Ecology

Step 1: Understanding the Concept:
The question asks to identify the source material that is converted into ammonia during the process of ammonification in the nitrogen cycle.
Step 2: Detailed Explanation:
Ammonification is the process of decomposition. When plants and animals die, or when animals excrete waste, the organic matter contains complex nitrogen-containing compounds such as proteins, nucleic acids, and urea.
Microbial decomposers (bacteria and fungi) break down these complex organic molecules. Proteins are broken down into their constituent building blocks, which are amino acids.
These decomposers then metabolize the amino acids, removing the amino group (-NH\textsubscript{2}) and converting it into ammonia ( ) or ammonium ions ( ), releasing it back into the soil.
The other options are incorrect:
Nitrates and Nitrites are converted to ammonia via a different process (dissimilatory nitrate reduction), not ammonification.
Nitrogen gas ( ) is converted to ammonia via nitrogen fixation.
Step 3: Final Answer:
Ammonification is the generation of ammonia from the breakdown of organic nitrogen, primarily from amino acids derived from proteins.

Step 1: Understanding the Concept:
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems. The question requires arranging the key processes in a logical sequence.
Step 2: Detailed Explanation:
Let's trace the path of nitrogen through the ecosystem:
A. Nitrogen fixation: The cycle begins with bringing atmospheric nitrogen ( ), which is unusable by most organisms, into the ecosystem. Nitrogen-fixing bacteria convert into ammonia ( ) or ammonium ( ).
B. Nitrification: Nitrifying bacteria in the soil convert ammonium ( ) first into nitrites ( ) and then into nitrates ( ).
D. Assimilation: Plants absorb the usable forms of nitrogen (ammonium or nitrates) from the soil through their roots and incorporate them into biological molecules like proteins and nucleic acids. Animals then get nitrogen by eating plants.
E. Ammonification: When plants and animals die, decomposers (bacteria and fungi) break down their organic nitrogen compounds and release ammonium ( ) back into the soil.
C. Denitrification: Denitrifying bacteria convert nitrates ( ) back into atmospheric nitrogen gas ( ), which returns to the atmosphere, thus completing the cycle.
This logical flow corresponds to the sequence A B D E C.
Step 3: Final Answer:
The correct sequence of steps in the nitrogen cycle is Nitrogen fixation, Nitrification, Assimilation, Ammonification, and Denitrification.

Step 1: Understanding the Concept:
This question asks for the name of a specific process within the nitrogen cycle: the oxidation of ammonia to nitrates.
Step 2: Detailed Explanation:
Let's define the terms related to the nitrogen cycle:
Ammonification: The conversion of organic nitrogen from dead organisms into ammonia ( ) or ammonium ( ) by decomposers.
Assimilation: The process by which plants and other organisms absorb nitrates or ammonia from the soil and incorporate the nitrogen into their own proteins and nucleic acids.
Nitrification: This is a two-step process where ammonia/ammonium is oxidized first to nitrites ( ) by bacteria like Nitrosomonas, and then the nitrites are further oxidized to nitrates ( ) by bacteria like Nitrobacter. The overall conversion from ammonia to nitrates is called nitrification. This matches the question perfectly.
Denitrification: The process where nitrates ( ) are converted back into atmospheric nitrogen gas ( ) by denitrifying bacteria, returning nitrogen to the atmosphere.
Step 3: Final Answer:
The conversion of ammonia to nitrates is correctly termed nitrification.

Step 1: Understanding the Concept:
The question asks for the term that describes a pest management strategy based on using living organisms.
Step 2: Detailed Explanation:
Pest control methods can be broadly categorized:
Physical Control: Using barriers, traps, heat, or manual removal to manage pests.
Biological Control (Biocontrol): Using other living organisms, such as predators, parasitoids, or pathogens, to suppress a pest population. The use of a natural predator fits this definition perfectly. For example, using ladybugs to control aphids.
Chemical Control: Using synthetic pesticides or chemicals to kill pests.
Enzymatic Control: This is not a standard category of pest control. It would imply using specific enzymes, which is not what is described.
Step 3: Final Answer:
The use of natural predators to control pathogens or pests is the definition of biological control.