BIOLOGICAL CLASSIFICATION

In Chapter 2: Biological Classification – Term I, we study the characteristics of Kingdoms Monera, Protista & Fungi. The classification is based on the Whittaker System. The Plant & Animal kingdoms will further be dealt with in Chapters 3 & 4.

In this chapter, we are covering Kingdom Monera, Protista, Fungi, Plantae, Animalia, Viruses, Viroids & Lichens.

The topics covered in Class 11 Biology Chapter 2 includes –
  • Salient features and classification of Monera, Protista and Fungi into major groups;
  • Lichens, Viruses and Viroids.

The main criteria of classification into five-kingdoms were

  • Cell Structure
  • Body Organization
  • Mode of Nutrition
  • Reproduction
  • Phylogenetic Relationships

Bacteria were included in the Kingdom of Monera.

The above entities show a wide range of metabolism.

  • Single-celled Eukaryotes belong to the Kingdom Protista.
  • Kingdom Fungi species exhibit great diversity in structure and habitat.
  • Kingdom Plantae exhibit eukaryotic chlorophyll containing entities.
  • Kingdom Animalia includes heterotrophic eukaryotic multicellular entities which lack a cell wall.

1. Discuss how classification systems have undergone several changes over a period of time?

Answer

  • The first one to attempt to classify organisms with a scientific approach was Aristotle. He classified plants as trees, shrubs and herbs on the basis of morphological characteristics. He classified animals into anaemic (with red blood) and non-anaemic (without red blood).
  • Linnaeus gave Two Kingdom Classification of Plantae and Animalia Kingdoms with plants and animals respectively. The drawbacks of this system were that this did not distinguish between prokaryotes and eukaryotes, unicellular and multicellular organisms, and photosynthetic like algae and non-photosynthetic like fungi organisms. It was found inadequate after being used for a very long time.
  • R.H. Whittaker 1969 originated the Five Kingdom Classification. This included Monera, Protista, Fungi, Plantae, and Animalia. The criteria used by him to classify organisms were cell structure, thallus organisation, mode of nutrition, reproduction, reproduction, and phylogenetic relationships.
  • Carl Woese proposed the Three Domain System that divided Kingdom Monera into two different domains leaving the eukaryotic kingdom in the third domain. This created the Six Kingdom classification.

2. State two economically important uses of

(a) Heterotrophic bacteria and (b) Archaebacteria

Answer

(a) Majority of heterotrophic bacteria are decomposers. They help in the production of cur and antibiotics. They also fix nitrogen in the legume roots.
(b) Archaebacteria called methanogens are found in the guts of ruminants where they produce methane (biogas) from the dung of these animals.

3. What is the nature of cell-wall in the diatoms?

Answer – Diatoms have cell walls embedded with silica, which makes them indestructible. These leave behind their remains as a large amount of cell wall deposits called diatomaceous earth.

4. Find out what the terms ‘algal bloom’ and ‘red-tides’ signify.

Answer

  • Cyanobacteria or blue-green algae often form a bloom in contaminated water due to heavy growth. They inhale oxygen and cause its deficiency in the water bodies.
  • When red dinoflagellates like gonyaulax undergo very rapid multiplication and cause the sea to appear red. They release a toxin which kills other marine organisms.

5. How are viroids different from viruses?

Answer

  • Viroids are very smaller in size as compared to viruses.
  • Viroids are infectious free RNA molecules which lack protein coats which are found in viruses.
  • Viriods only infect plants while viruses infect plants, animals and microorganisms.

6. Describe briefly the four major groups of Protozoa.

Answer – Four major kinds of protozoa are as follows –

1. Amoeboid protozoans– They are found in aquatic environments. They use false feet or pseudopodia to move and capture their prey.
Example- Amoeba, Entamoeba, etc.

2. Flagellated protozoans– They are either free-living or parasitic. They use flagella for locomotion.
Example- Trypanosoma causes diseases such as sleeping sickness.

3. Ciliated protozoans– they live aquatic environment and use cilia for active movement. They have a cavity or gullet which opens up outside on the cell surface.
Example- paramoecium.

4. Sporozoans– They have an infectious sporotic stage in their life cycle.
Example- plasmodium.

7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?

Answer – Plants like insectivores and carnivores plants are partially heterotrophic. These plants are autotrophic and green with the presence of chloroplasts. They prey on and eat small insects for their nitrogen supply. Example- Venus Fly Trap, Bladderwort, Cuscuta, etc.

8. What do the terms phycobiont and mycobiont signify?

Answer – The lichens are the symbiotic association between algae and fungi. The phycobiont is the algal component which prepares food for fungi. The mycobiont is the fungal component which provides shelter and absorb nutrients and water for algae.

9. Give the comparative account of the classes of Kingdom Fungi under the following-

(i) mode of nutrition
(ii) mode of reproduction

Answer –

PHYCOMYCETESASCOMYCETESBASIDIOMYCETESDEUTROMYCETES
MODE OF NUTRITIONSaprophytic or obligate parasiticSaprophytic or decomposers or parasitic or coprophilous Parasitic or SaprophyticSaprophytic or parasitic or Decomposers
MODE OF REPRODUCTIONAsexual reproduction by zoospores(motile) or by alanospores (non-motile) 
Sexual reproduction by isogamous or anisogamous or oogamous gametes.
Asexual reproduction by the conidia spores
Sexual reproduction by ascospores
Vegetative reproduction by fragmentation and budding.
Fusion of somatic cells or vegetative structures to produce dikaryotic. It is called plasmogamy and produces basidiospores.
Asexual reproductions through conidia.

10. What are the characteristic features of Euglenoids?

Answer – The characteristic features of Euglenoids are –

  • They have a protein-rich layer called pellicle in place of the cell wall and this makes them flexible.
  • Euglenoids have two flagella, a short and a long one.
  • The pigments of euglenoids are similar to those present in plants.
  • They are autotrophic and photosynthetically active in presence of sunlight. Without sunlight, they are heterotropic and eat smaller organisms.

11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also, name four common viral diseases.

Answer – The viruses are non-cellular organisms which are found in crystalline structure when found outside the host cell. They have a protein coat which contains the genetic material RNA or DNA but never both. When they infect a cell, it takes over its machinery and replicates itself. The genetic material of the virus is truly infectious. Viruses infecting plants have single-stranded RNA while viruses infecting animals have either single or double-stranded RNA or double-stranded DNA. Bacterial viruses have double-stranded DNA.

Common viral diseases- mumps, smallpox, herpes and influenza.

12. Organize a discussion in your class on the topic- Are viruses living or non-living?

Answer – Viruses are non-living, because of the following reasons –

  1. They are found in the crystalline stage when outside the host cell.
  2. They have no cellular structure.
  3. There is no energy stored in the viruses.
  4. They cannot multiply on their own without hosts.

The living characteristics of viruses are as follows –

  • Presence of genetic material.
  • They can multiply.
  • Mutations occurring in them.
  • They are host-specific and obligate parasites.

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