CBSE Class 11 Biology Chapter 12: Mineral Nutrition NCERT Solutions

Plants absorb various elements from the soil, but not all absorbed elements are essential for their survival and proper physiological functioning. An element is considered essential if it fulfills specific criteria, such as being directly involved in the plant's metabolism or if its absence leads to a specific deficiency symptom that can be rectified by supplying that element. For example, plants growing near radioactive waste sites may accumulate radioactive metals, or plants near mining areas might accumulate gold or selenium. However, these elements are not required for the plant's normal growth and reproduction; their presence is incidental due to the environment. Therefore, the presence of an element in a plant does not automatically imply its essentiality.

Hydroponics is a technique where plants are grown in a nutrient solution without soil. This method is crucial for studying mineral nutrition because it allows for precise control over the elements available to the plant. Purification of water and nutrient salts is vital in hydroponics for several reasons:

• Absence of Contaminants: It ensures that the nutrient solution contains only the intended mineral elements and is free from impurities or unwanted substances that could interfere with plant growth or the experimental results.
• Accurate Nutrient Concentration: Purified components help maintain the exact concentration of each essential nutrient required for optimal plant growth.
• Preventing Toxicity: Impurities in water or salts could introduce toxic elements that might harm the plants or mimic deficiency symptoms of other nutrients.
• Controlled Environment: By using purified materials, researchers can create a controlled environment to accurately determine the specific role and requirement of each mineral element for plant development.

Without purification, the results of hydroponic experiments could be misleading due to the presence of unknown or excessive elements.

Essential Elements: These are elements that are indispensable for plant growth and reproduction. Their absence causes specific deficiency symptoms, and they play a direct role in the plant's metabolism. They are broadly classified into macronutrients and micronutrients based on the quantity required.

Macronutrients: These are elements required by plants in relatively large amounts. They are present in plant tissues at concentrations greater than 10 m mole of dry matter per kilogram. Examples include Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulphur (S).

Micronutrients: Also known as trace elements, these are required by plants in very small amounts, typically less than 10 m mole of dry matter per kilogram. Despite the small quantities, they are essential for plant life. Examples include Iron (Fe), Manganese (Mn), Copper (Cu), Molybdenum (Mo), Boron (B), Zinc (Zn), Chlorine (Cl), and Nickel (Ni).

Beneficial Nutrients: These are elements that may not be essential for the overall survival of all plants but can be beneficial for the growth of certain plant species. They often play roles in specific physiological processes or help plants cope with environmental stress. Examples include Sodium (Na), Silicon (Si), Cobalt (Co), and Selenium (Se) for some higher plants.

Toxic Elements: While micronutrients are essential in trace amounts, their excessive concentration can become toxic to plants. Toxicity can disrupt normal physiological processes, inhibit growth, and even lead to plant death. For example, high levels of Manganese (Mn) can induce toxicity symptoms, such as the appearance of brown spots on leaves, and can interfere with the uptake and utilization of other essential elements like Iron (Fe), Magnesium (Mg), and Calcium (Ca).

Deficiency of essential mineral nutrients in plants leads to characteristic symptoms. Here are five common deficiency symptoms and their associated mineral deficiencies:

1. Chlorosis: This is the loss of chlorophyll in leaves, resulting in yellowing. It is a widespread symptom caused by deficiencies of essential elements like Nitrogen (N), Potassium (K), Magnesium (Mg), Sulphur (S), Iron (Fe), Manganese (Mn), and Zinc (Zn). These elements are crucial for chlorophyll synthesis or function.
2. Necrosis: This refers to the death of plant tissues, particularly leaves, stems, or flowers. It is often a severe symptom and can be caused by deficiencies of Calcium (Ca), Magnesium (Mg), Copper (Cu), and Potassium (K). For instance, Calcium deficiency can lead to the death of young leaves and growing points.
3. Inhibition of Cell Division: Essential for growth, cell division can be significantly hampered by the lack of certain nutrients. Deficiencies in Nitrogen (N), Potassium (K), Sulphur (S), and Molybdenum (Mo) can lead to reduced cell division, particularly in meristematic tissues, resulting in stunted growth.
4. Delayed Flowering: The reproductive phase of plants, including flowering, is sensitive to nutrient availability. Deficiencies of Nitrogen (N), Sulphur (S), and Molybdenum (Mo) can delay or inhibit flowering, impacting the plant's ability to complete its life cycle.
5. Stunted Plant Growth: Overall growth retardation, where the plant remains smaller than normal, is a common symptom of multiple nutrient deficiencies. Deficiencies in elements like Copper (Cu) and Sulphur (S) can severely impact cell elongation, photosynthesis, and overall biomass production, leading to stunted growth.

It is important to note that symptoms can sometimes overlap, and a single deficiency can manifest in multiple ways, while multiple deficiencies can lead to complex symptoms.