Question

The undifferentiated layer present between the ectoderm and endoderm in coelenterate is (a) Mesophyll (b) Gastral layer (c) Archenteron (d) Mesoglea

Short answer

The correct answer is (d) Mesoglea. It is the undifferentiated jelly-like layer present in between the ectoderm and endoderm in coelenterates that provides structural support.

Step-by-step solution

Understand the Structure of Coelenterates

Coelenterates, such as jellyfish and sea anemones, are simple multicellular organisms. These animals are characterized by a special type of radial symmetry and are composed of three layers. The outermost layer is the ectoderm, the innermost layer is the endoderm, and there's a layer in between.

Identify the Correct Term for the Intermediary Layer

To answer this question, you must identify the correct term for the intermediary layer in a coelenterate, i.e., the layer between the ectoderm and endoderm. Among the options (a) Mesophyll, (b) Gastral layer, (c) Archenteron, (d) Mesoglea, the correct term is (d) Mesoglea. Mesoglea, a non-cellular, jelly-like layer found between the ectoderm and endoderm in coelenterates, acts as a sort of skeletal system providing structural support against gravity and buoyancy.

Key concepts

Ectoderm

The ectoderm is the outermost layer of cells in a coelenterate, such as in jellyfish or sea anemones. As the "outer skin," it plays an essential role in protecting the organism.

The ectoderm forms the external surface of these creatures, providing a barrier against the environment. It is responsible for the formation of several structures including:

• The epidermis, which is the outer protective layer
• Specialized cells like sensory receptors that help the organism interact with its surroundings
• In some species, the ectoderm even helps produce pigment cells that can affect the appearance of the animal

The ectoderm is crucial not only for protection but also for sensation, aiding in the organism's interaction with its surroundings. This makes it integral to the survival of coelenterates.

Endoderm

The endoderm is the innermost cellular layer in coelenterates and serves as the "inner skin." This layer is found lining the gastrovascular cavity, which is the primary digestive chamber of the organism.

Its functions are critical for digestion and nutrient absorption. The endoderm forms the lining of:

• The gastrovascular cavity, where digestion takes place
• Various specialized cells tasked with digestive enzyme secretion to break down food particles
• Nutrient-absorbing cells that facilitate nutrient transfer throughout the organism

The endoderm's role is vitally important for the feeding and nourishment of coelenterates, ensuring that they can sustain themselves in their aquatic environments.

Mesoglea

Mesoglea is the jelly-like, non-cellular layer that lies between the ectoderm and the endoderm in coelenterates. This intermediary layer has several functions vital to the life of these organisms.

Mesoglea serves as a type of skeletal support:

• It provides the necessary structure and durability to keep the animal's form due to its semi-solid, jelly-like consistency
• Supports buoyancy, allowing these creatures to maintain and control their position in the water
• Mitigates damage from physical impacts by providing a cushioning effect

Despite being non-cellular, the mesoglea's role is indispensable, facilitating both physical stability and protection in the fluid marine environment where coelenterates thrive.