NCERT Class 11-Biology: Chapter –2 Biological Classification Part 4

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Long Answer Type Questions

Question 1:

Algae are known to reproduce asexually by variety of spores under different environmental conditions. Name these spores and the conditions under which they are produced.

Answer:

Asexual reproduction takes place by the formation of various types of sporangia. The spores escape from the parent plants, undergo germination and give rise to new plants.

Explanation:

Algae reproduce asexually by a variety of spores such as,

(1) Zoospores: these are flagellated, often with an eyespot. Normally these are formed under favourable conditions e.g. Chlamydomonas.

In Vaucheria, compound zoospores called synzoospore are formed.

(2) Aplanospores: these are non-motile thin walled zoospores, formed by cleavage of protoplasts within a cell. They are formed under unfavourable conditions e.g. Ulothrix

(3) Akinetes: these are formed under unfavourable conditions as method of perinnation. They are thick walled and non-motile. On release they form new thalli e.g. Anabaena

(4) Hypnospores: these are thick walled aplanospores and are formed during unfavourable conditions. Under prolonged unfavourable conditions the protoplasm of Hypnospores divides to make cysts e.g. Chlamydomonas nivalis.

(5) Tetraspores: these are haploid thin walled non motile spores formed after reduction division in diploid tetrasporangia e.g. members of Rhodophyceae and Phaeophceae.

(6)Autospores: these are similar to the parent cell. In Chlorella and Scenedesmus autospores acquire all characteristics of parent cells before their discharge from sporangium.

Question 2:

Apart from chlorophyll, algae have several other pigments in their chloroplast. What pigments are found in blue-green, red and brown algae that are responsible for their characteristic colours?

Answer:

Algae have many other pigments in their chloroplast; in addition to chlorophyll. The following table shows various pigments in algae and color imparted by them:

Class, Common Name, Major Pigment , Colour Imparted
Class, Common name, Major pigment , Colour imparted

Class

Common name

Major pigment

Colour imparted

Chlorophyceae

Green algae

Chlorophyll a, b

Green

Phaeophyceae

Brown algae

Chlorophyll a, c, Fucoxanthin

(A xanthophyll pigment)

Brown

Rhodophyceae

Red algae

Chlorophyll a, d, r-phycoerythrin

Red

Question 3:

Make a list of algae and fungi that have commercial value as source of food, chemicals, medicines and fodder.

Answer:

Some algae of commercial importance:

Some Algae of Commercial Importance
Some algae of commercial importance

Type of use

Description

Agar (derived from red algae gelidium and Gracilaria)

Used as culture medium in laboratory.

Algin (Derived from brown algae) carrageen (derived from red algae)

Used as gelling agent in food and in medical dressing.

Biofuels (different types of algae)

It is being used to produce biofuels. The concept is still at experimental stage; with prototypes of automobile engine in working condition.

Fertilizer (different types of algae)

It has been used as fertilizer in many countries.

Food(Many species of porphyra, Laminaria, Sargassum)

These marine algae are used as food items; especially in the East Asian nations,

Single cell protein (Chlorella and Spirullina)

Many algae are rich in protein and are used as food supplements

Some fungi of commercial importance:

Some Fungi of Commercial Importance
Some fungi of commercial importance

Types of use

Description

Medicine

The fungus Penicillium notatum is used for producing antibiotics of penicillin group. Many traditional Chinese medicines are prepared from fungi.

Diseases

Many fungi causes disease in both animals and plants.

Food processing

Yeast has been in use since ages for fermentation. Alcoholic beverages and bakery items are made because of fermentation by yeast.

Food

Some varieties of Agaricus are used as food in many countries.

Ripening of cheese

Some varieties of fungi are used for ripening of cheese.

Spoilage of food

Rhizops (bread mould) spoils food items; like stale bread, fruits and vegetables.

Question 4:

‘Peat’ is an important source of domestic fuel in several countries. How is ‘peat’ formed in nature?

Answer:

Peat an organic fuel consisting of spongy material formed by the partial decomposition of organic matter, primarily plant material in wetlands such as swamps ferns and mosses. The development of peat is favoured by warm, moist climatic conditions

The main producers of peat Sphagum most occurs in bogs. The accumulation of Sphagnum plant in due course of time lead this plant to get hardened and change into peat.Peat is used in preparation of ethyl alcohol, peat, tar, ammonia, ormous value shown by peat for man-kind makes it as an important domestic fuel and economic source for man-kind.

Question 5:

Biological classification is a dynamic and ever evolving phenomenon which keeps changing with our understanding of life forms. Justify the statement taking any two examples.

Answer:

Biological classification keeps changing with our understanding of life forms. Initially, new characters were taken by Aristotle, Theophrastus, John Ray and Linnaeus. Linnaeus divided plants on the basis of sex organs only.

As more and more knowledge gathered for delimitation of taxa, the ways for natural system of classification became clear.

This can be understood by following examples

(i) Two kingdom classification was replaced by three kingdom classification when Haeckel (1866) proposed the kingdom of Protista.

(ii) It was converted into four kingdom classification by Copeland when he proposed the kingdom-Monera.

(iii) Whittaker in 1969 proposed five kingdom classification.

(iv) As the information about biochemistry of archaebacteria gathered, Woese raised another kingdom, Archaea.

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