Problem 5 - Objective Biology for NEET

Question

Which one of the following is Arnon's criterion for the essentiality of element? (a) In the absence of element, plants do not complete their life cycle or set the seeds. (b) Deficiency of element cannot be met by supplying other element. (c) The element must be directly involved in the metabolism of the plant.

Step-by-Step Solution

Answer

All the options (a), (b), and (c) are characteristic of Arnon's criterion for the essentiality of an element.

Step 1: Review Options

Review all the given options in the exercise and understanding the basic idea that each point represents.

Step 2: Match the Options with Arnon's Criteria

Now, match the statements with Arnon's criteria for essentiality of elements that a necessary element: \n1. Is one that the plant cannot complete its life cycle without. \n2. Cannot be replaced by another element. \n3. Is directly involved in the metabolism of the plant.

Step 3: Determine the Correct Answer

After matching, it becomes clear that all the options, i.e., (a), (b), and (c) are part of Arnon's criterion for the essentiality of an element.

Key Concepts

Essential Elements in Plants

Understanding the essential elements in plants is crucial for grasping how they grow, develop, and function. Essential elements are those that plants need to complete their life cycle and produce new seeds. According to Arnon's criterion, an element is considered essential if three conditions are met: the plant cannot complete its life cycle without it, the element cannot be replaced by another, and it is directly involved in the plant's metabolism.

For instance, nitrogen is required for the synthesis of amino acids, which in turn are the building blocks of proteins. Without nitrogen, a plant will exhibit stunted growth and yellowing leaves—a sign that it can't synthesize enough chlorophyll. Other elements like phosphorus and potassium are also critical; phosphorus is integral in energy transfer, while potassium regulates stomatal opening, affecting water use and photosynthesis.

Students often face challenges in identifying and remembering all essential elements, but a mnemonic like 'C. Hopkins Café, Mighty Good' can be helpful. It stands for Carbon, Hydrogen, Oxygen, Phosphorus, Potassium, Calcium, Iron, Magnesium, and Sulfur, which are all considered macro-nutrients and needed in larger quantities by plants.

Plant Metabolism

The metabolism of a plant includes all the biochemical processes that occur within it, necessary for its growth, reproduction, and maintenance of cellular structure. At the heart of plant metabolism lies photosynthesis, the process by which plants convert light energy into chemical energy, stored as sugars, which are then used to fuel other metabolic processes.

Diving deeper into plant metabolism, it encompasses two broad categories: catabolism, where molecules are broken down and energy is released, and anabolism, where small molecules are built into larger ones, effectively consuming energy. Plants require specific essential elements, like nitrogen, phosphorus, and potassium, for various metabolic pathways, such as DNA replication, ATP generation, and cell wall synthesis.

Nutrient Uptake and Metabolic Roles

Roots absorb essential elements from the soil, which are transported and utilized in various metabolic functions. For example, magnesium is at the core of the chlorophyll molecule and is thus indispensable for photosynthesis. Similarly, calcium stabilizes plant cell walls and is involved in cell signaling.

Nutrient Deficiency in Plants

When plants lack one or more essential elements, they exhibit specific deficiency symptoms that can hinder their growth and reproduction. Recognizing these symptoms is pivotal for diagnosing and remedying nutrient deficiencies.

Nutrient deficiency can lead to a variety of issues in plants, such as chlorosis (yellowing of leaves), necrosis (death of parts of leaves), and stunted growth. For example, a nitrogen deficiency often results in older leaves turning pale green to yellow because nitrogen is mobile in plants and shifts to support new growth. Conversely, a deficiency in a less mobile element like calcium will first appear in newer leaves or growing tips.

Preventing and Correcting Deficiencies

Regular soil testing can prevent deficiencies by indicating which nutrients are lacking so that appropriate fertilizers can be applied. It's also essential for educators to instill in students the ability to recognize symptoms associated with specific nutrient deficiencies. Engaging in case studies and practical diagnostics can improve such skills, as it's not just about knowing the element needed but applying that knowledge in real-world situations.