Cells aren't always the same.
In the classification of organisms, we have:
The Prokaryotes and the Eukaryotes. Prokaryotes have prokaryotic cells. Eukaryotes have eukaryotic cells. Eukaryotic cells have nucleus, a genetic material, and the membrane-bound organelles, while the prokaryotic cells lack of nucleus, and the membrane-bound organelles. In this way, all cells aren't the same. Even eukaryotic cells, aren't always the same. A sperm cell, and an egg cell is a eukaryotic cell. A sperm cell can be found only in a male organism, while an egg cell can be found only in a female organism, sperm cell and egg cell differs in shape, size, number, function, body structure, etc. Even sperm cells, they aren't always the same, some sperm cells are normal, some aren't normal, like for example: a single sperm cell have a regular flagellate, while another one have a very short flagellate, a single sperm cell's motility is regular, while another one is not moving.
Cells aren't always the same. Prokaryotes, are different from Eukaryotes. Even prokaryotes, differ from other prokeryotes and same with the Eukayotes.
Cells may differ in:
Sex of organism that carries the cell
Size
Shape
Motility
Genetic Material
Kind
Number
Function
etc.
