Which of the following best describes the following characteristics: water storage, clean energy, and flood prevention? positive impact of a density-dependent limiting factor positive impact of a hurricane positive impact of beavers in an ecosystem positive impacts of dams on society

The right answer is D. Positive impacts of dams on society.

Dams create reservoirs of water on streams. Thanks to turbines, they make it possible to produce electricity of renewable origin and with very little CO2 emissions. It's hydroelectric energy. Unlike wind or solar energy, it is possible to store it (water supply) and produce electricity when it is needed, by simply controlling the opening of the valves.

From an energy and climate point of view, dams are therefore positive.

On the other hand, the same is not true for ecology and sediment flows. Indeed, each dam, whether hydroelectric or not, constitutes an obstacle for the circulation of species and sediments (sand, silt ...).

For biodiversity, and more particularly for migratory species (salmon, eels, etc.), these dams block access to breeding areas and cause the death of many individuals, even when there are fish passes.

On the other hand, dams trap sediments, which accumulate and concentrate pollutants in the water catchment. The absence of new sediments downstream of the dam can cause erosion problems that modify aquatic environments, collapse banks or nibble beaches.

Dams are therefore two-sided pieces, with a positive side (energy, climate) and a negative side (ecology, sediments).

Most restriction enzymes recognize sequences of 20-25 bp in length

Explanation:

Sequences of DNA that are recognized by restriction enzymes are called recognition (or restriction) sites are usually are between 4 and 8 bases long. Many of them are palindromic, which means that they are the same when you read it backwards and forwards (mirror-like).

Restriction enzymes are endonucleases, which means they cut phosphodiiester bonds within DNA. These enzymes are from prokaryotic organisms (archea and bacteria) which use them as defending mechanism against viruses. Prokaryotes protect their own DNA via methylation, performed by methyltransferase.