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Vacuoles are single membranous cell organelles containing water and organic and inorganic compounds, including dissolved enzymes.
- The endoplasmic reticulum and Golgi apparatus release vesicles, which combine to form this cell organelle.
- They safeguard the cell from contaminants and collect waste products from the cell.
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Key Terms: Vacuoles, Plant Cell, Animal Cell, Cell, Cell Organelle
Key Highlights
- Newly formed plant cells usually have many tiny vacuoles that are not fixed in shape or size.
- They are responsible for storing water and maintaining the turgidity of the plant cell.
- In animal cells, waste products, ions, and water are stored in these organelles.
- In organisms such as algae, plants, and fungi, they serve an important role in protecting the cell from self-toxicity.
- The contractile vacuoles found in freshwater animals help in the removal of surplus water from their bodies, hence preventing damage.
What are Vacuoles?
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A vacuole is a membrane bound organelle present in some protists, fungi, and plants. It supports the turgor pressure in plant cells, which adds to the stiffness and strength of the plant.
- A cell can survive by storing water and nutrients in these organelles.
- Vacuoles in seeds and nutritional tissues store several compounds, including inorganic substances, naturally occurring acids, amino acids, and carbohydrates.
- As the cell grows older, smaller vacuoles fuse to form a big central vacuole.
- Within the cell, toxins are converted into a much safer molecule that can be disposed of easily by entering these cell organelles.
Structure of Vacuoles
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The type of cell determines the size and shape of these organelles, which usually resemble a water balloon structure.
- The outer membrane of the vacuole is called the tonoplast which is composed of proteins and phospholipids.
- Tonoplast acts as a barrier between the cytoplasm and the contents of these organelles.
- Cell sap refers to the diverse materials found within the vacuole, including water, ions, pigments, carbohydrates, toxic substances, and other dissolved compounds.
- The contents of the cell sap are different from the cytoplasmic matrix outside.
Functions of Vacuoles
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Following are some of the important functions of vacuoles in the cell:
Storage
Compounds such as proteins, lipids, salts, minerals, and pigments are all stored in cell vacuoles.
- This cell organelle facilitates the passage of protons inside and out of the cell, thus maintaining the acidic pH of the cell's membrane.
- Digestive enzymes are found in lysosomes that are connected to vacuoles.
Turgor Pressure
When a plant gets enough water, the liquid enters inside the vacuoles of the cells, causing them to swell. This process generates a strong turgor pressure, which supports the cell wall and maintains the plant's structural integrity.
Recycling
The process of recycling is important for plant cells as it strengthens the cell. During this process, degraded proteins are recycled with the help of vacuoles.
Cellular Defense
Vacuoles serve as a layer of defense for cells, protecting them from various types of potentially harmful risks. They have a crucial role in the isolation and removal of toxic substances.
Endocytosis & Exocytosis
Endocytosis and exocytosis are the processes that carry out intracellular digestion in vacuoles.
- Endocytosis is the process by which food particles are absorbed.
- The process by which digested food particles are eliminated is called exocytosis.
Sample Questions
Ques. Who discovered vacuole? (1 mark)
Ans. Dutch scientist Antonie van Leeuwenhoek made the initial discovery of the plant vacuole in 1676.
Ques. Is vacuole living or not? (2 marks)
Ans. Storage sacs that are not alive and are connected by a single membrane are called vacuoles. Both plant and animal cells possess this cell organelle. Animal cells are composed of numerous small, transient vacuoles, but plant cells have a single, big, permanent one that can occupy 50–90% of the cell volume.
Ques. What are the main functions of a Vacuole? (2 marks)
Ans. Vacuoles perform several essential tasks, such as:
- Preserving the pH of cells and turgor pressure,
- Managing the transportation and storage of materials,
- Directing the movement and localization of important proteins, and
- Responding to both biotic and abiotic stressors.
Ques. Does photosynthesis occur in vacuoles? (2 marks)
Ans. Chloroplasts contain chlorophyll, which is a necessary component of photosynthesis. However, chlorophyll is absent in vacuoles. Thus, photosynthesis does not take place in this cell organelle.
Ques. What is a real-life example of a vacuole? (2 marks)
Ans. A refrigerator is a real-world object that is similar to a vacuole since it is capable of storing food, liquids, and other materials. Like a refrigerator, this cell organelle found in plant cells serves as a reservoir for water and other molecules.
Ques. What function do vacuoles serve in intracellular digestion? (2 marks)
Ans. Vacuoles participate in intracellular digestion by receiving food nutrients through endocytosis and eliminating waste via exocytosis. The digestive enzymes are stored in lysosomes that are connected to vacuoles.
Ques. What is turgor pressure? (2 marks)
Ans. The force that the plasma membrane exerts against the cell wall is called turgor pressure.
- In plants, turgor pressure is essential for several functions, including development, flowering, signaling, growth, and responses to stress.
- Furthermore, this pressure gives tissues and individual cells their structural integrity.
Ques. What is the mechanism by which vacuoles eliminate waste? (2 marks)
Ans. Vacuoles and lysosomes have similar roles in the removal of waste.
- The pH of the environment inside a vacuole is approximately 5.0, making it mildly acidic.
- The remaining part of the cytosol is slightly alkaline (about pH 7.2).
- Under such conditions, acid hydrolase enzymes in vacuoles degrade big molecules that are transported for elimination.
Ques. What occurs in plant cells if there is no vacuole? (2 marks)
Ans. A vacuole is essential to the survival of a plant cell. They are necessary for the storage of water and the maintenance of structures. Both functions are unattainable in the absence of vacuoles and this will eventually result in the death of the cell. W
Ques. What are the main differences between plant and animal vacuole? (3 marks)
Ans. The difference between plant and animal vacuole are as follows:
| Plant Vacuole | Animal Vacuole |
|---|---|
| Plant cells have one large vacuole. | Two or more than two small vacuoles are present in animal cells. |
| In plant cells, they are permanent structures that store plant sap. | The temporary vacuole of animal cells stores water, ions, and waste products. |
| They play a significant role in maintaining the turgidity of cells. | Animal vacuoles are involved in the process of endocytosis and exocytosis of cells. |
Ques. How does a vacuole perform the recycling function in the cell? (2 marks)
Ans. Vacuoles play a crucial role in recycling cellular components that are damaged or no longer needed. Hydrolytic enzymes that are found in vacuoles are capable of breaking down a wide range of macromolecules, including polysaccharides, proteins, and nucleic acids.
Ques. What are the different types of vacuoles? (3 marks)
Ans. There are four different types of vacuoles: Sap Vacuole, Contractile Vacuole, Air Vacuole, and Gas Vacuole.
- Both immature plant cells and animal cells have several tiny sap vacuoles.
- A lysosome and a phagosome combine to form a food vacuole.
- In addition to providing buoyancy and mechanical strength, air vacuoles store gasses.
- Algal cells and some protistan, which are primarily found in freshwater, have contractile vacuoles.
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