Two opposite forces operate in the growth and development of every population. One of them is related to the ability to reproduce at a given rate. The force opposite to it is called

• fecundity

• environmental resistances

• biotic control

• mortality.

What is a keystone species

• A species which makes up only a small proportion of the total biomass of a community, yet has a huge impact on the community's organization and survival.

• A common species that has plenty of biomass, yet has a fairly low impact on the community's organization.

• A rare species that has minimal impact on the biomass and on other species in the community.

• A dominant a large proportion of the biomass and which affects many other species.

Assertion : Bursa fabricii lies on the ventral side of the cloaca in birds.

Reason : Bursa fabricii is related with flight adaptation.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

Assertion : The primitive atmosphere was reducing one i.e. without oxygen.

Reason : In the primitive atmosphere, oxygen was involved in forming ozone layer.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

Assertion : Jave Apeman, Peking man and Heidelberg man are the fossils of Homo erectus.

Reason : Homo erectus evolved from Homo habilis.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

Nicotiana sylvestris flowers only during long days and N.tabacum flowers only during short days. If raised in the laboratory under different photoperiods, they can be induced to flower at the same time and can be cross-fertilized to produce self-fertile offspring. What is the best reason for considering N.sylvestris and N.tabacum to be separate species

• They cannot interbreed in nature.

• They are reproductively distinct.

• They are physiologically distinct.

• They are morphologically distinct.

• human race

• human beings

• modern man

• none of these

Wings of pigeon, mosquito and bat show

• divergent evolution

• atavism

• convergent evolution

• all of these

Assertion : The earliest fossil form in the phylogeny of horse is eohippus.

Reason : Eohippus lived during the early pliocene epoch.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

Assertion: The earliest organisms that appeared on the Earth were non-green and presumably anaerobes.

Reason: The first autotrophic organisms were the chemoautotrophs that never released oxygen.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false.