2022 Solved Old Paper (BOT-101)

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Pigments and Reserve Food:-

> They are red in colour due to phycoerythrin and phycocyanin pigments. They have chlorophyll a and d molecules to capture the blue-green sunlight.

> These are photo-autotrophic, but some others are colourless, lack photosynthetic pigments and live as parasites on other photosynthetic red algae (Example- Harveyella).

> Reserve food is in the form of floridean starch and a soluble starch, floridoside.

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Heterocyst:-

> Blue green algae usually differentiate vegetative cells into heterocysts only when grown in the absence of combined nitrogen.

> This observation led Fogg (1949) to suggest that heterocysts are the sites of N2 fixation.

> Nitrogenase is located in the heterocysts under aerobic growth conditions.

> Heterocysts are suitable sites for nitrogenase because oxygen evolving Photosystem II is absent in them. 

> These algae fix N2 aerobically and microaerobically. 

> The most common N2-fixing species belong to the genera:

i. Anabaena

ii. Aulosira

iii. Calothrix

iv. Cylindrospermum

v. Nostoc

vi. Scytonema

vii. Tolypothrix

viii. Fischerella

ix. Mastigocladus

x. Stigonema. 

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Sexual reproduction (Genetic Recombination):- 3 methods -

a. Conjugation

b. Transformation

c. Transduction

a. Conjugation:- 

> It was first discovered in Escherichia coli by Lederberg and Tatum (1946). 

> Cell contact is required for this method.

b. Transformation:-

> The phenomenon was discovered by Griffith in 1928. Its mechanism was worked out by Avery (1944).

> It is the absorption of DNA segment from the surrounding medium by a living bacterium.

c. Transduction:-

> Transduction was first discovered by Zinder and his teacher Lederberg (1952) in Salmonella typhimurium.

> Here genetic material is transferred by phage virus between two bacteria.

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Marine Algae (समुंद्री शैवाल):- The algae are found in the sea. Such algae are never found in freshwater. Members of Rhodophyceae and Phaeophyceae mostly occur as marine algae. Eg.- Ectocarpus, Polysiphonia, Fucus, Caulerpa, Sargassum. Several members of the order Siphonales also inhabit seawater.

(शैवाल समुद्र में पाए जाते हैं। ऐसे शैवाल शुद्ध जल में कभी नहीं पाए जाते। रोडोफाइसी और फियोफाइसी के सदस्य अधिकतर समुद्री शैवाल के रूप में पाए जाते हैं। जैसे- एक्टोकार्पस, पॉलीसाइफ़ोनिया, फ़्यूकस, कौलेर्पा, सारगासम। साइफ़ोनेल्स गण के कई सदस्य भी समुद्री जल में निवास करते हैं।)

Halophytes or Salt water algae (लवणोदभिद या लवणीय जल शैवाल) :- Found in extreme salt water lakes. Eg.- Dunaliella, Stephoenoptera. Chlamydomonas chrenbegii is found growing in the slatish water of lakes Sambhar and Crimera.

(अत्यधिक खारे पानी की झीलों में पाया जाता है। जैसे- डुनेलीएला, स्टीफोनोप्टेरा। क्लैमाइडोमोनस च्रेनबेगी सांभर और क्रीमेरा झीलों के स्लैटिश जल में पाया जाता है।)

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Algal blooms:-

> An algal bloom is a rapid increase in the popullation of algae in an aquatic system. 

> Algal blooms may occur in freshwater as well as marine environments. 

> Result of an excess of nutrients (particularly p and n). 

> Their growth - cause for other plants to die.

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Gene therapy by Viruses:-

An innovative and transformative medicine called gene therapy uses non-disease-causing viruses to deliver a healthy copy of a gene that aims to treat the underlying cause of a disease. These viruses are used as vectors or vehicles that deliver genetic materials to specific cells.

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Sargassum:-

1. Classification:-

Division:- Phaeophyta

Class:- Phaeophyceae

Sub-class:- Cyclosporeae

Order:- Fucales

Family:- Sargassaceae

Genus:- Sargassum

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Biosensors:-

> A biosensor is an analytical device containing an immobilized biological material (enzyme, antibody, nucleic acid, hormone, organelle or whole cell) which can specifically interact with an analyte and produce physical, chemical or electrical signals that can be measured. An analyte is a compound (e.g. glucose, urea, drug, pesticide) whose concentration has to be measured.

> Biosensors basically involve the quantitative analysis of various substances by converting their biological actions into measurable signals. A great majority of biosensors have immobilized enzymes. The performance of the biosensors is mostly dependent on the specificity and sensitivity of the biological reaction, besides the stability of the enzyme.

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Antigens:-

Definition:- Antigens are substances which, when introduced into the body, stimulate the production of antibodies.

Chemical Nature:- The antigens are mostly the conjugated proteins like lipoproteins, glycoproteins and nucleoproteins.

Structure:- 

> Antigenic determinants or epitopes (Gk. epi – upon, topos- place) are components of antigen. 

> Each antigen carries many epitopes. 

> Each Y-shaped antibody mol­ecule has atleast two binding sites that can attach to a specific epitope on an antigen. 

> An antibody can also bind to identical epitopes of two different cells at the same time which can cause neighbouring cells to aggregate. 

> Antigens combine with the antibody. 

> The combination is very much like the lock and key analogy.

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Ans. 

थैलस संगठन की सीमा (Range of thallus organization):-

1. एककोशिकीय थैलस (Unicelluar Thallus)

2. बहुकोशिकीय थैलस (Multicellular Thallus)

1. एककोशिकीय थैलस (Unicelluar Thallus):- 

a. अचल एककोशिकीय (Non-motile uni cellular):- Eg.- Chlorella, Synechococcus

b. चल एककोशिकीय (Motile unicellular):- Eg.- Chlamydomonas

2. बहुकोशिकीय थैलस (Multicellular Thallus):- 

a. कोलोनीय शैवाल (Colonial Algae)

b. तन्तुमय शैवाल (Filamentous Algae)

a. कोलोनीय शैवाल (Colonial Algae):- 

i. अचल कॉलोनी (Non motile colony):- Eg.- Nostoc, Pediastrum, Scenedesmus

ii. चल कॉलोनी (Motile colony):- Eg.- Gonium, Pandorina, Eudorina, Volvox

b. तन्तुमय शैवाल (Filamentous Algae):- 

i. अशाखित तन्तु (Unbranched filaments):- Eg.- Zygnema (free floating), Anabaena, Spirulina, Ulothrix, Spirogyra, Oedogonium)

ii. शाखित तन्तु (Branched filaments):- Eg.- Cladophora, Pithophora, Bulbochaete

iii. नालनुमा तन्तु (Siphonaceous filaments):- बिना पट्ट के लम्बा पादप शरीर। एक सामान्य प्रोटोप्लाज्म में मौजूद कई केंद्रक को सीनोसाइटिक स्थिति कहा जाता है। जैसे- वाउचेरिया, बोट्रीडियम, कोडियम, ब्रायोप्सिस

(Elongated plant body without septation. Many nuclei present in a common protoplasm called as coenocytic condition. Eg.- Vaucheria, Botrydium, Codium, Bryopsis)

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Nitrogen fixation and soil fertility:- Certain bacteria are helpful in the fixation of atmospheric nitrogen. Azotobacter and Clostridium are present in the soil and help in nitrogen fixation. Species of Rhizobium bacteria are present in the root nodules of leguminous plants, and they increase the soil’s nitrogen content by fixing up atmospheric nitrogen. The process is known as symbiotic nitrogen fixation.

> Organic farming is increasing the production of pollutant-free crops. It involves the use of biofertilizers and biopesticides which increases the nutrient quality of the crop and controls any kind of pest and pathogen.

> Biofertilizers are microorganisms that add to the nutrient quality of the soil. Bacteria, fungi, and algae are some of the beneficial microorganisms that help in improving the fertility of the soil.

> Biofertilizers are classified as:

i. Free-living nitrogen-fixing bacteria like Azotobacter, and Rhodospirillum.

ii. Free-living nitrogen-fixing Cyanobacteria like Anabaena, and Nostoc.

iii. Loose association of nitrogen-fixing bacteria like Azospirillum.

iv. Symbiotic nitrogen-fixing bacteria like Rhizobium, and Frankia

Bacteria As Biofertilizers:- The following microorganisms are used as biofertilizers:

1. Rhizobium:- They form root nodules in leguminous plants and fix the atmospheric nitrogen into an organic form. Rhizobium also has no negative effect on soil quality and improves the quality, nutrient content, and growth of the plant.

2. Azotobacter:- These are free-living nitrogen fixers found in all types of upland crops. These not only fix nitrogen but also provide certain antibiotics and growth substances to the plant.

3. Azospirillum:- Unlike Azotobacter, these can be used in wetland areas. They are found inside the roots of the plant (non-free-living) where they fix the atmospheric nitrogen.

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Ultra structure of Bacteria:- 

1. Glycocalyx:- This layer is present on the outer surface of cell wall. It is of 2 types -

a. Slime layer

b. Capsule

a. Slime layer:- 

> It is an unorganised loosely associated extracellular layer that surrounds the bacterial cell wall. 

> It is made up of glycoproteins, glycolipids and exopolysaccharides. 

> Slime layers are amorphous in nature and are of varied thickness because they are produced depending on the cell type and environment. 

> Because they are loosely associated with the bacterial cell wall, the slime layer can be easily washed off.

> Functions:-

i. It protects the bacterial cell from physical damage such as desiccation and antibiotics.

ii. It helps the bacteria in adhering to smooth surfaces.

iii. A slime layer is mainly composed of polysaccharides and hence is overproduced in unfavourable times as extra food storage for survival.

iv. It is also produced in soil dwelling prokaryotes to prevent them from unnecessary drying during annual temperature and humidity shifts.

v. It sometimes helps the bacteria to survive sterilisation by chemicals such as iodine and chlorine.

b. Capsule:-

> A bacterial capsule is an organised and tightly associated extracellular layer present around the bacterial cell wall. 

> It is made up of simple sugars or polysaccharides. 

> Unlike the slime layer, it is tightly packed and hence cannot be easily washed off. 

> It can be found in both gram positive and gram negative bacteria. 

> Function:-

i. The capsules are water loving (hydrophilic) and hence prevent the bacterial cell from water loss or desiccation.

ii. It also protects the bacterial cell wall from engulfment by the white blood cells (phagocytosis).

iii. The presence of a capsule in bacteria determines its virulence factor. 

iv. It also helps the bacteria to adhere to various surfaces.

2. Cell wall:-

> It range in thickness around 0.02µ.

> It gives rigidity and shape to the bacterial cell.

> Chemical composition:- The three main constituents of cell wall are: 

i. N-acetyl glucosamine (NAG)

ii. N-acetyl muramic acid (NAM)

iii. A peptide chain of four or five amino acids. 

- These together form a polymer called peptidoglycan or mucopeptide.

- The NAG and NAM molecules which are arranged alternatively, run in one direction and the peptide chain run crosswise. The rigidity of bacterial cell wall is due to the presence of this polymer.

- Some other chemicals such as teichoic acid, Lipopolysaccharides are also deposited on it.

3. Plasma Membrane:-

> It is about 75 A° thick. 

> Chemically it is composed of a double layer of phospholipid molecules. 

> Proteins are found embedded in the lipid bilayers. 

> Mesosomes:- The membrane has many folded structures called mesosomes which are associated with number of activities like -

i. Site for protein synthesis

ii. Respiratory function

iii. Multiplication of chromosomal DNA

> Plasma membrane contains special receptor molecules that help bacteria detect and respond to

chemicals in their surroundings. 

> It also controls the entry of organic and inorganic molecules.

4. Cytoplasm:- 

> It is a complex mixture of carbohydrates, proteins, lipids, minerals, nucleic acids and water. 

> It stores organic material in the form of glycogen, rolutin and poly-β-hydroxy butyrate.

> The bacterial cell is devoid cell organelles but the photosynthetic bacteria have chromatophores in their cytoplasm.

> Ribosomes are the sites of protein synthesis and suspended freely in cytoplasm. Their number varies from 10,000 to 15,000 in a cell. Bacterial ribosmoes are 70s type (50s and 30s subunits) consists of two subunits.

5. Genetic material:-

a. Chromosomal DNA:- 

> The dsDNA molecule is approximately 1,000 µm long, usually forming ring like structure or sometimes remain diffused throughout the cytoplasm of the cell. 

> The Bacterial DNA is devoid of histones and referred to as bacterial chromosome.

b. Plasmids:-

> Lederberg (1952) gave the term plasmid.

> These are extra chromosomal ds circular DNA.

> They are self replicative.

> They contain different nonessential characters.

> Based on host properties, the plasmids are classified into different types as:

i. F - plasmid:- F-factor for fertility.

ii. Col - plasmid:- Col-factor for colicinogeny.

iii. R - plasmid:- R-factor for resistance.

iv. Ti - plasmid:- Tumor inducing plasmid (Agrobacterium).

v. Ri - plasmid:- Hairy root inducing plasmid (Agrobacterium).

6. Flagellation:- 

> The organ of the locomotion is small whips or hair like appendages called flagella.

> Distribution of flagella:- 

i. Atrichous:- Bacteia which lack flagella. Eg.- Lactobacillus

ii. Monotrichous:- One flagella at one end. Eg.- Vibrio chlolerae, Pseudomonas

iii. Amphitrichous:- One flagella at each end. Eg.- Nitosomonas, Spirillum

iv. Cephalotrichous:- Two or more flagella at one end only. Eg.- Pseudomonas fluorescens

v. Lophotrichous:- Tufts of flagella at both the ends, Eg.- Spirillum volutans

vi. Peritrichous:- Flagella distributed evenly all over the body, Eg.- Proteus vulgaris

> Structure of flagella:- The flagella is a helical structure composed of flagellin protein. The flagella structure is divided into three parts:

a. Basal body

b. Hook

c. Filament

a. Basal body:- 

- It is attached to the cell membrane and cytoplasmic membrane.

- It consists of rings surrounded by a pair of proteins called MotB. The rings include:

i. L-ring:- Outer ring anchored in the lipopolysaccharide layer and found in gram +ve bacteria.

ii. P-ring:- Anchored in the peptidoglycan layer.

iii. M-S ring:- Anchored in the cytoplasmic membrane

iv. C-ring:- Anchored in the cytoplasm

b. Hook:-

- It is a broader area present at the base of the filament.

- It connects filament to the motor protein in the base.

- The hook length is greater in gram +ve bacteria.

c. Filament:- Thin hair-like structure arising from the hook.

Ans.

Asexual Reproduction (अलैंगिक जनन):- The creation of some types of spores whether naked or freshly walled spores are needed for asexual reproduction. It is a mechanism of protoplast rejuvenation that does not involve sexual fusion. Every single spore develops into a plant. There occurs no alternation of generations in this process.

(अलैंगिक जनन के लिए कुछ प्रकार के बीजाणुओं का निर्माण, चाहे वे नग्न हों या ताज़ा भित्ति युक्त बीजाणु, आवश्यक होता है। यह प्रोटोप्लास्ट कायाकल्प का एक तंत्र है जिसमें लैंगिक संलयन शामिल नहीं होता है। प्रत्येक बीजाणु एक शेवाल के रूप में विकसित होता है। इस प्रक्रिया में पीढ़ियों का एकांतरण नहीं होता है।)

1. Zoospores (चलबीजाणु):-

> Zoospores are motile exposed spores containing two, four, or several flagella, and are respectively referred to as bi-, quadri-, or multi flagellated zoospores. 

(चलबीजाणु गतिशील बीजाणु होते हैं जिनमें दो, चार, या कई कशाभ होते हैं, और इन्हें क्रमशः द्वि-, चतुष-, या बहु कशाभिकीय चलबीजाणुओं के रूप में जाना जाता है।)

> Ulothrix, Chlamydomonas, and Ectocarpus produce biflagellate zoospores.

(यूलोथ्रिक्स, क्लैमाइडोमोनास, और एक्टोकार्पस द्विकशाभित चलबीजाणुओं का उत्पादन करते हैं।)

> Ulothrix produces quadriflagellate zoospores, and Oedogonium produces multiflagellate zoospores.

(यूलोथ्रिक्स चतुषकशाभित चलबीजाणुओं का उत्पादन करता है, और ऊडोगोनियम बहुकशाभिकीय चलबीजाणुओं का उत्पादन करता है।)

Palmella Stage (पालमेला अवस्था):- In some algae, such as Chlamydomonas, the zoospores alter their formation, are not able to get out of the parent cell, and remain involved in a mucilage sheath. The non-motile daughter cells may divide again and form a colony-like structure called the palmella stage.

(क्लैमाइडोमोनास जैसे कुछ शैवाल में, चलबीजाणु अपना गठन बदल देते हैं, पैतृक कोशिका से बाहर निकलने में सक्षम नहीं होते हैं, और श्लेष्मा आवरण से घिरे रहते हैं। अगतिशील पुत्री कोशिकाएं फिर से विभाजित हो सकती हैं और एक कॉलोनी जैसी संरचना बना सकती हैं जिसे पालमेला अवस्था कहा जाता है।)

2. Aplanospores (अचलबीजाणु):-

> Aplanospores are spores that are not mobile. 

(अचलबीजाणु ऐसे बीजाणु हैं जो गतिशील नहीं होते हैं।)

> Under unfavourable conditions, such as drought, such spores can develop singly or their protoplast can split to form several aplanospores within the sporangium (Eg.- Ulothrix, Microspora). 

[सूखे जैसी प्रतिकूल परिस्थितियों में, ऐसे बीजाणु अकेले विकसित हो सकते हैं या उनका जीवद्रव्य बीजाणुधानी के भीतर कई अचलबीजाणु बनाने के लिए विभाजित हो सकता है (जैसे- यूलोथ्रिक्स, माइक्रोस्पोरा)।]

> Some algae in semi-aquatic habitats may also produce aplanospores.

(अर्ध-जलीय आवासों में कुछ शैवाल भी अचलबीजाणुओं का उत्पादन कर सकते हैं।)

3. Autospores (स्वबीजाणु):- These are cells that tend to be similar to their parent cell. Eg.- Scenedesmus, Chlorella etc.

(ये ऐसी कोशिकाएँ हैं जो अपनी पैतृक कोशिका के समान होती हैं। जैसे- सेनडेसमस, क्लोरेला आदि।)

4. Hypnospores (हिप्नोबीजाणु):- These are aplanospores possessing a thickened surface and a large food reserve. Eg.-  Sphaerella, Pediastrum, etc.

(ये अचलबीजाणु हैं जिनकी भित्ति मोटी होती है और भोजन का भंडार बड़ा होता है। जैसे- स्फ़ीरेला, पेडिएस्ट्रम आदि।)

Sexual Reproduction (लैंगिक जनन):- Except for individuals of the Cyanophyceae class, almost all algae undergo sexual reproduction. Gametes unite to produce zygotes while sexual reproduction. The combination of gametes from different parents will result in a new genetic establishment.

(सायनोफाइसी वर्ग के सदस्यों को छोड़कर, लगभग सभी शैवाल लैंगिक जनन करते हैं। लैंगिक जनन के दौरान युग्मक संलयित होकर युग्मनज बनाते हैं। विभिन्न जनकों के युग्मकों के संलयन के परिणामस्वरूप एक नई आनुवंशिक स्थापना होती है।)

1. Isogamy (समयुग्मन):- 

> It is the merger of two gametes that are physiologically and morphologically identical, resulting in the formation of a zygote. 

(यह दो युग्मकों का संलयन है जो कार्यिकीय और आकारिकीय रूप से समान होते हैं, जिसके परिणामस्वरूप युग्मनज का निर्माण होता है।)

> These are typically flagellates, such as Chlamydomonas Eugametos, Ulothrix, and others.

(ये आम तौर पर कशाभ युक्त होते हैं, जैसे क्लैमाइडोमोनास यूगैमीटोस, यूलोथ्रिक्स और अन्य।)

2. Anisogamy (असमयुग्मन):- 

> The uniting gametes are physiologically and morphologically distinct during this phase. 

(इसके दौरान संलयित होने वाले युग्मक कार्यिकीय और आकारिकीय रूप से भिन्न होते हैं।)

> The microgamete (male) is small and more aggressive, while the macrogamete (female) is bigger and less active, such as Chlamydomonas braunii. 

[सूक्ष्मयुग्मक (नर) छोटा और अधिक आक्रामक होता है, जबकि वृहदयुग्मक (मादा) बड़ा और कम सक्रिय होता है, जैसे क्लैमाइडोमोनास ब्राउनी।]

> Physiological anisogamy differs from traditional anisogamy in that the uniting gametes share morphological similarities but vary physiologically. 

(कार्यिकीय असमयुग्मन पारंपरिक असमयुग्मन से इस मायने में भिन्न है कि संलयित होने वाले युग्मक आकारिकीय समानताएं साझा करते हैं लेकिन कार्यिकीय रूप से भिन्न होते हैं।)

> Zygnema, Spiro­gyra, can be some examples.

(जिग्नीमा, स्पायरोगायरा, कुछ उदाहरण हो सकते हैं।)

3. Oogamy (विषमयुग्मन):- 

> It is a complex process in which a small motile (non-motile in Rhodophyceae) male gamete (sperm or antherozoids) is fertilised by a large non-motile female gamete (egg or ovum). 

[यह एक जटिल प्रक्रिया है जिसमें एक छोटे गतिशील (रोडोफाइसी में गैर-गतिशील) नर युग्मक (शुक्राणु या एथेरोज़ोइड्स) को एक बड़े अगतिशील मादा युग्मक (अंडे या डिंब) द्वारा निषेचित किया जाता है।]

> Male gametes grow in antheridium, while female gametes grow in oogonium, such as Polysiphonia, Oedogonium, Chara, Batrachospermum, Vaucheria, Sargassum, Laminaria, and so on.

(नर युग्मक पुंधानी में बनते हैं, जबकि मादा युग्मक अंडधानी में बनते हैं, जैसे पॉलीसाइफोनिया, ऊडोगोनियम, कारा, बेट्रेकोस्पर्मम, वाउचेरिया, सारगसम, लैमिनेरिया, इत्यादि।)

Ans.

Reproduction (जनन):- 

> Anabaena is reproduced only by vegetative and asexual methods. 

(एनाबीना का जनन केवल कायिक और अलैंगिक विधियों से होता है।)

> The sexual reproduction is completely absent. 

(लैंगिक जनन पूर्णतः अनुपस्थित होता है।)

> Anabaena reproduce vegetatively by the following methods:

(एनाबीना निम्नलिखित विधियों द्वारा कायिक रूप से जनन करती है:)

i. Fragmentation (विखंडन)

ii. Hormogones (हॉर्मोगोन्स)

iii. Akinetes (एकाइनिट्स)

iv. Heterocyst (हिटेरोसिस्ट)

i. Fragmentation (विखंडन):-

- Old trichome becomes very large and irregular due to which it gets to break up into short fragments.

(पुराना ट्राइकोम बहुत बड़ा और अनियमित हो जाता है जिसके कारण यह छोटे-छोटे टुकड़ों में टूट जाता है।)

- These short fragments of trichome divide vegetative cells and develop into new trichome.

(ट्राइकोम के ये छोटे टुकड़े कायिक कोशिकाओं को विभाजित करते हैं और नए ट्राइकोम में विकसित हो जाते हैं।) 

ii. Hormogones (हॉर्मोगोन्स):-

- Hormogones are the short fragments of trichomes. Developed in the region of heterocyst. 

(हॉर्मोगोन ट्राइकोम के छोटे टुकड़े होते हैं। ये हिटेरोसिस्ट के क्षेत्र में विकसित होते हैं।)

- Then they came out of the trichome due to some movement.

(तभी कुछ हलचल होने पर ये ट्राइकोम से बाहर आ जाते हैं।)

- They divide vegetative cells and developed heterocyst and again surrounded by sheath. In this way new trichome is formed.

(ये कायिक कोशिकाओं को विभाजित करते हैं और हिटेरोसिस्ट विकसित करते हैं और फिर से आवरण से घिर जाते हैं। इस प्रकार नया ट्राइकोम बन जाता है।)

iii. Akinetes (एकाइनिट्स):-

- The akinetes are produced in mature colonies. 

(एकाइनिट्स परिपक्व कोलोनियों में निर्मित होते हैं।)

- They are formed in unfavorable conditions. 

(इनका निर्माण प्रतिकूल परिस्थितियों में होता है।)

- They are also called arthrospore or resting spore. 

(इन्हें आर्थ्रोस्पोर या विश्राम बीजाणु भी कहा जाता है।)

- They are penetrating bodies. 

(ये भेदक काय होते हैं।)

- In favorable conditions they directly or indirectly giving rise to new filaments. 

(अनुकूल परिस्थितियों में ये प्रत्यक्ष या अप्रत्यक्ष रूप से नये तंतुओं को जन्म देते हैं।)

- The contents of akinete divide into bits prior to germination.

(अंकुरण से पहले एकाइनिट की सामग्री टुकड़ों में विभाजित हो जाती है।)

iv. Heterocyst (हिटेरोसिस्ट):-

- Heterocyst cell divide transverly and form 2-4 celled hormogones. 

(हिटेरोसिस्ट कोशिका अनुप्रस्थ रूप से विभाजित होती है और 2-4 कोशिका वाले हॉर्मोगोन्स बनाती है।)

- These hormogones come out by bursting the thick wall of heterocyst and germination occurs to give rise to new trichome.

(ये हॉर्मोगोन्स हिटेरोसिस्ट की मोटी भित्ति को तोड़कर बाहर निकलते हैं और अंकुरण होकर नए ट्राइकोम को जन्म देते हैं।)

Ans.

Prions:-

> Prions are infectious agents, which are responsible for several neurodegenerative diseases in mammals. 

> These infectious agents are primarily composed of sialoglycoprotein – a combination of sialic acid and glycoprotein and usually lack nucleic acid.

> Stanley Prusiner, an American neurobiologist proposed that the prions are infectious proteins. 

> Based on his discoveries, he also proposed that they were responsible for the cause of scrapie. 

> Scrapie is a type of neurological disease, affecting the nervous systems of animals, especially sheep and goats. 

> Later, he coined the term prion for proteinaceous infectious.

> In both humans and animals, these infectious agents cause a variety of neurodegenerative diseases and are mainly caused due to the abnormal folding of the proteins in the brain.

> In humans, Creutzfeldt-Jakob disease, Fatal familial insomnia, Dementia are a few examples of diseases caused by prions.

Ans.

Division - Phaeophyta:-

Salient Features:-

> Cell construction:- Cellulose fibers bound with Alginic acid ,Fucuni acid, Fucoidan form cell walls.

> Food reserves:- laminarin, mannitol.

> Photosynthetic pigments:- chlorophyll a and c, beta carotene, Dinoxanthin ,violaxanthin, and Fucoxanthin. These pigments give brown algae color and Fucoxanthin pigment are dominant.

> Morphology:- Members of this division typically have three parts. They are:

i. Holdfast:- which attachment the alga to the substrate

ii. Stipe:- which is stem-like

iii. Laminae (blades):- which are leaf-like

> Phaeophyta (Sea weeds) belonging to order Laminarales are called kelps can reach to about 70 meters in length. Kelps are the only algae with a significant internal tissue differentiation. Kelp grows in "underwater forests" in shallow oceans, Though true conductive tissues , xylem and phloem are absent.

> Brown algal tissue differentiation:- Epidermis, Cortex and Medulla.

> They can adapt to a wide marine environment; tidal, intertidal and deep zones.

> Some members of phaeophyta have Containing bladders or airbags, meant for floating photosynthetic parts on or near the water surface for harvesting light.

> They often cause nuisance to aquarium environment by developing brown patches on any exposed surfaces such as rocks or gravel.

> Reproduction:- This takes place by both sexual and asexual means. Higher phaeophyta have life cycle consisting of both haploid, diploid stages and alternation of generation. The thallus representing haploid stage and diploid stage may be similar (isomorphic) or different (hreteromorphic).

Sargassum:-

1. Classification:-

Division:- Phaeophyta

Class:- Phaeophyceae

Sub-class:- Cyclosporeae

Order:- Fucales

Family:- Sargassaceae

Genus:- Sargassum

2. Habit and Habitat:- Sargassum is a seaweed (macroalgae). It is commonly known as gulfweed and sea holly. 

The common species found in India is S. tennerimum.

3. Thallus structure:-

> This algae grows to a length of several metres. 

> The plant body is dark green to brown in colour and consists of a holdfast, stipe and frond. 

> The thallus is branched and has berry-like structures called pneumatocysts. The pneumatocysts are filled with oxygen and help in buoyancy of the plant.

4. Reproduction:- Asexual mode of reproduction is absent.

a. Vegetative Reproduction:- By the means of fragmentation.

b. Sexual Reproduction:- Sexual reproduction in Sargassum is of oogamous type. 

i. Antheridium:- 

- The inner layers of the conceptacle have fertile and branched paraphyses that contain the antheridium. 

- Each antheridium is round, oval and double-layered and gives rise to 64 antherozoids after meiotic division.

- The antherozoids are biflagellate and pear-shaped. 

- The flagella arise sub-terminally and are unequal in size. 

- The wall of the antheridium breaks and all the antherozoids are released in water.

ii. Oogonium:- 

- The oogonial initials are also formed by the inner layers of the female conceptacle. 

- The oogonium is round and triple layered: outer exochite, middle mesochite and inner endochite.

- The nucleus of the oogonia is diploid which divides by meiotic divisions to form 8 haploid nuclei. 

- The haploid nuclei form 8 ova. Of these, 7 ova are aborted and one ovum goes further for fertilisation. 

- The oogonia remains attached to the inner walls of the conceptacle by a mucilaginous stalk.

> Fertilization:- 

- After fertilization of the antherozoid and ovum, a zygote is formed. 

- The oogonia remains attached to the conceptacle until the first transverse division happens in the zygote. 

- Of the two cells formed in the zygote, the lower cell makes the attaching organs and the upper cell works as an apical cell and forms an adult plant.

> Life Cycle:- 

- The main plant body is a diploid sporophyte. 

- The formation of antherozoids and ovum is the only representation of the haploid gametophyte stage in the life cycle of Sargassum.

Ans.

Transmission of Viruses:-

1. Seed Transmission of Virus:-

> Transmission through the seeds of the host plant was earlier considered to play a minor part in the spread of virus diseases. 

> Recently Bennett (1969) listed 53 viruses which are transmitted by seeds of about 124 plant species.

> The seeds are important in the spread of a few viruses of legumes, wild cucumber, tomatoes, and curly top virus of beet sugar. 

> In the latter case the seeds carry a high percentage of the virus. 

> The virus, however, does not enter the embryo. It is carried in a portion of the seed of the diseased plants.

2. Transmission by Vegetative Propagation:-

> It is one of the chief methods of transmission of virus diseases especially of Potato, Rose, Sugarcane, Raspberry, Strawberry, Turnips, Bulb plants, fruit trees and many ornamentals.

> The vegetative parts, the infected plants such as the tubers, bulbs, roots, offshoots, buds and scions which are used for propagation, will contain the virus present in the parent. 

> The new plants raised by the above-mentioned vegetative methods are nearly always infected.

3. Transmission by Mechanical Means:-

Many mosaic viruses are transmitted mechanically from diseased plants to healthy ones by the following methods:

(i) By contact of infected and healthy leaves brought about by wind.

(ii) By rubbing the juice of the diseased plants over the surface of the leaves of healthy plants.

(iii) By grafting infected buds on to healthy plants.

(iv) Agricultural implements also play quite an important part. The knife used for cutting the seed pieces and the pruning shears will spread the disease.

(v) Some viruses spread below ground by contact between the roots of diseased and healthy plants.

(vi) Handling plants at planting time and in cultural operation will also help in the spread of viruses such as Sugar beet. Curly top virus and Cucumber mosaic virus.

4. Transmission by Cuscuta:- In many cases Dodder (Cuscuta) serves as a transmitting agent and an effective bridge between the infected host and the healthy plants by establishing intimate biological contact through its haustoria.

5. Soil Transmission:-

> Quite a number of viruses are transmitted through the soil. 

> Common examples of soil borne viruses are Potato mosaic virus, Oat mosaic, Wheat mosaic, etc. 

> In all these cases the disease is contracted from the soil.

6. Insect Transmission:-

> Some plant and animal viruses are spread and complete particles introduced into host cells by arthropod vectors and even by dog-bite as in rabies. 

> Among the arthropods most important agents of spread of virus diseases are the insects.

> The insect which carries the disease is called a vector. 

> The insect vectors which play a major role in the dissemination of plant viruses are the Aphids, Leafhoppers, Flee beetles, Scale insects, thirps and White flies.

> Most of the insect vectors are sucking insects. 

> Aphids transmit more plant viruses than any other insects. Leafhoppers come next in the list. 

> About three hundred plant virus diseases are known to have insert vectors.

> The insert obtains virus through its mouth parts at the time of feeding on the diseased plant. It is then inoculated in the healthy plant by means of the mouth part. Inoculation in many cases must be in a certain tissue or upon young leaves.

> The virus may remain active in the body of the vector for many days. Instances are however, known when infectivity is soon lost. There are also cases where a vector cannot infect a healthy plant immediately after it has fed on a diseased plant.

> There is delay in the development of infective power within the vector. This period of development of infectivity for the virus within the vector is called the incubation period. The duration of the incubation period varies with different viruses from a few hours to days.

7. Transmission by Fungi:-

> The first proof of the fungus as a vector of plant viruses was found by Gorgon in 1958. 

> Fie found that the diseased lettuce was invariably infected by a soil chytrid, Olpidium. 

> Later he discovered that the fungus acts as a reservoir and vector of the big vein virus.

> The virus acquired by the fungus remains in the oospore. The latter germinates and produces the zoospores which function as infective agents and penetrate lettuce roots. 

> Similarly tobacco necrosis virus has been reported by Teakle (1960) to enter roots of its host by the zoospores of O. brassicae.

8. Some Soil Inhabiting Viruses have Nematode Vectors:-

> Animal viruses may gain access to the higher animals through the mouth and nose from dust or contaminated food. 

> Besides infection from outside, virus may also be transmitted from cell to cell but the internal transmission need not be in the form of virus particles.

Ans.

Algal biofertilizers:- 

Biofertilizers:-

> These are natural compounds that contain micro-organisms to enrich soil fertility to increase crop yield and plant growth.

> Microbial inoculants like bacteria, algae, and fungi can be used in biofertilizers.

> The biofertilizers having algae as an inoculant in them are known as algal biofertilizers.

> Biofertilizers can be used to fix nitrogen in the soil or they are also used to grow soil micro-flora to enhance soil health.

Algal biofertilizer:-

> BGA (blue-green algal) biofertilizers are used in fields to fix atmospheric nitrogen into the soil in organic form.

> BGA biofertilizers are not inhibited by the presence of any chemical fertilizers.

> Heterocyst is used to fix nitrogen into the soil.

Advantages of algal biofertilizers:-

> The algal biofertilizers can increase crop yield by 10-14%.

> Unlike chemical fertilizers they are eco-friendly.

> Low-cost input is required and thus is cheaper.

Benefits of BGA as a biofertilizer:-

> BGA is a biological nitrogen fixer, which concentrates the soil with organic matter and lowers the C: N ratio.

> Other uses of BGA are to improve the solubilization of immovable phosphates and to produce growth-promoting substances in soil.

> They improve the physical, chemical, and biological properties of the soil and contribute to long-term soil fertility.

> BGA has been reported to lower soil pH and help the soil retain exchangeable calcium.

> It has been reported that Nitrogen availability, particularly in the rice fields, to plants is increased due to the application of BGA.

> In India, BGAs such as Anabaena, Nostoc, and Carotrix are generally predominant and are widespread in rice-growing areas, with the exception of some acidic soils in Kerala, Assam, and Tamil Nadu. Other forms such as Cylindrosporum, Tolypothrix, Scytonema, and Aulosira had a local distribution.

> The prevalence of soils containing blue-green algae in India varies from 7% to 80% depending on the state.

Ans.

F.E. Fritsch’s Classification (1935):- 

> The most comprehensive and authorative classification of algae was given by F.E Fritsch (1935) in his book ‘The Structure and Reproduction of the Algae’.

[शैवाल का सबसे व्यापक और मान्य वर्गीकरण F.E Fritsch (1935) ने अपनी पुस्तक 'The Structure and Reproduction of the Algae' में दिया था।]

> His classification was based on such criteria as pigmentation, types of flagella, assimilatory products, thallus structure and methods of reproduction.

(उनका वर्गीकरण वर्णकता, कशाभों के प्रकार, आत्मसात उत्पाद, थैलस संरचना और जनन की विधियों जैसे मापदंडों पर आधारित था।)

> F.E. Fritsch (1935, 1948) divided algae into 11 classes on following basis:

(F.E. Fritsch (1935, 1948) ने निम्नलिखित आधार पर शैवाल को 11 वर्गों में विभाजित किया:)

1. Chlorophyceae:- 11 Orders (11 गण)

1. Volvocales:- 2 Families (2 कुल)

i. Chlamydomonadaceae:- Eg.- Chlamydomonas

ii. Volvocaceae:- Eg.- Volvox

2. Tetrasporales:- Eg.- Tetraspora

3. Ulotrichales:- 7 Families (7 कुल)

i. Ulotrichaceae:- Eg.- Ulothrix

ii. Microsporaceae:- Eg.- Microspora

iii. Cylindrocapsaceae:- Eg.- Cylindrocapsa

iv. Chaetophoraceae:- Eg.- Chaetophora

v. Protococcaceae:- Eg.- Protococcus

vi. Coleochaetaceae:- Eg.- Coleochaete

vii. Trentepohliaceae:- Eg.- Trentepohlia

4. Ulvales:- 2 Families (2 कुल)

i. Ulvaceae:- Eg.- Ulva, Acetabularia

ii. Schizomeridaceae:- Eg.- Schizomeris

5. Schizogoniales:- 1 Family (1 कुल)

i. Schizogoniaceae:- Eg.- Schizogonium

6. Cladophorales:- 2 Families (2 कुल)

i. Cladophoraceae:- Eg.- Cladophora

ii. Sphaeropleaceae:- Eg.- Sphaeroplea

7. Oedogoniales:- 1 Family (1 कुल)

i. Oedogoniaceae:- Eg.- Oedogonium, Bulbochaete

8. Zygnematales:- 2 Families (2 कुल)

i. Zygnemataceae:- Eg.- Zygnema

ii. Mesotaeniaceae:- Eg.- Mesotaenia

iii. Desmidiaceae:- Eg.- Desmidium, Closterium

9. Chlorococcales:- 7 Families (7 कुल)

i. Chlorococcaceae:- Eg.- Chlorococcum

ii. Endosphaeraceae:- Eg.- Endosphaera

iii. Characiaceae:- Eg.- Characium

iv. Protosiphonaceae:- Eg.- Protosiphon

v. Hydrodictyaceae:- Eg.- Hydrodictyon

vi. Oocystaceae:- Eg.- Oocystis

vii. Scenedesmaceae:- Eg.- Scenedesmus

10. Siphonales:- 7 Families (7 कुल)

i. Bryopsidaceae:- Eg.- Bryopsis

ii. Caulerpaceae:- Eg.- Caulerpa

iii. Halicystaceae:- Eg.- Halicystis

iv. Codiaceae:- Eg.- Codium

v. Derbesiaceae:- Eg.- Derbesia

vi. Vaucheriaceae:- Eg.- Vaucheria

vii. Phyllosiphonaceae:- Eg.- Phyllosiphon

11. Siphonocladiales:- 2 Families (2 कुल)

i. Valoniaceae:- Eg.- Valonia

ii. Dasycladaceae:- Eg.- Dasycladus

2. Xanthophyceae:-

6 Orders (6 गण):- 

i. Heterococcales:- Eg.- Chloromeson

ii. Rhizochloridales:- Eg.- Chlorachnion

iii. Heterocapsales:- Eg.- Gloeochloris

iv. Heterotrichales:- Eg.- Tribonema

v. Heterococcales:- Eg.- Botrydiopsis

vi. Heterosiphonales:- Eg.- Vaucheria, Botrydium

3. Chrysophyceae:-

Orders (गण):-

a. Chrysomonadales:-

Sub-orders (उपगण):-

i. Cromulinae:- Eg.- Mallomonas

ii. Isochrysidineae:- Eg.- Synura

iii. Ochromonadineae:- Eg.- Dinobryon

b. Rhizochrysidales:- Eg.- Chrysamoeba

c. Chrysocapsales:- Eg.- Hydrurus

d. Chrysotrichales:- Eg.- Phaeothamnion

e. Chrysosphaerales:- Eg.- Epichrysis

4. Bacillariophyceae:-

a. Order (गण):- Centrales

Families (कुल):-

i. Discoideae:- Eg.- Melosira.

ii. Solenoideae:- Eg.- Corethron

iii. Biddulphioideae:- Eg.- Biddulphia

iv. Rutilarioideae:- Eg.- Rutilaria

b. Order (गण):- Pennales

Families (कुल):-

i. Fragilarioideae:- Eg.- Synedra

ii. Eunotioideae:- Eg.- Eunotia

iii. Achnanthoideae:- Eg.- Cocconeis

iv. Naviculoideae:- Eg.- Navicula

v. Epithemioideae:- Eg.- Epiyhemia

vi. Nitzschioideae:- Eg.- Bacillaria

vii. Surirelloideae:- Eg.- Surirella

5. Cryptophyceae:-

Orders (गण):-

i. Goniomonadales:- Eg.- Goniomonas

ii. Cryptomonadales:- Eg.- Cryptomonas

iii. Chroomonadales:- Eg.- Chroomonas

6. Dinophyceae:-

a. Sub-class (उपवर्ग):- Gymnodiniphycidae

Order (गण):- Gymnodiniales

Families (कुल):-

i. Gymnodiniaceae:- Barrufeta, Gymnodinium, 

ii. Chytriodiniaceae:- Chytriodinium

iii. Warnowiaceae:- Warnowia

b. Sub-class (उपवर्ग):- Peridiniphycidae

Order:- Prorocentrales

Families (कुल):-

i. Haplodiniaceae:- Haplodinium

ii. Prorocentraceae:- Prorocentrum

7. Chloromonadophyceae:-

Orders (गण):-

i. Actinophryida:- Actinosphaerium

ii. Chattonellales:- Chattonella

iii. Commatiida:- Commation

iv. Raphidomonadales:- Fibrocapsa

8. Euglenophyceae:-

Order (गण):- Euglenales

Family (कुल):- Euglenaceae

Eg.- 

i. Euglena

ii. Astasia

iii. Trachelomonas

iv. Colacium

v. Phacus

vi. Peranema

vii. Petalomonas cantuscygni

9. Phaeophyceae:-

3 Sub-classes (उपवर्ग):-

a. Isogeneratae:- Isomorphic alternation of generation.

Order (गण):- Ectocarpales

Eg.- Ectocarpus

b. Hetrogeneratae:- Heteromorphic alternation of generation.

Order (गण):- Laminarales “Kelp or Rock weed"

Eg.- Laminaria

c. Cyclosporeae:- 

Order (गण):- Fucales

Eg.- Fucus, Sargassum

10. Rhodophyceae:-

3 Sub-classes (उपवर्ग):-

a. Porphyridae:-

Order (गण):- Porphyridales

Eg.- Porphyridium

b. Bangidae:-

Order (गण):- Bangiales

Eg.- Bangia, Porphyra

c. Floridae:-

i. Order (गण):- Nemaliales

Eg.- Nemalion

ii. Order (गण):- Ceramiales

Eg.- Ceramium, Polysiphonia, Batrachospermum

11. Myxophyceae (Cyaophyceae):-

6 orders (गण):-

i. Chroococcales:- Chroococcus

ii. Gloeobacterales:- Gloeobacter

iii. Nostocales:- Nostoc

iv. Oscillatoriales:- Oscillatoria

v. Pleurocapsales:- Pleurocapsa

vi. Spirulinales:- Spirulina

Ans.

Nutrition of Bacteria:- 2 types of bacteria based upon nutrition -

1. Autotrophic

2. Heterotrophic

1. Autotrophic:- The bacteria which synthesis their own food from the simple inorganic compound, are called autotrophic. 2 types -

a. Chemosynthertic

b. Photosynthertic

a. Chemosynthertic:- These bacteria prepare their food by using chemical energy. They get energy for food synthesis by the oxidation of certain inorganic substances such as ammonia, nitrites, nitrate, ferrous iron, hydrogen sulphides and a number of metalic or non matelic materials avialable in the environment.

i. Sulphur bacteria:- They use chemical energy while there is oxidation of sulphur compound. 

Eg.- Thiobacillus

2H₂S    +    O₂       ➔   2S    +    2H₂O    +    Energy

ii. Iron bacteria:- They use chemical energy while there is oxidation compound (Fe2+ to Fe3+). 

Eg.- Leptothrix, Ferobacillus, Cladothrix

4FeCO₃    +    O₂    +   6H2O      ➔     4Fe(OH)₃    +     4CO₂    +    Energy

iii. Hydrogen bacteria:- They use chemical energy while there is oxidation of molecular hydrogen.

Eg.- Pseudomonas, Hydrogenomonas, Bacillus pectotrophus.

H₂     +      ½ O₂     ➔     H₂O     +      Energy

iv. Nitrifying bacteria:- They use chemical energy while there is oxidation of nitrogen compound.

Eg.- Nitrosomonas, Nitrobacter

2NO₂        +     O₂      ➔      2NO₃       +         Energy

b. Photosynthertic:- They can prepare their food by using solar energy in the presence of

photosynthetic pigment bacteriochlorophyll and chlorobium chlorophyll. Photosynthesis in

bacteria differs from other green plants because there is no release of oxygen in photosynthesis.

Such photosynthesis is called anoxygenic photosynthesis. It is of following types:

i. Green sulphur bacteria:- The photosynthetic pigment is chlorobium chlorophyll and sulphur is by-product. Eg.- Chlorobium

6CO₂   +   12H₂S   +    Light      ➔     C₆H₁₂O₆     +     12S    +     6H₂O

ii. Purple sulphur bacteria:- The photosynthetic pigment is bacteriochlorophyll and sulphur is by-product. Eg.- Chromatium

6CO₂   +   12H₂S   +    Light      ➔     C₆H₁₂O₆     +     12S    +     6H₂O

iii. Non-sulphur bacteria:- The photosynthetic pigment bacteriochlorophyll and sulphur is not a by-product. Eg.- Rhodopseudomonas

6CO₂   +   12H₂   +    Light      ➔     C₆H₁₂O₆        +     6H₂O

2. Heterotrophic:- They cannot synthesized organic compounds from the simple inorganic substances.

a. Saprophytic

b. Parasitic

c. Symbiotic 

a. Saprophytic:- 

> They grow in dead, decaying organic material and live by digesting and absorbing them. 

> These bacteria gradually break down complex organic compounds into simpler products. For doing so they secreting the enzymes. 

> The break down of carbohydrate is called fermentation (Lactic acid bacteria). 

> The break down of protein material called putrefaction (Nitrifying bacteria).

b. Parasitic:-

> They live on and within other organisms (host) and they obtain their nutrition from the host. 

> They live on or within the organisms both plants and animals. 

> If the parasitic bacteria cause diseases and are harmful for their host they are called pathogenic. Many diseases including plant and animal including the man are caused by the pathogenic bacteria. Eg.- Vibrio cholerae, Diplococcus pneumoniae. 

> If the parasitic bacteria cannot cause diseases and are harmless for their host they are called nonpathogenic. 

c. Symbiotic:-

> They live in close association with other living organisms so that they both are benefited to each other, neither of them is harmed. 

> Certain plants establish a symbiotic relationship with bacteria, enabling them to produce nodules that

facilitate the conversion of atmospheric nitrogen to ammonia. Eg.- Rhizobium. 

> It appears that not only must the plant have a need for nitrogen fixing bacteria, but they must also be able to synthesize cytokinins which promote the production of root nodules, required for nitrogen fixation.

Ans.

Acetabularia:-

1. Thallus structure:-

> Acetabularia has an unusual structure by being large, unicellular and possessing features that might be considered organs -‘ roots, stems and leaves’. 

> The single cell is attached to the substrate by root-like cellular extensions. These extensions connect to an elongate stalk that ends in an umbrella-like cap which is often 1 cm or more across. 

> The single nucleus of this remarkable organism is found at the base of the stem.  

> If the stalk is cut it can regenerate a new top and the top can generate a new base, although it is short-lived, presumably because it lacks a nucleus.

2. Reproduction:-

> Sexual reproduction in Acetabularia is initiated when the single (diploid) nucleus goes through multiple mitotic divisions.

> These nuclei subsequently undergo meiosis and migrate to the cap where they are released in cysts that break open to release mobile gametes. 

> If these gametes find gametes from another alga they fuse to form a zygote that attaches to a substrate and grows into the mature form. 

> Asexual reproduction is also possible if mobile (diploid) zoospores are released and behave like zygotes, attaching to a substrate and developing into the mature form.

Ans.

Lytic cycle:- 

- The replication process in which the host cell experiences death is called the lytic cycle of reproduction. 

- The viruses so produced are free to infect and replicate in other host cells in the area.

Ans.

Lysogeny:- 

- Not all viruses multiply by the lytic cycle of reproduction. 

- Certain viruses remain active within their host cells for a long period without replicating. 

- This cycle is called the lysogenic cycle. 

- The viruses are called temperate viruses, or proviruses, because they do not bring death to the host cell immediately.

- In lysogeny, the temperate virus exists in a latent form within the host cell and is usually integrated into the chromosome. 

- Bacteriophages that remain latent within their bacterial host cell are called prophages. This process is a key element in the recombination process known as transduction.

- An example of lysogeny occurs in HIV infection. In this case, the human immunodeficiency virus remains latent within the host T-lymphocyte. 

Ans.

Division - Dinophyta:-

General characteristics:-

1. Structure:- 

> Dinoflagellates are mostly marine but also found in freshwater. Their distribution is related to the temperature, pH and depth.

> Dinoflagellates are unicellular having a eukaryotic cell.

> They can be red, blue, green, yellow or brown depending on the pigment present in the cell.

> Theca or lorica is a rigid coat present on their body. It consists of two or more articulated or sculptured plates of cellulose and pectin. Due to this feature, they are called armoured dinoflagellates. 

> In their theca, they have two grooves. One is the sulcus and the other is the cingulum. The sulcus is longitudinal and the cingulum is a transverse groove.

> Dinoflagellates typically have two flagella. One of the flagella wraps around the transverse groove like a belt and the other flagellum projects behind the cell and present in the longitudinal groove, that is perpendicular to the transverse groove.

> Dinoflagellates move like a spinning top with the help of flagella.

> The cell of dinoflagellates has all common membrane-bound organelles such as mitochondria, Golgi bodies, rough and smooth endoplasmic reticulum and food vacuoles.

> The nucleus of the dinoflagellates is called dinokaryon.

> Dinokaryon nucleus has chromosome attached to the nuclear membrane and condensed throughout. They lack histones and have a fibrillar appearance.

> The mitosis is closed type, i.e. the nuclear envelope does not break during mitosis. The mitotic spindle is extranuclear.

> Rapid multiplication gives rise to sudden population explosions, or blooms, which is responsible for the red colour of the sea, the famous Red Tide. The toxins released by the blooms may kill fishes and reach humans, who eat those fishes.

> Many dinoflagellates are bioluminescent and emit blue-green light.

> Dinoflagellates also produce lipids and sterols. One of the sterols is known as dinosterol.

2. Nutrition:-

> Dinoflagellates are mostly photosynthetic autotrophs.

> Heterotrophic dinoflagellates ingest other microorganisms and protozoans to get nutrients.

> They are also present as endosymbionts in marine invertebrates such as corals, jellyfishes, etc.

> The photosynthetic endosymbionts are called Zooxanthellae, they provide carbohydrate to their hosts.

> Endosymbiont dinoflagellates, which lack pigments are dependent on their hosts and live like a parasite.

> Dinoflagellates are important producers in the marine ecosystem.

> The chloroplast of dinoflagellates is bound by three membranes and originated from engulfing algae.

> It contains chlorophyll a, c and may contain various accessory pigments such as peridinin, fucoxanthin, etc.

> Some dinoflagellates are photosynthetic as well as heterotrophic, they are known as mixotrophic.

3. Reproduction:-

> Reproduction in dinoflagellates is primarily asexual through binary fission. The cells are haploid.

> Sexual reproduction occurs by fusion to form a zygote. The zygote may form a resting stage known as dinocyst or may remain motile.

> The zygote later undergoes meiosis to form haploid cells.

> In unfavourable conditions, vegetative cells of dinoflagellates fuse together to form Planozygote. It takes in excess fat and oil, its shell becomes harder and size increases, the stage is known as Hypnozygote, that is very similar to the hibernating stage. Sometimes even spikes are formed.

> Under favourable conditions, dinoflagellates break out the shell and present in a temporary stage known as Planomeiocyte. They quickly reorganise to their actual shape as a dinoflagellate.

4. Bioluminescence:-

> Bioluminescence is the characteristic feature of dinoflagellates. More than 18 genera of dinoflagellates are bioluminescent.

> Bioluminescent dinoflagellates have an enzyme called luciferase, present in the cytoplasmic bodies known as scintillons. The substrate of the light-producing biochemical reaction is luciferin. This reaction is pH-dependent and when the pH drops, luciferin binds to luciferase due to change in the shape of the enzyme.

> Examples of the ecosystem having bioluminescent dinoflagellate are:

i. 3 of the 5 bioluminescent bays are present in Puerto Rico

ii. Montego Bay in Jamaica 

iii. Indian river Lagoon in Central Florida

> Blooms of dinoflagellates emit short flashes of light when disturbed mechanically by waves, ships or swimming. This appears as a bluish flicker in the ocean water at night.

> Dinoflagellates use bioluminescence as a defence mechanism against their predators. Their predators become more vulnerable and in turn become prey of organisms of higher trophic levels.

5. Red Tide:-

> Dinoflagellates sometimes multiply rapidly, resulting in population explosions or blooms. Bloom may contain more than a million cells per ml of water.

> Rapid multiplication is due to the presence of abundant nutrient present in the water. This might be due to human activities or other natural reasons. Human input of phosphate accelerates the formation of red tides.

> These blooms have known to create shellfish poisoning as they release a neurotoxin which kills the fishes. The colour of the sea appears red so it is known as “Red Tide”. This phenomenon is also referred to as “Harmful algal bloom (HAB)”. It may cause fatal or non-fatal illness in various other species eating contaminated fish including humans. After eating contaminated fishes, birds may die. Red tide has been found to cause the death of dolphins and manatees too.

> All the blooms are not harmful.

> The species of dinoflagellates causing red tide are:

i. Karenia brevis:- Causing red tide in the Gulf of Mexico produces a neurotoxin called brevetoxin.

ii. Alexendrium fundyense:- It is responsible for the red tide in the Gulf of Maine, produces a toxin named saxitoxin.

iii. Pfiesteria:- It is a colourless dinoflagellate causing the toxic bloom.

Division - Cryptophyta:-

General characteristics:-

1. Introduction:- 

> This group is composed primarily of flagellates that occur in both marine and freshwater environments; palmelloid phases can also be formed, and some members are known to be zooxanthellae in host invertebrates or within certain marine ciliates.

> Cryptophyte algae are mixotrophic, capable of phototropy and phagotrophy.

> Phagocytotic ingestion of bacteria is thought primarily to provide a source of phosphorus and nitrogen in nutrient limiting conditions.

> These algae are also chemotactic, swimming in a straight line until they reach a patch of high-nutrient concentration.

> Cryptophytes are the dominant algae in the freshwater lakes of Antarctica.

> The lakes are fed by glacial melt streams that flow for 6–10 weeks during the brief austral (southern) summer.

> Cryptophytes dominate the lower stratified levels where they live heterotrophically during winter months, taking up about one bacterium per hour by phagocytosis.

> During the summer months, the cryptophytes are mixotrophic (combining heterotrophy and autotrophy by photosynthesis).

> A key to the survival of cryptophytes in this environment is maintaining the population in the vegetative state, rather than entering a resting state. The cryptophyte population can respond quickly when “good” conditions return in the short Antarctic summer.

2. Cell structure:-

> There are two apically or laterally attached flagella at the base of a depression.

> Each flagellum is approximately the same length as the body of the cell.

> Depending on the species, there are one or two rows of microtubular hairs attached to the flagellum.

> Small, organic scales are common on the flagellar surface and sometimes on the cell body.

> Corps de Maupas (CM):- It is a large vesicular structure in the anterior portion of the cell. Its main function is probably that of disposing of unwanted protoplasmic structures by digestion.

> The cells contain chlorophylls a and c and phycobiliproteins that occur inside the thylakoids of the chloroplast.

> The cell body is asymmetric with a clearly defined dorsiventrally construction. The asymmetric cell shape results in a peculiar swaying motion during swimming.

> Chloroplast:-

- Most cryptophytes have a single lobed chloroplast with a central pyrenoid. The chloroplast most likely evolved from a symbiosis between phagocytic organism and a red alga.

- The chloroplast is surrounded by two membranes of chloroplast endoplasmic reticulum and the two membranes of the chloroplast envelope.

- Between the outer pair of membranes and the inner pair of membranes of the chloroplast endoplasmic reticulum (periplastidial space) are starch grains and a nucleomorph, probably the remnant of the nucleus of the endosymbiont in the event that led to chloroplast E.R.

- The nucleomorph contains three minute paired-chromosomes with 531 genes that encode 30 proteins targeted into the chloroplast.

- The nucleomorph is surrounded by an envelope that has pores similar to those in a nuclear envelope.

- The cryptophytes are the only algae that form their storage product in the periplastidial space.

- The starch is an α-1,4-glucan composed of about 30% amylose and amylopectin.

- Cryptophycean starch is similar to potato starch and starch found in the green algae and dinoflagellates.

- Sometimes an eyespot formed by spherical globules is present inside the plastid.

- In the chloroplast, the thylakoids are grouped in pairs, and there are no connections between adjacent thylakoids. The Cryptophyta is the only group to have this arrangement of thylakoids.

- Chlorophylls a and c are present.

- The major carotenoid present is α-carotene, and the major xanthophyll, diatoxanthin.

- Phycobilins are present in the thylakoid lumen rather than in phycobilisomes on the stromal side of the thylakoids as occurs in the cyanobacteria and red algae.

-  Each photosynthetic cryptophyte has only one species of phycobiliprotein – either a phycoerythrin or a phycocyanin – but never both.

- No allophycocyanin is present.

> Ejectisomes:- 

- The Cryptophyceae have projectiles called ejectisomes, which are of different structure from the trichocysts of the Dinophyceae.

- There are usually large ejectisomes near the anterior depression and smaller ejectisomes around the cell periphery.

- Both sizes of ejectisomes have the same structure; they are made up of two unequal-sized bodies enclosed within a single membrane.

- The ejectisomes discharge when the organism is irritated.

- The discharge of the ejectisome results in a movement of the organism in the opposite direction. The discharge of the ejectisome could function as an escape mechanism, or it could be a direct defense mechanism causing damage to an offending organism.

> Cryptophytes will often undergo diel vertical migrations with an amplitude less than 5 meters.

> In small humic forest lakes, species of Cryptomonas are positively phototactic in the morning, moving into the phosphorus-depleted upper layer. Later in the day the cells move away from the uppermost water layer, avoiding high levels of irradiance, and move into the phosphorus-rich hypolimnion. A further advantage of this cycle is the reduction of grazing pressure by zooplankton (for which cryptophytes are a preferred food) which often migrate in the reverse direction.

3. Symbiotic associations:-

> Mesodinium rubrum is a marine planktonic holotrich ciliate of extremely wide geographical distribution that colors the water in which it is growing red.

> It is usually associated with regions of upwelling and in such conditions the blooms have been recorded as extending over areas as large as 100 square miles.

> The color of the ciliate is due to numerous reddish-brown chloroplasts, which belong to a single cryptophycean alga that lives symbiotically inside the ciliate.

> The association is probably similar to that of symbiotes in other classes, with the endosymbiont providing the host with photosynthate and the host providing the endosymbiont with a protected environment.

4. Reproduction:- 

> Asexual reproduction is carried out by either normal mitotic cell division or zoospore formation.

> Under nutrient deprivation, the star-shaped vegetative cells become resting cells by retracting their reticulopodia, rounding up and secreting a thin cell wall.

> The resting cells apparently rely principally on photosynthate from the chloroplasts as a food source.

> The resting cells germinate to star-shaped vegetative cells under favorable conditions.

> Zoosporogenesis occurs by a resting cell dividing twice to produce four ovoid zoospores, each with a single flagellum wrapped around the cell body.

> The zoospores settle to produce the star-shaped vegetative cells.

> Sexual reproduction characterized by heterogamy and occurs when a non-motile female gamete is approached by a motile, star-shaped, male gamete.

> The gametes fuse producing a zygote that germinates into a star-shaped vegetative cell.