Problem 7 - Biology

Question

Which of the following organisms is most likely to be a diploblast? a. sea star b. shrimp c. jellyfish d. insect

Step-by-Step Solution

Answer

c. jellyfish

Step 1: Understand Diploblasts

Diploblasts are organisms that develop from only two primary germ layers: the ectoderm and the endoderm. They lack a mesoderm, which is present in triploblasts.

Step 2: Identify Triploblasts

Triploblasts develop from three germ layers: ectoderm, mesoderm, and endoderm. Most complex organisms, such as sea stars (a), shrimp (b), and insects (d), are triploblasts.

Step 3: Know Which Organisms Are Diploblasts

Diploblastic organisms are typically simpler and belong to the phyla Cnidaria and Ctenophora. Common examples include jellyfish, corals, and comb jellies.

Step 4: Identify the Jellyfish

Recognize that jellyfish (c) belong to the phylum Cnidaria and are diploblastic organisms. Therefore, the correct answer is jellyfish.

Key Concepts

germ layers

Germ layers are foundational tissues that form during the early developmental phases of animals. These layers differentiate and give rise to all the structures and organs of the body. In simpler organisms, there are typically only two germ layers: the ectoderm and endoderm. In more complex animals, a third layer called the mesoderm appears.

Ectoderm: This is the outermost layer, which forms structures such as the skin and nervous system.
Endoderm: The innermost layer, responsible for developing into the digestive tract and associated organs.
Mesoderm: Found in more complex organisms, this middle layer forms muscles, bones, and the circulatory system.
Understanding these layers is crucial to distinguishing between diploblastic and triploblastic organisms. Diploblasts have two layers, while triploblasts have all three.

triploblasts

Triploblasts are animals that develop from three primary germ layers: ectoderm, mesoderm, and endoderm. This additional layer, the mesoderm, allows for greater complexity in body structure and function.
Triploblasts include:

• Sea stars
• Shrimp
• Insects

Having three germ layers enables these animals to develop complex organs and systems. The mesoderm specifically allows for the formation of muscles, bones, and blood vessels, contributing to the complexity and functionality of triploblastic organisms. This also explains why most advanced and active organisms fall into this category.

Cnidaria

The phylum Cnidaria includes organisms such as jellyfish, corals, and sea anemones. These creatures are usually simpler than triploblastic organisms and have a diploblastic body plan, containing only ectoderm and endoderm.

Key Characteristics:

• Radial symmetry
• Stinging cells called cnidocytes
• A simple digestive cavity

Diploblastic nature of cnidarians means they lack a mesoderm, limiting their structural and physiological complexity compared to triploblasts. However, they are perfectly adapted to their environments, usually aquatic, where their simpler body plan is advantageous. Understanding these distinctions can help you easily identify organisms that belong to this phylum and their unique adaptations.