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21
Diatoms are also called as 'pearls of ocean', why? What is diatomaceous earth?
Explanation
Diatoms and desmids are inducted under chrysophytes, kingdom-Protista. These are the main producers in the ocean. They prepare food not only for themselves but also for the other life forms in the ocean. This is the reason they are also called as 'pearls of ocean. Body of diatoms is covered by siliceous shell known as frustule. 'Diatomaceous earth' is the accumulation of large deposits of diatoms that forms a siliceous covering extending for several 100 m formed in billions of years. The material obtained from these deposits is used in polishing and filteration of oils and syrups.
22

There is a myth that immediately after heavy rains in forest, mushrooms appear in large number and make a very large ring or circle, which may be several metres in diameter. These are called as 'fairy rings'. Can you explain this myth of fairy rings in biological terms?

Discuss the mycilial structure in Agaricus and its soil borne nature.

Explanation

The fruiting bodies in Agaricus known as basidiocarps form a concentric ring like structure from the mycelium present in the soil. These basidiocarps resemble button in shape and develop to form a ring like structure.

This fairy ring structure in Agaricus have reported stimulation of plants productivity. This rings are infact fruiting bodies of this fungus and the diameter of this fairy ring increases every year due to spread of mycelium.

23
Neurospora an ascomycetes fungus has been used as a biological tool to understand the mechanism of plant genetics much in the same way as Drosophila has been used to study animal genetics. What makes Neurospora so important as a genetic tool?
Explanation
Neurospora fungus was selected to be a very good tool in genetics because this fungus can be grown easily under laboratory conditions by providing 'minimal medium' like inorganic salts, carbohydrates source and vitamin (biotin). Also under X-ray treatment the mutations can be easily introduced in the fungal cells and meiotic division can be easily seen.
24

Cyanobacteria and heterotrophic bacteria have been clubbed together in eubacteria of kingdom-Monera as per the 'five kingdom classification' even though the two are vastly different from each other. Is this grouping of the two types of taxa in the same kingdom justified? If so, why?

Discuss the cellular composition of cyanobacteria and heterotrophic bacteria that make them introduced in eubacteria.

Explanation

Although the two are vastly different from each other. They still bear some common characters, on the basis of which they are introduced in eubacteria of kingdom-Monera. These characters are as follows

(i) Both the groups do not possess well defined nucleus.

(ii) Nucleus lacks nucleous and nuclear membrane.

(iii) DNA (genetic material) lies freely in the cytoplasm.

(iv) They possess 70 S type of ribosomes.

25

At a stage of their cycle, ascomycetes fungi produce the fruiting bodies like apothecium, perithecium or cleistothecium. How are these three types of fruiting bodies different from each other?

Discuss the type of fruiting bodies formed by ascomycetes fungus and differentiate accordingly on the basic of there structures.

Explanation

Ascomycetes Consist of sporangial sac called ascus. Asci (singular-ascus) may occur freely or get aggregated with dikaryotic mycelium to form the fruitification called ascocarps.

The fruitification formed by asci are like

(i) Apothecium is a cup like structure, e.g., Peziza.

(ii) Perithecium flask shaped, e.g., Neurospora.

(iii) Cleistothecium closed with a slit, e.g., Penicillium

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