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Given that they contain the biological molecules and machinery required by all life forms, it\u2019s ironic that cells were named after empty spaces.<\/p>\n
When the 17th-century polymath Robert Hooke looked down a microscope at the structure of cork, its repeating units of spaces reminded him of the sleeping quarters in a prison or monastery. Hooke called those units \u2018cells\u2019, from the Latin for \u2018little rooms\u2019.<\/p>\n
It depends on how you define life! Viruses aren\u2019t made of cells, but some biologists consider them alive. A virus can\u2019t replicate without using a host cell, though, so we can sidestep the philosophical discussion of \u201cWhat is life?\u201d and say all life uses cells.<\/p>\n
Life forms that are made of cells are called organisms. They\u2019re either unicellular (single-celled) \u2013 bacteria, for example \u2013 or multicellular. Unicellular organisms must do all the work needed to sustain life, but multicellular life forms can have a body with a division of labour: different types of cell play specific roles in the organism.<\/p>\n <\/p><\/div> <\/section> Every cell has a fatty membrane that establishes its boundary and controls which substances go in or out of its watery internal fluid, the cytoplasm. A cell will almost always contain genetic material, too.<\/p>\n The biggest distinction between cells is how they hold genetic material. In eukaryote cells, the DNA is enclosed with a \u2018nut\u2019 or envelope called the nucleus (hence eukaryote meaning \u2018true nut\u2019 in Greek). Meanwhile, in prokaryote cells \u2013 bacteria and archaea, descendants of life forms that didn\u2019t evolve to have a nucleus \u2013 the DNA floats freely in the cytoplasm (prokaryote means \u2018before nuts\u2019 in Greek).<\/p>\n Eukaryote cells are more complex because they\u2019re organised into compartments with structures known as organelles (\u2018little organs\u2019) with separate functions, analogous to the organs of a body \u2013 as in energy-generating mitochondria that breathe oxygen like lungs.<\/p>\nYou may also like:\u00a0<\/h4>\n
What do cells have in common?<\/h2>\n
What\u2019s the difference between eukaryote and prokaryote cells?<\/h2>\n