Most mature plant cells contain a single large permanent vacuole, which may take up most of the volume of the cell. The cytoplasm is pushed into a thin layer between the vacuole and the cell wall.Structure
The vacuole is surrounded by a single, partially permeable membrane called the tonoplast. The tonoplast contains transport proteins that control which substances move between the cytoplasm and the vacuole.The vacuole is filled with cell sap, a watery solution of sugars, mineral ions (such as K+), amino acids, pigments and waste products.Functions
• Maintaining turgor: the solutes in the cell sap give it a low (more negative) water potential. Water enters the vacuole by osmosis, so it swells and pushes the cytoplasm against the cell wall. The cell becomes turgid, which supports non-woody plants and keeps leaves firm. If a plant loses too much water, cells lose turgor and the plant wilts.
• Storage of sugars, ions, amino acids and proteins (for example, protein stores in seeds).
• Pigments: anthocyanins in the cell sap give red, blue and purple colours to petals, fruits and beetroot, attracting pollinators and seed dispersers.
• Isolating harmful substances, such as waste products and some toxic chemicals, which can also deter herbivores.
• Some vacuoles contain hydrolytic enzymes and act like lysosomes.A large vacuole also lets a plant cell grow bigger cheaply, by taking up water rather than making lots of new cytoplasm.
The vacuole is surrounded by a single, partially permeable membrane called the tonoplast. The tonoplast contains transport proteins that control which substances move between the cytoplasm and the vacuole.The vacuole is filled with cell sap, a watery solution of sugars, mineral ions (such as K+), amino acids, pigments and waste products.Functions
• Maintaining turgor: the solutes in the cell sap give it a low (more negative) water potential. Water enters the vacuole by osmosis, so it swells and pushes the cytoplasm against the cell wall. The cell becomes turgid, which supports non-woody plants and keeps leaves firm. If a plant loses too much water, cells lose turgor and the plant wilts.
• Storage of sugars, ions, amino acids and proteins (for example, protein stores in seeds).
• Pigments: anthocyanins in the cell sap give red, blue and purple colours to petals, fruits and beetroot, attracting pollinators and seed dispersers.
• Isolating harmful substances, such as waste products and some toxic chemicals, which can also deter herbivores.
• Some vacuoles contain hydrolytic enzymes and act like lysosomes.A large vacuole also lets a plant cell grow bigger cheaply, by taking up water rather than making lots of new cytoplasm.