edubun
English
English한국어EspañolPortuguêsFrançaisDeutschItalianoNederlandsРусскийBahasa Indonesia日本語
Home›Biology

Microbes

In 1676 Antonie van Leeuwenhoek told the Royal Society that a single drop of pepper water held upwards of a million living creatures. Meet bacteria, archaea, fungi, protists and viruses, grow a bacterial culture on a graph, and follow how scientists proved that germs exist.

Progress

About this course

In 1676 Antonie van Leeuwenhoek told the Royal Society that a single drop of pepper water held upwards of a million living creatures. His first observations reached the Royal Society in London in 1673, introduced by the physician Regnier de Graaf, and he wrote to the Society until his death in 1723.

The six units are what microbes are, bacteria and archaea, how fast bacteria multiply, fungi and protists, viruses, and how germs were discovered. Most bacteria reproduce by binary fission, a simple division into two, though genes can still be exchanged by horizontal gene transfer. The growth unit uses the OpenStax example of one cell with a 30-minute doubling time over 24 hours, and switching to a log scale turns the curve into a straight line. You also work out how many cells 100,000 become after 2 hours of growth. Virus capsids come in three broad shapes: helical rods like tobacco mosaic virus, polyhedral, and complex ones like bacteriophages with a head, a tail and tail fibres.

The history unit follows the proof that germs exist. In 1668 Francesco Redi put meat in six jars, left two open, covered two with gauze and sealed two, and only the open jars grew maggots. In 1847 Ignaz Semmelweis noticed that mothers in wards run by doctors and medical students who came straight from autopsies died of fever after childbirth at a rate of 10 to 20 percent. In 1892 Dmitri Ivanovski passed sap from sick tobacco plants through a porcelain filter that stopped all bacteria, and the sap could still make plants sick. In 1928 Alexander Fleming found that a Penicillium mold had grown on one of his culture plates and the bacteria near it had failed to grow.

Before you start

Most microbes are single cells, so Cells is the best preparation, especially the difference between cells with and without a nucleus. The growth unit doubles numbers again and again, so being at ease with powers of two will make those questions quicker.

When you finish

Afterwards you can compare the sizes of bacteria, fungi, protists and viruses, explain what makes bread dough rise, and count the cells after a number of doublings. You can name the phases of bacterial growth, tell the story of Fleming's mould and penicillin, say what a virus contains, and explain why Pasteur's swan-neck flasks stayed clear while Redi's open jars did not.

  1. 1What microbes areYou can just see something about 100 micrometres wide with the naked eye; a typical bacterium is about one hundredth of that.
  2. 2Bacteria and archaeaUnder good laboratory conditions one E. coli cell can become two in about 20 minutes.
  3. 3How fast bacteria multiplyOne cell that divides every 30 minutes would, with unlimited food, become 281,474,976,710,656 cells in 24 hours.
  4. 4Fungi and protistsIn 1928 Alexander Fleming noticed that a mold growing on one of his culture plates at St Mary’s Hospital in London had stopped the bacteria around it.
  5. 5VirusesIn 1892 Dmitri Ivanovski passed sap from sick tobacco plants through a porcelain filter that stopped all bacteria, and the sap could still make plants sick.
  6. 6How germs were discoveredIn 1668 Francesco Redi put meat in six jars, left two open, covered two with gauze and sealed two, and only the open jars grew maggots in the meat.

Related courses

  • Cells
    Every living thing is built from cells, and most of them are far too small to see. This course starts with the people who first saw cells, measures them in micrometers, takes an animal cell and a plant cell apart in 3D, and ends with how one cell becomes two. Pick an organelle in the model, cut the cell open and read the scale bar as you zoom.
  • Genetics
    A short stretch of human DNA in 3D: turn the double helix, unzip it, watch it copy itself and watch a gene being read. The course goes from genes and base pairs to chromosomes, Mendel's peas, Punnett squares, mutations and the tools used to copy, read and edit DNA. It is general information, not medical or genetic-counselling advice.
  • Evolution
    Run a natural selection lab: made-up beetles on bark of different shades, with sliders for selection pressure and mutation rate and a bar chart for each generation. The course follows Darwin and Wallace, variation and inheritance, natural selection, fossils and rock layers, family trees of life, how new species form and how humans evolved, using OpenStax Biology, the Natural History Museum in London and the Smithsonian's Human Origins Program.
  • Plants
    A 5-pound willow shoot grew into a 169-pound tree in five years while its soil lost about 2 ounces. Find out where that mass came from, change light, CO₂ and temperature in a photosynthesis lab, open a leaf, follow water from root to stoma, and see how flowers turn into seeds and fruit.
Sources for this course (15)
  • OpenStax Microbiology 1.1 What Our Ancestors Knew (fermented drink from rice, honey and fruit in Neolithic China by 7000 BC, Saccharomyces cerevisiae in bread, Leeuwenhoek 1675 "animalcules" in rain water, Golden Age of Microbiology 1857 to 1914; openstax.org/books/microbiology/pages/1-1-what-our-ancestors-knew)
  • 1.3 Types of Microorganisms (about 100 µm to see with the eye, animal cell about 10 µm, bacteria about 1 µm, viruses about 100 nm, three domains, coccus/bacillus/spirillum, archaea without peptidoglycan and in extreme places such as Morning Glory pool, protists, algae, diatoms 2 to 200 µm, protozoa with cilia, flagella or pseudopods, fungi with chitin walls, more than 1000 yeast species, molds and penicillin, helminths, prions about one-tenth of a virus; .../1-3-types-of-microorganisms)
  • 3.1 Spontaneous Generation (Aristotle, van Helmont's mice recipe of 3 weeks, Redi 1668 with six jars, Needham 1745, Spallanzani, Pasteur 1858 gun-cotton filter, swan-neck flasks, Alhumbert Prize 1862, 1864 lecture; .../3-1-spontaneous-generation)
  • 3.2 Foundations of Modern Cell Theory (Semmelweis 1847, 10 to 20 percent vs 1 percent, chlorinated lime; Snow; Pasteur 1856 fermentation; Lister 1867 carbolic acid; Koch's postulates; .../3-2-foundations-of-modern-cell-theory)
  • 6.1 Viruses (acellular, obligate intracellular parasites, DNA or RNA never both, capsid, envelope, spikes, helical/polyhedral/complex, 20 nm to 900 nm, Ivanovski 1892 with the Chamberland filter of 1884, pore 0.1 µm, Beijerinck 1898 and virus = poison, Stanley 1935, host range, bacteriophages, FDA 2006 phage spray on lunch meats; .../6-1-viruses)
  • 9.1 How Microbes Grow (binary fission, FtsZ Z ring, generation time, E. coli 20 minutes, human generation 25 years, M. tuberculosis 15 to 20 hours, M. leprae 14 days, 2^48 = 281,474,976,710,656 after 24 h at 30 minutes, Nn = N0 2^n, lag/log/stationary/death, budding, fragmentation, Epulopiscium; .../9-1-how-microbes-grow)
  • Royal Society: Philosophical Transactions 12:821-831, published 25 March 1677, Leeuwenhoek's Dutch letter of 9 October 1676 "concerning little animals" (doi.org/10.1098/rstl.1677.0003)
  • Royal Society archive EL/L1/22 (letter to Oldenburg dated at Delft, 18 pages, partial translation by Oldenburg)
  • Royal Society blog "Celebrating Leeuwenhoek", 2023 (first letter via de Graaf, Phil. Trans. 19 May 1673; 190 letters in fifty years; died 26 August 1723 aged 90)
  • N. Lane 2015, Phil. Trans. R. Soc. B 370:20140344 (upwards of 1,000,000 creatures in a drop of pepper-water; letter read aloud over several sessions)
  • Lens on Leeuwenhoek, letter L-040 (Oldenburg printed less than half; Hooke succeeded later in 1677)
  • CDC MMWR 53(34):783, 2004, 150th Anniversary of John Snow and the Pump Handle (31 August 1854, handle removed 8 September 1854, Vibrio cholerae isolated 1883; cdc.gov/mmwr/preview/mmwrhtml/mm5334a1.htm)
  • CDC History of Smallpox and Smallpox timeline (Jenner 1796; 33rd World Health Assembly declared the world free of smallpox on 8 May 1980; cdc.gov/smallpox/about/history.html)
  • American Chemical Society, Discovery and Development of Penicillin landmark (Fleming 1928 at St Mary's Hospital London, paper June 1929, Florey and Chain at Oxford from 1939; acs.org/education/whatischemistry/landmarks/flemingpenicillin.html)
  • Fleming 1929, Br J Exp Pathol 10:226. Sender, Fuchs and Milo 2016, PLoS Biol 14:e1002533 (3.8 × 10^13 bacteria and 3.0 × 10^13 human cells in a 70 kg reference man, ratio about 1.3, bacteria about 0.2 kg).

Checked: 2026-10-17