11th Class Biology Cell - The Unit Of Life Microbodies

(1) Sphaerosomes

Discovery : These were first observed by Hanstein (1880) but discovered by Perner (1953). Term sphaerosomes was given by Dangeard.

Occurrence : These are found in all the plant cells which involves in the synthesis and storage of lipids i.e., endosperm and cotyledon of oil seeds.

Shape, size and structure : These are spherical or oval in shape about \[0.5-2.5\,\mu \,m\]in diameter. They contain hydrolytic enzymes like protease, ribonuclease, phosphatase, esterase etc. They are bounded by a single unit membrane.

Function : The main function of sphaerosomes is to help in lipid metabolism. These are also known as plant lysosomes.

(2) Peroxisomes (Uricosomes)

Discovery : These were first discovered by J. Rhodin (1954) in the cells of mouse kidney and were called microbodies. De Duve (1965) isolated certain sac like organelles from various types of animals and plants. These were called peroxisomes because these contain peroxide producing enzymes (oxidases) and peroxide destroying enzymes (catalases).

Occurrence : These are found in photosynthetic cells of plants. In animals peroxisomes are found in vertebrates (cells of liver, kidney), brain, small intestine, testis and adrenal cortex), invertebrates and protozoans e.g., Paramecium.

Shape, size and structure : These are spherical in shape, about \[1.5\,\mu \,m\] in size. They are bounded by a single unit membrane.

Their membrane is permeable to amino acids, uric acids, etc. They contain four enzymes of \[{{H}_{2}}{{O}_{2}}\] metabolism. The enzymes urate oxidase, d-amino oxidase, a-hydroxy acid oxidase produce \[{{H}_{2}}{{O}_{2}}\] whereas the catalases plays a significant protective role by degrading H₂O₂ because \[{{H}_{2}}{{O}_{2}}\] is toxic for cells.

Function : These are involved in the formation  and degrading of \[{{H}_{2}}{{O}_{2}}\]. Plant peroxisomes are also involved in photorespiration.

(3) Glyoxysomes

Discovery : These were discovered by Beevers in 1961 and Briedenbach in 1967.

Occurrence : These are found in fungi, some protists and germinating fatty seeds where insoluble lipid food reserves must be turned into soluble sugars. Absent in animal cell.

Shape, size and structure : These are spherical in shape, about \[0.5-1\,\mu \,m\]in size, they contain enzymes of metabolism of glycolic acid via glyoxylate cycle and bounded by a unit membrane. These are also contain enzymes for \[\beta -\]oxidation of fatty acids. Produced acetyl CoA. The better is metabolised in glyoxlate cycle to produced carbohydrates.

Functions : The main function of glyoxysomes is conversion of fats into carbohydrates.

(4) Lomasomes : These are sac like structures found between cell wall and plasmalemma in the haustoria of fungal hyphae. These were first discovered by Bowen and Berlin. Webster called them border bodies.