Flu vaccines need to be revised and changed every year because the flu virus constantly mutates. Flu viruses can change in two ways: drift or shift. Antigenic drift occurs when genes of the virus slowly change during replication until the immune system no longer recognizes it. On the other hand, antigenic shift occurs when a major change in the virus happens. This usually leads to a totally different kind of virus. This is what happened during the H1N1 scare in 2009.
DNA viruses like mumps are less prone to mutation due to the presence of DNA polymerase. RNA viruses are more prone to mutation because they undergo reverse transcription to simulate the role of DNA.
Answer:
Mississippian fossils are abundant in portions of the Midwest and South and include vast beds of limestone and marble.
Explanation:
For example, the domed ceiling of the Jefferson Memorial in Washington, D.C., is made of Indiana limestone that was deposited during the Mississippian Period.By the end of the Carboniferous, reptiles had migrated well toward the interior of Pangea. These early pioneers went on to spawn the archosaurs, pelycosaurs, and therapsids of the ensuing Permian period. (It was the archosaurs that went on to spawn the first dinosaurs nearly a hundred million years later.)
Well, I know logically that both life and environment change over time. So I think the answer would be C, studying fossils shows us that both life and environments change over time. Hope this helps.
Answer:
c. daytime conductive heat gain from adjacent ground surface would be greater
Explanation:
The plants in the tundra had to adapt to survive so they became short and developed closer together, this can create a sort of cushion that locks in the heat that the sun can provide, conductive heat from the adjacent soil is also taken advantage of and the leaves on the plant absorbe as much heat from the sunlight as they can, growin closer together also helps them mantain the heat.
The risk of lung cancer death is no different between medium, low, and very low-tar cigarettes.
People who smoke low-tar cigarettes compensate the lack of tar by changing their breathing habits, for example, they will take deeper drags or hold the smoke in for a longer period of time, basically negating the supposed " low-tar" effect.
