24. Where do barophilic prokaryotes chiefly thrive?
[AIPMT Prelims, 2005]
(A) In frozen alkaline mountain ponds
(B) Only in barium-rich water
(C) In deep marine sediments under great pressure
(D) In water containing soluble barium salts
Answer: (C) In deep marine sediments under great pressure
Explanation: Barophiles, also called piezophiles, have adapted to very high hydrostatic pressure, such as that found in deep-sea sediments. The name derives from pressure rather than from the chemical element barium.
23. Auxospores and hormocysts are produced respectively by which organisms?
[AIPMT Prelims, 2005]
(A) Many diatoms and a few cyanobacteria
(B) Cyanobacteria and diatoms in that order
(C) A few diatoms and numerous cyanobacteria
(D) Many cyanobacteria and diatoms
Answer: (A) Many diatoms and a few cyanobacteria
Explanation: Auxospores allow diatoms to restore their cell size after successive divisions. Hormocysts are thick-walled specialised filaments formed by certain cyanobacteria. These reproductive or resting structures occur in different groups.
22. Which unicellular organism contains a macronucleus for routine activity and micronuclei for reproduction?
[AIPMT Prelims, 2005]
(A) Euglena
(B) Amoeba
(C) Paramecium
(D) Trypanosoma
Answer: (C) Paramecium
Explanation: Paramecium shows nuclear dimorphism typical of ciliates. The macronucleus regulates cellular activity, whereas the micronucleus is important in sexual processes such as conjugation. This arrangement distinguishes ciliates from many other protists.
21. Which feature is especially characteristic of mammals?
[AIPMT, 2004]
(A) Muscular diaphragm
(B) Four-chambered heart
(C) Rib cage
(D) Warm-blooded nature
Answer: (A) Muscular diaphragm
Explanation: A muscular diaphragm separating chest and abdominal cavities is a distinctive mammalian adaptation assisting breathing. Birds also possess a four-chambered heart and endothermy, while rib cages occur in several other vertebrate groups.
20. In which arthropod class is the body normally divided into head, thorax and abdomen?
[AIPMT, 2004]
(A) Myriapoda
(B) Crustacea
(C) Arachnida and Crustacea
(D) Insecta
Answer: (D) Insecta
Explanation: Insects ordinarily have three clear tagmata: head, thorax and abdomen. Spiders commonly have a cephalothorax and abdomen, whereas other arthropods show different patterns of segment grouping.
19. Which matches of animals and respiratory organs are accurate:
A. silverfish-tracheae;
B. scorpion-book lungs;
C. sea squirt-pharyngeal gills;
D. dolphin-skin?
[AIPMT, 2003]
(A) A and D
(B) A, B and C
(C) B and D
(D) C and D
Answer: (B) A, B and C
Explanation: Silverfish breathe through tracheal tubes, scorpions through book lungs and sea squirts through pharyngeal gill slits. Dolphins are mammals that breathe air through lungs rather than through skin.
18. Which pairing correctly associates an animal with a phenomenon?
[AIPMT, 2003]
(A) Pheretima-sexual dimorphism
(B) Musca-complete metamorphosis
(C) Chameleon-mimicry
(D) Taenia-polymorphism
Answer: (B) Musca-complete metamorphosis
Explanation: Musca, the housefly, undergoes complete metamorphosis through egg, larva, pupa and adult. Earthworms are generally hermaphroditic, and the other pairings do not describe the standard textbook examples intended here.
17. Through which structures does Hydra eliminate undigested food and dissolved nitrogenous wastes respectively?
[AIPMT, 2001]
(A) Mouth and mouth
(B) Body wall and body wall
(C) Mouth and body wall
(D) Mouth and tentacles
Answer: (C) Mouth and body wall
Explanation: Hydra has one gastrovascular opening, its mouth, used for food intake and expulsion of undigested material. Dissolved metabolic wastes diffuse across its thin body wall because it lacks specialised excretory organs.
16. Which organism in the following list has a post-anal tail?
[AIPMT, 2001]
(A) Earthworm
(B) A lower non-chordate invertebrate
(C) Scorpion
(D) Snake
Answer: (D) Snake
Explanation: A post-anal tail is a defining chordate character, present at least during development. Snakes are vertebrate chordates, although their external anatomy is specialised. A scorpion’s posterior sting-bearing region is not a chordate post-anal tail.
15. Which statement about mammals is correct?
[AIPMT, 2000]
(A) Platypus lays eggs
(B) Bats possess feathers
(C) Elephants are ovoviviparous
(D) Mammals do not have diaphragms
Answer: (A) Platypus lays eggs
Explanation: The platypus is a monotreme, an egg-laying mammal. Bats have hair rather than feathers, elephants give birth to live young, and a muscular diaphragm is characteristic of mammals.
