Samacheer Class 11 Bio Botany - Mineral Nutrition

Higher plants are unable to directly utilize the abundant atmospheric nitrogen because it exists in a gaseous diatomic form (N2), which is highly stable due to a strong triple covalent bond. Plants can only absorb nitrogen in its fixed forms, primarily as nitrate (NO3-) or ammonium (NH4+) ions from the soil. Therefore, atmospheric nitrogen must undergo a process called nitrogen fixation, where it is converted into these usable forms. This fixation can occur through non-biological means, such as industrial processes (Haber-Bosch process) or natural phenomena like lightning, which provides enough energy to break the N2 bond. More importantly for biological systems, nitrogen fixation is carried out by certain prokaryotes (bacteria and cyanobacteria) through biological means, either free-living in the soil or in symbiotic association with plant roots. These microorganisms possess the enzyme nitrogenase, which catalyzes the conversion of atmospheric nitrogen into ammonia, which is then further converted into nitrates. Without this crucial conversion, higher plants lack the enzymatic machinery to directly assimilate gaseous nitrogen, making them dependent on the fixed forms available in the soil.

Deficiency symptoms appear at different locations in plants depending on the mobility of minerals within the plant body. Minerals are classified into two categories based on their mobility. Actively mobile minerals include nitrogen, phosphorus, potassium, magnesium, chlorine, sodium, zinc, and molybdenum. When these minerals become deficient, the plant translocates them from older leaves to younger leaves because younger leaves are metabolically more active and have higher nutrient demands. Consequently, deficiency symptoms first appear on old and senescent leaves, which lose their mineral content to support the growth of younger tissues. In contrast, relatively immobile minerals such as calcium, sulfur, iron, boron, and copper cannot be easily translocated from mature to young leaves. When these minerals are deficient, the plant cannot redistribute them effectively, so deficiency symptoms first appear on young leaves and growing points where these minerals are being actively utilized for growth and development. This difference in symptom appearance is a direct consequence of the physiological mobility of different mineral elements within the plant's vascular system.

The nitrogenase enzyme complex plays a crucial role in nitrogen fixation, the process by which atmospheric nitrogen gas (N₂) is converted into ammonia (NH₃) that can be utilized by plants. Nitrogen fixation is the first and most important step in the nitrogen cycle. The nitrogenase enzyme is highly sensitive to oxygen and functions only under anaerobic conditions. To create and maintain the anaerobic environment necessary for nitrogenase activity, root nodules synthesize a specialized pigment called leghaemoglobin. Leghaemoglobin acts as an oxygen scavenger, binding and removing free oxygen from the nodule environment, thereby protecting the nitrogenase enzyme from inactivation. This oxygen-scavenging function is essential for the continuous operation of the nitrogen fixation process. Without leghaemoglobin, oxygen would accumulate in the nodules and irreversibly denature the nitrogenase enzyme, halting nitrogen fixation. Thus, the nitrogenase enzyme and leghaemoglobin work together as an integrated system to enable nitrogen-fixing bacteria to convert atmospheric nitrogen into biologically available forms.

Plants which are growing in nitrogen deficient areas develop insectivorous habit to resolve nitrogen deficiency.
* Nepenthes (Pitcher plant): Pitcher is a modified leaft and contains digestive enzymes. Rim of the pitcher is provided with nectar glands and acts as an attractive lid. When insect is trapped, proteolytic enzymes will digest the insect.
* Drosera (Sundew): It consists of long club shaped tentacles which secrete sticky digestive fluid which looks like a sundew.
* Utricularia (Bladder wort): Submerged plant in which leaf is modified into a bladder to collect insect in water.
* Dionaea (Venus fly trap): Leaf of this plant modified into a colourful trap. Two folds of lamina consist of sensitive trigger hairs and when insects touch the hairs it will close.
Insectivorous Plants
1. Nepenthes (Pitcher Plant)
2. Drosera (Sundew)
3. Dlonaca (Venus Fly tray)
Part – II
11th Bio Botany Guide Mineral Nutrition Additional Important Questions and Answers
I. Choose the Correct Answers

The correct answer is (c) (I) is wrong (II) is correct. Statement (I) is incorrect because Dionaea muscipula (Venus flytrap) is not a submerged hydrophyte but rather a terrestrial carnivorous plant. Although it does have leaves modified into bladders or traps to capture insects, it grows in wetland habitats on land, not submerged in water. The bladder-like structures in Dionaea are specialized leaf modifications for trapping prey, not for buoyancy as in true aquatic plants. Statement (II) is correct because Loranthus is indeed a partial stem parasite, also known as a hemiparasite. It absorbs water and mineral nutrients from the xylem of its host plant through specialized structures called haustoria, while still maintaining some photosynthetic capability of its own.

Some minerals are classified as unclassified minerals because, while they are not universally considered essential nutrients for all plants based on strict criteria (such as being directly involved in metabolism or required for completion of the life cycle), they play specific beneficial roles in certain plant species or under particular environmental conditions. These minerals, such as Sodium (Na), Silicon (Si), Cobalt (Co), and Selenium (Se), can enhance plant growth, improve stress tolerance, or fulfill specific physiological functions in some plants. For instance, Silicon is highly beneficial for many plants, especially grasses, Equisetaceae, and Cyperaceae, where it aids in cell wall formation, providing structural rigidity and enhancing resistance to pests and diseases. It also helps in preventing water lodging and improving drought tolerance. Cobalt is essential for nitrogen-fixing bacteria in legumes, as it is a component of vitamin B12, which is required for leghemoglobin synthesis. Sodium can be beneficial for C4 plants and halophytes, influencing osmotic regulation and water balance. Thus, their importance is context-dependent rather than universal, leading to their classification as unclassified or beneficial elements.

Hydroponics and aeroponics are both soilless cultivation techniques but differ fundamentally in how nutrients are delivered to plant roots. In hydroponics, plants are grown in a nutrient solution with their roots completely immersed in the liquid medium. Air is supplied to the roots through tubes or air stones to ensure adequate oxygen availability, as roots require both nutrients and oxygen for respiration and growth. In aeroponics, by contrast, the roots are suspended in air rather than being immersed in liquid. A nutrient solution is stored in a tank and is sprayed onto the suspended roots at regular intervals by a motor-driven rotor, creating a fine mist. This mist provides both nutrients and oxygen to the roots, allowing them to absorb what they need while remaining in air. Aeroponics typically uses less water than hydroponics and allows for better oxygen availability to the roots, potentially resulting in faster growth rates. Both systems eliminate the need for soil and allow precise control over nutrient delivery, making them valuable for research, commercial cultivation, and growing plants in areas with poor soil conditions.

• Macro elements which commonly remain deficient in the soil are called Critical elements, (ie) N.P.K.
• The fertilizer which contain critical elements are called complete fertilizer. They are expressed in the ratio 15: 15: 15(N:P: K)

Mineral toxicity refers to the harmful effects that occur when the concentration of mineral nutrients in plant tissues exceeds the normal or optimal level required for healthy growth. While mineral nutrients are essential for plant development, excessive accumulation of these elements can interfere with normal metabolic processes and cause damage to plant tissues. The critical concentration is the nutrient level below which deficiency symptoms appear, while toxicity occurs when nutrient concentration rises significantly above the optimal range. Toxicity is technically defined as that particular concentration of a mineral nutrient at which the dry weight of plant tissue is reduced by approximately ten percent compared to plants receiving optimal nutrient levels. Different minerals have different toxicity thresholds, and toxicity symptoms vary depending on which element is in excess. For example, excess boron can cause leaf scorch, while excess manganese can cause brown spot disease. Toxicity can result from excessive fertilizer application, contaminated water sources, or naturally high mineral content in certain soils, and it represents an important consideration in plant nutrition management.

Two prominent examples of symbiotic mode of nutrition in the plant kingdom include Lichens and Mycorrhizae. Lichens represent a remarkable mutualistic association between an alga (or cyanobacterium) and a fungus. In this partnership, the algal component, being photosynthetic, produces food through photosynthesis, providing carbohydrates to the fungus. In return, the fungal component absorbs water and minerals from the environment, provides a protective thallus structure, and offers a stable habitat for the alga. This symbiotic relationship allows lichens to thrive in harsh environments where neither organism could survive alone. Mycorrhizae exemplify another crucial symbiotic relationship, involving fungi and the roots of higher plants, including gymnosperms like Pinus. The fungi extend their hyphae into the soil, vastly increasing the surface area for nutrient absorption, particularly phosphorus and water, which they then supply to the plant. In exchange, the plant provides the fungi with carbohydrates produced during photosynthesis. This mutualistic interaction is vital for the growth and survival of many plant species, especially in nutrient-poor soils, as seen in the obligate mycorrhizal association of Pinus, where its seeds cannot germinate and establish without the presence of its specific fungal partner.

Symbiotic association refers to a close and intimate relationship between two different organisms in which both organisms derive mutual benefits. This type of association is fundamental to many ecological relationships and plant nutrition. A classic example is the symbiotic relationship between nitrogen-fixing bacteria such as Rhizobium and leguminous plants. The bacteria live in specialized root nodules of plants like beans, peas, and clover, where they fix atmospheric nitrogen into ammonia that the plant can utilize for growth. In return, the plant provides carbohydrates and other organic compounds produced through photosynthesis to nourish the bacteria. Another important example is mycorrhiza, which is a symbiotic association between fungi and the roots of higher plants. The fungal hyphae penetrate the root cells and extend into the soil, greatly increasing the surface area for nutrient and water absorption. The plant provides sugars and organic compounds to the fungus, while the fungus enhances the plant's ability to absorb phosphorus, nitrogen, and other minerals from the soil. Both symbiotic associations are essential for plant nutrition and survival in natural ecosystems.

• FTWS – means floating treatment wet lands.
• It works on the principle of hydroponics recently FTWS work on the principle of hydroponics, helping to solve pollution that come up due to Eutrophication.

Haustoria are specialized absorbing structures found in parasitic plants that enable them to extract nutrients and water from their host plants. Total parasites and partial parasites develop haustoria as modifications of their roots or stems that penetrate into the tissues of the host plant. These structures are designed to make direct contact with the vascular tissues of the host, particularly the phloem and xylem. Through haustoria, parasitic plants can directly absorb organic compounds, minerals, and water from the host plant's vascular system. The haustoria essentially function as a bridge between the parasite and host, allowing the parasite to tap into the host's nutrient supply. Examples of parasitic plants with haustoria include Cuscuta (dodder) and Orobanche (broomrape). The presence of haustoria is a key adaptation that allows parasitic plants to survive without producing their own food through photosynthesis.

Unclassified minerals are elements such as Sodium, Silicon, Cobalt, and Selenium that are not included in the list of universally essential nutrients but are required by certain plants for specific physiological functions and are therefore placed in a separate category. These minerals are needed only in trace amounts and play specialized roles in particular plant groups. Silicon is particularly essential for plants in the families Equisetaceae (horsetails), Cyperaceae (sedges), and Gramineae (grasses). In these plants, Silicon strengthens cell walls, enhances pest and disease resistance, prevents water logging by reducing water loss, and aids in the structural integrity of plant tissues. Sodium, while not essential for most plants, is required by some halophytes and plants adapted to saline environments. Cobalt is essential for nitrogen-fixing bacteria as it is a component of vitamin B12, which is necessary for their metabolic processes. Selenium functions as an antioxidant in some plants and helps protect against oxidative stress. These unclassified minerals demonstrate that plant nutrition extends beyond the traditionally recognized essential elements and that different plant species have evolved specific nutritional requirements based on their ecological niches and evolutionary adaptations.

Potassium is an essential macronutrient absorbed by plants primarily as K+ ions, playing a multifaceted role in plant physiology. Its primary functions include maintaining cell turgidity and osmotic potential, which is crucial for cell expansion, stomatal movement, and overall plant rigidity. Potassium is vital for the opening and closure of stomata, regulating water loss and gas exchange. It is also deeply involved in phloem translocation, facilitating the movement of sugars from leaves to other parts of the plant. Furthermore, potassium stimulates the activity of numerous enzymes involved in various metabolic pathways, including photosynthesis and respiration. It plays a critical role in maintaining anion and cation balance within cells through ion-exchange mechanisms. Deficiency symptoms of potassium are often quite distinct and can severely impact plant health. These include marginal chlorosis, where the edges of older leaves turn yellow, followed by necrosis, leading to the death of leaf tissue. Other symptoms include low cambial activity, which impairs secondary growth, loss of apical dominance, resulting in bushy growth, lodging in cereals (weakening of stems causing them to fall over), and characteristic curled leaf margins. These symptoms collectively indicate the plant's inability to perform essential physiological processes effectively due to insufficient potassium.

Critical concentration of minerals refers to the minimum concentration of a mineral nutrient in plant tissue below which deficiency symptoms appear and plant growth is reduced. This concept is essential for understanding plant nutrition and optimizing agricultural productivity while avoiding mineral toxicity. When the concentration of a mineral nutrient falls below its critical concentration, the plant exhibits visible deficiency symptoms such as chlorosis, stunted growth, or abnormal development. Conversely, when the concentration of a mineral nutrient exceeds the normal optimal level, it can cause toxicity symptoms that damage plant tissues and reduce productivity. The critical concentration is specifically defined as the concentration at which the dry weight of plant tissue is reduced by 10 percent compared to plants with adequate nutrient supply. Knowledge of critical concentrations for different minerals and plant species is crucial for farmers and horticulturists to maintain optimal nutrient levels in soil and nutrient solutions. This information helps in making informed decisions about fertilizer application, preventing both nutrient deficiencies and toxicities, and maximizing crop yield and quality.

Nitrogen fixation is a biochemical process that is exclusively carried out by prokaryotes and not by eukaryotes, a distinction that reflects fundamental differences in their cellular machinery and enzymatic capabilities. The key reason for this limitation is that the enzyme nitrogenase, which is absolutely essential for reducing atmospheric nitrogen gas to ammonia, is present exclusively in prokaryotic organisms. Nitrogenase is a complex metalloenzyme that catalyzes the conversion of inert atmospheric nitrogen into ammonia, a form that can be utilized by living organisms. Eukaryotic organisms, including plants, fungi, and animals, lack the genetic information and cellular machinery necessary to synthesize and maintain functional nitrogenase enzymes. Prokaryotes that possess nitrogenase are called nitrogen fixers and include free-living bacteria such as Azotobacter and Clostridium, as well as symbiotic bacteria such as Rhizobium that live in association with leguminous plants. This prokaryotic monopoly on nitrogen fixation is one of the most important biochemical processes in the biosphere, as it makes atmospheric nitrogen available to all other organisms through the nitrogen cycle. The inability of eukaryotes to fix nitrogen is why they depend on prokaryotes and on the nitrogen cycle for their nitrogen nutrition.

Hydroponics, or soilless culture, is a method of growing plants in nutrient solutions without soil, and its development involved contributions from several pioneering scientists. Wilhelm Knop developed early nutrient solutions in 1865, creating what became known as Knop solution, which was one of the first successful formulations for growing plants in water. Later, in 1940, Arnon and Hoagland developed an improved nutrient solution known as Arnon and Hoagland solution, which provided better nutrient balance and became widely used in research and commercial applications. The term hydroponics itself was coined by William Frederick Gericke in 1940, who also developed and introduced commercial techniques for large-scale hydroponic cultivation. In hydroponic systems, plant roots are immersed directly in a nutrient solution containing all essential minerals in appropriate concentrations, and air is supplied to the roots through tubes or aeration systems to ensure adequate oxygen for respiration. This method allows for precise control of nutrient delivery, water availability, and environmental conditions, making it highly efficient for plant production. Hydroponics has become increasingly important in modern agriculture, particularly in regions with poor soil quality, limited water availability, or for producing high-value crops in controlled environments.

Name of the deficiency disease and symptoms:
* Chlorosis (Overall)
* Interveinal chlorosis
* Marginal chlorosis
* Necrosis (Death of the tissue)
* Stunted growth
* Anthocyanin formation
* Delayed flowering
* Die back of shoot, Reclamation disease, Exanthema in citrus (gums on bark)
* Hooked leaf tip
* Little Leaf
* Brown heart of turnip and Internal cork of apple
* Whiptail of cauliflower and cabbage
* Curled leaf margin
Deficiency minerals:
* Nitrogen, Potassium, Magnesium, Sulphur, Iron, Manganese, Zinc and Molybdenum. Magnesium, Iron, Manganese and Zinc Potassium
* Magnesium, Potassium, Calcium, Zinc, Molybdenum and Copper.
* Nitrogen, Phosphorus, Calcium, Potassium and Sulphur.
* Nitrogen, Phosphorus, Magnesium and Sulphur
* Nitrogen, Sulphur and Molybdenum
* Copper
* Calcium
* Zinc
* Boron
* Molybdenum
* Potassium

NPK fertilizers are critically important for plant growth and development because they supply three primary macronutrients: Nitrogen (N), Phosphorus (P), and Potassium (K), which are required in large quantities by plants. Nitrogen is a fundamental component of all amino acids, proteins, nucleic acids (DNA and RNA), vitamins, hormones, and chlorophyll. It is essential for vigorous vegetative growth, leaf development, and overall plant metabolism. A deficiency in nitrogen leads to stunted growth and yellowing of leaves. Phosphorus is a vital constituent of cell membranes (phospholipids), nucleic acids, ATP (the energy currency of the cell), NADP, and various proteins. It plays a crucial role in energy transfer reactions, photosynthesis, respiration, root development, flowering, and fruit/seed formation. Phosphorus deficiency can result in poor root growth and delayed maturity. Potassium is essential for maintaining cell turgidity and osmotic potential, regulating the opening and closure of stomata, and facilitating phloem translocation of sugars. It also activates numerous enzymes involved in photosynthesis, respiration, and protein synthesis, and helps in maintaining the anion-cation balance within cells. Potassium enhances disease resistance and improves fruit quality. Therefore, providing these three nutrients in the right proportion through NPK fertilizers is crucial for farmers to ensure healthy plant growth, maximize crop yield, and improve the quality of agricultural produce, as a deficiency in any of these can severely limit plant productivity.

The formation of root nodules in leguminous plants, a complex symbiotic process with Rhizobium bacteria, involves several distinct stages. The first stage is Attraction, where legume roots secrete specific phenolic compounds and flavonoids into the rhizosphere. These chemical signals attract compatible Rhizobium bacteria towards the root surface. The second stage is Infection, initiated when Rhizobium bacteria reach the rhizosphere and then move towards the root hairs. The chemical signals from the root hairs cause the root hairs to curl and deform, creating an entry point for the bacteria. The bacteria then penetrate the root hair cell wall. The third stage involves Spreading and Multiplication, where the bacteria multiply within the root hair and induce the formation of an 'infection thread'. This thread, composed of plant cell wall material, grows inwards through the root cortical cells, carrying the bacteria along with it. The infected area becomes separated from the normal tissue. The fourth stage is Bacteroid formation. Once the infection thread reaches the inner cortical cells, the bacteria are released from the thread into the cytoplasm of the host cells. Here, they undergo morphological changes, swelling and becoming pleomorphic, and are enveloped by a host-derived membrane, forming membrane-bound structures called bacteroids. These bacteroids are the actual nitrogen-fixing units. The final stage is Nodule formation. The presence of bacteroids and the release of plant hormones, specifically cytokinins produced by the bacteria and auxins from the legume roots, together promote rapid cell division and enlargement in the infected cortical cells. This uncontrolled cell proliferation leads to the development of the characteristic root nodule structure, which provides a protected, anaerobic environment suitable for the nitrogenase enzyme's activity, enabling efficient nitrogen fixation.

Ammonia ions are quite toxic to plants, and hence cannot accumulate in the plants.
* It should be converted into Amino acids.
There are 3 methods by which it is done.
I) Reductive amination:
In this ammonia reacts with Ketoglutaric acid and form glutamic acid.
II) Transamination:
* It involves the transfer of amino group from one amino acid to the ketogroup of another keto acid.
* Glutamic acid is the main amino acid from which the transfer of NH2 (amino group) takes place and other amino acids are fonned through transamination.
* The enzyme Transaminase + Pyridoxus phosphate (COenz) reactions.
Example:
III) Catalytic Amination (GS/GOGAT path way)

Definition:
Organism deriving their nuitrients from another organism (host and causing damage/disease to the host is known as parasite. Stem parasite Root parasite Stem parasite Root parasite.
I) Obligate or Total parasite:
* Completely depends on host for their survival produce haustoria.
Total stem parasite:
* Leafless plant twine around the host. Eg. Cuscuta on Zizipus, citrus etc.
Total root parasite:
* Plants do not have stem axis – so grow in the roots of host plants produce haustoria.
Eg. Rafflesia, Orobanche and Balanophora.
II) Partial parasite:
Plant have chlorophyll on their leaves dependent on water and mineral requirements.
* Partial stem parasite: The plant grow an fig and mango and absorb water and minerals from xylem of host through haustoria.
Eg. Loranthus.
* Partial root parasite: This plant in its juvenile stages produces haustoria which grow on roots of many forest trees.
Eg. Sandal wood tree (santalum album)

Saprophytic mode of nutrition in angiosperms, though rare, involves deriving nutrients from dead and decaying organic matter, similar to bacteria and fungi. Unlike typical photosynthetic angiosperms, these plants lack chlorophyll and therefore cannot produce their own food. They rely entirely on external sources for their nutritional requirements, primarily through a symbiotic association with mycorrhizal fungi that colonize the soil litter. A classic example is Neottia, commonly known as the Bird's Nest Orchid. Its roots form a close association with mycorrhizal fungi. These fungi penetrate the decaying organic matter in the soil, break down complex organic compounds, and absorb the released nutrients. The fungi then transfer these absorbed nutrients to the Neottia plant. Since Neottia leaves lack chlorophyll, it is completely dependent on this fungal partnership to obtain its sustenance from the decomposed litter. Another notable example is Monotropa, often called the Indian Pipe. Similar to Neottia, Monotropa also lacks chlorophyll and leaves. It establishes a mycorrhizal association with fungi, which in turn are often connected to the roots of nearby photosynthetic trees. This creates a complex three-way relationship where Monotropa indirectly obtains nutrients from the organic matter processed by the fungi, which might be further linked to the photosynthetic products of other trees. Thus, these saprophytic angiosperms are not directly consuming dead organic matter but are utilizing the intermediary role of fungi to access nutrients from the decomposed litter in the soil.