“Biological Classification: Three Domains, Microbes in the Laboratory and NEET Practice” is available to Standard subscribers.
Two kinds of bacteria can differ from each other as much as a bacterium differs from you. How do biologists know? In this course we read three ideas that the main chapter only touches: the three domains of life, how bacteria are stained, grown and counted in a laboratory, and how a virus takes over a cell. Then we solve harder problems and take a NEET style test.
3Lessons12Problems3Python Labs1Question Set1Mock Test
Extended reading: the three domains of life: The five kingdoms put all bacteria in Monera. By comparing the ribosomal RNA genes, Carl Woese found that the archaebacteria differ from the true bacteria as much as from the eukaryotes. In 1990 the three domains were proposed: Bacteria, Archaea and Eukarya. Archaea and Eukarya share a more recent ancestor. Monera splits into two domains, and the other four kingdoms are all in Eukarya.
Extended reading: bacteria in the laboratory: In the Gram stain, a bacterium with a thick peptidoglycan wall keeps the purple crystal violet (Gram-positive). One with a thin wall inside an outer membrane loses it and takes the pink safranin (Gram-negative). A culture grows through a lag, log, stationary and death phase. The number of live bacteria in a sample is found by dilution and plating: CFU per mL = colonies ÷ (dilution × volume plated in mL), using a plate with 30 to 300 colonies.
Extended reading: viruses in depth, and the proof of a cause: A bacteriophage multiplies by the lytic cycle: attachment, penetration, biosynthesis, assembly, and release by bursting the cell. Or it lives in the host in the lysogenic cycle, as a prophage copied with the host DNA, until induction starts the lytic cycle. One burst frees many new phages, so numbers grow very fast. Koch's postulates say how to prove that a microbe causes a disease, and viruses need a change in the second postulate.