Problem 4 - Campbell Biology

Question

. Which of the following combinations of phylum and description is incorrect? \begin{equation}\begin{array}{l}{\text { (A) Echinodermata - bilateral symmetry as a larva, coelomate }} \\ {\text { (B) Nematoda-roundworms, pseudocoelomate }} \\ {\text { (C) Platyhelminthes- flatworms, gastrovascular cavity, }} \\ {\text { acoelomate }} \\ {\text { (D) Porifera-gastrovascular cavity, coelomate }}\end{array}\end{equation}

Step-by-Step Solution

Answer

Option D is incorrect.

Step 1: Understand the Phyla

Review the characteristics of each phylum mentioned in the question: Echinodermata, Nematoda, Platyhelminthes, and Porifera.

Step 2: Analyze Each Description

Compare the given descriptions with the known characteristics of each phylum to identify any inconsistencies.

Step 3: Identify Inconsistencies

Check each pairing: - Echinodermata have bilateral symmetry as larvae and are coelomate. - Nematoda are roundworms and pseudocoelomate. - Platyhelminthes are flatworms with a gastrovascular cavity and are acoelomate. - Porifera do not have a gastrovascular cavity and are not coelomate.

Step 4: Choose the Incorrect Option

From the analysis, identify that the description of Porifera (Option D) is incorrect.

Key Concepts

Echinodermata bilateral symmetry

Echinodermata, a phylum that includes sea stars and sea urchins, exhibits interesting symmetry characteristics. As larvae, echinoderms have bilateral symmetry. This means that their body can be divided into two mirror-image halves. However, as adults, they typically exhibit radial symmetry, where their body parts are arranged around a central axis. This dual nature of symmetry is unique among animals. Additionally, echinoderms are coelomates, meaning they have a true coelom, a body cavity lined with tissue derived from mesoderm. The coelom plays a crucial role in the animal's circulation and the distribution of nutrients.

Nematoda pseudocoelomate

Nematoda, commonly known as roundworms, are notable for their pseudocoelomate body structure. A pseudocoelomate is an organism with a body cavity that is not completely lined by mesoderm-derived tissue. Instead, the cavity, called the pseudocoelom, lies between the mesoderm and the endoderm. This simple body cavity serves many functions, such as distributing nutrients, removing waste, and housing reproductive organs. Nematodes have a tubular digestive system with openings at both ends, a significant advancement over simpler animal forms. They are abundant in many environments and can be free-living or parasitic.

Platyhelminthes gastrovascular cavity

Platyhelminthes, or flatworms, are distinguished by their simple body plan that includes a gastrovascular cavity. This cavity serves both digestive and distribution functions, as these flatworms lack a true circulatory system. Food intake and waste expulsion occur through the same opening, making the digestive process less efficient than in more complex organisms. Platyhelminthes are acoelomate, meaning they do not have a coelom or body cavity. Their bodies are solid except for the digestive cavity. This lack of a body cavity is a defining characteristic and plays a significant role in their physiology and movement.

Porifera characteristics

Porifera, or sponges, are some of the simplest multicellular organisms. They lack complex tissues and organs, and instead rely on a porous structure that allows water to circulate through their bodies. Contrary to the incorrect option in the exercise, Porifera do not possess a gastrovascular cavity or a coelom. Instead, they have specialized cells called choanocytes that help in filtering food particles from the water. Their body structure is supported by a skeleton made of spicules and spongin. Sponges are sessile, meaning they are fixed in one place and grow attached to surfaces in aquatic environments.