Question

Hydra receives impulses and stimuli through (a) nerve net (b) nematocytes (c) sensory cells (d) neuron cells.

Short answer

Hydra receives impulses and stimuli through (a) nerve net.

Step-by-step solution

Understanding the Nervous System of Hydra

To address this exercise, one must have knowledge of the Hydra's nervous system. Hydra is a simple organism with a primitive nervous system. Unlike more complex organisms with a centralized nervous system, Hydra has a distributed network of nerve cells that allows it to respond to environmental stimuli.

Identifying the Correct Term

Among the options given, we need to choose the term that best describes how Hydra receives impulses and stimuli. (a) 'nerve net' refers to the simple mesh-like arrangement of nerves in Hydra that helps it sense and respond. (b) 'nematocytes' or cnidocytes are specialized cells for stinging and capturing prey, not for receiving stimuli. (c) 'sensory cells' are indeed involved in sensing, but they form part of the nerve net in the context of Hydra. (d) 'neuron cells' could be considered synonymous with nerve cells, but the term 'nerve net' typically encompasses the whole nervous system arrangement in Hydra.

Choosing the Most Appropriate Answer

Therefore, the correct answer is (a) 'nerve net' as it is the network through which Hydra receives impulses and stimuli.

Key concepts

Nerve Net

The nerve net in Hydra represents a fundamental approach to nervous system organization. Unlike the complex, centralized nervous systems found in more evolved animals, the Hydra's nerve net is a simple, diffuse network of interconnected neuron cells. This structure allows the Hydra to receive signals from all over its body.

Imagine a delicate mesh spread throughout the Hydra's body, with each intersection signifying a point of communication. Signals can travel in any direction, providing the animal with the ability to respond to stimuli from all around it. This net is particularly important for coordinating the Hydra's movements and behaviors despite the absence of a brain or central nervous system.

The nerve net is crucial for the Hydra’s survival, as it permits the organism to carry out complex behaviors like feeding, moving, and responding to external cues, with a relatively simple biological architecture.

Nematocytes

Hydra's nematocytes, also known as cnidocytes, are a fascinating set of cells that operate like biological traps. These cells are not part of the nervous system in their primary function, but instead play a pivotal role in the Hydra's ability to capture prey and defend itself.

How are they Triggered?

Each nematocyte contains a specialized structure called a cnidocil, which, when stimulated, triggers the nematocyte to deploy its harpoon-like structure, injecting toxins into its prey or potential threat. This swift action is a reflex that does not involve the nerve net directly, but it is critical for the survival of the hydra in its aquatic environment.

Nematocyte's Relation to the Nervous System

While nematocytes themselves aren't sensory cells, their activation may be modulated by the nerve net as the organism reacts to touch or the presence of prey nearby.

Sensory Cells

In the context of Hydra, sensory cells are specialized cells that work closely with the nerve net to help the organism sense its environment. These cells can detect changes in light, touch, and the chemical composition of the water around them.

The sensory cells of Hydra act as the eyes and ears of the organism. They relay information about the environment to the nerve net, which then processes the data and prompts a response from the hydra, such as contracting its body or moving its tentacles. It’s a symbiotic relationship where sensory cells gather the external data, and the nerve net executes the necessary response, ensuring that the Hydra can react appropriately to its surroundings.

Neuron Cells

Neuron cells, or nerve cells, are the individual building blocks of the nervous system in Hydra. While in more complex organisms these cells form elaborate circuits and pathways, in Hydra, they construct the more rudimentary nerve net.

Each neuron in Hydra is capable of sending and receiving nerve impulses, allowing the entire net to operate as a coordinated whole. The functioning of these neurons is essential for the Hydra to process stimuli such as light and pressure from the environment. The nerve cells enable the Hydra to engage in basic reflex actions and maintain its survival activities, such as feeding and locomotion, even without a central nervous system.

In summary, neuron cells in Hydra are critical for the seemingly simple yet intricate dance of life processes, enabling this organism to thrive in its aquatic ecosystem.