Question

Assertion : Many zooplankton species in lakes and ponds enter the state of diapause.
Reason : Diapause is a state of suspended development, in response to unfavourable conditions.

• A. Both assertion and reason are true and the reason is the correct explanation of the assertion
• B. Both assertion and reason are true but the reason is not the correct explanation of the assertion
• C. Assertion is true but the reason is false
• D. Both assertion and reason are false

Answer 1

The correct option is A Both assertion and reason are true and the reason is the correct explanation of the assertion

Responses of the organisms to the changes in abiotic factors (temperature, pH) in the environment can be in different ways. If the changes in the external environment are unfavourable, localised or short-lived, then many organisms choose to either move away to a more favourable environment (migrate) or suspend their activities till favourable conditions return.

Diapause is a state of suspended development, in response to unfavourable conditions, which is seen in animal species such as insects, zooplanktons, etc. This mechanism holds the development of an animal at a particular developmental stage (embryo, larvae, etc) unless the unfavourable conditions pass over. This stage is marked by reduced metabolic activities in the organism.

Figure : Zooplanktons

Zooplanktons are microscopic animals in aquatic ecosystems that feed on microscopic plants or phytoplanktons. The eggs laid by some zooplankton species enter into a state of diapause. These eggs are encapsulated and can dry out or freeze and can hatch only under favourable conditions. Even if the eggs are ingested by fish, they are not digested and are released along with intestinal wastes. These eggs can remain viable for decades and then hatch when favourable conditions returns.

Thus both assertion and reason are true and the reason is the correct explanation of the assertion.