A reason is that multicellular organisms need special organs for exchange of gases with the environment because of prokaryotic cells found in the body. The cells are not in contact with the environment and therefore diffusion would not work in the exchange of gases. The organsin the body therefore serve this purpose.hope this could help you

• High metabolic rate: Multicellular organisms have a higher metabolic rate than unicellular organisms. They require more oxygen and produce more carbon dioxide, which cannot be exchanged by simple diffusion through the cell membrane.



• Limited surface area: As multicellular organisms grow in size, their surface area to volume ratio decreases. This means that there is less surface area available for gas exchange per unit of volume, making it harder for gases to diffuse in and out of the organism.



• Specialization of cells: Multicellular organisms have specialized cells that perform specific functions. Some cells are designed for gas exchange, such as the alveoli in the lungs, while others are designed for other functions such as digestion or movement.



• Protection: Specialized organs protect the gas exchange surfaces from damage or dehydration. For example, the lungs are protected by the rib cage and the mucus lining of the respiratory tract.



• Regulation: Specialized organs allow for the regulation of gas exchange. For example, the lungs can adjust the rate and depth of breathing to meet the body's changing oxygen demands.

Multicellular organisms require a specialized organ for the exchange of gases between their body and the environment due to several reasons. The high metabolic rate of multicellular organisms means that they require more oxygen and produce more carbon dioxide than unicellular organisms. Diffusion through the cell membrane is insufficient to meet these needs. Furthermore, the limited surface area to volume ratio of multicellular organisms means that there is less surface area available for gas exchange per unit volume, making it harder for gases to diffuse in and out of the organism.

Specialized cells in multicellular organisms perform specific functions, and some are designed for gas exchange. Specialized organs protect the gas exchange surfaces from damage or dehydration, as in the case of the lungs, which are protected by the rib cage and the mucus lining of the respiratory tract. Specialized organs also allow for the regulation of gas exchange, as in the case of the lungs, which can adjust the rate and depth of breathing to meet the body's changing oxygen demands.

In conclusion, the specialized organs in multicellular organisms are essential for efficient gas exchange, without which the organism would not be able to meet its metabolic needs.