Biology 3 Marks Question

Sometimes, green algae such as Chlorella, Scenedesmus and Spirogyra, etc., grow in excess in water bodies and impart green colour to the water. These are called algal blooms. Red. dinoflagellates (Gonyaulax) grow in abundance in sea and impart red colour to the ocean. This looks like red tides. Both due to algal blooms and 'red tide' the animal life declines due to toxins and deficiency of oxygen inside water.

Heterotrophic bacteria:

1. Many bacteria like Lactobacillus helps in the production of curd from milk.
2. They act as decomposers and help in the formation of humus e.g. Pseudomonas.
3. Many antibiotics are obtained from some species of bacteria like streptomyces, Bacillus etc.
4. Many soil bacteria help in fixation of atmospheric nitrogen like Rhizobium (Symbiotic), Azotobacter (Free living).

Viroids are the smallest known agent of infectious diseases that contain small single-stranded RNA molecule. They lack capsid and have no proteins associated with them. Viroids infect only plants. Whereas, viruses have genetic material surrounded by a protective coat of protein or lipoprotein. The genetic material of viruses are of 4 types – double-stranded DNA, double-stranded RNA, single-stranded DNA, single-stranded RNA. They infect both plants and animals.

Plants have autotrophic mode of nutrition as they contain chlorophyll pigment. Thus, they have the ability to prepare their own food by the process of photosynthesis. However, some insectivorous plants are partially heterotrophic. They have various means of capturing insects so as to supplement their diet with required nutrients derived from insects, causing proliferation of growth. The examples include pitcher plant (Nepenthes), Venus fly trap, bladderwort, and sundew plant.

Viruses are microscopic organisms that have characteristics of both living and non-living. A virus consists of a strand of DNA or RNA covered by a protein coat. This presence of nucleic acid (DNA or RNA) suggests that viruses are alive. In addition, they can also respond to their environment (inside the host cell) in a limited manner. However, some other characters, such as their inability to reproduce without using the host cell machinery and their acellular nature, indicate that viruses are non-living. Therefore, classifying viruses has remained a mystery for modern systematics.

The cell walls of diatoms are made of silica. Their cell wall construction is known as frustule. It consists of two thin overlapping shells that fit into each other such as a soap box. When the diatoms die, the silica in their cell walls gets deposited in the form of diatomaceous earth. This diatomaceous earth is very soft and quite inert. It is used in filtration of oils, sugars, and for other industrial purposes.

A bacteriophage consists of two main parts i.e., head and tail. Head: The head is in the form of bipyramidal hexagonal prism. It consists of proteinaceous membrane enclosing a core of viral DNA. The DNA is double-stranded. Tail: It is cylindrical. It has four components are:

1. A central core.
2. A protein sheath surrounding the core
3. A sheath connected to head by a collar and at distal end to a hexagonal basal plate.
4. Pins at the corners of basal plate. Basal plate also bears six long tail fibres which are the organs of attachment to the bacterial surface.

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1. Mycelium: Mycelium is coenocytic and non-septate or aseptate. Septa are formed only in connection with separation of old senescent parts and delimitation of reproductive structures.
2. Eucarpy and holocarpy: In eucarpy, only a portion of somatic body is transformed into reproductive body. In holocarpy, transformation of the whole somatic body into reproductive structure is found in only some primitive forms.
3. Asexual reproduction: It involves the formation of sporangia. The sporangia function as conidia in dry habitats as zoosporangia under wet conditions.

Fungus cells are eukaryotic. These cells contain all the eukaryotic organelles except plastids. Some of these organelles are nucleus, ribosomes, endoplasmic reticulum,mitochondria, Golgi bodies, etc. A fungal cell wall contains mostly chitin. Plasmalemma bears coiled membranous outgrowths called lomasomes. Nuclei are small and connected to endoplasmic reticulum. Nuclear division involves formation of internal spindle. Vacuoles are small. Near the hyphal tips, the cytoplasm contains small vesicles called chitosomes. Food reserve is in the form of glycogen and oil.

Species of Sphagnum, a moss, provide peat that has long been used as fuel and because of their capacity to hold water as packing material for trans-shipment of living material. Peat forms when plant material decaying fully by acidic and anaerobic conditions. Peat is soft and easily compressed. Under pressure, water in the peat is forced out. Upon drying, peat can be used as fuel.

1. AIDS (Acquired Immuno Deficiency Syndrome).
2. Small Pox.
3. Swine Flu.
4. Bird Flue.
5. Common cold.

Chemosynthetic bacteria are autotrophic bacteria. They are able to manufacture their organic food from inorganic raw materials with the help of energy derived from exergonic chemical reactions involving oxidation of an inorganic substance present in the external medium. Thus, these bacteria are chemoautotrophic. The chemical energy obtained from oxidation reaction is trapped in ATP molecules. Examples are nitrifying bacteria, sulphur oxidising bacteria, and iron bacteria.

1. By pseudopodia - e.g. Amoeba
2. By flagella - e.g. Trypanosoma
3. By cilia - e.g. Paramoecium.

Several cyanobacteria have the ability to fix atmospheric nitrogen. The filamentous forms possess special large pale cells or hetrocysts specialised to perform nitrogen fixation. 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 fertilisers, and. thus helps in crop improvement.

1. Ringworm.
2. Candidiasis.
3. Dandruff.

Viruses have the following features that make them similar to living things:

1. They have DNA or RNA.
2. Their nucleic acid can undergo mutation.
3. They can reproduce only in living host cells.
4. They infect different types of host cells.
5. The nucleic acids of viruses are identical in composition to those of other organisms.

1. Paramylon: These are found in euglenoids. These are the products of photosynthesis which can be stored in the cytoplasm.
2. Pseudoplasmodia: These are found in slime moulds. Pseudoplasmodia are formed when the food supply of the medium is exhausted.
3. Heterocysts: Present in cyanobacteria. They are the sites of nitrogen-fixation.

Ascomycetes Consist of sporangial sac called ascus . Asci (singular-ascus) may occur freely or get aggregated with dikaryotic mycelium to form the f ratification called ascocarps, The trustification formed by asci are like.

1. Apothecium is a cup like structure, e.g., Peziza.

2. Perithecium flask shaped, e.g., Neurospora.

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3. Cleistothecium closed with a slit, e.g., Penicillium.

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The main criteria used for five kingdom system of classification are:

1. Complexity of cell structure.
2. Complexity of organism's body.
3. Mode of obtaining nutrition.
4. Life cycle and phylogenetic relationship.

1. Plasmodium causes malaria.
2. Entamoeba histolytica causes amoebic dysentery.
3. Trypanosoma causes sleeping sickness.

The three kingdom classification system was proposed by Ernst Haeckel in 1866. He did not distinguish bacteria from other living beings. They were incorrectly placed under kingdom-Protista. This shortcoming was removed by Copeland in 1956, when he placed all the bacteria and related organisms into another kingdom-Monera. Copeland's system of classification was able to separate prokaryotic organisms from eukaryotic organisms which was a major drawback of Haeckel's system of classification.

Criteria used to classify fungi are:

1. Morphology and appearance of fungus.
2. Life-cycle.
3. Types of spores and their dispersal.
4. Physiology and biochemistry.

• Aristotle attempted a more scientific basis for classification.
• He classified plants into trees, shrubs and herbs.
• He classified animals into two groups:

1. Those which have red blood.
2. Those without red blood.

All fungi pass through two phases or stages in their life cycle. These phases are vegetative or assimilative phase and reproductive phase. Vegetative phase: In this phase, they go speedily in the food giving substratum. The food substratum may be bread, cheese, wood, etc. Coprophilous fungi grow well on cow dung, dead parts of plants like fallen leaves. Reproductive phase: In this phase, erect hyphae develop which produce reproductive structure. In unicellular yeasts, the entire cell becomes a reproductive structure. This is the holocarpic condition. In other fungi, reproductive structures develop from a part of the vegetative body and the condition is called eucarpic.

1. The interior of bacterial cell seems simple and granular because the membrane bound organellesare not present in it.
2. Mucilage, cell wall and plasma membrane are together called cell envelope.
3. Mucilage or glycocalyx gives gummy or sticky trait to cells.

Though it is not essential for bacterial survival, glycocalyx has several functions such as:

1. Protection from dessication and toxins.
2. Preventing host phagocytes to get attached to the bacterium.
3. Holding cells together.
4. Storing chemicals for virulence.

Option (i) is the correct option because it talks about classification of a particular term into specific categories. Other options are not related to classification of anything. Segregation of students into different classes has many benefits. The level of course would be different for students of different age groups; which necessitates progression of students through various stages of classes. Segregation of students of a class into different sections makes the life easy for students as well as for teachers. It is easier for teachers to manage a smaller group. For students also, learning in a small group makes the learning easy. Studying in a very large group would mean that most of the students would be unable to pay proper attention in the class.

Differences between Monera and Protista are:

S. No.	Monera	Protista
1.	Cell wall is made up of peptidoglycan.	It is made up of cellulose.
2.	Respiratory apparatus is present in respiratory membrane.	It is present in mitochondria.
3.	Ribosomes are 70S type.	Ribosomes are 80S type.
4.	These are prokaryotic and have naked circular DNA.	Eukaryotic, linear DNA is present in nucleus.
5.	Extrachromosomal DNA is present in the form of plasnids.	Extrachromosomal DNA is present in organelles like mitochondria and chloroplast.

The mycelium of a fungus /mushroom growing in the ground absorbs nutrients by secretion of enzymes from the tips of the hyphae (threads making up the mycelium). This breaks down larger molecules in the soil into smaller molecules that are then absorbed through the walls of the hyphae near their growing tips. The mycelium moves outward from the center when the nutrients in the center are exhausted. The center dies, thereby forming a living ring. These rings are known as fairy rings especially in Europe.

1. Basidiocarp: It may be minute or very large structure which bears basidia, e.g., Bracket fungi, puffballs.
2. Basidia: These are special reproductive bodies of Basidiomycetes where karyogamy, meiosis and basidiospore formation occurs.
3. Basidiospores: These are meiospores of Basidiomycetes. Basidiospores are borne at the tips of sterigmata or outgrowths of basidia.

1. Toadstools.
2. Mushrooms and young puffballs.
3. Brewer's yeast (Saccharomyces cerevisiae).
4. Truffles (tuber-like underground fungus).
5. Rhizomorphs perennate during periods of scarcity of food and water.
6. Basidiospores (develop exogenously).
7. Sclerotia under favourable conditions each one forms a new mycelium.

Fungi are cosmopolitan in occurrence being present in air, water, soil, over and inside plants and animals. Fungi have both beneficial and harmful roles. For example, yeasts are used in brewing industry, baking industry as well as it causes various plant and animal diseases. Commercial antibiotic penicillin has been obtained from fungus Penicillium. Morels and mushrooms are group of edible fungi. However, Aspergillus another fungus contaminates food stuff like bread, jam, butter, syrups and also laboratory cultures.

1. Sporozoans are intracellular endoparasites of invertebrates and vertebrates.
2. They have nutrition which is mostly absorptive type and rarely digestive.
3. Sporozoans are commonly uninucleate.
4. Asexual reproduction occurs by multiple fission and sexual reproduction involves fusion of gametes.
5. Examples Plasmodium, Toxoplasma, Monocystis and Eimeria.

1. Staphylococcus aureus and Clostridium botulinum.
2. Thiobacillus denitrificans and Micrococcus denitnficans.
3. Lactobacillus acidophyllus.
4. Acetobacter acetic.
5. Pseudomonas fluorescens and Clostridium sp.
6. Escherichia coli and Agrobacterium tumefaciens.

Reproduction in fungi occurs by asexual and sexual methods. Asexually, it takes place either by formation of motile spores (zoospores) or by formation of non-motile spores (aplanospores) or conidia. In lower fungi like Phycomycetes, sex organs like the unicellular antheridia (male) and unicellular oogonia (female) are produced. In higher fungi like Basidiomycetes, sex organs are absent but sexual process is present. Ascomycetes and Basidiomycetes fungi produce fruiting bodies by sexual process called ascospores and basidiospores, respectively.

Phylogeny is the evolutionary history of an organism. It shows the true kinship of organism. Such relationships are not clear in all cases. Only fossil record can provide such relationships, but complete records are not available for such studies. Hence, the phylogenetic relationships are ascertained from morphology, cytology, genetics, physiology and biochemistry for the correct classification of the organisms.

1. Growth promotion: Fungus produces growth promoting hormones. In the absence of this association, Pinus and Berth show stunted growth despite providing all types of nutrients.
2. Antimicrobial substance: Fungus protects the root from parasitic fungi and harmful bacteria by secreting antimicrobial substances.
3. Nourishment: In orchids, the fungus absorbs nourishment from outside transports it over to the germinating seed.
4. Adverse environment: Allows plants to grow in mineral deficient soil, saline soil, unfavourable pH and temperature.
5. Absorption of water: Fungal association increases water availability to the root.

S.No.	Ascospores	Conidia
1.	These are the spores formed after sexual formed reproduction.	There are the spores for asexual reproduction.
2.	Spores are formed endogenously in the asci.	Spores are produced exogenously on condiophores.
3.	Eight spores are formed in an ascus.	Many are formed on a conidiophore.
4.	Spores formed are genetically dissimilar.	Spores formed are genetically similar.

Alternation of Generation: Life cycle of plants has two distinct phases the diploid sporophytic and the haploid gametophytic that alternate with each other. The lengths of the haploid and diploid phases, and whether these phases are free living or dependent on others, vary among different groups in plants. This phenomenon is called alternation of generation.

1. They are mostly marine.
2. They are unicellular and eukaryotic.
3. They appear yellow, brown, blue, green or red, depending on the main pigments present in them.
4. The cell wall has stiff cellulosic plates on the S outer surface.
5. Most of them have two flagella-one lies longitudinally and the other transversely in afurrow between the cell wall plates
6. Some red dinoflagellate like Gonyaulax undergoes such a rapid multiplication that it causes red tide in the ocean and the toxin secreted by it kills aquatic animals.

Mycorrhiza is a mutually beneficial or symbiotic association of fungi with roots of higher plants. Orchids grow as epiphyte on plants, have their roots associated with fungi right from the seedling stage. Many orchids cannot survive without mycorrhizae associations. Many forest trees such as piles appear stunted if mycorrhizal associations are absent. In the presence of these associations, these plants absorb 2-3 times more nitrogen, potassium and phosphorus compared to without them.

Algae produce different spores under different conditions:

Type of Spores	Description	Conditions for production
Zoospore.	Mobile spores with flagella.	Formed under favourable conditions.
Aplanospore.	Non-motile spores without flagella.	Formed under unfavourable conditions.
Hynospore.	Spores having thick walls for protection.	Formed under unfavourable conditions.
Akinetes.	Resting cells formed from the vegetative cells.	Formed under unfavourable conditions.
Statospores.	Similar to akinetes and found in ddiatoms.	Formed under unfavourable conditions.

Differences between pili and fimbriae are:

S. No.	Pili	Fimbriae
1.	They are tube-like outgrowths of bacterial cells.	They are solid outgrowths bacterial cells.
2.	Their length is about 18-20m.	Their length is about 0. 15-1.5m.
3.	Only 1-4 pill occur per cell.	About 300-400 fimbriae occur per cell.
4.	They help in conjugation.	They help in clinging to various objects.

Deuteromycetes is an artificial class of fungi which has been created to include all those fungi (fungi imperfect) in which sexual stage is either absent or not known. Their mycelium is usually septate. Coenocytic forms are not known. Clamp connections, typical of Basidiomycetes are absent. It is believed that most members of Deuteromycetes are actually Ascomycetes in which sexual reproduction is either absent or yet to be discovered.

Cyanobacteria and heterotrophic bacteria have been clubbed together in Eubacteria of Kingdom Monera as per the “Five Kingdom Classification” because they do not have nuclear envelope and membrane bound organelles. Their genetic material is naked. They have 70S type of ribosomes. So, cyanobacteria and heterotrophic bacteria are prokaryotes and belong, to Kingdom Monera.

The two kingdom classification system was given by Linnaeus in 1758. Lesser number of organisms were known then in comparison to what the world knows today. He classified all the known living beings into two categories-Animalia and Plantae on the basis of the presence or absence of cell wall in their cells. As bacteria, blue-green algae, fungi, algae, mosses, ferns, gymnosperms and angiosperms have their cells surrounded by cell walls, unlike animals, therefore, they were placed together under kingdom-Plantae.

S.No.	Phycomycetes	Ascomycetes
1.	Hyphae are aseptate and coenocytic.	Hyphae are septate and branched.
2.	A sexual spores are zoospores sporangiospores (aplanospores).	Asexual spores are or conidia.
3.	Asexual spores are formed endogenously within the sporangia.	Asexual spores are formed exogenously on conidiophore
4.	No dikaryophase is seen.	A dikaryophase is seen in some.
5.	No fruiting body is ascocarp is formed.	A fruiting body, formed.

There are millions of species on this planet. The largest phylum Arthropoda alone comprises of millions of species. To study all of them properly we need some system for categorizing them, based on some common characteristics. Apart from that think of the differences in language and you will find different names for the same species in different languages. In the absence of a system of nomenclature it would have been difficult to share scientific knowledge among the scientists of different nations. To make things easier and systematic the need for classification was felt. Earlier attempts by people like Aristotle segregated living beings into plants and animals. This was good point to start with, but there are certain living beings which do not fit in either of plants or animals. So a three kingdom classification was devised. The three kingdom classification was used for some time. But as none of the scientific theory is permanent so further discoveries led to creation of a five kingdom classification. The five kingdom classification is the most accepted system of classification.

1. Heterocysts are present in some cyanobacteria. It is a large-sized, pale coloured, thick-walled cell which occurs in terminal, intercalary or lateral position in filamentous cyanobacteria, e.g., Nostoc.
2. Features of cyanobacteria are:

1. Mucilage sheath is present.
2. Thylakoids lack phycobilins. Therefore, photosynthesis is absent, but cyclic photophosphorylation occurs.
3. Heterocyst is dependent for its nourishment on adjacent vegetative cells.

The thick wall is impermeable to oxygen, but permeable to nitrogen. It has enzyme nitrogenase which is specialised to perform nitrogen-fixation.