Model Essay Paragraphs

AO1:

The importance of interactions between organisms is evident in the nitrogen cycle where organisms like saprobionts interact with the environment and nitrifying bacteria to produce nitrates for plants. When plants or animals die, the nitrogen found within them in the form of DNA/ATP/amino acids gets released back into the soil via decomposers (saprobionts) and also when animals excrete urea. Decomposition releases ammonia which gets converted into ammonium ions in the soil via ammonification. Nitrifying bacteria then convert the ammonium ions into nitrites and then nitrates in a series of oxidation reactions. These nitrates are then taken up by the plant using active transport. Although these nitrates are needed by the plant for the creation of DNA/ATP/amino acids, the active transport of them into the roots also lowers the water potential of the roots, more importantly making it lower than the water potential of the soil, meaning more water enters the roots via osmosis. Mutualistic nitrogen fixing bacteria also interact with leguminous plants via attaching to their root nodules. They `fix` nitrogen gas into ammonia and give that to the plant. In exchange the plant gives the bacteria carbohydrates so both organisms benefit, hence the mutualistic relationship. Fungi called mycorhizae also have a mutualistic relationship with plants but work slightly differently by attaching to the roots and increasing the surface area of the roots to increase the amount of water taken in via osmosis.

AO2:

The importance of the interactions between organisms in the nitrogen cycle is to eventually allow the uptake of nitrates into plants which can then be converted into amino acids to make proteins during translation. The amino acids are brought to the ribosome, specifically the mRNA strand by a tRNA molecule which has a complementary anticodon to the codon on the mRNA strand. Once two amino acids are present a peptide bond can form between them using the enzyme peptidyl transferase which is found in ribosomes and this process continues until a stop codon is reached to ultimately produce a protein such as enzymes which would not be able to be produced without the amino acids that were synthesized from nitrates.