#INTRODUCTION:
-> Vacuoles are membrane-bound sacs.
-> They are present in the cytoplasm of both plant and animal cells.
-> They are actually like storage bubbles that hold water, nutrients, and waste products.
-> Vacuoles are much larger in size in plant cells as compared to animal cells.
# STRUCTURE :
A) SHAPE AND SIZE :
-> In a plant cell, there is usually one large central vacuole that can occupy up to 90% of the cell volume.
-> In animal cells, the vacuoles are small and numerous.
B) MEMBRANE :
-> The vacuole is surrounded by a single membrane called the tonoplast. It is a selectively permeable membrane.
[Note; selective permeable means it allows only certain molecules to pass in or out. ]
C) VACUOLAR FLUID :
-> The inside of the vacuole is filled with cell sap and waste toxins.
D) ORIGIN OF VACUOLE :
-> Vacuoles are formed by fusion of vesicles from the endoplasmic reticulum and Golgi apparatus.
# FUNCTIONS :
1) In plant cells ;
A) STORAGE :
-> It stores nutrients, sugars, amino acids, organic acids and ions.
-> It also stores waste products and toxic substances to protect the cytoplasm.
B) MAINTAIN TURGOR PRESSURE :
-> The Vacuole helps to maintain turgidity by storing water, as it pushes the cytoplasm against the cell wall, helping plants to stay upright.
C) pH AND IONIC STRENGTH :
-> It maintains the acidic environment ( pH approx 5 ) inside the vacuoles, which regulates ion concentration within the cell.
D) DIGESTION AND BREAKDOWN :
-> They contain hydrolytic enzymes that help to break down macromolecules.
E) PIGMENT STORAGE :
-> They store pigments, anthocyanins, which give colour to the flower, fruit and leaf of the plant.
F) WASTE DISPOSAL :
-> They actually act as the dumping ground for waste and harmful materials.
G) DEFENSE :
-> Some vacuoles contain toxic compounds or secondary metabolites that deter herbivores or pathogens.
2) In animal cells ;
A) ENDOCYTOSIS AND EXOCYTOSIS SUPPORT :
-> They help in the uptake of materials and release of waste by fusing with the plasma membrane.
B) STORAGE AND TRANSPORT :
-> Temporary storage of nutrients and ions helps in the transport of substances within the cell.
C) OSMOREGULATION :
-> They maintain water balance within the cell.
D) PHAGOCYTIC VACUOLES : ( Food Vacuoles)
-> They are formed when amoeba or white blood cells engulf food or foreign material.
3) In unicellular organisms (protozoa)
A) CONTRACTILE VACUOLES :
-> It is present in amoeba and paramecium and regulate water balance by expelling excess water ( prevents bursting ).
-> They are important for osmoregulation.
B) FOOD VACUOLES :
-> They are formed after engulfing food particles, in which enzymes digest the food vacuole.
At last, the vacuole acts as the cell’s multi-purpose storage and support hub, essential for maintaining structural integrity and internal balance.
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