Radial symmetry in the adult stage is not seen in Hemichordata. They are bilaterally symmetrical as adults, with a tripartite body plan (proboscis, collar, trunk). In contrast, Echinodermata show radial symmetry as adults (pentaradial in many). Ctenophora are radially organized, usually with biradial features. Coelenterata (Cnidaria) show radial symmetry in adults (jellyfishes, corals). Hence, the correct option is 3, Hemichordata.
🧠 Did You Know?
Hemichordates are known for their collar-gill slits and protochordate features, linking them to vertebrates in evolutionary discussions.
💡 NCERT Memory Line:
Adults of Echinodermata and Cnidaria show radial symmetry; Hemichordata are bilaterally symmetrical as adults.
The unique mammalian characteristics listed by NCERT include the presence of hairs, pinna (external ears), and mammary glands. These features are characteristic of mammals and help in identification. Among the options, only option 3 mentions hairs, pinna and mammary glands, making it the correct choice.
🧠 Did You Know?
Monotremes (egg-laying mammals) also have these features, but the combination of hairs, pinna, and mammary glands is broadly used to define mammals in NCERT texts.
💡 NCERT Memory Line:
Hairs, pinna and mammary glands are characteristic features of mammals.
Select the correct statements with reference to chordates.
A. Presence of a mid-dorsal, solid and double nerve cord.
B. Presence of closed circulatory system.
C. Presence of paired pharyngeal gills
D. Presence of dorsal heart
E. Triploblastic pseudocoelomate animals.
Choose the correct answer from the options given below:
Explanation:
Correct statements: B and C. Chordates have a closed circulatory system (blood confined to vessels). They possess pharyngeal gill slits (often paired) at some life stage. A is incorrect because the nerve cord in chordates is a dorsal hollow nerve cord, not a solid or double one. D is incorrect since the heart is typically ventral in chordates. E is incorrect because chordates are triploblastic and coelomate, not pseudocoelomate. Thus, B and C only are correct.
🧠 Did You Know?
NCERT emphasizes the five distinguishing features: notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail, and segmented body plan with a closed circulatory system in chordates.
💡 NCERT Memory Line:
Chordates: triploblastic coelomates with a dorsal hollow nerve cord and closed circulatory system, plus pharyngeal gill slits in at least some life stage.
Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): All vertebrates are chordates but all chordates are not vertebrates. Reason (R): Notochord is replaced by vertebral column in the adult vertebrates.
In the light of the above statements, choose the most appropriate answer from the option given below :
Explanation:
Statement A is true: every vertebrate is a chordate, but not every chordate is a vertebrate. Statement R is true: in vertebrates, the notochord is replaced by the vertebral column during development. However, R does not explain why vertebrates are chordates; it explains a developmental change within vertebrates. Therefore, both are correct, but R is not the direct explanation of A. The correct option is 2.
🧠 Did You Know?
In many vertebrates, the notochord is replaced by the vertebral column, but remnants may persist as intervertebral discs.
💡 NCERT Memory Line:
“All vertebrates are chordates, but all chordates are not vertebrates. In vertebrates, the notochord is replaced by the vertebral column.”
Which one of the following organisms bears hollow
and pneumatic long bones?
Explanation:
Option 1, Neophron, is a bird. Birds have hollow and pneumatic long bones that are connected to air sacs, making the bones light for flight. This feature is described in NCERT biology when explaining the skeletal system of birds. The other options are non-bird animals: Hemidactylus is a reptile (gecko); Macropus is a mammal (kangaroo); Ornithorhynchus is a monotreme mammal (platypus). Their bones are not hollow and pneumatic like birds’ bones.
🧠 Did You Know?
Bird bones are often filled with air spaces that reduce weight without sacrificing strength, aiding flight.
💡 NCERT Memory Line:
Birds possess hollow, pneumatic long bones connected to air sacs, aiding flight and reducing weight.
Read the following statements.
A. Metagenesis is observed in Helminths.
B. Echinoderms are triploblastic and coelomate
animals.
C. Round worms have organ-system level of body
organization.
D. Comb plates present in ctenophores help in
digestion.
E. Water vascular system is characteristic of
Echinoderms.
Choose the correct answer from the options given
below.
