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For about 100 years, scientists thought that peptic ulcers were caused by stress, spicy food, and alcohol. Later, researchers added stomach acid to the list of causes and began treating ulcers with antacids. Now it is known that peptic ulcers are predominantly caused by Helicobacter pylori, a spiral-shaped bacterium that normally exist in the stomach.
The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
Amoebae are the simplest type of protozoans, and are characterized by a feeding and dividing trophozoite stage that moves by temporary extensions called pseudopodia or false feet.
In women, pharmacodynamic differences include increased sensitivity to (and increased effectiveness of) beta-blockers, opioids, selective serotonin reuptake inhibitors, and typical antipsychotics.
![Normal development of posture and spinal curves. (A) Toddler: Protruding abdomen; lumbar lordosis. (](https://biology-forums.com/gallery/47/medium_14755_24_09_12_7_41_29_8960395.jpeg)
![Deciduous and permanent teeth. (A) The deciduous teeth, with the age of eruption given in months; (B](https://biology-forums.com/gallery/47/medium_14755_30_09_12_4_39_18_91421720.jpeg)