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Q.1. Describe the nervous system in Hydra. Sketch and label the nerve net in Hydra. [3 Marks] Ans:

1. Hydra (Cnidarian) shows diffused type of nervous system. It is the most primitive nervous system.
2. Nervous system of Hydra consists of the sensory cells and the nerve cells (neurons) along with their fibres.
3. The nerve cells are distributed throughout the body and interconnected to each other by synapses between their fibres to form the nerve net.
4. There are two nerve nets in the mesoglea of Hydra, one connected towards the epidermis and the other towards the gastro-dermis.
5. Hydra lacks specialized sense organs however, it has sensory cells scattered in the body wall and tentacles.
6. The nerve cells have fibres but there are no sensory and motor nerves.
7. In Hydra, the nerve impulses show no polarity or direction. This is because the sensory cells are activated at any point and from this point the impulse can be carried throughout the body in any direction, thus causing movements of the body or tentacles. e.g. Catching of Nerve net prey during feeding.

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