Vacuoles:-

                              Vacuoles are the membrane-bound organelles found in all plant cells, bacterial, fungal, and animal cells too. It is a storage structure in a cell. These are the empty space organelles found in the cytoplasm and filled with watery fluid that contains various substances. These vacuoles are the important cell organelles in the cell as they help in the storage of nutrients required by a cell to survive and can also store the waste from the cell thereby preventing the cell from contamination. Plant cells store nutrients, metabolites, and waste in their vacuoles and also use them for transporting from one cell to another. The vacuoles in plants are larger than the animal cells.

Structure of vacuole:-

             It is a membrane-bound structure present in the cellular matrix of a cell. Generally, there is no basic shape or size for this vacuole. The vacuoles are usually small during immature or undividing stages and arise initially to become a large ones. Actually plant cells have larger vacuoles than animal cells as they require more water, organic and inorganic components for the proper functioning of cells.  A vacuole is surrounded by a membrane called "tonoplast" or "vacuolar membrane". 

                      This tonoplast separates the vacuolar contents from the cell's cytoplasm. This membrane mainly involves in the regulation of ions in the cell. It also helps in isolating the particles that are thought to be a threat to the cell. The components of the vacuole is known as 'cell sap' that differs entirely different from the cytoplasm. There may be several vacuoles in a cell and this tonoplast helps to separate from the cytoplasm. These vacuoles are relatively similar to lysosomes as they also contain a wide range of hydrolytic enzymes.

Types of Vacuoles:- 

                  There are various types of vacuoles present in the cells and some of them are:-

(i)Sap vacuoles:- These sap vacuoles are found mostly in plant cells and consist of a number of transport systems for the passage of different substances. A large central vacuole is present in higher plants. The fluid present in this vacuole is known as 'sap'. 

(ii)Contractile vacuoles:- These are found in freshwater algal cells and some protists such as paramoecium. These contractile vacuoles take part in osmoregulation and excretion.

(iii)Food vacuoles:- It is formed by the fusion of lysosome and phagosome and it consists of digestive enzymes by which food and the other nutrients are digested. These food vacuoles are found in protists, protozoa, and other higher animals, etc.

(iv)Gas vacuoles:- These are also called as 'air vacuoles' and store gases. Apart from storing gases, they also help in providing buoyancy, mechanical strength, and protection from harmful radiations. These vacuoles are found in prokaryotes.

Gas vacuoles

Functions of vacuoles:-

• Storage:- Vacuoles help in the storage of salts, minerals, organic acids, and other proteins within the cell. A large number of lipids are stored in the vacuoles. Some waste products are also stored here.
• Transportation in plant cells:- Proteins found in the tonoplast control the flow of water in and out of the vacuole through active transport and also pump potassium ions in and out of the vacuolar interior. It also helps in endocytosis and exocytosis of various substances and lysosomes are the vesicles that intake food and digest it.
• Turgor pressure:- Vacuoles are completely filled with water by which it exerts a force on the cell wall. This is known as turgor pressure. Also, the salts present in vacuole add to the osmotic activity of the vacuole thereby contributing to turgor pressure. This pressure helps in cell elongation, withstand extreme conditions, supporting plants in an upright position, and also provides a shape to the cell.
• The vacuole pushes up all the contents of the cell's cytoplasm against the cellular membrane thus keeping the chloroplasts closer to the light so that the light-absorbing efficiency is improved.
•  The pH of the plant vacuoles may be as 9 to 10 due to large quantities of alkaline substances or as low as 3 due to the accumulation of quantities of acids.
• In fungal cells, vacuoles are involved in many processes such as homeostasis of cell pH, osmoregulation, the concentration of ions and degradative processes, etc.