NEET · Biology · STD 12 - 13. biodiversity and conservation

Since the origin and diversification of life on Earth, there have been five episodes of mass extinction of species. How is the sixth extinction which is in progress, different from the previous episodes ?

A The present net species extinction rate is zero.
B The current species extinction rate is nearly \(10\) times faster than that in previous episodes.
C The present species extinction rates are 100 to 1000 times faster than in the pre-human times.
D The current species extinction rates are far lower than those in previous episodes.

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Answer & Solution

Correct Answer

(C) The present species extinction rates are 100 to 1000 times faster than in the pre-human times.

Step-by-step Solution

Detailed explanation

(C) The present species extinction rates are 100 to 1000 times faster than in the pre-human times.
According to the standard biological literature, during the long period since the origin and diversification of life on Earth, there have been five episodes of mass extinction of species.
The 'Sixth Extinction' presently in progress is different from the previous episodes primarily in terms of the rate of extinction.
The current species extinction rates are estimated to be 100 to 1000 times faster than in the pre-human times, and human activities are responsible for these accelerated rates.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

Select the correct option. Column I - Column II

Column \(I\)	Column \(II\)
(A) Synapsis aligns homologous chromosomes	(i) Anaphase \(II\)
(B) Synthesis of \(RNA\) and protein	(ii) Zygotene
(C) Action of enzyme recombinase	(iii) \(G_2\) phase
(D) Centromeres do not separate but chromatids move towards opposite poles	(iv) Anaphase \(I\)
	(v) Pachytene

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