The sponge have no respiratory organs because they

Options

A. Are sedentary
B. Do not need respiratory organs
C. respire anaerobically
D. Have highly porous body

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks why sponges do not have respiratory organs.

2. **Identifying the Characteristics of Sponges**: Sponges belong to the phylum Porifera. They are simple organisms that have a cellular level of organization and are asymmetrical in shape.

3. **Water Transport System**: Sponges have a unique water transport system that involves minute pores called ostia. Water enters the sponge through these pores, flows into a central cavity known as the spongocoel, and exits through a larger opening called the osculum.

4. **Function of Water Circulation**: The movement of water through the sponge serves multiple purposes: it aids in food gathering, gas exchange (respiration), and waste removal. This means that sponges can exchange gases directly with the water flowing through their bodies.

5. **Role of Choanocytes**: The inner lining of the spongocoel is made up of specialized cells called choanocytes (or collar cells), which have cilia. These cilia help in creating a current that facilitates the movement of water, enhancing the sponge's ability to absorb nutrients and perform gas exchange.

6. **Conclusion**: Given that sponges rely on their highly porous body and the water flow for respiration and do not require specialized respiratory organs, the correct answer to the question is that sponges do not have respiratory organs because they have a highly porous body.

**Final Answer**: D. Sponges do not have respiratory organs because they have a highly porous body.

---