
Concept explainers
Test your Understanding
Know and Comprehend
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.
Want to see more full solutions like this?
Chapter 42 Solutions
Biology (MindTap Course List)
- (A) 25 20 20 15 NPP (Mg C/ha/yr) 10 10 5 0 0 2,000 4,000 6,000 ECOLOGY 4e, Figure 20.11 (Part 1) 2017 Sinauer Associates, Inc. Average annual precipitation (mm) 8,000arrow_forwardexplain the cascade of events (starting with relaxing trade winds) that occurs during El Niño in the eastern Pacific (off the coasts of California/North America and Peru/South America) and which lead to food-chain collapse - start with changes in the physical/oceanographic conditions, andthen systematically describe the cascading effects at each level of the food chain -arrow_forward3) Which statement(s) about the Pacific Decadal Oscillation (PDO) is/are TRUE? CIRCLE ALL THAT APPLY. A. It is a major driver of salmon populations in the Pacific B. It affects sea surface temperatures in the eastern Pacific C. Its cycles typically do not last as long as those of ENSO D. Evidence that it has occurred over many centuries has been gathered from tree ring dataarrow_forward
- 4.arrow_forward2arrow_forward1. 2. 3. Marine fish cells are hypotonic compared to their seawater environment; their cells lose water by osmosis and gain solutes. If you add heterotrophic respiration and autotrophic respiration together and then subtract that value from gross primary productivity, then you have a more refined estimate of ecosystem carbon storage than NEE. Differential heating due to the earth's tilt generates the global wind AND oceanic circulation patternsarrow_forward
- Biology (MindTap Course List)BiologyISBN:9781337392938Author:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. BergPublisher:Cengage LearningBiology: The Dynamic Science (MindTap Course List)BiologyISBN:9781305389892Author:Peter J. Russell, Paul E. Hertz, Beverly McMillanPublisher:Cengage Learning
- Biology 2eBiologyISBN:9781947172517Author:Matthew Douglas, Jung Choi, Mary Ann ClarkPublisher:OpenStaxBiology: The Unity and Diversity of Life (MindTap...BiologyISBN:9781305073951Author:Cecie Starr, Ralph Taggart, Christine Evers, Lisa StarrPublisher:Cengage Learning




