2019 Solved Old Paper (BOT-101)

-
Ans.
Phytoplasma:-

> Mycoplasmas are the smallest among the known aerobic prokaryotes. 

> They were first discovered by Pasteur in 1843, during his work on the possible causal agent of pleuropneu­monia of cattle. Thus they were called pleuro- pneumonia-like organism (PPLO). Pasteur was unable to isolate them in pure culture.
> Later, Nocard and Roux (1898), the French microbio­logists, were successful in growing them in pure culture-medium containing serum and confirmed by inoculation and subsequent expression of disease in healthy cattle.
> Mycoplasmas are commonly found in soil, hot spring, sewage water and also in plants and animals including man. Borrel (1910) named these organisms Asterococcus mycoides. Later, in 1929, Nowak placed them under the genus Mycoplasma.
Ans.
Ans.
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. 
Ans.
Xanthophyta:-
> The plastids are yellow-green in colour. The photosynthetic pigments are chlorophyll a, chlorophyll e (very little), P-carotene (fairly high concentration) and xanthophylls. The chief xanthophyll is diadinoxanthin. The other xanthophylls are violaxanthin, lutein, neoxanthin, flavoxanthin and flavacin. The carotenoides are normally present in excess amount than chlorophyll. Chlorophyll b is absent.
> The reserve food is oil, lipid and lucosin. Starch is not formed.
Phaeophyta:-
> Photosynthetic pigments:- chlorophyll a and c, beta carotene, Dinoxanthin ,violaxanthin, and Fucoxanthin. These pigments give brown algae color and Fucoxanthin pigment are dominant.
> Food reserves:- laminarin, mannitol.
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.
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.
Ans.
> Gonium is a small, motile, colonial green alga consisting of biflagellate cells in a flat plate. 
> The cells use their pair of flagella to swim with a rotating motion. 
> Different species may have 4, 8, 16, or 32 cells that are ovoid or angular in shape. 
> Each cell has an eyespot, two contractile vacuoles at the base of the flagella, and a large cup-shaped chloroplast with at least one pyrenoid. 
> Each cell is enclosed within a mucilage sheath, which join together to form the colony. 
> Unlike the larger volvocalean colonies such as Volvox or Eudorina, the cells of Gonium colonies are identical and show no evidence of specialization.
Ans.
Division - Rhodophyta:-
Salient Features:-
> Red Algae are an ancient group of algae with over 5,000 living species.
> Majority of them are marine. A few (example- Batrachospermum, Lemnaea) are freshwater aquatic or subaquatic terrestrial (example- Porphyridium).
> Their size varies from unicellular microscopic forms to half a metre in length. Several species of red algae are graceful and lace-like plants. Some red algae secrete CaCO3 on their walls and form coralline algae.
> They are red in colour due to phycoerythrin and phycocyanin pigments. They have chlorophyll a molecule 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.
> Flagellate forms and stages are completely absent.
> Cell Wall consists of cellulose and pectic compounds. Sulphated geloses or phycocolloids occur in most red algae. The important ones are agar, carrageenin and funori.
> Vegetative reproduction occurs by fragmentation, gemmae and regeneration of holdfast.
> Reproduction occurs by both sexual and asexual methods. The spores are non-motile. Sexual reproduction is highly specialised. Male gametes are non-motile and called spermatia. Spermatia are carried by water currents to elongated tip trichogyne of female sex organ carpogonium. Following fertilisation, the zygote may produce carpospores. Example- Poryphyra by division directly or indirectly from zygote as in Batrachospermum and Polysiphonia.
> The life cycle of many red algae like Polysiphonia has an alternation of haploid and diploid multicellular generations.
Ans.
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.
Harmful algal blooms (HAB):-
> A harmful algal blooms is an algal bloom that causes negative impacts to aquatic organisms via production of natural toxins, mechanical damage to aquatic organism. 
> HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisonings and also fin fishes and other aquatic organisms .
> HABs in India:-
- Researchers have found toxic bloom has increased around 15 percent over the 12 years in indian seas. 
- There was 80 harmful bloom recorded between the 1998-2010 in indian water. 
> Worldwide Effects of HABs:-
- Light penetration levels in water decrease altering photosynthesis rate. 
- Algal blooms may be harmful to seagrass and coral reef ecosystems and the connected food webs. 
- Shellfish may accumulate algal toxins by feeding on the toxic phytoplankton resulting in fish kills, marine mammal distress, human illness and possible death.
> Reasons for Increase in HABs:-
- Global climate changes producing wider ranges for some species. 
- Human contributions of increased nutrients and pollution in coastal waters and also fresh waters. 
- Changes in local ecosystems that may allow exotic species to thrive if introduced.
- Upwelling. 
- Formation of mud banks. 
- Nutrients discharge on sea or fresh water through river.
- Eutrophication:- It is a process where by water bodies receive excessive amounts of nutrients, which results in excessive plant growth and formed algal bloom.
> Factors that can contribute to HABs:-
i. Excess nutrients (Eg.- phosphorus or nitrogen) 
ii. Sunlight 
iii. Low-water levels or low-flow conditions 
iv. Calm water (low-wind conditions) 
v. Warmer temperatures
> Examples of some HABs:-
i. Cyanobacteria (blue-green algae) 
ii. Redtides:- Neurotoxic shellfish poisoning 
iii. Ciguatera:- Gambierdiscus toxicus 
iv. Alexandrium 
v. Gymnodium 
vi. Dynophysis 
vii. Coolia monotis 
viii. Prorocentrum lima.
Harmful effect of algal bloom:-
> Changes in levels of chemicals such as nitrogen and phosphorus from fertilizer, in the water. 
> Algal blooms can deplete the oxygen and block the sunlight that other organisms need to live. 
> Some can produce toxins that are harmful to the health of the environment- plants, animals, and people etc. 
> Aquaculture industries.
Control method:-
> Biological:- Bacteria (Gymnodinium mikimotoi), Virus, Bivalves, Zooplankton etc. 
> Chemical:- Copper sulfate, Alum etc. 
> Physical
Ans.
Cyanobacteria:- 
1. Salient Features:-
> Most of the species are fresh water (e.g., Oscillatoria, Rivularia), a few are marine (e.g., Trichodesmium, Darmocarpa), and some species of Oscillatoria and Nostoc are grown on terrestrial habitat.
> 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).
> Many filamentous members possess specia­lized cells of disputed function (supposed to be the centre of N2 fixation) known as heterocysts.
> Reproduction takes place by vegetative and asexual methods. Vegetative reproduction takes place by cell division, fragmentation etc. Asexual reproduction takes place by endospores, exospores, akinetes, nannospores etc.
> Sexual reproduction is completely absent.
2. Biological Importance:-
i. They are one of the early colonizers of bare and barren areas. They provide suitable conditions for the growth of other organisms even in the most hostile environment.
ii. Blue green algae function as food to several aquatic animals. Spirulina is regularly collected for human consumption in parts of Africa. Nostoc is similarly used in China. In Rajasthan Anabaena and Spirulina are collected from Sambar Lake and used as fodder and manure. Spirulina is very easily cultivated in tanks and can be used as a palatable protein rich food supplement for humans and animals.
iii. Several cyanobacteria have the ability of nitrogen fixation. The filamentous forms possess special large pale cells or heterocyst’s for this. Some of the fixed nitrogen comes out as excretion. After death of cyanobacteria the substratum becomes rich in nitro­gen. Such nitrogen fixing cyanobacteria are now regularly inoculated in the rice fields. This saves consumption of nitrogen fertilizers.
iv. Nitrogen fixing cyanobacteria are often used for reclaiming usar soils, e.g., Nostoc, Anabaena. These cyanobacteria produce acidic chemicals for counteracting alkalinity of the soil and nitrogenous compounds which are generally deficient in these soils.
v. Antibiotic can be manufactured from extract of Lyngbia.
vi. Species of Anabaena and Aulosira do not allow mosquito larvae to grow nearby. Such cyanobacteria can be inoculated in village ponds and rice fields to prevent the growth of mosquitoes.
vii. Cyanobacteria can grow on the walls and roofs of buildings during the rainy seasons causing discolouration, corrosion and leakage.
viii. They produce water blooms, imparting bad odour and colour to water bodies.
ix. Some cyanobacteria produce toxins harmful to most aquatic animals. They may prove equally toxic to human beings drinking or bathing in such water. The important toxins producing cyanobacteria are Microcytic aeruginosa (= Anacystis cyanea), Anabaena flosaquae, Aphanizomenon flos-aquae.
Ans.
Sexual Reproduction:- 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.
1. Autogamy:- 
> Fusing gametes are formed from the very same mother cell throughout this process, and then after fusion, these produce a zygote. 
> For the reasons mentioned above, autogamous plants do not display the emergence of any new characteristics, such as Diatoms (Amphora normani).
2. Hologamy:- 
> Vegetative cells of various strains (+ and -) act as gametes in certain unicellular members, and then after fusion, they result in the formation of a zygote. 
> This seems to be an inefficient method in terms of multiplication, however, it does result in the creation of new genetic varieties, such as Chlamydomonas.
3. Isogamy:- 
> It is the merger of two gametes that are physiologically and morphologically identical, resulting in the formation of a zygote. Isogametes are a form of gamete. 
> These are typically flagellates, such as Chlamydomonas Eugametos, Ulothrix, and others.
4. Anisogamy:- 
> The uniting gametes are physiologically and morphologically distinct during this phase. 
> The microgamete (male) is small and more aggressive, while the macrogamete (female) is bigger and less active, such as Chlamydomonas braunii. 
> Physiological anisogamy differs from traditional anisogamy in that the uniting gametes share morphological similarities but vary physiologically. 
> Zygnema, Spiro­gyra, can be some examples.
5. Oogamy:- 
> 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). 
> Male gametes grow in antheridium, while female gametes grow in oogonium, such as Polysiphonia, Oedogonium, Chara, Batrachospermum, Vaucheria, Sargassum, Laminaria, and so on.