Problem 21 - Objective Biology for NEET

Question

Select the incorrect match: Element Absorbable form (a) Nitrogen \(-\mathrm{NO}_{3}^{-}, \mathrm{NO}_{2}^{-}, \mathrm{NH}_{4}^{+}\), (b) Sulphur \(\mathrm{S}^{2-}\) (c) Iron \(\mathrm{Fe}^{3+}\) (d) Boron \(-\quad \mathrm{BO}_{3}^{3-}, \mathrm{B}_{4} \mathrm{O}_{7}^{2-}\)

Step-by-Step Solution

Answer

The incorrect match is Sulphur (b) listed with the ion \(\mathrm{S}^{2-}\). The correct form of Sulphur absorbed by plants is \(\mathrm{SO}_{4}^{2-}\).

Step 1: Review the Absorption Form of Nitrogen

Plants usually absorb Nitrogen \(\mathrm{NO}_{3}^{-}, \mathrm{NO}_{2}^{-}, \mathrm{NH}_{4}^{+}\). So the first element is correctly matched.

Step 2: Review the Absorption Form of Sulphur

Sulphur is usually absorbed as sulphate ion \(\mathrm{SO}_{4}^{2-}\), not as \(\mathrm{S}^{2-}\). Therefore, this is the incorrect match as the plant can't uptake Sulphur in \(\mathrm{S}^{2-}\) form.

Step 3: Review the Absorption Forms of Iron and Boron

Although we already found the incorrectly paired element in the previous steps, it is beneficial to also review the other options for completeness. Iron is absorbed by plants in the form of \(\mathrm{Fe}^{2+}\) and \(\mathrm{Fe}^{3+}\), and Boron in the form of \(\mathrm{BO}_{3}^{3-}\) and \(\mathrm{B}_{4} \mathrm{O}_{7}^{2-}\). These both are correctly matched with their absorbable forms.

Key Concepts

Nitrogen Absorption

Nitrogen is one of the most essential nutrients for plant growth and development. Plants absorb nitrogen primarily in the form of nitrate \(\mathrm{NO}_{3}^{-}\), which is the most oxidized and readily available form in the soil. Nitrogen can also be absorbed as nitrite \(\mathrm{NO}_{2}^{-}\) and ammonium \(\mathrm{NH}_{4}^{+}\), though these forms are less common compared to nitrate.

• Nitrate \(\mathrm{NO}_{3}^{-}\) is highly soluble and is typically the dominant form of nitrogen found absorbed by plants in well-aerated soils.
• Ammonium \(\mathrm{NH}_{4}^{+}\) contributes to plant nutrition primarily in soils that have lower pH or are waterlogged.

It's crucial for nitrogen to be efficiently absorbed because it plays a vital role in forming amino acids and chlorophylls. This makes nitrogen indispensable for photosynthesis and protein synthesis.

Sulphur Absorption

Sulphur plays a key role in the formation of proteins, enzymes, and vitamins. The plant absorbs sulphur in the form of sulphate \(\mathrm{SO}_{4}^{2-}\), which is an essential anion for plant nutrition. Unlike the incorrect \(\mathrm{S}^{2-}\) form mentioned in the original solution, plants can effectively utilize the sulphate form.

• Sulphate \(\mathrm{SO}_{4}^{2-}\) travels through the plant in the xylem from roots to shoots, where it's used to synthesize essential compounds like amino acids.
• Sulphur is crucial for the synthesis of methionine and cysteine – two amino acids important for protein structure.

Deficiency in sulphur can lead to yellowing of young leaves and general stunted growth, underscoring its importance in overall plant health.

Plant Nutrition

Plant nutrition involves the uptake of nutrients by plants to support their growth and metabolic processes. The major nutrients required by plants can be categorized into macronutrients and micronutrients. Macronutrients are required in larger amounts, while micronutrients are needed in smaller quantities but are equally crucial.

• Macronutrients include elements like nitrogen, phosphorus, and potassium, which play a significant role in the functioning of plants.
• Micronutrients such as iron, manganese, and boron, though needed in trace amounts, are essential for enzymatic processes and plant metabolism.

Proper absorption and utilization of these nutrients are critical for maintaining plant vigor, enabling them to undergo photosynthesis, flower, and bear fruit efficiently. When any of these nutrients are deficient, symptoms such as chlorosis, weak structural integrity, and lower yield can occur, hence highlighting the importance of balanced plant nutrition.