Test: Biodiversity (NCERT) - NEET MCQ

Among all the species in the world, approximately 70% are animals and 22% are plants. In animals, insects account for 70% -80%, which is the maximum (represented as A). According to, IUCN (2009) there are 10,25,000 species of insects and 70,000 species of molluscs (represented as B).

Excessive exploitation of a species, whether a plant or animal reduces size of its population such that it becomes vulnerable to extinction. Dodo, passenger pigeon and Steller's sea cow become extinct in the last 500 years due to over-exploitation by humans.

Barring arid/semi-arid and aquatic habitat, biodiversite shows a latitudinal and altitudinal gradients. There is little biodiversity at the poles. It increases in temperate areas but reaches the maximum in tropical rain forests at equator. It is because the tropical rain forests have favorable environmental conditions not only for speciation but also for supporting both variety and number of organisms.

The relationship between species richness and area is rectangular hyperbola for a wide variety of taxa whether they are birds, bats, freshwater fishes or flowering plants and the equation can be given as S = CA^Z. On a logarithmic scale it is straight line described by the equation logS = logC + ZlogA. Where S is species richness, Z is slope of line or regression coefficient, C is Y-intercept while A is area.

The world is facing acceleration rates of species extinctions, largely due to human interference. There are four major causes collectively called as the evil quarter, it includes (i) Habitat loss and fragmentation, (ii) Oven exploitation, (iii) Alien species invasions and (iv) Co-extinctions.

Lantana, Eichhornia and African catfish. are exotic species. Non-native or exotic species are often uses. They introduced inadvertently for their economic and other uses. They often becomes invasive and drive away the local species. These species are considered to be second major cause of extinction of species are considered to be second major cause of extinction of species. Such invasive exotic species have proved harmful to both aquatic and terrestrial ecosystems.

Lantana, Eichhornia and Parthenium are all exotic species, which had been introduced in India. Lantana camara has replaced many species in forests of Uttar Pradesh and Madhya Pradesh. Eichhornia (Water hyacinth) has clogged water bodies including wetlands resulting in death of servral aquatic plants and animals. Parthenium has pushed out several herbs and shrubs from open places in the plains.

Among vertebrates, fish account for the maximum share with approximately 26,959 species. Birds have 9,700 identified species and reptiles have 7,150 species.

There are 2,70,000 species of higher plants and 72,000 species of fungi and in the world.

Nile Perch (a predator fish) was introduced in lake Victoria of East Africa. It killed and eliminated ecoligically unique assemblage of over 200 native species of small cichild fish.

Clarias gariepinus, the African catifish has been illegally introduced for aquaculture in India. It is threatening native catfishes of Indian rivers.

Extinction of one species automatically causes extinction of the other species in certain obligatory mutualistic relationships. This is called co-extinction, e.g., mutualism between Pronuba yuccasella and Yucca.

A stable community is self-perpetuating and final biotic community that is in perfect harmony with the physical environment. It does not show much of changes and is usually resilient to natural or man made disturbances. It is also resistant to invasion by alien species.

Natural or background extinction is a slow process of replacement of existing species with the better adapted species due to alternate evolution, changes in environmental conditions, predators and diseases. A small population due to inbreeding depression (reduces genetic variability) and normal population fluctuations during unfavourable periods like drought, harsh winter or severe summer.

Animals constitute more than 70% of all the species recorded whereas plants constitute around 22% of total number of species.

The number of species of aves, reptiles, amphibians and mammals are 1232, 456, 209 and 300 respectively.

• The biosphere of Earth is heterogeneous in nature and shows immense diversity.
• There are more than slightly more than 1.5 million species known and still many species are yet to be discovered and described.

Biodiversity changes with the changes in altitude. It increases as one moves from higher to lower altitudes. Decrease in temperature and greater seasonal variability are the two major factors responsible for lower diversity at higher altitudes.

Robert May estimated that about 7 million species are present on earth.

India is one of the twelve of the twelve megadiversity regions of the world with 8.1% of genetic resources of the world. Wildlife Insitute of India has divided the country into 10 biogeographical regions-1. Trans-Himalayas, 2. Himalayas, 3. Desert, 4. Semi-arid, 5. Western Ghats, 6. Deccan Peninsula, 7. Gangetic Plain, 8. North East, 9. Coasts, 10. Island.

• Robert McCredie May is a theoretical ecologist and promoter of science.
• He estimated that there are almost 7 million species globally.

• The mutualistic relationship between a fungus and photosynthesizing algae is called lichens.
• Of all the plant species recorded, lichens have the minimum number of species.
• They are used in the food industry, making dyes and have medicinal use.

Tropical rainforests are disappearing fastly from India due to deforestation, habitat loss and fragmentation. These forests are of extreme value since they contain the maximum biodiversity.

IUCN is International Union of Conservation of Nature and Natural Resources, which is now called world conservation Union (WCU). It has its headquarters at Morges, Switzerland. It maintains a Red Data Book or Red List which is a catalogue of taxa facing risk of extinction.

About 20% of the world oxygen is produced in the amazon rainforests. They are described as the 'lungs of the planet because they provide the assential world environmental service of continously recycling CO₂ into O₂.

In the absence of their natural predators, exotic species flourish better and pose a threat to indigenous species.

Genetic diversity is the diversity in the numbers and types of genes as well as chromosomes present in different species and the variations in the genes and their alleles in the same species. The genetic variation in Rauwolfia vomitoria growing in different Himalayan range indicates genetic diversity. Another example is of presence of more than 50,000 genetically different strains of rice, and 1000 varieties of mango in India.

Species diversity is the variety in the number and richness of the species of a region. Western ghats have greater amphibian species diversity as compared to Eastern ghats. The number of the species per unit area is called species richness. Number of individuals of different species represent species evenness or species equitability.

Keystone species are those which have significant and disproportionately large influence on the community structure and characteristics. It has often considerably low abundance and biomass as compared to dominant species. Removal of such species causes serious disruption in structure and function of community.

A. Beta diversity - Between community diversity
B. Rich biodiversity - Tropical areas
C. Gamma diversity - Diversity of whole geographical region
D. Extinct species - Dodo
E. Critically endangered species - Great Indian bustard