14. Which structure is NOT universally present in all chordates?
[AIPMT, 2000]
(A) Diaphragm
(B) Coelom
(C) Pharyngeal clefts during development
(D) Dorsal hollow nerve cord
Answer: (A) Diaphragm
Explanation: A muscular diaphragm is characteristic of mammals, not every chordate. The chordate body plan includes a dorsal hollow nerve cord, a notochord and pharyngeal slits at some developmental stage.
13. What feature is shared by Ascaris lumbricoides and Anopheles stephensi?
[AIPMT, 2000]
(A) Sexual dimorphism
(B) Metameric segmentation
(C) Obligate anaerobic respiration
(D) Endoparasitism
Answer: (A) Sexual dimorphism
Explanation: Male and female roundworms differ in size and tail structure, while male and female mosquitoes also differ in morphology. Ascaris is a nematode endoparasite, whereas Anopheles is an arthropod vector.
12. Which animal shows tissue-level organisation rather than cellular organisation?
[AIPMT, 2000]
(A) Sponge
(B) Hydra
(C) A liver fluke
(D) Ascaris
Answer: (B) Hydra
Explanation: Cnidarians such as Hydra exhibit tissue-level organisation, with specialised cell layers and a nerve net. Sponges show cellular-level organisation, while more complex flatworms and nematodes possess organs or organ systems.
11. Air-filled pneumatic bones occur prominently in which vertebrate class?
[AIPMT, 1998]
(A) Mammalia
(B) Reptilia
(C) Urodela
(D) Aves
Answer: (D) Aves
Explanation: Many birds possess hollow bones linked with air-sac systems, reducing skeletal mass while maintaining strength. This pneumatic skeleton is an important adaptation associated with avian flight and respiration.
10. Solenocytes are excretory cells found in which phylum?
[AIPMT, 1998]
(A) Platyhelminthes
(B) Arthropoda
(C) Annelida
(D) Aschelminthes
Answer: (A) Platyhelminthes
Explanation: Solenocytes are specialised terminal cells of protonephridial excretory systems described in certain flatworms. Their flagella or cilia drive filtrate through fine ducts. They are not the typical excretory organs of insects or annelids.
9. Which phenomenon is characteristic of the cnidarian Obelia?
[AIPMT, 1998]
(A) Metagenesis
(B) Morphogenesis
(C) Apolysis
(D) Paedogenesis
Answer: (A) Metagenesis
Explanation: Obelia exhibits alternation of polyp and medusa forms. Asexual budding in the polyp stage gives rise to reproductive medusae that produce gametes. This alternation is commonly termed metagenesis.
8. Which category accounts for the greatest number of described species among these groups?
[UPSC Civil Services Preliminary Examination, 1996]
(A) Fungi
(B) Flowering plants
(C) Insects
(D) Bacteria
Answer: (C) Insects
Explanation: Insects form the largest group of described animal species and substantially outnumber the listed alternatives. Their success is associated with small body size, flight, metamorphosis and adaptation to diverse terrestrial habitats.
7. What does the two-part scientific naming system introduced by Linnaeus signify?
[AIPMT, 1993]
(A) Two names assigned by different taxonomists
(B) One local and one Latin name
(C) A scientific and common name together
(D) A generic name followed by a specific epithet
Answer: (D) A generic name followed by a specific epithet
Explanation: Binomial nomenclature assigns a species a Latinised genus name and a specific epithet. The genus begins with a capital letter, whereas the epithet is lowercase; both are italicised when printed.
6. Which term refers to viruses infecting algae?
[AIPMT, 1993]
(A) Binal viruses
(B) Cyanophages
(C) Mycophages
(D) Phycophages
Answer: (D) Phycophages
Explanation: Phycophages are viruses whose hosts are algae. Cyanophages specifically infect cyanobacteria, while mycophages infect fungi. Such host-based terms classify viruses according to the organisms they parasitise.
5. All true fungi can be described as which type of organisms?
[AIPMT, 1993]
(A) Heterotrophs
(B) Autotrophs
(C) Only saprophytes
(D) Only parasites
Answer: (A) Heterotrophs
Explanation: All true fungi obtain organic food from other organisms or their remains. Some are saprotrophs, others parasites, and many form symbioses. They lack chlorophyll and therefore cannot be classified as photosynthetic autotrophs.
