Question

Nitrogen-fixing bacteria are abundant in soils and convert atmospheric nitrogen into nitrates. Plants are able to use the nitrates to synthesize plant proteins. This is an example of (A) mutualism (B) parasitism (C) commensalism (D) competition (E) tropism

Short answer

The relationship between nitrogen-fixing bacteria and plants in this context can be classified as \(A\) mutualism, as both organisms benefit from the relationship.

Step-by-step solution

Understand The Interaction

First you have to understand what interaction is going on between the two organisms. Here plants are utilizing nitrates produced by nitrogen-fixing bacteria to synthesize their proteins.

Classify The Interaction

Next you have to classify this interaction. As both are benefiting from this interaction, it can be classified as mutualistic as opposed to parasitic (where one organism benefits and the other is harmed), commensalism (one organism benefits, the other is unaffected), competition (both organisms are harmed) or tropism (growth or turning movement of a biological organism in response to an environmental stimulus).

Key concepts

Mutualism in the Nitrogen Cycle

Mutualism is a type of interaction between two different species where both participants receive benefits from their relationship. In the nitrogen cycle, mutualism is evident between plants and nitrogen-fixing bacteria.

Nitrogen-fixing bacteria convert inert atmospheric nitrogen (\( N_2 \)) into nitrates, which are a form of nitrogen that plants can readily absorb and utilize. This conversion is essential as plants cannot use atmospheric nitrogen directly. The bacteria often reside in the soil or sometimes in root nodules of plants like legumes.

In return for converting nitrogen into a plant-usable form, plants provide bacteria with carbohydrates and a habitat, essentially offering food and shelter. This win-win situation is a hallmark of mutualism:

• Plants get essential nitrates for growth and protein synthesis.
• Bacteria receive nutrients to survive and thrive within the plant environment.

This collaboration enhances the fertility of the soil, benefits plant growth, and maintains ecosystem balance.

Role of Nitrogen-Fixing Bacteria

Nitrogen-fixing bacteria play a crucial role in the nitrogen cycle by making nitrogen accessible to plants. Without these bacteria, most plants wouldn’t have access to inactive atmospheric nitrogen, which makes up about 78% of the air.

These microscopic organisms include Rhizobium species that have a symbiotic relationship with legume plants. They form root nodules where nitrogen fixation takes place. Here's a closer look at their role:

• Conversion process: Nitrogen-fixing bacteria possess an enzyme called nitrogenase that helps convert atmospheric nitrogen into ammonia (\( NH_3 \)), which is further transformed into nitrates (\( NO_3^- \)).
• Support plant growth: By transforming nitrogen to a usable form, these bacteria support plant growth by aiding in protein and nucleic acid synthesis.
• Enhance soil fertility: More usable nitrogen in the soil means better crop yields and healthier ecosystems.

Thus, their function directly strengthens the base of food chains, fundamentally supporting life on Earth.

Nitrate Assimilation in Plants

Once nitrogen-fixing bacteria have done their job, plants engage in a process called nitrate assimilation. This involves absorbing nitrates from the soil and converting them into organic molecules used for growth and development.

Plants take up nitrates through their root system. The nitrates are reduced and assimilated within the plant to form amino acids, which are the building blocks of proteins. This process is crucial for plant vitality and function:

• Protein synthesis: Nitrates are vital for synthesizing proteins that aid in plant structure and function, affecting everything from photosynthesis to reproduction.
• Growth and repair: Amino acids formed from nitrates are used in cell division and repair, essential for maintaining healthy plant tissues.
• Energy production: Nitrates contribute to the formation of enzymes and co-enzymes that are necessary for energy-producing metabolic processes.

Nitrate assimilation ensures that plants have the nutrients needed to grow robustly, setting the stage for ecosystems to flourish.