Question

Deficiency symptoms of readily mobilised essential elements will first appear in (a) younger tissues (b) older tissues (c) roots (d) shoots

Short answer

Deficiency symptoms of readily mobilised essential elements will first appear in (b) older tissues.

Step-by-step solution

Identify Essential Element Characteristics

Essential elements that are readily mobilised within plants are typically translocated from older tissues to newer ones when the plant is deficient in these nutrients. These elements are often used in the growth of new tissues and, thus, are taken from the older parts where they are less needed.

Understanding Deficiency Symptoms

When a plant experiences a deficiency of mobilisable nutrients, it will show symptoms first in the parts of the plant that are given lower priority for the use of these nutrients. Since the essential elements in question are readily mobilised, it means that the plant can redistribute these nutrients from older tissues to newer ones to maintain growth and function.

Selecting the Correct Option

Based on the characteristics of mobilisable essential elements, the deficiency symptoms will first appear in the older tissues, as the plant will prioritize the newer tissues for growth and will mobilise nutrients away from the older ones, leaving them deficient first.

Key concepts

Essential Elements in Plants

Plants require various chemical elements for their growth and development, much like humans need vitamins and minerals. These are known as essential elements, and they play a critical role in a plant's life cycle. There are primarily 17 essential elements that plants obtain from the soil and their environment. These include macronutrients like nitrogen (N), phosphorus (P), and potassium (K), which are needed in larger quantities, and micronutrients like iron (Fe), manganese (Mn), and zinc (Zn), needed in smaller amounts.

Each of these elements has a unique role; for example, nitrogen is pivotal for leaf growth and chlorophyll synthesis, while potassium regulates osmotic balance. Without an adequate supply of these essential elements, plants can exhibit various physiological problems, harming their growth and survival.

Mobilisation of Nutrients

The mobilisation of nutrients within a plant refers to the movement of essential elements from one part of the plant to another. This process is crucial when the external supply of nutrients is insufficient. Plants have evolved mechanisms that allow them to allocate available nutrients to where they are most needed, often prioritizing new growth over older tissues. For instance, nitrogen is commonly mobilized from older leaves to new shoots or developing seeds, as younger tissues typically have higher metabolic demands.

Mobility of nutrients in plants varies; some are highly mobile, like nitrogen and phosphorus, while others, including calcium and boron, are immobile. This difference in nutrient mobility can significantly affect how deficiency symptoms manifest throughout the plant, which brings us to understanding the importance of recognizing such symptoms for proper plant management and care.

Deficiency Symptoms in Plants

Recognizing deficiency symptoms in plants is vital for early intervention and correction of nutrient imbalances. These symptoms often include chlorosis, or the yellowing of leaves, stunted growth, and necrosis. They emerge due to a plant's inability to fulfill its physiological and biochemical processes without the necessary elements.

As nutrients are redirected from older to younger tissues, older leaves or parts may show signs of deficiencies first. For example, a nitrogen deficiency might result in yellowing older leaves because nitrogen is transferred to support new growth. Other elements, however, like calcium, do not move around once deposited in older tissues, meaning that deficiency symptoms will appear in young growth where the element is insufficient. By observing these symptoms and understanding the mobility of specific nutrients, one can take corrective actions, such as adjusting soil pH to improve nutrient availability or applying targeted fertilizers to address specific deficiencies.