Vacuole
A vacuole is a membrane-bound organelle found in the cytoplasm of cells that stores water, nutrients, waste products, and other materials. In plant cells, the large central vacuole can occupy up to 90% of the cell's volume and plays a critical role in maintaining turgor pressure. Vacuoles help regulate cell volume, pH balance, and the disposal of cellular waste through a process called autophagy.
Comparison of Vacuoles in Different Cell Types
| Cell Type | Vacuole Size | Primary Function | Number | Membrane Name |
|---|---|---|---|---|
| Plant cell | Large (up to 90% volume) | Turgor pressure, storage | Usually 1 | Tonoplast |
| Animal cell | Small, numerous | Temporary storage, waste | Many small | Vacuolar membrane |
| Fungal cell | Medium | pH regulation, storage | 1–several | Tonoplast |
| Protist (Amoeba) | Variable | Food digestion, osmoregulation | Contractile type | Vacuolar membrane |
| Yeast cell | Medium | Ion homeostasis, autophagy | 1–2 | Tonoplast |
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Related Terms
Lysosome
A lysosome is a membrane-bound organelle found primarily in animal cells that contains hydrolytic enzymes capable of breaking down all types of biological polymers, including proteins, nucleic acids, carbohydrates, and lipids. Lysosomes maintain an acidic internal pH of around 4.5–5.0, which is optimal for the activity of their digestive enzymes. They play a central role in autophagy, phagocytosis, and cellular homeostasis by recycling cellular components.
Osmosis (Biology)
Osmosis is the passive movement of water molecules across a selectively permeable membrane from a region of higher water potential (lower solute concentration) to a region of lower water potential (higher solute concentration). This net movement continues until equilibrium is reached or until an opposing pressure prevents further flow. Osmosis is fundamental to cell function, driving turgor pressure in plant cells, reabsorption of water in kidney tubules, and the movement of water into roots from soil.
Cell Wall
The cell wall is a rigid or semi-rigid layer located outside the plasma membrane in plant cells, fungi, bacteria, and some algae, providing structural support and protection against mechanical stress and osmotic lysis. In plants, the primary cell wall is composed mainly of cellulose microfibrils embedded in a matrix of hemicellulose and pectin, while the secondary cell wall may also contain lignin for added rigidity. The cell wall is absent in animal cells, which instead rely on the extracellular matrix for structural support.
From Latin "vacuus" meaning empty. The term was introduced in the 19th century to describe the apparently empty spaces observed in cells under early microscopes.