What is Vacuole

A Vacuole is a membrane-bound organelle that is found in the cells of most organisms, including Plants, Animals and bacteria. It is a type of vesicle that plays a vital role in various cellular functions such as storage, transportation and degradation of various substances. The size, shape and function of Vacuoles vary among different types of cells and organisms. In Plant Cells, a large central Vacuole is present that occupies most of the cell’s volume and is involved in various functions such as storage of water, ions, pigments and other metabolites, as well as maintenance of turgor pressure. 

In Animal Cells, Vacuoles are smaller and mainly involved in processes such as Lysosomal degradation and Autophagy. In Bacteria, Vacuoles are involved in processes such as Symbiosis and Pathogenesis.

Vacuole Definition

A Vacuole is a membrane-bound organelle found in the cells of organisms, including Plants, Animals and bacteria. It functions as a storage unit for various substances, including water, ions, nutrients and waste products.

Who Discovered Vacuoles

The term “Vacuole” was coined by scientist Dujardin to describe the star-shaped contractile Vacuole that was first observed by Spallanzi in Protozoa in 1776. De Vries gave the name “Tonoplast” to the Vacuole membrane in 1885. Vacuoles grow by the combination of many membrane vesicles and are surrounded by a type of Cytoplasmic Membrane known as Tonoplast. 

Structure of Vacuoles

A Vacuole is a membrane-bound organelle found in the Cytoplasmic matrix of a cell. Its size and shape vary depending on the requirements of the cell. In immature and actively dividing plant cells, the Vacuoles are quite small and arise initially in young dividing cells, probably by the progressive fusion of vesicles derived from the Golgi apparatus. The membrane surrounding the Vacuole is known as the Tonoplast or vacuolar membrane, which is composed of phospholipids and embedded with proteins that help in transporting molecules across the membrane.

The Tonoplast is the Cytoplasmic Membrane surrounding a Vacuole, separating the vacuolar contents from the cell’s cytoplasm. As a membrane, it is mainly involved in regulating the movements of ions around the cell and isolating materials that might be harmful or a threat to the cell. Vacuoles are structurally and functionally related to lysosomes in animal cells and may contain a wide range of hydrolytic enzymes.

The Vacuole is filled with cell sap, which is a combination of different substances such as sugars, salts, acids, and nitrogenous compounds such as alkaloids and anthocyanin pigments. The pH of plant Vacuoles may be as high as 9 to 10 due to large quantities of alkaline substances or as low as 3 due to the accumulation of quantities of acids (e.g., citric, oxalic, and tartaric acids).

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Vacuole Diagram

Types of Vacuoles

Vacuoles are non-cytoplasmic regions present within the cytoplasm that are later separated by a special membrane. The Vacuoles are supposed to be formed by expansion and pinching from the ER. Depending on the contents and functions, There are four types of Vacuoles – 

• Central Vacuole (Sap Vacuole)
• Contractile Vacuole
• Food Vacuoles
• Gas Vacuoles

Central Vacuole (Sap Vacuole)

The central Vacuole, also known as the sap Vacuole, is the largest Vacuole in the Plant Cell, which can occupy up to 90% of the total cell volume. It is found in Plant Cells and is responsible for storing various substances such as water, ions, metabolites and pigments. The central Vacuole is surrounded by a single membrane called the Tonoplast, which separates its contents from the cytoplasm.

Function and structure of Central Vacuole (Sap Vacuole)

• The central Vacuole is responsible for regulating the turgor pressure within the cell.
• It helps in the maintenance of the pH balance, ion concentration and osmotic pressure of the cell.
• The central Vacuole plays a crucial role in Plant growth and development by storing and releasing ions, metabolites and pigments as required.

Role of Central Vacuole (Sap Vacuole) in Plant growth and development

• The central Vacuole helps in the regulation of cell growth and differentiation by storing and releasing various substances.
• It maintains the cell shape and turgor pressure, which is essential for the structural integrity of the Plant.
• The central Vacuole also plays a role in the storage and release of water, which is essential for the Plant’s survival during periods of drought and other environmental stresses.

Contractile Vacuole

The contractile Vacuole is a specialised type of Vacuole found in unicellular organisms such as amoeba and paramecium. It is responsible for maintaining the osmotic balance of the cell by expelling excess water and waste products from the cell.

Function and structure of Contractile Vacuole

• The contractile Vacuole consists of a single membrane that surrounds a fluid-filled cavity.
• The Vacuole periodically contracts, expelling the excess water and waste products from the cell.
• The contraction is powered by the energy generated by ATP hydrolysis.

Role of Contractile Vacuole osmoregulation and excretion

• The contractile Vacuole is responsible for maintaining the osmotic balance of the cell by expelling excess water and waste products from the cell.
• It helps in the removal of waste products such as ammonia and carbon dioxide from the cell.

Food Vacuole

Food Vacuoles are specialised Vacuoles found in protozoans, which are responsible for the ingestion and digestion of food particles.

Function and structure of Food Vacuoles

• The food Vacuole is formed by the fusion of the cell membrane with a food particle.
• The food Vacuole contains digestive enzymes that break down the food particles into smaller molecules.
• The nutrients are then absorbed into the cytoplasm.

Role of Food Vacuole digestion and nutrient absorption

• The food Vacuole is responsible for the ingestion and digestion of food particles.
• It helps in the absorption of nutrients, which are essential for the survival of the organism.

Gas Vacuole

Gas Vacuoles are found in many aquatic prokaryotes such as cyanobacteria, purple and green bacteria. These Vacuoles are responsible for providing buoyancy to the cell and also play a role in photosynthesis. The gas Vacuole is a proteinaceous structure that is enclosed by a lipid membrane.

Function and structure of Gas Vacuoles

The primary function of the gas Vacuole is to provide buoyancy to the cell. The Vacuole contains a gas-filled compartment that helps the cell to float in the water column. The size and number of gas Vacuoles vary depending on the environment in which the organism lives. In addition to providing buoyancy, gas Vacuoles also play a role in photosynthesis. The Vacuole provides a surface area for the attachment of photosynthetic pigments and enzymes, thus enhancing the efficiency of photosynthesis.

Functions of Vacuoles

Vacuoles are membrane-bound organelles found in eukaryotic cells, which perform a variety of functions. Here are some of the functions of Vacuoles-

• Storage of water and other Substances– One of the most important functions of the Vacuole is to store water and other substances such as ions, nutrients and pigments. In Plant Cells, the large central Vacuole can occupy up to 90% of the cell volume, storing water and other molecules to maintain cell turgor pressure.
• Maintenance of cell Turgor Pressure– The Vacuole plays a crucial role in maintaining the turgor pressure of Plant Cells. Turgor pressure is the pressure that builds up inside the cell when the Vacuole is full of water. This pressure allows Plants to maintain their shape and structure and resist external pressures such as wind or rain.
• Storage of pigments and other metabolic products– Vacuoles also store pigments and other metabolic products such as anthocyanins, tannins and alkaloids. These pigments give Plants their colour and protect them from environmental stresses such as UV radiation.
• Regulation of ion and nutrient balance– Vacuoles play a role in the regulation of ion and nutrient balance in cells. They can selectively absorb or expel ions and nutrients to maintain the proper balance within the cell.
• Protection against stress and toxins– Vacuoles can also protect cells from stress and toxins. They can store waste products and harmful substances in a compartment that is isolated from the rest of the cell, reducing their potential toxicity.

In addition to these general functions, Vacuoles can have specific functions depending on the cell type and organism. Here are few examples-

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Endocytosis and Exocytosis

 Vacuoles are involved in Endocytosis and exocytosis, which are processes that transport materials into and out of the cell. In Plant Cells, Vacuoles are involved in the uptake and storage of nutrients and the removal of waste products.

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Other Storage Functions

 Vacuoles can store a variety of molecules, including salts, minerals, pigments and proteins. For example, fat cells can store large quantities of lipids in Vacuoles, which can be used for energy when resources are scarce. Vacuoles can also be used to build complete ecosystems, such as in coral reefs, where algae are stored in Vacuoles within coral polyps.

Significance of Vacuoles in Different Organisms

Significance of Plant Vacuoles

Plant Vacuoles play a crucial role in the growth and development of Plants. Some of the significant functions of Plant Vacuoles are-

• Storage– Plant Vacuoles store various materials such as water, ions and metabolites. They can occupy up to 90% of the cell volume, helping to maintain cell shape and turgor pressure.
• Homeostasis- Plant Vacuoles maintain the pH balance, osmotic pressure and ion balance of the cytoplasm.
• Degradation– Plant Vacuoles contain enzymes that are responsible for breaking down and recycling cellular waste.
• Defence– Some Plant Vacuoles store compounds that protect against herbivores, pathogens and environmental stresses.

Plant Vacuoles exhibit structural and functional adaptations that vary across different Plant tissues. For example, the Vacuoles in the epidermal cells of leaves and fruits store pigments that attract pollinators or seed dispersers. In contrast, the Vacuoles in the root cells store nutrients such as starch and minerals.

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Significance of Animal Vacuoles

Animal Cells contain several types of Vacuoles, including lysosomes and autophagosomes. The significant functions of Animal Vacuoles are-

• Degradation– Lysosomes contain hydrolytic enzymes that degrade and recycle cellular waste, foreign substances and pathogens. This process is crucial for maintaining cellular homeostasis and preventing disease.
• Autophagy– Autophagosomes are specialised Vacuoles that participate in the degradation and recycling of damaged or dysfunctional cellular components. This process is essential for maintaining cell health and preventing the accumulation of toxic substances.
• Storage– Some Animal Cells contain Vacuoles that store materials such as water, ions and nutrients.
• Transport– Animal Cells use Vacuoles for transporting materials between organelles and cells.

The dysfunction of Animal Vacuoles can have significant implications for human health and disease. For example-  lysosomal storage disorders result from the deficiency of lysosomal enzymes, leading to the accumulation of undegraded substrates and cellular dysfunction.

Significance of Bacterial Vacuoles

Bacterial Vacuoles are specialised compartments that play critical roles in bacterial physiology, symbiosis and pathogenesis. Some of the significant functions of bacterial Vacuoles are-

• Nutrient acquisition- Bacterial Vacuoles enable the uptake and storage of nutrients such as nitrogen, carbon and iron.
• Symbiosis- Bacterial Vacuoles can form symbiotic relationships with other organisms, such as in the case of nitrogen-fixing bacteria in Plant root nodules.
• Pathogenesis- Some bacterial Vacuoles are involved in pathogenesis, helping bacteria to survive and replicate inside host cells.
• Adaptation- Bacterial Vacuoles can adapt to changing environments, allowing bacteria to survive and thrive in different conditions.

Frequently asked questions on Vacuoles 

What is a Vacuole?

Answer – A Vacuole is a membrane-bound organelle that is found in the cells of most organisms, including Plants, Animals and bacteria. It functions as a storage unit for various substances, including water, ions, nutrients and waste products.

Who discovered Vacuoles?

Answer – The term “Vacuole” was coined by scientist Dujardin to describe the star-shaped contractile Vacuole, which was first observed by Spallanzi in protozoa in 1776. De Vries gave the name “Tonoplast” to the Vacuole membrane in 1885.

What is the structure of Vacuoles?

Answer – Vacuoles are membrane-bound organelles that are surrounded by a single lipid bilayer membrane, known as the Tonoplast in Plant Cells and the vacuolar membrane in Animal Cells. The Tonoplast is a specialised membrane that is derived from the endoplasmic reticulum (ER) and is rich in specific transporters and channels that regulate the transport of molecules across the membrane.

What are the types of Vacuoles?

Answer – There are four types of Vacuoles, depending on their contents and functions – sap Vacuoles, compressible Vacuoles, food Vacuoles and air Vacuoles. The central Vacuole, also known as the sap Vacuole, is the largest Vacuole in the Plant Cell and is responsible for storing various substances such as water, ions, metabolites and pigments. The other types of Vacuoles have specific functions such as storing gases, digest

What is the function of the Tonoplast?

Answer – The Tonoplast is the Cytoplasmic Membrane surrounding a Vacuole, which is mainly involved in regulating the movements of ions around the cell and isolating materials that might be harmful or a threat to the cell.

What are the components of the cell sap found in the Vacuole?

Answer – The cell sap found in the Vacuole is a combination of different substances such as sugars, salts, acids, and nitrogenous compounds such as alkaloids and anthocyanin pigments.

How does the size and shape of the Vacuole vary in different cells?

Answer – The size and shape of the Vacuole vary depending on the requirements of the cell. In immature and actively dividing plant cells, the Vacuoles are quite small and arise initially in young dividing cells, probably by the progressive fusion of vesicles derived from the Golgi apparatus.

What is the primary function of the contractile Vacuole?

Answer – The contractile Vacuole is responsible for maintaining the osmotic balance of the cell by expelling excess water and waste products from the cell. It helps in the removal of waste products such as ammonia and carbon dioxide from the cell.

What is the function of the food Vacuole?

Answer – The food Vacuole is responsible for the ingestion and digestion of food particles. It helps in the absorption of nutrients, which are essential for the survival of the organism.

What is the function of the gas Vacuole?

Answer –  The primary function of the gas Vacuole is to provide buoyancy to the cell. The Vacuole contains a gas-filled compartment that helps the cell to float in the water column. In addition to providing buoyancy, gas Vacuoles also play a role in photosynthesis.

What are some of the general functions of Vacuoles?

Answer –  Vacuoles perform a variety of functions, including storage of water and other substances, maintenance of cell turgor pressure, storage of pigments and other metabolic products, regulation of ion and nutrient balance and protection against stress and toxins.

What is the significance of Plant Vacuoles?

Answer –  Plant Vacuoles play a crucial role in the growth and development of Plants. Some of the significant functions of Plant Vacuoles are storage, homeostasis, degradation and defence. Plant Vacuoles exhibit structural and functional adaptations that vary across different Plant tissues.

What are some specific functions of Vacuoles in Animal Cells?

Answer – Animal Cells contain several types of Vacuoles, including lysosomes, which are responsible for the breakdown of cellular waste and phagocytic Vacuoles, which are involved in the ingestion and destruction of foreign particles.

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Also Check – What is the Difference between Plant Vacuoles and Animal Vacuoles?

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Also Check – Why do Plant cells possess Large Sized Vacuoles ?