cell pH, storage of amino acids, osmoregulation, etc.
In animals cells, vacuoles play a subordinate role in the processes of endocytosis and exocytosis. In exocytosis, proteins and lipids are expelled from cells. Vacuoles don't play a direct role in the extrusion of lipids and proteins; however, they act as containers of lipids and proteins. The process of endocytosis is just the reverse of exocytosis.
Maintaining the turgor pressure and pH in cells are the important vacuole functions. Taking into account these and other functions mentioned above, we can say that vacuole plays an important role in the functioning of plant cells.