NCERT solutions- Mineral nutrition Class 11 Notes | EduRev

Class 11 : NCERT solutions- Mineral nutrition Class 11 Notes | EduRev

 Page 1


Mineral Nutrition 
Question 1. ‘All elements that are present in a plant need not be essential to its 
survival’. Comment. 
Answer: - The criteria for essentiality of an element are given below: 
(a) The element must be absolutely necessary for supporting normal growth and 
reproduction. In the absence of the element the plants do not complete their life 
cycle or set the seeds. 
(b) The requirement of the element must be specific and not replaceable by another 
element. In other words, deficiency of any one element cannot be met by supplying 
some other element. 
(c) The element must be directly involved in the metabolism of the plant. 
All elements that are present in a plant do not fulfill these criteria hence cannot be 
essential for plant survival. 
Question 2. Why is purification of water and nutrient salts so important in 
studies involving mineral nutrition using hydroponics. 
Answer: - In 1860, Julius von Sachs, a prominent German botanist, demonstrated, 
for the first time, that plants could be grown to maturity in a defined nutrient solution 
in complete absence of soil. The essence of all these methods involves the culture of 
plants in a soil-free, defined mineral solution. These methods require purified water 
and mineral nutrient salts. 
Purification of water and nutrient salt is important to rule out other influencing factors. 
The presence of pure nutrients will give the clear cut scientific results. This will help 
in making a sound basis for the right prediction. 
Question 3. Explain with examples: macronutrients, micronutrients, beneficial 
nutrients, toxic elements and essential elements. 
Answer: - 
Macronutrients: Macronutrients are generally present in plant tissues in large 
amounts (in excess of 10 mmole Kg
–1
 of dry matter). The macronutrients include 
carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and 
magnesium. Of these, carbon, hydrogen and oxygen are mainly obtained from 
CO
2
 and H
2
O, while the others are absorbed from the soil as mineral nutrition. 
Micronutrients: Micronutrients or trace elements, are needed in very small amounts 
(less than 10 mmole Kg
–1
 of dry matter). These include iron, manganese, copper, 
molybdenum, zinc, boron, chlorine and nickel. 
Page 2


Mineral Nutrition 
Question 1. ‘All elements that are present in a plant need not be essential to its 
survival’. Comment. 
Answer: - The criteria for essentiality of an element are given below: 
(a) The element must be absolutely necessary for supporting normal growth and 
reproduction. In the absence of the element the plants do not complete their life 
cycle or set the seeds. 
(b) The requirement of the element must be specific and not replaceable by another 
element. In other words, deficiency of any one element cannot be met by supplying 
some other element. 
(c) The element must be directly involved in the metabolism of the plant. 
All elements that are present in a plant do not fulfill these criteria hence cannot be 
essential for plant survival. 
Question 2. Why is purification of water and nutrient salts so important in 
studies involving mineral nutrition using hydroponics. 
Answer: - In 1860, Julius von Sachs, a prominent German botanist, demonstrated, 
for the first time, that plants could be grown to maturity in a defined nutrient solution 
in complete absence of soil. The essence of all these methods involves the culture of 
plants in a soil-free, defined mineral solution. These methods require purified water 
and mineral nutrient salts. 
Purification of water and nutrient salt is important to rule out other influencing factors. 
The presence of pure nutrients will give the clear cut scientific results. This will help 
in making a sound basis for the right prediction. 
Question 3. Explain with examples: macronutrients, micronutrients, beneficial 
nutrients, toxic elements and essential elements. 
Answer: - 
Macronutrients: Macronutrients are generally present in plant tissues in large 
amounts (in excess of 10 mmole Kg
–1
 of dry matter). The macronutrients include 
carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and 
magnesium. Of these, carbon, hydrogen and oxygen are mainly obtained from 
CO
2
 and H
2
O, while the others are absorbed from the soil as mineral nutrition. 
Micronutrients: Micronutrients or trace elements, are needed in very small amounts 
(less than 10 mmole Kg
–1
 of dry matter). These include iron, manganese, copper, 
molybdenum, zinc, boron, chlorine and nickel. 
Beneficial Elements: In addition to the 17 essential elements named above, there 
are some beneficial elements such as sodium, silicon, cobalt and selenium. They are 
required by higher plants. 
Toxic Elements: The requirement of micronutrients is always in low amounts while 
their moderate decrease causes the deficiency symptoms and a moderate increase 
causes toxicity. In other words, there is a narrow range of concentration at which the 
elements are optimum. Any mineral ion concentration in tissues that reduces the dry 
weight of tissues by about 10 per cent is considered toxic. Such critical 
concentrations vary widely among different micronutrients. The toxicity symptoms 
are difficult to identify. Toxicity levels for any element also vary for different plants. 
Question 4. Name at least five different deficiency symptoms in plants. 
Describe them and correlate them with the concerned mineral deficiency. 
Answer: 
Iron Deficiency: 
Iron (Fe) deficiency is a plant disorder also known as "lime-induced chlorosis". It can 
be confused with manganese deficiency. A deficiency in the soil is rare but iron can 
be unavailable for absorption if soil pH is not between about 5 and 6.5. A common 
problem is when the soil is too alkaline (the pH is above 6.5). Also, iron deficiency 
can develop if the soil is too waterlogged or has been overfertilised. Elements like 
calcium, zinc, manganese, phosphorus, or copper can tie up iron if they are present 
in high amounts. 
Iron is needed to produce chlorophyll, hence its deficiency causes chlorosis. For 
example, iron is used in the active site of glutamyl-tRNA reductase, an enzyme 
needed for the formation of 5-Aminolevulinic acid which is a precursor of heme and 
chlorophyll. 
Symptoms: Symptoms include leaves turning yellow or brown in the margins 
between the veins which may remain green, while young leaves may appear to be 
bleached. Fruit would be of poor quality and quantity. Any plant may be affected, but 
raspberries and pears are particularly susceptible, as well as most acid-loving plants 
such as azaleas and camellias. 
Treatment: Iron deficiency can be avoided by choosing appropriate soil for the 
growing conditions (e.g., avoid growing acid loving plants on lime soils), or by adding 
well-rotted manure or compost. 
Potassium Deficiency: 
Plants require potassium ions (K
+
) for protein synthesis and for the opening and 
closing of stomata, which is regulated by proton pumps to make surrounding guard 
cells either turgid or flaccid. A deficiency of potassium ions can impair a plant's ability 
to maintain these processes. 
Page 3


Mineral Nutrition 
Question 1. ‘All elements that are present in a plant need not be essential to its 
survival’. Comment. 
Answer: - The criteria for essentiality of an element are given below: 
(a) The element must be absolutely necessary for supporting normal growth and 
reproduction. In the absence of the element the plants do not complete their life 
cycle or set the seeds. 
(b) The requirement of the element must be specific and not replaceable by another 
element. In other words, deficiency of any one element cannot be met by supplying 
some other element. 
(c) The element must be directly involved in the metabolism of the plant. 
All elements that are present in a plant do not fulfill these criteria hence cannot be 
essential for plant survival. 
Question 2. Why is purification of water and nutrient salts so important in 
studies involving mineral nutrition using hydroponics. 
Answer: - In 1860, Julius von Sachs, a prominent German botanist, demonstrated, 
for the first time, that plants could be grown to maturity in a defined nutrient solution 
in complete absence of soil. The essence of all these methods involves the culture of 
plants in a soil-free, defined mineral solution. These methods require purified water 
and mineral nutrient salts. 
Purification of water and nutrient salt is important to rule out other influencing factors. 
The presence of pure nutrients will give the clear cut scientific results. This will help 
in making a sound basis for the right prediction. 
Question 3. Explain with examples: macronutrients, micronutrients, beneficial 
nutrients, toxic elements and essential elements. 
Answer: - 
Macronutrients: Macronutrients are generally present in plant tissues in large 
amounts (in excess of 10 mmole Kg
–1
 of dry matter). The macronutrients include 
carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and 
magnesium. Of these, carbon, hydrogen and oxygen are mainly obtained from 
CO
2
 and H
2
O, while the others are absorbed from the soil as mineral nutrition. 
Micronutrients: Micronutrients or trace elements, are needed in very small amounts 
(less than 10 mmole Kg
–1
 of dry matter). These include iron, manganese, copper, 
molybdenum, zinc, boron, chlorine and nickel. 
Beneficial Elements: In addition to the 17 essential elements named above, there 
are some beneficial elements such as sodium, silicon, cobalt and selenium. They are 
required by higher plants. 
Toxic Elements: The requirement of micronutrients is always in low amounts while 
their moderate decrease causes the deficiency symptoms and a moderate increase 
causes toxicity. In other words, there is a narrow range of concentration at which the 
elements are optimum. Any mineral ion concentration in tissues that reduces the dry 
weight of tissues by about 10 per cent is considered toxic. Such critical 
concentrations vary widely among different micronutrients. The toxicity symptoms 
are difficult to identify. Toxicity levels for any element also vary for different plants. 
Question 4. Name at least five different deficiency symptoms in plants. 
Describe them and correlate them with the concerned mineral deficiency. 
Answer: 
Iron Deficiency: 
Iron (Fe) deficiency is a plant disorder also known as "lime-induced chlorosis". It can 
be confused with manganese deficiency. A deficiency in the soil is rare but iron can 
be unavailable for absorption if soil pH is not between about 5 and 6.5. A common 
problem is when the soil is too alkaline (the pH is above 6.5). Also, iron deficiency 
can develop if the soil is too waterlogged or has been overfertilised. Elements like 
calcium, zinc, manganese, phosphorus, or copper can tie up iron if they are present 
in high amounts. 
Iron is needed to produce chlorophyll, hence its deficiency causes chlorosis. For 
example, iron is used in the active site of glutamyl-tRNA reductase, an enzyme 
needed for the formation of 5-Aminolevulinic acid which is a precursor of heme and 
chlorophyll. 
Symptoms: Symptoms include leaves turning yellow or brown in the margins 
between the veins which may remain green, while young leaves may appear to be 
bleached. Fruit would be of poor quality and quantity. Any plant may be affected, but 
raspberries and pears are particularly susceptible, as well as most acid-loving plants 
such as azaleas and camellias. 
Treatment: Iron deficiency can be avoided by choosing appropriate soil for the 
growing conditions (e.g., avoid growing acid loving plants on lime soils), or by adding 
well-rotted manure or compost. 
Potassium Deficiency: 
Plants require potassium ions (K
+
) for protein synthesis and for the opening and 
closing of stomata, which is regulated by proton pumps to make surrounding guard 
cells either turgid or flaccid. A deficiency of potassium ions can impair a plant's ability 
to maintain these processes. 
Symptoms: The deficiency most commonly affects fruits and vegetables, notably 
potatoes, tomatoes, apples, currants, and gooseberries, and typical symptoms are 
brown scorching and curling of leaf tips, and yellowing of leaf veins. Purple spots 
may also appear on the leaf undersides. 
Deficient plants may be more prone to frost damage and disease, and their 
symptoms can often be confused with wind scorch or drought. 
Prevention and Cure: Prevention and cure can be achieved in the shorter term by 
feeding with home-made comfrey liquid, adding seaweed meal, composted bracken 
or other organic potassium-rich fertilisers. In the longer term the soil structure should 
be improved by adding plenty of well rotted compost or manure. Wood ash has high 
potassium content, but should be composted first as it is in a highly soluble form. 
Calcium Deficiency: 
Calcium (Ca) deficiency is a plant disorder that can be caused by insufficient calcium 
in the growing medium, but is more frequently a product of a compromised nutrient 
mobility system in the plant. This may be due to water shortages, which slow the 
transportation of calcium to the plant, or can be caused by excessive usage of 
potassium or nitrogen fertilizers. 
Symptoms: Calcium deficiency symptoms appear initially as generally stunted plant 
growth, necrotic leaf margins on young leaves or curling of the leaves, and eventual 
death of terminal buds and root tips. Generally the new growth of the plant is 
affected first. The mature leaves may be affected if the problem persists. 
Treatment: Calcium deficiency can be rectified by adding Agricultural lime to acid 
soils, aiming at a pH of 6.5, unless the plant in question specifically prefers acidic 
soil. Organic matter should be added to the soil in order to improve its moisture-
retaining capacity. 
Plant damage is difficult to reverse, so take corrective action immediately. Make 
supplemental applications of calcium nitrate at 200 ppm nitrogen. Test and correct 
the pH if needed because calcium deficiency is often associated with low pH. 
Nitrogen Deficiency: 
Nitrogen (N) deficiency in plants can occur when woody material such as sawdust is 
added to the soil. Soil organisms will utilise any nitrogen in order to break this down, 
thus making it temporarily unavailable to growing plants. 'Nitrogen robbery' is more 
likely on light soils and those low in organic matter content, although all soils are 
susceptible. Cold weather, especially early in the season, can also cause a 
temporary shortage. 
Symptoms: All vegetables apart from nitrogen fixing legumes are prone to this 
disorder. Symptoms include poor plant growth, leaves are pale green or yellow in the 
case of brassicas. Lower leaves show symptoms first. Leaves in this state are said to 
be etiolated with reduced chlorophyll. Flowering and fruiting may be delayed. 
Page 4


Mineral Nutrition 
Question 1. ‘All elements that are present in a plant need not be essential to its 
survival’. Comment. 
Answer: - The criteria for essentiality of an element are given below: 
(a) The element must be absolutely necessary for supporting normal growth and 
reproduction. In the absence of the element the plants do not complete their life 
cycle or set the seeds. 
(b) The requirement of the element must be specific and not replaceable by another 
element. In other words, deficiency of any one element cannot be met by supplying 
some other element. 
(c) The element must be directly involved in the metabolism of the plant. 
All elements that are present in a plant do not fulfill these criteria hence cannot be 
essential for plant survival. 
Question 2. Why is purification of water and nutrient salts so important in 
studies involving mineral nutrition using hydroponics. 
Answer: - In 1860, Julius von Sachs, a prominent German botanist, demonstrated, 
for the first time, that plants could be grown to maturity in a defined nutrient solution 
in complete absence of soil. The essence of all these methods involves the culture of 
plants in a soil-free, defined mineral solution. These methods require purified water 
and mineral nutrient salts. 
Purification of water and nutrient salt is important to rule out other influencing factors. 
The presence of pure nutrients will give the clear cut scientific results. This will help 
in making a sound basis for the right prediction. 
Question 3. Explain with examples: macronutrients, micronutrients, beneficial 
nutrients, toxic elements and essential elements. 
Answer: - 
Macronutrients: Macronutrients are generally present in plant tissues in large 
amounts (in excess of 10 mmole Kg
–1
 of dry matter). The macronutrients include 
carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and 
magnesium. Of these, carbon, hydrogen and oxygen are mainly obtained from 
CO
2
 and H
2
O, while the others are absorbed from the soil as mineral nutrition. 
Micronutrients: Micronutrients or trace elements, are needed in very small amounts 
(less than 10 mmole Kg
–1
 of dry matter). These include iron, manganese, copper, 
molybdenum, zinc, boron, chlorine and nickel. 
Beneficial Elements: In addition to the 17 essential elements named above, there 
are some beneficial elements such as sodium, silicon, cobalt and selenium. They are 
required by higher plants. 
Toxic Elements: The requirement of micronutrients is always in low amounts while 
their moderate decrease causes the deficiency symptoms and a moderate increase 
causes toxicity. In other words, there is a narrow range of concentration at which the 
elements are optimum. Any mineral ion concentration in tissues that reduces the dry 
weight of tissues by about 10 per cent is considered toxic. Such critical 
concentrations vary widely among different micronutrients. The toxicity symptoms 
are difficult to identify. Toxicity levels for any element also vary for different plants. 
Question 4. Name at least five different deficiency symptoms in plants. 
Describe them and correlate them with the concerned mineral deficiency. 
Answer: 
Iron Deficiency: 
Iron (Fe) deficiency is a plant disorder also known as "lime-induced chlorosis". It can 
be confused with manganese deficiency. A deficiency in the soil is rare but iron can 
be unavailable for absorption if soil pH is not between about 5 and 6.5. A common 
problem is when the soil is too alkaline (the pH is above 6.5). Also, iron deficiency 
can develop if the soil is too waterlogged or has been overfertilised. Elements like 
calcium, zinc, manganese, phosphorus, or copper can tie up iron if they are present 
in high amounts. 
Iron is needed to produce chlorophyll, hence its deficiency causes chlorosis. For 
example, iron is used in the active site of glutamyl-tRNA reductase, an enzyme 
needed for the formation of 5-Aminolevulinic acid which is a precursor of heme and 
chlorophyll. 
Symptoms: Symptoms include leaves turning yellow or brown in the margins 
between the veins which may remain green, while young leaves may appear to be 
bleached. Fruit would be of poor quality and quantity. Any plant may be affected, but 
raspberries and pears are particularly susceptible, as well as most acid-loving plants 
such as azaleas and camellias. 
Treatment: Iron deficiency can be avoided by choosing appropriate soil for the 
growing conditions (e.g., avoid growing acid loving plants on lime soils), or by adding 
well-rotted manure or compost. 
Potassium Deficiency: 
Plants require potassium ions (K
+
) for protein synthesis and for the opening and 
closing of stomata, which is regulated by proton pumps to make surrounding guard 
cells either turgid or flaccid. A deficiency of potassium ions can impair a plant's ability 
to maintain these processes. 
Symptoms: The deficiency most commonly affects fruits and vegetables, notably 
potatoes, tomatoes, apples, currants, and gooseberries, and typical symptoms are 
brown scorching and curling of leaf tips, and yellowing of leaf veins. Purple spots 
may also appear on the leaf undersides. 
Deficient plants may be more prone to frost damage and disease, and their 
symptoms can often be confused with wind scorch or drought. 
Prevention and Cure: Prevention and cure can be achieved in the shorter term by 
feeding with home-made comfrey liquid, adding seaweed meal, composted bracken 
or other organic potassium-rich fertilisers. In the longer term the soil structure should 
be improved by adding plenty of well rotted compost or manure. Wood ash has high 
potassium content, but should be composted first as it is in a highly soluble form. 
Calcium Deficiency: 
Calcium (Ca) deficiency is a plant disorder that can be caused by insufficient calcium 
in the growing medium, but is more frequently a product of a compromised nutrient 
mobility system in the plant. This may be due to water shortages, which slow the 
transportation of calcium to the plant, or can be caused by excessive usage of 
potassium or nitrogen fertilizers. 
Symptoms: Calcium deficiency symptoms appear initially as generally stunted plant 
growth, necrotic leaf margins on young leaves or curling of the leaves, and eventual 
death of terminal buds and root tips. Generally the new growth of the plant is 
affected first. The mature leaves may be affected if the problem persists. 
Treatment: Calcium deficiency can be rectified by adding Agricultural lime to acid 
soils, aiming at a pH of 6.5, unless the plant in question specifically prefers acidic 
soil. Organic matter should be added to the soil in order to improve its moisture-
retaining capacity. 
Plant damage is difficult to reverse, so take corrective action immediately. Make 
supplemental applications of calcium nitrate at 200 ppm nitrogen. Test and correct 
the pH if needed because calcium deficiency is often associated with low pH. 
Nitrogen Deficiency: 
Nitrogen (N) deficiency in plants can occur when woody material such as sawdust is 
added to the soil. Soil organisms will utilise any nitrogen in order to break this down, 
thus making it temporarily unavailable to growing plants. 'Nitrogen robbery' is more 
likely on light soils and those low in organic matter content, although all soils are 
susceptible. Cold weather, especially early in the season, can also cause a 
temporary shortage. 
Symptoms: All vegetables apart from nitrogen fixing legumes are prone to this 
disorder. Symptoms include poor plant growth, leaves are pale green or yellow in the 
case of brassicas. Lower leaves show symptoms first. Leaves in this state are said to 
be etiolated with reduced chlorophyll. Flowering and fruiting may be delayed. 
Prevention and Control: Prevention and control of nitrogen deficiency can be 
achieved in the short term by using grass mowings as a mulch, or foliar feeding with 
manure, and in the longer term by building up levels of organic matter in the soil. 
Sowing green manure crops such as grazing rye to cover soil over the winter will 
help to prevent nitrogen leaching, while leguminous green manures such as winter 
tares will fix additional nitrogen from the atmosphere 
Manganese Deficiency: 
Manganese (Mn) deficiency is a plant disorder that is often confused with, and 
occurs with, iron deficiency. Most common in poorly drained soils, also where 
organic matter levels are high. Manganese may be unavailable to plants where pH is 
high. 
Symptoms: Affected plants include onion, apple, peas, French beans, cherry and 
raspberry, and symptoms include yellowing of leaves with smallest leaf veins 
remaining green to produce a ‘chequered’ effect. The plant may seem to grow away 
from the problem so that younger leaves may appear to be unaffected. Brown spots 
may appear on leaf surfaces, and severely affected leaves turn brown and wither. 
Prevention: Prevention can be achieved by improving soil structure. Do not over-
lime. 
Question 5. How are the minerals absorbed by the plants? 
Answer: Plants uptake essential elements from the soil through their roots and from 
the air through their leaves. Nutrient uptake in the soil is achieved by cation 
exchange, wherein root hairs pump hydrogen ions (H
+
) into the soil through proton 
pumps. These hydrogen ions displace cations attached to negatively charged soil 
particles so that the cations are available for uptake by the root. In the leaves, 
stomata open to take in carbon dioxide and expel oxygen. The carbon dioxide 
molecules are used as the carbon source in photosynthesis. 
Though nitrogen is plentiful in the earth's atmosphere, relatively few plants engage in 
nitrogen fixation (conversion of atmospheric nitrogen to a biologically useful form). 
Most plants therefore require nitrogen compounds to be present in the soil in which 
they grow. 
Question 6. What are the conditions necessary for fixation of atmospheric 
nitrogen by Rhizobium. What is their role in N2 -fixation? 
Answer: Rhizobia are unique because they live in a symbiotic relationship with 
legumes. Common crop and forage legumes are peas, beans, clover, and soy. 
Infection and signal exchange 
The symbiotic relationship implies a signal change between both partners that leads 
to mutual recognition and development of symbiotic structures. Rhizobia live in the 
soil where they are able to sense flavonoids secreted by the root of their host legume 
plant. Flavonoids trigger the secretion of Nod factors, which in turn are recognized by 
Page 5


Mineral Nutrition 
Question 1. ‘All elements that are present in a plant need not be essential to its 
survival’. Comment. 
Answer: - The criteria for essentiality of an element are given below: 
(a) The element must be absolutely necessary for supporting normal growth and 
reproduction. In the absence of the element the plants do not complete their life 
cycle or set the seeds. 
(b) The requirement of the element must be specific and not replaceable by another 
element. In other words, deficiency of any one element cannot be met by supplying 
some other element. 
(c) The element must be directly involved in the metabolism of the plant. 
All elements that are present in a plant do not fulfill these criteria hence cannot be 
essential for plant survival. 
Question 2. Why is purification of water and nutrient salts so important in 
studies involving mineral nutrition using hydroponics. 
Answer: - In 1860, Julius von Sachs, a prominent German botanist, demonstrated, 
for the first time, that plants could be grown to maturity in a defined nutrient solution 
in complete absence of soil. The essence of all these methods involves the culture of 
plants in a soil-free, defined mineral solution. These methods require purified water 
and mineral nutrient salts. 
Purification of water and nutrient salt is important to rule out other influencing factors. 
The presence of pure nutrients will give the clear cut scientific results. This will help 
in making a sound basis for the right prediction. 
Question 3. Explain with examples: macronutrients, micronutrients, beneficial 
nutrients, toxic elements and essential elements. 
Answer: - 
Macronutrients: Macronutrients are generally present in plant tissues in large 
amounts (in excess of 10 mmole Kg
–1
 of dry matter). The macronutrients include 
carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and 
magnesium. Of these, carbon, hydrogen and oxygen are mainly obtained from 
CO
2
 and H
2
O, while the others are absorbed from the soil as mineral nutrition. 
Micronutrients: Micronutrients or trace elements, are needed in very small amounts 
(less than 10 mmole Kg
–1
 of dry matter). These include iron, manganese, copper, 
molybdenum, zinc, boron, chlorine and nickel. 
Beneficial Elements: In addition to the 17 essential elements named above, there 
are some beneficial elements such as sodium, silicon, cobalt and selenium. They are 
required by higher plants. 
Toxic Elements: The requirement of micronutrients is always in low amounts while 
their moderate decrease causes the deficiency symptoms and a moderate increase 
causes toxicity. In other words, there is a narrow range of concentration at which the 
elements are optimum. Any mineral ion concentration in tissues that reduces the dry 
weight of tissues by about 10 per cent is considered toxic. Such critical 
concentrations vary widely among different micronutrients. The toxicity symptoms 
are difficult to identify. Toxicity levels for any element also vary for different plants. 
Question 4. Name at least five different deficiency symptoms in plants. 
Describe them and correlate them with the concerned mineral deficiency. 
Answer: 
Iron Deficiency: 
Iron (Fe) deficiency is a plant disorder also known as "lime-induced chlorosis". It can 
be confused with manganese deficiency. A deficiency in the soil is rare but iron can 
be unavailable for absorption if soil pH is not between about 5 and 6.5. A common 
problem is when the soil is too alkaline (the pH is above 6.5). Also, iron deficiency 
can develop if the soil is too waterlogged or has been overfertilised. Elements like 
calcium, zinc, manganese, phosphorus, or copper can tie up iron if they are present 
in high amounts. 
Iron is needed to produce chlorophyll, hence its deficiency causes chlorosis. For 
example, iron is used in the active site of glutamyl-tRNA reductase, an enzyme 
needed for the formation of 5-Aminolevulinic acid which is a precursor of heme and 
chlorophyll. 
Symptoms: Symptoms include leaves turning yellow or brown in the margins 
between the veins which may remain green, while young leaves may appear to be 
bleached. Fruit would be of poor quality and quantity. Any plant may be affected, but 
raspberries and pears are particularly susceptible, as well as most acid-loving plants 
such as azaleas and camellias. 
Treatment: Iron deficiency can be avoided by choosing appropriate soil for the 
growing conditions (e.g., avoid growing acid loving plants on lime soils), or by adding 
well-rotted manure or compost. 
Potassium Deficiency: 
Plants require potassium ions (K
+
) for protein synthesis and for the opening and 
closing of stomata, which is regulated by proton pumps to make surrounding guard 
cells either turgid or flaccid. A deficiency of potassium ions can impair a plant's ability 
to maintain these processes. 
Symptoms: The deficiency most commonly affects fruits and vegetables, notably 
potatoes, tomatoes, apples, currants, and gooseberries, and typical symptoms are 
brown scorching and curling of leaf tips, and yellowing of leaf veins. Purple spots 
may also appear on the leaf undersides. 
Deficient plants may be more prone to frost damage and disease, and their 
symptoms can often be confused with wind scorch or drought. 
Prevention and Cure: Prevention and cure can be achieved in the shorter term by 
feeding with home-made comfrey liquid, adding seaweed meal, composted bracken 
or other organic potassium-rich fertilisers. In the longer term the soil structure should 
be improved by adding plenty of well rotted compost or manure. Wood ash has high 
potassium content, but should be composted first as it is in a highly soluble form. 
Calcium Deficiency: 
Calcium (Ca) deficiency is a plant disorder that can be caused by insufficient calcium 
in the growing medium, but is more frequently a product of a compromised nutrient 
mobility system in the plant. This may be due to water shortages, which slow the 
transportation of calcium to the plant, or can be caused by excessive usage of 
potassium or nitrogen fertilizers. 
Symptoms: Calcium deficiency symptoms appear initially as generally stunted plant 
growth, necrotic leaf margins on young leaves or curling of the leaves, and eventual 
death of terminal buds and root tips. Generally the new growth of the plant is 
affected first. The mature leaves may be affected if the problem persists. 
Treatment: Calcium deficiency can be rectified by adding Agricultural lime to acid 
soils, aiming at a pH of 6.5, unless the plant in question specifically prefers acidic 
soil. Organic matter should be added to the soil in order to improve its moisture-
retaining capacity. 
Plant damage is difficult to reverse, so take corrective action immediately. Make 
supplemental applications of calcium nitrate at 200 ppm nitrogen. Test and correct 
the pH if needed because calcium deficiency is often associated with low pH. 
Nitrogen Deficiency: 
Nitrogen (N) deficiency in plants can occur when woody material such as sawdust is 
added to the soil. Soil organisms will utilise any nitrogen in order to break this down, 
thus making it temporarily unavailable to growing plants. 'Nitrogen robbery' is more 
likely on light soils and those low in organic matter content, although all soils are 
susceptible. Cold weather, especially early in the season, can also cause a 
temporary shortage. 
Symptoms: All vegetables apart from nitrogen fixing legumes are prone to this 
disorder. Symptoms include poor plant growth, leaves are pale green or yellow in the 
case of brassicas. Lower leaves show symptoms first. Leaves in this state are said to 
be etiolated with reduced chlorophyll. Flowering and fruiting may be delayed. 
Prevention and Control: Prevention and control of nitrogen deficiency can be 
achieved in the short term by using grass mowings as a mulch, or foliar feeding with 
manure, and in the longer term by building up levels of organic matter in the soil. 
Sowing green manure crops such as grazing rye to cover soil over the winter will 
help to prevent nitrogen leaching, while leguminous green manures such as winter 
tares will fix additional nitrogen from the atmosphere 
Manganese Deficiency: 
Manganese (Mn) deficiency is a plant disorder that is often confused with, and 
occurs with, iron deficiency. Most common in poorly drained soils, also where 
organic matter levels are high. Manganese may be unavailable to plants where pH is 
high. 
Symptoms: Affected plants include onion, apple, peas, French beans, cherry and 
raspberry, and symptoms include yellowing of leaves with smallest leaf veins 
remaining green to produce a ‘chequered’ effect. The plant may seem to grow away 
from the problem so that younger leaves may appear to be unaffected. Brown spots 
may appear on leaf surfaces, and severely affected leaves turn brown and wither. 
Prevention: Prevention can be achieved by improving soil structure. Do not over-
lime. 
Question 5. How are the minerals absorbed by the plants? 
Answer: Plants uptake essential elements from the soil through their roots and from 
the air through their leaves. Nutrient uptake in the soil is achieved by cation 
exchange, wherein root hairs pump hydrogen ions (H
+
) into the soil through proton 
pumps. These hydrogen ions displace cations attached to negatively charged soil 
particles so that the cations are available for uptake by the root. In the leaves, 
stomata open to take in carbon dioxide and expel oxygen. The carbon dioxide 
molecules are used as the carbon source in photosynthesis. 
Though nitrogen is plentiful in the earth's atmosphere, relatively few plants engage in 
nitrogen fixation (conversion of atmospheric nitrogen to a biologically useful form). 
Most plants therefore require nitrogen compounds to be present in the soil in which 
they grow. 
Question 6. What are the conditions necessary for fixation of atmospheric 
nitrogen by Rhizobium. What is their role in N2 -fixation? 
Answer: Rhizobia are unique because they live in a symbiotic relationship with 
legumes. Common crop and forage legumes are peas, beans, clover, and soy. 
Infection and signal exchange 
The symbiotic relationship implies a signal change between both partners that leads 
to mutual recognition and development of symbiotic structures. Rhizobia live in the 
soil where they are able to sense flavonoids secreted by the root of their host legume 
plant. Flavonoids trigger the secretion of Nod factors, which in turn are recognized by 
the host plant and can lead to root hair deformation and several cellular responses 
such as ion fluxes. The best known infection mechanism is called intracellular 
infection, in this case the rhizobia enter through a deformed root hair in a similar way 
to endocytosis, forming an intracellular tube called the infection thread. A second 
mechanism is called "crack entry", in this case no root hair deformation is observed 
and the bacteria penetrate between cells, though cracks produced by lateral root 
emergence. Later on bacteria become intracellular and an infection thread is formed 
like in intracellular infections. The infection triggers cell division in the cortex of the 
root where a new organ, the nodule appears. 
Nodule formation and functioning 
Infection threads grow to the nodule, infect its central tissue and release the rhizobia 
in these cells where they differentiate morphologically into bacteroids and fix nitrogen 
from the atmosphere into a plant usable form, ammonium (NH4
+
), utilizing the 
enzyme nitrogenase. In return the plant supplies the bacteria with carbohydrates, 
proteins, and sufficient enough oxygen so as not to interfere with the fixation 
process. Leghaemoglobins, plant proteins similar to human hemoglobins help to 
provide oxygen for respiration while keeping the free oxygen concentration low 
enough not to inhibit nitrogenase activity. 
The legume – Rhizobia symbiosis is a classic example of mutualism — Rhizobia 
supply ammonia or amino acids to the plant and in return receive organic acids 
(principally as the dicarboxylic acids malate and succinate) as a carbon and energy 
source — but its evolutionary persistence is actually somewhat surprising. Because 
several unrelated strains infect each individual plant, any one strain could redirect 
resources from nitrogen fixation to its own reproduction without killing the host plant 
upon which they all depend. But this form of cheating should be equally tempting for 
all strains, a classic tragedy of the commons. It turns out that legume plants guide 
the evolution of Rhizobia towards greater mutualism by reducing the oxygen supply 
to nodules that fix less nitrogen, thereby reducing the frequency of cheaters in the 
next generation. 
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