Answer:
D) a genetic bottleneck
Explanation:
Genetic bottleneck refers to the sudden reduction in the population size due to some adverse climatic factors such as natural calamities. It changes the allele frequencies since the survivor population mostly have different allele frequencies than the original population.
In the given example, an earthquake kills 98% of the squirrels. The survivor population exhibits different allele frequencies for the gene responsible for the thickness of stripes. Therefore, it represents a genetic bottleneck.
There are several things that can cause water erosion. The one that is not a means of water erosion is natural springs. The correct answer is C.
Answer:
B) Nitrogen-fixing bacteria and lightning
Explanation:
Nitrogen cycle is the natural process in which atmospheric nitrogen is converted into nitrite and nitrate with the help of bacteria.
Nitrogen cycle is directly dependent on nitrogen-fixing bacteria and lightning.
As bacteria are responsible for most of the chemical conversion in the nitrogen cycle such as nitrogen fixation (first step) is done by soil bacteria (Cyanobacteria) that form ammonia, which is toxic to plants; nitrification in which ammonia is converted into nitrites and nitrates with the help of Nitrobacter and denitrification bacteria involve Pseudomonas, and Achromobacter which convert nitrite and nitrate into nitrogen.
The lightning breaks nitrogen molecules and allow it to combine with oxygen in atmosphere which further dissolve in rain and form nitrates.
Hence, the nitrogen cycle is most directly dependent upon nitrogen-fixing bacteria and lightning and the correct option is B.
