The correct answer is B: "All of their functions are performed by a single cell." Unicellular organisms have all of their functions performed by a single cell. They do not possess tissues and organs, are usually microscopic, and do not have specialized cells for specific functions.
The characteristic of unicellular organisms is that all of their functions are performed by a single cell. This means that unicellular organisms are capable of carrying out all essential life processes within a single cell, including reproduction, obtaining and using energy, and responding to the environment.
Option A, "They can possess tissues and organs," is incorrect because unicellular organisms do not have tissues or organs. Tissues and organs are specialized structures that are composed of multiple cells working together, which is a characteristic of multicellular organisms.
Option C, "They are usually microscopic," is generally true for unicellular organisms. Most unicellular organisms are microscopic in size because they are made up of a single cell and do not have the complex structures and systems found in larger organisms.
Option D, "Each of their cells is specialized to perform a specific function," is incorrect. Unicellular organisms do not have specialized cells that perform specific functions like in multicellular organisms. Instead, the single cell of a unicellular organism carries out all necessary functions for its survival.
Therefore, the correct answer is B: "All of their functions are performed by a single cell."
The question probable may be:
Which of the following is a characteristic of unicellular organisms?
A. They can possess tissues and organs
B. All of their functions are performed by a single cell.
C. They are usually microscopic.
D. Each of their cells is specialized to perform a specific function.