Explain the hygiene hypothesis and describe one example that supports it
What will be an ideal response?
The hygiene hypothesis proposes that decreasing the diversity and levels of microbes in our normal microbiota may negatively affect immune responses. (1 ) Studies performed on germ-free animals that were born and raised in microbe-free environments reveal that these animals have an underdeveloped immune system and struggle to combat pathogens. (2 ) People with chronic inflammatory disorders like irritable bowel disease (IBD) have clear shifts in the normal gut microbiota. In mouse models for IBD, Clostridia bacteria populations are especially decreased. (3 ) Pathogens face robust competition from the normal microbiota of the intestinal tract and may fail to find a niche to survive in unless the microbiota population is decreased. Clostridium difficile is a case in point of this. (4 ) Vaginal pH is kept low by lactic acid—producing bacteria called lactobacilli. A reduction in lactobacilli levels, as can occur following antibiotic therapies, leads to an increase in vaginal pH, which in turn allows the opportunistic pathogen Candida albicans (a yeast) to grow and cause a vaginal yeast infection.
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Many songbirds breed in North America in the spring and summer and then migrate to Central and South America in the fall. They spend the winter in these warmer areas, where they feed and prepare for the spring migration north and another breeding season
Two hypothetical species of sparrow, A and B, overwinter together in mixed flocks in Costa Rica. In spring, species A goes to the east coast of North America, and species B goes to the west coast. What can you say about the isolating mechanisms of these two species? A) They must have strong postzygotic isolating mechanisms to spend winter in such close proximity. B) They must have strong prezygotic isolating mechanisms to spend winter in such close proximity. C) Their winter habitat has no bearing on their degree of reproductive isolation. D) Reinforcement must be occurring when they winter together.
Which chemical group can act as an acid?
A) amino B) carbonyl C) carboxyl D) methyl
Lipids are insoluble in water because they are nonpolar.
Answer the following statement true (T) or false (F)
Mitosis and meiosis differ in a variety of ways. Which of the following is NOT a way in which both processes differ?
A) whether or not crossing over takes place B) the number of chromosomes in the daugther cells C) the number of daughter cells produced D) the stage of the cell cycle when DNA is duplicated