Page No: 205
Exercises
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 but all of them are not essential to its survival because they do not directly involved in the composition of their body. A nutrient is inessential for a plant if it is not directly involved in the plant’s physiology and metabolism. However, if the concentration of micronutrients such as Fe, Mn, Cu, Zn, Cl, etc., rise above their critical values, they appear to be toxic for the plant.
2.Why is purification of water and nutrient salts so important in studies involving mineral nutrition using hydroponics?
Answer
As in hydroponics, the plants are grown 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.
3. Explain with examples: macronutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.
Answer
→ Macronutrients: Elements which are present in large amounts in plant tissues are called macronutrients. They are present in plant tissues in amounts more than 10 mmole kg–1 of dry matter. Carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium are examples.
→ Micronutrients: Elements which are present in small amounts i.e. less than 10 mmole per kg of dry matter are called micronutrients. Iron, manganese, copper, molybdenum, zinc, copper, boron, chlorine and nickel are examples.
→ Beneficial Elements: The nutrients that may not be essential, but are beneficial to plants are called beneficial elements. Sodium, silicon, cobalt and selenium are examples.
→ Toxic elements: Any mineral ion concentration in tissues that reduces the dry weight of tissues by about 10 per cent is considered toxic. For example, when manganese is present in large amounts, it induces deficiencies of iron, magnesium, and calcium by interfering with their metabolism.
→ Essential elements: The elements which are absolutely necessary for plant growth and reproduction are called essential elements. The requirement of these elements is specific and non-replaceable. These elements are further divided into two broad categories based on their quantitative requirements.
4. Name at least five different deficiency symptoms in plants. Describe them and correlate them with the concerned mineral deficiency.
Answer
Five different deficiency symptoms in plants are:
→ Chlorosis is the 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.
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