Because cell structure is not uniform from every side and in every section.
<h3>Explanation:</h3>
A cell is a unit of life and it contains all the structure which are important for the functions of a life.
Cell contains nucleus for genetic material storage and replication. It contains mitochondria for respiration and ribosomes for protein production. Apart from these structures it contains golgi apparatus, endoplasmic reticulum, lysosomes and cell membrane. Except cell membrane their structures are not uniformally distributed.
That's why biologists often cut several sections from a cell to find out about its structure.
