Life, Ranked by Size

A blue whale is the biggest animal that has ever lived, but it's not the biggest living thing on Earth. Not even close. We rank life by size, step by step: from viruses (are they even alive?) and the smallest cells, a few hundred of them across a hair, past a tiny wasp no bigger than a single-celled paramecium, all the way up to a giant sequoia, a forest that is one tree, a fungus under an Oregon forest, and a seagrass plant spread across 180 km. On the way: why almost every cell stays tiny, why a whale isn't built from bigger cells than you, and the giant cells that seem to break the rule. No biology background needed. 0:00 Not even close 0:49 The smallest living thing 2:43 Climbing up 3:55 Why cells stay small 4:56 More cells, not bigger cells 5:45 Giant cells 7:27 The biggest living things 9:54 Recap The fine print (things the video simplifies) The blue whale: NOAA calls it the largest animal ever to live; a fossil whale, Perucetus, was proposed as a contender in 2023, but a 2024 re-estimate (Motani and Pyenson) puts it well below today's blue whales. The whale is drawn 27 m long; Antarctic blue whales reach about 33 m. Viruses: whether they count as alive is debated. They aren't cells and can only copy themselves inside a host cell. Influenza is about 100 nm across; Pithovirus, a giant virus, is 1.5 µm long. The smallest cells: mycoplasmas are 0.1 to 0.3 µm across. Mycoplasma genitalium has 482 protein-coding genes (525 genes in all), the smallest genome of any organism that can be grown on its own in the lab. Humans have about 20,000 protein-coding genes. The wasp is Megaphragma (adults about 0.2 mm); paramecia are 0.1 to 0.3 mm long; the one drawn is 250 by 50 µm. Your cell is drawn 20 µm across. In Megaphragma mymaripenne, most of the roughly 7,000 nerve cells lose their nucleus as the adult forms; only 339 to 372 nuclei remain. "Most kinds of cells are about the same size": red blood cells, liver cells and skin cells are, across mammals; nerve cells and fat cells grow bigger in bigger animals. The whale's cell count is an estimate from its weight (more than 150 tonnes, about 2,000 times a 70 kg person). The surface and the inside: for a cube or a ball, twice as wide means 4 times the surface and 8 times the volume. The glow in the video's cells comes from food particles doing random walks and being used up on the way. Long nerve cells: motor nerve cells of the spinal cord have fibers up to about a meter long; the path drawn down the leg is a picture. Thiomargarita magnifica (Volland et al., 2022): cells about 1 cm long on average, up to 2 cm, found on sunken mangrove leaves in Guadeloupe. Its central vacuole takes about three quarters of the cell; the living layer is about 3 µm thick, and its DNA sits in small membrane-bound packets. General Sherman: the largest tree by volume (about 1,487 cubic meters), 83.8 m tall; the National Park Service puts its trunk at nearly 1,400 tons. Pando: a clone of quaking aspen in Utah covering about 43 hectares, with about 47,000 stems that share one genotype; it spreads by sprouting new stems from its roots, and is often called the heaviest known organism (dry mass). Guinness puts the Oregon fungus at 7,500 to 35,000 US tons, and the seagrass clone has never been weighed. The Oregon fungus is Armillaria ostoyae (honey mushroom) in the Malheur National Forest: one genet covering about 965 hectares (3.8 km end to end). A soccer field here is 105 by 68 m. The seagrass is Posidonia australis in Shark Bay: one clone spanning at least 180 km, across about 200 square kilometers of meadows (not one unbroken patch). Its age was estimated at up to 4,500 years. Sources OpenStax Biology 2e (free): https://openstax.org/details/books/bi... (sections 1.2, 3.4, 4.2, 11.2, 21.1, 23.3, 24.1, 24.2, 32.3) Alberts et al., Molecular Biology of the Cell, 4th ed. (free on NCBI Bookshelf): "Eggs" Milo and Phillips, Cell Biology by the Numbers (book.bionumbers.org) NOAA Fisheries, "Blue Whale"; Motani and Pyenson, PeerJ 12:e16978 (2024) Fraser et al., Science 270:397 (1995); Glass et al., PNAS 103:425 (2006); Legendre et al., PNAS 111:4274 (2014) Polilov, Arthropod Structure and Development 41:29 (2012); Diakova, Makarova and Polilov, PeerJ (2018) Savage et al., PNAS 104:4718 (2007); Conlon and Raff, Cell 96:235 (1999); Sender, Fuchs and Milo, PLoS Biology 14:e1002533 (2016) Volland et al., "A centimeter-long bacterium with DNA contained in metabolically active, membrane-bound organelles", Science 376:1453 (2022) National Park Service, "The General Sherman Tree"; Rogers and McAvoy, PLoS ONE 13:e0203619 (2018); DeWoody et al., Western North American Naturalist 68:493 (2008) Ferguson et al., Canadian Journal of Forest Research 33:612 (2003); Guinness World Records, "Heaviest fungus"; Edgeloe et al., Proceedings of the Royal Society B 289:20220538 (2022) NOAA Ocean Service, "What is a mangrove forest?"