Long questions answers of Chapter 3 | Biodiversity | Biology Class 9 Notes

 

Q#1: Describe the history of classification in detail. 

History of classification

Like other fields of biology, the classification of living things (Taxonomy) also started in the Greek era and is still in research. The history of classification can be explained under the following headings.

1. Greek system of classification

One of the great Greek philosopher and scientist, Aristotle in 4^th B.C, classified the living things into animals and plants for the first time. Aristotle and his pupil’s classification system was simple because

Plants were classified into grasses, bushes, and trees and        

Animals were classified into aquatic (living in freshwater) and terrestrial (living on land).

2. Carolus Linnaeus’s system of classification (Two kingdom system)

The Initial (ابتدا) classification of dividing living things into animals and plants was accepted till the 16^th century i.e. the discovery of microorganisms. Organisms such as Bacteria, Euglena, and Algae become problematic for biologists. For this reason, a Swiss scientist, Carolus Linnaeus 1753, arranged living organisms into two kingdom system as follow                  

Kingdom Plantae includes all green plants, algae, fungi, and bacteria. Kingdom Animalia includes all unicellular as well as multicellular animals.

3. Robert Whittaker's system of classification (Five kingdom system)

Although C. Linnaeus’s classification was systemic something was still unrealistic with kingdom Plantae because of the merging of Algae, dual organisms like Euglena, and prokaryotes like bacteria and fungi. In order to remove discrepancies in Linnaeus’s two kingdom system, it was replaced by R. Whittaker's five kingdom system in 1969, which is as follows

• Kingdom Monera containing prokaryotes               
• Kingdom Protista contains all unicellular eukaryotic organisms
• Kingdom Fungi contain fungus                        
• Kingdom Animalia contains all types of multicellular animals
• Kingdom Plantae contains different plants

4. Margulis and Schwartz’s system of classification

Two scientists Margulis and Schwartz 1988 further modified (changed) Whittaker's five kingdom system on the basis of cellular structure, mode of nutrition, and method of reproduction as follow

Kingdom Monera was given the name Kingdom Prokaryotae

Kingdom Protista was renamed Kingdom Protoctista which was further increased by putting some multicellular organisms and some non-true fungi. 

Q#2:    Write down the characteristics of the five kingdom system.

Characteristics of organisms of five kingdom system

Today the most commonly used classification system is five kingdom system in which all the organisms of the world are divided into five kingdoms namely

• Kingdom Monera
• Kingdom Protista
• Kingdom Fungi
• Kingdom Animalia
• Kingdom Plantae                   

Following are the characteristics of organisms of each kingdom

1. Kingdom Monera

Organisms of Kingdom Monera have the following general characteristics

• They are the unicellular simplest organisms.                 
• Their cell wall is made up of murein and has no nuclear membrane.
• They are called Prokaryotes means that as they have no nuclear membrane so they lack (don’t have) an organized nucleus.
• Moneras can be found in the oldest fossils bearing rocks.     
• They also don’t have membrane-bound cytoplasmic organelles.

Examples are Bacteria and Blue-green algae (Cyanobacteria).

2. Kingdom Protista

Organisms of Kingdom Protista have the following general characteristics

• These organisms are more complex than Monera. 
• They are Eukaryotes means that they have an organized nucleus as well as membrane-bounded cytoplasmic organelles.
• They may be unicellular or multicellular.                          
• Some protists have chlorophyll so can make their food (autotrophs) while others don’t have chlorophyll so can’t make their own food (heterotrophs).

Examples Protozoan, Euglena, Chlamydomonas, Yeast, etc.

3. Kingdom Fungi

Organisms of Kingdom Fungi have the following general characteristics

• They are mostly multicellular eukaryotes organisms.      
• They lack chlorophyll so are not autotrophs but are heterotrophs.
• Being heterotrophs they live as                         

a. Saprophytes means they obtain their food from dead organic matter or                     

b. Parasites mean that they obtain their food from living organisms called hosts and cause diseases in them.

• They do not move about.

Examples are Breadmold, Mushrooms, Rust, and Smut fungi.

4. Kingdom Plantae

Organisms of Kingdom Plantae have the following general characteristics.

• This kingdom includes only plants of different types.      
• They contain chlorophyll so can prepare their food (autotrophs) by the process called Photosynthesis (photo = light, synthesis = preparing).                        
• Their cell wall is made up of cellulose.                     
• They are multicellular.                                      
• They have well developed vegetative body and can reproduce.

Examples Rose, Pinus, Mango plant, etc.

5. Kingdom Animalia

Organisms of Kingdom Animalia have the following general characteristics.

• They are all multicellular organisms.
• They are eukaryotes.
• They don’t have chlorophyll so can’t prepare their food and are so heterotrophs.
• Animals can broadly be divided into

Vertebrates: Those animals which have a vertebral column in their backbone are called vertebrates e.g. man, snake, cat, etc.

Invertebrates: Those animals which don’t have a vertebral column in their backbone are called invertebrates e.g. earthworms, starfish, etc.

Q#3: Write a detailed note on viruses. Why are they unique particles? 

Viruses      

The word virus is derived from the Latin word “Venom” which means “poisonous fluid”. The study of viruses is called virology.

‘A virus is an acellular (non-cellular) infectious particle containing DNA and RNA in an envelope of a protein called capsid’

Discovery

A Russian biologist named Iwanowsky 1892 for the first time discovered viruses.

Size of virus

Viruses are so small that we can’t see them through our naked eyes even if they are not visible through a light microscope they can be seen through an electron microscope or through a biochemical test. They are 10 to 1000 times smaller than bacteria. They range in size from 10 nm to 450 nm.

Shapes of viruses

Viruses are of different shapes i.e.

Rod shape:          e.g. TMV (Tobacco mosaic virus)

Round shape:     e.g. Polio virus, HIV

Tadpole shaped: e.g. Bacteriophage virus.

Many viruses are polyhedral (with many sides) such as plant and animal viruses.

Mode of nutrition

Viruses depend on other organisms for their nutrition and thus live as parasites. They grow and reproduce inside the living host and are called obligate parasites.

Taxonomical position

Viruses are excluded from the five-kingdom system because they are neither plants nor animals. They show the characteristics of both living and non-living organisms.

Viruses living or non-living

Viruses lie on the borderline between living and non-living.

1. Living characters of viruses

• They possess DNA or RNA.
• They show reproduction and growth.
• Viruses have the ability to infect other living things.

2. Non-living characters of viruses

• They don’t have a cellular structure.
• They don’t excrete.
• They can be crystallized.
• They can be stored like chemicals.
• They can’t respire.

Structure of viruses

A virus consists of the following two main parts

1. Protein coat

The outer protein coat is called a capsid. Tobacco mosaic virus has been shown to include 158 amino acids and 16 types of proteins. Capsid determines the shape of virus. In the case of bacteriophages, the protein coat consists of a head and tail.

2. Nucleic acid core

The inner nucleic acid core is either DNA or RNA in virus and is called its genome. Bacteriophages and some animal viruses contain DNA while viruses of higher plants contain DNA.