Peroxisomes are membrane-bound spherical structures found floating freely in the cytoplasm of all eukaryotic organisms, including animal and plant cells. They have the simplest structure of all eukaryotic organelles. 

Peroxisomes may vary in size and shape depending on the organism and the cell’s energy requirements as well as the environmental conditions. They are generally circular in cross-section and range in size from 0.1 to 1.0 μm (micrometer) in diameter.  

Each peroxisome is enclosed by a single lipid bilayer that encloses a granular, protein-rich matrix. They may exist within the cell as individual microperoxisomes or in the form of a network of interconnected tubules known as peroxisome reticulum.