Questions & explanations
1. Which of the following is a characteristic feature of Class Mammalia?
- Presence of mammary glands
- Two-chambered heart
- Cold-blooded
- Lay eggs with hard shells
Answer: Presence of mammary glands
Mammals are defined by the presence of mammary glands that produce milk to nourish their young. They have a four-chambered heart, are warm-blooded, and most are viviparous. Two-chambered hearts are found in fish, cold-bloodedness is typical of reptiles and amphibians, and egg-laying with hard shells is characteristic of birds and some reptiles.
2. Which class of vertebrates has a four-chambered heart, is warm-blooded, and has hair or fur on the skin?
- Aves
- Reptilia
- Mammalia
- Amphibia
Answer: Mammalia
Mammals have a four-chambered heart, are warm-blooded (endothermic), and possess hair or fur. Aves (birds) also have a four-chambered heart and are warm-blooded but have feathers, not hair. Reptiles have a three-chambered heart (except crocodilians) and are cold-blooded. Amphibians have a three-chambered heart and are cold-blooded.
3. Which of the following is a characteristic feature of the coelenteron (gastrovascular cavity) in Cnidarians?
- It has two openings, mouth and anus.
- It is a blind sac with a single opening that serves both for ingestion and egestion.
- It is lined by mesoderm.
- It is absent in polyp forms.
Answer: It is a blind sac with a single opening that serves both for ingestion and egestion.
Cnidarians possess a gastrovascular cavity called coelenteron that has only one opening, the mouth, through which food is taken in and waste is expelled. It is not a complete digestive tract with separate mouth and anus. The cavity is lined by gastrodermis (endoderm), not mesoderm. It is present in both polyp and medusa forms.
4. Which of the following is a fundamental chordate character?
- Dorsal solid nerve cord
- Notochord
- Ventral heart
- Post-anal tail
Answer: Notochord
The notochord is a defining feature of chordates, providing skeletal support. The dorsal hollow nerve cord is another key character, not a solid one. Ventral heart and post-anal tail are also chordate features but not among the three fundamental ones (notochord, dorsal hollow nerve cord, paired pharyngeal gill slits).
5. Which of the following correctly distinguishes chordates from non-chordates?
- Notochord present in chordates, absent in non-chordates
- Nerve cord is ventral in chordates, dorsal in non-chordates
- Heart is dorsal in chordates, ventral in non-chordates
- Post-anal tail absent in chordates
Answer: Notochord present in chordates, absent in non-chordates
The presence of a notochord is a key distinguishing feature of chordates; it is absent in non-chordates. In chordates, the nerve cord is dorsal and hollow, while in non-chordates it is ventral and solid. The heart is ventral in chordates and dorsal in non-chordates. Post-anal tail is present in chordates.
6. Which of the following cnidarians exhibits a colonial form with division of labour, including specialized individuals for feeding, reproduction, and defense?
- Hydra
- Aurelia
- Physalia
- Adamsia
Answer: Physalia
Physalia (Portuguese man-of-war) is a colonial cnidarian composed of multiple specialized zooids (e.g., gastrozooids for feeding, gonozooids for reproduction, dactylozooids for defense) showing division of labour. Hydra is solitary, Aurelia is a solitary medusa, and Adamsia is a solitary sea anemone.
7. In Cnidarians, the phenomenon of alternation between polyp and medusa forms in the life cycle is called:
- Metamorphosis
- Metagenesis
- Parthenogenesis
- Gametogenesis
Answer: Metagenesis
Metagenesis refers to the alternation of generations between asexual polyp and sexual medusa forms in cnidarians. Metamorphosis is a change in form during development, parthenogenesis is development from unfertilized eggs, and gametogenesis is the formation of gametes.
8. Which of the following is a characteristic of subphylum Cephalochordata?
- Notochord present only in larval tail
- Notochord extends from head to tail and persists throughout life
- Notochord replaced by vertebral column in adults
- Notochord absent
Answer: Notochord extends from head to tail and persists throughout life
In Cephalochordata (e.g., Branchiostoma/Amphioxus), the notochord extends from head to tail and persists throughout life. It is not replaced by a vertebral column. Urochordates have notochord only in larval tail; vertebrates have notochord replaced by vertebral column.
9. Which of the following is true about phylum Hemichordata?
- They possess a true notochord
- They are worm-like marine animals with a stomochord
- They are closely related to echinoderms
- They have a dorsal hollow nerve cord
Answer: They are worm-like marine animals with a stomochord
Hemichordates are worm-like marine animals that have a stomochord, a rudimentary structure similar to notochord but not homologous. They lack a true notochord and dorsal hollow nerve cord. They were formerly grouped with chordates but are now considered separate.
10. The nervous system of annelids consists of:
- A dorsal nerve cord and ganglia
- Paired ganglia, lateral nerves, and a ventral nerve cord
- A nerve net
- A brain and a dorsal hollow nerve cord
Answer: Paired ganglia, lateral nerves, and a ventral nerve cord
Annelids have a nervous system with paired ganglia, lateral nerves, and a ventral nerve cord. The other options describe nervous systems of other phyla: dorsal nerve cord in some invertebrates, nerve net in cnidarians, and dorsal hollow nerve cord in chordates.
11. Which of the following statements is true regarding the reproductive characteristics of most arthropods?
- They are hermaphroditic and oviparous with indirect development only.
- They are mostly dioecious, oviparous, and may have direct or indirect development.
- They are viviparous and show direct development only.
- They are dioecious but exhibit ovoviviparity and indirect development.
Answer: They are mostly dioecious, oviparous, and may have direct or indirect development.
Most arthropods are dioecious (separate sexes), oviparous (lay eggs), and exhibit either direct or indirect development. Hermaphroditism is rare, and viviparity is not typical. Thus, the correct option accurately describes the general reproductive pattern.
12. Which of the following is an additional chordate feature, besides the three fundamental characters?
- Open circulatory system
- Post-anal tail
- Ventral nerve cord
- Exoskeleton
Answer: Post-anal tail
Chordates possess a post-anal tail and a closed circulatory system as additional features. An open circulatory system is found in arthropods, not chordates. Ventral nerve cord is characteristic of non-chordates. Exoskeleton is not a chordate feature.