Biodiversity and classification 

Biodiversity means the diversity of life forms. It is a word commonly used to refer to the variety of life forms found in a particular region. 

Diverse life forms share the environment and are affected by each other too. As a result, a stable community of different species comes into existence.

Regions of megadiversity

The warm and humid tropical regions of the earth, between the tropic of Cancer and the tropic of Capricorn, are rich in diversity of plant and animal life. This is called the region of megadiversity. 

Of the biodiversity on the planet, more than half is concentrated in a few countries — Brazil, Colombia, Ecuador, Peru, Mexico, Zaire, Madagascar, Australia, China, India, Indonesia and Malaysia.

Classification

Greek thinker Aristotle classified animals according to whether they lived on land, in water or in the air. This is a very simple way of looking at life, but misleading too.

The method of arranging organisms into groups on the basis of their similarities and differences is called classification

 advantages of classification

1.  it provides information regarding the existing diversity of plants and animals
2.  it it creates a convenient environment to study a wide variety of organisms
3.  it helps us understand  the process of evolution
4.  it provides the basis for the development of other biological science like Ecology biochemistry and other disciplines of biology

Basis of classification

•  The  complexity of cell structure
  • Eukaryotic cell –  the membrane-bound organelles are present along with the nucleus it efficiently allows the isolated cellular processes to be carried out
  •  Prokaryotic cell –  the membrane-bound organelles and a membrane-bound nucleus are absent
•  The body structure
  • Unicellular-  having single cell;    amoeba
  •  Multicellular –  having a group of cells;  worm
•  Mode of nutrition
  •  autotrophic organisms –  which can make their own food through the process of photosynthesis that is plants
  •  heterotrophic organisms –  which depends on autotrophic organisms and other animals for food
•  Levels of organisation of the body
  •  
•  Functional organisation

Classification and evolution

Evolution is a process by which early organisms on the earth diversifIED and developed into various forms through a slow and continuous process which helps in the development required for survival and growth

We will find some groups of organisms which have ancient body designs that have not changed very much. 

We will also find other groups of organisms that have acquired their particular body designs relatively recently. 

Those in the first group are frequently referred to as ‘primitive’ or ‘lower’ organisms, while those in the second group are called ‘advanced’ or ‘higher’ organisms.

Hierarchy of classification

Biologists, such as Ernst Haeckel (1894), Robert Whittaker (1969) and Carl Woese (1977) have tried to classify all living organisms into broad categories, called kingdoms

The classification Whittaker proposed has five kingdoms: 

Monera, Protista, Fungi, Plantae and Animalia, and is widely used. 

These groups are formed on the basis of their cell structure, mode and source of nutrition and body organisation.

The modification Woese introduced by dividing the Monera into Archaebacteria (or Archaea) and Eubacteria (or Bacteria) is also in use

Further classification is done by naming the sub-groups at various levels as given in the following scheme: 

• Kingdom Phylum (for animals) / Division (for plants)

•  Class 

• Order

•  Family

•  Genus

•  Species

By separating organisms on the basis of a hierarchy of characteristics into smaller and smaller groups, we arrive at the basic unit of classification, which is a ‘species’. 

So what organisms can be said to belong to the same species? 

Broadly, a species includes all organisms that are similar enough to breed and perpetuate.

The brief idea of the taxonomic categories are given below:

•  Species
•  GenUS
•  Family
•  order
•  Class
•  Phylum
•  Kingdom

Five kingdom classification

•  cell structure –  prokaryotic or Eukaryotic’
•  modes and source of Nutrition –  autotrophic or heterotrophic
•  body organisation –  unicellular or multicellular

The classification Whittaker proposed has five kingdoms: 

The important characteristics of these kingdoms are as follows

1. Monera GK  monerEs- single
   1. These organisms do not have a defined nucleus or organelles
   2. do any of them show multi-cellular body designs
   3. The mode of nutrition of organisms in this group can be either by synthesising their own food (autotrophic) or getting it from the environment (heterotrophic).
   4. Some of them have cell walls while some do not. 
   5. Having or not having a cell wall has very different effects on body design here from having or not having a cell wall in multicellular organisms.
   6. This group includes bacteria, blue-green algae or cyanobacteria, and mycoplasma.
2.  Protista – PROTISTS  –  primitive for the very first
   1. This group includes many kinds of unicellular eukaryotic organisms. 
   2. Their mode of nutrition can be autotrophic or heterotrophic.
   3. Some of these organisms use appendages, such as hair-like cilia or whip-like flagella for moving around.
   4. Examples are unicellular algae, diatoms and protozoans 
3.  Fungi –  fungus –  mushroom
   1. These are heterotrophic eukaryotic organisms.
   2. Some of them use decaying organic material as food and are therefore called saprotrophs.
   3. Others require a living protoplasm of a host organism for food. They are called parasites.
   4. Many of them have the capacity to become multicellular organisms at certain stages in their lives
   5. They have cell walls made of a tough complex sugar called chitin. 
   6. Some fungal species live in permanent mutually dependent relationships with Bluegreen algae (or cyanobacteria). Such relationships are called symbiotic.
      1. These symbiotic life forms are called lichens. We have all seen lichens as the slow-growing large coloured patches on the bark of trees.
   7. Examples are yeasts, moulds and mushrooms
4.  Plantae
   1. These are multicellular eukaryotes with cell walls.
   2. They are autotrophs and use chlorophyll for photosynthesis. Thus, all plants are included in this group.
   3. Unlimited growth and it continues till death
   4.  they are always fixed at one side and cannot move like animals
5.  Animalia
   1. These include all organisms which are multicellular eukaryotes without cell walls. They are heterotrophs.
   2.  

Kingdom Plantae

The first level of classification among plants depends on whether the plant body possesses well-differentiated distinct cellular components or not

 CryptoGAMAE

 The thallophytes, bryophytes and pteridophytes do not have external flowers or seeds and have naked embryos called Sports. these plans are therefore called cryptogams meaning with hidden reproductive organs because their reproductive organs are inconspicuous 

1. Thallophyta –  THALLOS –  undifferentiated; PHYTON –  plants
2.  Bryophyta – BRYON – moss ; PHYTON –  plant
3.  Pteridophyta – PTERIS –  fern; PHYTON –  plant

 PhaneroGAMAE 

 plants that make seeds and have well-differentiated reproductive tissues are called phanerogams

 on the basis of whether the seeds are naked or enclosed in fruits, these are divided into two groups

1.  Gymnosperms  – gymnOS-  naked;SPERMA –  seed
   
   
2.  Angiosperms – ANGION –  covered SPERMA- seed
   
   the characteristics of angiosperms are as follows
   1.  these are also called flowering plants the seeds develop inside an organ called over it becomes a fruit after developing
   2.  plant embryos in seas have structures called cotyledons and they are also called seed leaves because in many cases they emerge and become green when the seed germinates
      
      
      •  the angiosperms are divided into two groups on the basis of the numbers of cotyledons present in the seed
        • Dicotyledonous plants or  dicots 
        •  monocotyledonous plants for monocots