Important Topic Of Biology: Mineral Nutrition

Every organism in this world needs nutrition. The meaning of the word “Nutrition” is those substances or chemicals which are essentially required by our body for survival. We eat food to break it down to all these essential elements as our body cannot synthesize them. 

Plants extract these minerals through the soil. Other organisms take minerals through their environment (air, water, soil, etc) a well. This article contains important information about types of minerals in food and various essential minerals for the body.

A brief note:

Search for various essential minerals for the body:

• Now the treasure run for finding these important minerals started and our first scientist to work on it was Julius Von Sachs.
• He put a plant in a mineral solution, a solution that might or might not contain all the minerals required by the plant.
• He studied the effects of the same – if the plant showed no symptom at all, the plant got all the important minerals to survive, if not, the symptom was studied and the mineral responsible for the symptom was identified.
• This is how we got a list of important minerals used by the plant to grow. The technique we used earlier (bathing the plant in a mineral solution)is called “Hydroponics”.

Criteria for essentiality:

Just as we humans eat junk food, food that might be harmful or unnecessary for the body), plants also intake minerals that are not very essential for their survival.

After we got to know that around sixty elements like gold, selenium, and even radioactive strontium were found in plants, we had to build criteria for what minerals are absolutely essential for plants, or without which the plant will die. These criteria were –

• The element must be essential for the reproduction and growth of plants.
• The deficiency of that element cannot be replaced by supplementing some other elements.
• Plants must use the element in metabolic processes.

After all the research work, minerals were cut down to two main categories –

• Macro Minerals (Macronutrients)

Minerals present in more than 10 mmol Kg –1 in dry matter (or present in large amounts). These are carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium,calcium, and magnesium.

• Micro Minerals (Micronutrients)

Minerals present in less than 10 mmol Kg –1 in dry matter (present in less amount). These are iron, manganese, copper, molybdenum, zinc, boron, chlorine, and nickel.

Some important minerals are –

• Carbon, Hydrogen, and Oxygen make up most biochemical structures.
• Magnesium is present in chlorophyll and phosphorus is present in ATP.
• Magnesium, Zinc, and Molybdenum are the activators of important enzymes RuBisCO, Alcohol dehydrogenase, and Nitrogenase respectively.
• Potassium is used in the opening and closing of stomata.

Roles of some Essential Minerals:

• Nitrogen – It is absorbed as nitrite, nitrate, or ammonium form. Used in the plant for protein formation, nucleic acid, vitamin, and hormone formation. It is a mineral found in plants in large amounts.
• Phosphorus – Absorbed in the form of phosphate ions. Used information of cell membrane, nucleic acid, protein, ATP, and nucleotides.
• Calcium – Absorbed in the form of Calcium ions. Used at the time of cell division for cell wall formation. Helps in the formation of mitotic spindles, cell membranes as well.
• Magnesium – Absorbed in the form of Magnesium ion. Used as an activator for respiration and photosynthetic enzymes. Also, Mg is a structural mineral present in Chlorophyll and helps in maintaining ribosomal structure.
• Sulfur – Absorbed as Sulphate ion. Present in cysteine and methionine amino acids. Sulfur is a structural mineral for various coenzymes, vitamins, and ferredoxin.
• Iron – Absorbed in the form of ferric ions. It is a structural element for ferredoxin and cytochromes. It also helps in activating catalase enzymes.
• Zinc – Absorbed in the form of Zn ions. It is used in the formation of the hormone auxin.
• Copper – Absorbed in the form of Cupric ions. It is required for metabolic processes and is used in redox reactions.

Deficiency of Elements:

• When the concentration of elements goes to a point where plant growth is retarded, this concentration is referred to as “Critical Concentration”.
• Due to deficiency of minerals, the plant shows physical changes referred to as ‘Deficiency Symptoms’.
• These symptoms go away when the required mineral is provided to the plant.
• The need for minerals is most during the initial growth of a plant when the plant is young.
• Chlorosis: The yellowing of leaves due to chlorophyll loss is caused by deficiency of N, K, Mg, S, Fe, Mn, Zn, and Mo.
• Necrosis: Death of leaf tissues is caused due to lack of Ca, Mg, Cu, K.
• Inhibition of Cell Division: Caused due to lack of N, K, S, Mo.
• Delay in Flowering: Caused due to lack of N, S, Mo.

Toxicity of Micro Minerals

• When minerals that are required in low amounts are absorbed in a large quantity, this condition is known as Toxicity.
• For instance, Manganese competes with iron, calcium, and magnesium and when it is present in toxic amounts, many diseases are observed.

Absorption and translocation of Minerals and Solutes:

• The free and rapid uptake of ions is “Passive” into the apoplast of the plant cell with the help of ion channels and selective pores.
• Exit or entry of ions through the symplast of the plant cell takes place “Actively” with the help of pumps by energy expenditure.
• Minerals are translocated in the plant with the help of the “Xylem”.

Nitrogen uptake:

• Since Nitrogen is the most abundant mineral present in plants, it’s important to observe how it is absorbed by plants.
• Nitrogen has three covalent bonds and they are fixed by converting this nitrogen into ammonia by “Nitrogen Fixation”.
• Nitrogen present in dead decaying plants and animals converts to Ammonia is called Ammonification.
• Chemoautotrophs convert this ammonia to nitrite and then nitrate which is absorbed by plants.
• The conversion of Nitrate to Nitrogen by bacteria is called “Denitrification”.

Bacterial Nitrogen Fixation:

• Free-living bacteria (Azotobacter, Rhodospirillum) help in converting Nitrogen to Ammonia by an enzyme “Nitrogenase” (but it is a little sensitive to oxygen so a compound known as Leg-Haemoglobin helps in preventing the interaction between oxygen and nitrogenase).
• Symbiotic bacteria (Rhizobium, Frankia) found in association with Leguminous and Non Leguminous plants respectively help in nitrogen fixation by the formation of nodules within these plants.
• The ammonia produced after these processes is used by the cells of plants to incorporate into amino acids.