There are two types of cells on Earth, prokaryotic cells and eukaryotic cells.

Prokaryotic cells, which are the most primitive kind of cells, do not have nuclei or other membrane-bound structures.

A eukaryotic cell has membrane-bound structures, known as organelles, including a nucleus that contains genetic material.

Organisms with prokaryotic cells are known as prokaryotes. There are two forms of prokaryotes on Earth - bacteria and archaea. These are one-celled organisms and were the first living things to appear on Earth.

Eukaryotes are organisms that contain eukaryotic cells. Unlike prokaryotes, eukaryotes can have one cell or they can be multicellular.

The nucleus of a eukaryotic cell is surrounded by a nuclear membrane, or nuclear envelope.

Chromatin, the substance that makes up chromosomes, can be found within the nucleus. Chromatin contains DNA and proteins.

A spherical body known as the nucleolus, or nucleole, is also contained within the nucleus.

The nucleolus contains ribonucleic acid (RNA).

RNA is a nucleic acid with a structure that is very similar to the structure of DNA.

RNA carries genetic information from DNA to ribosomes, which use this information to make protein from amino acids.

The part of a eukaryotic cell that is outside of the nucleus is known as the cytoplasm.

It is surrounded by a cell membrane.

The cytoplasm contains soluble enzymes and free ribosomes.

It also has other organelles (membrane-bound bodies.)

The Golgi apparatus is an organelle in the cytoplasm that helps to synthesize proteins and lipids.

Mitochondria, which are also found in the cytoplasm, are involved with respiration, supplying energy to the cell, cell division and cell growth.

Chloroplasts, which are only found in plant cells, are involved with photosynthesis.

Mitochondria and chloroplasts have their own DNA. They may originally have been prokaryotes that developed a symbiotic relationship with eukaryotic cells.