CBSE Class 11 Biology Chapter 14 Mineral Nutrition NCERT Solutions

Plants absorb various elements from their environment, but not all absorbed elements are essential for the plant's life processes. An element is considered essential if it fulfills specific criteria: it must be directly involved in the plant's metabolism, its deficiency must cause a specific physiological disorder that can be rectified by supplying the element, and it must be directly involved in the plant's nutrition. For instance, plants growing near radioactive sites may accumulate radioactive metals, or plants near mining areas might accumulate gold or selenium. However, these elements do not play any vital role in the plant's growth or survival and are therefore not essential nutrients.

Hydroponics is a technique where plants are grown without soil, using mineral nutrient solutions. In this method, the plant roots are directly immersed in a limited volume of nutrient solution. Therefore, it is crucial to purify both the water and the nutrient salts used. Purification ensures that the solution contains only the intended essential minerals in the correct concentrations and is free from any impurities or toxic substances that could interfere with plant growth or lead to erroneous experimental results. Maintaining the purity of the solution is vital for the optimal growth and health of the plants and for obtaining accurate data on mineral nutrition.

Here's an explanation of the different categories of nutrients and elements in plants:

Macronutrients: These are mineral elements required by plants in relatively large quantities. They are typically present in plant tissues at concentrations greater than 10 millimoles per kilogram (m mole kg⁻¹) of dry matter. Examples include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.

Micronutrients: Also known as trace elements, these are mineral elements required by plants in very small amounts. Their concentrations in plant tissues are usually less than 10 m mole kg⁻¹ of dry matter. Examples include iron, manganese, copper, zinc, boron, molybdenum, chlorine, and nickel.

Beneficial Nutrients: Some elements, while not strictly essential for all plants, can be beneficial for their growth, development, or physiological functions. These might include elements like sodium (Na), silicon (Si), cobalt (Co), and selenium (Se), which can play roles in specific plant species or under certain environmental conditions.

Toxic Elements: Micronutrients are needed in small quantities, but their excessive concentration can become toxic to plants. For example, high levels of manganese (Mn) can induce toxicity, leading to symptoms like chlorosis and impaired growth. Excess manganese can also interfere with the uptake and metabolism of other essential nutrients like iron, magnesium, and calcium.

Essential Elements: These are elements that are indispensable for the normal growth and reproduction of plants. Their requirement is specific, and they cannot be replaced by any other element. Essential elements are further categorized based on the quantity required as macronutrients and micronutrients.

Deficiency of essential mineral elements can lead to various visible symptoms in plants. Here are five common deficiency symptoms:

1. Chlorosis: This symptom is characterized by the yellowing of leaves, particularly in younger leaves or specific parts of older leaves. It occurs due to a reduction in chlorophyll content. Chlorosis is commonly caused by the deficiency of essential elements like nitrogen (N), potassium (K), magnesium (Mg), sulfur (S), iron (Fe), manganese (Mn), zinc (Zn), and molybdenum (Mo), as these are crucial components of chlorophyll or enzymes involved in its synthesis.
2. Necrosis: This refers to the death of plant tissues, which can appear as brown or black patches on leaves, stems, or flowers. Necrosis is often a severe symptom resulting from the deficiency of elements like calcium (Ca), magnesium (Mg), copper (Cu), and potassium (K), which are vital for maintaining cell membrane integrity and metabolic processes.
3. Inhibition of Cell Division: The growth of plants relies on cell division. A deficiency in certain minerals can significantly slow down or halt cell division, particularly in meristematic tissues like root tips and shoot apices. This is often associated with deficiencies of nitrogen (N), potassium (K), sulfur (S), and molybdenum (Mo), which are involved in nucleic acid synthesis and protein metabolism.
4. Delayed Flowering: The reproductive phase of plants, including flowering, is sensitive to nutrient availability. Delayed or reduced flowering can occur due to the deficiency of elements like nitrogen (N), sulfur (S), and molybdenum (Mo). These elements play roles in hormone synthesis and metabolic pathways essential for reproductive development.
5. Stunted Plant Growth: Overall growth retardation, where the plant remains smaller than normal, is a general symptom of nutrient deficiency. This can result from the lack of various essential elements that are critical for cell enlargement, photosynthesis, and overall metabolism. Deficiencies in elements like copper (Cu) and sulfur (S) are particularly noted to cause stunted growth, alongside deficiencies in macronutrients like nitrogen and phosphorus.