Answer

(b) Changing the soil chemistry is not a role of the essential element. Whereas rest all are the characteristics of an essential element. These are directly involved in the metabolism of plants.

• (a) Being a component of biomolecules: Essential elements are indeed components of biomolecules, such as proteins, nucleic acids, and lipids, which are crucial for the structure and function of living organisms.

• (c) Being a structural component of energy-related chemicals: Essential elements play a role in the structure of molecules involved in energy transfer and storage, such as ATP, which is vital for cellular processes.

• (d) Activation or inhibition of enzymes: Essential elements often act as cofactors that are necessary for the activation or inhibition of enzymes, thereby regulating various biochemical reactions in the organism.

Answer

(a) The concentration of the essential element below which the plant growth is retarded is termed as critical concentration. Plants start showing deficiency symptoms if a particular element is present below the critical concentration.

• (b) Essential element concentration below which plant growth becomes enhanced: This is incorrect because a deficiency in an essential element would not enhance plant growth. Instead, it would hinder growth and cause deficiency symptoms.

• (c) Essential element concentration below which plant remains in the vegetative phase: This is incorrect because the critical concentration refers to the point below which overall plant growth is retarded, not specifically that the plant remains in the vegetative phase. Deficiency affects the plant’s overall health and development, not just a specific growth phase.

• (d) None of the above: This is incorrect because option (a) correctly defines the critical concentration of an essential element.

Thinking Process

Plants show deficiency symptoms of the elements when that particular nutrient is not available to the plants or if it is available, the plant is not able to use it.

Answer

(a) The sulphur is needed by young leaves, stem and root tips. If it is not available, these parts would show the deficiency symptoms which include

(i) reduced growth

(ii) extensive root growth

(iii) hard and woody stem

(iv) chlorosis of young leaves.

The immobile elements are transported in plant upto the tip level, so their deficiency appear first at the tips of growing apices of roots and shoot.

• Magnesium: Magnesium is a mobile element in plants. Deficiency symptoms of magnesium typically appear first in older leaves because the plant can translocate magnesium from older tissues to younger ones. Symptoms include interveinal chlorosis and necrosis in older leaves.

• Nitrogen: Nitrogen is also a mobile element in plants. When there is a deficiency, nitrogen can be moved from older leaves to younger ones, causing older leaves to show symptoms first. These symptoms include yellowing (chlorosis) and stunted growth.

• Potassium: Potassium is another mobile element in plants. Deficiency symptoms of potassium usually appear first in older leaves as the plant reallocates potassium to younger tissues. Symptoms include chlorosis, necrosis, and curling of leaf tips and margins in older leaves.

Answer

(d) Manganese is an essential micronutrient which is mainly required by the leaves and seeds of plants. Manganese becomes toxic when absorded by plants in higher amounts. Its toxicity cause reduced uptake of $\mathrm{Fe}^{2}, \mathrm{Mg}^{2+}$ and $\mathrm{N}$, inhibition of $\mathrm{Ca}^{2+}$ translocation in shoot apex, brown spots surrounded by chlorotic veins etc.

• (a) Calcium translocation in shoot apex is inhibited: This is a symptom of manganese toxicity, as high levels of manganese can interfere with the movement of calcium within the plant.

• (b) Deficiency in both iron and nitrogen induced: Manganese toxicity can lead to deficiencies in other essential nutrients such as iron and nitrogen, as it affects their uptake and utilization.

• (c) Appearance of brown spot surrounded by chlorotic veins: This is a common symptom of manganese toxicity, where excess manganese causes the formation of brown spots on leaves, often surrounded by areas of chlorosis (yellowing).

Answer

(d) Option (d) is not true because the bacteria involved in the process are not photoautotrophs but are chemoautotrophs. These bacteria oxidise inorganic substances like $NH_{3}$ and $NO_{2}$ and use the released energy hence are called chemoautotrophs.

Simultaneously, they help in the conversion of ammonia $\left(NH_{3}\right)$ to absorbable form $\left(NO_{2}{ }^{-}\right.$and $\left.\mathrm{NO}_{3}^{-}\right)$of nitrogen.

• Option (a) is correct because Nitrosomonas and Nitrococcus are indeed the bacteria that carry out the conversion of ammonia ($NH_{3}$) to nitrite ($NO_{2}^{-}$) in step (i).

• Option (b) is correct because Nitrobacter is the bacterium that carries out the conversion of nitrite ($NO_{2}^{-}$) to nitrate ($NO_{3}^{-}$) in step (ii).

• Option (c) is correct because both steps (i) and (ii) are part of the nitrification process, which involves the conversion of ammonia to nitrate through intermediate nitrite.

Answer

(a) The enzyme, nitrogenase which is capable of nitrogen reduction is present exclusively in prokaryotes (e.g., Rhizobium). It is highly sensitive to $\mathrm{O}_{2}$ and gets inactivated when exposed to it, thus does not require oxygen for its functioning. Other statements (b), (c) and (d) are true.

• (b) Nitrogenase is indeed a Mo-Fe protein, so this statement is correct and not a reason for being incorrect.
• (c) Leg-haemoglobin is indeed a pink coloured pigment, so this statement is correct and not a reason for being incorrect.
• (d) Nitrogenase does help to convert $\mathrm{N}_{2}$ gas into two molecules of ammonia, so this statement is correct and not a reason for being incorrect.

Thinking Process

The plants require few minerals in large quantities and few in small quantities. Thus, they are called macro and microelements respectively. The B, Mn, Zn and Fe are the elements required by the plants in smaller quantities but are very much essential for normal growth, development and reproduction of the plants.

Answer

(b) Correct match is as follows

• Option (a) $1,2,3,4,5$:

  • This option incorrectly matches all elements with their functions/roles. Specifically:
    • Boron is not involved in the splitting of $\mathrm{H}_2\mathrm{O}$ to liberate $\mathrm{O}_2$ during photosynthesis.
    • Manganese is not needed for the synthesis of auxins.
    • Molybdenum is not involved in pollen germination.
    • Zinc is not a component of ferredoxin.
    • Iron is not involved in the splitting of $\mathrm{H}_2\mathrm{O}$ to liberate $\mathrm{O}_2$ during photosynthesis.

• Option (c) $3,2,4,5,1$:

  • This option incorrectly matches all elements with their functions/roles. Specifically:
    • Boron is not a component of nitrogenase.
    • Manganese is not needed for the synthesis of auxins.
    • Molybdenum is not involved in pollen germination.
    • Zinc is not a component of ferredoxin.
    • Iron is not involved in the splitting of $\mathrm{H}_2\mathrm{O}$ to liberate $\mathrm{O}_2$ during photosynthesis.

• Option (d) $2,3,5,1,4$:

  • This option incorrectly matches all elements with their functions/roles. Specifically:
    • Boron is not needed for the synthesis of auxins.
    • Manganese is not a component of nitrogenase.
    • Molybdenum is not a component of ferredoxin.
    • Zinc is not involved in the splitting of $\mathrm{H}_2\mathrm{O}$ to liberate $\mathrm{O}_2$ during photosynthesis.
    • Iron is not involved in pollen germination.

Answer

(c) The plants can be grown in any medium either water or soil if it is supported with all essential elements. Medium does not affect the plant growth but availability of all elements does affect the growth of the plants.

• (a) soil with essential nutrients: This option is correct because plants can indeed grow in soil that contains all the essential nutrients they need.

• (b) water with essential nutrients: This option is correct because plants can also grow in water (hydroponics) if it contains all the essential nutrients required for their growth.

• (d) water or soil without essential nutrients: This option is incorrect because plants cannot grow properly in either water or soil if they lack the essential nutrients needed for their development and survival.

Thinking Process

There are few macro elements and micro elements needed by all plants for the completion of their life cycle in a normal way. But few plants have some specific requirements for some elements like $\mathrm{Na}, \mathrm{Si}, \mathrm{Cl}$ and $\mathrm{Ni}$.

Answer

Oryza sativa and Triticum aestivum are silicon accumulators. These plants actively absorb silicon and accumulate them in their biomass.

Answer

A mycorrhiza is a symbiotic association between a fungus and the roots of vascular plants (mainly gymnosperms). This mutualistic association provides fungus a constant and direct supply of carbohydrates (glucose and sucrose).

In return, plant gains the benefit of the mycelium of fungus which enhances its absorptive capacity for water and minerals due to the large surface area of mycelium.

Answer

Few prokaryotes like Rhizobium, Anabaena and Nostoc contains the enzyme nitrogenase, needed for the biological nitrogen-fixation. Eukaryotes do not possess this enzyme, therefore are unable to fix nitrogen.

Answer

Nepenthes and venus fly trap grow in nitrogen deficient soil. So, they make up their nitrogen deficiency by trapping insects for which they have developed special adaptations.

Answer

An angiospermic plant called Monotrapa do not contain chlorophyll. It grows on some other plant as a parasite and derive nutrition from the host plant. This plant is commonly known as ghost plant.

Answer

(i) Dischidia (ii) Utricularia

Answer

Azotobacter is a free living bacteria in the soil. It helps some cereal crops like maize (Zea mays) in nitrogen fixation. The farmer adds Azotobacter culture to the maize field for enhancing the nitrogen element in the soil by the process of biological nitrogen-fixation.

Answer

Leghaemoglobin is responsible for creating anaerobic conditions in the root nodules of the legume plant. It acts as an oxygen scavenger, protecting enzyme nitrogenase to come in contact with oxygen and help in the proper functioning of enzyme, i.e., conversion of atmospheric nitrogen to ammonia $\left(\mathrm{NH}_{3}\right)$.

Answer

All the above mentioned plants are carnivorous (insectivorous) plants. These trap insects and digest them by proteolytic enzymes and thus, make up their nitrogen deficiency.

Answer

Plant with zinc deficiency shows, reduced biosynthesis of auxin. Zinc is the microelement that is absorbed by almost all parts of the plant in the form of $\mathrm{Zn}^{2+}$ ion.

It functions as a constituent of carbonic anhydrase and auxin. It also activates various enzymes especially carboxylases and dehydrogenases.

Answer

Yellowish edges or chlorosis appears in the leaves, deficient in nitrogen. Nitrogen deficiency also causes delaying of flowering, interference in protein synthesis and dormacy of lateral buds.

Answer

Carbon is an essential element. Plant take it from atmosphere in the form of $CO_{2}$. It’s concentration in atmosphere is about $0.03 \%$. Plants use $CO_{2}$ for photosynthesis (as a source of carbon) to synthesises glucose.

Answer

Azotobacter is a non-symbotic nitrogen fixing prokaryote. It flourishs in the rice fields.

Answer

Rice fields remain logged with excess water which harbour the great microbial activity. Many anaerobic bacteria also grow in these areas and release methane which is a green house gas

Answer

Reductive Amination Ammonia combines with a keto acid (like $\alpha$-ketoglutaric acid or oxaloacetic acid) to form amino acid in presence of a reduced coenzyme (NADH, NADPH) and enzyme dehydrogenase (e.g., glutamate dehydrogenase, aspartate dehydrogenase).

$\alpha$-ketoglutaric acid $+\mathrm{NH}_4^{+}+\mathrm{NAD}(\mathrm{P}) \mathrm{H} \xrightarrow[{\text { dehydrogenase }}]{\text { Glutamate }}$ Glutamate $+\mathrm{H}_2 \mathrm{O}+\mathrm{NAD}(\mathrm{P})$

Oxaloacetic acid $+\mathrm{NH}_4^{+}+\mathrm{NAD}(\mathrm{P}) \mathrm{H} \xrightarrow[\text { dehydrogenase }]{\text { Aspartate }}$ Asparatate $+\mathrm{H}_2 \mathrm{O}+\mathrm{NAD}(\mathrm{P})$

Answer

Manganese $\left(\mathrm{Mn}^{2+}\right)$ becomes toxic when absorbed by plants in higher amounts. The toxicity expressed in form of brown spots surrounded by chlorotic vein.

It is due to the following reasons

(i) Reduction in uptake of $\mathrm{Fe}^{3+}$ and $\mathrm{Mn}^{2+}$

(ii) Inhibition of binding of $\mathrm{Mn}^{2+}$ to specific enzymes.

(iii) Inhibition of $\mathrm{Ca}^{2+}$ translocation in shoot apex.

Thus, excess of $\mathrm{Mn}^{2+}$ causes deficiency of iron, magnesium and calcium.

Thinking Process

Sulphur is a macronutrient and is important for normal plant growth and development. It is an integral part of some amino acids and proteins and helps in deciding the secondary structure of proteins as it forms disulphide bonds.

Answer

Sulphur (S) is an important macronutrient in plants that is absorbed by the plants as $\mathrm{SO}_{4}^{2-}$ ion. It mainly functions as a component of vitamins (biotin, thiamine), proteins, coenzyme-A, amino acid (cystein and methionine) etc. It is also an essential component of ally sulphide (onion, garlic) and sinigrin (mustard).

Deficiency of sulphur can lead to chlorosis in young leaves, extensive root growth, formation of hard and woody stem. It also causes the reduction in juice content of citrus fruit and tea yellow disease of tea.

Sulphur is found in amino acids systeine, methionione, etc.

Thinking Process

Biological nitrogen fixation is a process is which gaseous nitrogen is converted to nitrogen which can be used by the plants as a nutrient.

Answer

In biological nitrogen fixation, the atmospheric $N_{2}$ gets reduced to $NH_{3}$ by nitrogenase reductase present in some prokaryotes. $NH_{3}$ is then oxidises to $NO_{2}$ and $NO_{3}$ by some other bacteria (Nitrosomonas and Nitrobacter). Various steps involved in nitrogenfixation are as follows

Pseudomonas and Thiobacillus are involved in the process of denitrification. They convert nitrate $\left(NO_{3}^{-}\right)$and nitrite $NO_{2}^{-}$into free nitrogen $N_{2})$, which is released into the atmosphere.

Answer

(a) Hydroponics, Julius Von Sachs (1860)

(b) (i) Solanum lycopersicum (tomato)

(ii) Hibiscus asculentus (ladiesfinger)

(iii) Solanum melongena (brinjal)

(c)Aerating tube Provides oxygen for the normal growth and development of the roots growing in the liquid solution. Feeding funnel is used to add water and nutrients in the hydroponic system when required.

Answer

Nitrogenase is the most crucial enzyme found in the root nodules for $\mathrm{N}_{2}$-fixation. It is a Mo - Fe protein that catalyses the conversion of atomospheric nitrogen to ammonia. Pink coloured pigment called leghaemoglobin creates anaerobic conditions for the functioning of nitrogenase enzyme.

Answer

Answer

Carnivorous (insectivorous) plants are mainly found in nitrogen deficient soil. To make up the nitrogen deficiency, they have developed insect trapping mechanism in which leaves have taken the shape of a pitcher containing insect digesting proteolytic enzymes. They trap insect and absorb the nitrogen derived from them.

Answer

Plant can tolerate a specific amount of micronutrients. A slight lesser amount of it can cause deficiency symptoms and a slight higher amount can cause toxicity. The mineral ion concentration which reduces the dry weight of the tissues by $10 \%$ is called toxic concentration.

This concentration is different for different micronutrients as well as for different plants, e.g., $\mathrm{Mn}^{2+}$ is toxic beyond $600 \mathrm{\mu gg}^{-1}$ for soyabean and beyond $5300 \mathrm{\mu gg}^{-1}$ for sunflower.

It has also been observed that the toxicity of one micronutrient causes the deficiency of other nutrients. To overcome such problems, farmers should use these nutrients in prescribed concentration so that the excess uptake of one element do not reduce the uptake of other element.

Answer

(a) The plants try to supply more nutrients to its younger leaves than the older leaves. When nutrients are mobile, the deficiency symptoms are shown by the older leaves first because that particular nutrient reaches the top first and lower leaves does not get that nutrient.

(b) Highly mobile elements are $\mathrm{P}, \mathrm{K}$ and $\mathrm{Mn}$. Less mobile elements are $\mathrm{Ca}^{+}$and $\mathrm{K}^{+}$.

(c) The aspect of mobility of essential elements is important in horticulture and agriculture in the following ways

(i) A crop in which older leaves are harvested if show deficiency symptoms, will decrease its economic value.

(ii) The crops in which flowers, fruits and inflorescence are harvested, the immobile nutrients will not reach to the apex/tip because of immobility, so this will reduce the yield.

Answer

(a) Artificial induction in leguminous and non-leguminous plants have been tried by scientists. It’s success rate is very low because gene expression is highly specific phenomenon.

Even if desired gene is introduced, it may not work because conditions for its expressions are very specific.

(b) Symbiotic mutualistic relationship (mutualism) is found between the pine roots and mycorrhiza as both are benefitted mutually.

(c) Yes, microbe has to be in close association, to develop a physical relationship for example Rhizobium gets into the root and involve root tissues, then only helps in nitrogen-fixation.

Answer

An element is essential to plants if it is necessary for supporting its normal growth and reproduction. The requirement of this element must be specific and is not replaceable by any another element in the soil. They must be directly involved in the metabolism of the plant.

Criteria for Essentiality

An element can not be considered as essential merely on the basis of its presence in the plant. It is considered essential on the basis of the following criteria

(i) The plant is unable to grow normally and complete its life cycle in the absence of the element.

(ii) The element is specific and can not be replaced by another element.

(iii) The element plays a direct role in the metabolism of the plants.

The essential elements are further classified into two categories

(a) Macroelements These are the elements required by plants in larger quantities. These are $\mathrm{C}, \mathrm{H}, \mathrm{O}, \mathrm{N}, \mathrm{P}, \mathrm{K}, \mathrm{Mg}, \mathrm{Ca}$ and $\mathrm{S}$.

(b) Microelements (Trace elements) These are required by plants in low quantities (often less than $1 \mathrm{ppm}$ ). These include $\mathrm{B}, \mathrm{Zn}, \mathrm{Mn}, \mathrm{Cu}, \mathrm{Mo}, \mathrm{Cl}, \mathrm{Fe}$ and $\mathrm{Ni}$.

Answer

Essential elements are involved in performing variety of functions in plants. Some of the major functions are enlisted below

(i) Frame work elements Essential elements as components of biomolecules and hence are structural elements of the cell. Carbon, hydrogen and oxygen are considered as framework elements because they constitute carbohydrates which form cell wall.

(ii) Protoplasmic elements $\mathrm{N}, \mathrm{P}$ and $\mathrm{S}$ are considered as protoplasmic elements as they form protoplasm along with $\mathrm{C}, \mathrm{H}$ and oxygen.

(iii) Catalytic enzyme Essential elements that activates or inhibit enzymes, i.e., without the presence of these elements some enzymes can not function e.g., $\mathrm{Mg}^{2+}$ acts as an activator for both ribulose biphosphate carboxylase oxygenase (Rubisco) and phosphoenol pyruvate carboxylase (PEP carboxylase).

Both are the critical enzymes involved in photosynthetic carbon fixation in plants.

(iv) Balancing elements Elements counteract the toxic effect of other minerals by causing ionic balance (e.g., calcium, magnesium and potassium).

(v) Influencing on the osmotic pressure of the cellSome essential elements alters the osmotic potential of the cell. Plant cells contain dissolved mineral elements in the cell sap influencing osmotic pressure of the cell, e.g., $\mathrm{K}$ is involved in opening and closing of stomata.

Answer

Plants can tolerate a specific amount of micronutrient. A slight lesser amount of it can cause deficiency symptom and a slight higher amount can cause toxicity. The mineral ion concentration which reduces the dry weight of a tissue by $10 \%$ is called toxic concentration.

This concentration is different for different micronutrients as well as for different plant, e.g., $\mathrm{Mn}^{2+}$ is toxic beyond $600 \mathrm{\mu gg}^{-1}$ for soyabean and beyond $5300 \mathrm{\mu gg}^{-1}$ for sunflower.

It is very difficult to identify the toxicity symptoms of mineral ion. It is because excess uptake of one element can reduces the uptake of other element at a time.

e.g., manganese $\left(\mathrm{Mn}^{2+}\right)$ becomes toxic when absorbed by plants in higher amounts. The toxicity is expressed in form of brown spots surrounded by chlorotic vein.

It is due to the following

(i) Reduction in uptake of $\mathrm{Fe}^{3+}$ and $\mathrm{Mg}^{2+}$.

(ii) Inhibition of binding of $\mathrm{Mg}^{2+}$ to specific enzymes.

(iii) Inhibition of $\mathrm{Ca}^{2+}$ translocation in shoot apex.

Thus, excess of $\mathrm{Mn}^{2+}$ causes deficiency of iron, magnesium and calcium.

Answer

Formation of Root Nodule The coordinated activities of the legume and the Rhizobium bacteria depend on the chemical interaction between the symbiotic partners.

The principle stages in the nodule formation are summerised in the following diagram

Leg haemoglobin is an oxygen scavenger, it protects nitrogenase enzyme from $O_{2}$ and also creates anaerobic conditions for the reduction of $N_{2}$ to $NH_{3}$ by Rhizobium.

Answer

Formation of root nodule in pulse plant is the result of infection of roots by Rhizobium. The following figure shows the process of nodule formation

	(a) Rhizobiun divide near the root hair
	(b) Successful infection of the root hair causes it to curl
	(c) Infected thread carries the bacteria to enter the cortex. Bacteria cause cortical and pericycle cells to divide, lead to nodule formation.
	(d) Mature nodule with vascular tissues continuous with those of the roots.

The chemical reaction is as follows $$ \mathrm{N_{2}+8 e^{-}+8 H^{+}+16 \text { ATP } \quad \rightarrow 2 NH_{3}+H_{2}+16 ADP+P_{1} {i}} $$

The reaction takes place in presence of enzyme nitrogenase which acts in anaerobic conditions created by leghaemoglobin.

Fate of Ammonia

There are two ways by which ammonia is further used

(a) Reductive Amination

$\alpha$-ketoglutaric acid $+ NH_{4}^{+}+\mathrm{NADPH} \quad \xrightarrow[{\text { Dehydrogenase }}]{\text { Glutamate }} $ glutamate $+ H_{2} \mathrm{O}+\mathrm{NADP}$

Ammonia reacts with $\alpha$-ketoglutaric acid to form glutamate.

(b) Transamination

In this process, transfer of $\mathrm{NH}_{2}$ group take place from one amino acid to other amino acid; enzyme transaminase catalyses this reaction.

Thinking Process

Hydroponics is a soil less culture of plants. Many plants have been grown in nutrient rich solutions but it has certain drawbacks too.

Answer

Although, hydrophonics is a successful technique for plants still many crops are grown on land because

(i) The cost is the major concern. The setting and handling of hydrophonics requires much more investment than that of the soil based production.

(ii) Sanitization is extremely important especially with indoor hydroponic environments. Water borne disease can spread quickly through some methods of hydroponic production.

(iii) Hydroponics is relatively a new technique and not used by the traditional farmers due to lack of knowledge.

(iv) Plants are less adaptable to the surrounding atmosphere. Hot weather and narrow oxygenation may minimise the production and quality of plant produce/yield.