All plant and animal species are made up of cells. Anton Von Leeuwenhoek, an amateur Dutch scientist was the first person to see and describe living cells. Later, Robert Brown discovered the nucleus of the cell. Later, Matthias Schleiden found that plants have different types of cells. A year later, Theodore Schwann discovered that both plant and animal cells have a cell membrane, and only plant cells have a cell wall.
Schleiden and Schwann together formulated the Cell Theory, which states that both plants and animals are made up of cells. However, the cell theory did not explain the formation of new cells, which was clarified by Rudolf Virchow in 1855. He coined the Latin phrase ‘Omnis cellula-e cellula’, which meant that new cells are formed from pre-existing cells.
The invention of the electron microscope enabled scientists to observe the variation in the structure of plant and animal cells. The nucleus in both animal and plant cells is bound by a nuclear membrane. Such cells are called eukaryotic cells. They are found in the members of Kingdom Protista, Kingdom Fungi, Kingdom Plantae and Kingdom Animalia.
On the other hand, cells without a membrane bound nucleus are called prokaryotic cells, and members of Kingdom Monera possess such cells.
Eukaryotic cells have membrane-bound organelles such as the endoplasmic reticulum, the golgi complex, lysosomes, mitochondria, microbodies and vacuoles as well as non-membrane bound organelles such as ribosomes in both plants and animals. Moreover, animal cells possess another non-membrane bound organelle called the centriole, which aids in cell division.
Prokaryotic cells lack membrane-bound organelles but contain ribosomes and fragments of extra chromosomal DNA called plasmids.
Cells usually differ in size and shape. Moreover, the shape of cells range from disc-like to thread-like and from polygonal to columnar and cuboid.