Correct answer: B. Bacteria. Eukaryotes and prokaryotes differ from each other in a lot of aspects. Eukaryotes contain membrane-bound organelles (eg, nucleus), while prokaryotes do not. Other important features of eukaryotes are the presence of mitochondria (creates energy in form of ATP for the cell), chloroplasts (give color to plants), cell wall, and the sophisticated structure of the chromosomal DNA. Prokaryotic cells have a so-called plasmid (a single circular chromosome) to store their genetic information, are usually unicellular. In other words, eukaryotes are more sophisticated organisms than prokaryotes.
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Bacteria are prokaryotic organisms that differ in shape (morphology), metabolism etc. These organisms are notorious for causing diseases in humans (such as pneumonia, or lung infection), but they also play an important role in the human gut flora, where they are responsible for producing vitamins which human cells cannot produce. They are also widely use in the dairy industry of cheese and yogurt through fermentation. Answer B. Yeasts are eukaryotic organisms that belong to the fungus kingdom. Example: Candida albicans, which causes yeast infections in women; they are also commonly used for the manufacturing of wine since they can convert “sugars” (glucose and fructose) which are found in grape juice into ethanol through a process called fermentation. This experiment was done by Pasteur. Answer C. Molds are also fungi, but different from yeasts, molds consist of multicellular filaments called hyphae (branching hyphae are called mycelium), whereas yeasts are single-celled. Penicillin, the first antibiotic, was extracted from a mold called Penicillium notatum by Alexander Fleming. Penicillium is also found in cheeses such as Brie and Blue cheese. Answer D. Protozoa are unicellular eukaryotes, many of which are symbionts or parasites. The main difference between protozoa and bacteria is that protozoa exchange genetic material by a process called conjugation, whereas bacteria are asexual organisms which receive the exact same genetic material from their parents. A good example is the protozoa which cause malaria, known as Plasmodium, a disease transmitted by mosquitos that cause a possibly fatal disease in humans.