Biology Class 11 NCERT Solutions: Chapter 12 Mineral Nutrition Part 1

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Q: 1. 'All elements that are present in a plant need not be essential to its survival'. Comment.

Answer:

Plants tend to absorb different kinds of nutrients from soil. However, a nutrient is inessential for a plant if it is not involved in the plant's physiology and metabolism. For example, plants growing near radioactive sites tend to accumulate radioactive metals. Similarly, gold and selenium get accumulated in plants growing near mining sites. However, this does not mean that radioactive metals, gold, or selenium are essential nutrients for the survival of these plants.

Q: 2. Why is purification of water and nutrient salts so important in studies involving mineral nutrition using hydroponics?

Answer:

Hydroponics is the art of growing plants in a nutrient solution in the absence of soil. Since the plant roots are exposed to a limited amount of the solution, there are chances that the concentrations of oxygen and other minerals in the plant roots would reduce. Therefore, in studies involving mineral nutrition using hydroponics, purification of water and nutrient salts is essential so as to maintain an optimum growth of the plants.

Image shows the hydroponics

Image Shows the Hydroponics

Image shows the hydroponics

Q: 3. Explain with examples: macronutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.

Answer:

Macronutrients: They are the nutrients required by plants in large amounts. They are present in plant tissues in amounts more than of dry matter. Examples include hydrogen, oxygen, and nitrogen.

Micronutrients: They are also called trace elements and are present in plant bodies in very small amounts, i.e., amounts less than of dry matter. Examples include cobalt, manganese, zinc, etc.

Image of the macronutrients and micronutrients

Image of the Macronutrients and Micronutrients

Image of the macronutrients and micronutrients

Beneficial nutrients: They are plant nutrients that may not be essential, but are beneficial to plants. Sodium, silicon, cobalt, and selenium are beneficial to higher plants.

Toxic elements: Micronutrients are required by plants in small quantities. An excess of these nutrients may induce toxicity in plants. For example, when manganese is present in large amounts, it induces deficiencies of iron, magnesium, and calcium by interfering with their metabolism.

Essential elements: These elements are absolutely necessary for plant growth and reproduction. The requirement of these elements is specific and non-replaceable. They are further classified as macro and micronutrients.

Q: 4. Name at least five different deficiency symptoms in plants. Describe them and correlate them with the concerned mineral deficiency.

Answer:

The five main deficiency symptoms arising in plants are:

Five main deficiency symptoms arising in plants

Five Main Deficiency Symptoms Arising in Plants

Five main deficiency symptoms arising in plants

Chlorosis or loss of chlorophyll leads to the yellowing of leaves. It is caused by the deficiencies of nitrogen, potassium, magnesium, sulphur, iron, manganese, zinc, and molybdenum.

Necrosis is the death of plant tissues as a result of the deficiencies of calcium, magnesium, copper, and potassium.

Inhibition of cell division is caused by the deficiencies of nitrogen, potassium, sulphur, and molybdenum.

Delayed flowering is caused by the deficiencies of nitrogen, sulphur, and molybdenum.

Stunted plant growth is a result of the deficiencies of copper and sulphur.

Q: 5. If a plant shows a symptom which could develop due to deficiency of more than one nutrient, how would you find out experimentally, the real deficient mineral element?

Answer:

In plants, the deficiency of a nutrient can cause multiple symptoms. For example, the deficiency of nitrogen causes chlorosis and delayed flowering. In a similar way, the deficiency of a nutrient can cause the same symptom as that caused by the deficiency of another nutrient. For example, necrosis is caused by the deficiency of calcium, magnesium, copper, and potassium.

Another point to be considered is that different plants respond in different ways to the deficiency of the same nutrient.

Hence, to identify the nutrient deficient in a plant, all the symptoms developed in its different parts must be studied and compared with the available standard tables.

Q: 6. Why is that in certain plants deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs?

Answer:

Deficiency symptoms are morphological changes in plants, indicating nutrient deficiency. Deficiency symptoms vary from one element to another. The plant part in which a deficiency symptom occurs depends on the mobility of the deficient element in the plant. Elements such as nitrogen, potassium, and magnesium are highly mobile. These elements move from the mature organs to the younger parts of a plant. Therefore, the symptoms for the deficiencies of these elements first appear in the older parts of the plant. Elements such as calcium and sulphur are relatively immobile. These elements are not transported out of the older parts of a plant. Therefore, the symptoms for the deficiencies of these elements first appear in the younger parts of the plant.

Q: 7. How are the minerals absorbed by the plants?

Answer:

The absorption of soil nutrients by the roots of plants occurs in two main phases - apoplast and symplast.

During the initial phase or apoplast, there is a rapid uptake of nutrients from the soil into the free spaces of plant cells. This process is passive and it usually occurs through trans-membrane proteins and ion-channels.

In the second phase or symplast, the ions are taken slowly into the inner spaces of the cells. This pathway generally involves the expenditure of energy in the form of ATP.