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6.9.2.3. Vacuoles

Vacuoles

The vacuoles and inclusions are places inside the cell in which substances accumulate. If they are surrounded by a membrane they are called vacuoles; otherwise, inclusions .

They are organelles surrounded by a simple membrane, with a rounded shape and containing substances that are not involved in any metabolic process. They are formed in young cells, by fusion of vesicles derived from the endoplasmic reticulum and the Golgi apparatus.

The animals eukaryotic cells  have vacuoles enough. The eukaryotic plant cells, when they are young, have many vacuoles, but when they are mature they can have a single cell that occupies 90% of the cell volume.

Inside the vacuole is the amorphous vacuolar juice, formed by water and which can contain various storage or waste substances.

The set of vacuoles in a cell is called a vacuome.

Types of vacuoles

Vegetable vacuole

Young plant cells have many small vacuoles because they contain little water, but as they grow, they increase in size and fuse to form a large central vacuole that occupies most of the cytoplasm.

Plant vacuoles are generally colorless (except those in flower petals). The membrane that forms the plant vacuole is called the tonoplast.

The main function of vacuoles in vegetables is to store substances.

Contractile vacuole (pulsatile vacuole)

In animal cells, the vacuoles are related aparat or Golgi, with functions substance storage, transportation, etc. We have already talked about them when we looked at lysosomesdigestive vacuoles and autophagic vacuoles.

Among animal vacuoles, the pulsatile vacuoles present in cells that live in hypotonic environments, as is the case of many protozoa, stand out and are used to regulate buoyancy by pumping excess water to the outside by active transport.

Functions of vacuoles

The main functions of vacuoles are:

  • Maintenance of cell turgor. The osmotic pressure within the vacuoles is very high due to the high concentration of substances. Water tends to penetrate the vacuoles by osmosis, which causes the cell to remain turgid, helping the plant to stand upright.
  • They allow the plant cell to increase in size, without involving excessive energy expenditure on their part.
  • Storage of various substances. Vacuoles can serve as stores for many cell molecules:
    • Water.
    • Reserve substances, such as carbohydrates, fatty acids and proteins.
    • Waste products.
    • Pigments, such as anthocyanins and flavones from flower petals.
    • Waste substances resulting from cellular metabolism and that can be toxic to the plant if they are free in the cytoplasm. For example, nicotine or cyanide.