Vacuole, Definition, Structure, Functions for NEET Exam

A vacuole is a membrane-bound cell organelle. In animal cells, vacuoles are generally small and help sequester waste products. In plant cells, vacuoles help maintain water balance, which is vital for the cell's structural integrity. Sometimes, a single vacuole can occupy most of the plant cell's interior, playing a significant role in storage and homeostasis.

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Vacuole Definition

Vacuole Structure

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Types of Vacuoles

• Sap Vacuoles : Sap vacuoles are responsible for transporting various substances. Small sap vacuoles are found in animal and young plant cells. In mature plant cells, these small vacuoles fuse to form a large central vacuole, which can occupy up to 90% of the cell's volume. This large vacuole spreads the cytoplasm into a thin layer, allowing for quick exchange with the environment. The fluid inside sap vacuoles is called sap or vacuolar sap.
• Contractile Vacuoles: These vacuoles are found in some protists and algae, mainly in freshwater environments. A contractile vacuole has a flexible membrane and is connected to feeding canals that collect water and waste from the cytoplasm. It swells as it fills with water (diastole) and then collapses (systole), expelling its contents outside the cell. Contractile vacuoles help with osmoregulation and excretion.
• Food Vacuoles: Food vacuoles are present in protozoans, lower animals, and phagocytes in higher animals. They form when a phagosome fuses with a lysosome and contain digestive enzymes that break down nutrients. The digested materials are then released into the surrounding cytoplasm.
• Air Vacuoles: Air vacuoles are found only in prokaryotes and consist of multiple small vesicles, each surrounded by a protein membrane. They store gases and provide buoyancy, mechanical strength, and protection from harmful radiation.

Function of Vacuole

• Maintaining Cell Acidity : Vacuoles help regulate the cell's internal pH, creating an acidic environment that supports various cellular processes. In plant cells, vacuoles maintain turgor pressure by storing water, which keeps the plant rigid and prevents wilting.
• Storage and Transport of Substances : Vacuoles act as storage units for essential molecules such as amino acids, sugars, and ions. These substances can be transported through specific channel proteins on the vacuole membrane, known as the tonoplast. They also play a key role in transporting proteins through endocytic and lysosomal-vacuolar pathways.
• Regulation of Water Transport : Vacuoles regulate long-distance water transport in plants via tonoplast aquaporins. These channels allow water to move in and out of the vacuole, helping the plant respond to environmental stresses like drought and flooding.
• Role in Stomatal Function : The morphology of stomata, which control gas exchange in plants, depends on the water content of vacuoles. This regulation is crucial for controlling transpiration and gas exchange rates in plants.
• Storage of Secondary Metabolites : Vacuoles play a key role in secondary metabolism. They store potentially harmful secondary metabolites, isolating them from the cytoplasm to protect the cell. These compounds are often involved in the plant's defense mechanisms, stress responses, and seed development.
• Waste Management and Detoxification : Vacuoles manage waste by sequestering harmful substances, ensuring they are kept away from other cellular components, thus protecting the cell from damage.

MCQs of Vacuole

Q1. The vacuoles are bubble-like sacs bounded by a single unit membrane called:

1. tonoplast.
2. chloroplast.
3. ribosomes.
4. All of these.

Q2. Vacuoles are filled with a fluid called:

1. central vacuoles.
2. tonoplast.
3. cell sap.
4. all of these.

Q3. The tonoplast in vacuoles is different:

1. impermeable.
2. permeable.
3. semi-permeable.
4. All of these.

Answers of MCQs of Vacuole