Concept explainers
Which of the following groups contains radially symmetrical organisms?
arthropods
cnidarians
mollusks
roundworms
Introduction:
Body symmetry was not evident in the earlier eukaryotes. It is noted down when tissues were developed in the animals. There are various types of body symmetry. In radial body symmetry, any plane going through the central axis divides the organism into equal halves. In bilateral symmetry, animals can be divided into almost mirror-image halves only among one particular plane through central axis.
Answer to Problem 1MC
Correct answer:
Radially symmetrical organisms are found in cnidarians group among the given groups.
Explanation of Solution
Explanation for the correct answer:
Option (b) is given that radially symmetrical organisms are found in cnidarians. The body plan of cnidarians is unique as any plane passing through their central axis divides these animals into equal halves. This property makes cnidarians different from the organisms evolved before them. Hence, option (b) is a correct answer.
Explanation for incorrect answers:
Option (a) is given that radially symmetrical organisms are found in arthropods. Arthropods are bilaterally symmetrical organisms as there is only one plane that passes through the central axis that can divide them into mirror-image halves. So, it is an incorrect option.
Option (c) is given that radially symmetrical organisms are found in molluscs. Molluscs are bilaterally symmetrical organisms as there is only one plane that passes through the central axis that can divide them into mirror-image halves. So, it is an incorrect option.
Option (d) is given that roundworm possesses radial symmetry. Roundworms are bilaterally symmetrical organisms as there is only one plane that passes through the central axis that can divide them into mirror-image halves. So, it is an incorrect option.
Hence, options (a), (c), and (d) are incorrect.
Therefore, it can be concluded that from the given groups, radially symmetrical organisms are found in cnidarians.
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Chapter 24 Solutions
Biology: Life on Earth (11th Edition)
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