BIOLOGY 5 Marks Questions

Viruses are non-cellular, ultramicroscopic, infectious particles. They are made up of envelope, capsid, nucleoid and occasionally one or two enzymes. Viruses possess an outer thin loose covering called envelope. The central portion of nucleoid is surrounded by capsid that is made up of smaller sub-units known as capsomeres. The nucleic acid present in the viruses is known as nucleoid. It is the infective part of the virus which utilises the host cell machinery. The genetic material of viruses is of four types:

1. Double stranded DNA (dsDNA) as found in pox virus, hepatitis-B virus and herpes virus, etc.
2. Single stranded DNA (ssDNA) occur in coliphage fd, coliphage fx174.
3. Double Stranded RNA (cteRNA) occurs in Reo virus
4. Single stranded RNA: (dsRNA) occur in TMV virus, polio virus, etc. Four common viral diseases are (i) Polio, (ii) AIDS, (iii) Hepatitis-B, (iv) Rabies.

The four major groups of Protozoa are:

1. Amoeboid protozoans: These organisms live in fresh water, sea water or moist soil. They move and capture their prey by putting out pseudopodia (false feet) as in Amoeba. Marine forms have silica shells on their surface. Some of them such as Entamoeba are parasites.

2. Flagellated protozoans: The members of this group are either free-living or parasitic. They have flagella. The parasitic forms cause diaseases such as sleeping sickness. Example: Trypanosoma.

3. Ciliated protozoa or ciliates: They are aquatic individuals that form a large group of protozoa. Their characteristic features are the presence of numerous cilia on the entire body surface and the presence of two types of nuclei. All the cilia beat in the same direction to move the water laden food inside a cavity called gullet. Example: Paramoecium, Vorticella,etc.

4. Sporozoans: They include disease causing endoparasites and other pathogens. They are uninucleate and their body is covered by a pellicle. They do not possess cilia or flagella. They include the malaria causing parasite Plasmodium.

1. Phycomycetes- This group of fungi includes members such as Rhizopus, Albugo, etc.

• Mode of nutrition: They are obligate parasites on plants or are found on decaying matter such as wood.
• Mode of reproduction: Asexual reproduction takes place through motile zoospores or non-motile aplanospores that are produced endogenously in sporangium. Sexual reproduction may be of isogamous, anisogamous, or oogamous type. It results in the formation of thick-walled zygospore.

2. Ascomycetes- This group of fungi includes members such as Penicillium, Aspergillus, Claviceps, and Neurospora.

• Mode of nutrition: They are sporophytic, decomposers, parasitic or coprophilous.
• Mode of reproduction: Asexual reproduction occurs through asexual spores produced exogenously, such as conidia produced on conidiophores. Sexual reproduction takes place through ascospores produced endogenously in sac - like asci and arranged inside ascocarps.

3. Basidiomycetes- This group of fungi includes members such as Ustilago, Agaricus and Puccinia.

• Mode of nutrition: They grow as decomposers in soil or on logs and tree stumps. They also occur as parasites in plants causing diseases such as rusts and smuts.
• Mode of reproduction: Asexual reproduction takes place commonly through fragmentation. Asexual spores are absent. Sex organs are absent but sexual reproduction takes place through plasmogamy. It involves fusion of two different strains of hyphae. The resulting dikaryon gives rise to a basidium. Four basidiospores are produced inside a basidium.

4. Deuteromycetes- This group of fungi includes members such as Alternaria, Trichoderma, and Colletotrichum.

• Mode of nutrition: Some members are saprophytes while others are parasites. However, a large number act as decomposers of leaf litter.
• Mode of reproduction: Asexual reproduction is the only way of reproduction in deuteromycetes. It occurs through asexual spores called conidia. Sexual reproduction is absent in deuteromycetes.

	Food	Chemical	Medicines	Fodder
ALGAE	Spirulina Chlorella Ulva Porphyra Chondrus Crispus	Brown algea (Phycocolloids including agar, alginic acid etc.) Chondrus crispus (Carrageenin) Laminaria, fucus etc. (Iodine)	Corollina (Cures worm infection) Polysiphonia (Has antibacterial property) Laminaria (Source of an anticoagulant) Ascophyllum and Laminaria etc. (Antibiotic) Durvillea (Vermifuge proprties)	Pelvetia canaliculata Sargassum Fucus Laminaria Macrocystis
FUNGI	Mushrooms Morchella Lycoperdon Volvaria yeast Clavatia	Aspergillus niger (Citric and gluconic acid) Rhizopus stolonifer (Fumaric acid) P.glaucum (Gallic acid) A.oryzae (Amylase, pectinase etc.) Yeast (Invertase)	Pencillium (Antibiotic) Calviceps (Ergotine) Trichoderma (Cyclosporin A) Aspergillus flavus (flavin) Gibberella baccater (Baccatin A)	Saccharomyces Pleurotus

Two kingdom classification was unable to accommodate certain living beings as they neither had properties of animals nor of plants. Through two kingdom classification it was not possible to include every set of characters in a particular kingdom. Five kingdom classification could accommodate more set of characters. As a result it was easier to categorize all living beings. For example bacteria can be autotrophic as well as heterotrophic. It was a difficult question to categorize them either under plant or animal. A separate kingdom was the most logical choice. Similarly, viruses are a borderline case between living and non-living. When they don't get host then they behave like a non-living. Once, inside a host they spring to life. Although the five kingdom classification does not have room for virus but it opened the way for a better and more inclusive system of classification.

This is true that biological classification is a dynamic and ever evolving phenomenon which keeps changing our understanding of life forms. At the beginning, living being were broadly classified into two groups, viz. animals and plants. This classification was based on apparent morphological features which were quite easy to understand. But when the scientists discovered certain flaws in this classification, they began to think about a better system of classification. The most accepted system of classification today is the Five-Kingdom Classification; proposed by Robert Whittaker. The Five-Kingdom Classification takes into account structural organization and phylogenetic relationship; while classifying the living beings. As per this system; all prokaryotes have been kept under one kingdom, i.e. Monera. Furthermore, eukaryotes have been divided into four.

Diseases caused by different classes of fungi are given below:

S. No.	Phycomycetes	Ascomycetes	Basidomycetes	Deuteromycetes
1.	Club rot of crucifers	Stem galls of coriander	Loose smut of wheat	Red rot of sugarcane
2.	Wart disease of potato	Leaf curl of peach	Smut of corn	Blast of rice
3.	Rhizome rot of ginger	Powdery mildew of grapes	Black rust of wheat	Wilt of potato, tomato, cotton and banana
4.	White rust of crucifers	Powdery mildew of peas	Yellow rust of wheat	Tikka disease
5.	Downy mildew of grapes	Ergot rye and grasses	Rust ofpeas	Early blight of potato
6.	Lare blight of potato	Brown rot of pear	Leaf rust of coffee	Die back of chilies

• Reproduction in Fungi: Reproduction in fungi can be vegetative, asexual or sexual.

1. Vegetative Reproduction: Reproduction in fungi can take place by vegetative means-fragmentation, fission and budding.
2. Asexual Reproduction: Asexual reproduction is by spores called conidia or sporangiospores or zoospores.
3. Sexual Reproduction: Sexual reproduction is by oospores, ascospores and basidiospores. The various spores are produced in distinct structures called fruiting bodies.

• The sexual cycle involves the following three steps:

1. Plasmogamy: Fusion of protoplasms between two motile or non-motile gametes is called plasmogamy.
2. Karyogamy: Fusion of two nuclei is called karyogamy.
3. Meiosis in zygote resulting in haploid spores: When a fungus reproduces sexually, two haploid hyphae of compatible mating types come together and fuse. In some fungi the fusion of two haploid cells immediately results in diploid cells (2n). However, in other fungi (ascomycetes and basidiomycetes), an intervening dikaryotic stage (n + n i.e. two nuclei per cell) occurs; such a condition is called a dikaryon and the phase is called dikaryophase of fungus. Later, the parental nuclei fuse and the cells become diploid. The fungi form fruiting bodies in which reduction division occurs, leading to formation of haploid spores.

1. Division of Kingdom Fungi:

The morphology of the mycelium, mode of spore formation and fruiting bodies form the basis for the division of the kingdom into various classes.

2. Phycomycetes:

• Habit and Habitat: Members of phycomycetes are found in aquatic habitats and on decaying wood in moist and damp places or as obligate parasites on plants.
• Mycelium: The mycelium is aseptate and coenocytic.
• Reproduction: Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile).

3. Ascomycetes

• Habit and Habitat: Commonly known as sac-fungi, the ascomycetes are unicellular, e.g., yeast (Sacharomyces) or multicellular, e.g., Penicillium. They are saprophytic, decomposers, parasitic or coprophilous (growing on dung).
• Mycelium: Mycelium is branched and septate.
• Reproduction: The asexual spores are conidia, produced exogenously on the special mycelium called conidiophores.

4. Basidiomycetes:

• Habit and Habitat: Commonly known forms of basidiomycetes are mushrooms, bracket fungi or puffballs. They grow in soil, on logs and tree stumps and in living plant bodies as parasites, e.g., rusts and smuts.
• Mycelium: The mycelium is branched and septate.
• Reproduction: The asexual spores are generally not found, but vegetative reproduction by fragmentation is common.

5. Deuteromycetes:

• Habit and Habitat: Some members are saprophytes or parasites while a large number of them are decomposers of litter and help in mineral cycling. Some examples are Alternaria, Colletotrichum and Trichoderma.
• Reproduction: The deuteromycetes reproduce only by asexual spores known as conidia. The mycelium is septate and branched.

Differences between ascocarp and basidiocarp are given below:

S. No.	Ascocarp	Basidiocarp
1.	It is a fructification found in Ascomycetes.	It is a fructification found in Basidiomycetes.
2.	It is simpler construction.	It is more elaborate in construction.
3.	Ascocarp contains numerous asci.	Basidiocarp contains several basidia.
4.	Ascus is generally aseptate.	Basidium may be septate or aseptate.
5.	An ascus forms eight ascocarps.	A basidium produces four basidiospores.
6.	These are formed endogenously.	These are formed exogeneously.