Category: Biology Second Paper

The mineral salt absorption organ of aquatic plants is not known exactly. However, submerged aquatic plants are thought to absorb mineral salts through their organs. Land plants absorb mineral salts through the young cells of rhizomes and roots. Bryophytes absorb mineral salts with rhizoids and lichens with rhizines.

Proponents of this theory, Jenny & Overstreet (1939), believe that the root shell ions and the colloidal grain shell ions are never fixed. Both ions are always vibrating. Cation exchange occurs when the ions face each other during movement.

According to this theory, CO2 is produced in the process of respiration in plant roots. CO2 reacts with water to form carbonic acid. Carbonic acid breaks down to produce hydrogen ions (H+) and bicarbonate ions (HCO3-). Exchange occurs between root H+ and soil cations and between root HCO3- and soil anions.

Mineral salts remain dissolved in the soil solution and some cations adhere to the colloidal grains. The ions attached to the colloidal granules enter the plant body through the ion exchange process. There are two theories about ion exchange. These are-
1. Carbonic acid exchange theory: According to this theory, CO2 is produced in the process of respiration in plant roots. CO2 reacts with water to form carbonic acid. Carbonic acid breaks down to produce hydrogen ions (H+) and bicarbonate ions (HCO3-). Exchange occurs between root H+ and soil cations and between root HCO3- and soil anions.
2. Cation exchange theory: Proponents of this theory, Jenny & Overstreet (1939), believe that the root shell ions and the colloidal grain shell ions are never fixed. Both ions are always vibrating. Cation exchange occurs when the ions face each other during movement.

Those elements which are specially required by certain plants are called beneficial elements. Silicon is beneficial for grass plants, sodium for C4 plants, cobalt for nitrogen-fixing leguminous plants and iodine for marine algae.

Nutrients that are required in small amounts by plants are called micronutrients. Nutrients present in amounts of 0.1 mg or less per gram of weight are called micronutrients. The number of micromoles is 8. Iron, copper, zinc, manganese, sodium, molybdenum, boron and chlorine. Sodium micromole for C4 plants.

Nutrients that are required in large quantities by plants are called macromolecules. The number of macromolecules is 9. Nutrients in amounts of 1-10 mg or more per gram of weight are called macronutrients. Macro elements are oxygen, carbon, hydrogen, phosphorus, sulphur, nitrogen, magnesium, potassium and calcium. Among them, except for carbon, hydrogen and oxygen, the remaining 6 elements are absorbed by plants from the soil. Magnesium forms chlorophyll and chlorophyll causes photosynthesis. A lack of phosphorus causes the leaves, flowers and fruits of plants to fall off. Silicon macromolecules (quantity-30) for grass plants.

The elements required for normal growth, development and survival of plants are called essential nutrients. According to scientist E. Epstein (1972), those elements that cause the normal life cycle of plants and play a role in body structure or metabolism are called essential elements. The branch of plant physiology that deals with mineral salts absorption from soil, storage, distribution to various organs and role in normal growth is called mineral nutrition. The process of absorption of mineral salts for healthy growth, physical development and replenishment of the plant body is called nutrition. 17 essential substances are essential for normal growth and physical development of plants. These elements are of two types. Macronutrients or macromolecules and micronutrients or micromolecules.

Plant physiology is mainly divided into three parts.
1. Nutrition and Metabolic Physiology
2. Growth, Development and Reproductive Physiology
3. Environmental Physiology

The word physiology is derived from the Greek words physis meaning nature and logos meaning discourse. Physiology means the discussion of nature. The branch of plant science which discusses, researches and studies various biological functions of plants is called plant physiology. In 1727, the British scientist Stephen Hales stated that plants receive some food from the atmosphere and participate in sunlight. For this reason he is called the father of plant physiology.