Problem 65 - Objective Biology for NEET

Question

Which of the following is incorrect about \(\mathrm{NH}_{4}^{+}\) ion? (a) It is formed by the protonation of \(\mathrm{NH}_{3}\). (b) Less toxic so it can be accumulated in plants. (c) It is used to synthesize amino acid in plants. (d) All the above

Step-by-Step Solution

Answer

All the statements (a), (b) and (c) about \(\mathrm{NH}_{4}^{+}\) are correct.

Step 1: Assess statement (a)

Statement (a) states that \(\mathrm{NH}_{4}^{+}\) is formed by the protonation of \(\mathrm{NH}_{3}\). This is a correct statement. When a proton (H\(^{+}\)) is added to \(\mathrm{NH}_{3}\), it forms the \(\mathrm{NH}_{4}^{+}\) ion.

Step 2: Assess statement (b)

Statement (b) states that \(\mathrm{NH}_{4}^{+}\) is less toxic so it can be accumulated in plants. This is also a correct statement. The \(\mathrm{NH}_{4}^{+}\) ion is a source of nitrogen for plants, and high concentrations are less harmful than those of many other ions.

Step 3: Assess statement (c)

Statement (c) states that \(\mathrm{NH}_{4}^{+}\) is used to synthesize amino acids in plants. This is a correct statement. Nitrogen from \(\mathrm{NH}_{4}^{+}\) is used by plants in the synthesis of amino acids and other essential compounds.

Key Concepts

Protonation

Protonation is a fundamental concept in chemistry. It refers to the addition of a proton (H\(^{+}\)) to an atom, molecule, or ion. This process is pivotal in forming new substances and impacting reactions.
When ammonia (\(\mathrm{NH}_{3}\)) undergoes protonation, it gains a proton to become the ammonium ion (\(\mathrm{NH}_{4}^{+}\)). This transformation is crucial because it alters the properties and reactivity of the molecule.

• \(\mathrm{NH}_{3}\), neutral in charge, becomes \(\mathrm{NH}_{4}^{+}\), acquiring a positive charge.
• This change influences how the molecule interacts with other substances, including solubility and stability.

In aqueous solutions, protonation is influenced by the pH level. A higher concentration of hydrogen ions (or lower pH) can drive the reaction towards forming \(\mathrm{NH}_{4}^{+}\).
This conversion is not only a textbook example but also a step often involved in many biological and chemical processes.

Amino Acid Synthesis

Amino acid synthesis is a vital biological process. Plants, as well as other organisms, rely heavily on it for growth and metabolic functions. Ammonium ions (\(\mathrm{NH}_{4}^{+}\)) play a significant role in this process.
In plants, \(\mathrm{NH}_{4}^{+}\) provides a source of nitrogen, an element essential for building amino acids. These small organic compounds are the building blocks of proteins, which perform countless crucial tasks within organisms.

• The \((\mathrm{NH}_{4}^{+}\)) ion is readily assimilated by plant roots and transported into cells.
• Once inside, it is converted into various amino acids through enzymatic reactions.
• This synthesis process supports plant growth, development, and reproduction.

Nitrogen availability is a critical factor affecting how efficiently plants can produce amino acids. \(\mathrm{NH}_{4}^{+}\) offers a more direct and often less energy-intensive option compared to other nitrogen sources like nitrate (\(\mathrm{NO}_3^{-}\)).
This makes \(\mathrm{NH}_{4}^{+}\) an invaluable resource in both natural ecosystems and agriculture.

Nutrient Absorption in Plants

Nutrient absorption is an essential function of plants, allowing them to gather the necessary elements for their survival. The ammonium ion \(\mathrm{NH}_{4}^{+}\) is a key player in this process.
Plants absorb nutrients primarily through their roots. These roots are equipped with specialized cells that facilitate the uptake of ions like \(\mathrm{NH}_{4}^{+}\) from the soil.

• \(\mathrm{NH}_{4}^{+}\) is absorbed efficiently due to its size and charge, fitting well within the root's ion transport channels.
• Once inside, it participates in various metabolic pathways, contributing to the plant's nutritional needs.

Due to the critical role of nitrogen in plant biology, \(\mathrm{NH}_{4}^{+}\) is a highly sought-after nutrient. It supports not only amino acid and protein synthesis but also the production of nucleic acids and other vital molecules.
In managed agricultural systems, understanding and optimizing \(\mathrm{NH}_{4}^{+}\) absorption can lead to better yields and healthier crops. Advances in fertilizers and sustainable farming practices consider the balance and availability of nutrients like \(\mathrm{NH}_{4}^{+}\) to ensure efficient plant growth.