Which of the following is not a microbody ?

Question

Accepted Answer

The correct option is 4: Centrosome

The Centrosome is the correct answer because it is structurally and functionally distinct from the cell organelles collectively termed 'microbodies.' Microbodies are broadly defined as a group of small, roughly spherical organelles that are enclosed by a single lipid membrane and contain a specialized set of enzymes for various metabolic functions. Examples include Peroxisomes and Glyoxisomes. In stark contrast, the Centrosome is a non-membranous organelle, meaning it is not enclosed by a lipid bilayer. Its primary role is not metabolic, but rather organizational, as it serves as the cell’s main Microtubule Organizing Center (MTOC). The Centrosome is crucial for cell division, containing two barrel-shaped structures called centrioles, which are responsible for the formation of the mitotic spindle and the organization of the cellular cytoskeleton. This fundamental difference in membrane structure, composition, and core function—mechanics and structure versus metabolism—excludes the Centrosome from the microbody category.

The incorrect option is 1: Peroxisome

Peroxisomes are a classic and universally recognized type of microbody found in almost all eukaryotic cells. They are small, single-membrane-bound vesicles that primarily house oxidative enzymes, most notably catalase and urate oxidase. The essential metabolic function of peroxisomes is to safely carry out oxidation reactions, such as the breakdown of very long-chain fatty acids, which produces hydrogen peroxide. As hydrogen peroxide is toxic, the catalase enzyme immediately breaks it down into water and oxygen. Their characteristic structure and metabolic role firmly establish them as microbodies.

The incorrect option is 2: Glyoxisome

Glyoxisomes are specialized microbodies found exclusively in plant cells, particularly in the fat-storing tissues of germinating seeds. Structurally, they are single-membrane-bound, just like peroxisomes, but they contain the unique set of enzymes required for the glyoxylate cycle. This metabolic pathway is vital for plant life as it allows the seed to convert stored lipids (fats) into carbohydrates, which are essential energy sources for the growth of the young seedling until it is capable of photosynthesis. Due to their single-membrane structure and specialized enzyme-driven metabolic function, Glyoxisomes are considered a highly specialized class of microbody.

The incorrect option is 3: Sphaerosome

Sphaerosomes (or Oleosomes/Lipid Droplets) are generally classified as a specialized type of microbody, particularly in the context of plant cell biology. They are minute, spherical bodies with a single, unique half-unit membrane (a phospholipid monolayer) and function primarily as the storage site for fats and oils in cells, especially in seeds. Although their primary function is lipid storage and they sometimes contain hydrolytic enzymes, their small, spherical shape and single-membrane enclosure lead to their inclusion within the broader conceptual group of microbodies in many introductory biology texts. Therefore, while modern biochemistry may classify them slightly differently, they are much closer to the definition of a microbody than the Centrosome.