Problem 5 - Objective Biology for NEET

Question

In which of the following, gaseous exchange between \(\mathrm{O}_{2}\) and \(\mathrm{CO}_{2}\) occurs through the entire body surface? (a) Sponges (b) Flatworms (c) Coelenterates (d) All of these

Step-by-Step Solution

Answer

The correct answer is (d) All of these. Sponges, Flatworms, and Coelenterates all exchange \(\mathrm{O}_{2}\) and \(\mathrm{CO}_{2}\) through their entire body surface.

Step 1: Understanding the Biological Process in Sponges

Sponges are simple multicellular organisms without any specialized respiratory organs. They depend on the process of diffusion through their body surface for the exchange of gases. Thus, gaseous exchange in sponges occurs through the entire body surface.

Step 2: Understanding the Biological Process in Flatworms

Flatworms, also known as Platyhelminthes, are acoelomate animals that do not possess any respiratory organs. As a result, they too rely on diffusion through the body surface for gaseous exchange which occurs across their entire body surface.

Step 3: Understanding the Biological Process in Coelenterates

Coelenterates or Cnidarians, which include sea anemones and jellyfish, also don't have special respiratory organs. They carry out gaseous exchange through the process of diffusion across their entire body surface.

Step 4: Concluding the Answer Based on the Understanding

Since all three organisms, i.e., sponges, flatworms, and coelenterates perform the exchange of gases through diffusion across their body surface, all of them exchange \(\mathrm{O}_{2}\) and \(\mathrm{CO}_{2}\) through their entire body surface.

Key Concepts

Diffusion

Diffusion is a natural process crucial for gaseous exchange in many simple organisms. It involves the movement of molecules from an area of high concentration to an area of low concentration. For organisms without specialized respiratory systems, like sponges, flatworms, and coelenterates, diffusion is their primary method for obtaining oxygen and expelling carbon dioxide.

• It is a passive process, meaning it does not require energy input.
• The effectiveness of diffusion depends on the surface area and the thinness of the organism's body.
• Diffusion is more effective in smaller and simpler organisms, which have a higher surface-area-to-volume ratio.

Understanding diffusion is vital because it explains how these organisms have adapted to survive without the complex respiratory organs we see in more evolved species.

Sponges

Sponges are one of the simplest multicellular organisms on Earth. They belong to the phylum Porifera and are aquatic, mostly marine creatures. Sponges have a porous body and a simple organization, which allows for efficient diffusion of gases.

• They lack tissues and organs, which includes the absence of respiratory systems.
• Sponges rely entirely on diffusion for the exchange of oxygen and carbon dioxide.
• Water flows through their pores, bringing in oxygen and carrying away waste gases.

Due to their simple body structure, sponges illustrate how organisms can sustain themselves with minimal systems, highlighting the adaptability of life.

Flatworms

Flatworms, scientifically known as Platyhelminthes, are simple acoelomate creatures. These flat-bodied worms lack specialized organ systems for respiration, further emphasizing the role of diffusion.

• The flattened shape increases their surface area relative to their volume, enhancing diffusion efficiency.
• The lack of a body cavity simplifies the direct exposure of their cells to the environment.
• Flatworms thrive in moist environments, where diffusion can readily occur across their entire body surface.

These adaptations enable flatworms to effectively exchange gases, underscoring nature's ingenuity in leveraging basic principles for survival.

Coelenterates

Coelenterates, also known as Cnidarians, include creatures like jellyfish, sea anemones, and corals. These organisms are characterized by their simple morphology and aquatic habitat, relying on diffusion for respiration.

• They have a single opening serving as both mouth and anus, which simplifies their body plan.
• Like sponges and flatworms, they lack specialized respiratory structures.
• Their thin body walls allow gases to seamlessly diffuse in and out.

The reliance on diffusion aids their survival in water-rich environments, displaying yet another example of how simple life forms efficiently manage basic biological processes without complex systems.