Cellular structure refers to the organization and arrangement of cells, which are the basic building blocks of all living organisms. Each cell is surrounded by a protective membrane and contains various components, such as the nucleus, which houses genetic material, and organelles like mitochondria that produce energy. These structures work together to perform essential functions that sustain life. Cells can be classified into two main types: prokaryotic and eukaryotic. Prokaryotic cells, like those found in bacteria, are simpler and lack a nucleus, while eukaryotic cells, found in plants and animals, have a more complex structure with a defined nucleus. Understanding cellular structure is crucial for studying biology and medicine.