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A radially symmetrical animal such as Hydra is likely to have (a) a forebrain (b) a nerve net (c) cerebral ganglia (d) a ventral nerve cord (e) cerebral ganglia and a nerve net

Introduction: Hydra is a freshwater organism of the phylum Cnidaria. They have very high regenerative ability. They are radially symmetrical invertebrates and have tentacles to capture their food.
Answer to Problem 1TYU
Correct answer: Radially symmetrical organisms such as Hydra have simple nervous systems like the nerve net. Hence, the correct answer is option (b).
Explanation of Solution
Reason for the correct answer:
Radial symmetry is generally present in simpler organisms such as Hydra. Organisms belonging to simpler classes in the animal kingdom have less complexed nervous systems. They usually have interconnected networks of neurons, and no central control system is present in such simpler neural systems. Such connection of neurons forms the nerve net.
Option (b) is given as “a nerve net”.
Radially symmetrical organisms such as Hydra have simpler body organization and simpler nervous systems such as the nerve nets. Hence, the correct answer is option (b).
Reasons for incorrect answers:
Option (a) is given as “a forebrain”.
A forebrain is a part of a complex nervous system that is found in higher organisms with a complex body organization. The forebrain is not found in simpler organisms such as Hydra. Hence, option (a) is incorrect.
Option (c) is given as “cerebral ganglia”.
Radially symmetrical organisms have simple nervous systems that do not have any control center. Cerebral ganglia act as a control center in the nervous systems. Hence, option (c) is incorrect.
Option (d) is given as “a ventral nerve cord”.
Ventral and dorsal sides can be defined only in organisms with bilateral symmetry. In organisms with simple body organization, there is no nerve cord present. Thus, radially symmetrical organisms cannot have a ventral nerve cord. Hence, option (d) is incorrect.
Option (e) is given as “cerebral ganglia and a nerve net”.
Simpler organisms do not have cerebral ganglia in their nervous systems. Hence, option (e) is incorrect.
Hence, options (a), (c), (d), and (e) are incorrect.
Organisms with radial symmetry in their body organization, such as Hydra, have a nervous system consisting only of nerve nets.
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Chapter 42 Solutions
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