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What are the steps involved in formation of root nodule


Steps of root nodules :
(1) Rhizobium bacteria makes contact with a susceptible root hair and divide near it. 

(2) After successful infection of the root hair causes the root hair curls,

(3) Infected thread carries the bacteria to the inner cortex. The bacteria  modifies into rod-shaped bacteroids and cause inner cortical and pericycle cells to divide. Division and growth of cortical and pericycle cells lead to the nodule formation,

(4) A mature nodule forms with vascular tissues continuous with those of the root.

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If a plant shows a symptom which could develop due to the deficiency of more than one nutrient how would you find out experimentally, the real deficit mineral?

To find out if the deficiency symptom is due to the deficiency of which nutrient , in the case when more than one nutrient can cause the symptom, a number of wide mouthed bottles is taken. Each is fitted with split cork.

One of them has the normal culture and is called control. While the other bottles have deficiency of one mineral each. For example necrosis is caused by the deficiency of Ca, Mg or K. 
Thus three bottles having defieciency of Ca, Mg and K respectively is taken and the plant is grown in each.

The plants in the three bottles are checked if they have developed chlorosis. If the symptom is corrected by the supply of the particular mineral. Then it is concluded that the deficiency was because of that mineral. 

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

Macronutrients - Those nutrients that are needed by the plants in large quantities are known as macronutrients. They are generally present in the plant tissues in large amounts i.e. in excess of 10 mmole Kg-1  of dry matter. For e.g - carbon, hydrogen etc. 

Micronutrients - Are the elements which are needed by the plants in very small quantities i.e less than 10 Kg-1  of dry matter. For e.g. zinc, boron etc. 

Beneficial elements - The elements are plant nutrients that may not be essential, but are beneficial to plants. For e.g/ - Selenium is  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 element - The elements that are absolutely necessary for plant growth and reproduction. The requirement of these elements is specific and non-replaceable. For example carbon, magnesium , phosphorous , zinc etc. 

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Which of the following statements are true? If false, correct them.
1. Boron deficiency leads to stout axis.
2. Every mineral element that is present in the cell is needed by cell.
3. Nitrogen as a nutrient is highly immobile in the plants.
4. It is very easy to establish the essentiality of micronutrients, because they are required in traces.


1. True. Boron deficiency leads to stout axis.

2. False. Every mineral element present in the cell is not needed by the plant.

3. False. Nitrogen is highly mobile.

4. False. It is very difficult to establish essentiality of micronutrients because they are required in traces.

 
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How are the minerals absorbed by the plants?

Absorption of minerals : The minerals are absorbed by the plants in two ways.

1. Passive absorption through the apoplast pathway - The movement of ions generally take place through the ion channels that is the transmembrane protein that function as selective pores. It does not require energy. 

2. Active absorption through the symplast pathway - It requires the expenditure of energy. The ions are slowly into  the inner space.

 

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