Questions - Answers 
 

Very Short Answer Type Questions 
 

1. Define hydroponics.
A: The technique of growing plants in a standard, specific, nutritional liquid medium or solution without or outside the soil is called Hydroponics. It was first started by Julius von Sachs. It is also called soil - less culture or solution culture.
 

2. How do you categorise a particular essential element as a macro or micro nutrient?
A:  The essential element which is required in large amounts (more than 10 m mole kg^-1 of dry matter) and forms a part of the protoplasm is called macro nutrient or major element.
e.g.: Mg, Ca.
The essential element which is required in less amounts (less than 10 m mole kg^-1 of dry matter) is called micro or minor or trace element. It do not forms a constituent of the protoplasm.
e.g.: Fd, Zn.

3. Give examples two essential elements that act as activators for enzymes.
A:  Iron - Minor element - Activator for Catalase.
Manganese - Minor element - Activator for IAA Oxidase.

4. Name the essential mineral elements that play an important role in photolysis of water.
A: Calcium, Manganese and Chlorine play important role in photolysis of water. Chlorine is not a mineral element.

5. Out of the 17 essential elements, which elements are called non - mineral essential elements.
A: Carbon, Hydrogen, Oxygen are non - mineral, essential macro elements. They are absorbed in the form of CO₂, H₂O and O₂. Thus out of 17 essential elements/ are non - mineral essential elements.

6. Name Z amino acids in which Sulphur is present.
A: Cysteine, Cystine and Methionine consist Sulphur.

7. When is an essential element said to be deficient?
A: The concentration of the essential element below which plant growth is retarded is termed as critical concentration. The element is said to be deficient when present below the critical concentration.

8. Name 2 elements whose deficiency symptoms first appear in young leaves.
A: Deficiency symptoms of Sulphur and Calcium first appear in young leaves as they are not mobile elements.

9. Explain the role of pink colour pigment in the root nodules of legume plants. What is it called?
A: The pink colour pigment protects nitrogenase enzyme from Oxygen. It is called Leg - haemoglobin. It is an Oxygen scavenger.

10. Excess Mn in soils leads to deficiency of Ca, Mg and Fe. Justify.
A: Manganese competes with Iron and Magnesium for Uptake Manganese competes with Magnesium for binding with Enzyme. Manganese inhibits the translocation of Calcium in the shoot apex. Therefore excess of Mn in soil leads to the deficiency of Ca, Mg & Fe.

11. What acts as a reservoir of essential elements for plants? By what process it is formed?
A: Soil is reservoir of essential elements for plants. They are formed physical weathering and break down of rocks.

12. Which element is regarded as the 17th essential element? Name a disease caused by its deficiency.
A: Nickel is the 17th essential element. The physiological disease caused by its deficiency is Mouse ear in Barley.

Short Answer Type Questions

1.'All elements that are present in a plant need not be essential for its survival'. Justify.
A: Plants absorb 60 or even more mineral elements from the soil. All 60 are not present in one plant. In the same way all elements present in a plant are useful to it. Only the useful elements are called essential elements. There are some essential elements also.

2. Name at least 5 different deficiency symptoms in plants. Describe them, and correlate them with concerned mineral deficiency.
A: Deficiency symptoms of
1) Zinc
* Little leaf disease
* Leaf rosette
* Mottled leaf
* Interveinal chlorosis - Necrosis.
Zinc is a mobile, micro mineral essential element. It is an activator for Carboxylase. It is needed for the synthesis of Auxins. It is absorbed in the form of Zn2+
2) Copper
* Die back disease of shoots in Citrus
* Necrosis of young leaf tips.
* Exanthema
* Reclamation disease of cereals and legumes.
* Blackening potato tubers.
3) Boron
* Heart rot in beets (Brown heart)
* Water core in turnip
* Heart rot in Carrot
* Fibres in apple fruit
* Death of root tip and stem tip
4) Molybdenum
* Whiptail disease in Cauliflower
* Intervenal chlorosis
* Inhibition of flowering
* Mottled chlorosis
* Upper half leaf shows withering
5) Chlorine
* Bronzing in legumes
* Flower abscission
* Swollen root tips

3. Explain the steps involved in the formation of root nodule.
A: The following steps are observed in the formation of root nodules
* Bacteria are attracted by sugars, amino acids and flavonoids secreted by the roots of Leguminous plants.
* Legumes select compatible strains of Rhizobium by specific proteins called Lectins.
* Bacteria multiply and secrete curling factor. Root hairs show curting which is called Shepherds crook.
* Bacteria invade the root hair and produce cellulase, Pectinase to digest the cell wall.
* Bacteria breach the cell wall. Plasma membrane invaginates forms infection thread and carries bacteria into Cortical cell.
* Cortical cells produce Auxins multiply and root nodule is formed into which bacteria are released.
* Bacteria also stimulate pericycle cells to divide.
* The nodule develops vascular connection.
* It consists leghaemoglobin (Pink coloured), Nitrogenase. The bacterial cells in the nodule become spherical & called bacteriod.

4. Some angiospermic plants have adapted to absorb molecular nitrogen from atmosphere. Explain citing 2 examples.
A: Leguminaceae members and some plant like Myrica, Alnus, Casuarina have adapted to absorb molecular Nitrogen with the help of bacteria. It occurs through symbiotic Nitrogen fixation. Rhizobium fixes molecular Nitrogen to legumes and also to a non - leguminous member called Parasponia. Filamentous, Actinomycetus bacteria like Frankia fixes atmospheric molecular Nitrogen in Alnus, Casuarina and Myrica. Nostoc fixes Nitrogen in the Stem glands of Gunnera. Azospirillum, an associated symbiont fixes nitrogen in Maize, Sorghum, Wheat, Barley and Finger millets.

5. What will happen if a healthy plant is supplied with excess essential elements.
A: If excess of Nitrogen is supplied to a healthy plant its vegetative growth is more but reproductive growth is inhibited. It results in poor yield. Moderate increase in the concentration of micro nutrients causes toxicity. Any mineral ion concentration in tissues that reduces dry weight of tissues by about 10% is considered toxic. Excess of one element may inhibibit the uptake of another element. Excess of Manganese shows Brown spots in the leaf surrounded by Chlorotic veins. Excess of Manganese competes with other micro elements (Fe, Ca and Mg) and inhibits their uptake. So symptoms of Mn toxicity also results in the deficiency symptoms of Fe, Ca and Mg.

6. Explain in brief how plants absorb essential elements?
A: Plants absorb mineral elements in the form of cations and anions. It occurs both day and night. The part of the root below the root hairs which consists young cells is useful in mineral absorption. All essential elements except C, H and O₂ are absorbed from soil.
There are steps in mineral absorption.
 

1) First Step:
Minerals from the soil enter into apoplast or free space (cell wall and inter cellular spaces). It is a passive process.
 

2) Second Step:
Mineral elements pass from apoplast to symplast or inner space. It may be active.
The movement of ions is called flux. Movement of the ions into the cells is called influx, and outward movement is called efflux.
 

Passive Absorption
It do not requires metabolic energy. So it is independent of metabolism of the plant. It occurs according to concentration gradient. It is rapid. It occurs by diffusion or mass flow or ionic exchange (Donna's equilibrium)
 

Active absorption
It requires metabolic energy (ATP). Plants absorb more salts in the form ions by active absorption. It occurs against to the concentration gradient. Proteins present in the plasma membrane act as carriers or channels for efflux and influx. Carriers are specific.

7. Nitrogen is fixed into the soil not only by biological processes. Elaborate.
A. Fixation of Nitrogen:
Conversion of atmospheric molecular Nitrogen to Ammonia is called Nitrogen fixation. If it occurs without the involvement of micro organisms, it is called Abiological Nitrogen fixation. It is rare or it is very less. It is Physico - chemical process.
Thunders and lightening produce much energy. It is useful to convert
N₂ + O_2 →  2 NO (Nitric Oxide)
2 NO + O_2→ 2 NO₂ (Nitrogen dioxide)
These Oxides dissolve in rain water that follows thunders.
2 NO₂ + 2 H₂O _→ HNO + HNO₂
2 NO₂ + H₂O _→ HNO₃ (Nitric oxide) + HNO₂ (Nitrous oxide)
These oxides dissolve in water and form nitrous and nitric acids. These acids react with alkali radicals in the soil and form nitrates. These are soluble and directly taken by the plants.
Ozonisation, industrial combustions, forest fires, automobile exhausts and power generating stations are also sources through which Nitrogen oxides are formed.
Industrially NH₃ is produced by Haber - Bosch process at 450°C with 100 bars of pressure. Urea is also produced. It is another form of Nitrogen absorbed by plants.