5. Cell Structure And Organization - part 09 - Vacuoles

 

5. Cell Structure And Organization - part 09 - Vacuoles


Vacuoles :

  • Vacuoles are membrane bound sacs prominently found in plant cells. 
  • In animal cells, whenever present they are few in number and smaller in size. Generally, there are two or three permanent vacuoles in a plant cell.
  • In some large plant cells, a single large vacuole occupies the central part of the cell. It is called central vacuole. 
  • In such cells vacuole can occupy as much as 90% of the total volume of the cell.
  • The vacuoles are bound by semipermeable membrane, called tonoplast membrane. 
  • This membrane helps in maintaining the composition of vacuolar fluid; the cell sap, different from that of the cytosol. 
  • Composition of cell sap differs in different types of cells. 
  • The cell sap of central vacuole is a store house of various ions and thus is hypertonic to cytosol.
  • Small vacuoles in seeds of certain plants store organic materials like proteins. 
  • Vacuoles store excretory products or even compounds that are harmful or unpalatable to herbivores, thereby protecting the plants. 
  • Attractive colours of the petals are due to storage of such pigments in vacuoles.
  • Intake of food or foreign particle by phagocytosis involves formation of food vacuole. 
  • In fresh water unicellular forms like Paramoecium, excretion and osmoregulation takes place by contractile vacuoles. 
  • Vacuoles maintain turgidity of the cell.
  • In addition to endomembrane system, there are several other cell organelles bound by single layer of plasma membrane in the cell.

Microbodies : 

  • Microbodies are found in both plant and animal cells. 
  • These are minute membrane bound sacs. 
  • Microbodies contain various types of enzymes based on which they are classified into different types; few of which are explained here :

1. Sphaerosomes : 

  • These are found mainly in cells involved in synthesis and storage of fats. e. g. endosperm of oil seeds. 
  • The membrane of sphaerosome is half unit membrane i.e. this membrane has only one phospholipid layer.

2. Peroxisomes : 

  • Peroxisomes contain enzymes that remove hydrogen atoms from substrate and produce toxic hydrogen peroxide by utilisation of oxygen. 
  • At the same time peroxisome also contains enzymes that convert toxic H2O2 to water. 
  • Conversion of toxic substances like alcohol takes place in liver cells by peroxisomes.

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