Problem 13 - Biology: The Unity and Diversity of Life

Question

Nitrogen fixation converts _______ to ___________. a. nitrogen gas; ammonia d. ammonia; nitrates b. nitrates; nitrites e. nitrogen gas; nitrogen c. ammonia; nitrogen gas oxides

Step-by-Step Solution

Answer

Nitrogen fixation converts nitrogen gas to ammonia; option (a) is correct.

Step 1: Understand the Process of Nitrogen Fixation

Nitrogen fixation is a biological process whereby nitrogen gas ( 2) from the atmosphere is converted into ammonia (NH3) by certain bacteria. This process is crucial for incorporating atmospheric nitrogen into organic molecules, making it available for plants and other organisms.

Step 2: Identify Key Terms

In nitrogen fixation, the key terms are 'nitrogen gas' and 'ammonia'. Nitrogen gas is the form of nitrogen in the atmosphere, and ammonia is the product of nitrogen fixation utilized by plants as a nutrient.

Step 3: Match the Terms with Options

Look through the options provided in the exercise. The correct match for 'Nitrogen fixation converts ___ to ___' is converting 'nitrogen gas' to 'ammonia'.

Step 4: Select Correct Option

Based on our breakdown, the correct answer matches option (a): nitrogen gas; ammonia. The process involves converting atmospheric nitrogen gas into a biologically usable form, which in this case is ammonia.

Key Concepts

Ammonia

Ammonia, with the formula \( NH_3 \), is a compound comprised of one nitrogen and three hydrogen atoms. It plays a critical role in the lives of plants and acts as a major form of nitrogen that plants absorb from the soil. When nitrogen gas from the atmosphere undergoes nitrogen fixation, ammonia is the primary end product. This fixed nitrogen in the form of ammonia is what plants use to create proteins and other important macromolecules.

Ammonia also serves as a precursor to many fertilizers. It is favorable for plants but in small amounts. Excess ammonia can lead to toxicity in plants, so balance is key. Importantly, ammonia's presence in the soil is due to activities often conducted by specialized bacteria found in the root nodules of legume plants, indicating an incredible relationship within ecosystems.

Nitrogen Gas

Nitrogen gas is the abundant form of nitrogen found in Earth's atmosphere, making up about 78% of it. Despite its abundance, this diatomic molecule \( N_2 \) is inert and not directly usable by most organisms. The challenge lies in the strong triple bond between the nitrogen atoms, which makes the molecule remarkably stable. This stability prevents it from reacting easily to form other compounds.

For plants and animals to utilize nitrogen, it must be "fixed" or converted into a more accessible form. This is where the process of nitrogen fixation comes in, enabling the transformation of inert nitrogen gas into ammonia. Without this conversion, life as we know it would be drastically different, as the unavailability of nitrogen would severely limit biological growth and productivity. Understanding nitrogen gas is crucial to understanding the essential cycles that sustain ecosystems.

Biological Process

A biological process refers to the various processes that occur within living organisms. Nitrogen fixation is a prime example of such a process. It is primarily a natural process carried out by certain types of bacteria, including those in the soil or symbiotically associated with plant roots. These bacteria possess an enzyme called nitrogenase, which facilitates the conversion of nitrogen gas into ammonia.

The significance of nitrogen fixation being a biological process lies in its ability to sustainably cycle nitrogen in ecosystems. It bridges the gap between free nitrogen in the atmosphere and biologically usable nitrogen in the form of ammonia, aiding in fueling the growth of plants, which are the base of most terrestrial food chains.

In agriculture, leveraging biological nitrogen fixation can reduce the need for chemical fertilizers, highlighting the importance of understanding and supporting these natural processes for environmentally-friendly farming methods.