Eukaryotes

Most living things which are visible to the naked eye in their adult form are eukaryotes, includinghumans. However, a large number of eukaryotes are also microorganisms. Unlike bacteria andarchaea, eukaryotes contain organelles such as the cell nucleus, the Golgi apparatus andmitochondria in their cells. The nucleus is an organelle which houses the DNA that makes up a cell'sgenome. DNA itself is arranged in complex chromosomes.^[39] Mitochondria are organelles vital inmetabolism as they are the site of the citric acid cycle and oxidative phosphorylation. They evolved from symbiotic bacteria and retain a remnant genome.^[40] Like bacteria, plant cells have cell walls, and contain organelles such as chloroplasts in addition to the organelles in other eukaryotes. Chloroplasts produce energy from light by photosynthesis, and were also originally symbiotic bacteria.^[40]

Unicellular eukaryotes are those eukaryotic organisms that consist of a single cell throughout their life cycle. This qualification is significant since most multicellular eukaryotes consist of a single cell called a zygote at the beginning of their life cycles. Microbial eukaryotes can be either haploid or diploid, and some organisms have multiple cell nuclei (see coenocyte).