When first used in medicine in the 1940s, penicillin was uniformly effective in killing the bacterium Staphylococcus aureus. Today, has led to an increase in antibiotic-resistant alleles, and humans are increasingly at risk from untreatable Staphylococcus aureus infections.

When first used in medicine in the 1940s, penicillin was uniformly effective in killing the bacterium Staphylococcus aureus. Today, the Darwinian selection has led to an increase in antibiotic-resistant alleles, and humans are increasingly at risk from untreatable Staphylococcus aureus infections.

Explanation:

Those bacterias which were affected by the penicillin were filtered off from the environment since the offspring of those susceptible bacterias were decrease by time until total extinction.

But by the natural mutation of bacterias, some bacterias can originate a offspring of bacterias which were capable of resist the action of an antibiotic. Those genes could also be carried out by a plasmid conjugation creating new colonies which are resistant to the penicillin.  

step 1 ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. this is called nitrification. 2. step 2 the deer eats the plants and uses the nitrogen-containing proteins for cell growth. 3. step 3 bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium. 4. step 4 some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere. 5. step 5 nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification. 6. step 6 plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.

helicase, i think thats it