To avoid the unfavourable conditions, the zooplanktons enter into :

The correct answer is Option (3) → Diapause

Option (1) Migration — Incorrect. Migration is moving away for a time from the stressful habitat to a more hospitable area. Zooplankton in lakes and ponds do not move away; they escape in time by entering diapause.

Option (2) Hibernation — Incorrect. Hibernation is the winter sleep of animals such as bears.

Option (3) Diapause — Correct. Many zooplankton species in lakes and ponds escape bad conditions by entering diapause, a stage of suspended development. They resume growth when conditions improve.

Option (4) Aestivation — Incorrect. Aestivation is summer dormancy, as in snails and fish.

Note 1: A similar question was also asked in CUET (UG) 2023 on 13-06-2023 (Slot 3).

Note 2: This question is from the topic “Responses to Abiotic Factors” in Chapter 13, Organisms and Populations, of the pre-rationalised NCERT book. This portion is not in the present NCERT book, where the chapter is now Chapter 11, Organisms and Populations. The extract below is from the pre-rationalised edition.

NCERT Extract (Pre-rationalised edition, Chapter 13, Organisms and Populations):
Responses to Abiotic Factors – “… In animals, the organism, if unable to migrate, might avoid the stress by escaping in time. The familiar case of bears going into hibernation during winter is an example of escape in time. Some snails and fish go into aestivation to avoid summer–related problems-heat and dessication. Under unfavourable conditions many zooplankton species in lakes and ponds are known to enter diapause, a stage of suspended development.”