Q11. Animals with only two germ layers, the ectoderm and endoderm, are classified as:
a) Diploblastic
b) Triploblastic
c) Acoelomates
d) Pseudocoelomates
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Correct Answer: a) Diploblastic
Explanation: Diploblastic animals, like those from phyla Cnidaria (jellyfish, corals) and Ctenophora (comb jellies) have bodies arising from two embryonic germ layers. The ectoderm gives rise to the outer covering or skin and the endoderm forms the digestive system.
Q12. Flatworms (phylum Platyhelminthes) and humans both exhibit:
a) Diploblastic organization
b) Triploblastic organization
c) Radial symmetry
d) Asymmetry
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Correct Answer: b) Triploblastic organization
Explanation: Triploblastic organisms develop from three primary germ layers: ectoderm, mesoderm, and endoderm. These layers give rise to complex tissues and organs systems. While simple in structure, flatworms, as well as humans, are classified as triploblastic animals.
Q13. The presence of a third germ layer, the mesoderm, allows for the development of:
a) More complex internal organs
b) Radial symmetry
c) Simplified body systems
d) Diploblastic organization
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Correct Answer: a) More complex internal organs
Explanation: The mesoderm, absent in diploblastic animals, provides the basis for complex organ systems. In triploblastic animals, muscle, the circulatory system, the reproductive system, and other important structures develop from the mesodermal tissue layer.
Q14. Which of the following phyla exhibit diploblastic organization?
a) Annelida
b) Platyhelminthes
c) Cnidaria
d) Chordata
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Correct Answer: c) Cnidaria
Explanation: Jellyfish, corals, and other members of phylum Cnidaria exhibit diploblastic organization. With only an ectoderm and endoderm, their body plan is simpler than animals with three germ layers. Cnidarians have radial symmetry and possess stinging cells for capturing prey.
Q15. Which germ layer gives rise to the body covering, nervous system, and sense organs?
a) Ectoderm
b) Mesoderm
c) Endoderm
d) Blastopore
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Correct Answer: a) Ectoderm
Explanation: The ectoderm is the outermost germ layer. It forms skin, sensory organs like the eyes, and the entire nervous system, which plays a key role in perceiving the external environment and responding to it.
Q16. Animals lacking a true body cavity are classified as:
a) Acoelomates
b) Pseudocoelomates
c) Coelomates
d) Enterocoelomates
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Correct Answer: a) Acoelomates
Explanation: Acoelomates, like flatworms, lack a fluid-filled body cavity (coelom). Their internal organs are embedded in a solid tissue derived from the mesoderm. This simpler body plan limits the development of complex organ systems.
Q17. A body cavity partially lined with mesoderm is characteristic of:
a) Acoelomates
b) Pseudocoelomates
c) Coelomates
d) Radiates
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Correct Answer: b) Pseudocoelomates
Explanation: Roundworms (Nematoda) are examples of pseudocoelomates. Their body cavity is not completely lined with mesoderm, unlike in true coelomates. However, a pseudocoelom offers more space than acoelomate body plans, allowing for some organ development.
Q18. Humans and earthworms both possess a:
a) Acoelomate body cavity
b) Pseudocoelomate body cavity
c) True coelom
d) Diploblastic organization
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Correct Answer: c) True coelom
Explanation: Coelomates have a true coelom, a body cavity fully lined with mesoderm. This space between the body wall and the gut allows for organ development, circulation of fluids, and cushioning of internal organs.
Q19. Animals that give birth to live young and nourish them with milk are classified as:
a) Oviparous
b) Viviparous
c) Amniotes
d) Placental mammals
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Correct Answer: d) Placental mammals
Explanation: Placental mammals develop a placenta during pregnancy, facilitating exchange of nutrients and waste between the mother and fetus. They nourish their young with milk from mammary glands. Most mammals fall into this category.
Q20. Which type of body cavity provides the most efficient support for complex internal organs and enhances independent movement of these organs?
a) Acoelomate
b) Pseudocoelomate
c) True coelom
d) None of the above
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Correct Answer: c) True coelom
Explanation: The true coelom allows organs to grow and move independently of the body wall, facilitating more complex organ systems. The cushioning fluid serves and a hydrostatic skeleton, providing support.