Multicellular organisms are living beings composed of more than one cell, which work together to perform various functions. These organisms can be as simple as sponges or as complex as humans. The cells in multicellular organisms are specialized, meaning they have different roles, such as muscle cells for movement and nerve cells for communication. These organisms can be found in various environments, from oceans to forests. They exhibit a wide range of forms and sizes, showcasing the incredible diversity of life on Earth. Examples include plants, animals, and fungi, each playing a vital role in their ecosystems.