A vacuole is a sac in the cytoplasm surrounded by a single membrane and filled with fluid. Vacuoles are found in many eukaryotic cells, but they differ greatly in size and function.Vacuoles in animal cells
Animal cells have no large central vacuole. Instead they may contain several small, often temporary, vacuoles and vesicles, for example:
• Food vacuoles (phagocytic vacuoles): formed when a cell engulfs material by phagocytosis. A white blood cell surrounds a bacterium with its membrane, trapping it in a vacuole. Lysosomes then fuse with the vacuole and digest its contents.
• Storage vacuoles, for example containing fat droplets.Vacuoles in protoctists
Single-celled protoctists that live in fresh water, such as Amoeba and Paramecium, have contractile vacuoles. Water constantly enters these cells by osmosis. The contractile vacuole collects the excess water and then contracts, expelling it from the cell. This process needs energy from ATP and stops the cell swelling and bursting.Vacuoles in plant and fungal cells
Mature plant cells, and many fungal cells, have a single large permanent vacuole surrounded by a membrane called the tonoplast. It is a much more important and long-lasting structure, so it is covered in its own lesson.A key difference to remember is that small vacuoles in animal cells are temporary and form and disappear as needed, while the large vacuole of a plant cell is permanent.
Animal cells have no large central vacuole. Instead they may contain several small, often temporary, vacuoles and vesicles, for example:
• Food vacuoles (phagocytic vacuoles): formed when a cell engulfs material by phagocytosis. A white blood cell surrounds a bacterium with its membrane, trapping it in a vacuole. Lysosomes then fuse with the vacuole and digest its contents.
• Storage vacuoles, for example containing fat droplets.Vacuoles in protoctists
Single-celled protoctists that live in fresh water, such as Amoeba and Paramecium, have contractile vacuoles. Water constantly enters these cells by osmosis. The contractile vacuole collects the excess water and then contracts, expelling it from the cell. This process needs energy from ATP and stops the cell swelling and bursting.Vacuoles in plant and fungal cells
Mature plant cells, and many fungal cells, have a single large permanent vacuole surrounded by a membrane called the tonoplast. It is a much more important and long-lasting structure, so it is covered in its own lesson.A key difference to remember is that small vacuoles in animal cells are temporary and form and disappear as needed, while the large vacuole of a plant cell is permanent.