Which organism has a central brain? A. sponge B. hydra C. flatworm D. fish
The correct answer and explanation is:
The correct answer is D. fish.
Explanation:
Organisms vary greatly in their nervous system complexity. Among the options given—sponge, hydra, flatworm, and fish—the presence of a central brain is found only in the fish.
A. Sponge:
Sponges are very simple animals that lack any nervous system. They rely on the flow of water through their porous bodies to obtain nutrients and oxygen and to remove waste. There are no neurons or brain structures in sponges, only specialized cells that perform basic functions.
B. Hydra:
Hydra are simple cnidarians with a nerve net, a decentralized arrangement of neurons spread throughout their body. They lack a central brain. Their nerve net allows basic responses like contracting or extending tentacles but does not constitute a centralized brain.
C. Flatworm:
Flatworms are more complex than hydra and sponges. They have a simple nervous system that includes a pair of nerve cords and two cerebral ganglia—clusters of nerve cells that function somewhat like a rudimentary brain. However, this is not a true central brain but rather a simple cluster of neurons. Flatworms lack a complex brain with distinct regions.
D. Fish:
Fish are vertebrates and have a well-developed central nervous system, which includes a true brain located in the head region. The fish brain is complex, with specialized parts like the cerebrum, cerebellum, and brainstem, responsible for processing sensory information, motor control, and coordinating behavior. This central brain allows fish to perform complex behaviors like swimming, hunting, and social interaction.
Summary:
- Sponges: No nervous system, no brain.
- Hydra: Nerve net, no central brain.
- Flatworm: Simple nerve clusters, no true brain.
- Fish: Well-developed central brain with specialized regions.
Thus, only fish among these have a central brain, enabling complex behaviors and coordination.