2020 Solved Old Paper (BOT-101)

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Nitrogen Fixers (Diazotrophs):- Among the earth’s organisms, only some prokaryotes like bacteria and cyanobacteria can fix atmosphere nitrogen. They are called nitrogen fixers or diazotrophs. They fix about 95% of the total global nitrogen fixed annually by natural process.

a. Asymbionts (Free living)

b. Symbionts

a. Asymbionts (Free living):-

Bacteria:- They add up to 10-25 kg, of nitrogen/ha/annum.

> Azotobacter (Aerobic, Saprophytic)

> Beijerinckia (Aerobic, Saprophytic)

> Clostridium (Anaerobic, Saprophytic)

> Desulphovibrio (Chemotrophic)

> Rhodopseudomonas (Photoautotrophic)

> Rhodospirillum (Photoautotrophic)

> Chromatium (Photoautotrophic)

b. Symbionts:- Live in close symbiotic association with other plants.

Bacteria:- 

> Rhizobium:- It is aerobic, gram negative nitrogen fixing bacterial symbionts of legume roots. Sesbania rostrata has Rhizobium in root nodules and Aerorhizobium in stem nodules. 

> Frankia:- It is symbiont in root nodules of many non-leguminous plants like Casuarina and Alnus.

> Xanthomonas and Mycobacterium:- They occur as symbiont in the leaves of some members of the families Rubiaceae and Myrsinaceae (e.g., Ardisia). 

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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

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Evolution of sex:- In the evolution of sex, the trend is same in various classes of algae and the sex in all orders and genera has evolved from asexual bodies. Isogamy is the simplest mode of sexual reproduction where two morphological similar gametes fuse e.g.: chlamydomonas media and ulothrix. Isogamy gives rise to anisogamy where two morphologically dissimilar gametes fuse. Anisogamy may be advanced and primitive depending upon the difference in size and behaviour of the gametes e.g.: Pandoriva, Eudoriva, species of chlamydomonas.

> Oogamy is most advanced type of sexuality where the two gametes are so dissimilar in shape, size, structure and function that one of them is known as oogonuim and other as antheridium e.g.: volvox, chlamydomonas and ordogobium. In chlorophyceae evolution of sex may be seen from isogam to oogamy when we study individual genera like chlamydomonas (C. media iroamous, C. brounii anisogamous, C. Coccifera oogamous) or order volvocales in which pandorina and endorina are anisogamous and volox is oogamous. In order ulotrichales family ulvaceae genus enteromarphs sexually ranges from isogamy to oogamy.

> In Rhodophyceae isogamy and anisogamy are found. In Polysiphomia advanced oogamy is present in phacophycal ectocarpus shows isogamy and anisogamy. Anisogamy is also seen in cutariales. Fucus shows primitive type of oogornium. Sargassum shows advanced oogany because only one ovum is produced in oogonium after fertilization takes place.

> It may concluded that in the evolution of sex in algae, the differentiation of gametes is associated with the differentiation of sex organ. It also shows that evolution of sex in algae has taken place from simplest type of the highest evolved type. 

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> The individual cells are prokaryotic in nature. The nucleus is incipient type and they lack membrane bound organelles.

> Both vegetative and reproductive cells are non-flagellate.

> Cell wall is made up of microfibrils and is differentiated into four (4) layers. The cell wall composed of mucopeptide, along with carbohydrates, amino acids and fatty acids.

> Locomotion is generally absent, but when occurs, it is of gliding or jerky type.

> The principal pigments are chlorophylls a (green), c-phycocyanin (blue) and c-phyco- erythrin (red). In addition, other pigments like β-carotene and different xanthophylls like myxoxanthin and myxoxanthophyll are also present.

> Membrane bound chromatophore are absent. Pigments are found embedded in thylakoids.

> The reserve foods are cyanophycean starch and cyanophycean granules (protein).

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Industrial Uses of Bacteria:- A large number of products are obtained due to bacterial activity, directly proportional to the economic importance of Bacteria.

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Archaebacteria and Eubacteria:-

1. Alternative Names:-

Archaebacteria:- Archaebacteria are called ancient bacteria.

Eubacteria:- Eubacteria are called true bacteria.

2. Size:-

Archaebacteria:- Individual archaebacterium is 0.1-15 μm in diameter.

Eubacteria:- Individual eubacterium is 0.5-5 μm in diameter.

3. Shape:-

Archaebacteria:- Archaebacteria are spheres, rods, plates, spiral, flat or square-shaped.

Eubacteria:- Eubacteria are cocci, bacilli,  vibrio, rods, filaments or spirochetes in shape.

4. Complexity:-

Archaebacteria:- Archaebacteria are simple in their organization.

Eubacteria:- Eubacteria are more complex than archaebacteria.

5. Habitat:-

Archaebacteria:- Archaebacteria are found in extreme environments.

Eubacteria:- Eubacteria are found everywhere on earth.

6. Cell Wall:-

Archaebacteria:- Cell wall is composed of pseudo peptidoglycans.

Eubacteria:- Cell wall is composed of peptidoglycans with muramic acid.

7. Membrane Lipids:-

Archaebacteria:- Membrane lipids of archaebacteria is ether-linked, branched, aliphatic chains, containing D-glycerol phosphate.

Eubacteria:- Membrane lipids of eubacteria are ester-linked, straight chains of fatty acids, containing L-glycerol phosphates.

8. RNA Polymerase:-

Archaebacteria:- RNA polymerase of archaebacteria consists of a complex subunit pattern, which is similar to eukaryotic RNA polymerase.

Eubacteria:- RNA polymerase of eubacteria consists of a simple subunit pattern.

9. Transfer RNA:-

Archaebacteria:- No thymine is present in the TψC arm of the tRNA, carrying methionine. 

Eubacteria:- Thymine is present in most of the tRNA, carrying N-formyl methionine.

10. Introns:-

Archaebacteria:- Introns are present in archaebacteria.

Eubacteria:- Introns are absent in eubacteria.

11. Growth and Reproduction:-

Archaebacteria:- Asexual reproduction methods like binary fission, budding and fragmentation are used by archaebacteria during their reproduction.

Eubacteria:- Other than binary fission, budding and fragmentation, eubacteria are capable of producing spores in order to remain dormant during unfavorable conditions.

12. Glycolysis/Kreb’s cycle:-

Archaebacteria:- Archaebacteria exhibit neither glycolysis nor Kreb’s cycle.

Eubacteria:- Eubacteria exhibit both glycolysis and Kreb’s cycle.

13. Types:-

Archaebacteria:- Archaebacteria are three types: methanogens, halophiles and thermophiles.

Eubacteria:- Eubacteria are two types: gram positive and gram negative.

14. Examples:-

Archaebacteria:- Halobacterium, Lokiarchaeum, Thermoproteus, Pyrobaculum, Thermoplasma and Ferroplasma are the examples of archaebacteria.  

Eubacteria:- Mycobacteria, Bacillus, Sporohalobacter, Clostridium and Anaerobacter are the examples of eubacteria.

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Allergy and its types:-

Allergy:- 

> An allergy is an immunological hypersensitivity mediated by immunoglobulin E antibody (IgE). 

> It is not related to any disease or infections. 

> Allergies can be seen in many organs, but most commonly, they affect the skin and mucous membranes.

> Our body is sensitive to specific particles in the environment, and these particles are called allergens. 

> Allergies are mostly a type of antigen that produces an abnormally vigorous immune response.

Types of Allergies:-

a. Type I:- 

> This reaction is initiated by the antigen reacting with tissue mast cells passively sensitized by antibodies (IgE) elsewhere, leading to pharmacologically active mediator release.

> The reaction is manifested within seconds or minutes after exposure and referred to as immediate hypersensitivity. 

> It includes general anaphylaxis and local manifestation of symptoms in various organs or systems. 

> The examples include bronchial asthma, rhinitis, urticaria, vomiting, diarrhoea, etc.

b. Type II:- 

> In this case the antibody (IgG/IgM) is directed against the antigen on an individuals’ own cells (target cells) or foreign antigen, e.g., transfused red blood cells. 

> This may lead to cytotoxic action by killer cells or by complement mediated lysis. 

> The examples are mismatched blood transfusion, transplant rejection, etc.

c. Type III:- 

> In a type III reaction, antibodies (IgG and IgM) form complexes with antigen and complement, generating neutrophil generating factors. 

> The immune complexes are deposited in the tissue. 

> The complement cascade is activated and polymorphs are attracted to the site of deposition causing local damage. 

> The examples include the Arthus reaction, serum sickness, etc.

d. Type IV:-

> This type of reaction is initiated by the action of antigen sensitized T-lymphocytes, releasing lymphokines following a secondary contact with the same antigen. 

> Lymphokines induce inflammatory reaction and activate macrophages which release mediators. 

> The reaction takes more than 12 hours to develop. 

> The examples are tuberculin hypersensitivity, graft rejection, contact dermatitis, etc.

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General account of immunology:-

> Immunology is the study of the immune system and is a very important branch of the medical and biological sciences. 

> The immune system protects us from infection through various lines of defence. 

> If the immune system is not functioning as it should, it can result in disease, such as autoimmunity, allergy and cancer.

> The immune system consists of a complex network of cells and molecules, and their interactions.

Types of immunity:- There are two major types of immunity:

1. Innate Immunity or Natural or Non-specific Immunity

2. Acquired Immunity or Adaptive Immunity

1. Innate Immunity or Natural or Non-specific Immunity:-

> This type of immunity is present in an organism by birth.

> This is activated immediately when the pathogen attacks. Innate immunity includes certain barriers and defence mechanisms that keep foreign particles out of the body.

> Innate immunity refers to the body’s defence system.

> This immunity helps us by providing the natural resistance components including salivary enzymes, natural killer cells, intact skin and neutrophils, etc. which produce an initial response against the infections at birth prior to exposure to a pathogen or antigens.

> It is a long-term immunity in which our body produces the antibodies on its own. Our body has few natural barriers to prevent the entry of pathogens.

Types of Barriers:- The four types of barriers are:

i. Physical barrier:-

- These include the skin, body hair, cilia, eyelashes, the respiratory tract, and the gastrointestinal tract. 

- These form the first line of defence.

- The skin does more than providing us with fair or dark complexions. 

- Our skin acts as a physical barrier to the entry of pathogens. 

- The mucus coating in our nose and ear is a protective barrier which traps the pathogen before it gets inside.

ii. Physiological barriers:-

- We know that our stomach uses hydrochloric acid to break down the food molecules. 

- Due to such a strongly acidic environment, most of the germs that enter our body along with the food are killed before the further process is carried on.

- Saliva in our mouth and tears in our eyes also have the antibiotic property that does not allow the growth of pathogens even though they are exposed all day.

iii. Cellular barriers:-

- In spite of the physical and physiological barriers, certain pathogens manage to enter our body. 

- The cells involved in this barrier are leukocytes (WBC), neutrophils, lymphocytes, basophil, eosinophil, and monocytes. All these cells are all present in the blood and tissues.

iv. Cytokine barriers:- The cells in our body are smarter than we give them credit for. For instance, in case a cell in our body experiences a virus invasion, it automatically secretes proteins called interferons which forms a coating around the infected cell and prevents the cells around it from further infections.

Cells Involved In Innate Immunity:-

i. Phagocytes:- These circulate through the body and look for any foreign substance. They engulf and destroy it defending the body against that pathogen.

ii. Macrophages:- These have the ability to move across the walls of the circulatory system. They release certain signals as cytokines to recruit other cells at the site of infections.

iii. Mast Cells:- These are important for healing wounds and defence against infections.

iv. Neutrophils:- These contain granules that are toxic in nature and kill any pathogen that comes in contact.

v. Eosinophils:- These contain highly toxic proteins that kill any bacteria or parasite in contact.

vi. Basophils:- These attack multicellular parasites. Like the mast cells, these release histamine.

vii. Natural Killer Cells:- These stop the spread of infections by destroying the infected host cells.

viii. Dendritic Cells:- These are located in the tissues that are the points for initial infections. These cells sense the infection and send the message to the rest of the immune system by antigen presentation.

2. Acquired Immunity or Adaptive Immunity:-

> Acquired immunity or adaptive immunity is the immunity that our body acquires or gains over time. Unlike the innate immunity, this is not present by birth.

> The ability of the immune system to adapt itself to disease and to generate pathogen-specific immunity is termed as acquired immunity. It is also known as adaptive immunity.

> An individual acquires the immunity after the birth, hence is called as the acquired immunity.

> It is specific and mediated by antibodies or lymphocytes which make the antigen harmless.

> The main function of acquired immunity is to relieve the victim of the infectious disease and also prevent its attack in future.

> It mainly consists of an advanced lymphatic defence system which functions by recognizing the own body cells and not reacting to them.

> The immune system of our body identifies the pathogens which have encountered in the past. It is mainly caused when a person comes in contact with the pathogen or its antigen.

> Our body starts producing antibodies to engulf the pathogen and destroy its antigen.

> When it encounters for the first time, it is called a primary response. Once a body gets used to these pathogens, antibodies are ready to attack them for the second time and are known as naturally acquired immunity.

> The acquired immunity in our body has certain special features.

Features of Acquired Immunity:-

i. Specificity:- Our body has the ability to differentiate between different types of pathogens, whether it is harmful or not, and devise ways to destroy them.

ii. Diversity:- Our body can detect vast varieties of pathogens, ranging from protozoa to viruses.

iii. Differentiate between self and non-self:- Our body has the unique ability to differentiate between its own cells and foreign cells. It immediately starts rejecting any foreign cell in the body.

iv. Memory:- Once our body encounters a pathogen, it activates the immune system to destroy it. It also remembers what antibodies were released in response to that pathogen, so that, the next time it enters, a similar procedure is followed by the body to eliminate it.

Cells Involved in Acquired Immunity:- The acquired immunity involves two types of cells: B-cells and T-cells.

i. B-cells:-

- They develop in the bone marrow.

- These cells are activated on their encounter with foreign agents. These foreign particles act as foreign markers.

- The B-cells immediately differentiate into plasma cells which produce antibodies specific to that foreign particle or so-called antigen.

- These antibodies attach to the surface of the antigen/foreign agent.

- These antibodies detect any antigen in the body and destroy it.

- The immunity dependent on B-cells is called humoral immunity.

ii. T-cells:-

- They originate in the bone marrow and develop in the thymus.

- T-cells differentiate into helper cells, cytotoxic cells, and regulatory cells. These cells are released into the bloodstream.

- When these cells are triggered by an antigen, helper T-cells release cytokines that act as messengers.

- These cytokines initiate the differentiation of B-cells into plasma cells which release antibodies against the antigens.

- The cytotoxic T-cells kills the cancer cells.

- Regulatory T-cells regulate immune reactions.

Types of Acquired Immunity:-

i. Humoral Immunity:-

- The antibodies produced by B-lymphocytes are present in the blood cells and they are transported all over the body. This is why it is called the humoral immune response as it consists of an antibody produced by the lymphocytes.

- It depends upon the action of antibodies circulating in the body. When an antibody on a B-cell binds with an antigen, humoral immunity comes into play. The antigen is internalized by the B cell and presented on the helper T cell. This activates the B-cell.

- The activated B cells grow and produce plasma cells.

- These plasma cells release antibodies in the bloodstream. The memory B cells retain the information about the pathogen to prevent any disease caused by that pathogen in the near future.

ii. Cell-mediated Immunity:-

- Cell-mediated immunity is initiated by the T helper cells.

- The cytotoxic T cells eliminate the infected cells from the body by releasing toxins, thereby, promoting apoptosis or programmed cell death.

- The T helper cells help to activate other immune cells. Cell-mediated immunity becomes clear in the case of transplant patients.

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Economic importance of algae:-

A. Useful activities:-

1. Primary Producers:-

> Algae are the main Oxygen producers in aquatic areas.

> They are also useful in decreasing water pollution by realizing Oxygen.

> 10% of photosynthesis is occurred by the algae in total photosynthesis quantity.

2. Algae as food:-

> Algae species are used as food in several countries in several forms.

> Algae species have proteins, vitamins (A, B, C and E), lipids, and minerals.

> Laminaria species is the important edible seaweed in Japan and the food item ‘Kombu’ is prepared

from it.

> ‘Aonori’ from Monostroma; ‘Asakusa Nori’ from Porphyra are prepared in different countries.

> Porphyra has 35% protein, 45% carbohydrates, Vitamins B and C and Niacin.

> Nostoc is used as food material in South America.

3. Algae as fodder for cattle:-

> Rhodymenia palmate is used as food for sheeps in Narvey. 

> The most widely used microalgae for protein-rich feed supplements include species of Chlorella, Arthrospira, Dunaliella, Tetraselmis, Phaeodactylum, Skeletonema, and Scenedesmus.

> Cultivation of Spirulina is gaining importance as feed for fish, poultry and cattle.

4. Algae as fertilizers:-

> Blue-green algae are treated as biofertilizers from olden days.

> Nostoc, Oscillatoria, Scytonema, Spirulina, etc. are used as fertilizers to rice fields.

> All these algae are fixed the atmosphere Nitrogen in to ground.

5. Algae in Pisi culture:-

> Sea algae are used as food for fishes. So they play an important role in Pisi culture.

> Some green-algae, Diatoms, some blue-green algae are used as food material to fishes.

> These are also making the water clean, by realizing Oxygen.

6. Alginates:-

> Alginates are the salts of alginic acid found in the cell wall of phaeophyceae.

> Alginates are extracted from Fucus, Laminaria, Macrocystis and Ecklonia.

> Alginates are used in the preparation of flameproof fibrics, plastics, paints, gauze material in surgical dressing, soups, ice creams etc.

7. Algea in industry:-

a. Iodine:-

> Iodine industry is mainly depended upon algae.

> Algae belonging to Phaeophyceae, like Laminaria, Ecklonia, Eisenia, etc. are used in the industry to prepare Iodine in industries.

> Phyllophora is used to prepare Iodine in Russia.

b. Agar-Agar:- 

> Agar-agar is a jelly like substance of great economic value.

> It is obtained from certain red algae like Gelidium, Graciliaria and Gigartina.

> Agar is used as a culture medium for growing callus in tissue culture.

c. Carrageenin:-

> It is extracted from cell walls of red algae like Chondrus and Gigartina.

> It is a polysaccharide esterfied with sulphate.

> It is used as emulsifier in pharmaceutical industry and also in textile, leather, cosmetics and brewing industries.

d. Diatomite:- 

> Diatoms deposits at marine and fresh water areas.

> Diatoms are rich with silica. It is called as diatomite.

> diatomite is used in the preparation of Dynamite in olden days.

> But now diatomite is used in different industries like glass, metal polishing, paints, tooth pasts, soups, etc.

e. Minerals:-

> The brown sea weeds popularly called as kelpyield potash, soda, and iodine.

> Some sea weeds are rich source of iron, zinc, copper, manganese and boron.

> Bromine is extracted from red algae such as Polysiphonia and Rhodymenia.

f. Funori:-

> It is a type of glue obtained from a red alga Gloipeltis furcata.

> It is used as an adhesive as well as sizing agent for paper and cloth.

> Chemically it is similar to agar-agar except that there is no sulphate ester group.

8. Algae in reclamation of alkaline or Usar soils:-

> Our country has more number of alkaline soils or sterile soils.

> Blue-green algae like Nostoc, Oscillatoria, Scytonema, Spirulina are modified the soils in to fertile soils. Because they fixed Nitrogen in to soil.

> Nearly they fixed 400 K.g. of Nitrogen per year.

> Soil erosion is also reduced by these algae.

9. Antibiotics and Medicines:-

> Antibiotic Chlorellin, obtained from Chlorella is effective against a number of pathogenic bacteria.

> Extracts from Cladophora, Lyngbya can kill pathogenic Pseudomonas and Mycobacterium.

> Laminaria is used as one of the modern tools for abortion.

> Seaweeds have beneficial effect on gall bladders, pancreas, kidneys, uterus and thyroid glands.

10. Role of Algae in Sewage Disposal:-

> Some species like Chlamydomonas, Scenedesmus, Chlorella, Pondorhina, Euridina, etc are living in sewage water.

> They are mainly useful to clean the water by realizing Oxygen.

> They also modified the carbonate material in the water into N, P, K fertilizers.

11. Algae as research material:-

> In biological research algae are useful because of their rapid growth, brief life span and easy mode of cultivation. 

> Chlorella, Scenedesmus and Anacystis are used in investigations in photosynthesis. Blue-green

algae are used in studies on nitrogen fixation.

> Researches in Genetics and Cytology are carried out on Acetabularia.

12. Algae in Space:- Chlorella and Synechococcus are finding application in space ships and nuclear submarines as oxygen regenerating and food and water recycling organisms.

B. Harmful activities:-

> Some algae species like Microcystis, Lyngbya are develop water blooms in water areas. They secrete toxic materials into water. That they polluted the water.

> The algae, Cephaleuros virescence causes for red rust tea in tea plant.

> Some algae species are caused for some skin diseases.

> Dianophlagellate is caused for the death of fishes in water.

> Because of their production of oxygen and their role in the food web, algae are normally beneficial to aquatic life.

> However, a bloom (a large and sudden growth in the population of phytoplankton) can cause the death of many fish.

> In most cases fish die because the decomposition of large amounts of algae depletes the oxygen in the

water.

> Phytoplankton that produce blooms called red tides produce toxins that kill fish directly. These toxins are also poisonous to humans; persons who eat shellfish contaminated with the toxins can become seriously ill.

> Most blooms occur in bodies of water that have been polluted with sewage or with runoff containing organic substances such as fertilizers.

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1. Haplontic Life Cycle:-

> In this life cycle plants are haploid.

> The Haplontic Life Cycle is a diphasic cycle and considered as the simplest and most primitive type of lifecycle.

> There is two-stage in haplontic life cycle such as gametophyte (haploid) and sporophyte (diploid) which is represented only by zygote.

> The Hap­loid gametes are developed within the gametangium of the gametophytic plant. Then two haploid gametes are fused and formed a zygote and enter to the diploid stage or sporophytic phase of the life cycle.

> During the germination, the zygotes are meiotically divided into haploid (n) zoospores, which are then developed into haploid plants. This is known as the gametophyte (haploid) stage.

> The haplontic life cycle is also known as the monogenic life cycle.

> Example:- Mostly found in Chlamydomonas, Ulothrix, Oedogonium, Spirogyra.

2. Diplontic Life Cycle:-

> In this life cycle plants are diploid.

> At first, the sporophytic plant body develops sex organs.

> Then sex organs undergo meiosis processes and develop gametes. These gametes represent the gametophytic stage.

> After that, the gametes are fertilized and form a zygote.

> This zygote forms a sporo­phytic plant body.

> Example:- Bacillariophyceae, Sargassum, Fucus Phaeophyceae.

3. Diplohaplontic Life Cycle:-

> The diplohaplontic life cycle has equally prominent haploid and diploid phases which are represented by two distinct vegetative individuals.

> Their chromosome number and function are different.

> The reproduction of the haploid gametophytic plant is followed by the sexual method whereas the diploid sporophytic plant by the asexual process.

> In this life cycle, the sporogenic meiosis and fusion of gametes is responsible for the alternation of two vegetative individuals.

4. Triphasic Life Cycle:-

> Algae have two different types of Triphasic life cycles:

i. Haplobiontic

ii. Diplobiontic

> Both these triphasic life cycles are unique. In simple words, the haplobiontic life cycle consists of two haploid generations and one diploid generation as shown in the below image:

> On other hand, the diplobiontic life cycle consists of two diploid generations and one haploid generation as shown below:

> The haploid gametophyte phase is dominant in the haplobiontic life cycle. In contrast, diploid sporophytes are the dominant stage in the diplobiontic triphasic life cycle. An example of this life cycle is found in the red algae of the genus Polysiphonia.

> Thus, from the above discussion, it is clear that there are several alternations of generations in algae and they do not have any fixed life cycle patterns as found in higher plants

Ans.

Work Of Indian Phycologists:-

> Indian Researchers started their work on Algae from 1919 onwards. 

> Ghosh( 1919- 32) carried on observations on blue- green algae of Burma and Punjab. 

> Later M.O.P Iyengar and his students Balakrishnan, Desikachary, Ramanathan and Subramaniam published a number of papers on algae of South India.

1. Mandayam Osuri Parthasarathy (M.O.P) Iyengar (1886-1963):-

- He was born in Madras. 

- He started his Research in Phycology especially about volvocales. 

- The great algologist Fritch was the guide of M.O.P. Iyengar for algal studies at london.

- He worked on lifehistory of Cylindrocapsa geminella, Microdictyon tenius. 

- He discovered new species like Fritschiella, Gilbertsmithia, Ecballocystopsis and Characiosiphon. 

- For his contribution in the field of phycology he is called as “Father of Modern Phycology of India”.

- Iyengar was the president of Phycological society of india. 

- His huge collections of specimens and herberium sheets were handovered to Dept of Botany, University of Madras.

2. Thamarapu Vedanta Desikachary:-

- He was born in Tirupati. 

- He was the student of M.O.P. Iyengar. 

- He gave rebirth to the unpublished papers of M.O.P.Iyengaras “Contribution to our Knowledge of  South Indian Algae”

- He published large number of Research Papers namely “ Monograph on Cyanophyta”, “Taxonomy and Biology of Blue green algae”, “Marine plants and Volvocales” 

- He published “ Rhodophyta and Phaeophyta”, “Monumental atlas of Indian Diatoms” in 5 Volumes. 

- He made critical studies on Life History of Red Algae.

- He discovered new generas like Iyengariella, Iyengariomonas, Schilleriomonas, Mantoniella and Rossiella. 

- He was the Chief Editor of Phykos. 

- Phycological Society of America honoured him for his life time contribution in Phycology. 

- His massive algal collections are even today present in University of Madras.

3. Yajnavalkya Bhardwaja:-

- He completed PhD from University of London and was H.O.D of botany in BHU. 

- He opened a school of Algal studies at BHU and it is famous world over for its contributions.

- He discovered Draparnaldiopsis indica , two species of Scytonemataceae, Spelaeopogon kashyapi and Scytonema malaviyaensis.

4. M.S.Randhawa(1932-59):-

- Mohinder Singh Randhawa was born in Punjab. 

- He got selected in ICS(Indian civil service). 

- He was one of the chief editors of Phykos.

- He published series of papers on Zygnemaceae, Oedogoniales and Vaucheriaceae. 

- He recorded 70 species of Zygnemaceae.(A.V.S.S. Sambamurthy 2005) 

- He discovered new species such as Zygogonium kumaoense, Oedocladium himalayense, Zygnema terrestre. 

- He recorded a new type of akinite formation in Vaucheria.

5. Rama Nagina Singh:-

- He was the student of Y.Bhardwaja and studied in BHU. 

- He was credited for his work on cyanobacteria and it uses in agricultural fields. 

- He discovered Aulosira fertilissima.

- He described life history of Fritschiella tuberosa and Draparnaldiopsis indica. 

- He is also known for his work on reclamation of usar lands in india.

- The discoveries of new generas created a scope for research in phycology in india and more species were discovered in later years. 

- The achievements of these phycologists made many more researchers to enter in the field of phycology.

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Phylogenetic Relationships of Phaeophyceae:-

> The Phaeophyta form a well-marked taxon not very closely related to the other algae. The nature of swarmer’s suggests that the Phaeophyta possibly arose from flagellate unicellular organisms.

> The Phaeophyta are often considered parallel to the Chlorophyta in the nature of plant body and in the method of reproduction, although the Phaeophyta have evolved multicellular reproductive organs and a higher type of vegetative body.

> The apically growing thallus of the Phaeophyta developing into an elaborate structure is often differentiated into epidermis, cortex, and medulla. Besides this, the development of sieve-tube cells and in some cases development of a cambium­ like region are the features which can very well justify a very high position for the Phaeophyta in the evolutionary scale.

> Since they lack xylem for conduction and sup­port, a cuticle for protection against evaporation, jacket layers around their multi­cellular reproductive organs for protection against desiccation, and the mode of sexual reproduction is not well advanced, the Phaeophyta did not receive any higher position although they possess high degree of specialization in their plant body.

> The pigmentation of the Phaeophyta suggests a relationship to both the Ghrysophyta and the Pyrrophyta. All these groups have an excess of carotinoid pigments over chlorophylls, as compared to the Chlorophyta. Chlorophyll c is known only in the Phaeophyta, Chrysophyta and Pyrrophyta. Fucoxanthin, the principal xanthophyll of the Phaeophyta occurs also in the Chryosophyta but is unknown among the Pyrrophyta.

> The sum of the evidence indicates that the Phaeophyta originated from a prechrysophytan stock after the pyrrophytan line had already diverged from the ancestors of this same stock.

> A common ancestry of the Phaeophyta with the Chrysophyta has also been sug­gested considering the similarity of the flagellate cells in both these taxa.

> The fossil record is hardly useful in determining relationships of the Phaeophyta. Fossils more or less resembling Fucus and other members of the Phaeophyta occur in rocks of the early Paleozoic. But they are not well preserved to be placed in any algal taxa, and hence they provide no indication of the ancestry of the Phaeophyta.

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Replication of Viruses:- During the process of viral replication, a virus induces a living host cell to synthesize the essential components for the synthesis of new viral particles. The particles are then assembled into the correct structure, and the newly formed virions escape from the cell to infect other cells.

1. Attachment:-

> The first step in the replication process is attachment. 

> In this step, the virus adsorbs to a susceptible host cell. 

> High specificity exists between virus and cell, and the envelope spikes may unite with cell surface receptors. 

> Receptors may exist on bacterial pili or flagella or on the host cell membrane.

2. Penetration:-

> The next step is penetration of the virus or the viral genome into the cell. 

> This step may occur by phagocytosis; or the envelope of the virus may blend with the cell membrane; or the virus may “inject” its genome into the host cell. 

> The latter situation occurs with the bacteriophage when the tail of the phage unites with the bacterial cell wall and enzymes open a hole in the wall. The DNA of the phage penetrates through this hole.

3. Replication:-

> The replication steps of the process occur next. 

> The protein capsid is stripped away from the genome, and the genome is freed in the cell cytoplasm. 

> If the genome consists of RNA, the genome acts as a messenger RNA molecule and provides the genetic codes for the synthesis of enzymes. 

> The enzymes are used for the synthesis of viral genomes and capsomeres and the assembly of these components into new viruses. 

> If the viral genome consists of DNA, it provides the genetic code for the synthesis of messenger RNA molecules, and the process proceeds.

>In some cases, such as in HIV infection (as discussed below), the RNA of the virus serves as a template for the synthesis of a DNA molecule. The enzyme reverse transcriptase catalyzes the DNA's production. The DNA molecule then remains as part of the host cell's chromosome for an unspecified period. From this location, it encodes messenger RNA molecules for the synthesis of enzymes and viral components.

4. Assembly:-

> Once the viral genomes and capsomeres have been synthesized, they are assembled to form new virions. This assembly may take place in the cytoplasm or in the nucleus of the host cell. 

> After the assembly is complete, the virions are ready to be released into the environment.

5. Release:-

>For the release of new viral particles, any of a number of processes may occur. For example, the host cell may be “biochemically exhausted,” and it may disintegrate, thereby releasing the virions. 

> For enveloped viruses, the nucleocapsids move toward the membrane of the host cell, where they force themselves through that membrane in a process called budding. During budding, a portion of cell membrane pinches off and surrounds the nucleocapsid as an envelope. 

Lytic Cycle and Lysogeny:-

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.

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. 

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.

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The reproduction takes place by means of vegetative, asexual and sexual methods.

1. Vegetative reproduction:- In majority of cases it takes place by fragmentation.

2. Asexual reproduction:-

> The asexual reproduction of the gametophytes takes place by neutral spores, monospores, and polyspores. The neutral spores develop in ordinary cells of thallus, e.g., Asterocystis. The monospores are developed in sporangia. A single spore develops in each sporangium, e.g., Scinaia. The polyspores are formed in larger number in the sporangium.

> The asexual reproduction of the sporophytes takes place by tetraspores formed in tetrads in the tetrasporangia, e.g., Polysiphouia and paraspore borne inside parasporangium in greater numbers. During the development of tetraspores reduction division takes place. In the development of paraspores there is no reduction division.

3. Sexual reproduction:-

> The sexual reproduction is always oogamous. The oogamy is of special type. The sex organs of Rhodophyceae have a distinguished terminology. The male structures are called the spermatangia developing non-motile spermatia (male gametes) in them. The female sex organ is called the procarp. It has a carpogonium bearing a receptive structure trichogyne. The egg develops in the basal swollen part of carpogonium. The auxiliary cell may or may not be formed. In Ceramiales the auxiliary cell is formed after fertilization.

> Zygote and its germination:- In sub-class Bangioideae the zygote divides by vertical and transverse divisions. The number of cells may be 2, 4, or 16. The spores are known as carpospores. They are naked and liberated by disintegration of zygote wall and move about in amoeboid fashion. The first division of the nucleus of the zygote is reductional. In sub-class Florideae the carpospores develop indirectly from the zygote.