What is biological magnification and how does it relate to the health warnings given to pregnant women about the consumption of certain fish?

Biological magnification refers to a phenomenon where some of the substances like heavy metals or pesticides move up the food chain, make their way into the lakes or rivers, and are eventually consumed by aquatic species like fish. This, in turn, is further consumed by large species like large birds, humans or animals.  

This is associated with the health warnings given to pregnant women as too much eating of some kind of fish may influence the immune systems, that is, may affect the health of women who are pregnant.  

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.