Biodiversity: The Variability of Life- part I


Literally, “bio” means “life” & “diversity” means “variety”, so it is ‘the study of variety & richness of life in biosphere’. Biodiversity is a term used to describe the variability of life on Earth. It can be used more specifically to refer to all of the species in one region or ecosystem. Biodiversity refers to every living thing, including plants, bacteria, animals, and humans.

In key respects all organisms alike-

  • They consist of same kinds of substances, put together according to same laws that govern matter
    and energy, which they must obtain from environment.
  • All organisms sense and respond to changing conditions in environment.
  • They all grow and reproduce, based on instructions contained in their DNA.

What is life?

  • Life is an outcome of ancient events by which non-living material become assembled into first living cells.
  • It is a way of capturing and using energy and raw materials.
  • A way of sensing and responding to changes in environment.
  • A capacity to reproduce, grow and develop.

Life evolves meaning, details in body plan and functions or organs can change
through successive generations.

Unity and diversity

Immense diversity in the world of life, millions of different organisms inhabit in the Earth and many millions more lived and became extinct over past 3.8 billion years back.

Each kind of organism unique in some of its traits i.e., in some aspects of its body plan, body function and behaviour.


Biosphere- portion of earth where all
living organisms present, interacting with surrounding environment.

(i)  upper limit 9000 m above MSL &
(ii) lower limit 10000 m below sea.

Fig: Biosphere

Requirements for Biosphere

Ample solar energy, liquid water & places where liquid, solid & gas all meet seems to be requirements for biosphere to exist where biological cycles of H2O, O2, mineral, N, C, etc. functions.

Interaction between organisms of biosphere and environment performs via ecosystem functioning.


Any area that includes all organisms interacting with physical environment where flow of energy leads to clearly defined pathways, trophic structure, biotic diversity & material recycles called ecosystem e.g., coral reef, tropical rainforest, etc. (Tansley, 1935).

Genus and Species

Species – Kind of plant or animal in which all members related, descendents of same ancestor/s; should look alike in fundamental structure and other characters maintained in nature through out innumerable generations;
interbred to produce fertile offspring.

Genus – Similar & related spp group e.g., white oak, red oak-all make up genus Quercus, white Oak Q. alba

Early History of the Subject

Biodiversity proposed by Walter Rosen in 1986.

In Bangladesh, course named “Plant Diversity” in Dept. of Botany, DU was started in 1979 by National Prof. Dr. A. K. M. Nurul Islam.

In 2007, it was redesigned and renamed as “Biodiversity”.

Biodiversity- a Science

Totality of genetic, taxonomic, ecosystemic & domestic richness & variation within micro-organisms, fungi, plants & animals.

If earth would have been created 4600 million years back & 1st life appeared 3800 million years back then how different spp. evolved & grew on the basis of Biodiversity?

So far 1.5 million living spp. & 0.3 million fossil spp. identified and described.

Why Biodiversity is a hot issue?

World Environment‘- debatable issue between Developed & Underdeveloped nations.

Attempts to reach a common goal:
1st world conference held in Stockholm, Sweden from June 5-16 in 1972.

  • Developed nations asked poor nations to reduce environmentally destructive development.
  • Poor nations wished economic development even at cost of pollution and degradation of environment.

2nd UN attempt ‘Earth Summit in Rio de Jeneiro, Brazil, from June 3-14, 1992, 180 govt. present developed nations again focused on 3 items:

  1. Climate change;
  2. Destruction of tropical forests &
  3. Species loss.

but poor nations again desperate for economic improvement.
Two themes finally emerged,

  1. Sustainable development.
  2. World Biodiversity-scarcely heard a decade before Rio, gained global audience.

‘Earth Summit’ established 4 major agreements-

  1. Rio declaration citing rights & responsibilities of individual states.
  2. Convention of climatic change.
  3. Agenda 21 (wide ranging objectives & approaches for sustainable development).
  4. Convention on Biological Diversity signed by 155 states.

US didn’t sign, others maintained strong
environmental agenda, so it became political issue.

Bio-diversity became popular and gained
familiarity greater than any other ecological concept shortly.

In 2012, the United Nations Conference on Sustainable Development was held in Rio de Janeiro from 13-22 June.


This Article is completely based on by the lecture of Dr. Azmal Hossain Bhuiyan, Professor, Department of Botany, University of Dhaka.

Some info and pictures have been added by author.

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About Syeda Nusrat Jahan Mili

Syeda Nusrat Jahan Mili
A girl with a lot of dreams to accomplish and make her parents proud. Currently studying in 1st year of B.Sc in University of Dhaka. Want to walk with Plantlet a long way. Interested with debate, music, photography and poem recitation.
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