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Essential Nutrients of Plants

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Essential Nutrients of Plants - Lesson Summary

Plants and animals require nourishment for growth. This nourishment is provided to them in the form of chemical substances called nutrients. Nourishment is the process of absorption of various mineral ions by plants for their growth and development. Plants absorb inorganic elements like hydrogen, oxygen, carbon and nitrogen from air or water. Water absorbed from the soil contains dissolved nutrients like nitrogen, phosphorus, potassium, calcium and magnesium, amongst others. As the sources of these inorganic elements are minerals, the elements are called mineral nutrients, and thus, the nutrition is known as mineral nutrition.

Roots absorb sixty of the hundred and five elements found in nature. However, only 17 of them are considered essential for plant growth and development.

In 1939, Arnon and Stout proposed the characters that make an element essential to a plant.

(a) The element must be absolutely essential for supporting normal growth and reproduction, which cannot proceed without it.
(b) The requirement of the element must be specific and cannot be replaceable by another element.
(c) The element must be directly involved in the metabolism of the plant.

Based on the above criteria, the essential elements are further divided into:
(i) Macronutrients, and (ii) Micronutrients

The elements that are required by a plant in large amounts are called macronutrients. Carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium are macronutrients. Of these, carbon, hydrogen and oxygen are mainly obtained from CO 2 and H 2O, while the others are absorbed from the soil.

The elements that are required in minute quantities are called micronutrients or trace elements. Iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel are examples of micronutrients. In addition to the 17 essential elements, there are some beneficial elements such as sodium, silicon, cobalt and selenium. Higher plants require them for their metabolism.

Essential elements have different functions, based on which they are classified as  structural elements of cells, components of energy releasing chemical compounds, activator or inhibitor of enzymes, and elements that maintain osmotic potential. Elements like carbon, hydrogen, oxygen and nitrogen are the components of biomolecules that are essential to a plant.

Elements like magnesium and phosphorous are the components of energy-releasing chemical compounds like chlorophyll and ATP. Magnesium is an activator for certain enzymes like Ribulose biphosphate. Potassium is responsible for the opening and closing of the stomata. Minerals play an important role in maintaining the water potential of a cell.

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