Round dark sac like structures found in the cytoplasm are called vacuole.
These round structures are membrane bound spaces which are filled with sap or syrupy type of content comprised of water sugars, amino acids, proteins, minerals and metabolic waste etc.
The membrane is known as tonoplast.
Structure:
Vacuole is a dead organelle surrounded by single unit membrane.
They have empty spaces meant for storage of various material in plant and animal cells.
Vacuoles in animal cells are much small, temporary and large in number.
In animals, they serve as storage sac for various materials like water, protein and glycogen.
Vacuole in animal cell
Large and permanent vacuoles are common in plant cells.
Their function is to store various components of the cell like water, sugars, amino acids, proteins, minerals and metabolic waste etc.
Vacuole in plant cell
In unicellular organisms, it serves for various functions like digestion through food vacuole.
Example: amoeba engulfs the food with the help of pseudopodia and digests it inside the vacuole containing digestive enzymes.
Functions of vacuole:
Storage of material:
These are storage sac meant for storing various products like oils carbohydrates or those synthesised by cells.
Osmoregulation:
Membrane is associated with osmoregulatory functions, i.e., maintenance of water level in the cells.
Turgidity and rigidity:
It also provides rigidity and turgidity to the cell as they are filled with cell sap.
Food vacuole:
In unicellular organisms, food vacuole contains complex substances, digest it and help the organism in consuming it.
Exocytosis:
It also helps in expelling out waste material as well as excess of water in unicellular organisms.
