Concept 27.4

Question:
I. Although individual prokaryotes may be tiny, they are giants in their collective impact on Earth and its life. Explain.

Answer:
a) Although prokaryotes are small, mostly unicellular organisms, they play key roles in ecosystems by decomposing wastes, recycling chemicals, and providing nutrients to other organisms.

Question:
II. Explain how the relationship between humans and B. thetaiotaomicron is an example of mutualism.

Answer:
a) This bacteria, B. thetaiotaomicron, includes a large array of genes involved in synthesizing carbohydrates, vitamins, and other nutrients needed by humans. Signals form the bacterium activate human genes that build the network of intestinal blood vessels necessary to absorb food. Other signal induce human cells to produce antimicrobial compounds to which B. thetaiotaomicron is not susceptible. Keeping other competing bacteria out of the intestines benefits B. thetaiotaomicron as well as its human host.
b)Bacteroides thetaiotatomicron, which lives inside the human intestine, benefits by obtaining nutrients from the digestive system and by receiving protection from competing bacteria from host-produced antimicrobial compounds to which it is not sensitive. The human host benefits because the manufactures carbohydrates, vitamins and other nutrients.