Question

Assertion (A): In Euglena, forward movement is produced mainly by the effective stroke of the flagellum.
Reason (R): During the recovery stroke, the flagellum becomes stiff and pushes the body forward.

• A. Both (A) and (R) are true. (R) is correct explanation for (A)
• B. Both (A) and (R) are true. (R) is not correct explanation for (A)
• C. (A) is true. But (R) is false
• D. (A) is false. But (R) is true

Hint:

Effective stroke = Rigid, powerful backward sweep.
Recovery stroke = Flexible, low-resistance forward return.
This dual-phase movement is similar to the swimming stroke used by a human swimmer.

Answer 1

The Correct Option is C

Step 1: Separate the assertion from the reason.
Check whether forward movement really comes from the effective stroke first, then separately check what the recovery stroke actually does to the flagellum.
Step 2: Confirm the assertion.
During the effective stroke the flagellum stays fairly stiff and sweeps back like an oar, pushing water backward and the cell forward, so the assertion is correct.
Step 3: Test the reason against known flagellar mechanics.
The recovery stroke is the opposite of what the reason claims, the flagellum goes soft and flexible and is drawn forward close to the body with minimal resistance, it does not stiffen and push the body forward.
Final answer: Option 3, assertion true but reason false.