BIOLOGY Assertion (A) & Reason (B) MCQ

1. Both assertion and reason are true and reason is the correct explanation of assertion.

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

Explanation:

The world is facing accelerated rates of species extinctions, largely due to human interference. There are four major causes  - (i) habitat loss and fragmentation, (ii) over-exploitation, (iii) alien species invasions and (iv) co-extinctions.

Non-native or alien species are often introduced inadvertently for their economic and other uses. They often become invasive and drive away the local species. The exotic species are considered to be second major cause of extinction of species (the first being habitat destruction).

3. Assertion is true but reason is false.

Explanation:

Lower diversity in a species leads to uniformity, as is the case with large monocultures of genetically similar crop plants. This has advantage when increased crop production is a consideration, but can be a problem when an insect or a fungal disease attacks the field and poses a threat to the whole crop.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

3. Assertion is true but reason is false.

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

Explanation:

Hotspots are areas with high density of biodiversity or megadiversity which are also the most threatened ones. Ecologically hotspots are determined by four factors.

1. Number of specieslspecies diversity.
2. Degree of endemism.
3. Degree of threat to habitat due to its degradation and fragmentation.
4. Degree of exploitation.

Myers (1988) initially identified 12 hotspots. Today the number of hotspots identified by ecologists is 36.

4. Both assertion and reason are false.

Explanation:

There is little biodiversity at the poles. lt increases in temperate areas but reaches the maximum in tropics. The tropical rain forests have favourable environmental conditions for speciation and for support the variety and number of organisms.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Sacred forests are forest patches around places of worship which are held in high esteem by tribal communities. These are the most undisturbed forest patches. As a result many endemic species can be seen to flourish here.

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

4. Both assertion and reason are false.

Explanation:

Diversity at the level of community and ecosystem has three perspectives which are called Alpha, Beta and Gamma diversity. Alpha diversity (within - community diversity) refers to the diversity of organisms sharing the same community/ habitat. A combination of species richness and equitability/ evenness is used to represent diversity within a community or habitat. Species richness is the number of species per unit area. The number of species increases with the area of the site. Generally, greater the species richness, greater is the species diversity. However, number of individuals among the species may also vary, resulting into differences in evenness or equitability and consequently in diversity.

Species frequently change when habitat or community changes. The rate of replacement of species along a gradient of habitats or communities is called beta diversity (between - community diversity). There are differences in species composition of communities along environmental gradients, e.g., altitudinal gradient, moisture gradient, etc. Higher the heterogeneity in the habitats in a region or greater the dissimilarlty between communities, higher is the beta diversity. Diversity of the habitats over the total landscape or geographical area is called gamma diversity.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

In Modern Era, a high yielding variety developed at one place is immediately distributed to all parts of the globe. Naturally the low yielding wild varieties are discarded. The discarded wild varieties automatically disappear. They and their genes cannot be regained.

3. Assertion is true but reason is false.

3. Assertion is true but reason is false.

Explanation:

Communities with more species is more stable than the communities with less species. Large number and varieties of species influences biotic interactions among the community and therefore stability of the community. It is able to resist occasional disturbances.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

4. Both assertion and reason are false.

Explanation:

Coral reefs are believed to have highest biodiversity occupying less than one percent of the ocean floor, coral reefs are home to more than 25% of marine life. Coral reefs generally are confined to tropical and semi-tropical waters.