Problem 10 - Biology: Concepts and Applications

Question

The _______ have a coelom and are radial as adults. a. cnidarians b. echinoderms c. annelids d. placozoans

Step-by-Step Solution

Answer

The correct answer is b. echinoderms.

Step 1: Understanding the Coelom

A coelom is a fluid-filled cavity that is completely surrounded by mesoderm tissue. Not all animals have a coelom, but those that do are referred to as coelomates or eucoelomates.

Step 2: Recognizing Radial Symmetry

Radial symmetry refers to the arrangement of body parts around a central axis. Animals that exhibit radial symmetry appear to be similar on all sides. This type of symmetry is distinct from bilateral symmetry, where organisms have a left and right side.

Step 3: Identifying Echinoderms

Echinoderms are a group of marine animals that include starfish, sea urchins, and sea cucumbers. They are coelomates that have a coelom, and as adults, they exhibit radial symmetry.

Step 4: Evaluating the Other Options

- Cnidarians: such as jellyfish and corals, exhibit radial symmetry but lack a true coelom (they have a gelatinous layer instead). - Annelids: such as earthworms, are coelomates but are not radially symmetrical (they are bilaterally symmetrical). - Placozoans: are simple animals lacking complex structures like a coelom and do not have radial symmetry.

Step 5: Choosing the Correct Answer

Given that echinoderms have both a coelom and exhibit radial symmetry as adults, the correct choice is b. echinoderms.

Key Concepts

Coelom

The coelom is an essential anatomical feature found in some animals, distinguished as a fluid-filled cavity entirely enclosed by mesoderm, the middle layer of embryonic tissue. This structure plays a significant role in the physiological functioning of these animals.

Here are some key characteristics and functions:

• Provides a cushion for internal organs, protecting them from shocks and impacts.
• Facilitates the growth and development of complex organ systems by allowing space for them to move independently from the body wall.
• Assists with the circulation of nutrients and waste products throughout the organism due to its fluid nature.

Animals with a coelom are termed coelomates or eucoelomates. This group includes a diverse range of animal phyla, highlighting the evolutionary importance of this structural feature in the animal kingdom.

Radial Symmetry

Radial symmetry is a fascinating body plan observed in some animal species, where body parts are arranged around a central axis. This type of symmetry contrasts with bilateral symmetry, where animals have a distinct left and right side.

Here are some points on radial symmetry:

• Allows organisms to interact with their environment from all directions, which is beneficial for sessile or slow-moving animals.
• Enhances capability for reacting to stimuli that can occur from multiple directions at once.
• Typically associated with animals that have a top (oral) and bottom (aboral) side, but do not have distinct front or back ends.

This arrangement is particularly effective in marine environments, where many radially symmetrical animals such as echinoderms thrive.

Coelomates

Coelomates are animals that possess a true coelom, which is a body cavity entirely lined with mesodermal tissue. This feature is a major distinction in the animal kingdom.

Important features of coelomates include:

• Highly developed organ systems, due to the separation of the digestive tract from the outer body wall.
• Enhanced movement and flexibility, as the coelom allows for more complex musculature.
• A wide diversity of animal forms and functions, underscoring the evolutionary adaptiveness of having a coelom.

Echinoderms, mollusks, annelids, and arthropods are all examples of coelomates, showcasing how this trait has been instrumental in the evolution of complex multicellular life.