Q.64 Given below are two statements, one is labelled as
Assertion (A) and the other is labelled as
Reason (R) :
Assertion (A) :
Four distinctive characteristics of phylum Chordata are notochord; single, dorsal, tubular nerve cord;
pharyngeal pouches and postanal tail.
Reason (R) :
The distinctive characteristics of phylum Chordata remain unchanged throughout the life of these animals.
In the light of the above statements, choose the
most appropriate answer from the options given below :
- Both (A) and (R) are correct and (R) is the correct explanation of (A)
- Both (A) and (R) are correct but (R) is not the correct explanation of (A)
- (A) is correct but (R) is not correct
- (A) is not correct but (R) is correct
Phylum Chordata defines animals from tunicates to humans via four hallmark traits, but do they last a lifetime? This classic NEET zoology question clarifies chordate diagnostic features.
Correct Answer: Option (3) – (A) is correct but (R) is not correct
Assertion (A) accurately lists Chordata’s defining traits, present at some life stage. Reason (R) fails because these features are often transient—replaced in adults (e.g., notochord becomes vertebral column in vertebrates).
Detailed Explanation of All Options
-
Option (1): Both correct, (R) explains (A)
Incorrect. While (A) holds, (R) doesn’t explain it—the traits define Chordata regardless of persistence, not because they’re permanent.
-
Option (2): Both correct, but (R) not explanation
Incorrect. (R) is false; lancelets retain traits lifelong, but frogs lose tails, humans resorb notochord/pouches (gill slits become Eustachian tubes).
-
Option (3): (A) correct, (R) not correct
Correct. (A) matches textbook Chordata synapomorphies. (R) wrong—traits diagnostic if seen in embryonic/adult stages (e.g., human embryo has all four).
-
Option (4): (A) not correct, (R) correct
Incorrect. Both false; (A) is standard, (R) contradicted by tunicates (adult loses notochord/tail) and vertebrates.
Chordata’s Four Key Traits
| Trait |
Description |
Life Stage Example |
| Notochord |
Flexible rod for support |
Adult lamprey; embryonic humans |
| Dorsal nerve cord |
Hollow, brain-to-tail |
Persists as spinal cord |
| Pharyngeal pouches |
Gill slit precursors |
Human embryos (turn to tonsils) |
| Postanal tail |
Tail beyond anus |
Human fetuses (regresses) |
